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Area Forecast Discussion
Issued by NWS Sterling, VA
Issued by NWS Sterling, VA
101 FXUS61 KLWX 151927 CCA AFDLWX Area Forecast Discussion...CORRECTED National Weather Service Baltimore MD/Washington DC 327 PM EDT Thu Aug 15 2024 .SYNOPSIS... Dry weather conditions are expected through tonight as the result of broad high pressure nearby. Shower and thunderstorm chances return Friday as a warm frontal boundary lifts in from the Ohio River Valley. Additional shower and thunderstorm chances are likely this weekend with a cold front slowly crossing the region. Shower chances will linger into Monday before cool Canadian high pressure builds in by the middle of next week. && .NEAR TERM /THROUGH TONIGHT/... A fair weather cumulus deck has settled over the area with dry conditions continuing through the remainder of the day and into tonight. Highs are topping out in the mid to upper 80s for areas east of the Allegheny Front (mid 70s more common). Surface high pressure will slowly move further east offshore later today and into tonight, allowing a southerly flow to build in overnight and into Friday morning. Overnight lows will drop down into the upper 50s across the Allegheny Front, with 60s further east. && .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... 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 be 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. By Saturday, activity should become more widespread as the warm front will have lifted further north and ushered in a warmer, moist airmass to work with. Showers and thunderstorms will be most common for the afternoon and evening hours. Some storms may be strong to severe but it is really going to be dependent on the timing of a cold front expected to slowly approach the area later in the day on Saturday. Should the timing not match up with peak heating, severe chances diminish. As of now, there should be enough instability around to spawn a few strong storms later in the day. Highs will climb into the mid to upper 80s for the afternoon and evening hours. Precipitation chances will likely continue into Saturday night as the front slowly moves through the Mid-Atlantic going into Sunday. Overnight lows will drop down into the 60s west of the Blue Ridge, with low 70s more common further east. && .LONG TERM /SUNDAY THROUGH THURSDAY/... 1) Continued precipitation chances Sunday and Monday as a slow moving cold front and trailing shortwave trough slide east. 2) Near to slightly below normal temperatures expected through the extended period. Synoptically, not too much of a change as we continue to monitor a slow moving occluded frontal system cross the region. Meanwhile, eyes will turn toward the Atlantic as Hurricane Ernesto works its way northward from Bermuda. The upper-level trough overhead and slow moving front will help steer Ernesto away from our region and off the East Coast heading into early next week. One indirect effect will be for those traveling to the beaches where waves and rip currents will likely increase Sunday into the middle part of next week. With the front slow to cross the region Sunday expect continued chances for showers and thunderstorms. No washouts are expected with a focus during the afternoon and evening hours. Outside of the precipitation chances mostly cloudy skies are expected leaving high temperatures east of the Alleghenies in the upper 70s and low to mid 80s. Shower activity will likely linger along and east of US-15 and toward the I-95 metros through Sunday night as the front is slow to progress toward the coast. It`s not until Monday when the front pushes offshore. Some additional shower and thunderstorm chances may linger into Monday as the upper-level trough swings through. Once again the focus will be during the afternoon and evening hours starting in the west and progressing eastward throughout the day. Skies will remain mostly cloudy with clearing skies late as the trough exits east of the area. High temperatures Monday will push back into the mid to upper 80s east of the Alleghenies with lows in the 50s and 60s. Winds will switch to the west and northwest in the wake of the departing trough Monday afternoon and evening. A broad area of Canadian high pressure looks to settle over the region Tuesday through Thursday leading to dry conditions and lower humidity. Most locations will see high temperatures in the upper 70s to low 80s which comes with dew points in the mid 50s to low 60s. Overnight lows should fall into the upper 50s to mid 60s. For those along the I-81 corridor and points westward, widespread low/mid 50s are possible (upper 40s along the Allegheny ridges). Next chance for rain comes late next week into next weekend as another front approaches the region. && .AVIATION /18Z THURSDAY THROUGH TUESDAY/... VFR conditions are expected through Friday. Light north- northwest flow today shifts southerly later tonight into Friday as surface high pressure slides east. Rain chances increase west to east on Friday, but precip likely doesn`t reach any of the main terminals until Friday evening or later. Winds could gust 15-20 kts Friday afternoon. Showers and thunderstorms are expected Saturday behind a warm front and ahead of an approaching cold front, particularly in the afternoon and evening. Similar to Friday, these could bring restrictions to terminals, and gusts to 15-20 kts are possible outside of thunderstorms before winds diminish overnight. Shower and thunderstorm chances look to continue Sunday and Monday as a slow moving cold front pushes through. This will lead to additional sub-VFR restrictions at times especially during the afternoon and evening hours when convection looks to peak. Outside of the precipitation/thunderstorm threat, VFR conditions will persist. Southerly winds with gusts up to 15 kts are possible Sunday switching to the west and northwest Monday and Tuesday as the front/upper-level trough exits offshore. && .MARINE... Light north-northwest winds over the waters today will turn southerly tonight into Friday as surface high pressure slides east. Winds increase out of the south on Friday and could reach SCA criteria by the afternoon hours. Winds diminish slightly overnight Friday but could still hover around SCA criteria, especially over the southern waters. SCA conditions continue through Saturday afternoon and evening. Additionally, showers and thunderstorms possible Friday and Saturday could bring stronger gusts to the waters. Stronger storms could require Special Marine Warnings on Saturday. Additional SCAs may be needed into Sunday as southerly channeling looks to linger. The highest confidence for this will be over the central and southern waters. Winds will decrease Monday while switching to the west and northwest. SCAs may be needed Monday night into Tuesday as the gradient tightens between the exiting trough and incoming high pressure system. Shower and thunderstorm chances loom through early next week, with the greater coverage of storms likely on Sunday with the cold front just off to the east. Thus, some hazardous conditions are expected over the waters at times through Monday. && .TIDES/COASTAL FLOODING... With high pressure over the area, light north to northwesterly winds will persist today. This keeps sensitive tidal sites (i.e., Havre de Grace, Annapolis, and D.C. Southwest Waterfront) near Action stage during high tides (especially the early morning higher astronomical tide) through Friday morning. Expect an additional boost of the tidal anomalies as winds shift to southerly late tonight, continuing through Friday and into the weekend. At this point, the forecast carries locations like Havre de Grace and Annapolis into Minor coastal flooding by Saturday morning. This threat likely persists further into the weekend with continued southerly winds along and ahead of the approaching cold front. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...None. && $$ SYNOPSIS...EST NEAR TERM...ADM SHORT TERM...ADM/EST LONG TERM...EST AVIATION...ADM/EST MARINE...ADM/EST TIDES/COASTAL FLOODING...LWX