Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 250033 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 833 PM EDT Sun Mar 24 2019 .SYNOPSIS... A weak warm front will approach the region tonight and then stall across the area. A low pressure system will track along this boundary Monday, bringing a cold front across the region late Monday afternoon into Monday evening. High pressure settle southward across the area for Tuesday through Friday. && .NEAR TERM /THROUGH MONDAY/... Forecast issued earlier this afternoon remains largely on track, and only minor modifications were made for this evening`s package. High pressure has pushed into the Atlantic, which south flow across the area. Although the upper layers are moistening, the boundary layer is bone dry (relative humidity 20%/dewpoint depression near 40 degrees). Eventually, the veil of high clouds will thicken, and slowly lower tonight. Weak positive vorticity advection and isentropic upglide will allow clouds to lower. However, given how dry it is below 850 mb, am less optimistic with respect to precipitation tonight. Am keeping a chance of rain northwest of Washington DC, but precipitation (sprinkles?) will barely be enough to wet the ground. && .SHORT TERM /MONDAY NIGHT THROUGH TUESDAY NIGHT/... The associated weak warm front will stall across the area Monday morning and then slowly drop south again as low pressure tracks across the area during the afternoon. Forcing from the low and 500 mb shortwave will be the catalysts for rainfall; this will occur during the afternoon hours, supporting likely- categorical PoPs. It may be just cloudy and damp prior to it. Do believe there will be a fairly sharp precip gradient near the Mason-Dixon line. Although temperatures forecasts for Monday remain somewhat tricky due to the position of the warm front/track of the low, model output remain somewhat consistent resulting in only minor adjustments. Since it may not be all that wet early Charlottesville-Fredericksburg, and these locations should be on the south side of the system, anticipate central Virginia should be able to reach 60 degrees. The bigger question will be the Potomac Highlands; am keeping the forecast there lower-mid 50s. A wetter solution, especially in the morning, could make that forecast too warm. Cold advection will arrive on the back side of the low Monday evening. There is a chance that temperatures will cool sufficiently to end the precip as snow, especially across the ridge tops, but do not have high confidence that there will be much precip left by that point (winds will be due north...not an upslope direction). Allowed for a coating on some ridges, but nothing elsewhere. A large area of high pressure will settle south from the Great Lakes (and Canada) Tuesday. Subsidence will result in sunny and dry conditions, but it won`t be warm. Highs will only be in the 40s (with subzero 850 mb temperatures) and lows Tuesday night in the 20s away from the urban downtowns. && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... Surface high pressure will push off the east coast on Wednesday, and remain there through the early part of the weekend. Additionally, the region will be stuck under an upper ridge, resulting in dry weather for the entire area through Saturday. Temperatures will moderate slightly on Wednesday, but will likely be slightly below average, with highs into the low to mid 50s. The warming trend will continue through Saturday. Highs on Thursday will be near 60, with Friday reaching into the mid to upper 60s. Surface low pressure forms over the Central Plains Friday into Saturday as an upper shortwave ejects out of the Pacific Northwest. The low will then strengthen on Saturday as the aforementioned shortwave phases with another piece of shortwave energy diving out of central Canada. On Saturday, this will enhance the return flow for our region, resulting in temperatures well above normal. Could see high temperatures into the low 70s on Saturday, with dry conditions expected. Though, as the low tracks into the Great Lakes, the attendant cold front will push through our region either Saturday or Sunday. So, could potentially see some precipitation later in the day on Saturday, but uncertainty is still high in terms of timing of the frontal passage. && .AVIATION /01Z MONDAY THROUGH FRIDAY/... VFR conditions anticipated tonight as high clouds thicken and lower. There could be a sprinkle toward dawn, which will lower ceilings further (still VFR, but BKN-OVC050-060). Rain will arrive during Monday afternoon. MVFR likely during this time. Would not rule out a period of IFR, most likely MRB. Flight restrictions probably will linger into Monday evening. High pressure returns Monday night, moves overhead by midweek, and offshore by the end of the week. VFR conditions expected. && .MARINE... Guidance insists that the middle bay will experience some stronger southerly channeling overnight, so have issued a SCA for the rest of tonight. Elsewhere, winds will likely diminish overnight. Warm front will stall across the waters late tonight and an area of low pressure and cold front will follow on Monday. In the wake of these features, mixing will improve substantially. Small Craft Advisories are now in effect Monday night and will likely be needed Tuesday. No marine hazards are expected Wednesday through Friday at this time, as high pressure will become anchored off the east coast, resulting in light southerly flow. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory from 6 PM Monday to 6 AM EDT Tuesday for ANZ532>534-537-539>543. Small Craft Advisory from midnight Monday night to 6 AM EDT Tuesday for ANZ530-531-535-536-538. Small Craft Advisory until 6 AM EDT Monday for ANZ534-543. && $$ SYNOPSIS...HTS NEAR TERM...HTS/RCM SHORT TERM...HTS/RCM LONG TERM...CJL AVIATION...HTS/CJL/RCM MARINE...HTS/CJL/RCM is the U.S. government's official web portal to all federal, state and local government web resources and services.