Saturday, August 17, 2013

MESO: Mesoscale Discussion 1734

ACUS11 KWNS 172021
SWOMCD
SPC MCD 172020
MTZ000-IDZ000-ORZ000-WAZ000-172245-

MESOSCALE DISCUSSION 1734
NWS STORM PREDICTION CENTER NORMAN OK
0320 PM CDT SAT AUG 17 2013

AREAS AFFECTED...PORTIONS OF CNTRL/W-CNTRL MT...NRN/CNTRL ID...FAR
NERN ORE

CONCERNING...SEVERE POTENTIAL...WATCH UNLIKELY

VALID 172020Z - 172245Z

PROBABILITY OF WATCH ISSUANCE...5 PERCENT

SUMMARY...A VERY ISOLATED...MARGINAL SVR THUNDERSTORM POTENTIAL
COULD EXIST INTO THE EVENING HOURS.

DISCUSSION...WATER VAPOR LOOPS DEPICT THE MANIFESTATION OF A
MID-LEVEL SHORTWAVE TROUGH ENTERING THE NRN INTERMOUNTAIN WEST
THROUGH ITS EFFECTS OF DEFORMATION ON A WAVY...NARROW MID-LEVEL DRY
SLOT BRANCHING NE OF AN E-PACIFIC CYCLONE. A MINOR INFLECTION IN
THIS DRY SLOT STRUCTURE APPEARS TO BE APPROACHING THE MUTUAL
INTERSECTION POINT OF THE WA/ORE/ID BORDERS...AND IS PRECEDED BY A
LOBE OF ASCENT. THIS ASCENT IS SERVING TO STEEPEN MID-LEVEL LAPSE
RATES. AND...WITH SFC DEWPOINTS HAVING MIXED OUT THROUGH THE 40S IN
MANY LOCATIONS BENEATH A PLUME OF MODEST MID-LEVEL MOISTURE
SUPPORTING PW VALUES AROUND 0.8-1.0 INCH PER GPS DATA...SFC-BASED
BUOYANCY CONTINUES TO INCREASE. MLCAPE VALUES ARE APPROXIMATED TO BE
AROUND 300-1200 J/KG ACROSS THE AREA.

VISIBLE SATELLITE IMAGERY DEPICTS RECENT AGITATION TO CUMULUS
CONGESTUS FIELDS WITHIN THE OVERLAPPING CORRIDOR OF THE
AFOREMENTIONED PW VALUES AND MID-LEVEL ASCENT...AIDED BY LIFT
PROVIDED BY DIURNALLY DEEPENING/STRENGTHENING OROGRAPHIC
CIRCULATIONS. SUCH CIRCULATIONS ARE ALSO SUPPORTING CUMULUS
DEVELOPMENT DOWNSTREAM OF STRONGER...LARGER-SCALE AGEOSTROPHIC
CIRCULATIONS ACCOMPANYING THE SHORTWAVE TROUGH -- I.E. INVOF MORE
ISOLATED MOUNTAINS IN CNTRL MONTANA INCLUDING THE LITTLE BELT
MOUNTAINS SE OF GREAT FALLS.

VERY ISOLATED THUNDERSTORMS COULD DEVELOP DURING THE NEXT FEW HOURS
FROM THIS CUMULUS AND CONTINUE INTO THE EVENING HOURS. THE
AFOREMENTIONED BUOYANCY...COMBINED WITH AROUND 30-40 KT OF EFFECTIVE
DEEP SHEAR...MAY CONDITIONALLY SUPPORT A FEW ORGANIZED STORM
STRUCTURES/POSSIBLE SUPERCELLS. MARGINALLY SVR HAIL/WIND CANNOT BE
RULED OUT WITH THE MOST INTENSE STORMS...WITH SFC WIND GUSTS BEING
ENHANCED BY LARGE SFC TEMPERATURE-DEWPOINT SPREADS AROUND 30-40F
ACCOMPANYING DEEP INVERTED-VEE THERMODYNAMIC PROFILES. HOWEVER...THE
LACK OF RICHER TROPOSPHERIC MOISTURE AND/OR EVEN STRONGER DEEP
FORCING FOR ASCENT WILL LIKELY LIMIT THE COVERAGE/INTENSITY OF DEEP
CONVECTION.

..COHEN/KERR.. 08/17/2013

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

ATTN...WFO...BYZ...GGW...TFX...MSO...BOI...OTX...PDT...

LAT...LON 44811860 45261841 45991724 46821536 48011233 48591023
48570872 47900783 46920836 46171048 44821604 44441802
44811860

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