Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 201359 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 959 AM EDT FRI MAY 20 2016 .SYNOPSIS... High pressure will retreat to the northeast this afternoon. Low pressure will track east across North Carolina tonight before turning up the Mid-Atlantic coast Saturday. Upper level low pressure will persist along the Mid-Atlantic coast Saturday night through Monday night. High pressure returns Tuesday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Going forecast in good shape, and relatively few changes needed to the forecast. On the whole, a quiet day is expected as the high moves toward the northern Mid-Atlantic coast. Mid and high level clouds will be increasing by afternoon ahead of a low pressure system in the TN Valley. These clouds have already reached the Potomac Highlands. Any chance should hold off until after mid- afternoon. There should be enough sun for most of the area to push into the 70s, although clouds may restrict temperatures to the south. && .SHORT TERM /6 PM THIS EVENING THROUGH SUNDAY NIGHT/... As mid/upper level trough pushes east tonight into Saturday, energy will transfer to a coastal low which will lift NE up the Mid- Atlantic seaboard. A SE low level jet will inject a tongue of higher PWs tonight into early Saturday. Still looking at a swath of moderate to locally heavy rain to push across the area, although it may not make it to the metro areas until around daybreak Saturday. Hydro concerns are minimal -- see section below. There may be some breaks, or at least lightening, of the rain Saturday afternoon, but wrap-around moisture will at least make for some off and on rain or drizzle. Temperatures will struggle to rise much, possibly failing to reach 60F in many places. Saturday night into Sunday will continue to be unsettled with the upper level system closing off over the area. There may be an embedded disturbance which enhances shower chances Saturday night. On Sunday, the showers may take on more of a diurnal flavor with the upper low directly overhead. Have not added thunder at this point as instability doesn`t look deep. Knocked a degree or two off highs for Sunday (mainly upper 60s now) as cloud cover may win out at times, especially by afternoon. The low will inch eastward Sunday night, so have a gradual decreasing of shower chances. Minimum temperatures don`t change much through the period...upper 40s to lower 50s. && .LONG TERM /MONDAY THROUGH THURSDAY/... Deep upper level low pressure will remain over the area Monday. It will only very slowly shift northeastward away from our area Monday night and Tuesday. Upper level ridging will gradually become dominant Wednesday and Thursday. At the surface, this means low pressure will remain to the east on Monday but cold air aloft will result in showers and perhaps even a thunderstorm. As the system shfits northeast Tuesday, warming temperatures aloft combined with convergence in the wake of the system and building high pressure will result in a dry day. Wednesday looks like it will remain mostly dry. By Thursday, a front will approach from the west, heights may drop a bit, and we may end up getting some instability showers or thunderstorms especially over the mountains. Monday will remain cooler than normal with the upper low overhead. By Tuesday, temperatures will return to normal, while Wednesday and Thursday should exceed normal by several degrees. && .AVIATION /14Z FRIDAY THROUGH TUESDAY/... VFR with light winds today as the high moves east. Clouds increase and lower tonight in advance of low pressure system. Expect a swath of moderate to perhaps heavy rain late tonight into Saturday morning. Would expect a period of IFR conditions. There may be some improvement Saturday afternoon, but showers and low cigs will remain in the area through Saturday night and possibly Sunday with N to NE flow. Any showers should taper off by Sunday night. Sub-VFR conditions remain possible Monday with the upper low nearby and showers around. VFR should dominate Tuesday with dry weather returning. && .MARINE... Light E to SE flow today as high pressure moves offshore. Rain overspreads the area late tonight into Saturday which will inhibit mixing, but as low pressure moves offshore, gradient will be strong enough for SCA conditions. Have hoisted the SCA starting late tonight for the southern waters, then for all waters during the day Saturday. This may need to be extended for portions of the waters Saturday night. N to NW flow now looks to stay 15 kt or less for Sunday and beyond. && .HYDROLOGY... Period of moderate to heavy rain has the potential to bring 1-2 inches of rainfall to the area, with the highest amounts focused on the southern CWA. This will not be a convective (1hr FFG) type of event, and would probably need at least 1.5 inches in 3 hours to begin hydro concerns. Certainly not out of the question and will need to be monitored, but the rain may be just spread out enough to preclude any major issues. Ensemble mean of MMEFS keeps all river points below flood stage, so small streams and urban areas will be the places to watch. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory from 8 AM to 6 PM EDT Saturday for ANZ530>533-535-536-538>541. Small Craft Advisory from 4 AM to 6 PM EDT Saturday for ANZ534- 537-542-543. && $$ SYNOPSIS...RCM NEAR TERM...ADS/HTS SHORT TERM...ADS LONG TERM...RCM AVIATION...ADS/RCM MARINE...ADS/RCM HYDROLOGY...ADS

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