DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 190100
SWODY1
SPC AC 190058

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0758 PM CDT WED APR 18 2007

VALID 190100Z - 191200Z

..THERE IS A SLGT RISK OF SVR TSTMS PORTIONS NERN WY...ERN MT...

..SYNOPSIS...
HIGHLY AMPLIFIED UPPER AIR PATTERN EXISTS ACROSS
CONUS...CHARACTERIZED PRIMARILY BY UPPER LOW CENTERED OVER SRN
ID...RIDGING FROM NWRN ONT HIGH SSWWD TO LOWER TX COAST...AND NEARLY
ZONALLY ORIENTED ERN TROUGH. TROUGH ASSOCIATED WITH ID LOW WILL
BECOME PROGRESSIVELY MORE NEGATIVELY TILTED THROUGH REMAINDER
PERIOD...REACHING WRN CO AND CENTRAL WY WHILE PARENT CYCLONE ONLY
SLOWLY EJECTS TOWARD YELLOWSTONE AREA. MOISTURE CHANNEL IMAGERY
INDICATES MID/UPPER LOW OVER NRN INDIANA...ASSOCIATED WITH LARGER
SCALE ERN TROUGH. THIS FEATURE IS FCST TO MOVE SEWD ACROSS OH RIVER
TO NRN KY BY 12Z AND SUPPORT ISOLATED TSTMS...WHILE DOWNSTREAM
SHORTWAVE NOW OVER GA COAST AND SC EJECTS RAPIDLY EWD OVER ATLANTIC.

AT SFC...SEVERAL LOWS ARE EVIDENT ALONG PRONOUNCED FRONTAL ZONE THAT
EXTENDS FROM E-CENTRAL MT SWD THROUGH CENTRAL WY...THEN SWWD ACROSS
SERN UT AND WRN AZ. THIS FRONT IS FCST TO SURGE EWD THROUGH CENTRAL
ROCKIES OVERNIGHT AS PRIMARY SFC CYCLONE CONSOLIDATES ACROSS SERN
MT.

..NRN/CENTRAL HIGH PLAINS...
WIDELY SCATTERED TO SCATTERED TSTMS IN CLUSTERS -- SOME SVR -- WILL
CONTINUE FOR SEVERAL MORE HOURS ACROSS PORTIONS ERN MT...BECOMING
ISOLATED TO WIDELY SCATTERED FARTHER S ACROSS WY WHERE LOW LEVEL
FORCING IS SOMEWHAT WEAKER. ACTIVITY WILL REMAIN RATHER HIGH BASED
GIVEN SFC DEW POINTS UPPER 30S TO MID 40S. LARGE HAIL AND STG-SVR
GUSTS WILL REMAIN POSSIBLE. AS MID-UPPER TROUGH BECOMES MORE
NEGATIVELY TILTED...MEAN WIND VECTOR WILL BACK AND ATTAIN MORE
PRONOUNCED ELY COMPONENT...FROM NERN WY NWD THROUGH ERN MT. THIS IN
TURN WILL SUPPORT MERIDIONAL TO NWWD STORM MOTIONS -- MODULATED
SOMEWHAT BY SFC FORCING ASSOCIATED WITH NEWD-DIRECTED OUTFLOW POOLS
-- AND BY EXTENSION...KEEP SVR POTENTIAL FROM SPREADING MUCH FARTHER
EWD ACROSS NRN HIGH PLAINS.

SVR POTENTIAL WILL BE MORE SPORADIC WITH SWD EXTENT INTO CENTRAL
HIGH PLAINS...HOWEVER STRENGTHENING WIND FIELDS ALOFT AHEAD OF
MIDLEVEL TROUGH WILL ENSURE SUFFICIENT VERTICAL SHEAR FOR
SUPERCELLS. HOWEVER...ACTIVITY IS STRONGLY DIURNALLY DRIVEN...WITH
HEATING AND RESULTANT VERTICAL MIXING OF BOUNDARY LAYER REDUCING
CINH ENOUGH TO SUPPORT DEVELOPMENT. SBCINH SHOULD AGAIN INCREASE
RAPIDLY AS RELATIVELY DRY SFC AIR COOLS RAPIDLY AFTER SUNSET.
THERFORE TIME WINDOW WILL BE SHORT FOR SVR POTENTIAL FROM HIGH-BASED
TSTMS -- NOW EVIDENT IN VIS IMAGERY E OF FRONT/LARAMIE RANGES.
GIVEN LIMITED COVERAGE/DURATION OF POTENTIAL...WILL KEEP
PROBABILITIES MRGL.

.EDWARDS.. 04/19/2007

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MESO: Mesoscale Discussion 0515

ACUS11 KWNS 182051
SWOMCD
SPC MCD 182051
WYZ000-MTZ000-182215-

MESOSCALE DISCUSSION 0515
NWS STORM PREDICTION CENTER NORMAN OK
0351 PM CDT WED APR 18 2007

AREAS AFFECTED...NRN WY AND SRN MT

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE

VALID 182051Z - 182215Z

A SEVERE THREAT WILL LIKELY DEVELOP OVER NRN WY AND SRN MT OVER THE
NEXT FEW HOURS. LARGE HAIL WILL BE THE PRIMARY THREAT ALTHOUGH
ISOLATED WIND DAMAGE WILL ALSO BE POSSIBLE. A WW MAY BECOME
NECESSARY LATE THIS AFTERNOON ACROSS THE REGION.

LATEST SFC ANALYSIS SHOWS A SFC LOW NEAR RIVERTON WY WITH A COLD
FRONT EXTENDING SWD ACROSS SW WY INTO ERN UT. A LOW-LEVEL MOIST AXIS
EXISTS ACROSS WRN SD...ERN MT AND NE WY WHERE SFC DEWPOINTS RANGE
FROM THE 30S F TO THE LOWER 40S F. SFC HEATING ALONG THE MOIST AXIS
IS RESULTING IN INSTABILITY WITH MLCAPE VALUES GENERALLY AROUND 500
J/KG. IN ADDITION...RUC ANALYSIS AND WATER VAPOR IMAGERY SHOW A
SERIES OF SUBTLE SHORTWAVE TROUGHS EMBEDDED IN A LARGER WRN U.S.
UPPER-LEVEL TROUGH. AS THESE FEATURES MOVE NNEWD ACROSS THE REGION
WILL INCREASE LARGE-SCALE ASCENT PROVIDING A FOCUS FOR SCATTERED
THUNDERSTORM DEVELOPMENT OVER THE NEXT FEW HOURS. AS THUNDERSTORMS
INCREASE IN COVERAGE AND MATURE...MODERATE VERTICAL SHEAR AND LAPSE
RATES EXCEEDING 9.0 C/KM SHOWN ON FORECAST SOUNDINGS SHOULD BE
SUFFICIENT FOR ISOLATED SUPERCELLS WITH LARGE HAIL. WIND DAMAGE
SHOULD BE MORE ISOLATED BUT MAY ALSO ACCOMPANY ANY SUPERCELLS THAT
DEVELOP.

.BROYLES.. 04/18/2007

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

ATTN...WFO...UNR...CYS...BYZ...RIW...

43330757 43790910 44171040 44661072 45381067 45980996
46120879 45640682 45100554 44160444 42920478 42730615

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DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 181952
SWODY1
SPC AC 181950

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0250 PM CDT WED APR 18 2007

VALID 182000Z - 191200Z

..THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE HIGH PLAINS FROM ERN
MT INTO ERN WY...

..LOWER OH VALLEY...

DEEP CONVECTION HAS STRUGGLED TO DEVELOP WITHIN EXIT REGION OF UPPER
JET ACROSS IL/IND INTO KY THIS AFTERNOON. THOUGH ISOLATED
THUNDERSTORMS HAVE BEEN NOTED ACROSS SRN KY AT TIMES...BOUNDARY
LAYER APPEARS TO BE SOMEWHAT LACKING IN CONVERGENCE FARTHER NW IN
ADVANCE OF UPPER SPEED MAX. ADDITIONALLY...MID LEVEL LAPSE RATES
HAVE YET TO ADJUST SUFFICIENTLY FOR PARCELS TO ASCEND FREELY DESPITE
STRONG SFC HEATING. NET RESULT WILL BE FOR THE CONTINUATION OF
STRUGGLING UPDRAFTS WITH ONLY A FEW THUNDERSTORMS INTO THE EVENING
HOURS.

..LEE OF NRN/CNTRL ROCKIES...

DEEP LARGE SCALE FORCING IS SPREADING ACROSS ERN ID/UT/WRN WY THIS
AFTERNOON...PER EWD ADVANCEMENT OF THICKER CLOUD
SHIELD/PRECIPITATION. ISOLATED THUNDERSTORMS HAVE BEEN OBSERVED
WITHIN THIS STRONG BAROCLINIC ZONE ACROSS NWRN WY INTO SWRN
MT...THOUGH HAVE RECENTLY DECREASED IN COVERAGE/INTENSITY.
DOWNSTREAM...STRONG SFC HEATING IS UNDERWAY FROM NERN CO...NWD INTO
ERN MT WHERE SFC-3 KM LAPSE RATES ARE APPROACHING DRY ADIABATIC.
WITH THE BOUNDARY LAYER MOISTURE EXTREMELY LIMITED ACROSS THE HIGHER
TERRAIN OF WRN WY INTO ERN UT IT APPEARS STRONGER THUNDERSTORM
ACTIVITY MAY TEND TO DEVELOP JUST DOWNSTREAM WHERE SFC DEW POINTS
ARE APPROACHING 40F. PARCEL BUOYANCY IS MUCH STRONGER ACROSS THIS
REGION WITH MLCAPE VALUES NOW ON THE ORDER OF 500 J/KG ACROSS ERN WY
INTO SERN MT. ADDITIONALLY...LATEST VIS IMAGERY SUGGESTS CU FIELD
IS DEEPENING/EXPANDING FROM THE NRN SLOPES OF THE LARAMIE MOUNTAINS
NEAR CPR...NWD INTO EXTREME SERN MT. STRONG THUNDERSTORMS SHOULD
EVOLVE WITHIN THIS AGITATED CU FIELD WITHIN THE NEXT FEW HOURS.
DEEP LAYER SHEAR IS MORE THAN ADEQUATE FOR SUSTAINING ORGANIZED
ROTATING UPDRAFTS CAPABLE OF PRODUCING HAIL AND GUSTY WINDS. GIVEN
THE STRENGTH OF THE KINEMATIC FIELDS AND THE LIKELIHOOD FOR DEEP
SFC-BASED CONVECTION...SLIGHT RISK CERTAINLY SEEMS APPROPRIATE FOR
LARGE HAIL AND ISOLATED DAMAGING WINDS.

.DARROW.. 04/18/2007

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DAY2SVR: Nws Storm Prediction Center Norman Ok

ACUS02 KWNS 181752
SWODY2
SPC AC 181750

DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1250 PM CDT WED APR 18 2007

VALID 191200Z - 201200Z

..NO SVR TSTM AREAS FORECAST...

..WESTERN NC/SOUTH CAROLINA...

WELL DEFINED UPPER SPEED MAX WILL DIG SEWD ACROSS THE TN VALLEY INTO
ERN GA DURING THE AFTERNOON HOURS WHILE UPPER LOW SLOWLY LOSES
CIRCULATION IDENTITY OVER THE SRN APPALACHIANS. EVEN SO...VERY COLD
H5 TEMPERATURES...AOB MINUS 20C...WILL OVERSPREAD NW-SE ORIENTED LOW
LEVEL BAROCLINIC ZONE FROM ERN TN TO NEAR THE GA/SC COAST WHICH
SHOULD BE THE MAIN FOCUS FOR THUNDERSTORM DEVELOPMENT DURING THE
DAYLIGHT HOURS. IT APPEARS SUFFICIENT BOUNDARY LAYER MOISTURE WILL
HOLD ALONG THIS BAROCLINIC ZONE AS WARM SECTOR ACROSS GA HEATS
SUBSTANTIALLY DURING THE AFTERNOON HOURS. AS A RESULT...SFC-BASED
THUNDERSTORMS CAPABLE OF GENERATING MARGINALLY SEVERE HAIL SHOULD
DEVELOP/PROPAGATE SEWD ALONG THE SC/GA BORDER. DEEP LAYER SHEAR IS
ACTUALLY FORECAST TO BE STRONG ENOUGH TO WARRANT STORM
ROTATION...AND POSSIBLY WEAK SUPERCELL DEVELOPMENT...ESPECIALLY IF
SFC DEW POINTS CAN RISE INTO THE LOWER 50S AHEAD OF DEVELOPMENT.
WILL MONITOR THIS REGION FOR POSSIBLE UPGRADE IN LATER OUTLOOKS.

..NORTHERN/CENTRAL PLAINS...

STRONG SHORTWAVE TROUGH WITH SUBSTANTIAL HEIGHT FALLS WILL SPREAD
ACROSS WY INTO THE NRN HIGH PLAINS DURING THE DAY WHICH SHOULD FORCE
A WELL DEFINED COLD FRONT ACROSS THE DAKOTAS. A NARROW ZONE OF WEAK
INSTABILITY WILL DEVELOP JUST AHEAD OF THIS STRONGLY
CONVERGENT/FORCED WIND SHIFT. LATEST THINKING IS CONVECTION...WITH
A FEW ISOLATED THUNDERSTORMS...WILL EVOLVE IN ADVANCE OF THIS STRONG
SHORTWAVE. THOUGH FORECAST SOUNDINGS ARE NOT PARTICULARLY
UNSTABLE...SUFFICIENT BUOYANCY SHOULD EXIST FOR AT LEAST A LOW
PROBABILITY FOR GUSTY WINDS OR PERHAPS SOME HAIL.

FARTHER SOUTH ACROSS KS...WEAK RIDGING IN THE WAKE OF NRN PLAINS
SHORTWAVE TROUGH MAY SUPPRESS CONVECTIVE POTENTIAL ALONG TRAILING
FRONT DURING THE MID DAY HOURS. STRONG HEATING WILL BE NECESSARY
FOR DESTABILIZATION AND ANY HOPES FOR ROBUST CONVECTIVE DEVELOPMENT
ACROSS THIS REGION. UNTIL HIGHER QUALITY MOISTURE SURGES INTO WRN
KS LATE IN THE PERIOD IT WILL PROVE DIFFICULT DESTABILIZING THIS
REGION ADEQUATELY FOR SEVERE THUNDERSTORMS. A FEW STORMS MAY
HOWEVER EVOLVE WITHIN INCREASING WARM ADVECTION DURING THE EVENING
HOURS...A FEW OF WHICH MAY GENERATE SOME HAIL OR GUSTY WINDS.

.DARROW.. 04/18/2007

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DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 181551
SWODY1
SPC AC 181548

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1048 AM CDT WED APR 18 2007

VALID 181630Z - 191200Z

..NO SVR TSTM AREAS FORECAST...

VERY STRONG UPPER TROUGH CURRENTLY OVER NV IS FORECAST TO ROTATE
EASTWARD ACROSS THE CENTRAL/NORTHERN ROCKIES TODAY.
MEANWHILE...RAPID SURFACE CYCLOGENESIS IS EXPECTED ACROSS PARTS OF
MT/WY...WITH LEE TROUGH EXTENDING SOUTHWARD INTO EASTERN CO. LARGE
SCALE FORCING THROUGHOUT THIS REGION...COMBINED WITH FAVORABLE
/ALBEIT RELATIVELY DRY/ THERMODYNAMIC PROFILES WILL FAVOR SCATTERED
THUNDERSTORMS CAPABLE OF GUSTY WINDS AND HAIL OVER MUCH OF WY/MT/CO
AND PARTS OF EASTERN UT.

..WESTERN WY/CO AND EASTERN UT...
MORNING SURFACE ANALYSIS SHOWS LOW NORTH OF SLC...WITH STRONG COLD
FRONT SURGING EASTWARD ACROSS WESTERN UT. THIS FRONT WILL PROGRESS
EASTWARD TODAY INTO WESTERN WY/CO. FORECAST SOUNDINGS OVER THIS
REGION SHOW STEEP LOW/MID LEVEL LAPSE RATES AND STRONG SOUTHWEST
FLOW THROUGH A DEEP LAYER. DEEP MIXING WILL YIELD STRONG GRADIENT
WINDS...WHICH WILL ONLY BE ENHANCED THIS AFTERNOON AS SCATTERED
THUNDERSTORMS DEVELOP NEAR THE FRONT. COLD TEMPERATURES ALOFT COULD
ALSO RESULT IN HAIL IN STRONGER STORMS.

..EASTERN CO/WY AND MUCH OF MT...
BY LATE THIS AFTERNOON...LEE TROUGH IS FORECAST TO EXTEND FROM MAIN
SYNOPTIC LOW OVER EASTERN MT INTO EASTERN WY/CO. STRONG
SOUTHEASTERLY LOW LEVEL WINDS OVER THE HIGH PLAINS OF MT/WY/CO WILL
MAINTAIN SURFACE DEWPOINTS GENERALLY IN THE 30S TO LOWER 40S...AS
WELL AS RESULT IN FAVORABLE CONVERGENCE AND SHEAR PROFILES FOR
ISOLATED THUNDERSTORM DEVELOPMENT. CONVECTION WILL LIKELY INITIATE
FIRST NEAR LOW OVER SOUTH CENTRAL MT...SPREADING NORTHWARD ACROSS MT
THROUGH THE EVENING. THESE STORMS WILL HAVE A RISK OF GUSTY WINDS
AND HAIL. OTHER MORE ISOLATED ACTIVITY IS ANTICIPATED ALONG THE LEE
TROUGH AS FAR SOUTH AS EAST-CENTRAL CO. THESE STORMS WILL BE WIDELY
SPACED...BUT COULD BE HIGH-BASED SUPERCELLS CAPABLE OF LOCALLY
DAMAGING WINDS AND HAIL AS WELL. OVERALL COVERAGE OF SEVERE STORMS
DOES NOT APPEAR TO WARRANT A SLIGHT RISK AT THIS TIME. HOWEVER...WE
WILL CONTINUE TO MONITOR FOR GREATER DESTABILIZATION THAN CURRENTLY
EXPECTED.

..OH VALLEY...
WEAK SURFACE LOW IS CURRENTLY NEAR SDF...WITH COLD FRONT EXTENDING
WESTWARD INTO SOUTHERN IL/SOUTHEAST MO. LOW CLOUDS ALONG/AHEAD OF
FRONT ACROSS THE LOWER OH AND TN VALLEYS ARE SLOWLY ERODING...WHICH
SHOULD ALLOW POCKETS OF DAYTIME HEATING AND DESTABILIZATION.
DEWPOINTS IN THE 40S TO NEAR 50F WILL YIELD AFTERNOON MLCAPE VALUES
UP TO 500 J/KG. MODEL GUIDANCE IS CONSISTENT IN THE DEVELOPMENT OF
SCATTERED THUNDERSTORMS OVER PARTS OF IND/KY THIS AFTERNOON...WHERE
THE STRONGEST STORMS COULD PRODUCE HAIL. ORGANIZED SEVERE STORMS
ARE NOT ANTICIPATED AT THIS TIME.

.HART/GUYER.. 04/18/2007

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DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 181251
SWODY1
SPC AC 181248

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0748 AM CDT WED APR 18 2007

VALID 181300Z - 191200Z

..NO SVR TSTM AREAS FORECAST...

..SYNOPSIS...
A LARGE SCALE OMEGA-TYPE BLOCKING PATTERN IS BECOMING ESTABLISHED
OVER N AMERICA WITH THE PRIMARY RIDGE AXIS FROM THE ERN PLAINS NWD
TO A DEVELOPING CLOSED HIGH OVER WRN ONTARIO. FLANKING RIDGE ARE A
DOWNSTREAM TROUGH INVOF THE ATLANTIC COAST...AND AN UPSTREAM MEAN
TROUGH OVER THE GREAT BASIN. WITHIN THE WRN MEAN TROUGH...ONE
STRONG SHORTWAVE TROUGH OVER NV THIS MORNING WILL MOVE EWD TO THE
CENTRAL ROCKIES THIS EVENING AND NEWD TO THE CENTRAL/NRN HIGH PLAINS
BY EARLY THURSDAY...AS ANOTHER UPSTREAM TROUGH APPROACHES NRN
CA/ORE. CYCLOGENESIS WILL OCCUR IN THE IMMEDIATE LEE OF THE NRN
ROCKIES IN ADVANCE OF THIS MID LEVEL WAVE...WHILE A COLD FRONT
SURGES EWD ACROSS CO/WY TO THE S OF THE SURFACE CYCLONE IN CENTRAL
MT.

..CO/WY/MT THIS AFTERNOON INTO TONIGHT...
THUNDERSTORMS WILL BE POSSIBLE TODAY FROM NRN UT/NWRN CO NWD INTO
SRN MT WHERE STRONG ASCENT IS EXPECTED ALONG THE DEEP LAYER
BAROCLINIC ZONE NOW PROGRESSING EWD INTO UT/ID. HOWEVER... LIMITED
LOW-LEVEL MOISTURE...AS WELL AS INCREASING CLOUDS AND RELATIVELY
EARLY ARRIVAL OF THE FRONT WILL TEND TO LIMIT INSTABILITY IN THIS
AREA. STRONG VERTICAL SHEAR AND STEEP LAPSE RATES COULD STILL
SUPPORT STORMS WITH STRONG WINDS TODAY. FARTHER E OVER THE HIGH
PLAINS...STRONGER SURFACE HEATING /AFTERNOON TEMPERATURES REACHING
65-75 F/ AND STEEP MID LEVEL LAPSE RATES WILL SUPPORT LATE AFTERNOON
MLCAPE VALUES AOA 500 J/KG FROM THE HIGH PLAINS OF N CENTRAL CO NWD
ACROSS ERN WY INTO SE MT...DESPITE BOUNDARY LAYER DEWPOINTS ONLY IN
THE MID-UPPER 30S. THUNDERSTORM COVERAGE SHOULD INCREASE OVER AND E
OF THE MOUNTAINS BY LATE EVENING AS THE COLD FRONT OVERTAKES THE LEE
TROUGH AND ASCENT INCREASES. THE INITIALLY SURFACE-BASED STORMS
SHOULD PERSIST AND SPREAD EWD OVER THE HIGH PLAINS AS ELEVATED
CONVECTION.

THE STEEP MID LEVEL LAPSE RATES AND RELATIVELY COOL MID LEVEL
TEMPERATURES...ALONG WITH INCREASING VERTICAL SHEAR FROM N TO S IN
CLOSER PROXIMITY TO THE MID LEVEL JET...SHOULD SUPPORT A FEW STORMS
WITH MARGINALLY SEVERE HAIL. ALSO...INVERTED-V PROFILES IN THE LOW
LEVELS SHOULD BE CONDUCIVE TO STRONG OUTFLOW WINDS AS THUNDERSTORM
COVERAGE INCREASES DURING THE EVENING.

..LOWER OH VALLEY THIS AFTERNOON...
A COMPLEX INTERACTION WILL OCCUR BETWEEN MULTIPLE MID LEVEL WAVES
OVER THE MS/OH VALLEYS AND THE SE STATES TODAY. THE SRN STREAM
TROUGH OVER THE LOWER MS VALLEY THIS MORNING WILL LOSE AMPLITUDE AND
ACCELERATE INTO THE CONFLUENT FLOW REGIME OFF THE SE ATLANTIC COAST
BY THIS EVENING. MEANWHILE...A COMPACT NRN STREAM CLOSED LOW OVER
SRN LAKE MI WILL ROTATE SWD TO THE LOWER OH VALLEY AS PART OF THE
LARGER SCALE TROUGH ON THE ERN FLANK OF THE OMEGA BLOCK. THE THICK
CLOUDS WITH THE SRN STREAM WAVE SHOULD CLEAR THE LOWER OH VALLEY BY
MIDDAY...ALLOWING SOME SURFACE HEATING OF THE BOUNDARY LAYER WITH
RESIDUAL DEWPOINTS OF 45-50 F NEAR A WEAK SURFACE LOW AND ALONG A
WEAK COLD FRONT MOVING SWD TOWARD THE OH RIVER. THOUGH TOTAL CAPE
SHOULD REMAIN AOB 500 J/KG AND VERTICAL SHEAR WILL BE WEAK...THE
RELATIVELY STEEP LAPSE RATES AND COLD MID LEVEL TEMPERATURES COULD
SUPPORT MARGINALLY SEVERE HAIL FOR A FEW HOURS THIS AFTERNOON.

.THOMPSON/GRAMS.. 04/18/2007

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DAY48SVR: Nws Storm Prediction Center Norman Ok

ACUS48 KWNS 180856
SWOD48
SPC AC 180856

DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0356 AM CDT WED APR 18 2007

VALID 211200Z - 261200Z

..DISCUSSION...
GFS AND ECMWF ARE REMARKABLY CONSISTENT IN HANDLING THE STRONG
SHORT-WAVE TROUGH EXITING THE ROCKIES/ENTERING THE PLAINS DAY 4
/SAT. APR. 21/. NOT ONLY ARE THE MODEL SOLUTIONS FROM THE CURRENT
RUN EXTREMELY SIMILAR...BUT A GREAT DEAL OF MODEL CONSISTENCY HAS
EXISTED FOR THE PAST SEVERAL DAYS IN DEPICTING THIS FEATURE MOVING
INTO THE CENTRAL CONUS FOR SAT. APR. 21.

THE BIGGEST NEGATIVE ATTM APPEARS TO BE THE DEGREE OF BOUNDARY-LAYER
MOISTURE RETURN...AS TRAJECTORIES OFF THE GULF/INTO TX REMAIN
ELY/ESELY AROUND A LARGE HIGH OVER THE ERN HALF OF THE CONUS/GULF OF
MEXICO. HAVING SAID THIS...CONFIDENCE REMAINS HIGH THAT THE
STRENGTH OF THE EJECTING TROUGH AND ASSOCIATED WIND FIELD WILL
SUPPORT A FAIRLY SIGNIFICANT SEVERE EVENT DESPITE THE POSSIBILITY OF
RELATIVELY LIMITED INSTABILITY. THEREFORE...WILL MAINTAIN A THREAT
FOR SAT. /DAY 4/ ACROSS A LARGE PORTION OF THE PLAINS.

THE POSSIBLE LACK OF MOISTURE MAY BECOME MORE OF A LIMITING FACTOR
FOR DAY 5...AS THE UPPER TROUGH EJECTS NEWD ACROSS THE PLAINS AND
EVENTUALLY ACROSS THE UPPER GREAT LAKES REGION. WHILE SOME SEVERE
POTENTIAL WILL EXIST INTO THE MID/UPPER MS AND LOWER OH VALLEYS AND
POSSIBLY THE UPPER GREAT LAKES...OVERALL DEGREE OF SEVERE MAY BE
LIMITED DUE TO AN OVERALL LACK OF FAVORABLE INSTABILITY.
THEREFORE...WILL NOT HIGHLIGHT THE POTENTIAL FOR A SIGNIFICANT EVENT
FOR DAY 5 ATTM.

MODEL DIVERGENCE INCREASES -- AT LEAST WITH RESPECT TO TIMING -- FOR
DAYS 6-8. WHILE BOTH MODELS BRING A STRONG TROUGH/CLOSED LOW INTO
THE CENTRAL AND SRN PLAINS DURING THIS TIME FRAME...THE GFS IS CLOSE
TO 24 HOURS FASTER WITH THIS FEATURE THAN THE ECMWF. THUS...WILL
REFRAIN ATTM FROM HIGHLIGHTING THE SEVERE POTENTIAL ASSOCIATED WITH
THIS FEATURE ATTM...THOUGH CONFIDENCE IS INCREASING THAT A SEVERE
EVENT WILL INDEED OCCUR SOMETIME IN THE DAY 6-8 TIME FRAME OVER THE
SRN PLAINS.

.GOSS.. 04/18/2007

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DAY3SVR: Nws Storm Prediction Center Norman Ok

ACUS03 KWNS 180731
SWODY3
SPC AC 180729

DAY 3 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0229 AM CDT WED APR 18 2007

VALID 201200Z - 211200Z

..NO SVR TSTM AREAS FORECAST...

..SYNOPSIS...
LARGE-SCALE RIDGE WILL PREVAIL OVER THE CENTRAL CONUS THIS
PERIOD...UPSTREAM OF A TROUGH CENTERED OVER THE WRN ATLANTIC AND
DOWNSTREAM OF A SECOND TROUGH ADVANCING EWD ACROSS THE WRN CONUS.
THE WRN TROUGH IS FORECAST TO REMAIN TOO FAR W TO DIRECTLY AFFECT
THE CONVECTIVE POTENTIAL OVER THE PLAINS STATES THIS PERIOD...BUT
MODELS HINT THAT A WEAK LEAD IMPULSE WITHIN SWLY FLOW AHEAD OF THIS
FEATURE MAY TRAVERSE THE HIGH PLAINS. THIS COMBINED WITH THE LIKELY
PRESENCE OF A HIGH PLAINS DRYLINE -- AND POSSIBLY A WEAK W-E WARM
FRONT LIFTING NWD ACROSS KS/OK...COULD RESULT IN A FEW
ISOLATED/SEVERE STORMS THIS PERIOD.

..CENTRAL AND SRN HIGH PLAINS INTO SRN KS/NRN OK...
A SLOW NWD INCREASE IN BOUNDARY-LAYER DEWPOINTS SHOULD OCCUR INTO
OK/KS/THE CENTRAL AND SRN HIGH PLAINS THIS PERIOD...AS BROAD AREA OF
LOW-LEVEL SELY FLOW DEVELOPS AHEAD OF APPROACHING LARGE-SCALE
TROUGH. THIS COMBINED WITH DAYTIME HEATING AND STEEPENING LAPSE
RATES -- PARTICULARLY OVER THE HIGH PLAINS -- SUGGESTS MODERATE
DESTABILIZATION WILL OCCUR BY LATE AFTERNOON.

WHILE THE NAM FORECAST SOUNDINGS REVEAL THE MODELS TYPICAL BIAS OF
AGGRESSIVELY ERODING THE CAPPING INVERSION WHILE ALSO
MOISTENING/STEEPENING THE LAPSE RATES WITHIN THE BOUNDARY
LAYER...THE NAMKF SHOWS A STRONGER -- AND LIKELY MORE ACCURATE --
DEPICTION OF A MORE PERSISTENT CAP.

ALONG THESE SAME LINES...THE NAM MUCH MORE AGGRESSIVELY DEVELOPS
PRECIPITATION -- BOTH ALONG THE WARM FRONT OVER NERN OK/SERN
KS...AND ALONG THE DRYLINE. ATTM...IT APPEARS THAT CONVECTIVE
DEVELOPMENT WILL BE QUITE LIMITED -- PERHAPS TO JUST A FEW ISOLATED
CELLS. HAVING SAID THAT...ANY STORMS WHICH DO DEVELOP WOULD FIND
THEMSELVES IN AN ENVIRONMENT -- BOTH THERMODYNAMICALLY AND
KINEMATICALLY -- SUPPORTIVE OF SUPERCELLS. THEREFORE...WILL
INTRODUCE A 5%/CONDITIONAL SEVERE THREAT ACROSS THE CENTRAL AND SRN
HIGH PLAINS...AND EWD INTO OK/KS ALONG THE POSSIBLE WARM FRONT.

.GOSS.. 04/18/2007

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DAY2SVR: Nws Storm Prediction Center Norman Ok

ACUS02 KWNS 180601
SWODY2
SPC AC 180559

DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1259 AM CDT WED APR 18 2007

VALID 191200Z - 201200Z

..NO SVR TSTM AREAS FORECAST...

..SYNOPSIS...
WHILE CYCLONIC FLOW ALOFT OVER THE ERN CONUS WILL CONTINUE TO SHIFT
EWD INTO THE ATLANTIC...LARGE/COMPLEX UPPER TROUGH WILL CONTINUE TO
INTENSIFY/EXPAND OVER THE WEST. A NEGATIVELY-TILTED SHORT-WAVE
TROUGH WITHIN THE EVOLVING LARGER-SCALE TROUGH WILL CONTINUE TO BE
SHUNTED NEWD ACROSS THE NRN PLAINS...AS IT IMPINGES ON THE RIDGE
OVER THE PLAINS. MEANWHILE...A SECOND/STRONGER SHORT-WAVE FEATURE
SHOULD MOVE RAPIDLY SSEWD ALONG THE W COAST.

AT THE SURFACE...LEE TROUGH IS FORECAST TO MOVE EWD INTO THE PLAINS
AND WEAKEN WITH TIME...BUT STILL MAY PROVIDE A FOCUS FOR SCATTERED
AFTERNOON STORMS.

..NRN PLAINS SEWD INTO THE MID MO VALLEY/KS/NRN OK...
SHOWERS AND A FEW THUNDERSTORMS SHOULD BE ONGOING AT THE START OF
THE PERIOD AHEAD OF LEE TROUGH/SHORT-WAVE UPPER FEATURE OVER THE NRN
HIGH PLAINS AND VICINITY. THIS CONVECTION SHOULD CONTINUE MOVING
EWD THROUGH THE DAY...LIKELY REMAINING WEAK DUE TO LIMITED
INSTABILITY.

FURTHER S...INSTABILITY SHOULD INCREASE...THOUGH SUBSIDENCE/CAPPING
WILL LIKEWISE INCREASE WITH SWD EXTENT WHERE THE UPPER RIDGE WILL
PREVAIL.

ATTM...IT APPEARS THAT SOMEWHERE BETWEEN THE STRONGER UVV TO THE N
AND STRONGER CAP TO THE S...A SMALL ZONE OF SUFFICIENT INSTABILITY
AND A WEAKENING CAP ON THE SRN FRINGES OF THE UPPER FEATURE MAY
ALLOW A FEW AFTERNOON STORMS TO DEVELOP -- MOST LIKELY ACROSS
CENTRAL AND ERN KS. WITH 500 J/KG MEAN-LAYER CAPE AND 40 TO 50 KT
DEEP-LAYER SHEAR...A FEW STRONGER/POSSIBLY-ROTATING STORMS MAY
EVOLVE. GIVEN CAP ISSUES AND LIKELIHOOD THAT STORMS WILL REMAIN
ISOLATED...WILL INTRODUCE ONLY 5% SEVERE PROBABILITY ATTM.
CONVECTION/SEVERE THREAT SHOULD DECREASE INTO THE EVENING WITH THE
ONSET OF DIURNAL STABILIZATION.

.GOSS.. 04/18/2007

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DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 180542
SWODY1
SPC AC 180539

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1239 AM CDT WED APR 18 2007

VALID 181200Z - 191200Z

..NO SVR TSTM AREAS FORECAST...

..SYNOPSIS...

LARGE OMEGA BLOCKING PATTERN WILL CONTINUE ACROSS THE MID AND HIGH
LATITUDES OF N. AMERICA WITH AN UNDERCUTTING STREAM OF STRONGER
ZONAL FLOW FROM THE ERN PACIFIC ACROSS THE SRN STATES. WITHIN THIS
LARGER-SCALE REGIME...MID-LEVEL TROUGH CURRENTLY DIGGING OVER THE
PACIFIC NW INTO GREAT BASIN WILL SHIFT MORE EWD PRIOR TO EJECTING IN
NEGATIVE TILT FASHION INTO THE NRN AND CNTRL HIGH PLAINS.

IN THE LOW-LEVELS...A RELATIVELY STRONG PACIFIC COLD FRONT ATTENDANT
TO THIS UPPER SYSTEM WILL PUSH EWD THROUGH THE ROCKIES INTO ADJACENT
HIGH PLAINS. ASSOCIATED SURFACE LOW IS FORECAST TO DEEPEN AS IT
DEVELOPS FROM NWRN WY INTO SERN MT BY THURSDAY MORNING.

..NRN/CNTRL ROCKIES INTO HIGH PLAINS...

LOW-LEVEL AIR MASS IS EXPECTED TO REMAIN RELATIVELY DRY AHEAD OF
PACIFIC COLD FRONT WITH DEWPOINTS COMMONLY IN THE 20S AND 30S.
HOWEVER...DAYTIME HEATING COUPLED WITH DYNAMIC COOLING ASSOCIATED
WITH CONCENTRATED HEIGHT FALL CENTER AHEAD OF UPPER SYSTEM WILL
RESULT IN THE DEVELOPMENT OF STEEP LOW TO MID-LEVEL LAPSE RATES
WITHIN PRE-FRONTAL AIR MASS. EXPECT SBCAPES TO RANGE FROM 200-400
J/KG OVER PORTIONS OF NERN UT/CO...TO 500-900 J/KG OVER S-CNTRL INTO
SERN MT.

TSTMS WILL LIKELY INITIALLY DEVELOP BY EARLY TO MID AFTERNOON ALONG
FRONT OR IN IMMEDIATE POST-FRONTAL AIR MASS FROM S-CNTRL MT SWD INTO
WRN WY AND NERN UT. SUBSEQUENT STORM DEVELOPMENT WILL THEN OCCUR
OVER PORTIONS OF CNTRL/ERN PARTS OF MT/WY SWD INTO WRN/CNTRL CO
THROUGH THE REMAINDER OF THE AFTERNOON INTO TONIGHT. THE STEEP
LAPSE RATES COUPLED WITH INCREASING VERTICAL SHEAR INDICATE THE
POTENTIAL FOR A FEW ORGANIZED STORMS CAPABLE OF SEVERE HAIL AND
LOCALLY DAMAGING WINDS.

FORECAST SOUNDINGS AND PLAN VIEW PROGNOSTIC FIELDS INDICATE THAT THE
STRONGEST VERTICAL SHEAR WILL REMAIN UPSTREAM OF THE STRONGER
INSTABILITY IN PLACE OVER MT...LEAVING SOME UNCERTAINTY AS TO WHERE
THE GREATEST SEVERE WEATHER THREAT WILL LIKELY EXIST.
THEREFORE...LOW WIND/HAIL PROBABILITIES HAVE BEEN ASSIGNED TO A
BROADER GEOGRAPHICAL AREA TO ADDRESS THIS UNCERTAINTY.

..WRN/CNTRL KY...

MID-LEVEL COLD POOL ATTENDANT TO UPPER LOW OVER THE OH VALLEY IS
EXPECTED TO CONTRIBUTE TO STEEPENING LAPSE RATES AND WEAK CONVECTIVE
INSTABILITY /SBCAPES OF 400-600 J PER KG/ INVOF WEAK SURFACE LOW AND
FRONT THIS AFTERNOON. ISOLATED/SCATTERED TSTMS WILL BECOME
INCREASINGLY LIKELY BY AFTERNOON ACROSS THE AREA...A FEW OF WHICH
COULD PRODUCE SOME SMALL HAIL. ANY SEVERE WEATHER THREAT APPEARS
TOO LOW TO WARRANT INCLUSION OF PROBABILITIES.

.MEAD/GRAMS.. 04/18/2007

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