Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 300129 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 929 PM EDT MON JUN 29 2015 .SYNOPSIS...
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HIGH PRESSURE MOVES EAST THIS EVENING. LOW PRESSURE OVER THE GREAT LAKES WILL RIDE A NEARLY STATIONARY FRONT TO THE NORTH...WITH THE ASSOCIATED COLD FRONT SWINGING INTO THE REGION ON WEDNESDAY. THIS FRONT WILL STALL OVER THE MID ATLANTIC THROUGH SATURDAY.
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&& .NEAR TERM /THROUGH TUESDAY NIGHT/...
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UPPER LVL TROUGH POSITIONED OVER MID WEST THIS EVENING...WITH TROUGH AXIS ORIENTED ACROSS OH RIVER VALLEY. 00Z SFC ANALYSIS INDICATING FRONTAL BOUNDARY EXTENDING WESTERN WV INTO CENTRAL PA. ON GOING CONVECTION ATTM IN THE VICINITY OF THIS SFC BOUNDARY WITH SUPPORT ALOFT COMING FROM EMBEDDED SHORTWAVE ROUNDING THE BASE OF THE TROUGH. PCPN HAS BEEN WEAKENING/DISSIPATING AS IT NEARS THE WESTERN FRINGES OF THE CWA WITH THE AREA HAVING BEEN CAPPED DURING THE DAY. SOME ELEVATED INSTABILITY ALREADY IN PLACE COULD AID IN CONTINUING THE CONVECTION FORMING TO THE WEST INTO AREAS WEST OF THE BLUE RIDGE AS THE SHORTWAVE SWINGS EASTWARD. MINIMAL SHEAR AND INSTABILITY OVERALL THOUGH WOULD SUGGEST A WEAKENING TREND...WITH ONLY ISO-SCT SHOWERS EXPECTED. WILL HOLD OFF ON TSTM MENTION UNTIL TUES MORNING. MOST OF THE AREA WILL REMAIN DRY FOR TONIGHT. SFC LOW OVER THE OH RIVER VALLEY WILL RIDE THE NEARLY STATIONARY FRONT ON TUES...REACHING THE EASTERN GREAT LAKES BY TUES EVENING. MODELS DEVELOP SFC TROUGH ALONG EASTERN EDGE OF THE BLUE RIDGE BY THE AFTN...WHICH WILL AID IN TRIGGERING AFTN CONVECTION WHEN THE BEST SUPPORT FROM ALOFT ROUNDS THE BASE OF THE UPPER LVL TROUGH. STRONG SURGE OF BOTH WAA AND MOISTURE ADVECTION...ESP EAST OF THE BLUE RIDGE...WILL LEAD TO INCREASING INSTABILITY...WITH SBCAPE VALUES BETWEEN 500-1000 J/KG. DEEP LAYER SHEAR IS FORECASTED 25-35 KTS...WHICH COMBINED WITH THE INCREASED INSTABILITY COULD LEAD TO ISO STRONG TO SVR STORMS. TUESDAY NIGHT...TROUGH LINGERS OVER THE AREA...ACTIVITY SHOULD SHIFT EAST TO THE BAY THROUGH THE NIGHT. THE UPR TROUGH ENTERS THE CNTRL APPALACHIANS LATE IN THE NIGHT...WITH SCATTERED SHOWERS POSSIBLE. MIN TEMPS LOW TO MID 60S WEST OF THE BLUE RIDGE...UPR 60S TO LOW 70S EAST...MID 70S NEAR SHORE.
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&& .SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/... TROF AXIS MOVE SLGTLY EAST ON WED WHILE CDFNT CREEPS SEWD TWD AREA. OVERALL FORCING MECHANISMS DO NOT LOOK THAT GREAT. HWVR...IF EURO DEPICTION OF S/WV CROSSING MD DURING THE DAY PANS OUT...THEN THERE WL BE A BETTER CHC AT TSRA. SHEAR EXITS ELY...BUT STILL HV FVRBL INSTBY PARAMETERS. HV TAKEN POPS DOWN A BIT...FCST GNLY ARND 30-40 PCT...BUT PLACED A BIT MORE EMPHASIS IN THE LEE TROF LT IN THE DAY. DIMINISHED PCPN AFTER LOSS OF DAYTIME HEATING. KEPT TEMPS NEAR NORMAL. && .LONG TERM /THURSDAY THROUGH MONDAY/... AT 12Z THU MEANDERING FRONT IS CURRENTLY PROGGED TO BE ALONG OUR NORTHERN BORDER WITH MOST...IF NOT ALL...OF OUR AREA IN THE WARM SECTOR. SOME QUESTION REMAINS WITH REGARDS TO TIMING OF FRONTAL PASSAGE...WITH SOME GUIDANCE SUGGESTING FRONT PASSES THROUGH EARLY...WHILE OTHERS SUGGEST A LATER PASSAGE. REGARDLESS...SFC LP TRACKS ALONG THE FRONT AND...WITH BAROCLINICITY...SOME UPPER LEVEL SUPPORT...AND DEEP MOISTURE...COULD SETUP A RATHER WET PERIOD. UPPER LEVEL FLOW NOT OVERLY IMPRESSIVE (AOB 30 KTS AT 5H) AS SUBTLE SHORT WAVE APPROACHES THE AREA...SO NOT EXPECTING EXTREMELY ORGANIZED STORMS...THOUGH COULD BE ENOUGH INSTABILITY FOR STRONGER PULSE-TYPE STORMS. FRONT OSCILLATES AROUND THE AREA THROUGH THE REMAINDER OF THE PERIOD...WHICH KEEPS FORECAST MUDDLED. CHC POPS REMAIN IN THE FORECAST EACH DAY FOR MAINLY DIURNAL TSTM ACTIVITY. WITH THE TYPICALLY FAVORED HIGHER TERRAIN LOCATIONS HAVING THE HIGHEST POPS. TEMPS EXPECTED TO REMAIN NEAR NORMAL THROUGH THE EXTENDED PERIOD...WITH A SLIGHT INCREASE THROUGH THE WEEKEND. DEWPOINTS NOT OVERLY OPPRESSIVE...GENERALLY AOB 70F...WHICH SHOULD KEEP IT FROM GETTING TOO UNCOMFORTABLE. && .AVIATION /01Z TUESDAY THROUGH SATURDAY/...
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MAINLY VFR CONDITIONS THRU THE TAF PERIOD EXPECTED. LIGHT SLY FLOW TONIGHT...INCRSG 12-14Z TUES. OCNL GUSTS TO 20 KTS PSBL MIDDAY. GENERALLY DRY WX TONIGHT...KMRB COULD SEE A STRAY SHOWER. INCRG CHC OF SHOWER/TSTM ON TUES...ESP DC/BALTIMORE TAF SITES. HARD TO PINPOINT TIMING AT THIS TIME...SO WILL MAINTAIN VCTS THRU THE AFTN HOURS. ANY TSTM COULD REDUCE CONDITIONS MVFR OR LOWER...AS WELL AS BRING A BRIEF PERIOD OF GUSTY-STRONG WINDS AND HEAVY RAIN. LOW CONFIDENCE IN FLGT RESTRICTIONS WED. POTL CERTAINLY THERE...BUT TIMING/PLACEMENT A REAL STRUGGLE. VFR SHUD PREVAIL MOST OF THE TIME. MOST PERIODS THU THRU SAT WILL BE VFR...THOUGH EXPECT SUB-VFR CONDS IN ANY TSTM ACTIVITY. VARIABLE WINDS EXPECTED THROUGH THE PERIOD.
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&& .MARINE...
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SUB-SCA CONDITIONS TONIGHT. SLY FLOW INCREASES TO 15 TO 20 KT WITH GUSTS UP TO 25 KT ON TUES. SCA FOR ALL WATERS BEGINS AT 10AM TUES AND CONTINUES UNTIL 8PM...WILL CONTINUE THE SCA INTO THE OVERNIGHT FOR ALL WATERS MINUS NORTHERN ZONES OF THE CHESAPEAKE. SCATTERED GUSTY THUNDERSTORMS DEVELOP LATE TUESDAY AFTN AND CONTINUE THROUGH TUESDAY NIGHT. WINDS AOB 10 KT WED-WED NGT...MAINLY FM THE SW. WINDS EXPECTED TO REMAIN BELOW SCA CRITERIA THROUGH THE EXTENDED...THOUGH WILL NEED TO MONITOR AS FRONT WILL BE NEAR AREA EACH DAY. AFTN TSTMS ARE ALSO POSSIBLE EACH DAY...WHICH COULD IMPACT MARINE CONCERNS.
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&& .TIDES/COASTAL FLOODING...
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WATER LVLS WL BE INCREASING TONIGHT THRU MID WEEK. THE WATER LVLS MAY APPROACH MINOR THRESHOLDS AROUND SW DC HIGH TIDE TUES MORNING...AND THEN AGAIN WED ALONG THE WESTERN CHESAPEAKE DURING THE HIGHER HIGH TIDE...WHICH IS THE AM CYCLE /MIDNGT THRU NOON/.
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&& .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...SMALL CRAFT ADVISORY FROM 10 AM TUESDAY TO 4 AM EDT WEDNESDAY FOR ANZ531>534-536-537-539>543. SMALL CRAFT ADVISORY FROM 10 AM TO 8 PM EDT TUESDAY FOR ANZ530- 535-538. && $$ SYNOPSIS...BAJ NEAR TERM...BAJ/SEARS SHORT TERM...HTS LONG TERM...MSE AVIATION...MSE/HTS/SEARS MARINE...BAJ/MSE/HTS/SEARS TIDES/COASTAL FLOODING...HTS/SEARS

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