Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 171400 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 1000 AM EDT Mon Jul 17 2017 .SYNOPSIS... An upper level trough will affect the weather today 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 TONIGHT/... Morning analysis depicts upper level trough and surface front located across the Ohio Valley northward through western Pennsylvania and into western New York. While the surface boundary will stall and wash out over the next couple of days, the upper trough will move eastward and over the region through today. Relatively steep mid level lapse rates exist with this feature with the 12z IAD sounding and SPC mesoanalysis depicting 700-500 mb lapse rates in excess of 7 C/km. While these are projected to weaken some by the afternoon, these combined with the warmth and humidity will lead to the development of at least 1500-2000 J/KG of MLCAPE. It should also be noted that a capping inversion also exists between 700-800mb that should limit thunderstorm development for areas east of the Blue Ridge, while a weaker cap and daytime terrain circulations will lead to a greater risk for areas west. Some of the showers/thunderstorms that do develop across the terrain may tend to propagate eastward towards the metros while weakening later in the day. While shear profiles are weak, there is enough instability to warrant a marginal risk of severe thunderstorms. Highs today upper 80s to near 90F. Given lack of strong forcing, most convection should quickly dissipate this evening, and the balance of tonight will be dry with lingering clouds. Patchy valley fog is also possible, especially where it rains today. Lows will be a bit milder, with 70s becoming more common. && .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/... Upper trough slowly weakens and moves out of the area Tuesday and Wednesday as high to the southeast continues to bring in more warmth and humidity. Dew points will rise a bit more and so will temps, but right now, expect heat indices to peak in the mid-upper 90s Tuesday and upper 90s-low 100s Wednesday... just below criteria for a heat advisory. Conditions will not be quite as unstable overall on Tuesday as we are expecting today, but a lee side trough combined with less of a cap means that the chance of showers and t-storms along the I-95 corridor actually looks higher on Tuesday than it does today. By Wednesday, pops fall everywhere as what remains of the trough aloft is moving away and there is less of a lee side trough. Highs will generally be low-mid 90s with lows in the 70s. && .LONG TERM /THURSDAY THROUGH SUNDAY/... An upper trough present through the first half of the week over the eastern states will shift east off the coast by Thursday. A sprawling high centered over the southern Great Plains begins to control area weather in the wake of this trough. A shortwave trough crosses to the north on Thursday with a weak cold front entering the LWX CWA later in the day. This front looks to stall over the area and provide a focus for diurnally driven convective storms Thursday through the weekend. Heat will be a concern later in the week, particularly Thursday ahead of the cold front and Sunday after the stalled front moves out. As of now values around 100F seem reasonable for Thursday in urban areas. && .AVIATION /14Z MONDAY THROUGH FRIDAY/... VFR overall through the TAF period and beyond. The main weather concern today and Tuesday will be scattered showers/thunderstorms during the afternoons, with best coverage west of I-95 today, and near I-95 on Tuesday. Otherwise, patchy early morning fog is possible, especially Tuesday and Wednesday mornings and particularly where any rain falls the previous afternoon/evening. A weak cold front will then stall over the area later Thursday into the weekend which may allow sub-vfr conds during thunderstorms. && .MARINE... Generally sub-SCA today and Tuesday, though southerly channeling could result in near SCA conditions Wednesday. Other than that, main concern is for thunderstorms, which look more likely on the waters on Tuesday, but are also possible both today and Wednesday (just not as likely). Any storm could result in gusty winds over the next couple of days. Generally light NWly flow Thursday into the weekend behind a weak cold front. && .TIDES/COASTAL FLOODING... South flow persists across the Chesapeake Bay region through midweek. Water levels at the preferred high tide (late afternoon/evening) will approach minor coastal flooding thresholds at particularly sensitive sites like Straits Point (St. George Island in St. Mars county), Annapolis and SW DC Waterfront today through Wednesday. && .CLIMATE... Meteorological summer - June 1 to Aug 31, 92 days. Yesterday was day 46 of that, so we`re at the midpoint. Here are a few temperature stats on this summer so far. Site Average Temp Rank Record year (through yesterday) DCA 79.1 6 2010 Balt 75.7 35 2010 IAD 74.9 10 1994 && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...None. && $$ SYNOPSIS...RCM NEAR TERM...MM/RCM SHORT TERM...RCM LONG TERM...BAJ AVIATION...BAJ/MM/RCM MARINE...BAJ/MM/RCM TIDES/COASTAL FLOODING...BAJ CLIMATE...WFO LWX is the U.S. government's official web portal to all federal, state and local government web resources and services.