Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 270114 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 914 PM EDT SAT JUL 26 2014 .SYNOPSIS... A WARM FRONT WILL LIFT NORTH OF THE AREA EARLY SUNDAY. LOW PRESSURE IS EXPECTED TO TRACK ACROSS PENNSYLVANIA SUNDAY NIGHT WITH AN ASSOCIATED COLD FRONT MOVING ACROSS THE MID ATLANTIC. A REINFORCING FRONT WILL CROSS THE REGION MONDAY. HIGH PRESSURE WILL BUILD IN BEHIND THE FRONT BRINGING COOLER AND DRIER CONDITIONS DURING MIDWEEK. && .NEAR TERM /THROUGH SUNDAY/... WE WILL BE WATCHING MULTIPLE SHORTWAVES EMBEDDED WITHIN WEST/NORTHWEST FLOW ALOFT OVER THE NEXT 24 OR SO HOURS. CLOSEST UPSTREAM SHORTWAVE TO AFFECT THE CWA WAS MOVING INTO THE POTOMAC HIGHLANDS AT 01Z. CONVECTION WAS STRONGER WHEN IT WAS OVER OH/WV AND HAS WEAKENED SOME OVER THE PAST FEW HOURS. MODELS INCLUDING HIGH RESOLUTION GUIDANCE HAVE NOT BEEN ABLE TO HANDLE NEAR TERM CONVECTION VERY WELL THIS EVENING. MOST RECENT RUNS OF THE HRRR HAVE LATCHED ONTO UPSTREAM CONVECTION BUT HRRR HAS CONSISTENTLY BEEN DISSIPATING CONVECTION WHICH HASN/T HAPPENED YET. ENVIRONMENT IS NOT SUPPORTIVE FOR SEVERE WX AS IT WAS IN OH /AND THE SUN HAS NOW SET/...YET SHORTWAVE AND WARM ADVECTION WILL LIKELY BE ABLE TO MAINTAIN SOME CONVECTION FOR AT LEAST A COUPLE MORE HOURS INTO AT LEAST WESTERN MARYLAND...THE EASTERN WEST VIRGINIA PANHANDLE AND INTO THE SHENANDOAH VALLEY OF VIRGINIA. WHILE SEVERE WX IS NOT EXPECTED...HEAVY DOWNPOURS...LIGHTNING AND LOCALLY GUSTY WINDS MAY OCCUR. WHETHER OR NOT CONVECTION LASTS EAST OF THE BLUE RIDGE IS UNCERTAIN. CURRENT FORECAST LOWERS POPS AT THIS POINT AND WILL NEED TO CONTINUE TO MONITOR RADAR TRENDS IN CASE LATE EVENING POPS NEED TO BE INCREASED FURTHER DOWNSTREAM. IN THE WAKE OF THE AFOREMENTIONED SHORTWAVE/EVENING CONVECTION...ANOTHER SHORTWAVE OVER THE OHIO VALLEY MAY PROMOTE LATE NIGHT AND EARLY SUNDAY MORNING CONVECTION AND POPS RAMP UP /OR RE-RAMP UP/ FROM WEST TO EAST DURING THIS TIME. GIVEN TIME OF DAY...SEVERE WX IS NOT EXPECTED WITH THIS ROUND EITHER HOWEVER LOCALLY STRONG STORMS CAN/T BE RULED OUT. A THIRD AND POSSIBLY STRONGEST SHORTWAVE /ALONG WITH MULTIPLE LOW LEVEL BOUNDARIES/ THEN LOOKS TO PRODUCE MORE SHOWERS AND THUNDERSTORMS SUNDAY AFTERNOON AND EVENING. CLOUDS FROM POTENTIAL EARLY MORNING CONVECTION MAY HINDER INSTABILITY SLIGHTLY...BUT EXPECTATION IS FOR ENOUGH OF A WINDOW FOR BREAKS IN THE CLOUDS TO OCCUR TO CONTRIBUTE TO 1-2K J/KG CAPE COINCIDENT WITH 0-6KM SHEAR LIKELY IN EXCESS OF 40 KT. POTENTIAL EXISTS FOR A WIDESPREAD AND/OR SIGNIFICANT SEVERE EVENT SUNDAY AFTERNOON AND EVENING WITH ALL SEVERE HAZARD TYPES POSSIBLE INCLUDING DAMAGING WINDS...LARGE HAIL...FLASH FLOODING AND ALSO ISOLATED TORANDOES. && .SHORT TERM /SUNDAY NIGHT THROUGH MONDAY/... THUNDERSTORMS WILL CONTINUE INTO SUNDAY NIGHT AND EARLY MONDAY AS THE COLD FRONT CROSSES THE MID-ATLANTIC. SHOWERS SHOULD BE OUT OF THE REGION BY SUNRISE ON MONDAY AS THE LOW MOVES INTO NEW ENGLAND. THE UPPER LEVEL TROUGH WILL BE MOVING OVER THE PA MONDAY AND COLD AIR ADVECTION WILL LIKELY PRODUCE A CU FIELD ACROSS THE AREA. SHOWERS AND ISO THUNDERSTORMS WITH GUSTY WINDS DUE TO AN INVERTED V SIGNATURE WILL BE POSSIBLE. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... A LARGE AREA OF HIGH PRESSURE WILL BUILD SOUTH INTO THE AREA FROM CANADA...RESULTING TO MUCH DRIER AND COOLER CONDITIONS FOR THE MIDDLE PART OF THE WEEK. SUBSIDENCE WITH RIDGING ALOFT AND DRY AIR IN THE LOW LEVELS SHOULD PRECLUDE ANY CONVECTION DURING THIS TIME. TEMPERATURES WILL ALSO BE SEVERAL DEGREES BELOW NORMAL. THE RIDGE OF HIGH PRESSURE WILL BEGIN TO PUSH OFFSHORE LATER IN THE WEEK AS ANOTHER SLOW MOVING UPPER LEVEL TROUGH APPROACHES FROM THE WEST...RESULTING IN AN INCREASE IN SHOWER AND THUNDERSTORM CHANCES BY NEXT WEEKEND. && .AVIATION /01Z SUNDAY THROUGH THURSDAY/... MAIN CHALLENGE FOR THE TAFS REVOLVES AROUND POTENTIAL FOR CONVECTION THROUGH SUNDAY EVENING. FIRST SHORTWAVE LIKELY BRINGS SHRA OR TSRA TO MRB AND PERHAPS EVEN CHO IN THE 02Z-04Z WINDOW TONIGHT. EXPECTATION IS FOR THUNDERSTORMS TO WEAKEN/DISSIPATE LATER THIS EVENING AND NOT LAST MUCH FURTHER EAST. BUT HIGH RES GUIDANCE HAS NOT HANDLED TRENDS WELL AND THIS PROVIDES UNCERTAINTY WITH THE EASTWARD EXTENT. ANOTHER SHORTWAVE BRINGS A CHANCE OF SHRA OR TSRA LATE TONIGHT INTO EARLY SUNDAY MORNING...AND THEN A THIRD IS LIKELY TO PRODUCE TSRA SUNDAY AFTERNOON AND EVENING. THIRD ROUND MAY BE THE STRONGEST WITH HEAVY RAINFALL AND STRONG GUSTY WINDS. A COLD FRONT WILL CROSS THE REGION LATE SUNDAY NIGHT INTO MONDAY MORNING. WESTERLY WINDS WILL MOVE INTO THE REGION BEHIND THE FROPA MONDAY. VFR MON NIGHT-WED W/ NW FLOW 10-20 KTS...GUSTY MON NIGHT INTO TUE THEN DECREASING TO AROUND 10 KTS. && .MARINE... SOUTHERLY FLOW IS OCCURRING UP THE BAY AND IS EXPECTED TO CHANNEL FOR LOW END SCA WINDS TONIGHT. THUNDERSTORMS ARE LIKELY SUNDAY...PARTICULARLY AFTERNOON AND EVENING AND MAY CONTAIN LOW VIS IN HEAVY RAIN AND ALSO STRONG WINDS /AND EVEN ISOLATED WATERSPOUTS/ WHICH WOULD REQUIRE SMW/S. A COLD FRONT WILL CROSS THE WATERS MONDAY MORNING AND SCA WILL BE LIKELY. SCA CONDITIONS POSSIBLE IN GUSTY NW FLOW ASSOCIATED WITH PRESSURE SURGE BEHIND COLD FROPA MON EVE...SUBSIDING TUE THROUGH THU. && .TIDES/COASTAL FLOODING... SOUTHERLY WIND CONTINUES TO SUPPORT POSITIVE TIDAL DEPARTURES. MAIN CONCERN FOR THE NEXT HIGH TIDE CYCLE WILL BE AROUND ANNAPOLIS...WITH A HIGH TIDE TIME OF 623 AM AT THE US NAVAL ACADEMY. ANOMALY THERE IS AROUND 3/4 FT ABOVE. IF IT HOLDS THIS WOULD BRING WATER LEVELS ABOVE THE MINOR FLOOD THRESHOLD. IT COULD EVEN GO UP A TAD WITH SOUTHERLY FLOW. THEREFORE WILL ISSUE COASTAL FLOOD ADVISORY FOR ANNE ARUNDEL FOR A 2.4-2.5 FT MLLW EXPECTED WATER LEVEL AT HIGH TIDE. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...COASTAL FLOOD ADVISORY FROM 5 AM TO 9 AM EDT SUNDAY FOR MDZ014. VA...NONE. WV...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 6 AM EDT SUNDAY FOR ANZ531>534-537- 539>543. && $$ SYNOPSIS...BPP/HAS NEAR TERM...BPP/HAS SHORT TERM...HAS LONG TERM...DFH AVIATION...BPP/HAS/DFH MARINE...BPP/HAS/DFH TIDES/COASTAL FLOODING...BPP

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