Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 251356 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 956 AM EDT Mon Jul 25 2016 .SYNOPSIS... A cold front will approach from the northwest late tonight. This front may stall across the region during the middle of the week. Another cold front is expected at the end of the week. && .NEAR TERM /THROUGH TONIGHT/... A cold front is located across the Great Lakes region this morning, and a lee trough can be discerned east of the Appalachians. A warm and humid airmass is in place with 9 AM obs already rising quickly into the mid and upper 80s. Subsidence behind a departing shortwave should keep the area dry for the next few hours. Two hazards are expected today...heat and scattered strong thunderstorms. Warm air advection in the mid-levels will allow surface temperatures to climb into the mid-upper 90s with a few spots around the I-95 corridor potentially hitting 100. High moisture content will lead to heat indices solidly between 105-109 across much of the Mid-Atlantic with the exception of higher elevations and the Shenandoah Valley. A heat advisory is in effect from noon to 8pm today. It`s not out of the question a spot could briefly hit warning criteria of 110, but the 12Z sounding supports afternoon dew points in the lower 70s. The second hazard is for severe thunderstorms mainly along and north of U.S. Highway 50. Midday-early afternoon storm initialization should largely occur along the terrain and be isolated-scattered. Some of these storms may push east by mid-late afternoon, but coverage is uncertain. More organized storms may approach northern areas by early evening as outflow from activity currently near Lake Ontario initiates new storms across central PA. While any storm has the potential to be strong due to SBCAPE >2500 J/kg, the greatest severe threat may come with the organized storms from PA early this evening due to antecedent poor mid-level lapse rates. Shear will also be increasing during this time due to a shortwave trough. The main threats will be damaging winds from pulse downbursts or multicell clusters. Localized flooding can not be ruled out through tonight with PWAT near 2 inches and storm motions around 20 kt. Activity will likely sag southward across the southern outlook area late this evening and overnight. It should diminish some but thunderstorms are still likely overnight. && .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/... The cold front will be near the Mid-Atlantic Tuesday morning. Light northerly winds will give some relief to the heat and humidity however temps will still reach the low to mid 90s and indices into the upper 90s to near 100 Tuesday afternoon. Showers and thunderstorms are likely mainly across the southern half of the outlook area Tuesday afternoon and evening. Coverage seems to be isolated however confidence is low at this time due to the stalled frontal boundary. The front will be near the Mid-Atlantic through Wednesday night. Showers and thunderstorms can not be ruled out through this period. Light w-nw flow aloft will keep heat and humidity down however still be above normal for late July. Uncertainty exists for coverage and threat level of thunderstorms Wed-Wed night. && .LONG TERM /THURSDAY THROUGH SUNDAY/... A front will meander across the area through the end of the work week keeping the risk of t-storms Thu and Fri. With front stalled out across the area, we could see multiple rounds of convection with heavy rain becoming a bigger threat. It will still be hot and humid with temperatures in the mid 90s and heat indices at or above 100F. By the weekend, guidance shows a low pressure center developing off of the Delaware coast and moving northeast away from the coast with front clearing the fcst area and weak high pressure building in bringing lower humidities but with temps still around 90F. && .AVIATION /14Z MONDAY THROUGH FRIDAY/... VFR conditions expected this morning. More thunderstorms are expected this afternoon and evening and may impact the terminals. Activity may be rather isolated until mid-late afternoon. The most organized storms may impact the Baltimore area this evening. Some storms may be strong with gusty winds and heavy rain. Sub- vfr conditions expected in activity. The chance for thunderstorms persists through Wednesday as a frontal boundary stalls across the region. && .MARINE... Overall winds expected to be 10-15kts from the W or SW today and tonight. A brief surge of SW winds ahead of a cold front is possible across the southern Chesapeake Bay late tonight and will need to be monitored. Showers and thunderstorms are possible this morning as well as today and tonight as a hot and humid airmass stays in places. Coverage will increase this evening and overnight as thunderstorms track eastward. Some storms may be strong to severe resulting in gusty winds. SMWs will be likely through Tuesday morning. A cold front will move through the waters Tuesday morning and winds will become nrly behind it. Showers and thunderstorms are possible Tuesday afternoon mainly across the southern waters and again on Wednesday. && .CLIMATE... New record highs are possible today at DCA and IAD. Here are the record highs today: DCA...100 in 1930...79 in 1965 BWI...100 in 2010...77 in 1887 IAD... 98 in 2010...76 in 1965 Here are the last dates 100 degrees was reached: DCA...July 26, 2012 BWI...July 18, 2012 IAD...July 18, 2012 && .LWX WATCHES/WARNINGS/ADVISORIES... DC...Heat Advisory until 8 PM EDT this evening for DCZ001. MD...Heat Advisory until 8 PM EDT this evening for MDZ003>006-011- 013-014-016>018-503>508. VA...Heat Advisory until 8 PM EDT this evening for VAZ028-030-031- 036>040-050>057-501-502-505-506. WV...Heat Advisory until 8 PM EDT this evening for WVZ052-053. MARINE...None. && $$ SYNOPSIS...LFR NEAR TERM...ADS/HAS SHORT TERM...HAS LONG TERM...LFR AVIATION...ADS/HAS/LFR MARINE...ADS/HAS/LFR CLIMATE...LFR/ADS is the U.S. government's official web portal to all federal, state and local government web resources and services.