Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 131547 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 1047 AM EST Wed Dec 13 2017 .SYNOPSIS... Weak high pressure will be overhead today. An Alberta Clipper will pass nearby tonight through early Thursday. Developing low pressure will pass off the east coast late Friday and high pressure will return for Saturday. Low pressure may impact the area early next week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Strong northwest flow continues this morning on the backside of the departing low pressure system along the coast of Maine. Gusts up to 25-35 mph will likely start abating during the afternoon hours as weak ridging builds in. Snow showers in the upslope regions have abated, and clouds streaming into the region in the northwest flow will also lessen in coverage, with most locations becoming mostly sunny for a period into the early afternoon before clouds increase again ahead of the next fast moving clipper system. Temperatures will be around 10 degrees or so below climatological normals for the day with highs only reaching the 30s. With morning temperatures in the single digits and teens in the higher elevations, combined with the gusty northwest winds, Wind Chill Advisories remain in place through Noon for wind chills near -10F. && .SHORT TERM /6 PM THIS EVENING THROUGH FRIDAY NIGHT/... Fast-moving clipper low diving through the Midwest today will track eastward tonight, moving along or just north of the Mason Dixon line, and be off of the NJ coastline by sunrise Thursday. Warm air advection will begin late today and this evening, and some light snow will spread into parts of West Virginia and western Maryland during the late day and evening hours, and spread eastward during the first half of the night. With the warm front expected to set up just north of the PA/MD border, much of the precipitation should remain across PA, but some light snow is possible as far south as the metros during the late evening and first half of tonight. As the surface low tracks eastward, the surface cold front will move across the region from west to east, bringing a return to west/northwesterly flow by Thursday morning. Another period of upslope snow is likely along and west of the Allegheny Front between midnight and sunrise Thursday. Forecast NAM12 Froude numbers indicate relatively terrain-blocked low level flow until Thursday morning, which would focus much of the precip west of the Allegheny Front. With the combination of light snow from the warm air advection as well as the upslope, have issued Winter Weather Advisories for 2-4" of snow for the western portions of Grant, Mineral, and Allegheny Counties. The low will pull rapidly away during the day Thursday, with upslope snow showers diminishing. Gusty northwest winds to 25 mph or so are expected, with highs in the 30s/40s. High pressure will build in for Thursday night. Another fast-moving shortwave trough will move towards the region Friday, with a surface low tracking through the Great Lakes, and a secondary low developing offshore. This will bring the chance of a few additional snow showers. Temperatures remain cold, with highs in the 30s to around 40F for Friday. Lows mainly in the 20s. && .LONG TERM /SATURDAY THROUGH TUESDAY/... High pressure will build overhead Saturday through Saturday night...bringing dry and seasonably chilly conditions. The high will move offshore Sunday and a southerly flow will allow for milder conditions compared to recent days. However...low pressure and its associated cold front will approach later Sunday before passing through Sunday night into Monday. Showers are possible ahead of this system later Sunday into Monday. Another upper-level disturbance may impact the area later Monday or Tuesday...but confidence is low at this time. Seasonable temperatures are most likely during this time. && .AVIATION /16Z WEDNESDAY THROUGH SUNDAY/... Primarily VFR is expected for the region through Friday night. Gusty northwest winds up to around 30 knots will continue through the first half of today, gradually relaxing this afternoon. Some areas of light snow are possible this evening and tonight and brief reductions are possible, with MRB/BWI/MTN having the highest probabilities of seeing snow. Afterward, dry conditions expected Thursday and Thursday night, with another chance of some snow showers on Friday. VFR conditions are expected for Saturday through midday Sunday. A few showers are possible later Sunday into Sunday night. SubVFR conditions are possible during this time. && .MARINE... Gale Warning continues for the lower Tidal Potomac and Chesapeake Bay for the rest of the day, with SCA continuing for remaining waters. Winds will turn southerly tonight, with SCA in place over the lower Tidal Potomac and Chesapeake Bay. As a low pressure system crosses late tonight, gusty northwest winds return on Thursday, and SCA is in effect for all waters. Extended SCA into the evening for part of the bay, but it should go sub-SCA for all waters by midnight Thursday night. Winds will remain relaxed Friday with sub-SCA conditions forecast, but SCA winds possible again Friday night behind another low pressure system. High pressure will approach Saturday before building overhead Saturday night. A Small Craft Advisory may be needed for portions of the waters Saturday. Low pressure and its associated cold front may impact the waters later Sunday and Sunday night. && .TIDES/COASTAL FLOODING... Strong northwest winds have caused tidal anomalies to drop sharply. Blowout conditions are likely through the low tide this morning...especially across the middle portion of the Chesapeake Bay. Anomalies will increase later this afternoon through tonight as winds turn to the southwest. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...Wind Chill Advisory until noon EST today for MDZ501. Winter Weather Advisory from 7 PM this evening to 7 AM EST Thursday for MDZ501. VA...Wind Chill Advisory until noon EST today for VAZ503-504-507- 508. WV...Wind Chill Advisory until noon EST today for WVZ501-503-505- 506. Winter Weather Advisory from 7 PM this evening to 7 AM EST Thursday for WVZ501-503. MARINE...Small Craft Advisory from 6 PM this evening to midnight EST Thursday night for ANZ531>534-537-539>541-543. Gale Warning until 6 PM EST this evening for ANZ530>534-537- 539>541-543. Small Craft Advisory until 6 PM EST this evening for ANZ535- 536-538-542. Small Craft Advisory from 8 AM to 6 PM EST Thursday for ANZ535- 536-538-542. Small Craft Advisory from 6 PM this evening to 6 PM EST Thursday for ANZ530. && $$ SYNOPSIS...BJL/RCM NEAR TERM...MM/RCM SHORT TERM...MM LONG TERM...BJL AVIATION...BJL/MM/RCM MARINE...BJL/MM/RCM TIDES/COASTAL FLOODING...BJL is the U.S. government's official web portal to all federal, state and local government web resources and services.