Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 291842 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 242 PM EDT FRI AUG 29 2014 .SYNOPSIS... HIGH PRESSURE OVER THE NORTHERN MID-ATLANTIC THIS AFTERNOON WILL MOVE OFFSHORE FOR THE WEEKEND. A WARM FRONT WILL LIFT NORTH THROUGH THE AREA LATE SATURDAY. A COLD FRONT WILL APPROACH DURING THE FIRST PART OF NEXT WEEK. && .NEAR TERM /THROUGH TONIGHT/... ITS A DELIGHTFUL AFTN...AND THAT WL CONT INTO THE EVNG. HIPRES OVHD W/ TEMPS IN THE 70S AND DEWPTS IN THE LWR-MID 50S /EVEN SOME UPR 40S/. THE SFC RDG WL EASE OFFSHORE...BUT STILL HV PLENTY OF RDGG H7-5. WL DVLP A LGT SELY FLOW TNGT...ENUF TO BRING IN SOME LWR CLDS AFTR MIDNGT. WL KEEP PATCHY FOG REFERENCE TO THE CENTRAL SHEN VLY AND CENTRL FOOTHILLS. AM NOT REAL CONFIDENT THAT WL TAKE PLACE. THE ANTICIPATED MSTR ADVCTN SHUD BUMP DEWPTS TO NEAR 60F... AND THUS MIN-T LWR-MID 60S REASONABLE. && .SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... BELIEVE THAT THE RDGG ALOFT WL BE THE PRIMARY WX INFLUENCE SAT. GDNC SUGGESTING THAT A WMFNT WL ENTER CWFA MID-LT AFTN. SUBSEQUENTLY INSTBY INCREASES BHD FNT. GFS CURIOUSLY ATTEMPTING TO FIRE OFF TSRA ALONG WMFNT WHILE STRONG MID-LVL DIVERGENCE /SUBSIDENCE/ DOMINATES. SHEAR NIL. INSTEAD...BELIEVE THAT PRIMARY FOCUS FOR ANY STORMS WUD BE OROGRAPHICALLY INDUCED. HV BKN OR NEARLY BKN CLDS FOR THE DAY...BUT FOCUSED POPS ON THE MTNS. SINCE CAPE BUILDS THRU THE EVNG...CHC TSRA WL LINGER LATER INTO THE NGT. THE RDGG STARTS TO BREAK DOWN SUNDAY...W/ DEEPER SWLY FLOW PREVAILING. THAT WL SUPPORT A STREAM OF PWAT AOA 2 INCHES TO RIDE THRU CWFA COINCIDENT W/ DECENT INSTBY. WHILE EXACT CORRIDOR OF CAPE/MSTR LKLY WL ADJUST W/ FUTURE MODEL RUNS...SUSPECT THE MAIN IDEA WL REMAIN THE SAME. HENCE...XPCT DECENT CVRG OF TSRA...1ST IN THE MTNS BY MIDDAY...AND DROPPING INTO A DVLPG LEE TROF ALONG THE I-95 CORRIDOR BY END OF THE AFTN INTO THE EVNG. HV LKLY POPS IN GRIDS...AND PSBL HVY RAIN WORDING IN HWO. TEMPS WL BE MODERATING ON SAT. WL BE STAYING W/ THE WARMER MAX MAXT. MOS MEAN MAXT NOT FAR OFF FM GOING FCST SUN...AND CHGS MINIMAL. SIMILARLY...CHGS TO MIN-T SAT AND SUN NGT MINOR. IN GENERAL...FAVOR THE WARMER MET WHICH HAS BETTER SUPPORT FM FCST DEWPTS. WHILE IT WL BE HOT BY SUN...W/ DEWPTS AOA 70F...RESULTING HEAT INDEX VALUES SHUD REMAIN UNDER 100F. THEREFORE...DO NOT ANTICIPATE ANY HEAT HEADLINES...EVEN THO ITS A HOLIDAY WKND. && .LONG TERM /MONDAY THROUGH FRIDAY/... THE UPPER LEVEL SUBTROPICAL HIGH OVER THE SOUTHEAST WILL MIGRATE WESTWARD TO OVER THE MISSISSIPPI VALLEY MONDAY. THIS WILL CHANGE THE DIRECTION OF THE UPPER LEVEL FLOW LOCALLY TO BE A BIT MORE NORTHEASTERLY...WHICH WILL RESULT IN A MARGINAL ENHANCEMENT OF INSTABILITY MONDAY EVENING. AT THE SURFACE...A WELL DEFINED LEE TROUGH FORMING IN MOIST SOUTHERLY FLOW WILL FURTHER PROMOTE INSTABILITY...ESPECIALLY ALONG THE VA AND MD PIEDMONT REGIONS. PWATS MONDAY WILL BE SLIGHTLY LESS THAN SUNDAY...BUT WITH VALUES STILL AROUND 2 INCHES AND PLENTY OF INSTABILITY LOCALIZED FLASH FLOODING REMAINS A THREAT. DESPITE A NICELY CURVED HODOGRAPH...WEAK SHEAR...0-6 KM SHEAR VALUES OF LESS THAN 20 KTS...SHOULD KEEP THE SEVERE POTENTIAL LOW MONDAY EVENING. THUNDERSTORMS SHOULD BEGIN TO DIE OUT AFTER SUNSET AS THEY LOOSE THEIR DIURNAL ENHANCEMENT. HIGH PRESSURE OFF THE COAST WILL RIDGE DOWN ACROSS THE SOUTHEAST US TUESDAY. MEANWHILE...A DEEP LOW PRESSURE SYSTEM WELL NORTH OF THE GREAT LAKES WILL SWING A COLD FRONT SOUTH FROM THE OHIO VALLEY TO THE NEW ENGLAND STATES. THIS FRONT WILL STRUGGLE TO GET INTO THE MID-ATLANTIC TUESDAY DUE TO THE HIGH BUILDING TO OUR SOUTH. THE RESULT WILL BE A MORE WESTERLY/DOWNSLOPING COMPONENT TO THE LOW LEVEL FLOW. THIS SHOULD HELP TO SUPPRESS MOST CONVECTION TUESDAY...ESPECIALLY COMPARED TO SUNDAY AND MONDAY. IF THUNDERSTORMS DO FORM...THE MOST LIKELY LOCATION WILL BE ALONG THE MASON-DIXON...WHERE THE FLOW WILL BE MORE SOUTHERLY THAN ACROSS THE SOUTHERN PART OF THE CWA. THE FRONT WILL FINALLY REACH OUR AREA WEDNESDAY...THOUGH WITH LITTLE MOISTURE LEFT IT SHOULD BE MOSTLY DRY. THE PRIMARY IMPACT FROM THE FRONTAL PASSAGE...WHICH SHOULD OCCUR FROM NORTH TO SOUTH OVER THE COURSE OF THE DAY WEDNESDAY...WILL BE A DROP IN HUMIDITY AND SLIGHTLY COOLER TEMPS FOR THE SECOND HALF OF THE WORKWEEK. EXPECT HIGHS NEAR 90 MONDAY AND INTO THE LOWER 90S TUESDAY...THE WARMEST DAY OF THE WEEK...BEFORE DROPPING INTO THE UPPER 80S FOR THE SECOND HALF OF THE WORKWEEK. && .AVIATION /18Z FRIDAY THROUGH WEDNESDAY/... VFR THRU MUCH OF THE VALID TAF PD. A LGT SELY FLOW DVLPG AFDK MAY SUPPORT ADVCTN OF A LOWER CLD DECK AFTR MIDNGT. NOT COMPLETELY SOLD ON THAT...SPCLY IF THERE WL BE ANY SUBSEQUENT FLGT RESTRICTIONS. FLLWG LEAD OF PRVS TAF...CONFINING MVFR TO CHO ONLY. BY AFTN...CIGS LKLY BKN035-040 W/ SELY WNDS AOB 10 KT. SUN-TUE...SCT-NMRS TSRA...LRGLY DIURNALLY DRIVEN. LCL FLGT RESTRICTIONS PSBL...BUT CANNOT PINPOINT WHERE ATTM. WL BE POST-FROPA BY WED. VFR. && .MARINE... VRBL WINDS AOB 10 KT AS HIPRES OVHD. RDG WL MV E OF THE DELMARVA...SUPPORTING A SELY FLOW TNGT AND SAT...AND SLY FLOW BY SAT NGT. WNDS SHUD REMAIN AOB 10 KT THRU SAT. GRADIENT DOES INCR SAT NGT-SUN...BUT IT DOESNT LOOK LIKE GRADIENT FLOW WL MIX TO THE SFC. HV CAPPED WNDS AT 15 KT. HV A TSRA THREAT LT SUN INTO SUN EVE. A HIGH WIND THREAT WL ACCMPNY THESE STORMS. SPECIAL MARINE WRNGS PSBL...CONTG THRU MON. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...NONE. && $$ SYNOPSIS...HTS NEAR TERM...HTS SHORT TERM...HTS LONG TERM...CEB AVIATION...HTS MARINE...HTS

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