Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 071456 AFDLWX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE BALTIMORE MD/WASHINGTON DC 956 AM EST SUN FEB 7 2016 .SYNOPSIS... HIGH PRESSURE WILL REMAIN OVERHEAD THROUGH TONIGHT WHILE COASTAL LOW PRESSURE PASSES BY WELL TO OUR SOUTH AND EAST. ANOTHER LOW PRESSURE SYSTEM WILL DIVE SOUTH INTO THE OHIO VALLEY MONDAY BEFORE PASSING THROUGH OUR AREA MONDAY NIGHT INTO TUESDAY. HIGH PRESSURE WILL SLOWLY BUILD TOWARD OUR AREA DURING THE MIDDLE PORTION OF NEXT WEEK. && .NEAR TERM /THROUGH TONIGHT/... LOW PRESSURE IS OFF THE GA/SC COAST THIS MORNING. MID-HIGH LEVEL CLOUDS WILL CONTINUE TO MOVE NORTHWEST ACROSS THE MID-ATLANTIC REGION TODAY. CALM WINDS WILL BECOME LIGHT AND OUT OF THE NE ONCE MIXING INITIATES LATE THIS MORNING. TEMPS WILL REACH THE MID TO UPPER 40S ACROSS THE REGION. PREVIOUS DISCUSSION... SURFACE HIGH PRESSURE WILL REMAIN OVERHEAD WHILE LOW PRESSURE RAPIDLY INTENSIFIES OFF THE SOUTHEAST COAST. DRY CONDITIONS ARE EXPECTED ALONG WITH SEASONABLE TEMPERATURES. HOWEVER...THERE WILL BE SOME HIGH CLOUDS WELL NORTH OF THE LOW OFF THE SOUTHEAST COAST. A PARTLY TO MOSTLY CLOUDY SKY IS EXPECTED...WITH THE THICKEST CLOUD COVER MOST LIKELY ACROSS SOUTHERN MARYLAND. THE LOW WILL MOVE OUT TO SEA TONIGHT WHILE HIGH PRESSURE REMAINS OVERHEAD. DRY AND SEASONABLY CHILLY CONDITIONS ARE EXPECTED. && .SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/... A HIGH AMPLITUDE PATTERN SETS UP MONDAY THROUGH MONDAY NIGHT. AN UPPER-LEVEL RIDGE WILL BUILD OVER THE WESTERN CONUS WHILE A POTENT TROUGH AND UPPER-LEVEL LOW DIG SOUTH INTO THE OHIO AND TENNESSEE VALLEYS. THE SURFACE LOW ASSOCIATED WITH THIS SYSTEM OVER THE GREAT LAKES WILL TRANSFER ITS ENERGY INTO A COASTAL LOW LATER MONDAY/MONDAY NIGHT AS SHORTWAVE ENERGY AROUND THE UPPER-LEVEL LOW INTERACTS WITH THE BAROCLINIC ZONE ALONG THE MID-ATLANTIC COAST. A SURFACE TROUGH/OCCLUDED FRONT WILL EXTEND FROM THE LOW OVER THE GREAT LAKES SOUTHEAST THROUGH OUR AREA INTO THE LOW OVER THE MID-ATLANTIC COAST. AT THE SAME TIME...SHORTWAVE ENERGY WILL BE ROTATING AROUND THE UPPER-LEVEL LOW PASSING THROUGH OUR AREA. THESE MECHANISMS WILL LIKELY CAUSE PRECIPITATION TO DEVELOP OVER OUR AREA MONDAY AFTERNOON AND MONDAY NIGHT. TEMPERATURES WILL BE WELL ABOVE FREEZING MONDAY IN THE VALLEYS SO ANY PRECIPITATION MONDAY AFTERNOON INTO MONDAY EVENING WILL BE RAIN OR RAIN/SNOW MIX WITH LITTLE OR NO ACCUMULATION. HOWEVER...COLDER AIR IS EXPECTED TO WORK ITS WAY INTO THE AREA LATER MONDAY NIGHT INTO TUESDAY. GUIDANCE HAS COME INTO SOMEWHAT BETTER AGREEMENT AS TO WHERE THE OCCLUDED FRONT/SURFACE TROUGH WILL SETUP MONDAY NIGHT AND TUESDAY. THE BOUNDARY IS MOSTLY LIKELY TO SETUP FROM NEAR SOUTHERN MARYLAND NORTH AND WEST OVER THE WASHINGTON METROPOLITAN AREA...THEN TOWARD THE NORTHERN SHENANDOAH VALLEY BEFORE REACHING WESTERN MARYLAND. AT THE SAME TIME...THE UPPER-LEVEL LOW WILL BE BUILDING OVERHEAD. THE HEAVIEST PRECIPITATION WILL BE LOCATED ALONG AND TO THE NORTH AND EAST OF THIS BOUNDARY. WITH COLDER AIR WORKING ITS WAY IN...THIS MEANS THAT THE MAIN PTYPE WOULD BE SNOW EXCEPT PERHAPS ACROSS SOUTHERN MARYLAND AND RIGHT ALONG THE BAY WHERE WARMER AIR FROM THE WATERS MAY KEEP TEMPS UP A BIT. DESPITE THE BETTER AGREEMENT AMONG GUIDANCE...THERE ARE STILL SUBTLE DIFFERENCES AND WITH THE GRADIENT BETWEEN SIGNIFICANT SNOW ACCUMULATIONS VS. LITTLE OR NO SNOW OVERHEAD...ANY SLIGHT CHANGE TO WHERE THIS BOUNDARY IS LOCATED WILL HAVE SIGNIFICANT IMPACT ON THE FORECAST. AS OF NOW...THE LATEST FORECAST LEANS TOWARD A CONSENSUS AMONG THE GUIDANCE WHICH ALLOW FOR THE BEST CHANCE FOR SIGNIFICANT SNOW ACCUMULATIONS TO BE IN THE MOUNTAINS AS WELL AS ACROSS NORTHERN MARYLAND...NORTHERN VIRGINIA AND PERHAPS INTO THE WASHINGTON AND BALTIMORE METROPOLITAN AREAS. FARTHER SOUTH ACROSS SOUTHERN MARYLAND INTO CENTRAL VIRGINIA SNOW AMOUNTS WILL BE LIGHTER. AGAIN...WANT TO EMPHASIZE THAT WITH THE GRADIENT OVERHEAD ANY SLIGHT CHANGE WILL HAVE A SIGNIFICANT IMPACT ON THE FORECAST...THEREFORE CONFIDENCE REMAINS LOW. ANOTHER NOTE IS THAT 700MB-500MB MID-LEVEL LAPSE RATES WILL BE FAIRLY STEEP...6-8 DEGREES C/KM ALONG AND NORTH/EAST OF THE OCCLUDED BOUNDARY. THE CONVECTIVE ELEMENT MAY CAUSE HEAVIER BURSTS OF SNOW WITH LOCALLY HIGHER AMOUNTS. THE UPPER-LEVEL LOW WILL CONTINUE TO PASS THROUGH THE AREA TUESDAY NIGHT. THE DRY SLOT SHOULD MOVE OVERHEAD...ALLOWING FOR ANY LEFTOVER SNOW TO END FROM SOUTHWEST TO NORTHEAST. UPSLOPE SNOW SHOWERS ARE STILL EXPECTED ALONG AND WEST OF THE ALLEGHENY FRONT. && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... BY 12Z WED...00Z MODEL SUITE COMING INTO BETTER AGREEMENT ON THE HANDLING OF DEPARTING SFC/COASTAL LOW AND DEPTH OF BROAD UPPER LVL TROUGH. ATTENTION FOR THE LATTER HALF OF THE WEEK TURNS FROM PCPN THREATS AND LOOKS MORE TO AN EXTENDED PERIOD OF BELOW NORMAL TEMPS...WITH POTENTIAL WIND CHILL ADVISORY CONCERNS...ESP THE WESTERN HALF OF THE CWA. REGION REMAINS BETWEEN THE DEPARTING LOW AND APPROACHING SFC HIGH WED AND THURS. AXIS OF THE UPPER LVL TROUGH REMAINS EXTENDED SOUTH ACROSS THE MID-ATLANTIC...WITH THE BASE SETTLED OVER THE CAROLINAS. THE POTENTIAL FOR SNOW SHOWERS (MIXED WITH RAIN SOUTHERN MD) CONTINUES WED DESPITE DRYING AT THE SFC. HIGHER CONFIDENCE OF SEEING UPSLOPE SNOW SHOWERS POTOMAC HIGHLANDS MID WEEK ON THE WNW FLOW...AMOUNTING TO AN ADDITIONAL COUPLE OF INCHES. ANY SNOW TO THE EAST WILL GENERALLY AMOUNT TO LESS THAN AN INCH. 850MB TEMPS DROP TO BETWEEN -10 AND -15 DEGREES CELSIUS WED-THURS...RESULTING IN LOWS REACHING THE SINGLE DIGITS/TEENS WED NIGHT AND HIGHS ON THURS IN THE 20S. THESE TEMPS COMBINED WITH WINDS GUSTING INTO THE 20S...ESP HIGHER ELEVATIONS WEST OF THE BLUE RIDGE COULD SEE WIND CHILLS DROPPING BELOW ZERO WED NIGHT AND STAYING BELOW THRU THURS NIGHT. THIS IS HIGHLIGHTED IN THE HWO. BRIEF INCREASE IN TEMPS FRIDAY AS THE UPPER LVL TROUGH PIVOTS THROUGH THE REGION...LEADING TO BRIEF ZONAL FLOW ALOFT. HOWEVER...CLOSED LOW REMAINS POSITIONED OVER SOUTHEASTERN CANADA DURING THIS TIME PERIOD...RESULTING IN YET ANOTHER PLUNGE OF THE FLOW AS THE NEXT TROUGH DEEPENS ACROSS THE EASTERN HALF OF THE US. DEPENDING ON WHERE THE RIDGE AXIS ALIGNS OVER THE WESTERN HALF WILL DETERMINE HOW DEEP THIS TROUGH GOES...AND AS SUCH...HOW EXACTLY COLD IT GETS THIS COMING WEEKEND. ECMWF THE MUCH COLDER OF THE SOLUTIONS...SHOWING 850MB TEMPS BELOW -20 DEGREES CELSIUS. USING THE 00Z SUPERBLEND FOR NOW...PLAYING A MORE CONSERVATIVE ROUTE WITH TEMPS. EVEN SO...WIND CHILL ADVISORY LVL VALUES LOOK TO BE PSBL AGAIN OVER THE WEEKEND. && .AVIATION /15Z SUNDAY THROUGH THURSDAY/... VFR CONDITIONS ARE EXPECTED THROUGH MIDDAY MONDAY. LOW PRESSURE WILL MOVE INTO THE AREA LATER MONDAY AFTERNOON AND PERSIST THROUGH TUESDAY. PRECIPITATION WILL LIKELY OVERSPREAD THE TERMINALS DURING THIS TIME. THE STEADIEST PRECIPITATION IS MOST LIKELY ACROSS THE NORTHERN AND EASTERN TERMINALS. PTYPE OF RAIN OR RAIN AND SNOW MIX SHOULD CHANGE TO SNOW MONDAY NIGHT. IFR CONDITIONS ARE LIKELY MONDAY NIGHT INTO MUCH OF TUESDAY. CONDITIONS WILL IMPROVE LATER TUESDAY AND TUESDAY NIGHT AS DRIER AIR WORKS ITS WAY IN. GENERALLY VFR CONDITIONS WED THRU THE END OF THE WEEK. GUSTY NW WINDS WED AND THURS...WITH GUSTS BETWEEN 20-25 KTS. HIGH PRESSURE BUILDING IN BY THE END OF THE WEEK WILL WEAKEN THE WINDS TO LESS THAN 12 KTS. && .MARINE... LOW PRESSURE WILL PASS BY WELL TO THE SOUTH AND EAST OF THE WATERS LATER TODAY AND TONIGHT. HOWEVER...THE GRADIENT WILL STRENGTHEN SO A SMALL CRAFT ADVISORY IS IN EFFECT FOR THE MIDDLE PORTIONS OF THE BAY AND LOWER TIDAL POTOMAC RIVER LATE TODAY INTO MONDAY MORNING. THE GRADIENT SHOULD SUBSIDE MONDAY BUT LOW PRESSURE WILL IMPACT THE WATERS MONDAY NIGHT THROUGH TUESDAY NIGHT. A SMALL CRAFT ADVISORY MAY BE NEEDED FOR PORTIONS OF THE WATERS DURING THIS TIME. SCA CONDITIONS LIKELY ON THE CHESAPEAKE BAY AND LOWER TIDAL POTOMAC WED THRU THURS NIGHT. SCA ARE PSBL WED...BCMG MORE LIKELY THURS ON THE UPPER TIDAL POTOMAC. ALL WATERS DROP BELOW SCA CRITERIA FRI INTO THE WEEKEND. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...NONE. MD...NONE. VA...NONE. WV...NONE. MARINE...SMALL CRAFT ADVISORY FROM 6 PM THIS EVENING TO 9 AM EST MONDAY FOR ANZ532-533-540-541. SMALL CRAFT ADVISORY FROM 3 PM THIS AFTERNOON TO 9 AM EST MONDAY FOR ANZ534-537-543. && $$ SYNOPSIS...BJL NEAR TERM...BJL/HAS SHORT TERM...BJL LONG TERM...SEARS AVIATION...BJL/SEARS MARINE...BJL/SEARS

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