Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 162354 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 754 PM EDT Sun Jul 16 2017 .SYNOPSIS... High pressure will slide offshore tonight. An upper level trough will affect the weather Monday and Tuesday. After another period of tranquil weather during the middle of the week, another cold front may approach the region by the end of the week. && .NEAR TERM /THROUGH MONDAY/... Meteorological summer - June 1 to Aug 31, 92 days. Today is day 46 of that, so we`re at the midpoint. Technically we`d need to wait until after midnight so today could be included, but here are a few temperature stats on thIS summer so far. Site Average Temp Rank Record year (through today) DCA 79.1 6 2010 Balt 75.7 35 2010 IAD 74.9 10 1994 I was curious about why DC was ranked so high, given that it has not felt (to me) even remotely close to as hot as 2010, so I looked at max and min temps for the site to see how this year ranks: 11th for max temps, 7th for min temps. Expect a dry overnight with scattered clouds. Dewpoints will start to rebound, so low temperatures won`t be as cool as last night. Lows generally in the mid 60s..low 70s in the cities and along Bay, around 60 in the mountains. && .SHORT TERM /MONDAY NIGHT THROUGH TUESDAY NIGHT/... A trough axis will inch closer to the forecast area Monday, but doesn`t completely clear area. Instability will be able to build. Questions remain how much and whether it will be able to break the cap. Given lower heights and terrain circulations, storms will best be able to develop across the ridges...and the strongest storms will be capable of taking advantage of the cooler temperatures aloft to produce hail/local downdrafts. Marginal Risk from SPC takes these considerations into account. Shear will be a non-factor. Keeping likely PoPs only across the Potomac Highlands/Northern Shenandoah Valley/Western Maryland... only slight chance across far southern Maryland. The trough axis slowly lifts and fills Tuesday. The same ingredients will be in place, but in a weaker sense. Am keeping primarily diurnal chance PoPs, but with a mid-late morning start given minimal inhibition. && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... Bermuda high pressure across the western Atlantic will continue through Thursday into Friday. Near seasonable temperatures and high humidity expected with not much precipitation expected. Isolated thunderstorms are possible through the end of the week mainly associated with terrain circulation and river/bay boundaries. Some guidance hints at northwest flow setting up by the end of the week, which could bring into play any upstream leftover MCS activity, but confidence for this not high. By Friday models suggest a weak cold front will sag down into the area. This front is associated with a surface low passing well north of the region. Some guidance takes this front and drops it just south of our CWA on Friday providing for a brief respite from the high humidity. Other guidance suggests the front lingers over the area on Friday and continues into Saturday. Low confidence in how this will play out. Then sometime on the weekend, the front either washes out or moves north as a warm front. Moisture pooling south of this front allowing for higher humidities, with some guidance suggesting precipitable water values over 2.0 inches next weekend. && .AVIATION /00Z MONDAY THROUGH FRIDAY/... VFR through the valid TAF period. Southeast flow will continue Monday. Building instability will permit development of showers/thunderstorms by afternoon. The strongest of these storms may produce gusty winds and hail... especially for MRB and perhaps CHO. Areal coverage uncertainties preclude a TAF mention at this time. There will be similar considerations on Tuesday. Wednesday through Friday...expect VFR conditions overall, and generally dry weather. The threat of showers and thunderstorms is isolated at best both Wednesday and Thursday, but increases Friday ahead of the cold front. && .MARINE... Flow will be become south tonight but remain light (at or below 10 kt) through Tuesday. Overall surface pressure gradient mid-late week is fairly weak. Aside from southerly channeling on the Bay during the afternoon/evening, expecting to remain below SCA levels through the end of the week. The threat of thunderstorms will likely increase Friday. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...None. && $$ UPDATE...WOODY! PREVIOUS...HTS/SMZ

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