#827 Postby Texas Snowman » Tue Apr 19, 2016 5:28 am
Fort Worth discussion...
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000
FXUS64 KFWD 190920
AFDFWD
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE FORT WORTH TX
420 AM CDT TUE APR 19 2016
.SYNOPSIS...
PRIMARY CONCERN FOR THIS FORECAST WILL BE THE POTENTIAL FOR
STORMS THIS AFTERNOON AND THE DEVELOPMENT OF A QLCS THAT IS
EXPECTED TO IMPACT MUCH OF THE AREA OVERNIGHT TUESDAY NIGHT INTO
WEDNESDAY MORNING. THIS IS ALL DUE TO THE MASSIVE UPPER LOW THAT
CONTINUES TO DOMINATE SENSIBLE WEATHER ACROSS MUCH OF THE CENTRAL
U.S. WHICH WILL CONTINUE TO BRING CHANCES FOR SHOWERS AND STORMS
TO NORTH AND CENTRAL TEXAS AS A PARADE OF SHORTWAVE DISTURBANCES
ROTATE AROUND THE LOW.
&&
.SHORT TERM...
EARLY THIS MORNING...SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS
ARE MOVING ACROSS PORTIONS OF SOUTHERN OKLAHOMA AND WESTERN NORTH
AND CENTRAL TEXAS. THIS ACTIVITY IS ASSOCIATED WITH FORCING FROM A
WEAK SHORTWAVE EJECTING FROM THE UPPER LOW WHICH CAN BE SEEN ON
WATER VAPOR IMAGERY AS WELL AS WEAK LOW-LEVEL WARM ADVECTION.
THESE SHOWERS SHOULD LARGELY BE INCONSEQUENTIAL ASIDE FROM AN
OCCASIONAL LIGHTNING STRIKE. IN ADDITION...WIDESPREAD LOW CLOUDS
ARE PRESENT ACROSS MOST OF THE AREA WITH SOME MIST REDUCING
VISIBILITIES IN ISOLATED LOCATIONS. SKIES SHOULD REMAIN CLOUDY
THROUGH MUCH OF THE DAY WITH A FEW BREAKS IN THE CLOUDS POSSIBLE
LATER THIS AFTERNOON.
A RELATIVELY DIFFUSE SURFACE PATTERN IS EXPECTED TO REMAIN IN
PLACE TODAY AS THE UPPER LOW FILLS...ALLOWING LOW-LEVEL FLOW TO
REMAIN WEAK AND ILL-DEFINED. HOWEVER...WEAK LOW-LEVEL WARM
ADVECTION WILL ALLOW DEWPOINTS TO RISE SLIGHTLY INTO THE MID 60S
THIS AFTERNOON WITH TEMPERATURES CLIMBING INTO THE 70S DESPITE
WIDESPREAD CLOUDS HOLDING THROUGH MUCH OF THE DAY. THESE
CONDITIONS SHOULD YIELD 1000-2000 J/KG OF SBCAPE THIS AFTERNOON
WITH THE HIGHEST VALUES ACROSS OUR SOUTHEAST ZONES. HOWEVER...THE
AFOREMENTIONED WEAK LOW-LEVEL FLOW WILL INHIBIT WIND SHEAR VALUES
ACROSS THIS AREA. DO NOT EXPECT MUCH FORCING TO BE IN PLACE THIS
AFTERNOON...BUT WE SHOULD BE LARGELY UNCAPPED WHICH MEANS IF ANY
LIFT MANAGES TO OVERSPREAD NORTH OR CENTRAL TEXAS...ISOLATED
THUNDERSTORMS WILL BE CAPABLE OF DEVELOPING. WITH BULK SHEAR
EXPECTED TO BE AROUND 30 KTS...THIS WOULD SUPPORT MULTICELL
THUNDERSTORMS CAPABLE OF A BORDERLINE STRONG/SEVERE HAIL AND WIND
THREAT. HAVE LEFT POPS AROUND 30-40 PERCENT SINCE OVERALL AREAL
COVERAGE IS EXPECTED TO BE LIMITED.
THE BIGGER CONCERN FOR THE NEXT 24 HOURS WILL BE A QLCS THAT IS
EXPECTED TO DEVELOP IN THE TEXAS PANHANDLE THIS EVENING RESULTING
FROM A VIGOROUS SHORTWAVE ROTATING AROUND THE UPPER LOW. A SW-NE
ORIENTED SQUALL LINE SHOULD ENTER NORTH TEXAS AFTER 9PM...REACH
THE I-35 CORRIDOR BETWEEN MIDNIGHT AND 6AM...AND EXIT OUR EASTERN
ZONES BY MID-MORNING. HAVE THROWN OUT THE GFS FOR THE TIMING OF
THIS SYSTEM AND SIDED WITH CONVECTION ALLOWING MODELS THAT ARE
CURRENTLY WITHIN TIME RANGE...INCLUDING THE 4KM NAM AND TT WRF.
THE MAIN CONCERNS WITH THIS LINE WILL BE HEAVY RAIN AND LOCALIZED
FLOODING...BUT A SEVERE STORM THREAT CANNOT BE RULED OUT WITH THIS
LINE EITHER. CAPE VALUES ARE EXPECTED TO BE 1000-1500 J/KG AHEAD
OF THIS LINE...SOME OF WHICH MAY MANAGE TO STILL BE SURFACE BASED
OVERNIGHT. THE DIFFERENCE FROM THE AFTERNOON WILL BE THE PRESENCE
OF SLIGHTLY STRONGER WIND SHEAR OWING TO A DEVELOPING 850MB LOW
IN SOUTHERN KS ASSOCIATED WITH THE VORTICITY ADVECTION FROM THE
UPPER-LEVEL SHORTWAVE. THIS WILL INDUCE STRONGER SOUTHERLY 850MB
FLOW OF AROUND 25KTS ACROSS NORTH TX. WHILE THE WIND PROFILES
WON`T BE TERRIBLY CONDUCIVE FOR SEVERE THUNDERSTORMS...AM
CONCERNED ANY STRONG SEGMENTS THAT MANAGE TO DEVELOP WITHIN THE
LINE COULD BE CAPABLE OF ALL MODES OF SEVERE WEATHER...INCLUDING A
BRIEF SPIN-UP QLCS TORNADO. WHILE BULK SHEAR VALUES STILL DON`T
APPEAR SUFFICIENT FOR SUPERCELLULAR STORMS...BACKED INFLOW WINDS
COULD RESULT IN 0-1 SHEAR OF 10-20KTS ALONG THE LEADING EDGE OF
THE LINE. THE TT WRF SEEMS TO AGREE WITH THIS POTENTIAL AND IS
ADVERTISING LOCALLY HIGHER EHI VALUES ALONG/AHEAD OF THE LINE
ESPECIALLY NORTH OF I-20...AND ALSO MAINTAINING A FEW UPDRAFT
HELICITY TRACKS IN THIS AREA AS WELL. THIS POTENTIAL WILL NEED TO
BE MONITORED TODAY ESPECIALLY AS THIS TIME FRAME BECOMES INCLUDED
IN THE NEW DATA FROM ADDITIONAL CONVECTION ALLOWING MODELS.
THE NEXT FORECAST CONCERN WILL BE WEDNESDAY AFTERNOON AFTER THE
QLCS HAS EXITED THE AREA TO THE EAST. THE NAM IS VERY QUICK TO
RECOVER THE ENVIRONMENT BY BRINGING SOUTH WINDS BACK TO THE AREA
WEDNESDAY AFTERNOON AND OVERSPREADING MOST OF NORTH AND CENTRAL
TEXAS WITH SBCAPE NEAR 3000 J/KG. WHILE THIS INSTABILITY SEEMS
OVERDONE...THE GFS ISN`T TERRIBLY DIFFERENT ADVERTISING SBCAPE OF
2000-2500J/KG LATE WEDNESDAY AFTERNOON AND EVENING. THE QUESTION
WILL BE IF THERE IS SUFFICIENT LIFT IN PLACE SINCE THE SHORTWAVE
ASSOCIATED WITH THE MORNING QLCS WILL BE DEPARTING TO THE
NORTHEAST. IF STORMS ARE ABLE TO REDEVELOP WEDNESDAY
AFTERNOON...THEY WILL LIKELY BE MULTICELLULAR IN NATURE WITH SHEAR
LESS THAN 30KTS IN PLACE YET AGAIN...BUT WOULD STILL BE CAPABLE
OF A BORDERLINE SEVERE HAIL THREAT. THE ENVIRONMENT ON WEDNESDAY
AFTERNOON WILL NOT BE CLEAR UNTIL WE SEE THE EVOLUTION OF THE
ANTICIPATED SQUALL LINE EARLY WEDNESDAY MORNING.
THE LARGE UPPER LOW WILL...FINALLY...MOVE OFF TO THE NORTH AND
EAST ON THURSDAY BUT NOT BEFORE RESULTING IN ONE FINAL FORECAST
CHALLENGE. THE GFS AND NAM LAG A SHORTWAVE TROUGH BEHIND THE MAIN
VORTICITY LOBE AND MOVE IT ACROSS THE TEXAS PANHANDLE ON
WEDNESDAY EVENING. THIS SCENARIO WOULD PROVIDE SUFFICIENT FORCING
TO GENERATE THUNDERSTORMS IN THE PANHANDLE WHICH WOULD EVOLVE
INTO AN MCS AND MOVE INTO NORTH AND CENTRAL TEXAS EARLY THURSDAY
MORNING.THE LATEST ECMWF DOES NOT HAVE THIS FEATURE AND THUS KEEPS
SUBSIDENCE OVER THE AREA FOR MUCH OF THURSDAY. IF THE GFS/NAM ARE
CORRECT...THURSDAY MORNING WILL BE RAINY/STORMY AS THIS COMPLEX
MOVES THROUGH THE AREA PRIMARILY DURING THE MORNING HOURS. THIS
MCS SCENARIO IS ALSO SUPPORTED BY THE LATEST TT WRF. HAVE LEFT
POPS AROUND 30 PERCENT WITH LOW CONFIDENCE FOR THURSDAYS FORECAST
AT THIS TIME.
&&
.LONG TERM...
FRIDAY THROUGH SUNDAY SHOULD BE A NICE BREAK AS WE FINALLY SEE
PERSISTENT SUNSHINE AND TEMPERATURES WARMING INTO THE UPPER 70S
AND 80S EACH DAY. THIS IS OWING TO LARGE SCALE SUBSIDENCE BEHIND
THE EJECTING UPPER LOW WITH AN UPPER RIDGE DEVELOPING ACROSS THE
CENTRAL U.S.
THE NEXT STORM SYSTEM SHOULD BE APPROACHING THE WEST COAST ON
SATURDAY AND MOVING INTO THE FOUR CORNERS REGION ON SUNDAY. AT
THIS POINT...THE ECMWF IS THE OUTLIER ON THE HANDLING OF THIS
SYSTEM. THE GFS AND CANADIAN DIG THE CUTOFF LOW SOUTHWARD INTO NEW
MEXICO BY MONDAY. THE ECMWF ON THE OTHER HAND BRINGS THIS SYSTEM
IN TWO PHASES...A LEAD PROGRESSIVE SHORTWAVE THAT EJECTS ACROSS THE
CENTRAL PLAINS FOLLOWED BY A DEEPER CUTOFF LOW BY MIDWEEK. THE
GFS/CANADIAN SOLUTION WOULD ALLOW FOR A DRYLINE TO MOVE WEST INTO
NORTH/CENTRAL TEXAS ON MONDAY CAUSING STORMS TO DEVELOP AND VERY
WARM AFTERNOON TEMPERATURES IN EXCESS OF 90 DEGREES FOR AREAS WEST
OF I-35. THE ECMWF SOLUTION WOULD KEEP US MILD AND DRY FOR EARLY
NEXT WEEK BUT BRING A DRYLINE THUNDERSTORMS SETUP TO THE REGION ON
WEDNESDAY. AT THIS TIME...HAVE SIDED MORE TOWARD THE GFS/CANADIAN
SOLUTIONS WITH LOW CONFIDENCE. WE SHOULD CONTINUE TO SEE ACTIVE
WEATHER REGARDLESS AS THERE APPEARS TO BE LITTLE/NO CHANGE IN THE
LARGE SCALE PATTERN FOR THE NEXT COUPLE OF WEEKS.
STALLEY
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