Area Forecast Discussion
Issued by NWS Sterling, VA

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000
FXUS61 KLWX 220028
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
828 PM EDT TUE APR 21 2015

.SYNOPSIS...
LOW PRESSURE WILL SLOWLY PIVOT FROM THE GREAT LAKES TOWARD THE
SAINT LAWRENCE VALLEY THROUGH THE END OF THE WEEK. A COLD FRONT
TRAILING THE LOW WILL CROSS THE MID-ATLANTIC WEDNESDAY.

&&

.NEAR TERM /THROUGH WEDNESDAY NIGHT/...
WK RDGG ACRS THE CWFA TDA. THE PRIMARY SYNOP FEATURE IS DP LOPRES N
OF THE GRTLKS. WLY FLOW HAS BEEN THE MAIN RESULT TDA...AND THAT WL
CONT INTO TNGT.

CDFNT WL CROSS CWFA TMRW...MAINLY DURING THE MIDDAY-AFTN HRS. THERES
A HEALTHY WIND FIELD ON BOTH SIDES OF THE FNT. INSTBY WL BE
MEAGER... BUT STEEP LAPSE RATES YIELD INVERTED-V TYPE SNDGS. BEST
MIXING SHUD BE ON THE BACK SIDE OF THE CDFNT...WHERE THERE SHUD BE
ENUF CNVGNC FOR SCT-NRMS SHRA. CONCERN WL BE FOR SHOWERS TO TAP
WINDS AT THE TOP OF THE MIXED LYR...WHICH MAY BE 40-50 KTS...AND
THIS WIND WL MIX TO THE SFC. AFTER COORD W/ SPC...AREA HAS BEEN
UPGRADED TO MRGL RISK OF SVR WX. DO NOT XPCT MUCH THUNDER ACTUALLY
SINCE CAPE ONLY A FEW HND J/KG...BUT GUSTY SHRA WL NEED TO BE
MONITORED CLOSELY. GOOD AGREEMENT AMONGST MOS FOR MAXT...AND BLEND
TAKEN.

CDFNT SHUD MAKE IT TO THE DELMARVA BY DARK. TRIMMED TO SHRA BY
THEN... AND ENDED POPS BY MIDNGT. ANY STRONG GUSTS SHUD DIMINISH BY
DARK...AND HV ENDED MOST GUSTS BY THE OVNGT HRS. EVEN HV PRTL OVNGT
CLRG. SINCE WINDS WONT OUTRIGHT DCPL...HV GONE WITH THE WARMER MET
MOS. TEMPS WL DROP INTO THE 30S W OF I-95. NO FROST XPCTD DUE TO
WINDS AND DRY AIR. THE ONLY PLACE WHERE SUBFRZG XPCTD THE GROWING
SEASON HASNT BEGUN YET.

&&

.SHORT TERM /THURSDAY THROUGH FRIDAY/...
THE ACTIVE WX FROM WED WILL BE GONE BUT THE LARGE UPPER LEVEL SYSTEM
WILL STILL NOT BE TOO FAR AWAY TO INFLUENCE THE AREA INTO THE
WEEKEND. ANOTHER UPPER WAVE...ALBEIT MUCH WEAKER...WILL SWING THRU
DURING THE DAYTIME HRS W/ YET ANOTHER COLD FRONT. THIS FRONT WILL BE
DRY BUT USHER-IN ANOTHER WAVE OF GUSTY WLY WINDS...FROM MID MRNG
THRU LATE EVE. THE COOL/DRY AIR WILL KEEP TEMPS MODERATED W/ HIGHS
ONLY REACHING THE L-M50S BY MIDDAY. A DAY OF DRY WEST WINDS WILL
ALLOW TEMPS TO PLUMMET AGAIN INTO THE 30S/40S FOR OVERNIGHT LOWS.
THE UPPER FLOW PATTERN FOR THU WILL BE FAIRLY ZONAL...BUT FRIDAY
WILL HAVE ANOTHER WAVE SWINGING THRU W/ MORE OF A LONGITUDINAL
COMPONENT. THIS WILL ALLOW SOME STRONGER GUSTS TO SWING OVER NERN MD
DURING THE AFTN HRS. TEMPS WILL BE CONSISTENT W/ THU`S CONDITIONS
AND DRY FOR MUCH OF THE DAY.

&&

.LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
RIDGING WILL MOVE ACROSS THE REGION FRIDAY NIGHT. LIGHT WINDS AND
GENERALLY CLEAR SKIES...ESPECIALLY IN THE EVENING...COULD RESULT
IN AREAS OF FROST OVER THE SHENANDOAH VALLEY AND POTOMAC
HIGHLANDS.

CLOUDS INCREASE QUICKLY BY SATURDAY AS A WARM FRONT APPROACHES THE
AREA. MID-LEVEL SHORTWAVE FORCING AND WARM ADVECTION IN THE LOW-
LEVEL WILL CONTRIBUTE TO AN AREA OF RAIN...BUT HOW FAR NORTH IT GETS
REMAINS IN QUESTION. A LARGE UPPER-LEVEL LOW STALLED OVER NEW
ENGLAND DURING THIS TIME WILL CAUSE A CONFLUENT ZONE TO ITS SOUTH
AND SUPPRESS PRECIPITATION SOMEWHAT...SO IT IS JUST A QUESTION OF
HOW FAR NORTH THE RAIN WILL SPREAD SATURDAY INTO SATURDAY EVENING.

A WAVE OF LOW PRESSURE PASSES QUICKLY TO THE SOUTH AND OUT TO SEA
COURTESY OF 180+ KT JET AT 250 MB. HIGH PRESSURE WILL BRIEFLY BUILD
OVER THE AREA SUNDAY INTO MONDAY...BEFORE A STRONG TROUGH OF LOW
PRESSURE DIVES TOWARDS THE EAST COAST BY TUESDAY.

&&

.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...

VFR OVRNGT.

WINDS WL INCR WED IN ADVC OF CDFNT. CUD SEE 30 KT EASILY W/IN MIXED
LYR. FORCING THEN INCREASES AS CDFNT ARRIVES...CPLD W/ MEAGER
INSTBY. CUD SEE NRMS SHRA DVLP BY NOON...EACH CONTAINING A STRONG
GUSTY WIND THREAT. FLGT RESTRICTIONS ANY SHRA MAY CONTAIN WUD BE
BRIEF. AREAL CVRG AND TIMING ARE THE MAIN UNCERTAINTIES. THREAT ENDS
BY DAR

BREEZY DAYS AGAIN ON THU AND FRI AFTNS. DRY BOTH DAYS...SO WINDS
WILL BE THE MAIN CONCERN TO CLOSE OUT THE WORK WEEK.

NWLY FLOW AOB 10 KT FRI NIGHT-SUN. SUB-VFR POSSIBLE IN -
RA SAT AFT/EVE.

&&

.MARINE...
WINDS HV DIMINISHED BLO SCA VALUES THIS EVE.

WED GALE WRNG IN EFFECT FOR ALL WATERS. AS THE CDFNT ARRIVES...
LLVL CNVGNC AND MEAGER INSTBY WL JOIN FORCES TO PERMIT NRMS SHRA
TO DVLP. CONCERNED THAT THESE MAY TAP THE HIER WINDS AND BRING
DOWN 40+ KT GUSTS. THE ADDED FREQUENT GUSTS SHUD EASILY MEET THAT
CRITERIA...BUT MAY NOT PRECLUDE THE NEED FOR SMW/S.

WNDS WL DECREASE AFTR DARK. SHUD HV A PD OF SCA...BUT DONT WISH
TO STEP UP AND DOWN ATTM...DO WL LEAVE THAT HEADLINE OUT FOR NOW.

SOLID SCA WINDS AGAIN POSSIBLE BOTH THU AND FRI AFTNS. LOW END GALES
POSSIBLE FRI OVER THE NRN CHES BAY.

WIND GUSTS SUBSIDE AS FLOW TURNS FROM NORTHERLY TO NORTHWESTERLY
FRIDAY NIGHT INTO SATURDAY. THE GRADIENT WILL RELAX SATURDAY AS A
WEAK WAVE OF LOW PRESSURE PASSES NEARBY. GRADIENT TIGHTENS AGAIN
IN WESTERLY SURGE SUNDAY...AND SMALL CRAFT ADVISORIES WILL LIKELY
BE NEEDED DURING THIS TIME.

&&

.TIDES/COASTAL FLOODING...
TIDE LVLS HV DROPPED SIGNIFICANTLY SINCE THE TUE MRNG TIDE CYCLE. WILL
HAVE TO MONITOR THIS FOR THE NEXT COUPLE OF DAYS...AS WATER
LEVELS WILL AT THE VERY LEAST REMAIN ELEVATED.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...NONE.
MD...NONE.
VA...NONE.
WV...NONE.
MARINE...GALE WARNING FROM 9 AM TO 8 PM EDT WEDNESDAY FOR
     ANZ530>543.

&&

$$
UPDATE...WOODY!
PRVS...HTS/GMS/DFH


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