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Feb 18, 2014 1300 UTC Day 1 Convective Outlook

February 18, 2014

Feb 18, 2014 1300 UTC Day 1 Convective Outlook

day1otlk

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0650 AM CST TUE FEB 18 2014

VALID 181300Z – 191200Z

…NO SVR TSTM AREAS FORECAST…

…SYNOPSIS…

A PROGRESSIVE…POLAR-BRANCH WAVE TRAIN WILL BE MAINTAINED ACROSS THE NRN TIER OF STATES THROUGH THE D1 PERIOD. WITHIN THIS BELT OF HIGH-MOMENTUM FLOW…A COMPACT BUT INTENSE UPPER LOW AND ASSOCIATED NEGATIVE-TILT SHORT-WAVE TROUGH FROM SWRN ONTARIO TO MID ATLANTIC WILL MOVE ENEWD THROUGH NEW ENGLAND INTO THE CANADIAN MARITIMES. UPSTREAM…A SHORT-WAVE TROUGH WILL TRACK FROM THE NRN HIGH PLAINS TO GREAT LAKES AND OH VALLEY WITH THIS SYSTEM FLANKED BY A WEAKENING LOWER-LATITUDE IMPULSE PROGRESSING FROM THE CNTRL ROCKIES TO GULF COAST STATES. IN THE WEST…A SHORT-WAVE TROUGH WILL AMPLIFY WHILE TRANSLATING FROM THE NERN PACIFIC INTO WRN CANADA AND THE PACIFIC NW.

IN THE LOW LEVELS…A SURFACE CYCLONE ASSOCIATED WITH THE NERN U.S. SYSTEM OVER SWRN ONTARIO AS OF 12Z WILL WEAKEN TODAY IN FAVOR OF SECONDARY LOW DEVELOPMENT ALONG OR AHEAD OF AN EWD-MOVING COLD FRONT OFF THE MID ATLANTIC COAST. THE COLD FRONT TRAILING THESE CYCLONES APPEARS TO HAVE STALLED ACROSS THE GULF COAST STATES INTO CNTRL TX. THIS BOUNDARY WILL BEGIN TO DEVELOP NWD AS A WARM FRONT TODAY IN RESPONSE TO THE MULTI-STREAM SHORT-WAVE TROUGH MENTIONED ABOVE.

…GULF COAST STATES/TN VALLEY LATE THIS AFTERNOON INTO TONIGHT…

12Z OBSERVED SOUNDINGS CONFIRM THE PRESENCE OF A SEASONABLY MOIST AIR MASS TO THE SOUTH OF THE STALLED FRONT WITH BOUNDARY LAYER DEWPOINTS IN THE UPPER 50S TO LOWER 60S AND LOWEST 100-MB MEAN-MIXING RATIOS OF 11-12 G/KG. THIS MOISTURE IS SURMOUNTED BY AN ELEVATED-MIXED LAYER /EML/ WHICH WILL CONTRIBUTE TO THE DEVELOPMENT OF WEAK TO MODERATE INSTABILITY BY AFTERNOON WITH MLCAPE APPROACHING 500-1000 J/KG.

NOTABLE VARIABILITY EXISTS AMONGST MODEL GUIDANCE WITH RESPECT TO THE TIMING AND LOCATION OF TSTM DEVELOPMENT LATER TODAY INTO TONIGHT. THIS IS POSSIBLY RELATED TO CAPPING ASSOCIATED WITH THE EML. THE GENERAL CONSENSUS WOULD SUGGEST THAT STORMS /LIKELY ELEVATED/ WILL BECOME INCREASINGLY POSSIBLE TOWARD 00Z NEAR OR JUST NORTH OF THE WARM FRONT AS WAA AND ISENTROPIC ASCENT ARE ENHANCED ALONG A STRENGTHENING SWLY LLJ. THESE FORCING MECHANISMS COUPLED WITH INCREASED DCVA ATTENDANT TO THE APPROACHING MULTI-STREAM TROUGH SHOULD PROMOTE A FURTHER INCREASE IN TSTM ACTIVITY THIS EVENING INTO OVERNIGHT ACROSS PARTS OF THE MID SOUTH…TN VALLEY INTO SRN APPALACHIANS.

MODEL-DERIVED FORECAST SOUNDINGS INDICATE THAT LOW-LEVEL AND DEEP-LAYER SHEAR WILL BE MORE THAN SUFFICIENT TO SUPPORT ORGANIZED STORM MODES…INCLUDING SUPERCELLS. THE PRIMARY UNCERTAINTY IS WHAT EFFECT THE RESIDUAL CAPPING AT THE BASE OF THE EML WILL HAVE ON PARCEL BUOYANCY AND RESULTANT UPDRAFT INTENSITY/LONGEVITY. AS SUCH…NO SEVERE PROBABILITIES WILL BE INCLUDED IN THIS FORECAST…THOUGH THE SITUATION WILL HAVE TO BE RE-EVALUATED IN SUBSEQUENT OUTLOOKS.

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