Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 190053 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 853 PM EDT MON MAY 18 2015 .SYNOPSIS... A WARM AND HUMID AIRMASS WILL BE IN PLACE TONIGHT. A COLD FRONT WILL MOVE ACROSS THE AREA ON TUESDAY. COOLER AND DRY HIGH PRESSURE WILL BUILD IN FROM MIDWEEK THROUGH THE EARLY PART OF THE WEEKEND. && .NEAR TERM /THROUGH TUESDAY/... A WARM AND HUMID AIRMASS IS IN PLACE ACROSS THE MID-ATLANTIC TONIGHT. SHOWERS AND THUNDERSTORMS HAVE BEEN ONGOING UNDER A 500MB RIDGE. INSTABILITY IS HIGH ACROSS MUCH OF THE REGION WITH ML CAPE 1K-2K J/KG. THE SHEAR IS STILL VERY LOW DUE TO THE UPPER LEVEL RIDGE AND THEREFORE THUNDERSTORMS HAVE NOT BEEN SEVERE. MOST STORMS HAVE BEEN INITIATING ON OUTFLOW BOUNDARIES AND MOVING SLOWLY DUE TO THE WEAK STEERING FLOW. HEAVY RAIN CONTINUES TO BE THE MAIN THREAT TONIGHT WITH PWATS AROUND 1.8 INCHES. LUCKILY STEERING FLOW IS WESTERLY SO STORMS HAVE BEEN PROGRESSING BUT SLOWLY. TWO MORE ROUNDS OF RAINFALL ARE EXPECTED FOR NRN MD TONIGHT. A MORE ORGAINIZED AREA OF SHOWERS AND THUNDERSTORMS IS MOVING ACROSS THE SHENANDOAH VALLEY AND EASTERN PANHANDLE THIS EVENING. THESE ARE EXPECTED TO SLOWLY MOVE EASTWARD TONIGHT. AN AREA OF CONCERN IS NORTH-CENTRAL/NE MD AS PAST STORMS PRODUCED 1-3 INCHES OF RAIN IN A SHORT AMT OF TIME. REPORTS WE HAVE SEEN ARE NUISANCE FLOODING IN POOR DRAINAGE AREAS AND PONDING ON ROADWAYS. RIVERS SEEM TO BE REACTLY SLOW ENOUGH TO NOT CAUSE ANY ISSUES AT THIS TIME BUT WILL NEED TO BE CLOSELY MONITORED INTO THE OVERNIGHT HOURS. FLASH FLOOD WARNINGS MAY BE ISSUED FOR LOCALIZED FLOODING. USE CAUTION WHILE DRIVING THIS EVENING AS IT IS HARD TO SEE FLOODED ROADWAYS. PREV DISCUSSION... TONIGHT WILL BE UNSEASONABLY WARM AND QUITE HUMID AGAIN WITH LOWS SIMILAR TO...IF NOT A DEGREE OR TWO WARMER THAN...THIS MORNING. A COLD FRONT MOVES THROUGH DURING THE DAY ON TUESDAY. CONVECTIVE TEMPS ARE AGAIN IN THE LOW/MID 80S...BUT THE MITIGATING FACTOR IS TIME-RELATED...WITH THE FRONT THROUGH MOST OF THE AREA BY EARLY AFTERNOON...AND WINDS SHIFTING OUT OF THE WEST...A MAJOR HINDRANCE TO PRECIP DEVELOPMENT. POPS WERE LOWERED WEST OF THE BLUE RIDGE...AND KEPT AT LESS THAN 50/50 WEST OF THE METRO AREAS. PWATS ARE ALSO NOT AS IMPRESSIVE TOMORROW...AND THERE IS MORE STEERING FLOW...SO THE HEAVY RAIN THREAT DECREASES TOO. && .SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY NIGHT/... GENERAL CONSENSUS AMONGST THE 12Z MODEL SUITE HAS THE COLD FRONT EXTENDING JUST EAST OF THE CHESAPEAKE BAY BY TUES EVENING. MOSTLY ZONAL FLOW ALOFT LACKING IN ANY SIGNIFICANT FORCING LENDS TO ANY PCPN ACTIVITY TUES EVENING BEING DRIVEN BY SFC INSTABILITY AND LIFT PRODUCED BY THE COLD FRONT. AS SUCH...SCT SHOWERS AND MAYBE AN ISO TSTM PSBL INITIALLY TUES EVENING...BUT WILL QUICKLY TAPER POPS OFF AS THE FRONT CLEARS THE AREA ALONG WITH LOSS OF DIURNAL HEATING. DRY WX BY THE SECOND HALF OF THE NIGHT AND LASTING THRU WED AS SFC HIGH PRESSURE OVER THE WESTERN GREAT LAKES BUILDS IN....WITH THE REGION REMAINING ON THE EASTERN PERIPHERY. SUBSIDENCE ALOFT AIDES IN MOSTLY SUNNY SKIES...WITH SCT CU PSBL. INCREASING CLOUDS WED NIGHT WITH SFC LOW PRESSURE ATTEMPTING TO ORGANIZE OVER THE SOUTHEASTERN. OVERRIDING PCPN COULD POSSIBLY MOVE IN BY LATE WED TO SOUTHWESTERN PORTIONS OF THE CWA...WITH MOST OF THE AREA STAYING DRY TILL AFTR DAYBREAK THURS MORNING. CAA BEHIND THE COLD FRONT WILL DROP TEMPS BACK TO MORE SEASONAL LVLS...LOWS 40S AND 50S AND HIGHS UPPER 60S TO MID 70S. && .LONG TERM /THURSDAY THROUGH MONDAY/... LOW PRES TO OUR SOUTH MOVES OFFSHORE THU NIGHT INTO FRI... BRINGING SOME SCATTERED SHOWERS MAINLY TO THE S AND SE OF THE CWA. SHOWERS LOCATION WILL DEPEND ON THE TRACK OF THIS LOW PRES... WHICH IS UNCERTAIN AT THIS MOMENT. HIGH PRES BUILDS INTO THE REGION FRI AND INTO SUN... BRINGING DRIER CONDITIONS FOR THE FIRST HALF OF THE WEEKEND. RETURN FLOW INCREASES MOISTURE TO THE REGION FOR SUN... AND THE CHANCE FOR SHOWERS AND AFTERNOON TSTMS. A WARM FRONT APPROACHES LATE ON SUN INTO MON. SOME SHOWERS AND AFTERNOON TSTMS ARE POSSIBLE ON MON AS WELL. HIGH TEMPS WILL BE IN THE UPR 70S TO LOW 80S FOR FRI AND SAT...IN THE LOW 80S FOR SUN... AND IN THE UPR 80S FOR MON. && .AVIATION /01Z TUESDAY THROUGH SATURDAY/... SHRA/TSRA CONTINUE TO MOVE ACROSS THE MID-ATLANTIC THIS EVENING. VFR CONDITIONS EXPECTED OUTSIDE ACTIVITY BUT HEAVY RAIN WILL CAUSE VSBYS TO DROP TO SUB-MVFR. MULTIPLE ROUNDS WILL LIKELY IMPACT THE BWI/MTN. LOW STRATUS MAY MOVE INTO BWI/MTN EARLY TUES MORNING AS A BOUNDARY MOVES SOUTHWARD. KEPT CIGS AT MVFR FOR NOW. ALSO CANNOT RULE OUT PATCHY FOG THOUGH OVERCAST SPREADING IN FROM THE WEST MAY KEEP THAT FROM BEING A BIG ISSUE. LOWER VSBYS POSSIBLE IN SCTD TO NUMEROUS SHRA/TSRA THROUGH EARLY EVENING TODAY. VFR CONDITIONS TUES NIGHT THROUGH FRIDAY. NW WINDS WED 10-15 KTS WED AFTN...PSBL GUSTS UP TO 20 KTS. SOME SCATTERED SHOWERS PSBL THU NIGHT. && .MARINE... LIGHT WINDS ON THE WATERS THROUGH TUESDAY. GUSTY WINDS POSSIBLE IN SHOWERS AND THUNDERSTORMS AND SMW CANNOT BE RULED OUT TONIGHT INTO TUESDAY. SCA CONDITIONS BCMG MORE LIKELY TUES NIGHT THRU WED MORNING BEHIND THE COLD FRONT ON THE CHESAPEAKE BAY AND MAYBE LOWER TIDAL POTOMAC. SCA GUSTS PSBL THRU WED AFTN...WITH ALL WATERS BCMG SUB- SCA BY WED NIGHT AND REMAINING THAT WAY THROUGH FRIDAY. && .CLIMATE... UNUSUALLY WARM WEATHER CONTINUES THROUGH TOMORROW. RECORD HIGH MINIMUMS MAY BE BROKEN AT DCA AND IAD TODAY /MAY 18TH/ AND COULD BE APPROACHED TOMORROW MORNING TOO. RECORD HI MINS FOLLOW... SITE...MAY 18TH.........MAY 19TH......... DCA....68 (1995*).......70 (1986/1962)... BWI....68 (1900/1896)...75 (1877)........ IAD....66 (1995)........66 (1969)........ *ALSO IN 1953...1943 AND 1900. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...NONE. && $$ SYNOPSIS...JCE NEAR TERM...JCE/HAS SHORT TERM...SEARS LONG TERM...IMR AVIATION...JCE/SEARS/HAS/IMR MARINE...JCE/SEARS/HAS/IMR CLIMATE...LWX

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