Area Forecast Discussion
Issued by NWS Sterling, VA

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009 FXUS61 KLWX 231900 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 200 PM EST Fri Feb 23 2018 .SYNOPSIS... A warm front will gradually push north across the region tonight through Sunday morning. A cold front will then cross the region Sunday night. High pressure will return early next week. && .NEAR TERM /THROUGH SATURDAY/... Latest surface analysis places low pressure near Lake Superior, hig pressure near Nova Scotia, and another high pressure betwen the Carolinas and Bermuda. A warm front extends between the two high pressures, westward across North Carolina, then northward along the Appalachians to the vicinity of Pittsburgh. There it turns west and meets the cold front extending southward from the low in the Great Lakes. The cold front then continues southwest toward Memphis and finally approaches Houston. Tonight through Saturday, the low pressure will head eastward to our north. Southerly flow will encourage the warm front to push northward as well, but the odds it reaches very far into our CWA are not high. The more pessimistic but often more realistic (in these situations, at least) NAM shows the warm front reaching portions of the West Virginia eastern Panhandle and the Shenandoah Valley, but struggling to reach any portion of the CWA east of the Blue Ridge. There may be an attempt at a little clearing this evening as this all tries to occur, but otherwise, clouds and drizzle with patchy mist/fog will likely continue. With the main forcing staying to our north, significant rainfall is not expected across our region, but a few showers could skim the region, particularly western Maryland. Temperatures will be fairly steady, perhaps even rising a bit, but large changes are not expected in most of the region. On Saturday, the front may actually sink back south a bit as the passage of the low to our north causes the flow to shift a bit more northerly. Thus, the morning should be more of the same...damp and dreary, but not a washout. Later in the morning and in the afternoon, low pressure developing to the west over the Plains will bring increased warm advection aloft and FGEN across western zones, spreading eastward late in the day. This will increase the risk of steadier rain. Given ample moisture available, some locally heavy rain could occur in the western portions of the forecast area, but confidence is low regarding any flooding risk, so have not issued any flood watches yet. Highs on Saturday will be a bit warmer than today as the warm front once again attempts to lift north, with 50s and 60s becoming more common. However, if the front ends up further south than currently expected, it could stay cooler. && .SHORT TERM /SATURDAY NIGHT THROUGH SUNDAY NIGHT/... Warm front makes more progress northward on Saturday night and Sunday as low pressure wave pushes northeastward to our northwest. This should allow temperatures to warm more significantly after the rain Saturday night, with 70s looking more likely on Sunday. An interval of relatively pleasant weather may occur late morning into early afternoon, with more sunshine, but then the cold front will approach from the northwest. Still some uncertainty on any severe threat, but certainly with the available moisture and warmth, some instability will be present, so allowed slight chance of thunder into the forecast Sunday afternoon. The front will slide southeast across the region Sunday night, so a drying, cooling trend will develop. However, the front will slow down overnight as yet another wave of low pressure develops to our southwest, so rain chances will not completely end in southern parts of the region. && .LONG TERM /MONDAY THROUGH FRIDAY/... With exception to a couple of lingering rain showers near Southern Maryland and parts of the central Chesapeake Bay Monday morning, conditions will dry out as a ridge of high pressure builds in from the west. The high will persist through Tuesday night before moving offshore early Wednesday. Interaction between the high pressure and a developing low pressure system over the central Great Plains will provide a southerly return flow into our region. Expect milder and more moist air to return Wednesday and Wednesday night. There could be a couple of rain showers develop over the Appalachians and in parts of the Central Shenandoah Valley later in the day Wednesday. A developing warm front over southwest Virginia and western North Carolina will work its way north across our region Wednesday night. Ahead of and along this warm front, additional rain showers will develop and spread northeastward across our region Wednesday night. Even more warmer and moist air is expected to follow the warm front northward Wednesday night into Thursday. Showers, some moderate at times, should persist into Thursday morning as the warm front moves to the Mason-Dixon region just ahead of an approaching cold front that should pass through our area Thursday night. Some drier and cooler air will work in behind the passing cold front; however, models are trying to push a cut-off low pressure system over the Great Lakes region eastward. This cut-off low, it`s upper level energy support, and a little daytime heating could spawn additional rain showers later Thursday night and during the day Friday. Northwesterly winds could become quite gusty as well in the wake of the passing surface cold front and ahead of the cut- off low pressure system. Overall, temperatures throughout next week will be mild with highs approaching 60 degrees or higher in any warm sector. Friday may be the exception and could be cooler, but for now we will keep temperatures near normal. && .AVIATION /19Z FRIDAY THROUGH WEDNESDAY/... Changeable conditions expected through the next 48-60 hours as a warm front remains stalled to our south much of the time, resulting periods of low clouds, fog, mist and drizzle. Guidance suggests a break in the low clouds could develop late this afternoon and this evening, but given the cold air damning wedge over the region, this does not seem likely, so have kept all the TAFs at least MVFR through the TAF period. If conditions do relax, it won`t be for long, as we will likely see fog or low clouds redevelop quickly overnight. The warm front will probably stay south of all the terminals, save perhaps CHO, during the day Saturday, resulting in more of the same. Steadier rain may overspread the region, especially the northern terminals, by Saturday night. Conditions look more likely to improve from DC on south and west on Sunday as a warm front lifts northward, but BWI/MTN may have trouble breaking out of the low clouds and fog as the front may struggle to pass that area. Cold front then finally drops southeast across the region, bringing showers and perhaps a thunderstorm Sunday afternoon, but likely resulting conditions finally going back to VFR with drier air filtering south Sunday night. VFR conditions expected Monday through Tuesday night. Winds northwest 5 knots or less Monday and Monday night. Winds becoming southwest around 5 knots Tuesday and Tuesday night. && .MARINE... With weak gradient and a front to the south, expect winds to stay below Small Craft Advisory strength through Saturday evening across all waters. Late Saturday night, warm front approaching from the south may finally lift north of the middle Bay, allowing the strong southerly flow to reach the surface and bring gusts up to SCA levels, but for now am waiting to issue a headline. SCA looks likely across at least the southern waters we cover, perhaps reaching up to the northern bay as well, as the warm front lifts north and gusty south winds develop in the warm sector. As with the recent round on Tuesday and Wednesday, this will be primarily near-shore gusts, with weaker winds over the open waters due to the chilly water temperatures limiting mixing. Cold front will push southeast across the waters Sunday night, but at this time SCA does not appear likely with this frontal passage. No marine hazards expected Monday through Tuesday night. Winds northwest 5 to 10 knots Monday and Monday night. Winds becoming southwest 5 to 10 knots Tuesday and Tuesday night. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...None. && $$ SYNOPSIS...RCM NEAR TERM...RCM SHORT TERM...RCM LONG TERM...KLW AVIATION...RCM/KLW MARINE...RCM/KLW

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