Area Forecast Discussion
Issued by NWS Sterling, VA

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219 FXUS61 KLWX 231825 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 225 PM EDT MON MAY 23 2016 .SYNOPSIS... Upper level low pressure system near Norfolk this afternoon will move northeastward towards New England and the Canadian Maritimes tonight and Tuesday. High pressure over the Midwest today will then slide southeastward into the western Atlantic on Tuesday, where it will remain through the rest of the week. && .NEAR TERM /THROUGH TONIGHT/... Closed upper level low remains stationed near Norfolk VA this afternoon and will slowly lift northeastward through tonight. The breaks of sun that formed today across northern VA, eastern WV, and into MD have allowed for temperatures to rise into the upper 60s and low 70s. The warming, coupled with lingering low level moisture, and cold temperatures aloft under the upper low have led to the development of some instability (seeing ML CAPE values between 300-800 J/KG), and in turn convective showers and a few thunderstorms. Severe weather is not expected, but with low freezing heights (7000-8000 feet AGL), could see some gusty winds and small hail in any of the stronger storms. Showers and a few thunderstorms will persist through the evening, but will decrease in coverage and intensity after sunset. Will also begin to see more clearing working into the region. This combined with lingering low level moisture and wet soils will lead to the development of some patchy fog across the area as temperatures cool. There will be some wind remaining in the boundary layer, so that and some lingering clouds should preclude a more widespread dense fog situation. Will see lows in the 50s for most, with some 40s north/west. && .SHORT TERM /TUESDAY 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 SUNDAY/... 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 /18Z MONDAY THROUGH SATURDAY/... VFR at most sites at most times through the rest of today and into this evening. Have seen the development of scattered showers and a few thunderstorms which may lead to brief reductions to MVFR/IFR at times this afternoon and into the evening. Later tonight, as showers end and skies begin to clear, may see the development of some patchy fog and Sub-VFR conditions. Will show with a 5-6SM and BR for now, as coverage and density is questionable with amount of cloud cover and residual winds in the boundary layer. 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. && .MARINE... Winds locally variable and less than 10 knots this afternoon and evening with scattered showers and few thunderstorms, which may create some isolated gusts to 20 knots. Plan to cover with Marine Weather Statements for now. Winds will increase out of the west/northwest Tuesday around departing low, but should stay below SCA criteria. 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. && .TIDES/COASTAL FLOODING... 12Z ESTOFS indicates potential for minor coastal flooding at Annapolis Tuesday morning. High tide there is at 746 AM. Big discrepancy between ESTOFS and ETSS surge but ESTOFS initialized much better. && .CLIMATE... 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 noon on the 23rd): 5.12" 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 noon on the 23rd): 4.48" 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 noon on the 23rd): 5.62" && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...None. && $$ SYNOPSIS...MM NEAR TERM...MM SHORT TERM...MM LONG TERM...MSE AVIATION...MM/MSE MARINE...MM/MSE TIDES/COASTAL FLOODING...LFR CLIMATE...DFH

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