DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 0745 AM CDT MON AUG 08 2016 VALID 081300Z - 091200Z ...THERE IS A MRGL RISK OF SVR TSTMS PORTIONS ND TO ERN CO...WITH LOBE EXTENDING TO SWRN MT.... ...SUMMARY... A FEW STRONG TO SEVERE STORMS WITH A THREAT OF DOWNBURST WINDS AND LARGE HAIL WILL BE POSSIBLE OVER PORTIONS OF THE NORTHERN PLAINS. ISOLATED SEVERE GUSTS SHOULD BE THE PRIMARY THREAT WITH WESTWARD EXTENT FROM EASTERN WYOMING TO THE SOUTHWEST MONTANA REGION. ...SYNOPSIS... DOMINANT MID/UPPER-LEVEL FEATURE FOR THIS FCST WILL BE PROMINENT CYCLONE CURRENTLY CENTERED OVER PUGET SOUND REGION. ASSOCIATED 500-MB LOW IS FCST TO MEANDER SLOWLY SEWD ACROSS WRN WA TOWARD COLUMBIA GORGE THROUGH PERIOD...WHILE SERIES OF LESSER SHORTWAVE PERTURBATIONS EJECT NEWD FROM ITS BASAL CYCLONIC-FLOW BELT. DOWNSTREAM...LOWER-AMPLITUDE TROUGH IS EVIDENT IN MOISTURE-CHANNEL IMAGERY OVER SRN SK AND NRN MT...EMBEDDED WITHIN LARGER/SYNOPTIC- SCALE RIDGING. THIS SHORTWAVE TROUGH IS FCST TO PIVOT EWD ACROSS SRN PORTIONS SK/MB THROUGH PERIOD...ITS TRAILING VORTICITY LOBE LIKELY ABSORBING AN EVEN WEAKER FEATURE CURRENTLY EJECTING NEWD FROM ID/WY BORDER REGION. MEANWHILE...SEVERAL RELATIVELY MINOR... CONVECTIVELY GENERATED/ENHANCED VORTICITY MAXIMA WILL TRAVERSE FIELD OF WEAKER WLYS FROM CENTRAL/SRN HIGH PLAINS TO LOWER OH VALLEY REGION. AT SFC...TROUGH WITH SOME FRONTOLYTIC TENDENCIES -- LOCATED INITIALLY OVER ERN MT AND NRN/CENTRAL WY -- IS FCST TO MOVE EWD SLOWLY THROUGH PERIOD...TRAILING FROM SFC LOW THAT PRECEDES SK/MB SHORTWAVE TROUGH. BY 00Z...FRONT/TROUGH SHOULD REACH CENTRAL ND...NWRN SD AND ERN WY...THEN BY 12Z...ERN ND AND BLACK HILLS. ...NRN PLAINS/ROCKIES REGION... OVER DAKOTAS...ISOLATED TSTMS ARE POSSIBLE INVOF FRONT/TROUGH THIS AFTN AND EVENING...WITH CONDITIONAL RISK FOR DAMAGING GUSTS AND LARGE HAIL. PARAMETER SPACE IS LIKELY TO BECOME FAVORABLE...WITHIN NARROW CORRIDOR INVOF FRONT...TO SUPPORT SUPERCELLS WITH ANY SUSTAINED/RELATIVELY DISCRETE CONVECTION. HOWEVER...AS WITH PRIOR OUTLOOK...CONCERNS REGARDING TIMING AND COVERAGE OF SFC-BASED CONVECTION STILL IMPART TOO MUCH UNCERTAINTY TO ASSIGN MORE THAN MRGL UNCONDITIONAL PROBABILITIES ATTM. MERIDIONALLY ORIENTED PLUME OF FAVORABLE MOISTURE...CHARACTERIZED BY 60S F SFC DEW POINTS... SHOULD PERSIST AND SHIFT EWD ACROSS OUTLOOK AREA AS MOIST ADVECTION OFFSETS VERTICAL MIXING TO SUBSTANTIAL EXTENT. MODIFIED FCST SOUNDINGS SUGGEST MLCAPE MAY EXCEED 2000 J/KG ATOP WELL-MIXED/ INVERTED-V PROFILES IN BOUNDARY LAYER. THESE CONDITIONS SHOULD BECOME JUXTAPOSED WITH CORRIDOR OF 60-75-KT WSWLY TO SWLY 250-MB FLOW AND 40-50-KT 500-MB WINDS ACROSS ND...CONTRIBUTING TO 35-45-KT EFFECTIVE-SHEAR MAGNITUDES. SOMEWHAT VEERED SFC WINDS ARE POSSIBLE GIVEN ISALLOBARIC FORCING ASSOCIATED WITH LOW TRACKING N OF CANADIAN BORDER...WHICH CAN RESTRICT HODOGRAPH SIZE. FARTHER S...DEVELOPMENT IS MORE CERTAIN TODAY ACROSS PORTIONS ERN WY AND NERN CO NEAR LEE TROUGH AND FRONT RANGE...SUPPORTED BY AREAS OF STG SFC HEATING AND DEW POINTS 50S AND 60S F. LOW-LEVEL FLOW GENERALLY WILL BE WEAK...WITH SMALL AND RELATIVELY STRAIGHT HODOGRAPHS. HOWEVER...FROM NERN CO NWD...DEEP SHEAR STILL WILL BE FAVORABLE FOR A FEW ORGANIZED TSTMS IN CLUSTERS WITH TRANSIENT SUPERCELL CHARACTERISTICS POSSIBLE EARLY. MOST INTENSE CELLS MAY PRODUCE HAIL AND SVR GUSTS. ISOLATED DAMAGING WINDS ARE POSSIBLE FARTHER S FROM CONVECTION MOVING EWD OFF HIGHER TERRAIN OVER E-CENTRAL CO. ISOLATED TO WIDELY SCATTERED TSTMS ALSO ARE POSSIBLE IN REGIME OF BACKED NEAR-SFC WINDS AND MOISTURE ADVECTION/TRANSPORT BEHIND SFC FRONT...ACROSS SRN MT/NRN WY REGION. THOUGH FAVORABLE DEEP/SPEED SHEAR IS EXPECTED...LIMITING FACTOR FOR MORE THAN ISOLATED/BRIEF SVR POTENTIAL WILL BE LACK OF MORE ROBUST MOISTURE/INSTABILITY. ..EDWARDS/GLEASON.. 08/08/2016Read more
from SPC Forecast Products http://ift.tt/rATNzD
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