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Area Forecast Discussion
Issued by NWS Sterling, VA
Issued by NWS Sterling, VA
267 FXUS61 KLWX 150120 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 920 PM EDT Wed Aug 14 2024 .SYNOPSIS... Quiet weather conditions are expected through Thursday before precipitation chances return with a slow moving low pressure system Friday into the weekend. A cold front will cross the region late Saturday into Sunday bringing the highest probability for showers and thunderstorms.This system exits off the coast Monday into Tuesday with high pressure set to return to the region by the middle of next week. && .NEAR TERM /THROUGH TODAY/... Smoke from Canadian wildfires continues to filter through the forecast area with levels expected to decrease overnight. Isolated showers are filtering south from PA so PoPs were increased to account for an isolated shower in NE Maryland. Otherwise, no changes were made to the forecast with mostly dry and mild conditions expected to continue. Previous Discussion follows: Upper level troughing will continue to exit off the Atlantic coast today while broad high pressure builds eastward from the Great Lakes region. Tranquil weather conditions are expected as a result with less cloud cover (stratocumulus) and low humidity. Highs today will rise into the low to mid 80s east of the Alleghenies with 70s along the higher ridges. One thing to note will be some Canadian wildfire smoke in the mid to upper troposphere. This smoke is evident on the GOES GeoColor this afternoon with a subtle band dropping south through northern and central MD. High-resolution smoke guidance also picks up on this with northerly flow carrying this elevated smoke plume through the area mid to late afternoon. Consequently, have opted to put haze in the forecast grids for areas along and east of U.S. 15 through at least sunset. While this could impact locations to the west, confidence was not high enough to do so. Smoke is unlikely to affect the surface, although some minor reductions in visibility (6- 8SM) are possible throughout the afternoon period. High pressure will rule the forecast tonight with plenty of subsidence overhead. Looking like a good radiational cooling set up with mainly clear skies and calm winds. This will allow temperatures to fall into the low to mid 60s east of the Blue Ridge with 50s west. Mountain and high valley locations could fall back into the 40s. Patchy river/valley fog is possible heading into daybreak Thursday. && .SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... One more day of quiet weather is expected Thursday as broad longwave ridging sits nearby. Humidity will remain low with light north to northwesterly flow for much of the day before the low level flow turns to the south Thursday night into Friday as surface high pressure slides offshore. Skies will trend mostly sunny to start with increasing clouds late in the afternoon and evening as a warm front moves toward the region from the Upper Midwest and Ohio River Valley. With persistent north to northwest winds expect low humidity to remain with dewpoints in the upper 50s and low 60s. High temperatures Thursday will push into the mid to upper 80s east of the mountains with metro areas potentially touching 90 degrees. Mountain locations will be a tad cooler in the mid to upper 70s and low 80s. Shower and thunderstorm chances return from the west Friday as longwave troughing over the Great Lakes advances east and a surface warm front lifts in from the Ohio River Valley. Ahead of this system expect increasing clouds with broad ascent and height falls slowly spreading across the Mid-Atlantic region. Meanwhile, high pressure will continue to kick off the New England coast allowing for increasing moisture from southerly low level flow. The added moisture combined with the associated warm front will lead to increased chances for scattered shower and thunderstorm activity starting west of the Alleghenies as early as Thursday night before spreading east toward the Blue Ridge Friday afternoon. Current 12z deterministic and ensemble guidance continues to hold this activity mainly west of I-95 through Friday evening with the bulk of widespread precipitation chances coming through during the late evening and overnight hours. As for severe weather, the threat remains low ,but will need to watched given a warm front lifting into the region. The flooding threat remains very low given several days of dry weather leading up to this event combined with current drought concerns. High temperatures Friday will remain near normal in the mid to upper 80s east of the mountains with 70s over the mountains. && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... An upper trough will continue to drop further south into the area Saturday as an associated warm front lifts further north. Increasing chances for showers and thunderstorms will be apparent for at least the early portion of the weekend. Given the warm sector, increased instability and flow, there may be a chance for strong to severe thunderstorms Saturday afternoon and evening. Main threats would be damaging winds and isolated instances of flooding. Afternoon highs will be in the upper 80s for most of the lower elevations, with mid 70s more common across the mountains. Timing of the cold front remains uncertain with this system, therefore there may be some areas that remain in the warm sector through Sunday mid-morning. Showers and thunderstorm chances remain in place for the afternoon and evening hours especially. Precipitation chances linger into the early part of the work week next week with highs on Monday remaining seasonable. High pressure builds in by Tuesday into the middle part of next week. && .AVIATION /01Z THURSDAY THROUGH MONDAY/... Prevailing VFR conditions are likely at all terminals through Friday midday. Some elevated smoke may impact terminals mainly east of the Blue Ridge mountains this afternoon and evening as northern Canadian wildfire smoke funnels south on light northerly flow. No large visibility reductions are expected with vsbys running between 5-8 SM (due to haze). Northerly winds are expected for the remainder of the afternoon with gusts 15 to 20 kts. Winds will turn light and variable overnight into Thursday as high pressure settles overhead. By Thursday night, winds will switch to the south as high pressure pushes toward the New England coast. VFR conditions will prevail although SCT-BKN mid and high level clouds will increase across the region. These clouds are in association with a longwave trough of low pressure and surface warm frontal boundary that will lift into the area Friday. Showers and thunderstorms will accompany this boundary at terminals west of the Blue Ridge Friday afternoon before spreading eastward into the corridor Friday evening and Friday night. This will lead to intermittent periods of sub-VFR conditions especially within the Friday evening and night timeframe when the bulk of the precipitation is expected to move through. Winds Friday will remain out of the south with gusts up to 15 kts. Sub-VFR conditions are possible Saturday and Sunday as showers and thunderstorms potentially impact the terminals during the afternoon and evening hours especially. Outside of these, VFR conditions will persist. && .MARINE... No marine hazards are expected through Friday morning as surface high pressure slowly slides east of the area. Light north to northwest winds are expected Thursday switching to the south Friday. Gusts of 10-15 kts can be expected each afternoon. SCA level winds may return as early as Friday afternoon and night due to southerly channeling. Additionally, showers and few thunderstorms may also impact the waters by late Friday. SCA conditions are becoming increasingly likely Saturday as a pressure gradient increases across the waters. Lower winds are expected Sunday as the front moves east of the waters. Cannot rule out an SMW for the waters with any strong to severe thunderstorms that impact the waters. && .TIDES/COASTAL FLOODING... Light north to northwest flow under broad high pressure will lead to sensitive tide sites (i.e Havre de Grace, Annapolis, and DC Waterfront) remaining near action stage during the next 3 high tide cycles (through Friday morning morning). Winds will turn to the south late Thursday into Friday allowing water levels and anomalies to increase later this week and into the weekend. As a result, some sensitive locations may approach Minor flooding. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...None. && $$ SYNOPSIS...EST NEAR TERM...AVS/EST SHORT TERM...EST LONG TERM...ADM AVIATION...BRO/ADM/EST MARINE...ADM/EST TIDES/COASTAL FLOODING...