Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 131846 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 246 PM EDT Thu May 13 2021 .SYNOPSIS... High pressure will gradually drift eastward from the Midwest today and Friday before reaching the east coast by Saturday. Mostly dry conditions and near seasonable temperatures are expected to continue during this time. A warm front may lift northward towards the area early next week and stall nearby. && .NEAR TERM /THROUGH TONIGHT/...
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An expansive area of high pressure, centered over the Great Lakes, extending across much of the eastern half of the CONUS continues. Aloft, a quasi-split flow continues as a string of shortwave energy slides across our south and east, resulting in some mid-level CU developing across the area that is expected to diminish late tonight. Some showers have developed across southwestern PA. However with a rather large dew point depression, expect conditions to remain dry during this time. Temperatures will remain just slightly below normal for this time of year; in the mid- upper 60s to low 70s for most with 50s in the mountains.
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&& .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/...
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A second piece of shortwave energy will slide across our south Friday as subsidence upstream continues to produce a large surface high across the Midwest. With the upper level jet positioned in a NW to SE orientation across the CWA, yields the potential for multiple waves of shortwave energy to cross the region through Saturday. However, with the aforementioned high to our west slowly traversing eastward during this time, should result in mostly dry conditions continuing throughout much of the weekend. However, cannot fully rule out a spot shower and/or thunderstorm during this time. CAPE values are rather low; ranging between 200-500 J/Kg with unimpressive mid-level lapse rates, forcing, and rather low dew points in conjunction with a lack of significant forcing. Therefore, think the potential for any convective activity is low at this point in time, but non- zero nonetheless. Best potential for any shower activity looks to be mainly during the afternoon hours and along and west of the Blue Ridge. Temperatures Friday will be a smidge higher than today, with highs Saturday reaching the low to mid 70s across the metros and upper 50s to low 60s over the mountains.
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&& .LONG TERM /SUNDAY THROUGH WEDNESDAY/...
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High pressure will relax and slide to the east Sunday. This will allow for a mid-level disturbance from the west and a jet streak aloft to bring a chance of showers and perhaps a thunderstorm or two to the region Sunday afternoon and evening. Highs will be in the 70s. The chance for showers lingers Sunday night and Monday as a weak surface boundary develops and meanders across our southern zones or just to our south. The chance for any thunderstorms seems more probable Monday afternoon with additional daytime heating and the surface boundary nearby. Highs Monday should be in the 70s as well. By Tuesday and Wednesday, the front will have dropped south into the Carolinas as an area of high pressure drops in from the north. Cooler and drier air should accompany the high Tuesday. As the high moves overhead Wednesday before pushing east, a return flow should develop and allow our temperatures on Wednesday to become more average or above average.
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&& .AVIATION /18Z THURSDAY THROUGH TUESDAY/...
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VFR conditions expected to continue across the terminals through the end of the weekend as high pressure maintains control. Although conditions are expected to remain dry during this time, cannot fully rule out the slight chance for an isolated shower and/or thunderstorm Friday and Saturday mainly west of I-95. High pressure will weaken and move east to allow for a chance of showers or perhaps a thunderstorm Sunday. VFR conditions. Any heavy showers could briefly reduce conditions to MVFR. Winds generally south 5 to 10 knots. Slight chance for showers Sunday night. Winds light and variable. A chance for showers and a thunderstorm or two Monday. VFR could become MVFR in heavier showers. Winds southeast 5 to 10 knots Monday.
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&& .MARINE...
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Mostly quiet weather is expected to continue over the waters through the weekend as high pressure slowly moves overhead, before shifting offshore by Sunday. Northerly winds are expected to continue before becoming more southerly on Sunday. Winds should remain below SCA criteria during this time, however cannot fully rule some isolated gusts up to 18 kts. High pressure to our east to allow for a chance for showers and perhaps a rumble of thunder Sunday. Slight chance to a chance for showers and thunderstorms Sunday night and Monday. However, no marine hazards expected at this time Sunday through Monday.
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&& .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...None. && $$ SYNOPSIS...MSS NEAR TERM...MSS SHORT TERM...MSS LONG TERM...KLW AVIATION...MSS/KLW MARINE...MSS/KLW

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