MESO: Mesoscale Discussion 0521

ACUS11 KWNS 210356
SWOMCD
SPC MCD 210356
MNZ000-SDZ000-NDZ000-NEZ000-210600-

MESOSCALE DISCUSSION 0521
NWS STORM PREDICTION CENTER NORMAN OK
1056 PM CDT FRI APR 20 2007

AREAS AFFECTED...CENTRAL NEB

CONCERNING...SEVERE THUNDERSTORM WATCH 153...

VALID 210356Z - 210600Z

THE SEVERE WEATHER THREAT FOR SEVERE THUNDERSTORM WATCH 153
CONTINUES.

CLUSTER OF STORMS INCLUDING A TORNADIC SUPERCELL CONTINUES TO MOVE
NEWD OVER SERN CUSTER COUNTY. THIS CELL PRODUCED SEVERAL TORNADO
REPORTS FROM MOOREFIELD THRU GOTHENBURG NEB. LOOKS ACTIVITY
DEVELOPED ON NOSE OF 40-50 KT LOW LEVEL JET JUST OVER SELY SURFACE
WINDS OF 25-30 KT ENHANCING 0-1 KM SHEAR. AIR MASS CONTINUES TO BE
VERY UNSTABLE AS WELL AS MLCAPE VALUES ARE AROUND 2500 J/KG ACROSS
THIS AREA.

RUC PFC SOUNDINGS SUPPORT THIS WITH SFC-1 KM SHEAR OF 32 KT WITH
FAVORABLE HODOGRAPH TO SUPPORT STRONG UPDRAFTS AS WELL AS MID LEVEL
LAPSE RATES OF 8C/KM. RADAR CONTINUES TO SHOW THIS CELL RECYCLING
AGAIN AT THIS TIME AND WILL CONTINUE TO DO SO AS STRONG SFC-LOW
LEVEL FLOW CONTINUES. THE AIR MASS REMAINS UNSTABLE NEWD INTO NORTH
CENTRAL NEB WHERE LATEST RUC FCST SHOWS ACTIVITY CONTINUING THRU
06Z.

.MCCARTHY.. 04/21/2007

..PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...

ATTN...WFO...FGF...FSD...OAX...ABR...BIS...LBF...UNR...

46629831 46629679 46309660 46019660 45679674 45599682
45469670 45379651 45339648 45329695 45299703 45299723
45139719 45139744 44539750 44539781 44179783 44189835
43489830 43499869 43399869 43179809 42989809 42859815
42859823 42949845 42969855 42970209 43130208 43150211
43420211 43500215 43650215 43660206 43770199 44520200
44530182 44580167 44580157 44620147 44690135 44730114
44990110 44990148 45470147 45450092 45490094 45460035
45570043 45640039 45690028 45720026 45900044 45940044
45939985 46279987 46279902 46629901

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WATCHES: Severe Thunderstorm Watch Number 153

WWUS20 KWNS 210142
SEL3
SPC WW 210142
NEZ000-210700-

URGENT - IMMEDIATE BROADCAST REQUESTED
SEVERE THUNDERSTORM WATCH NUMBER 153
NWS STORM PREDICTION CENTER NORMAN OK
840 PM CDT FRI APR 20 2007

THE NWS STORM PREDICTION CENTER HAS ISSUED A
SEVERE THUNDERSTORM WATCH FOR PORTIONS OF

SOUTHWEST AND CENTRAL NEBRASKA

EFFECTIVE THIS FRIDAY NIGHT AND SATURDAY MORNING FROM 840 PM
UNTIL 200 AM CDT.

HAIL TO 2 INCHES IN DIAMETER...THUNDERSTORM WIND GUSTS TO 70
MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS.

THE SEVERE THUNDERSTORM WATCH AREA IS APPROXIMATELY ALONG AND 60
STATUTE MILES EAST AND WEST OF A LINE FROM 30 MILES NORTH
NORTHEAST OF AINSWORTH NEBRASKA TO 50 MILES SOUTH OF NORTH PLATTE
NEBRASKA. FOR A COMPLETE DEPICTION OF THE WATCH SEE THE
ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU3).

REMEMBER...A SEVERE THUNDERSTORM WATCH MEANS CONDITIONS ARE
FAVORABLE FOR SEVERE THUNDERSTORMS IN AND CLOSE TO THE WATCH
AREA. PERSONS IN THESE AREAS SHOULD BE ON THE LOOKOUT FOR
THREATENING WEATHER CONDITIONS AND LISTEN FOR LATER STATEMENTS
AND POSSIBLE WARNINGS. SEVERE THUNDERSTORMS CAN AND OCCASIONALLY
DO PRODUCE TORNADOES.

OTHER WATCH INFORMATION...CONTINUE...WW 152...

DISCUSSION...ONGOING CLUSTER OF STRONG/SEVERE THUNDERSTORMS OVER
SWRN NEB WILL CONTINUE TO EXPAND/DEVELOP NNEWD ALONG NOSE OF
INCREASING SLY LLJ THIS EVENING. ENVIRONMENT IS CHARACTERIZED BY
VERY STEEP MID LEVEL LAPSE RATES...MODERATE MUCAPE AND MARGINALLY
SUFFICIENT DEEP SHEAR FOR SUPERCELLS. THIS SUPPORTS A CONTINUED
THREAT OF LARGE HAIL AND POSSIBLY AND ISOLATED STRONG/SEVERE WIND
GUST WITH STRONGER...ELEVATED CORES TONIGHT.

AVIATION...A FEW SEVERE THUNDERSTORMS WITH HAIL SURFACE AND ALOFT
TO 2 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60
KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 500. MEAN STORM
MOTION VECTOR 20025.

..EVANS

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DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 210100
SWODY1
SPC AC 210058

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0758 PM CDT FRI APR 20 2007

VALID 210100Z - 211200Z

..THERE IS A SLGT RISK OF SVR TSTMS PORTIONS WRN/NRN
NEB...SD...SERN ND...

..THERE IS A SLGT RISK OF SVR TSTMS PORTIONS TX PANHANDLE...

..SYNOPSIS...
HIGH AMPLITUDE WILL CHARACTERIZE MID-UPPER TROPOSPHERIC PATTERN
ACROSS CONUS THROUGH REMAINDER PERIOD...FEATURING SYNOPTIC TROUGH
OVER WRN STATES AND RIDGING FROM WRN GULF OF MEXICO TO HUDSON BAY.
BROAD FETCH OF SW FLOW ALOFT EXISTS DOWNSTREAM FROM PRONOUNCED
MID-UPPER LEVEL LOW THAT MOISTURE CHANNEL IMAGERY INDICATED OVER SRN
CA. THIS LOW IS FCST TO PIVOT EWD OVERNIGHT TO THE LOWER CO RIVER
VALLEY AND SWRN AZ.

AT SFC...LOW WAS ANALYZED OVER SWRN SD...WITH WARM FRONTAL ZONE NEWD
ACROSS ERN ND AND SWWD OVER E-CENTRAL/SERN WY. DIFFUSE LEE CYCLONE
NOW OVER ERN CO IS FCST TO LIFT NWD AND BECOME MORE SHARPLY DEFINED
OVERNIGHT ACROSS NEB PANHANDLE. ISALLOBARIC/ISALLOHYPSIC FORCING
ASSOCIATED WITH LEE CYCLONE/TROUGHING WILL MAINTAIN SELY SFC WINDS
OVER MUCH OF CENTRAL/SRN HIGH PLAINS. THIS SHOULD RESULT IN
CONSOLIDATION AND SLGT WWD RETREAT OF DOUBLE DRYLINE STRUCTURE
ANALYZED AT 23Z FROM SWRN SD SWD ACROSS W TX.
MEANWHILE...DECOUPLING BOUNDARY LAYER WILL LEAD TO INTENSIFICATION
OF 40-50 KT SLY LLJ FROM NRN COAHUILA TO OK PANHANDLE...VEERING TO
SSWLY ACROSS WRN KS TO ERN SD.

..NRN/CENTRAL PLAINS...
COMPLEX OF STG-SVR TSTMS -- SOME OF WHICH HAVE PRODUCED HAIL UP TO
1.75 INCH DURING PAST 1-2 HOURS -- SHOULD CONTINUE AND SHIFT NEWD
ACROSS ERN DAKOTAS THROUGH REMAINDER EVENING. REF WW 152 AND
RELATED MESOSCALE DISCUSSIONS FOR NEAR-TERM SVR FCST. ADDITIONAL
DEVELOPMENT/REJUVENATION OF ACTIVITY OVER THIS REGION MAY OCCUR
AFTER APPROXIMATELY 3Z...ASSOCIATED WITH STRENGTHENING LLJ AND
ASSOCIATED MOISTURE TRANSPORT AND ISENTROPIC LIFT.

APPARENTLY SFC-BASED DEVELOPMENT OCCURRING ATTM ACROSS SERN NEB ALSO
MAY EVOLVE INTO SEPARATE COMPLEX OF TSTMS DURING EVENING/OVERNIGHT
HOURS...WITH DAMAGING WIND POSSIBLE DURING FIRST 2-3 HOURS AND LARGE
HAIL BEING MAIN THREAT THEREAFTER. MODIFIED RAOBS AND FCST
SOUNDINGS SHOW MIDLEVEL LAPSE RATES OF 7-8 DEG C/KM...COMBINING WITH
SFC DEW POINTS LOW-MID 50S F TO SUPPORT MLCAPES AROUND 1000 J/KG.
ONCE BOUNDARY LAYER DECOUPLES SUFFICIENTLY FOR EFFECTIVE INFLOW
PARCELS TO BECOME ELEVATED...EXPECT MUCAPES NEAR 2000 J/KG WITH
FAVORABLE EFFECTIVE SHEAR VALUES FOR SVR...WITH LARGE HAIL MOST
PROBABLE.

..SRN HIGH PLAINS...
ISOLATED CLUSTER OF TSTMS HAS DEVELOPED INVOF ERN DRYLINE
SEGMENT...BETWEEN PVW-AMA...AMIDST STRONGLY HEATED/MIXED BOUNDARY
LAYER. ADDITIONAL DEVELOPMENT MAY OCCUR FOR ANOTHER 1-2 HOURS ON
SEGMENT OF TCU EXTENDING SWD TO BETWEEN PVW-LBB. AMA RAOB AND RUC
SOUNDINGS...ALONG WITH LIMITED DEPTH OF AVAILABLE VAD
WINDS...INDICATE FAVORABLE VERTICAL SHEAR PROFILES FOR SUPERCELLULAR
ORGANIZATION TO ARISE FROM THIS ACTIVITY. ADDITIONAL/ISOLATED
DEVELOPMENT MAY OCCUR FROM THIS REGION NWD ACROSS WRN KS...THOUGH
SBCINH WILL INCREASE THROUGH REMAINDER EVENING AS SFC COOLING
GRADUALLY OFFSETS THETAE ADVECTION. LARGE HAIL AND ISOLATED STG-SVR
GUSTS WILL BE POSSIBLE BEFORE ACTIVITY WEAKENS LATE THIS EVENING.

.EDWARDS.. 04/21/2007

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MESO: Mesoscale Discussion 0520

ACUS11 KWNS 202348
SWOMCD
SPC MCD 202348
MNZ000-SDZ000-NDZ000-NEZ000-210145-

MESOSCALE DISCUSSION 0520
NWS STORM PREDICTION CENTER NORMAN OK
0648 PM CDT FRI APR 20 2007

AREAS AFFECTED...CENTRAL SD AND SERN ND

CONCERNING...SEVERE THUNDERSTORM WATCH 152...

VALID 202348Z - 210145Z

THE SEVERE WEATHER THREAT FOR SEVERE THUNDERSTORM WATCH 152
CONTINUES.

LATEST MESOSCALE ANALYSIS SHOWS WARM FRONTAL BOUNDARY THAT EXTENDS
EWD FROM CENTRAL SD INTO W CENTRAL MN...WITH A COLD FRONT THAT
CONTINUES TO MOVE SEWD THRU ND AND NWRN SD. STRONGEST STORMS ARE
LOCATED OVER CENTRAL SD WHERE CONVECTIVE BOUNDARY INTERSECTS WARM
FRONTAL BOUNDARY. ACTIVITY CONTINUES TO BE DRIVEN BY LOW LEVEL WARM
ADVECTION WHERE LOW LEVEL JET OF 35 KT EXTENDS FROM ERN NEB NWD THRU
ERN SD. RUC SOUNDING VALID FOR 21/00Z INDICATED FAVORABLE VERTICAL
SHEAR PROFILE WITH DEEP LAYER SHEAR OF 49 KT SUFFICIENT TO SUSTAIN
UPDRAFTS ALONG WITH LOW-MID LEVEL LAPSE RATES JUST ABOVE 7.5C/KM.

LOOKS LIKE THE ACTIVITY N OF THE WARM FRONT IS ELEVATED WHILE THE
ACTIVITY IN CENTRAL SD IS MORE ROOTED JUST ABOVE THE SURFACE WITH
THE ADVECTION COMING IN FROM EAST CENTRAL SD. THUS...THIS ACTIVITY
LOOKS LIKE IT WILL CONTINUE ENEWD ALONG THE WARM FRONTAL BOUNDARY
WITH THE MAIN THREAT BEING LARGE HAIL DURING THE NEXT FEW HOURS.

.MCCARTHY.. 04/20/2007

..PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...

ATTN...WFO...FGF...FSD...OAX...ABR...BIS...LBF...UNR...

46629831 46629679 46309660 46019660 45679674 45599682
45469670 45379651 45339648 45329695 45299703 45299723
45139719 45139744 44539750 44539781 44179783 44189835
43489830 43499869 43399869 43179809 42989809 42859815
42859823 42949845 42969855 42970209 43130208 43150211
43420211 43500215 43650215 43660206 43770199 44520200
44530182 44580167 44580157 44620147 44690135 44730114
44990110 44990148 45470147 45450092 45490094 45460035
45570043 45640039 45690028 45720026 45900044 45940044
45939985 46279987 46279902 46629901

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MESO: Mesoscale Discussion 0519

ACUS11 KWNS 202031
SWOMCD
SPC MCD 202031
MNZ000-SDZ000-NDZ000-NEZ000-202230-

MESOSCALE DISCUSSION 0519
NWS STORM PREDICTION CENTER NORMAN OK
0331 PM CDT FRI APR 20 2007

AREAS AFFECTED...CNTRL/ERN SD AND EXTREME SERN ND

CONCERNING...SEVERE THUNDERSTORM WATCH 152...

VALID 202031Z - 202230Z

THE SEVERE WEATHER THREAT FOR SEVERE THUNDERSTORM WATCH 152
CONTINUES. /AUTO

INITIAL BURST OF ELEVATED TSTMS THAT YIELDED HAIL TO THE SIZE OF
NICKELS HAS WEAKENED THROUGH MID-AFTN ACROSS NERN SD...PRESUMABLY
OWING TO POSSIBLE STORM COMPETITION/INTERFERENCE. VSBL SATL AND
REGIONAL RADAR SHOW AGITATED ACCAS CONTINUING TO FORM UPSTREAM
ACROSS NCNTRL NEB...ALONG NRN EDGE OF A STRONGER CAP BENEATH THE
ELEVATED MIXED LAYER. THESE GENERATING CELLS WILL LIKELY GROW
UPSCALE INTO TSTMS ACROSS SCNTRL THROUGH NCNTRL/NERN SD THROUGH
EARLY THIS EVE. LAPSE RATES REMAIN STEEP ALOFT AND GIVEN ROUGHLY
40-45 KTS OF SHEAR IN THE CLOUD-LAYER...ROTATING UPDRAFTS WILL BE
LIKELY WITH LARGE HAIL. MOREOVER...LOW-LEVEL LAPSE RATES HAVE
IMPROVED THIS AFTN SUGGESTING THAT UPDRAFTS MAY ROOT INTO THE
BOUNDARY LAYER. THUS...DAMAGING WIND GUSTS ARE NOT OUT OF THE
QUESTION...PARTICULARLY ACROSS CNTRL/SRN SD.

.RACY.. 04/20/2007

..PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...

ATTN...WFO...FGF...FSD...OAX...ABR...BIS...LBF...UNR...

46629831 46629679 46309660 46019660 45679674 45599682
45469670 45379651 45339648 45329695 45299703 45299723
45139719 45139744 44539750 44539781 44179783 44189835
43489830 43499869 43399869 43179809 42989809 42859815
42859823 42949845 42969855 42970209 43130208 43150211
43420211 43500215 43650215 43660206 43770199 44520200
44530182 44580167 44580157 44620147 44690135 44730114
44990110 44990148 45470147 45450092 45490094 45460035
45570043 45640039 45690028 45720026 45900044 45940044
45939985 46279987 46279902 46629901

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DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 201956
SWODY1
SPC AC 201954

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0254 PM CDT FRI APR 20 2007

VALID 202000Z - 211200Z

..THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE NRN AND
CNTRL HIGH PLAINS...

..NRN PLAINS...
LATEST WATER VAPOR IMAGERY AND RUC ANALYSIS SHOW A SUBTLE SHORTWAVE
TROUGH MOVING NEWD ACROSS ERN CO AND THE CNTRL PLAINS ATTM. AS THIS
SYSTEM APPROACHES THE NRN PLAINS LATE THIS AFTERNOON...LARGE-SCALE
ASCENT WILL BECOME INCREASINGLY FAVORABLE FOR THUNDERSTORM
DEVELOPMENT ACROSS THE REGION INTO THE EVENING. IN
ADDITION...STRENGTHENING LOW-LEVEL FLOW AND INCREASING LOW-LEVEL
MOISTURE WILL BECOME MORE FAVORABLE WITH TIME.

OBJECTIVE ANALYSIS AND REGIONAL PROFILERS ACROSS THE NRN PLAINS
CURRENTLY SHOW 0-6 KM SHEAR VALUES IN THE 40 TO 55 KT RANGE. THIS
AMOUNT OF VERTICAL SHEAR WILL BE MARGINALLY SUFFICIENT FOR ROTATING
STORMS DUE TO THE WEAKER INSTABILITY IN PLACE. THE GREATEST
SUPERCELL THREAT SHOULD REMAIN FURTHER SOUTH SOUTHWEST WHERE
MODERATE INSTABILITY IS EXPECTED. THUNDERSTORM COVERAGE WILL
CONTINUE TO BE GREATEST ACROSS ECNTRL AND NERN SD WITH STORMS
GRADUALLY EXPANDING NWD INTO CNTRL AND ERN ND. FORECAST SOUNDINGS
THIS EVENING ACROSS MOST OF THE NRN PLAINS SHOW STEEP LAPSE
RATES...COLD TEMPS ALOFT /500 MB TEMPS < -16 C/ WHICH COMBINED WITH
THE STRONG VERTICAL SHEAR WILL BE ENOUGH FOR ISOLATED LARGE HAIL
WITH THE MORE ORGANIZED THUNDERSTORMS. CONSIDERING THE INSTABILITY
IS MOSTLY LOCATED ABOVE 700 MB...THUNDERSTORMS SHOULD REMAIN
PRIMARILY ELEVATED IN THE NRN PLAINS AND THE THREAT FOR WIND DAMAGE
SHOULD REMAIN MARGINAL.

..WRN NEB/WRN KS AND THE TX PANHANDLE...
LATEST SFC ANALYSIS SHOWS A MOIST AXIS EXTENDING NWD FROM WCNTRL OK
INTO CNTRL KS WITH SFC DEWPOINTS IN THE LOWER 60S F. ACCORDING TO
OBJECTIVE ANALYSIS...MODERATE INSTABILITY IS CURRENTLY PRESENT ALONG
THE MOIST AXIS AND SHORT-TERM MODEL FORECASTS MOVE THE INSTABILITY
WWD INTO THE CNTRL HIGH PLAINS THIS EVENING. A CAPPING INVERSION IS
PRESENT ALONG THE INSTABILITY AXIS AND THIS WILL INHIBIT CONVECTIVE
DEVELOPMENT THROUGH MOST OF THE AFTERNOON. ISOLATED CONVECTIVE
DEVELOPMENT MAY OCCUR IN A NARROW WINDOW LATE THIS AFTERNOON OR
EARLY THIS EVENING AS THE CAPPING INVERSION BECOMES WEAKER ACROSS
THE REGION. THE GREATEST POTENTIAL FOR THUNDERSTORMS WILL EXIST
ACROSS WRN NEB WHERE LARGE-SCALE ASCENT ASSOCIATED WITH A SHORTWAVE
TROUGH WILL BE MORE FAVORABLE.

FORECAST SOUNDINGS AND OBJECTIVE ANALYSIS ACROSS THE REGION EARLY
THIS EVENING SHOW MODERATE VERTICAL SHEAR IN PLACE WITH 0-6 KM SHEAR
VALUES IN THE 35 TO 45 KT RANGE. CONSIDERING MODERATE INSTABILITY IS
ALREADY PRESENT...SUPERCELLS WILL BE LIKELY WITH STORMS THAT
INITIATE. IN ADDITION...MID-LEVEL LAPSE RATES MAY INCREASE AS AN
ELEVATED MIXED LAYER OVER SE CO DRIFTS NEWD THIS EVENING. THIS ALONG
WITH THE INCREASING INSTABILITY AND ADEQUATE SHEAR WILL BE FAVORABLE
FOR LARGE HAIL WITH ANY SUPERCELL. IF A SUPERCELL OR TWO
DEVELOP...VERY LARGE HAIL AND ISOLATED WIND DAMAGE WILL ALSO BE
POSSIBLE.

.BROYLES.. 04/20/2007

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WATCHES: Severe Thunderstorm Watch Number 152

WWUS20 KWNS 201827
SEL2
SPC WW 201827
NDZ000-SDZ000-210200-

URGENT - IMMEDIATE BROADCAST REQUESTED
SEVERE THUNDERSTORM WATCH NUMBER 152
NWS STORM PREDICTION CENTER NORMAN OK
125 PM CDT FRI APR 20 2007

THE NWS STORM PREDICTION CENTER HAS ISSUED A
SEVERE THUNDERSTORM WATCH FOR PORTIONS OF

SOUTHEASTERN NORTH DAKOTA
A LARGE PART OF SOUTH DAKOTA

EFFECTIVE THIS FRIDAY AFTERNOON AND EVENING FROM 125 PM UNTIL 900
PM CDT.

HAIL TO 2 INCHES IN DIAMETER...THUNDERSTORM WIND GUSTS TO 70
MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS.

THE SEVERE THUNDERSTORM WATCH AREA IS APPROXIMATELY ALONG AND 65
STATUTE MILES EAST AND WEST OF A LINE FROM 80 MILES NORTH
NORTHEAST OF ABERDEEN SOUTH DAKOTA TO 75 MILES SOUTHWEST OF
CHAMBERLAIN SOUTH DAKOTA. FOR A COMPLETE DEPICTION OF THE WATCH
SEE THE ASSOCIATED WATCH OUTLINE UPDATE (WOUS64 KWNS WOU2).

REMEMBER...A SEVERE THUNDERSTORM WATCH MEANS CONDITIONS ARE
FAVORABLE FOR SEVERE THUNDERSTORMS IN AND CLOSE TO THE WATCH
AREA. PERSONS IN THESE AREAS SHOULD BE ON THE LOOKOUT FOR
THREATENING WEATHER CONDITIONS AND LISTEN FOR LATER STATEMENTS
AND POSSIBLE WARNINGS. SEVERE THUNDERSTORMS CAN AND OCCASIONALLY
DO PRODUCE TORNADOES.

DISCUSSION...WARM ADVECTION STORMS EXPECTED TO STRENGTHEN INVOF
FRONT STALLED SW/NE ACROSS SD. STEEP MID LEVEL LAPSE
RATES...ESPECIALLY FROM CNTRL SD NWD...AND INCREASING LOW LEVEL
MOISTURE INFLOW SHOULD SUPPORT POTENTIAL FOR LARGE HAIL AND POSSIBLY
HIGH WIND GIVEN 40+ KT CLOUD LAYER SHEAR DESPITE SLIGHTLY ELEVATED
NATURE OF STORMS.

AVIATION...A FEW SEVERE THUNDERSTORMS WITH HAIL SURFACE AND ALOFT
TO 2 INCHES. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60
KNOTS. A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 450. MEAN STORM
MOTION VECTOR 21030.

..CORFIDI

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MESO: Mesoscale Discussion 0518

ACUS11 KWNS 201806
SWOMCD
SPC MCD 201805
NDZ000-SDZ000-201900-

MESOSCALE DISCUSSION 0518
NWS STORM PREDICTION CENTER NORMAN OK
0105 PM CDT FRI APR 20 2007

AREAS AFFECTED...CNTRL/ERN SD...SCNTRL/SERN ND

CONCERNING...SEVERE POTENTIAL...WATCH LIKELY

VALID 201805Z - 201900Z

SEVERE TSTM WATCH WIBIS SHORTLY FOR PARTS OF THE AREA.

TSTMS HAVE ERUPTED A BIT SOONER THAN ANTICIPATED AND UPDRAFTS
ARE QUITE ROBUST WITH MESH 88D PRODUCTS SHOWING 1-1.5 INCH
HAIL. LLJ WILL CONTINUE TO BE AIMED INTO THIS AREA WITH SUFFICIENT
LAPSE RATES/EFFECTIVE SHEAR TO SUPPORT LARGE HAIL. GUSTY WINDS
COULD ALSO OCCUR. ACTIVITY MIGHT SPREAD NNEWD INTO PARTS OF ND
LATER THIS AFTN.

.RACY.. 04/20/2007

..PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...

ATTN...WFO...FGF...FSD...ABR...BIS...UNR...

43530112 45450092 46630034 46689836 45189818 43389933

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DAY2SVR: Nws Storm Prediction Center Norman Ok

ACUS02 KWNS 201712
SWODY2
SPC AC 201711

DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1211 PM CDT FRI APR 20 2007

VALID 211200Z - 221200Z

..THERE IS A MDT RISK OF SVR TSTMS ACROSS PARTS OF WEST TX AND WRN
KS...

..THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE SRN
PLAINS...CNTRL HIGH PLAINS AND NRN PLAINS...

..SEVERE THUNDERSTORM OUTBREAK POSSIBLE SATURDAY ACROSS PARTS OF
THE GREAT PLAINS ESPECIALLY ACROSS PARTS OF WEST TX AND WRN KS...

..SRN AND CNTRL PLAINS...
LATEST WATER VAPOR IMAGERY SHOWS A WELL-DEFINED UPPER-LEVEL TROUGH
AND CLOSED-OFF LOW JUST OFF THE CALIFORNIA COAST. THIS SYSTEM IS
FORECAST TO MOVE EWD ACROSS THE ROCKIES TONIGHT SPREADING STRONG
LARGE-SCALE ASCENT INTO THE SRN AND CNTRL PLAINS SATURDAY. IN
ADDITION...LOW-LEVEL MOISTURE...INSTABILITY AND SHEAR PROFILES SHOWN
ON MODEL FORECASTS AND FORECAST SOUNDINGS WILL BE ADEQUATE FOR
WIDESPREAD SEVERE THUNDERSTORMS SATURDAY AFTERNOON AND EVENING.
THUNDERSTORMS WILL DEVELOP ALONG A DRYLINE SATURDAY AFTERNOON AND
EXPAND IN COVERAGE ACROSS THE REGION LATE SATURDAY AFTERNOON INTO
THE EVENING. ALTHOUGH THERE ARE MINOR DIFFERENCES IN THE LAST THREE
RUNS OF THE NAM MODEL...THE OVERALL SOLUTIONS ARE RELATIVELY
CONSISTENT SUGGESTING CONFIDENCE IN WIDESPREAD SEVERE WEATHER
SATURDAY ACROSS THE WRN PORTION OF THE SRN AND CNTRL PLAINS IS HIGH
ATTM.

SOME UNCERTAINTIES STILL REMAIN INCLUDING CONVECTIVE MODE AND SEVERE
WEATHER REPORT TYPE. FORECAST SOUNDINGS ACROSS THE REGION SATURDAY
AFTERNOON SHOW 0-6 KM SHEAR VALUES IN THE 55 TO 75 KT RANGE ALONG
WITH MODERATE INSTABILITY SUGGEST SUPERCELLS WILL DEVELOP QUICKLY
AFTER INITIATION ALONG A NARROW AXIS JUST EAST OF THE DRYLINE. DUE
TO THE STRONG FORCING ASSOCIATED WITH THE APPROACHING
UPPER-TROUGH...THUNDERSTORM DEVELOPMENT SHOULD BE QUITE NUMEROUS
MAINLY FROM THE LUBBOCK AREA NWD ACROSS THE TX PANHANDLE INTO WRN
KS. A THREAT FOR TORNADOES...LARGE HAIL AND WIND DAMAGE WILL BE
LIKELY WITH SUPERCELLS ESPECIALLY AS THUNDERSTORMS INITIATE AND
MATURE SATURDAY AFTERNOON.

THE THREAT FOR SIGNIFICANT TORNADOES ACROSS THE REGION STILL REMAINS
UNCLEAR BECAUSE LOW-LEVEL WIND PROFILES SHOWN ON FORECAST SOUNDINGS
SHOULD BE SOMEWHAT BACKED EVEN TO 850 MB SATURDAY AFTERNOON.
HOWEVER...IF SUPERCELLS REMAIN DISCRETE FOR A LONG ENOUGH TIME...A
CLUSTER OF TORNADOES COULD OCCUR AND WOULD BE MOST LIKELY WWD FROM
THE LOW-LEVEL JET ACROSS THE TX PANHANDLE AND ON THE CAPROCK IN THE
VICINITY OF LUBBOCK. IF THUNDERSTORMS CONGEAL BY EARLY EVENING INTO
A LARGE LINEAR MCS WHICH MODEL FORECASTS SUGGEST MAY OCCUR...THEN
THE THREAT SHOULD TRANSITION TO MOSTLY LARGE HAIL AND WIND DAMAGE.
STEEP LAPSE RATES...MODERATE INSTABILITY AND STRONG VERTICAL SHEAR
PROFILES ON FORECAST SOUNDINGS COULD ALSO BE FAVORABLE FOR LARGE
HAIL OF AT LEAST TWO INCH DIAMETER AND A FEW VERY STRONG WIND GUSTS
SATURDAY AFTERNOON AND EVENING. ALTHOUGH THE SIGNIFICANT TORNADO
THREAT MAY BE SLIGHTLY LESS ACROSS WRN KS DUE TO THE POSITION OF THE
LOW-LEVEL JET MAXIMA...DAMAGING LARGE HAIL AND VERY STRONG WIND
GUSTS MAY ALSO OCCUR IN THAT PORTION OF THE MODERATE RISK. ANY
SEVERE THREAT MAY CONTINUE INTO THE OVERNIGHT PERIOD BUT SHOULD
BECOME MORE ISOLATED AS INSTABILITY DECREASES ACROSS THE REGION.

..NRN PLAINS...
LATEST WATER VAPOR IMAGERY SHOWS AN UPPER-LEVEL TROUGH ALONG THE
WEST COAST. THIS FEATURE WILL MOVE EWD ACROSS THE WRN U.S. AND INTO
THE ROCKIES SATURDAY. AHEAD OF THE SYSTEM...LOW-LEVEL MOISTURE WILL
INCREASE ACROSS THE NRN PLAINS WHICH SHOULD BE SUFFICIENT FOR
MODERATE INSTABILITY BY SATURDAY AFTERNOON. IN ADDITION...SUBTLE
SHORTWAVE ACTIVITY AHEAD OF THE UPPER-TROUGH SHOULD MOVE NNEWD
ACROSS THE REGION PROVIDING LARGE-SCALE ASCENT SUFFICIENT FOR
SCATTERED THUNDERSTORM DEVELOPMENT SATURDAY AFTERNOON AND EVENING.

FORECAST SOUNDINGS ACROSS THE NRN PLAINS SATURDAY AFTERNOON SHOW 0-6
KM SHEAR VALUES IN THE 45 TO 60 KT RANGE SUGGESTING SUPERCELL
DEVELOPMENT WILL BE LIKELY AS THUNDERSTORMS INITIATE IN THE
AFTERNOON. STEEP LAPSE RATES AND STRONG LOW-LEVEL FLOW SHOULD BE
CONDUCIVE FOR LARGE HAIL AND WIND DAMAGE SATURDAY AFTERNOON AND
EVENING ESPECIALLY IF A LINEAR MCS ORGANIZES BY EARLY EVENING.
TORNADOES ALSO APPEAR POSSIBLE WITH THE BETTER ORGANIZED SUPERCELLS
ESPECIALLY SINCE THE LOW-LEVEL JET HAS BECOME MORE DISTINCT IN THE
LATEST MODEL FORECASTS RUNS. THE SEVERE THREAT COVERAGE MAY BE
SUFFICIENT FOR A MODERATE RISK ACROSS PARTS OF THE REGION.
HOWEVER...UNCERTAINTY REMAINS TOO HIGH ESPECIALLY CONCERNING THE
QUALITY OF MOISTURE RETURN AND THUNDERSTORM COVERAGE FOR AN UPGRADE
ATTM.

.BROYLES.. 04/20/2007

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DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 201631
SWODY1
SPC AC 201629

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1129 AM CDT FRI APR 20 2007

VALID 201630Z - 211200Z

..THERE IS A SLGT RISK OF SVR TSTMS FROM SD SWD INTO WRN KS...

..SYNOPSIS...
UPR LOW EXPECTED TO CONTINUE SE ALONG THE CNTRL CA CST TODAY BEFORE
TURNING MORE E/SE ACROSS SRN CA/SW AZ EARLY SATURDAY. DOWNSTREAM
SYSTEM SHOULD WEAKEN AS IT LIFTS FARTHER N INTO SASKATCHEWAN/
MANITOBA...WHILE TRAILING COLD FRONT BECOMES STATIONARY NE/SW ACROSS
THE DAKOTAS. LEE TROUGH WILL STRENGTHEN OVER THE HI PLNS
..ESPECIALLY TONIGHT AND EARLY SATURDAY.

BOUNDARY LAYER MOISTURE...IN THE FORM OF A MODIFYING RETURNING POLAR
AIR...WILL SLOWLY INCREASE OVER THE HI PLNS...WITH DEWPOINTS ALONG
LEE TROUGH POSSIBLY REACHING THE LOW TO MID 50S NWD INTO WRN NEB BY
AFTERNOON. HEIGHT FALLS WITH CA SYSTEM WILL REMAIN W OF THE PLNS
UNTIL AFTER 06Z SATURDAY. THUS...WHILE LEE TROUGH/DRY LINE MAY MIX
A LITTLE E BY THIS AFTERNOON...FEATURE SHOULD REDEVELOP W INTO ERN
CO TONIGHT.

..CNTRL/SRN HI PLNS...
VEERING WIND PROFILES...STEEP LOW TO MID LEVEL LAPSE RATES AND
SLOWLY INCREASING LOW LEVEL MOISTURE WILL SUPPORT A CONDITIONAL
THREAT FOR SUPERCELL DEVELOPMENT BY LATE AFTERNOON ALONG LEE
TROUGH/DRY LINE FROM WRN NEB/KS SWD INTO W CNTRL TX.

SATELLITE AND MODEL DATA INDICATE THAT MID LEVEL COOLING/HEIGHT
FALLS WILL BE ABSENT ACROSS MOST OF THIS REGION THROUGH EARLY
TONIGHT. IN W CNTRL TX...WV IMAGERY DOES SUGGEST PRESENCE OF A WEAK
HI LEVEL IMPULSE NOW ENTERING FAR W TX THAT SHOULD REACH THE TX
SOUTH PLNS BY LATE IN THE DAY. FOR THE MOST PART...HOWEVER ...ANY
DEEP CONVECTIVE DEVELOPMENT WILL BE TIED TO CONVERGENCE/ HEATING
ALONG LEE TROUGH/DRY LINE.

ANY STORMS THAT DO FORM WILL HAVE THE POTENTIAL FOR LARGE HAIL
BEFORE BOUNDARY LAYER BEGINS TO DECOUPLE. RELATIVELY SPARSE
MOISTURE SUPPLY AND CONVERGENCE TOGETHER SHOULD LIMIT OVERALL STORM
COVERAGE.

..DAKOTAS...
A MORE WIDESPREAD AREA OF STORMS EXPECTED TO FORM LATER THIS
AFTERNOON THROUGH EARLY SATURDAY INVOF STALLING FRONT FROM NRN
NEB/SD NEWD INTO ND/NW MN AS SSWLY LLJ STRENGTHENS TO AOA 40-50 KTS.
MOST OF THIS ACTIVITY SHOULD BE ELEVATED. BUT WITH MUCAPE AOA 1000
J/KG AND CLOUD LAYER SHEAR AOA 40 KTS...STORMS COULD YIELD SEVERE
HAIL AND POSSIBLY HIGH WIND...ESPECIALLY IN NEB/SRN SD LATE TODAY
THROUGH EARLY TONIGHT.

..SRN CA...
AXIS OF ENHANCED DEEP SHEAR ASSOCIATED WITH UPR LOW DROPPING SE
ALONG THE CNTRL CA CST WILL REMAIN OFFSHORE TODAY...AND ENTER NW
MEXICO THIS EVENING. AT THE SAME TIME...THE AREAS MOST FAVORABLE
FOR DEEP ASCENT IN EXIT REGION OF ASSOCIATED JET STREAK ARE EXPECTED
TO REMAIN CLOUDY TODAY. THUS...PROSPECTS FOR STRONG STORMS IN THE
LAX OR SAN AREAS APPEARS LOW.

.CORFIDI/DARROW.. 04/20/2007

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DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 201224
SWODY1
SPC AC 201222

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0722 AM CDT FRI APR 20 2007

VALID 201300Z - 211200Z

..THERE IS A SLGT RISK OF SVR TSTMS FROM CENTRAL SOUTH DAKOTA SWD
TO NWRN KS...

..SYNOPSIS...

NEXT IN A SERIES OF POTENT S/WV TROUGHS DIGGING SEWD JUST OFF CA
COAST WITH DOWNSTREAM TROUGH RIDING NNEWD INTO SRN CANADA OVER THE
RIDGE IN THE CENTRAL CONUS. LEE TROUGHING E OF CENTRAL ROCKIES
CURRENTLY WILL INTENSIFY THROUGH THE AFTERNOON WITH CURRENT WEAK LOW
CENTER SERN CO SHIFTING INTO NEB PANHANDLE BY THIS EVENING.

LOW LEVEL MOISTURE SPREADING NWD E OF SURFACE TROUGH WITH DEWPOINTS
RISING INTO THE MID 50S NWD INTO WRN NEB BY THIS AFTERNOON. SURFACE
TROUGH/DRY LINE FROM CENTRAL TX PANHANDLE NWD ALONG KS/CO BORDER
WILL MIX A LITTLE E BY THIS AFTERNOON... RETURNING POSSIBLY AS FAR W
AS EXTREME CO BY THIS EVENING AS UPPER SUPPORT REMAINS WELL TO THE W
THROUGH THE FORECAST PERIOD.

..HIGH PLAINS...
VEERING SHEAR PROFILES...STEEP LAPSE RATES AND INCREASING LOW LEVEL
MOISTURE/INSTABILITY PROVIDE FOR A CONDITIONAL THREAT OF SUPERCELL
DEVELOPMENT BY MID/LATE AFTERNOON VICINITY LEE TROUGH/DRY LINE.
THERE WILL BE A LACK OF MID LEVEL COOLING AND UPPER SUPPORT ACROSS
THE DRY LINE TODAY AS THE CA TROUGH NOT EXPECTED TO BE A FACTOR
UNTIL SAT. THUS SURFACE INITIATION WILL BE TIED TO CONVERGENCE
VICINITY DRY LINE AND SURFACE HEATING.

MODEL GUIDANCE DOES SUPPORT AT LEAST A FEW SURFACE BASED STORMS
VICINITY CO/KS BORDER WITH A LITTLE GREATER THREAT INTO WRN NEB.
ANY STORMS THAT CAN DEVELOP COULD QUICKLY DEVELOP INTO A RELATIVELY
HIGH BASED SUPERCELL. PRIMARY THREAT WILL BE VERY LARGE HAIL THRU
THE EVENING WHEN SURFACE BOUNDARY LAYER SHOULD BEGIN DECOUPLING.
AMOUNT OF PRECIPITABLE WATER OF LESS THAN 3/4 INCHES SHOULD LIMIT
THE OVERALL STORM COVERAGE.

MORE WIDESPREAD THUNDERSTORMS EXPECTED OVERNIGHT NWD THRU THE
DAKOTAS AS INCREASING WARM ADVECTION ON 40-50KT LOW LEVEL JET
PROVIDES FAVORABLE LIFT. THESE STORMS SHOULD BE ROOTED WELL ABOVE
THE SURFACE...BUT GIVEN THE STEEP MID LEVEL LAPSE RATES AND
SHEAR...ROTATING STORMS AND ASSOCIATED MARGINAL SEVERE THREAT
EXPECTED...PRIMARILY LARGE HAIL.

.HALES/GRAMS.. 04/20/2007

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DAY48SVR: Nws Storm Prediction Center Norman Ok

ACUS48 KWNS 200829
SWOD48
SPC AC 200828

DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0328 AM CDT FRI APR 20 2007

VALID 231200Z - 281200Z

--ORGANIZED SEVERE WEATHER EPISODES WILL BE POSSIBLE OVER THE
SRN/CNTRL HIGH PLAINS MONDAY...APRIL 23RD...THE SRN/CNTRL PLAINS
TUESDAY...APRIL 24TH AND THE ARKLATEX INTO LOWER MS VALLEY
WEDNESDAY...APRIL 25TH.--

..DISCUSSION...

DESPITE SLIGHT DIFFERENCES IN TIMING...LATEST MEDIUM RANGE GUIDANCE
IS RELATIVELY CONSISTENT IN INTENSIFYING UPPER TROUGH OVER THE
ROCKIES ON DAY 4 /APRIL 23RD/...SHIFTING IT E INTO THE CNTRL/SRN
PLAINS ON DAY 5 /APRIL 24TH/...AND THEN DEAMPLIFYING IT AS IT
TRANSLATES EWD THROUGH THE REMAINDER OF THE EXTENDED PERIOD.
VERTICAL SHEAR WILL CORRESPONDINGLY INCREASE ACROSS A SUFFICIENTLY
MOIST WARM SECTOR SUCH THAT IT APPEARS THAT MULTIPLE SEVERE STORM
EPISODES WILL BE POSSIBLE.

THE GREATEST SEVERE WEATHER POTENTIAL APPEARS TO BE ON
MONDAY...APRIL 23RD OVER THE CNTRL/SRN HIGH PLAINS...TUESDAY...APRIL
24TH OVER THE SRN INTO CNTRL PLAINS AND THEN ON WEDNESDAY...APRIL
25TH OVER THE ARKLATEX INTO LOWER MS VALLEY. THEREAFTER...SOME
SEVERE WEATHER POTENTIAL WILL EXIST ALONG THE CNTRL/ERN GULF
COAST...THOUGH UNCERTAINTY IN EVOLUTION OF SYNOPTIC SYSTEM IS SUCH
THAT NO ADDITIONAL DAYS WILL BE DELINEATED.

.MEAD.. 04/20/2007

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DAY3SVR: Nws Storm Prediction Center Norman Ok

ACUS03 KWNS 200714
SWODY3
SPC AC 200713

DAY 3 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0213 AM CDT FRI APR 20 2007

VALID 221200Z - 231200Z

..THERE IS A SLGT RISK OF SVR TSTMS OVER PORTIONS OF THE MID AND
LOWER MO VALLEY INTO UPPER MIDWEST...

..SYNOPSIS...

LATEST MODEL GUIDANCE IS IN GOOD AGREEMENT IN INDICATING THAT
NEGATIVELY TILTED MID-LEVEL TROUGH INITIALLY OVER THE CNTRL PLAINS
SUNDAY MORNING WILL DEAMPLIFY AS IT TRANSLATES NEWD INTO THE GREAT
LAKES...CRESTING RIDGE AXIS IN PLACE OVER THE ERN STATES. IN THE
LOW-LEVELS...PRIMARY SURFACE LOW OVER NERN SD IS EXPECTED TO DEVELOP
NEWD INTO CNTRL ONTARIO WITH A SECONDARY WAVE DEVELOPING ALONG
TRAILING COLD FRONT FROM S-CNTRL NEB INTO WRN WI BY MONDAY MORNING.

..MID/LOWER MO VALLEY INTO UPPER MIDWEST...

TSTMS /SLIGHTLY ELEVATED/ ARE EXPECTED TO BE ONGOING SUNDAY MORNING
ALONG FRONTAL ZONE FROM NRN MN SWWD THROUGH ERN SD INTO CNTRL
PORTIONS OF NEB/KS. SOME HAIL WILL BE POSSIBLE WITH THE MORE
INTENSE STORMS INITIALLY...ESPECIALLY THOSE OVER KS INTO NEB IN
CLOSER PROXIMITY TO UPPER TROUGH WHERE BOTH INSTABILITY AND FORCING
FOR ASCENT WILL BE STRONGER.

ADDITIONAL...SURFACE-BASED STORMS WILL INCREASE ALONG COLD FRONT BY
EARLY AFTERNOON OVER ERN PARTS OF SD/NEB INTO WRN MN/IA...PERHAPS
SWD INTO NERN KS AND NRN MO WITHIN MARGINALLY TO MODERATELY UNSTABLE
AIR MASS. FORECAST SOUNDINGS SUGGEST THAT VERTICAL SHEAR WILL BE
SUFFICIENTLY STRONG FOR ORGANIZED...SEVERE STORMS INCLUDING BOWS
AND/OR SUPERCELLS. THE PRIMARY SEVERE WEATHER THREAT APPEAR TO BE
DAMAGING WINDS AND LARGE HAIL...THOUGH ISOLATED TORNADOES ARE
POSSIBLE WITH ANY STORMS THAT CAN REMAIN MORE DISCRETE.

STORMS SHOULD QUICKLY MOVE/DEVELOP EWD/NEWD INTO WI AND NRN IL
SUNDAY NIGHT WITH A CONTINUING THREAT OF ISOLATED DAMAGING WINDS AND
SOME HAIL.

.MEAD.. 04/20/2007

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DAY2SVR: Nws Storm Prediction Center Norman Ok

ACUS02 KWNS 200558
SWODY2
SPC AC 200556

DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1256 AM CDT FRI APR 20 2007

VALID 211200Z - 221200Z

..THERE IS A MDT RISK OF SVR TSTMS SATURDAY AFTERNOON AND EVENING
OVER WRN KS INTO PORTIONS OF THE OK/TX PNHDLS...

..THERE IS A SLGT RISK OF SVR TSTMS FROM WRN TX NWD INTO PORTIONS
OF THE NRN PLAINS...

..SYNOPSIS...

PROGRESSIVE LARGE-SCALE PATTERN WILL EXIST DURING THE DAY TWO PERIOD
WITH THE PRIMARY FEATURE OF INTEREST BEING SHORT WAVE TROUGH WHICH
WILL TRANSLATE EWD FROM THE LOWER CO VALLEY THROUGH THE SRN
ROCKIES...EVENTUALLY EJECTING NEWD AS A NEGATIVELY TILTED TROUGH
INTO THE CNTRL PLAINS BY SUNDAY MORNING.

IN THE LOW-LEVELS...SURFACE LOW INITIALLY OVER WRN NEB WILL DEVELOP
NEWD INTO THE RED RIVER VALLEY OF THE N BY THE END OF THE PERIOD
WHILE SECONDARY CYCLOGENESIS OCCURS SATURDAY OVER NERN CO. COLD
FRONT TRAILING FROM LEAD SURFACE LOW WILL PUSH SEWD FROM THE NRN
HIGH PLAINS THROUGH THE DAKOTAS AND WRN NEB. MEANWHILE...DRYLINE
ATTENDANT TO NERN CO LEE CYCLONE WILL BECOME INCREASINGLY SHARP
THROUGH THE DAY NEAR THE CO-KS BORDER SWD INTO THE WRN OR CNTRL TX
PNHDL AND INTO WRN TX.

..CNTRL/SRN HIGH PLAINS...

POOR LOW-LEVEL TRAJECTORIES ARISING FROM RIDGING OVER THE ERN U.S.
INTO GULF BASIN ARE EXPECTED TO LIMIT THE QUALITY OF BOUNDARY LAYER
MOISTURE WITHIN WARM SECTOR AIR MASS WITH NOTABLE DIFFERENCES
BETWEEN 20/00Z NAM/WRF AND GFS GUIDANCE IN THE EVOLUTION OF THE
MOISTURE/INSTABILITY FIELDS. FORECAST SOUNDINGS ALSO SUGGEST THAT
MID AND HIGH-LEVEL CLOUDINESS MAY TEND TO INCREASE AHEAD OF EJECTING
UPPER TROUGH...WHICH COULD TEMPER DAYTIME HEATING. HOWEVER...IT
DOES APPEAR THAT LOW/MID 50S DEWPOINTS WILL BE SUSTAINABLE WITH
AFTERNOON MIXING...WHICH WHEN COUPLED WITH STEEP MID-LEVEL LAPSE
RATES WILL CONTRIBUTE TO THE DEVELOPMENT OF AN AXIS OF MODERATE
INSTABILITY WITH MLCAPES OF 1000-1500 J/KG.

TSTMS WILL BECOME INCREASINGLY LIKELY BY AFTERNOON FROM PORTIONS OF
WRN/CNTRL NEB SWD THROUGH WRN KS INTO THE TX/OK PNHDLS AND WRN TX AS
INCREASED LARGE-SCALE FORCING FOR ASCENT AHEAD OF UPPER TROUGH AND
DEEPENING DRYLINE CIRCULATION ACT ON DESTABILIZING AIR MASS. SSWLY
50-70 KT MID-LEVEL JET STREAK WILL CONCURRENTLY PROPAGATE EWD ACROSS
WRN EDGE OF INSTABILITY AXIS WITH DEEP LAYER VERTICAL SHEAR BECOMING
INCREASINGLY SUPPORTIVE OF SUPERCELLS. LARGE HAIL /SOME
SIGNIFICANT/ WILL BE THE PRIMARY SEVERE WEATHER THREAT. TORNADOES
WILL ALSO BE POSSIBLE WITH THE MORE INTENSE STORMS GIVEN THE MODEST
LOW-LEVEL SHEAR AND LCL HEIGHTS. THIS SEVERE WEATHER IS EXPECTED TO
BE FAIRLY CONCENTRATED IN A N-S ZONE IMMEDIATELY E OF DRYLINE LATE
SATURDAY AFTERNOON AND EVENING.

SEVERE POTENTIAL SHOULD TEND TO DIMINISH SATURDAY NIGHT AS STORMS
SHIFT E OF INSTABILITY AXIS OVER THE HIGH PLAINS...THOUGH ISOLATED
LARGE HAIL AND/OR LOCALLY DAMAGING WINDS WILL REMAIN POSSIBLE WITH
THE MOST INTENSE CONVECTIVE ELEMENTS.

..NRN PLAINS...

TSTMS /PERHAPS SLIGHTLY ELEVATED/ MAY BE ONGOING SATURDAY MORNING
ALONG LOW-LEVEL FRONTAL ZONE FROM THE RED RIVER VALLEY SWWD INTO WRN
SD...DRIVEN LARGELY BY RATHER STRONG ISENTROPIC ASCENT INVOF OF THIS
BOUNDARY ON NOSE OF LLJ. THESE STORMS MAY PERSIST THROUGH THE DAY
NEAR FRONTAL ZONE DOWNSTREAM FROM DEVELOPING SURFACE LOW WHERE
ISENTROPIC ASCENT AND WAA WILL BE MAINTAINED BY LLJ. OTHER MORE
VIGOROUS SURFACE-BASED STORMS ARE EXPECTED BY AFTERNOON OVER CNTRL
INTO NERN SD ALONG SURFACE LOW TRACK WHERE AIR MASS WILL BECOME
MODERATELY UNSTABLE WITH MLCAPES OF 1000-1500 J/KG.

FORECAST SOUNDINGS SUGGEST THAT VERTICAL SHEAR WILL BE SUPPORTIVE OF
SUPERCELLS CAPABLE OF LARGE HAIL...DAMAGING WINDS AND PERHAPS A
COUPLE OF TORNADOES. OTHER STORMS...MORE LINEAR...WILL LIKELY
DEVELOP ALONG TRAILING COLD FRONT WHERE SEVERE HAIL AND LOCALLY
DAMAGING WINDS WILL BE POSSIBLE.

.MEAD.. 04/20/2007

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DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 200435
SWODY1
SPC AC 200433

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1133 PM CDT THU APR 19 2007

VALID 201200Z - 211200Z

..THERE IS A SLGT RISK OF SVR TSTMS PORTIONS CENTRAL PLAINS...

..SYNOPSIS...
HIGHLY AMPLIFIED UPPER AIR PATTERN FCST TO CONTINUE ACROSS CONUS --
DOMINATED BY WRN MEAN TROUGH AND RIDGING FROM WRN GULF TO HUDSON
BAY. MID-UPPER LEVEL LOW INITIALLY OVER ERN MT IS FCST TO EJECT NWD
OVER SASK TOWARD NWRN MB. UPSTREAM LOW -- NOW EVIDENT IN MOISTURE
CHANNEL IMAGERY JUST OFFSHORE NRN CA -- IS FCST TO DIG SEWD OVER SRN
CA/NRN BAJA REGION...THEN PIVOT EWD ACROSS NRN GULF OF CA AND LOWER
CO RIVER VALLEY BY 21/12Z.

AT SFC...DIFFUSE WARM FRONT -- ANALYZED ATTM OVER PORTIONS SRN
MO...ERN KS AND CENTRAL NEB -- IS FCST TO LIFT NWD ACROSS NRN NEB
AND SWRN SD...AND LINK WITH DEVELOPING LEE CYCLONE OVER ERN WY BY
21/00Z. PACIFIC FRONT ASSOCIATED WITH EJECTING MT TROUGH -- AND NOW
ANALYZED FROM CENTRAL NEB TO SWRN KS -- ALSO MARKS WRN EDGE OF
PARTIALLY MODIFIED RETURN FLOW AIR MASS AND ASSOCIATED 50S F SFC DEW
POINTS. THIS BOUNDARY WILL BECOME DIFFUSE AND BACK WWD TOWARD LEE
TROUGH...WITH RESULTING COMBINATION FORMING DRYLINE BETWEEN WRN NEB
AND NRN TX PANHANDLE. DRYLINE ALSO WILL EXTEND SWD ACROSS W TX TO
NRN COAHUILA BY MID/LATE AFTERNOON. NE-SW ALIGNED ZONE OF LOW LEVEL
FRONTOGENESIS ALSO WILL OCCUR FROM SFC LOW OVER ERN ND...ESPECIALLY
AFTER DARK.

SUBTROPICAL/SRN STREAM PERTURBATION IS EVIDENT IN MOISTURE CHANNEL
IMAGERY OVER SRN CHIHUAHUA/DURANGO REGION. DESPITE MISSING UPPER
AIR DATA INPUT FOR NGM/NAM OVER MEX...THIS FEATURE APPEARS TO BE
RESOLVED AND IS REASONABLY PROGGED TO MOVE NEWD ACROSS SWRN/CENTRAL
TX DURING THIS PERIOD. HOWEVER...ANTICYCLONIC FLOW/PRESSURE PATTERN
AT SFC AND ASSOCIATED LACK OF LOW LEVEL FORCING IN PATH OF MID-UPPER
TROUGH SHOULD PRECLUDE SIGNIFICANT CONVECTIVE POTENTIAL.

..CENTRAL/NRN PLAINS...AFTERNOON-EVENING...
ISOLATED TO WIDELY SCATTERED TSTMS ARE POSSIBLE BY LATE AFTERNOON
INVOF DRYLINE FROM WARM FRONTAL INTERSECTION SWD ACROSS WRN KS.
CAPPING BENEATH ROBUST ELEVATED MIXED LAYER SHOULD LIMIT OVERALL
COVERAGE/NUMBER OF TSTMS BY DAY. HOWEVER...ANY ACTIVITY THAT
DEVELOPS IN WARM SECTOR OR ALONG DRYLINE WILL BE IN FAVORABLE
KINEMATIC ENVIRONMENT TO ROTATE -- LARGE/DAMAGING HAIL BEING MAIN
THREAT...AND SVR GUSTS ALSO POSSIBLE. NON-NEGLIGIBLE TORNADO
POTENTIAL EXISTS FOR ANY SFC-BASED TSTMS THAT MAY INTERACT WITH WARM
FRONTAL ZONE OVER WRN/CENTRAL NEB BEFORE DIABATIC SFC COOLING
BECOMES TOO STG TO SUPPORT SFC-BASED EFFECTIVE INFLOW LAYER. SELY
SFC WINDS WILL CONTRIBUTE TO FAVORABLY VEERING WIND PROFILES WITH
HEIGHT AND ENLARGED LOW LEVEL HODOGRAPHS...WITH 0-3 KM SRH ROUGHLY
150-200 J/KG OVER WARM SECTOR PORTION OF CATEGORICAL SLGT RISK
AREA...AND 200-300 J/KG INVOF SFC WARM FRONT.
THERMODYNAMICALLY...MAIN QUESTIONS WILL CONCERN CAPPING AND BOUNDARY
LAYER MOISTURE. FAVORABLE MIDLEVEL LAPSE RATES OF 8-9 DEG C/KM --
OVER 50S F DEW POINTS -- WILL SUPPORT MLCAPES IN 1000-1500 J/KG
RANGE AND LOCALLY HIGHER DURING LATE AFTERNOON SFC THERMAL MAX.

WITH SWD EXTENT ALONG/AHEAD OF DRYLINE...EXPECT GEN INCREASE IN
SBCINH...AS WELL AS GRADUAL WEAKENING OF MIDLEVEL FLOW AND
ASSOCIATED DEEP-LAYER SHEAR. SVR POTENTIAL OVER SWRN KS SWD INTO
NRN TX PANHANDLE THEREFORE BECOMES MUCH MORE CONDITIONAL.

..CENTRAL/NRN PLAINS...AFTER 21/00Z...
CONVECTIVE COVERAGE IS FCST TO INCREASE NEAR AND N OF SFC WARM FRONT
FROM LATE EVENING INTO OVERNIGHT HOURS...SUPPORTED BY MOIST
ADVECTION AND ISENTROPIC ASCENT INVOF 40-50 KT LLJ. WITH EFFECTIVE
SHEAR REMAINING FAVORABLE AS ACTIVITY BUILDS NWD...LARGE HAIL
POTENTIAL LIKEWISE WILL SHIFT NWD OVER NRN NEB AND SD AFTER DARK.
THIS ALSO MAY INCLUDE ADDITIONAL/ELEVATED CONVECTIVE POTENTIAL LATE
IN PERIOD...IN ZONE OF ND FRONTOGENESIS.

.EDWARDS/GRAMS.. 04/20/2007

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