Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 292158 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 558 PM EDT SUN MAY 29 2016 .SYNOPSIS... Tropical Depression Bonnie will linger along the Carolina coast line through the first part of this week while an upper level trough will track north of the area through Monday. High pressure briefly builds in before a surface boundary impacts the region Tuesday. High pressure returns for the second half of the week with a cold front moving through late in the week. && .NEAR TERM /THROUGH MONDAY/...
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Update...a plume of moisture has emerged, positioned from King George Co. spreading northward toward Baltimore City. In this axis, widespread 1 in + seems likely. Precipitable water at BWI forecast to rise to 2 inches by early this evening. Radar has been underestimating thus far based on automated gauges near King George. Therefore, more areas of 3 or 4 inches in a couple hours plausible. With that in mind, opted to issue a Flash Flood Watch in this corridor. Heavy rain may spread west of there (as is happening now), but the duration component to cause concern seems to becoming concentrated along/east of I-95. Previous Discussion... Bonnie remains down along the South Carolina coast with moisture streaming to the north from the system. Please refer to the NHC for official forecasts. Rain impacting portions of the western CWA this afternoon and is timed to reach southern fringes of the area by 3 pm. Upper lvl trough is noted on water vapor imagery over the western Great Lakes region, which will aid in the placement of the moisture advection from the tropical system up across the Mid- Atlantic as it approaches from the west, producing a narrow conduit for the moisture in combination with the ridge sitting just to the east of us. As such, still anticipating more widespread rains to move in late this afternoon and into tonight, with latest hi-res model runs showing the best chance for moderate to periods of heavy rain coming this evening and then again late tonight mainly east of the Blue Ridge. While 1-2 inches of rain is expected, thinking that it will mostly occur over a temporal period that will keep flash flooding threats to a minimum. The main flooding concerns will be the typical urban, low lying areas.
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&& .SHORT TERM /MONDAY NIGHT THROUGH TUESDAY NIGHT/... The previously mentioned upper level trough will pass to the north Monday with ridging persisting just off shore. Energy associated with Bonnie will split off from the main area of low pressure and round the western fringe of the ridge, getting caught up with the passing trough and move through the Mid-Atlantic during the day. This will act as a trigger for afternoon convection across the CWA Monday with plenty of moisture and warmth leading to increased instability. Shear still on the weaker side so thinking it will just be another day of pulsey thunderstorms for areas west of the I-95 corridor. To the east where the bulk of the upper level forcing looks to align will be more persistent showers with embedded thunderstorms. Monday night ridging from the west begins to build in as high pressure returns at the surface. The precip will begin to taper off from west to east with the building subsidence. Many areas will see dry weather on Tuesday, though showers will be possible central Virginia into southern Maryland depending on how far north the remnants of Bonnie push. 12Z guidance is keeping these remnants to the south on the Carolina coast through midweek so not anticipating the precip to push much further north/west. && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... Low pressure over the North Carolina coast will slowly move north- northeast along the Mid-Atlantic coast Wednesday into Thursday. Moisture advection will allow for showers and thunderstorms for both days... but it will mainly depend on location of the low pressure system. Slow moving cold front will approach from the west late on Thursday into early Friday... and move across our CWA later on Friday. Front will stall through Saturday to our east as upper trough over the Great Lakes pushes east. These systems will allow for a continued pattern of showers and thunderstorms through the end of this period. High temperatures will be in the upper 70s and low to mid 80s... and low temperatures in the 50s and 60s. && .AVIATION /22Z SUNDAY THROUGH FRIDAY/... VFR conditions initially today with increasing clouds. As the rain moves in late this afternoon, should see diminishing cigs and vis. Holding at MVFR for now during the periods of heaviest rain, mainly evening/overnight, but cannot rule out periods of IFR tonight. Isolated thunderstorms possible during the evening hours. Winds 10 knots or less. Conditions improve back to VFR on Monday. VFR conditions expected for Wednesday through Friday, with some showers and thunderstorms possible, bringing periods of sub-VFR conditions. && .MARINE... Generally winds expected to remain below SCA values today through Tuesday. Rain will overspread the waters this afternoon, heavy at times tonight and Monday. With the rain comes the potential for gusts up to between 20-25 knots. Sub-SCA conditions expected as winds will be below SCA criteria. Showers and thunderstorms possible over the waters during this period. && .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...None. MD...Flash Flood Watch until 2 AM EDT Monday for MDZ011-013-014-016. VA...Flash Flood Watch until 2 AM EDT Monday for VAZ057. WV...None. MARINE...None.
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&& $$ SYNOPSIS...Sears NEAR TERM...HTS/Sears SHORT TERM...Sears LONG TERM...IMR AVIATION...Sears/IMR MARINE...Sears/IMR

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