Area Forecast Discussion
Issued by NWS Sterling, VA

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298 FXUS61 KLWX 251108 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 708 AM EDT Thu Aug 25 2016 .SYNOPSIS... High pressure remains over the region today. A cold front will cross the region on Friday. High pressure will return for the weekend. Another front may slowly slide southward into the area by the middle of next week. && .NEAR TERM /THROUGH TONIGHT/... High pressure is offshore this morning, extending to the southern Appalachians. Decaying convection is moving into the upper Ohio Valley. The remnants of the convection and associated vort max has led to some timing changes in the forecast, albeit minor due to high uncertainty. Some showers may reach the northern Potomac Highlands shortly after daybreak, generally dissipating as they continue eastward. Despite the diurnal minimum, some showers may survive in an environment of theta-e advection/isentropic lift. Diurnal convection along the terrain which was originally forecast, may be minimized in the wake of the vort max, which will skim the northern part of the area. It may be difficult for much to develop toward the I-95 corridor due to lessening instability and the building upper level ridge. Decaying convection originating from near Lake Erie may make a run at the northern Potomac Highlands late this evening, but should have a difficult time making it into our area. In summary, convection may have more of a nowcasting component today, but definitely lowering chances with SE extent across the area. Otherwise, expect a good bit of cirrus originating from the convection, at least for the first part of the day. This may take a slight edge off temperatures, but locations from DC/CHO east have a reasonable shot at 90F. Dew points will also be rising into the lower 70s. For tonight, those higher dew points will prevent many from falling below 70F. && .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... Weakening cold front will be sliding south across the area on Friday. There`s not a whole lot of airmass change with the front, but its timing (of which there is some spread in guidance) could have a role in temperature/dew point trends on Friday, as the flow will be more northwesterly behind the front. Lower to mid 90s should be common though. Heat indices will be in the 100-105 range east of the Blue Ridge. Although there will be some weak confluence along the boundary, there will be a lack of deep moisture, and the strengthening mid/upper ridge will help put a cap on convection. Have removed mentionable POPs except over the southern terrain. After the front slides to our south and largely dissipates, high pressure will build to the north. The northerly low level flow will knock a few degrees off the temperature and dew point, because otherwise, the mid and upper level ridge will nearly be centered over VA. Above average temperatures and dry weather expected. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... Guidance remains in relatively good agreement in the long term. Sunday morning a ridge of high pressure aloft will be sitting squarely over the region. A weak shortwave passing to the north will weaken the high a bit on Monday but it will remain over the region. Another shortwave may then slowly slide southward into the area by Wednesday...possibly accompanied by a weak cold front. While we will start mostly dry early Sunday with the surface high sliding to the northeast...increasingly southerly flow will promote moisture advection which will help some terrain convection going. This will be aided by the weak disturbance and front by Wednesday. This so far ignores any potential impacts of any tropical systems which various pieces of guidance are depicting impacting the United States. Uncertainty becomes very high as we head into the middle of next week. && .AVIATION /11Z THURSDAY THROUGH MONDAY/... Increasing high clouds this morning, which should put a damper on fog, although MRB is nearing its dew point. Today`s forecast is somewhat uncertain in regards to convection, as activity currently over Ohio should diminish as it crosses the mountains, although a few showers could survive, especially to MRB. Very little storms may redevelop however, and ones that do should be isolated. Mention will not be included in the TAFs at this time. Due to possibility of cloud cover and a light wind, fog formation for tonight is also in question. A weak front will slip through the area on Friday, with little more than a wind shift. While a rogue storm can`t be ruled out, it`s a very low probability. VFR conditions expected Saturday with high pressure to the north. Mainly VFR in the long term. && .MARINE... Southerly channeling continues on the waters with occasional 20 kt gusts. Hi-res guidance indicates that although there may be a lull this morning, winds may strengthen again by afternoon. Thought the simpler message would be to carry the SCA through the day and evening. Gusts will be last to subside on the southern waters late tonight. A weak front will slide through on Friday. Flow will gradually veer through Saturday, eventually becoming E, as high pressure moves to the north. At this time, sub-SCA conditions expected. Winds mainly sub SCA in long term. && .TIDES/COASTAL FLOODING... Increased southerly flow will cause water levels to rise today. By tonight, caution stage will be reached at several sites on the Bay. Annapolis could approach minor flood, although not all guidance sources support that solution. Winds will become west on Friday, so there should not be a concern beyond the Thursday night cycle. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory until 2 AM EDT Friday for ANZ531>533- 539>541. Small Craft Advisory until 6 AM EDT Friday for ANZ534-543. && $$ SYNOPSIS...RCM NEAR TERM...ADS SHORT TERM...ADS LONG TERM...RCM AVIATION...ADS/RCM MARINE...ADS/RCM TIDES/COASTAL FLOODING...RCM

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