Area Forecast Discussion
Issued by NWS Sterling, VA

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394 FXUS61 KLWX 171911 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 311 PM EDT Wed May 17 2017 .SYNOPSIS... High pressure will remain near Bermuda through Friday. A cold front will pass through the area late Friday into Friday night before stalling well to our south on Saturday. The boundary will return north as a warm front Sunday before a stronger cold front from the west passes through Monday into Monday night. High pressure may briefly return for Tuesday. && .NEAR TERM /THROUGH TONIGHT/... Satellite observation at 19z shows a cumulus field developing on and west of the Blue Ridge. The surface dewpoint depression is very high, in some places nearly 30 degrees. So a lack of moisture will be a limiting factor in convective development this afternoon. 16Z RAP at KIAD has CAPE about 1500 j/kg, but with weak shear and still some CINS. Contrary to this, both the HRRR and NCAR Ensemble convective allowing models forecast an area of showers and thunderstorms across north central Virginia into central Maryland between 3 PM and 8 PM. So have a slight chance of thunderstorms between these times for the remainder of the afternoon. A warm night tonight, with overnight min temps about 10 degrees above normal. Models develop a nocturnal 35-40kt jet at 950 mb in response to the contrast between the cold Atlantic and the warm air mass in place. However, inversion should quickly setup and not allow much of this wind to translate to the surface. && .SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... Thursday will start out much like today, but with surface dewpoints increasing 5-10 degrees above today, expecting more of an afternoon cumulus field. MAV guidance has decreased max temps by a couple of degrees for tomorrow, but still expecting 90F+ in most areas. Have used BCONSALL for guidance for both Thursday and Friday. Once again, without a forcing field, not expecting too much in the way of convection except perhaps terrain based circulations causing localized storms. Friday looks to have a good chance of showers and thunderstorms as a cold front drops through the region right about peak heating. Models CAPES are around 1000-1500 j/kg but only 20 kts of 0-6km shear, so expecting mainly non-severe day and evening. && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... Ridging aloft will persist over the area as high pressure wedges in from the northeast at the surface Saturday. The cold front that is forecast to cross the area from north to south at the end of the week will stall near the VA/NC border during this time, then return slowly north as a warm front by late Sunday. A broken overcast is likely over the weekend with easterly flow off the ocean. This will result in cooler temperatures closer to normal for this time of year (highs in the 70s, lows in the 50s). Despite the clouds, precipitation chances should be minimal over the weekend. Models continue to oscillate with regards to the timing of frontal passage on Monday. This front will bring the next chance of showers and possibly thunderstorms, but convective potential will rely heavily 1) on the exact timing of frontal passage, and 2) the amount of cloud cover/cloud debris from prior day`s convection over the Midwest. Moisture and shear both increase along/ahead of the cold front/shortwave driving it so storms that do develop will have the potential for organization if there is enough instability present. Behind the front, a slightly cooler/noticeably drier airmass will move in for later Tuesday into Wednesday of next week. && .AVIATION /18Z WEDNESDAY THROUGH MONDAY/... Sub-VFR psbl at times over the weekend w/ lower CIGS in moist ELY flow 10-15 kts. && .MARINE... Small Craft Advisory conditions may continue for portions of the waters over the weekend in easterly flow between high pressure to the north and a stalled front to the south. && .CLIMATE... Unusually hot conditions are expected today and Thursday. Record heat is possible during this time. Below are the record highs and high low temps for today through Thursday night... May 17th and 18th. Today`s (5/17) Record Highs: DCA: 92 in 1974, 1896 and 1877 BWI: 93 in 1896 IAD: 89 in 1986 Thursday (05/18) Record Warm Lows: DCA: 72 in 2015 BWI: 68 in 1900 and 1896 IAD: 68 in 2015 Thursday (05/18) Record Highs: DCA: 96 in 1877 BWI: 97 in 1962 IAD: 91 in 1987 && TIDES/COASTAL FLOODING... .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory from 6 PM this evening to 10 AM EDT Thursday for ANZ531>534-537-539>541-543. Small Craft Advisory until 7 PM EDT this evening for ANZ535- 536. && $$ SYNOPSIS...BJL NEAR TERM...Lee SHORT TERM...Lee LONG TERM...DFH AVIATION...Lee/DFH MARINE...Lee/DFH CLIMATE...DFH is the U.S. government's official web portal to all federal, state and local government web resources and services.