Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 220802 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 402 AM EDT FRI AUG 22 2014 .SYNOPSIS... AN AREA OF LOW PRESSURE WILL MOVE ALONG A STALLED FRONTAL BOUNDARY ACROSS THE MID ATLANTIC STATES LATE TODAY AND TONIGHT. THE FRONT WILL PUSH SOUTHWEST AS A COLD FRONT SATURDAY. HIGH PRESSURE WILL BUILD SOUTH FROM NEW ENGLAND INTO THE MID ATLANTIC THIS WEEKEND INTO EARLY NEXT WEEK. && .NEAR TERM /THROUGH SATURDAY/... THIS WEEK HAS BEEN FAIRLY CUT/PASTE EACH DAY W/ THE CONDITIONS OF TEMPS...HUMIDITY...SKY CONDITIONS AND POPS. THIS MOIST AIRMASS WILL FINALLY UNDERGO A TRANSITION AND BEGIN TO EXIT THE REGION...BUT NOT UNTIL SAT EVE. TILL THEN...ANOTHER SIMILAR DAY TO AT LEAST THE LAST TWO IS EXPECTED FOR THE AREA. DEWPOINTS CONTINUE TO HOVER WITHIN THE 65-70F RANGE WHICH IS PLENTY HUMID AND PREVENTING OUR TEMPS FROM DROPPING BELOW THE 70F MARK FOR MANY AREAS. GROUND FOG/LOW STRATUS NOT AS DENSE OR PREVALENT AT THIS TIME COMPARED TO LAST NIGHT...EVEN W/ CALM WINDS AND ANOTHER DAY OF RAIN ACCUMULATION STRANDS ACROSS THE REGION. UPPER DEBRIS CARRIED OUT AHEAD OF DISSIPATED CONVECTION FROM THE NW HAS OVERCOME MUCH OF THE AREA AND LIKELY LIMITING FOG FORMATION. STILL EXPECTING A BRIEF FEW HRS OF LOW STRATUS JUST W/IN THE BOUNDARY LAYER TOWARD DAWN WHEN THE TEMPS ARE AT THEIR MIN AND RADIATIONAL EFFECTS FROM THE RISING SUN BEGIN TO TRANSITION THE NEAR SFC LAYER - BUT ONLY PATCHY DENSE VLY FOG OR STRAITED BANDS OF LOW STRATUS FOR LOCALIZED AREAS. OUR AREA IS SURROUNDED TO THE EAST AND WEST BY CONTINUED SHOWER AND TSTM ACTIVITY OVERNIGHT...W/ THE ERN STORMS HEADING OFF THE COAST AND ANOTHER BATCH APPROACHING THE CNTRL APLCNS. A LOCAL UPPER IMPULSE LIKELY KICKING-OFF ANOTHER ROUND OF CELLS IN A LINEAR FASHION FROM ERN OH DOWN INTO NRN WV. HRRR AND MOST OTHER LOCAL WRF MEMBERS CARRYING THIS ACTIVITY OVER THE MTNS BUT THEN QUICKLY DISSIPATE IT TO AN INNOCUOUS BATCH OF LIGHT STRATIFORM SHOWERS. LIKE THE PREV FEW DAYS...TODAY WILL BE MOSTLY DRY - THOUGH HUMID - AND DODGING SCT SHOWERS/ISLD TSTMS LATER THIS AFTN/EVE. THE EARLIEST ACTIVITY WILL DICTATE THE LATER ACTIVITY...W/ LOCALLY HEAVY DOWNPOURS EXPECTED AND GUSTY WINDS W/ THE STRONGER CELLS. THE 00Z 4/22 KIAD SOUNDING SHOWS GOOD LAPSE RATES IN THE LOW LEVELS AND MOIST ADIABATIC HEADING UP THRU THE REST OF THE COLUMN...MUCH MORE MOIST THAN 24HRS PRIOR. THIS PROFILE IS EXPECTED TO CARRY OVER FOR TODAY`S ACTIVITY BUT END UP MORE STABLE THAN THU`S...AND A LESS FAVORABLE WIND PROFILE. WINDS BELOW 10KFT MAY HAVE A BULK AND MEAN SHEAR OF ONLY AROUND 5KT W/ A MUCH STRONGER UPPER FLOW. A POTENT UPPER JET OF 80-100KT WON`T HELP LOW-TOP CONVECTION MUCH AND MAY IN-FACT SHEAR OFF TALLER CELLS. THE LACK OF GOOD MID/LOW LEVEL STEERING FLOW INCREASES THE POTENTIAL FOR FLOODING AND FLASH FLOODING IN LOCALIZED AREAS...W/ A REGIME THAT MAY ALLOW FOR TRAINING CELLS UNDER THE RIGHT CONDITIONS OR ALONG A PRE-EXISTING BOUNDARY. WILL KEEP THIS THE HIGHLIGHT IN THE HWO...WHICH WILL BE THE BIGGEST THREAT OUTSIDE OF A FEW STRONG/MARGINALLY SVR TSTMS. SUNSET WILL AGAIN BE THE START OF TSTM DISSIPATION W/ ONLY A HANDFUL OF SHOWERS CONTINUING TO SLIDE ACROSS THE AREA INTO THE LATE NIGHT HRS. DEWPOINTS WILL CONTINUE TO HOVER NEAR 70F FOR ANOTHER HUMID OVERNIGHT. BATCHES OF MID CLOUD DECKS WILL ALSO HELP SHELTER THE AREA AND KEEP OVERNIGHT LOWS MODERATED NEAR THE 70F MARK. TOWARD SUNRISE SAT...THE DYNAMIC TRANSITION WILL BEGIN TO TAKE PLACE OFF TO OUR NORTH AND EAST. THE UPPER LOW SITTING OVER THE GREAT LAKES FOR THE PAST COUPLE OF DAYS WILL BE ABSORBED INTO THE UPPER FLOW AND HELP DIG THE RETROGRADED PORTION OF AN UPPER TROUGH BACK OVER THE AREA ON SAT. THE LAST ARM OF THIS FEATURE WILL DRIFT ACROSS THE REGION DURING THE DAYTIME HRS AND BRING MORE SCATTERED SHOWERS AND TSTMS. HIGH TEMPS WILL BE THEIR COOLEST IN DAYS BUT STILL REACHING THE L80S BY MID AFTN. HOWEVER...THE INSTABILITY PROFILE WILL LOOK MORE LIKE THU`S...W/ SFC-BASED CAPES POTENTIALLY IN THE 1-1.5K RANGE W/ A COOLER UPPER LEVEL TEMP PROFILE FROM THE UPPER TROUGH PASSAGE. STABILITY MAY COME HOWEVER IN THE FORM OF AN ELY LOW LEVEL WIND...WHICH COULD LIMIT THE CONVECTIVE INITIATION POTENTIAL IF THE CAP IS TOO STRONG AND SFC TEMPS DON`T REACH THE APPROPRIATE LEVELS - ESPEC CLOSER TO THE BAY AND NEAR THE MASON-DIXON LINE. && .SHORT TERM /SATURDAY NIGHT THROUGH SUNDAY NIGHT/... SFC HIPRES WL BE BLDG DOWN THE COAST SAT NGT-SUN. AS H5 RDG AXIS CONTS TO SHARPEN...DRIER AIR WL BE ENTRAINED...AND GRDLY ERODE THE LLVL MARITIME SATURATION. THAT WL HPPN FIRST ALONG I-95 SAT EVNG. THINK WE/LL NEED TO HOLD ONTO POPS FOR THE MTNS ALL NGT SAT. FIRST CLRG WL COME TO METRO BALT ELY SUN...AND WL SPREAD THAT TO THE SW ACRS THE REMAINDER OF THE CWFA THRUT THE DAY. SUNDAY WL BE A NICER DAY THAN SAT...EVEN FOR THE MTNS WHICH MAY AVG OUT AS PTSUN VS MOSUN /OR EVEN SUNNY/. SINCE ITLL BE CLDY...AND DEWPTS WL BE DROPPING THRU THE 60S...DIDNT LWR MIN-T AS MUCH AS I CUD HV. AM TAKING A RESERVED APPROACH...W/ MIN-T IN THE 60S AS WELL. DID GO ON THE COOLER EDGE OF MAXT GDNC FOR SUN...BUT BELIEVE PROLONGED ELY FETCH WL KEEP TEMPS FAIRLY CLOSE TO WATER TEMPS. && .LONG TERM /MONDAY THROUGH THURSDAY/... SFC HIPRES AND H5 RDG AXIS CONT TO BUILD OVER THE MID ATLC THRU THE XTNDD PD. FLOW WL BE LGT...BUT TEMPS WL GRDLY BE MODERATING BY MIDWEEK. A CDFNT DROPPING TWD THE AREA LT WK WL PROVIDE THE ONLY PCPN RISK DURING THE WORK WEEK. && .AVIATION /08Z FRIDAY THROUGH TUESDAY/... SOME AREAS OF GROUND/VLY FOG IN TYPICAL PIEDMONT AND COASTAL AREAS BUT NOT SEEING A DEVELOPING DENSE LOW CLOUD BANK EITHER ATTM. THE NEXT FEW HRS MAY SEE BATCHES OF LOW-END MVFR CIGS/VSBYS DEVELOP BUT LIKELY NOT IFR OR LOWER...OUTSIDE OF A BRIEF PERIOD. SKIES AFTER SUNRISE WILL AGAIN WAVER IN/OUT OF PARTLY SUNNY/MOSTLY CLOUDY SINCE WE STILL HAVE A MOIST ATMOS. SCATTERED SHOWERS AND LATE-DAY TSTMS POSSIBLE AGAIN ACROSS THE REGION. CONDS WILL IMPROVE AGAIN OVERNIGHT...THOUGH A FEW ISOLATED SHOWERS AND MORE DENSE CLOUD COVER IS EXPECTED INTO EARLY SAT W/ MORE SHOWER/TSTMS EXPECTED ON SAT. MAY HV SOME LOW CLDS OR PATCHY FOG TO START THE DAY SUN...OTRW VFR WL PREVAIL THRU TUE. && .MARINE... SCA CONDITIONS NOT ANTICIPATED TODAY OR TONIGHT. A FEW TSTMS POSSIBLE THIS AFTN/EVE OVER THE WATERS. ELY ONSHORE FLOW WILL STRENGTHEN INTO EARLY SAT...W/ SOME POSSIBLY MARGINAL SCA CONDITIONS ALONG THE WRN SHORES AND MAIN STEM OF THE MD BAY. ELY/NELY FLOW WL PREVAIL SAT NGT INTO SUN AS HIPRES DRAINS COOLER/DRIER AIR ACRS WATERS. GDNC SUGGESTS WNDS WL REMAIN AOB 15 KT DURING THIS TIME. WL GO THAT ROUTE IN THE FCST ATTM...BUT WUDNT BE SHOCKED IF A FEW HIER GUSTS APPROACHED SCA CRIT IN THE MAIN CHANNEL OF THE MID BAY. BYD THAT...WNDS WL LESSEN AS HIPRES BLDS. && .TIDES/COASTAL FLOODING... WATER LEVELS ONLY INCHES HIGHER THAN ASTRO NORMALS. SHOULD BE PROBLEM FREE FOR THE NEXT COUPLE OF DAYS. FLOW TURNS ONSHORE AGAIN THIS WEEKEND. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...NONE. && $$ SYNOPSIS...HTS NEAR TERM...GMS SHORT TERM...HTS LONG TERM...HTS AVIATION...GMS/HTS MARINE...GMS/HTS TIDES/COASTAL FLOODING...HTS

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