Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 221951 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 251 PM EST Sun Jan 22 2017 .SYNOPSIS... Low pressure will impact the area through Monday before moving away Tuesday. A cold front will pass through the area Wednesday into Wednesday night and an upper-level trough may build overhead for the end of the week. && .NEAR TERM /THROUGH MONDAY/... A weak wedge of high pressure is across the Mid-Atlantic region this afternoon. Low pressure has moved off the east coast. N-NE winds will continue across the region through tonight. Low clouds and patchy fog will persist into tonight. Rain is developing across the region this afternoon and will continue to move northward tonight. Light amounts are expected through tonight. Low pressure will deepen across the SE states this evening and the pressure gradient will become packed by midnight as the approaching system pushes the wedge of high pressure to the north. NE-E winds will strengthen across the region tonight becoming strong by Monday morning. Gusty winds up to 50 mph are expected across the Blue Ridge Mtns late tonight into Monday morning. A wind advisory is in effect for the Blue Ridge mtns from 1AM to 10AM. As high pressure stays in place across northern New England and the surface low migrates E-NE south of the outlook area...winds will continue to strengthen with the greatest winds across central Maryland and DC/Fairfax County. A wind advisory is in effect for these locations including Washington DC and Baltimore from 6AM to 4PM. The strongest across the metros will be Monday morning. As strong moisture advection occurs late tonight into Monday...moderate to heavy rain is expected across the Mid- Atlantic. Amounts will range from 1-1.5 inches with higher amounts on the eastern slope of the Blue Ridge mountains where enhancements due to upslope are expected. Amounts may reach 2-2.5 inches along the eastern slopes. Most of the soaking rain will occur between 1AM-1PM Monday. Can not rule out any nuisance flooding from poor drainage however widespread flooding is not expected at this time. Please see hydrology section below for more details. Due to the saturated ground and strong may be easier for trees to come down. The dry slot should enter the eastern half of the region by Monday afternoon. This may cause convective showers and an isolated thunderstorm to develop across southern Maryland and surrounding waters. Rain will continue on the back side of the sfc low as it moves off the east coast. Temperatures will slowly fall along the Allegheny Front into Monday night and rain will likely change to snow at higher elevations. && .SHORT TERM /MONDAY NIGHT THROUGH TUESDAY NIGHT/... Marginal temperatures and warmer air aloft will keep snow totals down across the higher elevations of the Allegheny Front. Around an inch of snow accumulation is possible. An upper level low will continue to spin across the region Monday night into Tuesday and rain showers are expected. Winds will become northwest Tuesday and rain showers will taper off. Dry air will move into the region and the sun should come out by Tuesday afternoon. Gusty winds up to 30 mph expected Tuesday afternoon due to the pressure gradient. && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... Dry conditions expected Wednesday as upper ridge axis to our east continues to move away, before a cold front moves across the region Wednesday night. Looks like moisture will be limited with this front, therefore not much precipitation is anticipated. Extensive upper level trough and westerly/northwesterly flow could bring persistent upslope precipitation in the form of snow showers from Thursday and into Sunday... mainly over the Allegheny Front... with maybe some showers reaching east of the mountains. Warmest day of this period is Wednesday with high temperatures in the 50s and 60s... followed by a drop in the temperatures of 10 to 20 degrees for the second half of the week and into Sunday. && .AVIATION /19Z SUNDAY THROUGH FRIDAY/... IFR/Sub-IFR conditions will continue through the next 24-36 hours. -RA is expected across the terminals this afternoon and evening. RA will increase in intensity tonight and Monday. Although cigs may flirt with MVFR due RA and stronger winds in the cloud layer...Vsbys will likely drop to IFR/SUB- IFR during the heavy rain but due to uncertainty with timing did not add to TAF. Winds rapidly increase late tonight through Monday afternoon with the strongest gusts expected Monday morning and at BWI/MTN/DCA. Gusts may reach 45 kts at times. Further south and east gusts up to 30-35 kts expected. Flight restrictions will continue Monday-Monday night. Gusty winds expected Tuesday afternoon. Dry conditions expected Wednesday before a cold front moves across Wednesday night... with limited precipitation associated to it. An upper level disturbance and west/northwest winds will bring cooler conditions for Thursday and Friday with possible isolated showers over our area. Mainly VFR conditions expected Wednesday through Friday, with possible sub-VFR conditions Wednesday night. Breezy conditions expected over higher elevations through this period. && .MARINE... Low pressure will approach the waters through this evening. Winds will gradually strengthen this afternoon through this evening. A Small Craft Advisory is in effect for the Bay and lower Tidal Potomac River this afternoon. Winds will continue to strengthen tonight and SCA is in effect for all waters. The pressure gradient will rapidly strengthen late tonight into early Monday morning before gradually dissipating from south to north later Monday. A Gale Warning is in effect for the waters from late tonight through Monday. East to northeast winds will gust around 35 to 40 knots during this time. A Small Craft Advisory will likely be needed for portions of the waters Monday night as the low slowly moves away from the area. Gusty NW winds exceeding SCA criteria remain Tuesday behind departing low pressure system. Winds slacken late Tuesday as influence from low wanes. Mostly dry cold front crosses the waters late Wednesday into Thursday...with gusty winds possibly to SCA criteria behind it Thursday afternoon. Dry conditions expected Wednesday before a cold front moves across Wednesday night... with limited precipitation associated to it. An upper level disturbance and west/northwest winds will bring cooler conditions for Thursday and Friday with possible isolated showers over our area. Breezy conditions expected during this period, possibly needing a small craft advisory. && .Hydrology... Moderate to heavy rain is expected across the Mid-Atlantic region late tonight into Monday afternoon. Widespread amounts will range from 1-1.5 inches with locally higher amts along the eastern slopes of the Blue Ridge Mtns. Rapid rises of rivers and streams are expected however flooding is not anticipated at this time. Amounts of 2-2.5 inches are possible and areas across the Central Foothills such as the western portions of Nelson, Albemarle, Greene, Madison. These areas should stay tuned to the forecast as well as any flood outlooks and future watches and/or warnings. Due to the recent dry stretch the ground should be able to handle this amount of rain and therefore flood watches were not issued. .TIDES/COASTAL FLOODING... Persistent easterly flow will increase the risk for minor tidal flooding during high tide cycles beginning Monday afternoon and lasting into early parts of Tuesday morning (especially at Annapolis, Solomons, and Straits). Developing westerly flow should allow for some decrease in anamolies later Tuesday. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...Wind Advisory from 5 AM to 4 PM EST Monday for DCZ001. MD...Wind Advisory from 5 AM to 4 PM EST Monday for MDZ004>006-011- 013-014-016>018-503>508. VA...Wind Advisory from 1 AM to 10 AM EST Monday for VAZ507-508. Wind Advisory from 5 AM to 4 PM EST Monday for VAZ053-054. WV...None. MARINE...Small Craft Advisory until 1 AM EST Monday for ANZ530>534- 537>543. Gale Warning from 1 AM to 6 PM EST Monday for ANZ530>543. Small Craft Advisory from 6 PM this evening to 1 AM EST Monday for ANZ535-536. && $$ SYNOPSIS...HSK NEAR TERM...BJL/HSK SHORT TERM...BJL/HSK LONG TERM...IMR AVIATION...BJL/HSK/IMR MARINE...BJL/HSK/IMR TIDES/COASTAL FLOODING...HSK is the U.S. government's official web portal to all federal, state and local government web resources and services.