Area Forecast Discussion
Issued by NWS Sterling, VA

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545
FXUS61 KLWX 300743
AFDLWX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC
343 AM EDT SAT APR 30 2016

.SYNOPSIS...
A STALLED FRONTAL BOUNDARY WILL WAVER ACROSS THE AREA TODAY. LOW
PRESSURE MOVES THROUGH THE MID- ATLANTIC SUNDAY INTO MONDAY...
PULLING THE FRONT TO THE NORTH ON SUNDAY...AND THEN SENDING A COLD
FRONT ACROSS THE REGION ON MONDAY. ANOTHER COLD FRONT WILL MOVE
THROUGH LATE NEXT WEEK.

&&

.NEAR TERM /THROUGH TONIGHT/...
CWFA REMAINS WITHIN AREA OF COLD AIR DAMMING...AND THIS WEDGE
APPEARS TO HOLD THROUGH THE DAY. THE RDGG DOWN THE COAST FM THE
GRTLKS APPEARS TO STRENGTHEN THRU THE DAY...WHICH HAS KEPT AREA
DRY OVNGT /ASIDE FM ANY PATCHY DZ/ AND SHUD HOLD OFF ANY APPRCHG
RAFL. AM SEEING THESE TRENDS IN LTST GFS/NAM RUNS...AND ITS SPCLY
PREVALENT IN RECENT RAP/HRRR/WRF-ARW4 RUNS. HV THEREFORE BACKED
OFF ON ARRIVAL OF PCPN TDA. THERE IS STILL A RIBBON OF STRONG
ISENT LIFT AHD OF LOPRES IN THE SRN PLAINS...AND PWATS STILL RISE
ABV AN INCH BY DAYS END.

THE IMPACT OF THESE TRENDS ARE TO KEEP PCPN OUT OF THE FCST
ENTIRELY IN NE MD TDA. ONLY CENTRAL FOOTHILLS/CENTRAL SHEN
VLY/SRN PTMC HIGHLANDS HV POPS HIER THAN LKLY-- AND THATS FOR ONLY
THE MID/LATE AFTN HRS. THE DAY WL START CLDY AND GREY AREAWIDE.
AS HIPRES WL BRIEFLY BE CONTROLLING...CLDS SHUD LIFT... AND MAY
SEE A FEW BRIGHT SPOTS. MAXT FCST WL REFLECT LESS OF A GRADIENT...
ALTHO BELIEVE THERE WL BE A LARGE MARGIN FOR ERROR CONTINGENT ON
IF/WHERE ANY SUN APPEARS.

THTE RDG/MSTR PLUME WL OVERSPREAD CWFA TNGT. POPS INCR TO CAT W/
POCKETS OF MDT RAFL. BASICALLY...IT WL BE A RAINY NGT...BUT NOT AT
A PACE WHERE FLOODING WUD BE A CONCERN.

&&

.SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/...
THERE LKLY WL BE LINGERING RAFL IN THE SRN CNTYS AT THE START OF
SUNDAY...BUT IT/LL BE EXITING TO THE EAST ALONG WITH THE LEADING
EDGE OF THE THTE RDG. THAT SHUD RESULT IN A PD OF DRYING...AND HV
ATTEMPTED TO REFLECT THAT BY LWRG OF POPS INTO CHC FOR THE MIDDAY.

SFC LOPRES AND H5 VORT TRACK UP THE OHVLY SUN-SUN NGT. THIS TRACK
WL ENCOURAGE STALLED BNDRY TO LIFT NWD...BUT IT/LL RUN INTO THE
STUBBORN CAD WEDGE. THIS PTTN ALWAYS A CHALLENGE FOR MDLS TO
FCST...AND THE RESULT USUALLY FAVORS PERSISTENCE. AM BEGINNING TO
ACTUALLY SEE THAT REFLECTED IN GDNC...SPCLY IN THE GFS...WHICH
HOLDS ONTO A STBL SFC LYR IN MD THRU THE DAY. BEST H8-5 LAPSE
RATES HOLD OVER THE APLCNS...BUT THERE CUD BE A LTL ELEVATED
INSTBY NE OF THERE.

THE MIDDAY DRYING AND HEATING SHUD PERMIT AFTN SHRA/TSRA TO DVLP.
IN DEFERENCE TO CLIMO...HV PULLED BACK ON THUNDER POTL THIS FCST
CYCLE. STILL SEE ENUF INSTBY/SHEAR SW OF BNDRY FOR TSTMS TO DVLP.
CHALLENGE WL E TO PINPOINT WHERE THAT AREA IS. ATTM WL PAINT IT S
OF CHO-SHD-EKN... FOR LATE IN THE DAY. SPC HAS PEGGED THAT AREA
FOR A MRGL RISK OF SVR. WL HV A THUNDER GRADIENT NEWD FM THERE.
SCHC THUNDER NE OF MRB-DCA WUD ONLY BE FOR A STRAY LATE DAY ELEV
RUMBLE. BEST LIFT WL ACTUALLY BE IN THAT AFOREMENTIONED AREA...ACRS
THE N/NERN CWFA...AGAIN DUE TO UPGLIDE. AFTN POPS WL HOVER IN THE
70-80 PCT RANGE.

SHUD LOSE ANY SFC-BASED INSTBY INSTBY W/ SUNSET...BUT LAPSE RATES
AND SHEAR REMAIN DECENT WELL INTO SUN NGT. THE PARENT LOW WL TRACK
TWD NEW ENGLAND...WHICH WL SEND THE CDFNT THRU OVNGT SUN OR MORE
LKLY MON MRNG. POPS GRDLY TAPER OFF THRU THAT PD. QPF POTL STILL
GOOD SUN EVE...AND WL CARRY SHRA W/ MDT RAFL AT THAT TIME. WL
TAPER OFF THEREAFTER. LKLY TO SEE SOME SUNSHINE BY MON AFTN.

TEMPS THIS PD REMAIN A CHALLENGE AS INSOLATION CUD RSLT IN TEMP
SPIKES. SUN MAXT REFLECT THAT GRADIENT ACRS CWFA. BETTER DRYING
AND SUBSIDENT WLY FLOW MON SUGGESTS THAT MON WL BE A WARMER DAY
REGARDLESS OF CFP.

&&

.LONG TERM /TUESDAY THROUGH FRIDAY/...
THE SYNOPSIS FOR NEXT WEEK WILL REMAIN COOL AND UNSETTLED. THE
MIDDLE PORTION OF THE WEEK FEATURES THE GREATEST UNCERTAINTY IN
TERMS OF SENSIBLE WEATHER IMPACTS. THE FRONT WHICH PASSES THROUGH
DURING THE EARLY PART OF THE WEEK WILL STALL ALONG THE SOUTHEAST
COAST WHILE TROUGHING ALOFT DEVELOPS OVER EASTERN NOAM.
MULTIPLE AREAS OF LOW PRESSURE WILL TRACK ALONG THE FRONT. IN
TERMS OF THE 00Z RUNS...ECMWF AND GEM OFFER WETTER SOLUTIONS (I.E.
LOW TRACKS CLOSER TO THE COAST) FOR THE LOCAL AREA...WHILE THE GFS
IS DRIER. WILL BE CARRYING LOW POPS ALMOST EVERY PERIOD AS TIMING
AND PLACEMENT DIFFERENCES WILL SPAN ACROSS THE DAY-PARTS OF THE
FORECAST. DESPITE THE PESSIMISTIC FORECAST...TOTAL RAINFALL AMOUNTS
SHOULD BE FAIRLY LIGHT UNLESS THE LOW TRACKS ARE MUCH FURTHER INLAND
THAN CURRENTLY FORECAST.

BY THURSDAY...ENERGY DIVING SE FROM CENTRAL CANADA WILL SEND A COLD
FRONT THROUGH THE REGION. AS THIS ENERGY INTERACTS WITH THE COASTAL
FRONT...A CLOSED LOW ALOFT IS EXPECTED TO DEVELOP. THIS WILL BE THE
EASTERN LOBE OF A DEVELOPING OMEGA BLOCK FOR THE END OF THE WEEK /
NEXT WEEKEND. THE RESULT WILL BE A SHOWERY PATTERN WITH PERHAPS
SOME LOW TOPPED CONVECTION. WITH NO REAL SOURCE OF WAA...TEMPERATURES
WILL LIKELY REMAIN BELOW NORMAL THROUGH THE WEEK. WITH THE STEEP
LAPSE RATES...THE ALLEGHENY FRONT MAY NOT BE TOO FAR FROM SEEING
SOME WET SNOW FLAKES MIX IN BY FRIDAY MORNING.

&&

.AVIATION /07Z SATURDAY THROUGH WEDNESDAY/...
LOW CLOUDS AND PATCHY DRIZZLE CONT ACRS THE TERMINALS ELY THIS
MRNG. RESTRICTIONS...MAINLY IFR...ARE A RESULT OF CIGS. CUD BE
HEADED TWD LIFR TWD SR. ALREADY SEEING HINTS OF THAT AT CHO.

CONDS WL GRDLY IMPRV DURING THE DAY. AM STARTING TO FEEL CONFIDENT
ENUF TO CARVE OUT A PD OF VFR FOR BALT-DC TERMINALS MID-LT AFTN.

FLGT CONDS WL DROP SAT EVE AS RA OVERSPREADS THE AREA. RA MAY BE
MDT TO BRIEFLY HVY SAT NGT INTO ELY SUN. FLGT RESTRICTIONS WL BE
WIDESPREAD...AT LEAST IFR IF NOT LIFR.

POOR FLYING CONDS CARRY OVER INTO SUN...THO BREAKS IN THE OVC LKLY
AS BDRY ATTEMPTS TO WIGGLE N OF THE TERMINALS. ONCE AGN XPCT
IMPRVMNT DURING THE DAY AS RAFL HEADS EAST. THAT WL RESULT IN A
RENEWED CHC AT SHRA DURING THE AFTN. CUD BE THUNDER TOO...SPCLY
INVOF CHO. CONDS BECOME MORE STBL TWD THE NE.

CDFNT WL CROSS THE TERMINALS ELY MON...WHICH SHUD RESULT IN W/NWLY
FLOW. MAY STILL HV RESTRICTIONS TO START...BUT AM HOPEFUL FOR
IMPROVEMENT TO VFR DURING THE DAY.

LOW CONFIDENCE FORECAST FOR TUESDAY-WEDNESDAY WITH FRONT STALLED
ALONG SE COAST. GFS SUGGESTS MAINLY VFR WHILE OTHER MODELS WOULD
BRING IN SOME PERIODS OF RAIN AND POSSIBLE IMPACTS TO CIGS/VSBYS.

&&

.MARINE...
LLVLS REMAIN STBL THROUGH THE WKND AS A WEDGE OF HIPRES REMAINS
TRAPPED E OF THE BLURDG. THAT WL RESULT IN MAINLY E FLOW AT 5 TO
10 KT...WITH OCNL PDS CLSR TO 15 KT. WNDS WL VEER A BIT MORE TWD
THE SE AS AN APPCHG WMFNT TRIES TO DISLODGE THE MARINE AMS. ALTHO
WINDS WL BE STRONGER ALOFT...DONT BELIEVE THE STBL LLVLS WL PERMIT
ANY STRONGER WINDS TO REACH THE WATERS EDGE. THEREFORE...HV BACKED
AWAY FROM SCA POTL.

LIGHT NW FLOW EXPECTED TUESDAY BEHIND DEPARTED COLD FRONT. WINDS MAY
BECOME SW BY WEDNESDAY BUT GRADIENT LOOKS WEAK ENOUGH TO KEEP WINDS
AT 10-15 KT. SHOULD A STRONGER LOW PRESSURE SYSTEM DEVELOP ALONG A
STALLED COASTAL FRONT...HIGHER WINDS MAY BE REALIZED.

&&

.TIDES/COASTAL FLOODING...
TIDAL ANOMALIES REMAIN AROUND ONE-HALF TO THREE QUARTERS OF A
FOOT ABOVE NORMAL. A PERSISTENT ONSHORE FLOW WILL CAUSE ANOMALIES
TO HOLD NEARLY STEADY OR EVEN INCREASE A BIT THROUGH THE WEEKEND.
HOWEVER...THE FLOW SHOULD BE LIGHT ENOUGH FOR WATER LEVELS TO
REMAIN BELOW MINOR FLOODING THRESHOLDS. THERES ROOM FOR THIS
FORECAST TO CHANGE...ESPECIALLY TOWARD SUNDAY...SO WE WILL
CONTINUE TO MONITOR THIS SITUATION.

&&

.LWX WATCHES/WARNINGS/ADVISORIES...
DC...NONE.
MD...NONE.
VA...NONE.
WV...NONE.
MARINE...NONE.

&&

$$
SYNOPSIS...HTS
NEAR TERM...HTS
SHORT TERM...HTS
LONG TERM...ADS
AVIATION...HTS/ADS
MARINE...HTS/ADS
TIDES/COASTAL FLOODING...HTS



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