Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 291444 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 944 AM EST THU JAN 29 2015 .SYNOPSIS... HIGH PRESSURE WILL MOVE OFF THE COAST THIS MORNING. A COLD FRONT WILL SWING THROUGH THE REGION LATE TODAY INTO TONIGHT. A STRONG PRESSURE GRADIENT AHEAD OF HIGH PRESSURE WILL BRING WINDY AND COLD CONDITIONS FRIDAY INTO FRIDAY NIGHT. HIGH PRESSURE WILL BUILD OVER THE AREA SATURDAY...BUT LOW PRESSURE MAY IMPACT THE AREA LATER SUNDAY INTO MONDAY. COLD HIGH PRESSURE WILL RETURN FOR THE MIDDLE PORTION OF NEXT WEEK. && .NEAR TERM /THROUGH TONIGHT/... MAIN CONCERN THIS MORNING IS THE WINTRY MIX EXPECTED THIS AFTERNOON AND EVENING FOR THE MID-ATLANTIC. THE OUTLOOK AREA DROPPED INTO THE TEENS FOR MOST OF THE AREA OVERNIGHT CAUSING SFC TEMPS TO REACH THE TEENS AND 20S. THIS WILL PLAY A ROLE TODAY AS PRECIPITATION AHEAD OF A COLD FRONT MOVES INTO THE REGION IN TIME FOR THE EVENING RUSH HOUR. A 40KT 925MB LLJ AHEAD OF AN APPROACHING COLD FRONT IS STILL WEST OF THE APPALACHIANS THIS MORNING. THIS WILL MOVE EASTWARD AHEAD OF THE COLD FRONT THIS AFTERNOON AND TEMPS AT 925MB WILL BECOME +32 F. 850MB TEMPS WILL ALSO CONTINUE TO BECOME +32 F TODAY. THIS WILL ALLOW FOR MIXED PRECIPITATION WITH WARM AIR OVER COLD AIR/SURFACES. SOUTHERLY FLOW AT THE SFC WILL ALLOW TEMPS AND DEWPTS TO RISE TODAY. SNOW PACK ACROSS THE NRN MID-ATLANTIC WILL SLOW TEMPS FROM RISING AS FAST AS CENTRAL VA AND SOUTHERN MD. SFC TEMPS WILL BE A CONCERN TODAY AS THE GROUND IS FROZEN IN MANY PLACES. CLOUD COVER MOVING OVERHEAD WILL ALSO SLOW TEMPS FROM RISING TODAY AS WELL. THAT BEING SAID...TEMPS WILL RANGE FROM THE LOW 30S NEAR THE MD/PA BORDER TO THE LOW 40S FROM DCA-CHO-NHK. THE SOUTHERLY FLOW WILL HELP SCOUR OUT VALLEYS WEST OF THE BLUE RIDGE AS WELL AND SHD-WOO-W99 SHOULD RISE INTO THE UPPER 30S. A CAVEAT IS THE HIGHER ELEVATIONS ON THE BLUE RIDGE AND WESTWARD. ZR IS POSSIBLE AS TEMPS MAY STAY BELOW FREEZING. WILL NEED TO MONITOR AND ADVISORY MAY BE NEEDED. A WINTER WX ADVISORY IS IN EFFECT FOR THIS AFTERNOON THROUGH THE EVENING FOR MUCH OF THE NRN OUTLOOK AREA. TEMPS WILL BE CLOSELY MONITORED TODAY. DCA IS ALREADY AT 31 DEGREES BUT SURROUNDING SUBURBS ARE IN THE 20S. THERE IS UNCERTAINTY REGARDING PTYPE NEAR THE I-95 CORRIDOR DURING THE EVENING RUSH HOUR. AT THIS TIME...TEMPS ARE FCST TO GO ABOVE FREEZING EAST OF THE WINTER WX ADVISORY. AS GUIDANCE COMES IN THIS MORNING DECISIONS WILL BE MADE IF WE NEED TO EXTEND THE ADVISORY FURTHER EAST. PREVIOUS DISCUSSION... PRECIPITATION WILL MOVE AWAY FROM MOST AREAS THIS EVENING AND THE COLD FRONT IS EXPECTED TO PASS THROUGH OVERNIGHT. GUSTY NORTHWEST WINDS ARE POSSIBLE LATE TONIGHT...ESPECIALLY ALONG THE RIDGES. UPSLOPE SNOW SHOWERS ARE EXPECTED TONIGHT ALONG AND WEST OF THE ALLEGHENY FRONT. A WINTER WEATHER ADVISORY IS IN EFFECT FOR THESE AREAS. && .SHORT TERM /FRIDAY THROUGH FRIDAY NIGHT/... LOW PRESSURE WILL INTENSIFY OVER NEW ENGLAND FRIDAY WHILE HIGH PRESSURE APPROACHES FROM THE MIDWEST. THE PRESSURE GRADIENT BETWEEN THESE SYSTEMS WILL BE QUITE STRONG...RESULTING IN GUSTY NORTHWEST WINDS. WIND GUSTS AROUND 45 TO 50 MPH ARE POSSIBLE AND A WIND ADVISORY MAY BE NEEDED FOR PORTIONS OF THE AREA. THE STRONG NORTHWEST WINDS WILL USHER IN COLD CONDITIONS. IN FACT...TEMPS MAY HOLD STEADY OR EVEN FALL THROUGHOUT THE DAY. TEMPS FRIDAY AFTERNOON WILL RANGE FROM THE SINGLE DIGITS IN ALLEGHENY HIGHLANDS TO THE LOWER AND MIDDLE 30S IN SOUTHERN MARYLAND. MORE UPSLOPE SNOW SHOWERS ARE EXPECTED ALONG AND WEST OF THE ALLEGHENY FRONT. THE WINTER WEATHER ADVISORY CONTINUES UNTIL NOON...BUT SNOW SHOWERS ARE POSSIBLE DURING THE AFTERNOON AS WELL. FOR LOCATIONS EAST OF THE ALLEGHENY FRONT...A FEW SNOW SHOWERS ARE POSSIBLE FRIDAY AS ANOTHER POTENT UPPER-LEVEL DISTURBANCE SWINGS THROUGH THE AREA. MOST AREAS WILL NOT SEE ACCUMULATING SNOW...BUT THERE WILL BE ENOUGH INSTABILITY TO COMBINE WITH STRONG COLD ADVECTION FOR THE POSSIBILITY OF A FEW BURSTS OF HEAVIER SNOW SHOWERS. THIS COULD LEAVE A QUICK COATING IN SPOTS AND WITH SUDDEN CHANGES IN VISIBILITY THAT COULD HAVE A SIGNIFICANT IMPACT ON TRAVEL...ALTHOUGH IT WOULD BE LOCALIZED. THE BEST CHANCE FOR THE HEAVIER SNOW SHOWERS WILL BE ACROSS NORTHERN MARYLAND...EASTERN WEST VIRGINIA AND NORTHERN VIRGINIA. COLD AND DRY CONDITIONS FRI NIGHT AS SFC HIGH PRESSURE BUILDS SOUTH AND EAST. LINGERING SNOW SHOWERS OVER THE ALLEGHENY FRONT FRI EVENING EXPECTED TO DIMINISH AS THE NW FLOW INJECTS MUCH DRIER AIR. MAIN CONCERN FOR FRIDAY NIGHT WILL BE THE WELL BELOW NORMAL TEMPS...ALMOST 10-15 DEGREES BELOW. COMBINING WITH NW WINDS WITH GUSTS 20-30 KTS...AND IN HIGHER ELEVATIONS 30-35 KTS...WIND CHILLS FORECASTED TO DROP TO AROUND -10 DEGREES CELSIUS POTOMAC HIGHLANDS...NEGATIVE SINGLE DIGITS ALONG THE MASON-DIXON LINE...AND POSITIVE SINGLE DIGITS THE REMAINDER OF THE AREA. WILL CONTINUE TO HIGHLIGHT THE WIND CHILL ADVISORY POTENTIAL IN THE HWO...MAINLY FOR THE FAR WESTERN AREAS. USED A BLEND OF ADJMETBC/MOSBC WHICH HAS BEEN TRENDING WELL FOR OVERNIGHT TEMPS. && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... CENTER OF THE HIGH SLIPS SOUTHEAST INTO THE SE US SAT WHILE A NEAR ZONAL FLOW SETS UP DURING THE DAY...AND WEAK RIDGING BUILDS SAT NIGHT-SUN MORNING. THE PATTERN KEEPS THE AREA DRY THOUGH COLD THRU SAT WITH TEMPS STILL RUNNING BELOW NORMAL. WARMING TREND BY SAT NIGHT AS WINDS BACK TO SW FLOW...WITH 850MB TEMPS WARMING TO AROUND -5 DEGREES CELSIUS. NEXT CHC FOR PCPN SUN-MON WITH SFC LOW DEVELOPING OVER GOM AND RIDING A NEAR STATIONARY FRONT TO OUR SOUTH. SOME QUESTION REMAINS ON PCPN TIMING AND INTENSITY...AND AS SUCH THEN P-TYPE. GFS/CMC STRONGER SOLUTIONS WITH THE LOW DEVELOPMENT AS UPPER LVL TROUGH DIGS DEEPER SOUTH...AND PICKS UP SHORTWAVE ENERGY RIDING THE SOUTHERN STREAM...WHILE THE ECMWF KEEPS MORE OF A SEPARATION. WENT WITH LIKELY POPS BY SUN AFTN OVER WESTERN AREAS TO HIGHLIGHT THE HIGHER CONFIDENCE OF PCPN...THEN SPREADING THE LIKELY POPS TO THE EAST FOR SUN NIGHT-MON. CONCERNING PCPN TYPE...MAINTAINED MAINLY A SNOW EVENT...WITH PSBL TRANSITION TO RAIN DURING THE AFTN SUN OVER JUST THE FAR SOUTHERN AREAS OF THE CWA. HIGHER CONFIDENCE ANY PCPN ON MONDAY REMAINS ALL SNOW WITH 850MB TEMPS DROPPING -10 TO -15 DEGREES CELSIUS DURING THE DAY. AS THE LOW BECOMES CLEARER ON SUBSEQUENT SHIFTS...WILL BE ABLE TO HAVE A BETTER HANDLE ON P-TYPE AND AMTS AT THE ONSET. PCPN CLEARS THE AREA BY TUES MORNING...WITH SFC HIGH BRINGING ANOTHER PERIOD OF DRY AND COLD TEMPS. TRENDED COLDER WITH HIGHS TUES AND LOWS TUES NIGHT AS A RESULT. MODEL DIVERGENCE BY MID WEEK ON THE HANDLING OF THE NEXT LOW PRESSURE SYSTEM...WITH PCPN PSBL ONCE AGAIN LATE WED-THURS. && .AVIATION /15Z THURSDAY THROUGH MONDAY/... SOUTHERLY WINDS ARE EXPECTED TODAY. A BRIEF PERIOD OF WINTRY PRECIPITATION IS POSSIBLE LATE THIS AFTERNOON INTO EARLY THIS EVENING. DRIER CONDITIONS WILL RETURN TONIGHT. STRONG NORTHWEST WINDS ARE EXPECTED FRIDAY WITH A COUPLE SNOW SHOWERS POSSIBLE. NORTHWEST WINDS WILL GUST AROUND 35 TO 40 KNOTS FRIDAY. FRIDAY NIGHT-SAT NIGHT...VFR LIKELY...PSBL SUB-VFR LATE SAT NIGHT. GUSTY NW WINDS 15-20 KTS WITH GUSTS TO 25 KTS FRI NIGHT...BCMG LESS THAN 10 KTS BY SAT AFTN. PSBL LLWS FRI NIGHT WITH 2KFT WINDS 40-50 KTS. SUN-MON...SUB-VFR LIKELY WITH PCPN...PSBL SUB-IFR SUN NIGHT/MON MORNING. WINTRY MIX PSBL. INCREASING NW WINDS MON...GUSTS TO 20 KTS. MON NIGHT-TUES NIGHT...VFR LIKELY. WED-WED NIGHT...SUB-VFR PSBL WITH PCPN. && .MARINE... SOUTHERLY WINDS ARE EXPECTED AHEAD OF A COLD FRONT TODAY. THE COLD FRONT WILL PASS THROUGH TONIGHT AND GUSTY NORTHWEST WINDS ARE EXPECTED BEHIND THE FRONT FRIDAY. A SMALL CRAFT ADVISORY IS IN EFFECT FOR PORTIONS OF THE WATERS THROUGH TONIGHT. A GALE WARNING IS IN EFFECT FOR THE WATERS FRIDAY. GALES LIKELY AT LEAST FIRST HALF OF FRIDAY NIGHT ON CHESAPEAKE BAY...AND POSSIBLY ON THE UPPER POTOMAC. OCNL GALES MAY LINGER TILL DAYBREAK SAT ON THE BAY. WINDS SUBSIDE SAT BUT REMAINING 15-20 KTS DURING THE DAY. WINDS DIMINISH SAT NIGHT...AND REMAIN SUB-SCA THROUGH SUNDAY. DEPENDING ON THE TRACK OF THE LOW SUN NIGHT-MON...SCA CONDITIONS WILL BECOME POSSIBLE AGAIN. SUB-SCA CONDITIONS RETURN FOR MID WEEK. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...WINTER WEATHER ADVISORY FROM 1 PM THIS AFTERNOON TO NOON EST FRIDAY FOR MDZ501. WINTER WEATHER ADVISORY FROM 1 PM THIS AFTERNOON TO 7 PM EST THIS EVENING FOR MDZ003-502. WINTER WEATHER ADVISORY FROM 3 PM THIS AFTERNOON TO 9 PM EST THIS EVENING FOR MDZ004-005-503-505. VA...WINTER WEATHER ADVISORY FROM 7 PM THIS EVENING TO NOON EST FRIDAY FOR VAZ503. WINTER WEATHER ADVISORY FROM 1 PM THIS AFTERNOON TO 7 PM EST THIS EVENING FOR VAZ028-031. WINTER WEATHER ADVISORY FROM 3 PM THIS AFTERNOON TO 9 PM EST THIS EVENING FOR VAZ505. WV...WINTER WEATHER ADVISORY FROM 1 PM THIS AFTERNOON TO NOON EST FRIDAY FOR WVZ503. WINTER WEATHER ADVISORY FROM 7 PM THIS EVENING TO NOON EST FRIDAY FOR WVZ501-505. WINTER WEATHER ADVISORY FROM 1 PM THIS AFTERNOON TO 7 PM EST THIS EVENING FOR WVZ050>053-504. MARINE...SMALL CRAFT ADVISORY FROM 1 PM THIS AFTERNOON TO 6 AM EST FRIDAY FOR ANZ530>534-537>543. GALE WARNING FROM 6 AM TO 6 PM EST FRIDAY FOR ANZ530>543. SMALL CRAFT ADVISORY FROM 1 PM THIS AFTERNOON TO 6 PM EST THIS EVENING FOR ANZ535-536. && $$ SYNOPSIS...BJL NEAR TERM...BJL/HAS SHORT TERM...BJL/SEARS LONG TERM...SEARS AVIATION...BJL/SEARS MARINE...BJL/SEARS

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