ACUS11 KWNS 170225
SWOMCD
SPC MCD 170225
MNZ000-NDZ000-SDZ000-170400-
MESOSCALE DISCUSSION 1636
NWS STORM PREDICTION CENTER NORMAN OK
0925 PM CDT SAT JUL 16 2011
AREAS AFFECTED...CENTRAL/ERN ND...NWRN MN...AND PARTS OF FAR NRN SD
CONCERNING...TORNADO WATCH 649...
VALID 170225Z - 170400Z
THE SEVERE WEATHER THREAT FOR TORNADO WATCH 649 CONTINUES.
...WW 649...
SURFACE ANALYSES DURING THE EARLY EVENING SHOWED A SSW-NNE ORIENTED
BOUNDARY MOVING SLOWLY EWD INTO NERN TO SOUTH CENTRAL ND...WITH THIS
BOUNDARY THEN EXTENDING SWWD TO AN AREA OF LOW PRESSURE LOCATED OVER
WEST CENTRAL SD. MEANWHILE...A WARM FRONT/DIFFERENTIAL HEATING
BOUNDARY EXTENDED FROM WEST CENTRAL WI/EAST CENTRAL MN WNWWD INTO
FAR NERN SD...AND THEN NWWD INTO SERN ND INTERSECTING THE SSW-NNE
BOUNDARY /NE OF BIS OR WNW OF JMS/. LOW LEVEL WAA ALONG A 20-25 KT
SSWLY LLJ ACROSS THE ERN DAKOTAS/WRN MN AND FORCING FOR ASCENT
WITHIN THE ENTRANCE REGION OF A 50 KT WLY MANITOBA/NRN ONTARIO
MIDLEVEL JET WILL PROVE FAVORABLE FOR ADDITIONAL STORM DEVELOPMENT
THROUGH THE EVENING.
OBJECTIVE ANALYSES INDICATED THE AIR MASS ACROSS WW 649 AND INTO ERN
SD REMAINS VERY UNSTABLE /MLCAPE 3000-4500 J PER KG/...WITH
EFFECTIVE BULK SHEAR AROUND 50 KT MORE THAN SUFFICIENT FOR
SUPERCELLS. GIVEN THE SHEAR VECTORS ORIENTED PERPENDICULAR TO THE
SSW-NNE ORIENTED BOUNDARY WHERE STORMS CONTINUE TO DEVELOP...THE
STORM MODE SHOULD REMAIN FOR DISCRETE STORMS WHICH WILL FAVOR A
GREATER POTENTIAL FOR A TORNADO THREAT. THUS FAR...TORNADOES HAVE
BEEN THE PRIMARY THREAT AS HIGH FREEZING LEVELS /AROUND 15 KFT PER
BIS/ABR 00Z SOUNDINGS/ HAVE TENDED TO LIMIT HAIL SIZE.
COUNTIES CAN CONTINUE TO BE REMOVED FROM WW 649 WEST OF THE SSW-NNE
ORIENTED SURFACE BOUNDARY...GIVEN THIS BOUNDARY HAS REMAINED THE
PRIMARY FOCI FOR STORM INITIATION AND A SURFACE RIDGE EXTENDS SWD
INTO WRN ND.
...NRN SD...
AT 0215Z...REGIONAL RADAR IMAGERY CONTINUED TO SHOW STORMS TRYING TO
DEVELOP SWD ALONG THE SSW-NNE SURFACE BOUNDARY INTO FAR NORTH
CENTRAL SD...WHERE THE AIR MASS IS ALSO VERY UNSTABLE AND STRONGLY
SHEARED PER EFFECTIVE BULK SHEAR OF 40-50 KT. HOWEVER...A STRONGER
CAP /PER ABR 00Z SOUNDING/ WITH SWD EXTENT SHOULD TEND TO LIMIT
STRONG TO SEVERE STORMS FROM AFFECTING MUCH OF SD THIS EVENING.
..PETERS.. 07/17/2011
...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...
ATTN...WFO...DLH...FGF...ABR...BIS...
LAT...LON 47419439 46279717 45629845 45520048 45830167 46770093
48079993 49009935 49019639 49359444 47419439
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