Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 161614 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 1114 AM EST Sat Dec 16 2017 .SYNOPSIS... High pressure will build across the Southeast U.S. today through early Sunday. A weak backdoor cold front will stall over the area on Sunday, lifting northward as a warm front on Monday. A surface trough will cross the region on Tuesday. High pressure will build over the region from the west northwest through Thursday before a cold front approaches on Friday. && .NEAR TERM /THROUGH TONIGHT/...
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Building high pressure across the southeastern U.S. is expected today and tonight. With southwesterly winds expected with the high to our south, temperatures will run 10 to 15 degrees warmer than we saw yesterday, however remaining near climatological normal for mid-December in the middle 40s. Mostly clear this afternoon with no threat of precipitation. Mostly clear skies and light southwesterly winds tonight will allow temperatures to bottom out in the upper 20s to near the freezing mark in the metro areas.
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&& .SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... The aforementioned high pressure area will shift off the southeast coast on Sunday, keeping winds light and southerly across our area, moderating temperatures in to the mid to upper 40s. This southerly flow will help transport moisture across the region as pieces of mid-level shortwave energy approaches from the southwest by Sunday evening. This will bring with it an increase in cloud coverage and the chance of light showers into early Monday morning, with perhaps a few flakes across our western and northern zones. Weak forcing and lack of moisture will result in only light precipitation. Temperatures will continue to moderate on Monday with highs reaching in to the lower 50s for most with a light southwesterly flow. Conditions will remain mostly dry with ample mid to high level clouds thanks to the proximity of the jet just to our north and some ragged pieces of mid-level energy passing overhead. There is a chance of some showers across our western zones Monday night, but any precipitation will be light and in a liquid form. Overnight temperatures Monday night will settle in to the upper 30s to near 40 degrees, some 10 to 15 degrees above normal. && .LONG TERM /TUESDAY THROUGH FRIDAY/... The upper air flow pattern for the week ahead will mainly be zonal, with separate northern and southern streams of the jet. It will be the southern stream that will be greater interest to the WFO LWX forecast area, as an impulse of energy traverses the country. Guidance has backed away from potential storminess Tuesday. A northern stream shortwave will be too far north to be a big player, and the southern stream low has not arrived yet. Probably the biggest issue will be how cloudy it will be, as a jetmax will be overhead. The northern wave likely will send a trough axis through, which could support increasing/gusty winds. Then comes the aforementioned wave. The GFS keeps it suppressed to the south as ridging builds. On the other hand, the ECMWF sends the energy across Virginia, but delayed to Wednesday night-early Thursday. If this were to happen, then p-type issues would ensue, as 850 mb warm advection would almost certainly result in a warm nose/ melting within the column. Have to acknowledge the chance of precip Wed night, and that it won`t be pure rain/snow. Beyond that, timing uncertainties magnify as a better amplified northern stream system approaches. However, PoP amount/type/timing questions abound. Daytime temps should be warm enough for just rain. We should be able to wiggle in a dry day Thursday as there will be ridging behind the southern stream system. The big question is what to do about precip at night. Am taking a middle-of-the-road approach until a more definitive clue can be discovered. && .AVIATION /16Z SATURDAY THROUGH WEDNESDAY/...
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Predominate VFR conditions are expected through Sunday across the terminals. Gusty southwesterly winds today, gusts 20 to 25 mph, before subsiding this evening. There is a slight chance of showers Sunday night in to early Monday morning, but only brief MVFR conditions would likely result. VFR conditions will persist Monday and Monday night with light southerly winds. VFR anticipated Tue-Wed. Flight restrictions, with possible mixed precip, may arrive late Wed...but there all sorts of uncertainties with that time frame.
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&& .MARINE... High pressure will build to our south today, but with a tightening pressure gradient, expect SCA conditions across our waters through late afternoon before subsiding below SCA criteria Saturday evening. The gradient will subside Saturday night and Sunday. A weak disturbance will pass through Sunday night. Sub SCA conditions expected Monday and Monday night. West/northwest flow Tuesday and Wednesday. Winds may increase behind a trough axis on Wednesday, which may reach Small Craft Advisory threshold. && .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory until 7 PM EST this evening for ANZ530>534-537-539>541-543. Small Craft Advisory until 7 PM EST this evening for ANZ535- 536-538-542.
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&& $$ SYNOPSIS...BKF NEAR TERM...BKF/RCM SHORT TERM...BKF LONG TERM...HTS AVIATION...BKF/HTS/RCM MARINE...BKF/HTS/RCM

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