Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 031536 AAA AFDLWX AREA FORECAST DISCUSSION...UPDATED NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 1036 AM EST TUE MAR 3 2015 .SYNOPSIS... HIGH PRESSURE WILL PERSIST OVER THE AREA BEFORE MOVING OFFSHORE LATER TODAY. A WARM FRONT WILL LIFT THROUGH THE AREA THIS AFTERNOON AND EVENING. A COLD FRONT WILL MOVE INTO THE REGION WEDNESDAY FOLLOWED BY HIGH PRESSURE FOR THURSDAY LASTING INTO THE WEEKEND. && .NEAR TERM /THROUGH TONIGHT/... VERY CHALLENGING FORECAST THIS AFTERNOON AND EVENING. LIFT FROM WARM AIR ADVECTION IS BEGINNING TO INCREASE ACROSS THE FORECAST AREA BUT PRECIPITATION IS HAVING A TOUGH TIME REACHING THE GROUND DUE TO DRY AIR AT THE MID LEVELS. THE COLUMN WILL GRADUALLY MOISTEN UP BUT PRECIPITATION WILL LIKELY START A BIT LATER THAN PREVIOUSLY EXPECTED. THE LATER START TIME WILL ALLOW FOR TEMPERATURES TO WARM A FEW DEGREES ESPECIALLY SOUTH OF THE METRO AREAS. THIS MAKES THE FORECAST PROBLEMATIC WITH MILDER TEMPERATURES...ESPECIALLY OVER CENTRAL AND SOUTHERN LOCALES. AREAS OF HIGHEST CONFIDENCE FOR ICING CONCERNS LOOK TO BE SETTING UP TO THE NORTH AND WEST OF THE BALTIMORE AND WASHINGTON DC METRO AREAS AND PORTIONS OF THE SHENANDOAH VALLEY AND HIGHLANDS. SHALLOW COLD AIR WILL LIKELY HOLD IN LONGEST AND POSE THE GREATEST CONCERN FOR SLIPPERY TRAVEL LATER THIS AFTERNOON INTO THIS EVENING. AREAS CLOSEST TO THE MASON DIXON LINE OVER NE MARYLAND MAY HOLD SUB FREEZING AIR INTO THE LATE EVENING. STILL CANNOT RULE OUT SOME ICING TO THE SOUTH WITH DEWPOINT DEPRESSIONS RUNNING 10 OR MORE DEGREES AND DRY POCKET ALOFT. PRECIPITATION WILL COOL THE COLUMN AT LEAST INITIALLY. P-TYPES NOW LOOK TO BE MOSTLY FREEZING RAIN WITH SOME SLEET AT THE START. LATER START TIMES LEND TO WARMING ALOFT WITH LESS POTENTIAL FOR SNOW. PRECIP IN ALL AREAS WILL BE LIGHT. TEMPERATURES RISE ABOVE FREEZING LATER TONIGHT FOR THE ENTIRE AREA. RAIN RATES INCREASE OVER ALLEGHENIES LATE...WILL NEED TO BE ON THE LOOKOUT FOR LOCALIZED FLOODING CONCERNS GIVEN EXPECTED SNOWPACK MELT WITH HIGHLAND TEMPERATURES RISING INTO THE 40S. && .SHORT TERM /WEDNESDAY THROUGH THURSDAY/... WEDNESDAY...COLD FRONT ENTERS CWA FROM THE WEST IN THE MORNING AND DRIFTS EAST. WARMEST AIR IN NEARLY A MONTH (60F AT KIAD ON FEB 8) AHEAD OF THE FRONT WITH LOW 50S (A LITTLE LOWER THAN PREVIOUS FORECASTS) EXPECTED GIVEN WIDESPREAD RAIN OVER THE AREA AT THE TIME. QPF QUARTER TO HALF INCH OF RAIN OVER THE AREA WEDNESDAY. MOST OF THE AREA LOOKS TO BE BETWEEN SHORTWAVES IN THE AFTERNOON...REDUCING RAIN RATES. WEATHER IMPACTS WILL INCREASE WEDNESDAY NIGHT. SFC BOUNDARY MAY HAVE PUSHED A GOOD PART OF THE WAY THROUGH DURING THE EVENING...AS A WEAK SFC WAVE IS PROJECTED TO CROSS THE CAROLINAS OVERNIGHT. HOWEVER... COLDER TEMPS...ESPECIALLY ALOFT...WILL BE SLOW TO WORK SOUTHWARD. PER COORDINATION WITH WPC...A GFS/ECMWF SOLUTION IS FAVORED...WHICH ALLOWS THERMAL PROFILES TO COOL A BIT MORE QUICKLY AMONGST THE MODEL SUITE. THIS ALSO GIVES A MORE DEFINITIVE RAIN-TO-SNOW TRANSITION VS A MORE PRONOUNCED WARM NOSE IN THE NAM (LIKELY DUE TO A STRONGER SSW LLJ IM THE 850-600MB LAYER) AND MORE MIXED PRECIP. CANNOT RULE OUT A PERIOD OF IP/FZRA...BUT DID NOT HAVE ENOUGH CONFIDENCE ON TIMING/PLACEMENT TO INCLUDE IN THE FORECAST AT THIS TIME. ON THE WHOLE THOUGH...THERE WAS A SLIGHT SLOWING TREND OVERALL IN THE TIMING OF PRECIP THROUGHOUT THE EVENT. ALL AREAS ARE FORECAST TO BE SNOW BY THURSDAY MORNING...WITH PRECIP ENDED NW-SE DURING THE DAY. TEMPERATURES WILL HOLD STEADY OR FALL. SNOWFALL AMOUNT FORECASTS WILL BE CHALLENGING GIVEN THE UNCERTAINTIES WITH PTYPES...TIMING...AND HOW MUCH MOISTURE FALLS IN THE COLD AIR. THERE WILL BE TREMENDOUS MOISTURE TRANSPORT WITH THE LLJ AS WELL AS LIFT ASSOCIATED WITH UPPER JET...BUT THE AXIS OF HIGHEST QPF WILL LIKELY BE VERY NEAR THE TRANSITION ZONE...WITH POTENTIAL FOR COLDER BUT DRIER AIR TO BEGIN WORKING INTO THE BACK SIDE. NOT MUCH CHANGE TO CURRENT FORECAST OVER PREVIOUS. IF THE QPF INDEED FALLS AFTER THE TRANSITION TO SNOW...OUR CURRENT FORECAST IS ON THE CONSERVATIVE SIDE. HOWEVER FEEL THERE IS STILL TOO WIDE OF A SPREAD IN SOLUTIONS TO GO HIGHER. SEE OUR WEBPAGE FOR THE PROB RANGES. WILL ALLOW DAYSHIFT TO DECIDE ON POTENTIAL FOR WATCHES. HIGHEST CONFIDENCE IN LARGER SNOW TOTALS ARE OVER THE HIGHLANDS AT THIS TIME. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... ARCTIC HIGH PRESSURE WILL QUICKLY BUILD IN THURSDAY NIGHT. THERE MAY BE A PERIOD OF UPSLOPE SNOW SHOWERS IN THE EVENING. NAM INDICATES SNOW SHOWERS WILL BE POSSIBLE EAST OF THE MOUNTAINS AS WELL AS A VORT MAX PASSES...BUT HAVE NOT INCLUDED THIS IN THE FORECAST NOW. TEMPERATURES HAVE TRENDED COLDER...SINGLE DIGITS EXCEPT IN THE METROS/NEAR THE BAY AND BELOW ZERO IN THE HIGHLANDS. IF GRADIENT DOES NOT RELAX...WIND CHILL ADVISORIES MAY BE NEEDED IN THE HIGHLANDS. THE HIGH WILL SLIDE EAST ACROSS THE AREA THROUGH SATURDAY. FRIDAY WILL STILL BE QUITE COLD BUT TEMPERATURES BEGIN TO MODERATE SATURDAY. MOISTURE STARVED COLD FRONTS TRAILING LOW PRESSURE CENTERS WELL TO THE NORTH WILL MAKE RUNS AT THE AREA SATURDAY NIGHT AND AGAIN MONDAY. FOR NOW HAVE ONLY INCLUDED POPS IN THE UPSLOPE AREAS. THERE ALSO WILL BE LITTLE EFFECT ON TEMPERATURES...WITH READINGS SLIGHTLY BELOW NORMAL EXPECTED. && .AVIATION /15Z TUESDAY THROUGH SATURDAY/... LIGHT WINTRY MIX OVERSPREADS THE TERMINALS THROUGH THE AFTERNOON AS A WARM FRONT APPROACHES. IFR CIGS EXPECTED LATE THIS AFTERNOON INTO THE OVERNIGHT. LIGHT SLEET/FREEZING RAIN AT ONSET CHANGING QUICKLY OVER TO FREEZING RAIN. WINTRY PRECIPITATION LIKELY TO CHANGE OVER TO RAIN BY TONIGHT. IFR CONDITIONS EXPECTED. RAIN IS FORECAST TO CHANGE TO SNOW THURSDAY NIGHT. VSBY/CIG REDUCTIONS WILL CONTINUE AND MAY DROP TO LIFR IF MODERATE/HEAVY SNOW DEVELOPS. THE SNOW WILL END ON THURSDAY. NO AVIATION HAZARDS EXPECTED THEREAFTER. && .MARINE... SMALL CRAFT ADVISORY NOW IN EFFECT FOR ALL OF THE WATERS THIS AFTERNOON INTO THIS EVENING. HIGH PRESSURE WILL MOVE OFFSHORE AND SOUTHERLY FLOW WILL INCREASE. WINDS ARE EXPECTED TO DIP BELOW ADVISORY LEVEL TONIGHT. VSBY RESTRICTIONS EXPECTED. A COLD FRONT WILL PASS THROUGH THE WATERS WEDNESDAY NIGHT. RAIN WILL CHANGE TO SNOW BY THURSDAY MORNING. SCA CONDITIONS ARE POSSIBLE FROM LATE WEDNESDAY NIGHT THROUGH THURSDAY NIGHT BEHIND THE FRONT. WINDS WILL SUBSIDE THEREAFTER UNDER HIGH PRESSURE. && .HYDROLOGY... LIQUID PRECIP FCST FROM WPC WEDNESDAY AND WEDNESDAY NIGHT AREA ONE TO ONE AND A HALF INCHES. WITH TEMPERATURES EXPECTED TO RISE INTO THE 50S ON WEDNESDAY...THERE WILL BE SOME...POSSIBLY A LOT OF...MELTING OF THE EXISTING SNOWPACK...WHICH COMPUTER MODELS AND OBSERVATIONS INDICATE CONTAINS ANYWHERE FROM 3/4 INCH TO 2 INCHES OF SNOW WATER EQUIVALENT. THIS COMBINATION MAY LEAD TO MINOR FLOODING AS THE RAIN FALLS ON WEDNESDAY. FURTHER COMPLICATING THIS FORECAST IS AN EXPECTED CHANGEOVER TO SNOW WEDNESDAY NIGHT FOR MUCH OF THE AREA. ALTHOUGH RIVER ICE IS NOT ESPECIALLY THICK...IT WILL HAVE TO BE MONITORED FOR POTENTIAL ROLE IN AFFECTING RUNOFF. ALSO...PLOWED SNOW IS LIKELY COVERING SOME OF THE DRAINS OUT THERE...WHICH COULD CAUSE MORE POOR DRAINAGE FLOODING THAN WOULD OTHERWISE USUALLY BE EXPECTED. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...WINTER WEATHER ADVISORY UNTIL 10 PM EST THIS EVENING FOR DCZ001. MD...WINTER WEATHER ADVISORY UNTIL 7 PM EST THIS EVENING FOR MDZ501- 502. WINTER WEATHER ADVISORY UNTIL 10 PM EST THIS EVENING FOR MDZ003. WINTER WEATHER ADVISORY UNTIL 10 PM EST THIS EVENING FOR MDZ004>006-011-013-014-503>508. WINTER WEATHER ADVISORY UNTIL 7 PM EST THIS EVENING FOR MDZ016>018. VA...WINTER WEATHER ADVISORY UNTIL 7 PM EST THIS EVENING FOR VAZ025>031-036>040-050-051-501>504-507-508. WINTER WEATHER ADVISORY UNTIL 10 PM EST THIS EVENING FOR VAZ053-054-505-506. WINTER WEATHER ADVISORY UNTIL 7 PM EST THIS EVENING FOR VAZ052- 055>057. WV...WINTER WEATHER ADVISORY UNTIL 7 PM EST THIS EVENING FOR WVZ050- 055-501>506. WINTER WEATHER ADVISORY UNTIL 10 PM EST THIS EVENING FOR WVZ051>053. MARINE...SMALL CRAFT ADVISORY UNTIL 8 PM EST THIS EVENING FOR ANZ530>543. && $$ SYNOPSIS...BAJ/ADS NEAR TERM...KRW SHORT TERM...BAJ/ADS LONG TERM...ADS AVIATION...ADS/KRW MARINE...ADS/KRW HYDROLOGY...JE

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