3/12/2014 National Weather Service Text Product Display National Weather Service National Headquarters National Weather Service Area Forecast Discussion Issued by NWS Sterling, VA Current Version | Previous Version | Text Only | Print | Product List | Glossary Off Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 -- Highlight Changed Discussion -- 000 FXUS61 KLWX 121343 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 943 AM EDT WED MAR 12 2014 .SYNOPSIS... A STRONG LOW PRESSURE CENTER AND ITS ASSOCIATED COLD FRONT WILL PASS THROUGH THE MID-ATLANTIC STATES THIS AFTERNOON AND EVENING. AN UPPER LEVEL TROUGH WILL MOVE ACROSS THE AREA TONIGHT...THEN CANADIAN HIGH PRESSURE WILL BUILD THROUGH THURSDAY NIGHT BEFORE MOVING OFF THE COAST FRIDAY. AN UPPER LEVEL TROUGH WILL PERSIST OVER THE REGION THIS WEEKEND...AND A WEAK COLD FRONT WILL DROP THROUGH THE MID ATLANTIC ON SATURDAY. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... WE SOMETIMES SAY THE FORECAST HAS SOMETHING FOR EVERYONE. I THINK WE CAN TAKE THAT LITERALLY AT THE MOMENT...AS THIS FORECAST HAS ALMOST EVERY POSSIBLE WEATHER TYPE/HAZARD...IN THE FIRST 36 HOURS. STRONG TO SEVERE STORMS...SNOW...WIND CHILLS...STRONG WINDS... UNSEASONABLY WARM TEMPS...UNSEASONABLY COLD TEMPS...POTENTIAL FIRE WEATHER CONCERNS...MINOR COASTAL FLOOD POTENTIAL...THERE IS NOT MUCH LEFT. SURFACE ANALYSIS THIS MORNING SHOWS LOW PRESSURE JUST EAST OF CINCINNATI MOVING EASTWARD AND DEEPENING...NOW DOWN TO 989 MB. CLOUD COVER HAS OVERSPREAD THE MID-ATLANTIC THIS MORNING...THOUGH VISIBLE SATELLITE DOES SHOW SOME CLEAR PATCHES MAINLY WEST OF THE BLUE RIDGE. THE PRIMARY STATIONARY FRONT IS TO OUR NORTH...WHICH WILL ALLOW FOR MOISTURE RETURN TODAY...BUT THAT MOISTURE RETURN IS BEING TEMPERED BY THE DEPARTING SOUTHERN STREAM TROUGH...FOR NOW. ONCE THAT IS OUT OF THE WAY...LOW-LEVEL MOISTURE WILL BE ABLE TO RACE IN LATER TODAY. THE SFC LOW WILL CONTINUE TO DEEPEN AS IT MOVES EASTWARD...MOVING NEAR OR JUST NORTH OF THE MASON-DIXON LINE. THIS KEEPS US IN THE WARM SECTOR. BASED ON RADAR AND HI-RES MODELS...THE SCENARIO FOR TODAY SHOULD BE AS FOLLOWS...PRE-FRONTAL SHRA OVERSPREAD THE AREA THIS MORNING INTO EARLY AFTERNOON. THIS WILL BE FOLLOWED BY A BREAK IN ACTIVITY AND THEN A LINE OF CONVECTION DEVELOPING ALONG THE FRONT. SOME OF THE HI-RES MODELS HINT AT THE CONVECTION BECOMING MORE DISORGANIZED EAST OF THE ALLEGHENY FRONT AND THEN ORGANIZING AGAIN EAST OF THE BLUE RIDGE. THIS IS NOT AN UNPLAUSIBLE SCENARIO. H8 WINDS INCREASE TO 40-50 KTS EVEN BEFORE ANY CONVECTIVE LINE MOVES IN...SO EVEN THE PREFRONTAL SHOWERS WILL HAVE THE POTENTIAL TO MIX DOWN SOME GUSTY WINDS. THE QUESTION FOR SEVERE POTENTIAL IS HOW MUCH OF A BREAK OCCURS PRIOR TO THE CONVECTIVE LINE...AND HOW MUCH HEATING OCCURS DURING THAT TIME. WIND SHEAR IS EXTREMELY HIGH BUT HOW MUCH INSTABILITY WILL BE REALIZED IS STILL SIGNIFICANTLY IN QUESTION AT THIS HOUR. BUT THE THREAT OF DAMAGING WIND GUSTS...BOTH IN A CONVECTIVE LINE AND BEHIND IT WITH GRADIENT WINDS...IS THERE. THE SHEAR LENDS ITSELF TO AN ISOLATED TORNADO THREAT AS WELL. FOR THE AFOREMENTIONED REASONS...HIGH TEMPS TODAY ARE TRICKY. DID NOT MAKE MANY CHANGES EXCEPT TO LOWER HIGHS JUST A LITTLE BIT IN THE HIGHLANDS. ELSEWHERE...BASED ON MORNING SOUNDINGS...AROUND OR EVEN OVER 70 IS EASILY ATTAINABLE IF CLOUDS BREAK. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/... COLD FRONT PASSES THROUGH THE AREA LATE THIS AFTERNOON...EARLY THIS AFTERNOON...WITH A VERY STRONG PRESSURE GRADIENT BUILDING AROUND THE BACK SIDE OF THE LOW. WIND ADVISORY IS UP FOR ALMOST THE ENTIRE FORECAST AREA FOR WIND GUSTS 40-50 MPH. THE AREA NOT CURRENTLY IN THE ADVISORY WILL BE VERY CLOSE TO CRITERIA AND MAY BE ADDED AT ALMOST ANY TIME. http://forecast.weather.gov/product.php?site=NWS&issuedby=LWX&product=AFD&format=CI&version=2&glossary=1&highlight=off 1/3 3/12/2014 National Weather Service Text Product Display THE OTHER THING THAT HAPPENS IS A RAPID DROP IN TEMPERATURES. BY 03Z TONIGHT...THE HIGHLANDS WILL BE NEAR 20 WHILE AREAS NEAR THE BAY COULD STILL BE AROUND 60. LOWS TONIGHT WILL ULTIMATELY BE 40 TO 50 DEGREES COOLER THAN TODAYS HIGHS. WITH THE GUSTY WINDS IN PLACE...SINGLE DIGIT WIND CHILLS CAN BE EXPECTED LATE TONIGHT... WITH SUBZERO WIND CHILLS IN THE POTOMAC HIGHLANDS. A WIND CHILL ADVISORY WILL LIKELY BE ISSUED LATE THIS MORNING FOR AFFECTED AREAS. IN TERMS OF PRECIPITATION...MOST OF THE AREA WILL DRY OUT QUICKLY...BUT UPSLOPE SNOW IS EXPECTED OVER THE POTOMAC HIGHLANDS. EXPECTING A COUPLE OF INCHES OF SNOW...BUT ACCUMULATIONS COULD BE HIGHER IF TEMPS DROP BELOW FREEZING EARLIER THAN FORECAST. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... THERE WL STILL BE A BIT OF A P-GRAD THU EVNG AS LOPRES MVS NEWD THRU THE CNDN MARITIMES AND HIPRES BLDS FM THE OH/TN VLYS...BUT XPCT SUBSIDENCE FM THE HIGH /AND DCPLG/ TO TAKE OVR DURING THE NGT. THAT WL BE REFLECTED BY CLR/CALM OVNGT CONDS. MIN-T GDNC FAIRLY UNIFORM. WENT ON THE COOLER END OF THAT. NOT MUCH TO DEAL WITH ON FRI EITHER AS HIPRES RDG OVHD...AND CENTER OF HIGH ENGULFS THE SERN CONUS. AS LOPRES TRACKS ACRS SRN CNDA... THE RTN FLOW DOES PROMOTE STRONG WAA. WHILE THE BULK OF IT WL BE N OF CWFA...THE EFFECTS WL BE TANGIBLE LCLLY AS WELL. TOOK A MDL BLEND...AS DO BELIEVE THAT A FULL TEMP RECOVERY WL BE A BIT DLAD ACRS NERN MD AND ALONG THE BAY. NONETHELESS...TEMPS WL BE MUCH CLSR TO AVG. THE AFOREMENTIONED LOW WL DROP A WK CDFNT ACRS THE NERN CONUS AND MID ATLC FRI NGT-SAT. IT WL BE OUTRUNNING MOST OF ITS VORT AND NRN STREAM JET SUPPORT...BUT IT MAY GET CLOSE TO THE LFQ OF A SRN STREAM JETMAX SAT...SO WUD PREFER TO NOT GO W/ A DRY FCST. HV 20-30 POPS... WHICH WUD MOSTLY BE SHRA XPCT FOR MTNS WHERE IT WUD BE COLD ENUF FOR SHSN. REGARDLESS...QPF LGT...AND NOTHING OF CONSEQUENCE. CNDN HIPRES BLDS BHD THE FNT SAT NGT AND INTO SUN MRNG. THE XNTDD FCST STILL LOOKING QUITE MURKY. IT WUD SEEM AS THO CYCLOGENESIS SHUD OCCUR SOMEWHERE ALONG THIS BNDRY AND TRACK NEWD FM THERE...BUT GDNC IN REAL POOR AGREEMENT ON HOW THIS WL TRANSPIRE. ACKNOWLEDGED THE POTL PRESENCE OF SOMETHING IN THE DATABASE LT SUN INTO MON NGT BY RAISING POPS...BUT OTRW WENT PRETTY GENERIC WITH DETAILS. && .AVIATION /13Z WEDNESDAY THROUGH SUNDAY/... SHOWERS AND THUNDERSTORMS WILL DEVELOP AS A COLD FRONT APPROACHES DURING THE AFTERNOON. POTENTIAL FOR AT LEAST OCCASIONAL IFR CONDITIONS IN HEAVY RAIN. ANY STORMS OR HEAVY SHOWERS WILL LIKELY BE ACCOMPANIED BY GUSTY WINDS. GUSTY NW WINDS EXPECTED OVERNIGHT...POSSIBLY UP TO 50 MPH AT ALL TERMINALS...EXCEPT KCHO WHERE WINDS SHOULD NOT BE QUITE AS STRONG. VFR THURSDAY WITH GUSTY WINDS NW WINDS CONTINUING...BUT GRADUALLY DIMINISHING DURING THE DAY. VFR SHUD PREVAIL THRU MUCH OF THE OUTLOOK. CIGS MAY FLIRT W/ MVFR SAT INVOF WK CDFNT DROPPING ACRS AREA. && .MARINE... SOUTHERLY WINDS ARE ON THE INCREASE...WITH SMALL CRAFT ADVISORIES POSTED. SHOWERS AND POSSIBLY THUNDERSTORMS EXPECTED LATE THIS AFTERNOON OR EVENING...WITH POTENTIAL FOR SPECIAL MARINE WARNINGS. GALES EXPECTED TONIGHT UNDER GUSTY NW WINDS...GUSTS LIKELY TO 40KT. GALE WARNING HAS BEEN EXTENDED INTO THURSDAY FOR ALL OF MARYLAND CHESAPEAKE BAY AND THE LOWER TIDAL POTOMAC. P-GRAD WL STILL BE PRESENT THU EVNG...AND XPCT AT LEAST SCA WL BE REQD AT THE START OF THE PD...BUT GRADIENT WL RELAX THRU THE EVNG. WL ALLOW RAMP-DOWN DETAILS TBD AS THE TIME COMES. A WK CDFNT WL DROP ACRS WATERS SAT. TIMING A BIT UNCERTAIN...AND MIXED PROFILES SHUD BE LESS THAN IDEAL. WL OPT TO CAP WINDS AT 15 KT ATTM. OTRW...NO HAZARDOUS CONDS XPCTD THRU THE WKND. && .FIRE WEATHER... ABUNDANTLY DRY AIR WILL ACCOMPANY THE ARCTIC AIRMASS INVADING THE AREA ON THURSDAY...WITH DEW POINTS BELOW ZERO EXPECTED. THIS WILL RESULT IN RELATIVE HUMIDITY VALUES BOTTOMING OUT IN THE TEENS THURSDAY AFTERNOON. THE DRY AND WINDY CONDITIONS MAY RESULT IN AN ENHANCED FIRE SPREAD POTENTIAL THURSDAY AFTERNOON DEPENDING ON HOW MUCH RAINFALL THE AREA RECEIVES TODAY. STAY TUNED. && http://forecast.weather.gov/product.php?site=NWS&issuedby=LWX&product=AFD&format=CI&version=2&glossary=1&highlight=off 2/3 3/12/2014 National Weather Service Text Product Display .TIDES/COASTAL FLOODING... TIDAL DEPARTURES RUNNING AROUND A FOOT THIS MORNING WITH SOUTHERLY WINDS CONTINUING TO INCREASE THE ANOMALY. LEVELS RUNNING CLOSE TO LATEST CBOFS MODEL OUTPUT...WHICH SHOWS CONDITIONS NEAR MINOR FLOOD CRITERIA NEAR ANNAPOLIS AND PERHAPS THE NORTH SHORE OF THE LOWER TIDAL POTOMAC. THE ANOMALY WOULD NEED TO INCREASE TO NEARLY 2 FEET FOR FLOODING IN BALTIMORE AND ABOUT 1.7 FEET FOR SOLOMONS ISLAND. WITH HIGH TIDE NOW JUST 3-8 HOURS AWAY...IT APPEARS UNLIKELY THOSE VALUES WILL BE REACHED. WILL KEEP THE COASTAL FLOOD ADVISORY AS IS FOR CALVERT/ANNE ARUNDEL/SAINT MARYS ONLY. WATER LEVELS WILL SHARPLY DECREASE FOLLOWING FRONTAL PASSAGE...AND A NEGATIVE ANOMALY OVER ONE FOOT IS LIKELY BY THURSDAY AFTERNOON. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...WIND ADVISORY FROM 6 PM THIS EVENING TO 11 AM EDT THURSDAY FOR DCZ001. MD...WIND ADVISORY FROM 6 PM THIS EVENING TO 11 AM EDT THURSDAY FOR MDZ003>007-009>011-013-014-016>018-501-502. COASTAL FLOOD ADVISORY UNTIL 5 PM EDT THIS AFTERNOON FOR MDZ014-017-018.