Area Forecast Discussion
Issued by NWS Sterling, VA

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699 FXUS61 KLWX 240114 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 914 PM EDT MON MAY 23 2016 .SYNOPSIS...
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Upper level low pressure off the Mid-Atlantic coast this evening will move northeastward towards New England overnight through Tuesday and then toward the Canadian Maritimes Tuesday night. High pressure will build overhead Wednesday before settling over the western Atlantic Thursday through Monday.
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&& .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
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Upper-level low pressure continues to spin just off the Delmarva Peninsula this evening. Convection this afternoon has dissipated due to the loss of daytime heating. However...shortwave energy aloft continues to rotate around the upper-level low so clouds and a few showers will continue through this evening. Coverage will be isolated or widely scattered since instability has diminished. The upper-level low will gradually shift northeast toward New England overnight. Drier air will move in from the north behind this system...allowing for clearing skies and mainly dry conditions overnight. An isolated shower cannot be ruled out east of the Blue Ridge Mountains...but any precipitation will be light and most of the time will be dry. Will see lows in the 50s for most, with some 40s north/west.
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&& .SHORT TERM /6 AM TUESDAY MORNING THROUGH WEDNESDAY NIGHT/... Upper low will continue pulling away on Tuesday, and we will see drier air wrapping in behind it. This should lead to more sun than today with some scattered instability cumulus and some cirrus. Could also see an isolated instability shower or sprinkle, but coverage will be spotty at best. Temperatures will be much warmer than recent days with highs in the upper 70s to around 80 degrees. Upper ridge builds into the region on Wednesday ushering in more summer-like weather. The surface high will slide south of the region, allowing for a warm southerly flow to develop. Wednesday should remain dry for much of the region with highs in the 80s area-wide. With dew points hovering in the 50s, should be quite nice, with relatively low humidity. Not expecting much in the way of shower/thunderstorm activity either, except for an isolated one or two possible in the mountains as a weak ripple moves through aloft. && .LONG TERM /THURSDAY THROUGH MONDAY/... Summer-like pattern begins Thursday, with Bermuda high promoting warm/moist advection across the Mid-Atlantic. Increasing moisture will lead to typical summertime diurnal thunderstorm activity Thursday and Friday, with the best chances over the higher terrain and fairly low chances east of the Blue Ridge. While instability will be in the moderate range during peak heating, rather anemic wind field keeps effective bulk shear generally less than 20 kts, suggesting pulse-type thunderstorms. Highs Thursday and Friday generally in the M/U80s, though a few 90s are possible, especially in areas bereft of thunderstorm activity. Mid-level heights begin to rise Saturday, which leads to poor mid- level lapse rates. As such, guidance has really backed off on QPF Saturday. Model spread increases by Sunday, so will take a blended approach for now until better agreement can be reached. && .AVIATION /01Z TUESDAY THROUGH SATURDAY/...
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VFR at most sites at most times through this evening. Recent rainfall and light winds along with clearing skies will allow for patchy fog to develop. Do feel that there should be just enough of a gradient wind to keep widespread fog from developing. However...MVFR vsbys are likely overnight. IFR conditions cannot be ruled out...but confidence is to low to put in the forecast at this time due to the light gradient wind. VFR returns Tuesday and should persist for most through at least Wednesday night. Winds will be light (less than 10 knots) and generally west/northwesterly through tonight and into Tuesday. Some gusts up to about 15 knots likely Tuesday afternoon. Light southwest flow then develops by Wednesday. While most of Thursday through Saturday will end up VFR, a few afternoon thunderstorms are possible.
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&& .MARINE...
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Winds will shift to the northwest tonight but speeds should remain below sca criteria. It may be close overnight into early Tuesday morning for middle portions of the bay and the lower tidal potomac river...but gusts have been capped at 15 knots for now due to a light gradient. Winds will continue out of the west/northwest Tuesday around the departing low with gusts around 15 knots expected. Southwest winds then develop Wednesday, but should also remain sub- SCA. While flow remains sub-SCA, a low chance of an afternoon thunderstorms exists over the waters Thursday and Friday.
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&& .TIDES/COASTAL FLOODING...
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CBOFS and 12 ESTOFS indicates potential for minor coastal flooding at Annapolis Tuesday morning. ETSS has water levels well below flooding criteria. Leaned the forecast closer to the ETSS this evening. Latest levels are running closer to the ETSS...and an offshore flow is expected with the low moving away from the area overnight into Tuesday.
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&& .CLIMATE...
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We put together some records (preliminary) of how this month compares to rainy Mays on record for our area. Washington, DC (records since 1871) Most days in May with at least a trace: 25 (in 1952 and 1943) So far in 2016 (through the 23rd): 19 Most days in May with at least 0.01": 20 (in 2003) So far in 2016 (through the 23rd): 18 Highest May monthly rainfall: 10.69" (in 1953 and 1889) So far in 2016 (through 4 PM on the 23rd): 5.13" Baltimore, MD (records since 1870) Most days in May with at least a trace: 25 (in 2003) So far in 2016 (through the 23rd): 19 Most days in May with at least 0.01": 21 (in 1882) So far in 2016 (through the 23rd): 15 Highest May monthly rainfall: 8.71" (in 1989) So far in 2016 (through 4 PM on the 23rd): 4.61" Dulles, VA Most days in May with at least a trace: 23 (in 2003) So far in 2016 (through the 23rd): 20 Most days in May with at least 0.01": 21 (in 2003) So far in 2016 (through the 23rd): 16 Highest May monthly rainfall: 10.26" (in 2009 and 1988) So far in 2016 (through 4 PM on the 23rd): 5.62"
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&& .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...None. && $$ SYNOPSIS...MM NEAR TERM...BJL/MM SHORT TERM...MM LONG TERM...MSE AVIATION...BJL/MM/MSE MARINE...BJL/MM/MSE TIDES/COASTAL FLOODING...BJL CLIMATE...DFH

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