663
FXUS61 KLWX 051850
AFDLWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
250 PM EDT WED AUG 5 2020
SYNOPSIS
A COLD FRONT STALLED JUST TO THE SOUTH OF THE REGION TODAY
WILL BEGIN TO SLOWLY PUSH BACK NORTH ACROSS THE REGION THROUGH
THE END OF THE WEEK. BRIEF HIGH PRESSURE BUILDS IN FOR THE FIRST
HALF OF THE WEEKEND, BEFORE UNSETTLED CONDITIONS RETURN LATER
SUNDAY INTO THE BEGINNING OF NEXT WEEK.
NEAR TERM /THROUGH TONIGHT/
A WEAK FRONTAL BOUNDARY HAS PUSHED SOUTH OF THE REGION AND IS
DRAPED ACROSS THE DELMARVA PENINSULA, THEN DOWN ALONG THE NC/VA
BORDER. MEANWHILE, SURFACE HIGH PRESSURE IS PUSHING INTO THE
OHIO VALLEY. ALOFT, A CLOSED UPPER LOW REMAINS OVER
QUEBEC/ONTARIO, WITH A TROUGH EXTENDING DOWN INTO THE OHIO
VALLEY.
WITH THE STATIONARY BOUNDARY LINGERING JUST SOUTH OF THE
FORECAST AREA, MUCH OF THE AREA REMAINS DRY FOR MUCH OF THE
AFTERNOON. WITH HIGH TEMPERATURES IN THE 80S AND DEW POINTS IN
THE 60S MOST OF THE DAY, IT WILL FEEL RELATIVELY COMFORTABLE AS
WELL.
LATER THIS AFTERNOON INTO THIS EVENING, COULD SEE SOME SHOWERS
AND STORMS FIRE IN OUR SOUTHWEST ZONES OVER CENTRAL VA ALONG A
WEAK PRESSURE TROUGH RELATED TO THE HIGHER TERRAIN. OTHERWISE,
A VERY WEAK DAY IN TERMS OF FORCING. THINK WE ARE TOO DRY OVER
NORTHERN VA, NORTHERN/CENTRAL MD, AND DC (SEE THE 12Z IAD RAOB,
WHICH DEPICTS SUBSTANTIAL DRY AIR ABOVE 600MB). EITHER WAY, NOT
SEEING MUCH OF A SEVERE THREAT, AS THE BEST MID-UPPER LEVEL FLOW
IS OFF TO THE NORTH AND EAST. THERE WILL BE CAPE IN THE
NEIGHBORHOOD OF 1000-1500 J/KG TO WORK WITH, BUT THIS WILL
LIKELY RESULT IN JUST SOME HEAVIER SHOWERS, AND PERHAPS A FEW
WEAKER THUNDERSTORMS.
THINGS GET A LITTLE INTERESTING OVERNIGHT, AS MOST HI-RES
GUIDANCE BRINGS A WEAK PIECE OF UPPER-LEVEL ENERGY ACROSS THE
REGION, WHILE THE AFOREMENTIONED FRONTAL BOUNDARY BEGINS TO
DRIFT NORTHWARD. THIS SHOULD RESULT IN A GREATER RISK OF
SHOWERS AND PERHAPS SOME ISOLATED THUNDERSTORMS SPREADING NORTH
ACROSS MOST OF THE REGION OVERNIGHT, AND ESPECIALLY EARLY
THURSDAY MORNING. LOWS WILL BE IN THE 60S TO LOW 70S.
SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/
THE BOUNDARY WILL CONTINUE TO LIFT NORTHWARD THROUGHOUT THE DAY
ON THURSDAY, AND LIKELY STALL SOMEWHERE OVER CENTRAL VA INTO
SOUTHERN MD. WITH UPPER-LEVEL ENERGY APPROACHING FROM THE WEST,
AND THE SURFACE FRONTOGENESIS OVER THE AREA, SHOWERS AND STORMS
ARE LIKELY ON THURSDAY AFTERNOON EVENING NEAR/ALONG THIS FRONTAL
BOUNDARY. MOIST AIR WILL BE FUNNELING BACK INTO THE REGION SOUTH
OF THIS BOUNDARY, AND GIVEN THE ORIENTATION OF THE FRONTAL
BOUNDARY COMPARED TO THE MID-UPPER LEVEL FLOW, FLOODING COULD
BECOME AN ISSUE (MORE ON THAT IN THE HYDROLOGY SECTION BELOW).
THE WEAK FRONTAL BOUNDARY WILL CONTINUE SLOWLY MIGRATING
NORTHWARD THURSDAY NIGHT THROUGH FRIDAY NIGHT AS IT GRADUALLY
FALLS APART. HOWEVER, A SHORTWAVE WILL BE MOVING OVERHEAD. THUS,
DESPITE THE DIMINISHED SURFACE FORCING, THE INCREASED UPPER
LEVEL SUPPORT SHOULD RESULT IN MORE SHOWERS AND THUNDERSTORMS
THROUGH THE END OF THE WEEK. THE RISK OF CLOUDS AND RAIN WILL
CONTINUE TO KEEP TEMPS LOWER, WITH HIGHS IN THE LOW-MID 80S
OVERALL. DESPITE THE COOLER TEMPS, DEW POINTS IN THE LOWER 70S
WILL MAKE IT FEEL QUITE HUMID. THE HIGH MOISTURE CONTENT WILL
CONTINUE TO RESULT IN A RISK OF ISOLATED FLOODING FROM
THUNDERSTORMS.
LONG TERM /SATURDAY THROUGH TUESDAY/
A STALLED BOUNDARY THAT HAS BEEN NEAR THE AREA STARTS TO SHIFT
SOUTHEASTWARD AWAY FROM THE REGION ON SATURDAY. A FEW SHOWERS AND
THUNDERSTORMS WILL CONTINUE TO BE POSSIBLE ON SATURDAY BUT THE MAIN
THREAT AREA SHOULD BE FOCUSED OVER CENTRAL VIRGINIA AND SOUTHERN
MARYLAND CLOSER TO THE BOUNDARY. THE FRONT SHOULD FINALLY SHIFT AWAY
FROM OUR AREA BY SUNDAY AND HIGH PRESSURE BRIEF BUILDS OVER OUR
REGION. A WESTERLY FLOW ALOFT COMBINED WITH A WEAK NORTHERLY FLOW AT
THE SURFACE SHOULD HELP LIMIT TEMPERATURES THIS WEEKEND TO THE MID
TO UPPER 80S WITH OVER NIGHT LOWS IN THE 60S AND LOWER 70S.
ANOTHER BOUNDARY IS FORECAST TO MOVE INTO OUR AREA AND STALL DURING
THE EARLY PARTS OF NEXT WEEK. MULTIPLE SHORTWAVES WILL LEAD TO
CONTINUED CHANCES FOR SHOWERS AND THUNDERSTORMS BOTH MONDAY AND
TUESDAY. A WESTERLY FLOW ALOFT MAY LIMIT THE COVERAGE OF STORMS AS
DRY AIR GETS PULLED INTO THE SYSTEM. TEMPERATURES SHOULD TREND
UPWARDS INTO THE LOWER 90S AS WE REMAIN MAINLY ON THE WARM SIDE OF
THE BOUNDARY.
V
AVIATION /18Z WEDNESDAY THROUGH MONDAY/
VFR FOR THE REST OF TODAY AT ALL TERMINALS. SHOWERS AND STORMS
POSSIBLE AT CHO LATER THIS AFTERNOON/EVENING. TRIED TO NARROW
DOWN A TIMEFRAME THERE IN THE LATEST TAFS. COULD SEE BRIEF
RESTRICTIONS IF A STORM PASSES OVER THE TERMINAL. OUTSIDE OF
CHO THOUGH, THINK ALL OTHERS REMAIN DRY.
LOW CLOUDS ASSOCIATED WITH A SLOW MOVING FRONTAL BOUNDARY COULD
CAUSE SOME RESTRICTIONS THURSDAY INTO FRIDAY. THINK THINGS STAY
LOW END VFR IN TERMS OF CIGS, BUT COULD BRIEFLY DIP INTO MVFR AT
TIMES AT ALL TERMINALS. ADDITIONALLY, MORNING FOG POSSIBLE EACH
MORNING, ASSOCIATED WITH MOISTURE FROM RECENT RAINS. CHO WOULD
BE THE BEST CANDIDATE FOR THIS.
VFR CONDITIONS EXPECTED THIS WEEKEND AND INTO EARLY NEXT WEEK BUT
SHOWERS AND THUNDERSTORMS MAY CAUSE BRIEF PERIODS OF
RESTRICTIONS.
MARINE
LIGHT WINDS EXPECTED THROUGH FRIDAY, OUTSIDE OF GUSTY WINDS IN
THUNDERSTORMS THURSDAY AND FRIDAY. TODAY SHOULD REMAIN DRY OVER
THE WATERS, AS SHOWERS AND STORMS SHOULD BE LIMITED TO THE
HIGHER ELEVATIONS. HOWEVER, CAN'T COMPLETELY RULE OUT A ROGUE
STORM OVER THE LOWER POTOMAC INTO THE CENTRAL BAY.
GREATEST CHANCE FOR SHOWERS AND STORMS IS THURSDAY AND FRIDAY,
AS THE FRONTAL BOUNDARY TO OUR SOUTH TODAY SLOWLY PUSHES
NORTHWARD, AND AN UPPER TROUGH MOVES OVERHEAD INTO FRIDAY.
NO SMALL CRAFT ADVISORIES EXPECTED AT THIS TIME FOR THIS
WEEKEND.
HYDROLOGY
THURSDAY AFTERNOON AND EVENING ARE GROWING A BIT MORE CONCERNING
OVER CENTRAL/SOUTHERN MD AND NORTHEAST VA, MAINLY SOUTHEAST OF
I-95. SEVERAL THINGS OF NOTE FOR THURSDAY AFTERNOON. FIRST, A
STALLED /SLOW-MOVING BOUNDARY WILL BE SITUATED OVER CENTRAL
VA/SOUTHERN MD. THIS BOUNDARY WILL BE ROUGHLY PARALLEL TO THE
WSW MID-UPPER LEVEL FLOW, WHICH WILL FAVOR TRAINING STORMS ALONG
THE FRONT. PWATS, WHILE NOT EXCEEDINGLY IMPRESSIVE, SHOULD BE
CLOSE TO 2 INCHES NEAR/SOUTH OF THE BOUNDARY. GIVEN THE RECENT
HEAVY RAINFALL FROM ISAIAS, FFG VALUES ARE QUITE LOW OVER
CENTRAL/SOUTHERN MD. MANY AREAS SAW 4-6 INCHES OF RAIN TUESDAY,
WITH SOME EVEN SEEING UP TO 7-8 INCHES. THE 12Z RUN OF THE HREF
SHOW THE POTENTIAL FOR SEVERAL INCHES OF RAIN OVER THIS REGION
IN ROUGHLY A 6 HOUR PERIOD THURSDAY AFTERNOON/EVENING. THIS
WOULD EASILY EXCEED FFG IF REALIZED. WPC HAS INTRODUCED THE
SLIGHT RISK OF EXCESSIVE RAINFALL OVER THIS AREA TOMORROW AS A
RESULT OF ALL OF THIS. MONITOR THE LATEST FORECAST FOR UPDATES.
LWX WATCHES/WARNINGS/ADVISORIES
DC...NONE.
MD...NONE.
VA...NONE.
WV...NONE.
MARINE...NONE.
SYNOPSIS...RCM
NEAR TERM...CJL
SHORT TERM...CJL/RCM
LONG TERM...JMG
AVIATION...CJL/JMG
MARINE...CJL/JMG
HYDROLOGY...CJL
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