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Area Forecast Discussion
Issued by NWS Sterling, VA
Issued by NWS Sterling, VA
901 FXUS61 KLWX 181415 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 1015 AM EDT Sun Aug 18 2024 .SYNOPSIS... A slow moving cold front will bring showers and thunderstorms to the forecast area today. Precipitation chances peak this afternoon and into the evening as the frontal boundary moves over the region. In the wake of the cold front, dry conditions and cooler temperatures return next week as Canadian high pressure builds in from the northwest. && .NEAR TERM /THROUGH TONIGHT/... 1015 AM Update: Early morning low clouds and fog are beginning to burn off for areas along and east of I-81. Think the clearing will be soon enough to keep severe/flood threat elevated further east. Still looks to be a multi-threat hazard day with an approaching cold front and already warm sector across our eastern areas allowing for amplified instability parameters. Most likely threat will be damaging winds and isolated instances of flooding but cannot rule out large hail or an isolated tornado given the increasing helicity at the lower levels for a brief period later today. Remain weather aware today, especially along and east of the Blue Ridge Mountains. Previous Discussion Follows: A slow moving cold front passing over the forecast area will bring scattered to numerous rain showers and thunderstorms to the forecast area today. Precipitation chances peak this afternoon and will persist into the evening as the cold front moves through. Atmospheric conditions will be similar to yesterday, with CAPE values of 1000-2000 J/kg, bulk shear values 20-30 knots, and lapse rates nearing 6 C/km. The area with more favorable conditions will be similar to yesterday with those east of the Blue Ridge in a slight risk for severe weather. Primary hazards for today will be damaging wind gusts and locally heavy rainfall. A Flood Watch is in effect from 2PM this afternoon through this evening for portions of NE Maryland and portions of the area surrounding DC. Multiple rounds of showers and thunderstorms are possible with some storms capable of producing rainfall rates of an inch or two per hour. Isolated instances of urban flooding could occur along with vulnerable positions being sensitive to flooding given recent rainfall. Precipitation chances decrease overnight as the frontal boundary departs the area. Temperatures will be in the 70s to 80s for most with overnight low temperatures in the 60s to low 70s. && .SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/... Precipitation chances linger on Monday as a surface trough lies to our west and a surface cold front departs offshore. By Monday morning, the aforementioned cold front will be draped over the coast of the Carolinas while a surface trough remains west of the Alleghenies. Precipitation chances peak Monday afternoon, though coverage will generally decrease as the frontal boundary moves farther away. With any convection, there is a marginal risk of severe weather for those south of DC and east of the Blue Ridge. Conditions dry out areawide Monday into Tuesday as surface high pressure builds in from the northwest. Temperatures on Monday will be in the upper 70s to low 80s areawide with higher elevations staying in the mid to upper 60s. Overnight lows will dip into the 50s and 60s areawide. Temperatures will be noticeably cooler on Tuesday with high temperatures in the 70s for most. Overnight lows on Tuesday will dip into the 50s for most with higher elevations dipping into the 40s. && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... Canadian high pressure will gradually build into the region through the end of the work week settling overhead by Friday morning. As a result, dry weather and cooler than normal temperatures are expected. Temperatures will feel more like late September than late August, some 10 degs below normal. && .AVIATION /14Z SUNDAY THROUGH THURSDAY/... Ceilings and visiblities will continue to improve late this morning as low clouds and fog burn off heading into the early afternoon. This afternoon, showers and thunderstorms will lead to sub-VFR conditions as heavy rainfall and gusty winds bring reduced ceilings and visibilities. Highest confidence for TSRA is at KIAD, KDCA, KBWI, and KMTN where there is a slight risk for severe weather. Outside of convection, expected southerly winds blowing 5-10 knots becoming light and variable overnight. Prevailing VFR conditions are expected on Monday, though afternoon showers and thunderstorms could lead to sub-VFR conditions. Winds will be out of the northwest, gusting up to 15 knots. Prevailing VFR conditions continue on Tuesday. No sig wx is expected Wed through Thu. && .MARINE... SCA conditions are likely this afternoon, particularly in the southern portions of the waters. SMWs are possible as strong to severe thunderstorms impact the waters. Primary hazards will be gusty winds,heavy rainfall, and frequent lightning strikes. SCA criteria winds return Monday night into Tuesday. SCA conditions are expected Wed with winds diminishing below SCA Wed evening as high pressure settles in. && .TIDES/COASTAL FLOODING... Minor coastal flooding will continue at all tidal locations through this afternoon`s high tide cycle with water levels receding tonight. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...Flood Watch from 2 PM this afternoon to 8 PM EDT this evening for DCZ001. MD...Small Craft Advisory until 8 PM EDT this evening for MDZ008. Flood Watch from 2 PM this afternoon to 8 PM EDT this evening for MDZ005-006-008-011-013-014-503>508. Coastal Flood Advisory until noon EDT today for MDZ508. VA...Flood Watch from 2 PM this afternoon to 8 PM EDT this evening for VAZ053-054-506. WV...None. MARINE...Small Craft Advisory until 8 PM EDT this evening for ANZ530>534-537>543. Flood Watch from 2 PM this afternoon to 8 PM EDT this evening for ANZ530. && $$ SYNOPSIS...AVS/ADM NEAR TERM...AVS/ADM SHORT TERM...AVS LONG TERM...LFR AVIATION...AVS/LFR/ADM MARINE...AVS/LFR TIDES/COASTAL FLOODING...LFR