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Apr 21, 2014 1300 UTC Day 1 Convective Outlook

April 21, 2014

Apr 21, 2014 1300 UTC Day 1 Convective Outlook

day1otlk

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0753 AM CDT MON APR 21 2014

VALID 211300Z – 221200Z

…THERE IS A SLGT RISK OF SVR TSTMS PORTIONS ARKLATEX REGION TO S-CENTRAL/SW TX…

…SUMMARY…
ISOLATED SEVERE STORMS MAY DEVELOP FROM PARTS OF THE ARKLATEX REGION TO SOUTH-CENTRAL TEXAS THIS AFTERNOON AND EVENING.

…SYNOPSIS…
IN MID-UPPER LEVELS…SPLIT-FLOW PATTERN STILL IS APPARENT OVER CONUS…BUT WITH SOME PHASING BETWEEN TROUGHING IN NRN AND SRN STREAM OVER CENTRAL CONUS. NRN-STREAM TROUGH — NOW EVIDENT IN MOISTURE-CHANNEL IMAGERY OVER MB/ONT BORDER AND SWD OVER MN — IS FCST TO EXTEND FROM NERN ONT TO LOWER MI BY 12Z. MEANWHILE…SRN-STREAM PERTURBATION — CURRENTLY LOCATED OVER OK AND N TX — WILL DEAMPLIFY SOMEWHAT WHILE MOVING SEWD OVER ARKLATEX REGION TO SRN AR…NRN LA AND E TX. NEAR END OF PERIOD…HIGH-AMPLITUDE SHORTWAVE TROUGH NOW OVER NERN PAC WILL APCH W COAST.

AT SFC…11Z ANALYSIS SHOWED BROAD AREA OF LOW PRESSURE WITH MULTIPLE/WEAK LOW CENTERS OVER UPPER MS VALLEY REGION…WITH COLD FRONT SSWWD ACROSS SERN NEB…W-CENTRAL KS…SWRN OK…TX SOUTH PLAINS REGION AND SERN NM. BY 00Z…FRONT SHOULD BE MOVING EWD/SEWD OVER PORTIONS LM…NRN IL…CENTRAL/SRN MO…SERN OK…AND CENTRAL TX. BY 12Z…FRONT SHOULD EXTEND FROM CYCLONE OVER SERN ONT…SWWD ACROSS OH…WRN TN…NWRN LA…AND S-CENTRAL TX. FRONT WILL OVERTAKE DRYLINE DRAWN AT 11Z FROM CENTRAL CAPROCK AREA SWWD ACROSS SERN CORNER OF NM THEN SWD INTO BIG BEND REGION.

WIDELY SCATTERED TO SCATTERED TSTMS MAY DEVELOP ALONG THAT FRONT FROM CENTRAL PLAINS TO WI TODAY…SOME OF WHICH MAY PRODUCE STG GUSTS. HOWEVER…MRGL BUOYANCY…LACK OF STRONGER LOW-LEVEL FLOW…AND WEAK VERTICAL SHEAR ALL APPEAR TO PRECLUDE AOA 5% UNCONDITIONAL SVR THREAT. HOWEVER…MORE ORGANIZED SVR POTENTIAL EXISTS FARTHER S…AHEAD OF FRONT AND DRYLINE…AND INVOF SRN-STREAM PERTURBATION ALOFT.

…ARKLATEX TO S-CENTRAL/SW TX…
SCATTERED TSTMS SHOULD DEVELOP THIS AFTN INTO EVENING…INITIALLY NEAR OUTFLOW BOUNDARIES OVER N-CENTRAL/NE TX AND SERN OK…THEN IN MORE ISOLATED TO WIDELY SCATTERED FORM IN CENTRAL TX AND EDWARDS PLATEAU. ACTIVITY SHOULD PROGRESS SEWD ACROSS OUTLOOK AREA WITH SOME AGGREGATION/UPSCALE GROWTH AND COLD-POOL DEVELOPMENT POSSIBLE ON MESOBETA SCALE. AS SUCH…SUBTLE TRANSITION SHOULD OCCUR IN SVR THREAT FROM HAIL-DOMINANT TO WIND-DOMINANT BEFORE TSTMS WEAKEN BELOW SVR LEVELS TONIGHT.

TSTM COVERAGE MAY DIMINISH WITH SWWD EXTENT BENEATH PROGRESSIVELY STRONGER EML…PER COMPARISON OF 12Z DRT/FWD RAOBS. HOWEVER…LAPSE RATES ALOFT…DURATION/INTENSITY OF ANTECEDENT DIABATIC HEATING…AND OVERALL BUOYANCY SHOULD BE STRONGER. THIS SUGGESTS THAT ANY SUSTAINED TSTMS THAT DO FORM WILL POSE THREAT FOR SVR GUSTS AND HAIL. PRECONVECTIVE MLCAPE SHOULD RANGE FROM AROUND 500 J/KG OVER NERN PARTS OF OUTLOOK TO 1500 J/KG IN CENTRAL/SW TX. WEAK BOUNDARY-LAYER WINDS WILL LIMIT HODOGRAPH SIZE…WHILE MIDLEVEL FLOW WEAKENS WITH TIME SE AND S OF DAMPENING MID-UPPER PERTURBATION. AS SUCH…MULTICELL CLUSTERS SHOULD PREDOMINATE…SOME ULTIMATELY DEVELOPING FORWARD-PROPAGATIONAL TSTM ARCS OR BOWS ALONG THEIR GUST FRONTS.

…RIO GRANDE VALLEY…
ISOLATED TO WIDELY SCATTERED TSTMS MAY CROSS RIO GRANDE INTO TX…FROM GENESIS ZONES IN SERRANIAS DEL BURRO RANGE AND ADJOINING FOOTHILLS OF NRN COAHUILA. WHILE WEAK LOW-LEVEL FLOW SHOULD RESTRICT POTENTIAL FOR MORE THAN TRANSIENT SUPERCELL STRUCTURES…ISOLATED SVR IS POSSIBLE GIVEN AMBIENT STEEP LAPSE RATES…AND 1500-2000 J/KG MLCAPE ATOP WELL-MIXED SUBCLOUD LAYERS.

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