991
FXUS62 KRAH 201456
AFDRAH
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE RALEIGH NC
1056 AM EDT SAT APR 20 2019
SYNOPSIS
A STRONG UPPER LEVEL LOW WILL ROTATE SLOWLY EAST ACROSS THE REGION
THROUGH THE WEEKEND. SURFACE HIGH PRESSURE WILL BUILD IN FROM THE
SOUTHWEST ON MONDAY.
NEAR TERM /THROUGH TONIGHT/
AS OF 1045 AM...
COOLING TEMPERATURES ALOFT AND FORCING FOR ASCENT, RELATED TO THE
EWD WOBBLE OF THE MID-UPR LOW OVER THE SRN APPALACHIANS, WILL FAVOR
THE DEVELOPMENT OF "INSTABILITY" CONVECTION WITH DIURNAL HEATING -
INTO AND/OR OVER THE NC PIEDMONT THIS AFTERNOON. MLCAPE WILL BE
LIMITED BY BOTH A DRY BOUNDARY LAYER CHARACTERIZED BY SURFACE
DEWPOINT TEMPERATURES IN THE 30S-40S, AND A COUPLE WARM/INVERSION
LAYERS BETWEEN 10-20 K FT EVIDENT ON BOTH THE 12Z RNK RAOB AND MODEL
FORECAST SOUNDINGS OVER CNTL NC THIS AFTERNOON. NONETHELESS, THE
UNSEASONABLY COLD TEMPERATURES ALOFT, AND LOWERING FREEZING LEVELS
THAT WERE ALREADY AS LOW AS 5 K FT AT RNK PER THE 12Z RAOB THERE,
MAY SUPPORT THE DEVELOPMENT/OCCURRENCE OF GRAUPEL/SMALL HAIL IN THE
STRONGEST/DEEPEST CELLS. OTHERWISE, THE PREVIOUS FORECAST AND
REASONING NEEDS LITTLE TO NO ADJUSTMENT THIS MORNING.
PREVIOUS DISCUSSION AS OF 420 AM SATURDAY...
THE MATURE MID/UPPER LEVEL LOW THAT WAS RESPONSIBLE FOR FRIDAY'S
SEVERE WEATHER WILL ROTATE SLOWLY ENE FROM THE SOUTHERN APPALACHIANS
TO OFF THE DELMARVA COAST THROUGH SUNDAY NIGHT/EARLY MONDAY.
ATTENDANT SURFACE FRONT THAT MARKS THE EDGE OF CONSIDERABLY DRIER
AIR WITH SFC DEWPOINTS IN THE 40S IS CURRENTLY MAKING IT'S WAY
ACROSS THE FORECAST AREA. THIS LOW-LEVEL DRY AIR ADVECTION IN TANDEM
WITH DRYING ALOFT WILL RESULT IN PARTIAL CLEARING THIS MORNING.
AIDED BY DAYTIME HEATING AND WEAK INSTABILITY, MOISTURE AND
LIFT(DCVA AND SYNOPTIC SCALE H5 FALLS) ASSOCIATED WITH THE UPPER LOW
WILL SUPPORT THE RE-DEVELOPMENT OF ISOLATED TO WIDELY SCATTERED
SHOWERS THIS AFTERNOON/EARLY EVENING, WITH THE BEST COVERAGE
EXPECTED ACROSS THE WESTERN/CENTRAL PIEDMONT COUNTIES. THE BULK OF
THESE SHOWERS DISSIPATE WITH LOSS OF HEATING. GUSTINESS WILL PICK UP
AGAIN BY MID TO LATE MORNING WITH FREQUENT SWLY WIND GUSTS OF 20 TO
30 KTS, HIGHEST IN THE EAST WHERE STRONGER DAYTIME HEATING IS
EXPECTED. PRESENCE OF THE UPPER LEVEL LOW IN OUR VICINITY AND ITS
ASSOCIATED COOL POOL OF AIR WILL RESULT IN COOLER THAN NORMAL
TEMPERATURES. HIGHS RANGING FROM MID TO UPPER 50S ACROSS THE NW
PIEDMONT WHERE EARLIER ARRIVAL AND GREATER COVERAGE OF SHOWERS AND
CLOUDS ARE EXPECTED TO UPPER 60S SE. LOWS TONIGHT IN THE LOW/MID 40S
WEST TO UPPER 40S EAST.
SHORT TERM /SUNDAY AND SUNDAY NIGHT/
AS OF 420 AM SATURDAY...
UPPER LOW WILL WOBBLE EASTWARD ACROSS SOUTHERN VA/NORTHERN NC DURING
THE DAY ON SUNDAY. WEAK CYCLOGENESIS OFF THE DELMARVA COAST IS
FORECAST TO ENSUE AS THE SYSTEM MOVES OFFSHORE. GIVEN PROXIMITY TO
THE LOW WILL KEEP A SLIGHT CHANCE OF SHOWERS ACROSS THE FAR
NORTHERN/NORTHEASTERN ZONES ON SUNDAY. OTHERWISE IT WILL BE DRY
ACROSS CENTRAL NC WITH DOWN SLOPE DRYING AND ADVECTION OF DRIER AIR
ON THE BACK-SIDE OF THE LOW/TROUGH LEADING TO WEST-EAST CLEARING
DURING THE AFTERNOON AND EVENING. SUNDAY WILL BE THE LAST DAY OF
COOL TEMPERATURES BEFORE TEMPERATURES MODERATE. HIGHS RANGING FROM
LOWER 60S NORTH TO MID/UPPER 60S SOUTH. LOWS IN THE MID TO UPPER
40S.
LONG TERM /MONDAY THROUGH SATURDAY/
AS OF 500 AM FRIDAY...
WE'LL FINALLY BE ABLE TO BREAK THE NEARLY STALLED UPPER TROUGHING
PATTERN MONDAY NIGHT AS THE UPPER LEVEL LOW FINALLY DRIFTS FURTHER
INTO THE MIDDLE ATLANTIC. THIS WILL ALLOW FOR A BRIEF RIDGING
PATTERN TO TAKE SHAPE THROUGH THE MIDDLE OF THE WEEK, WITH A MUCH
MILDER AIRMASS FILTERING IN UNDER THE GUIDANCE OF A SUB-TROPICAL
AREA OF SURFACE HIGH PRESSURE. THIS, COUPLED WITH A FAR WEAKER
SHORTWAVE PROGRESSION ON WEDNESDAY, WILL HELP TO EXTEND THE DRY
WEATHER PATTERN FOR AN ADDITIONAL DAY OR SO COMPARED TO PREVIOUS
RUNS, AND KEEP TEMPERATURES PREDOMINANTLY IN THE UPPER-70S TO LOW-
80S TUESDAY THROUGH THURSDAY AFTERNOONS. POPS RETURN ON THURSDAY AS
THE HIGH SHIFTS FURTHER OFFSHORE AND AN UPPER-LEVEL TROUGH SLIPS
EASTWARD OUT OF THE ARKLATEX REGION THROUGH THE DEEP SOUTH. SOME
PRETTY GOOD MODEL SPREAD AT THIS POINT, WITH BOTH THE GFS/CMC
FAVORING A MORE PROGRESSIVE TROUGH INDUCED FRONTAL PASSAGE THU/FRI
COMPARED TO THE ECMWF THAT FAVORS A MORE CLOSED-LOW TYPE SOLUTION,
HELPING TO SLOW PROGRESSION, STALLING AN UPPER-LOW JUST SOUTH OF
CENTRAL NC. FOR NOW, HAVE FAVORED THE MORE PROGRESSIVE SYSTEMS WHICH
HAVE TENDED TO PERFORM A LITTLE BETTER AS OF LATE. THIS MAY NEED
SOME MASSAGING AS THE WEEK GOES ON.
AVIATION /12Z SATURDAY THROUGH WEDNESDAY/
AS OF 738 AM SATURDAY...
DRIER AIR SPREADING INTO THE AREA FROM THE SW BEHIND THE SURFACE
COLD FRONT MOVING THROUGH THE AREA WILL SCATTER OUT THE LINGERING
MVFR CEILINGS FROM SW TO NE BETWEEN 06 TO 10Z. THE MID/UPPER LEVEL
LOW MOVING INTO THE SOUTHERN APPALACHIANS WILL ROTATE SLOWLY ENE
ACROSS THE AREA THIS AFTERNOON THROUGH SUNDAY. AIDED BY DAYTIME
HEATING AND WEAK INSTABILITY, MOISTURE AND LIFT ASSOCIATED WITH THE
UPPER LOW WILL SUPPORT THE RE-DEVELOPMENT OF SCATTERED SHOWERS THIS
AFTERNOON AND EVENING, PRIMARILY IN THE VICINITY OF KINT, KGSO. MVFR
TO LOW-END VFR CEILINGS WILL LIKELY ACCOMPANY THESE SHOWERS AS THE
SPREAD EAST WITH THE BULK OF THESE SHOWERS DISSIPATE WITH LOSS OF
HEATING. GUSTINESS WILL PICK UP AGAIN BY MID TO LATE MORNING WITH
FREQUENT SWLY WIND GUSTS OF 20 TO 27 KTS STRONGEST ACROSS THE
EASTERN TERMINALS(KFAY AND KRWI). A MIX OF MVFR(NORTHERN TAF SITES)
TO LOW-END VFR CEILINGS ARE EXPECTED SATURDAY NIGHT AND INTO THE DAY
ON SUNDAY AS THE UPPER TROUGH TRAVERSES THE AREA. ADDITIONALLY
CANNOT RULE OUT A STRAY SHOWER.
VFR CONDITIONS SHOULD OCCUR MONDAY THROUGH TUESDAY. A WEAK COLD
FRONT WILL DROP INTO CENTRAL NC WEDNESDAY, POSSIBLY ACCOMPANIED BY A
FEW SHOWERS AND AREAS OF MVFR/LOW END VFR CEILINGS.
RAH WATCHES/WARNINGS/ADVISORIES
NONE.
SYNOPSIS...KCP
NEAR TERM...MWS/CBL
SHORT TERM...CBL
LONG TERM...JJM
AVIATION...CBL/WSS
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