Area Forecast Discussion
Issued by NWS Sterling, VA

Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
007 FXUS61 KLWX 061502 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 1002 AM EST Tue Dec 6 2016 .SYNOPSIS... Coastal low pressure impacts the area through tonight before high pressure briefly returns Wednesday. A potent cold front will pass through Thursday. Arctic high pressure builds overhead Friday into the weekend. && .NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
Rain will continue to spread northward across the Mid-Atlantic region this morning. The precipitation has been fighting low level dry air as evident on the 12Z IAD raob and has been light. Sleet has been reported on the leading edge as evaporative cooling occurs. Sub- freezing temperatures are present at higher elevations above 1.5- 2k feet along and west of the Blue Ridge Mtns. Freezing rain is expected at these locations through the afternoon. Any breaks of precipitation will fill in by afternoon and a steady rain is expected through the afternoon and into the evening. Moderate rain is also possible across central VA and southern MD this afternoon. Previous discussion... Low pressure over the Tennessee Valley this morning will transfer its energy to a coastal low along the North Carolina coast this afternoon. The coastal low will slowly move off to the east tonight. Warm and moist air from the Gulf and Atlantic Ocean will overrun the surface cooler air in place...resulting in a soaking rain for most areas today into this evening. Rainfall amounts around one inch are expected. Evaporative cooling at the onset may result in sleet at the onset...but surface temps should be above freezing for most locations. Precipitation will overspread central Virginia around daybreak...eastern West Virginia into northern Virginia and the the Washington Metropolitan area between 8 am and 10 am this morning...and across northeastern Maryland by noon. A subfreezing layer of air aloft...generally above 1500 feet is expected to develop due to the evaporative cooling that will take place at the onset. This means that the ridges in the Allegheny and Potomac Highlands as well as the Blue Ridge Mountains will experience a period of freezing rain this morning into this afternoon. Warmer air should work its way in aloft...allowing for all locations to change to rain later this afternoon into this evening. Winter Weather Advisories are in effect for these areas. The main threat will be for slick spots on elevated surfaces due to freezing rain with temperatures near 32 degrees. Precipitation will end from southwest to northeast this evening into the overnight hours as the low slowly moves off to the east.
-- End Changed Discussion --
&& .SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/... High pressure will return for Wednesday into Wednesday evening. Dry and seasonable conditions are expected during this time. A cold front will approach from the west overnight Wednesday. A strong jetmax ahead of the front may bring a few showers...but details are uncertain at this time. && .LONG TERM /THURSDAY THROUGH MONDAY/... Strong cold front crosses the area Thursday into Friday. Potent upper level dynamics...with 140 kt jet streak over the area by late afternoon. Model spread with regards to QPF continues...with GFS/NAM far more bullish than ECMWF. Best chance for precipitation will be along/east of I-95...with snow showers across the upslope areas. Elsewhere...p-type appears to initially be rain as low-levels remain just warm enough. Though...could be a changeover to rain/snow mix or all snow on the back edge of precip shield. Any remaining precip will exit the area Thursday night...with CAA commencing. Coldest weather so far this season Friday and Saturday...as high pressure builds into the area. Highs generally 10-15F below normal...with most areas struggling to get out of the 30s...all areas AOB 30F during the overnights. High pressure moves offshore Sunday...with southerly flow allowing for slight airmass modification. Highs back into the 40s. Next chance for precipitation arrives late Sunday into Monday as another cold front approaches. && .AVIATION /15Z TUESDAY THROUGH SATURDAY/... Cigs/Vsbys will deteriorate this morning as rain overspreads the terminals from southwest to northeast. IFR/SubIFR conditions are expected this afternoon through this evening. Conditions may gradually improve late tonight as drier air works its way in behind a departing coastal low. However...confidence with the timing of improving conditions is low. Any leftover subvfr conditions early Wednesday morning will give way to VFR conditions as high pressure builds overhead. VFR conditions will continue Wednesday night. Brief period of sub-VFR conditions possible in rain/snow showers as cold front passes through the area Thursday. Return to VFR behind the front into the weekend...though, gusty NW winds in excess of 25 mph are possible Friday afternoon in the strong cold air advection. && .MARINE... Coastal low pressure will develop along the North Carolina coast today. The gradient will continue to strengthen and a Small Craft Advisory is in effect for middle portions of the Bay and the lower Tidal Potomac River. The Small Craft Advisory continues through this evening...but there may be a break in the gradient overnight as the low moves away. High pressure will approach for Wednesday and a northwest flow is expected. Wind gusts around 20 knots are possible...but confidence is too low at this time for a headline. Winds will become light for Wednesday night. Light winds across the waters through midday Thursday...before winds increase above SCA criteria Thursday afternoon as cold front crosses the waters. Solid SCA gusts continue Thursday night into Friday morning. Increased mixing during the day Friday could lead to marginal gale force winds...regardless...solid SCA will continue. Winds drop back below SCA Saturday morning as large area of high pressure builds overhead. && .TIDES/COASTAL FLOODING... Persistent and strengthening easterly flow will lead to an increase in tidal anomalies today. Action stage currently forecast at the sensitive sites for this evenings high tide cycle (e.g., Annapolis, Straits Point)...though marginal minor tidal flooding is possible if anamolies are slightly higher than currently forecast. && .LWX WATCHES/WARNINGS/ADVISORIES...
-- Changed Discussion --
DC...None. MD...Winter Weather Advisory until 3 PM EST this afternoon for MDZ502. Winter Weather Advisory until 7 PM EST this evening for MDZ501. VA...Winter Weather Advisory until 3 PM EST this afternoon for VAZ507-508. Winter Weather Advisory until 7 PM EST this evening for VAZ503- 504. WV...Winter Weather Advisory until 3 PM EST this afternoon for WVZ050-055-502-504. Winter Weather Advisory until 7 PM EST this evening for WVZ501- 503-505-506. MARINE...Small Craft Advisory until midnight EST tonight for ANZ532>534- 537-540>543. Small Craft Advisory from 1 PM this afternoon to midnight EST tonight for ANZ531-538-539.
-- End Changed Discussion --
&& $$ SYNOPSIS...MSE NEAR TERM...BJL/HSK SHORT TERM...BJL LONG TERM...MSE AVIATION...BJL/MSE MARINE...BJL/MSE TIDES/COASTAL FLOODING...LWX

USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.