Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 221911 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 311 PM EDT Mon May 22 2017 .SYNOPSIS...
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A cold front will move through the area later today. High pressure will briefly return tonight before low pressure develops over eastern Carolina Tuesday and moves northeast off the DelMarVa Tuesday night. Upper-level low pressure will move toward the area Wednesday through Friday.
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&& .NEAR TERM /THROUGH TONIGHT/...
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MCV is slowly moving through SE VA/NE NC this afternoon. That feature will pull the last of this morning`s rain away from southern MD. Cold front is currently near the spine of the Appalachians but only slowly moving eastward. In between the front and the rain/cloud-limited airmass across Baltimore/Washington, some limited instability has been able to develop due to insolation. As the front continues eastward, scattered showers and perhaps a few thunderstorms may develop. Have carried chance POPs eastward through this evening, but if the stable airmass never scours out, combined with sunset, any shower/storm may have difficulty reaching I-95. If the front makes it through the area tonight, it won`t be by much, but drier air should eventually filter in. Before it does so, some patchy fog may develop, mainly in southeastern areas. Lows will be in the 50s to lower 60s.
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&& .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
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Tuesday`s forecast has become increasingly tricky due to a gap between the synoptic and mesoscale models handling low pressure development along the front to our southeast. Have chatted with WPC, and they think the GFS/ECMWF could be suffering from feedback, and think the NAM/WRFs simulations may prove more accurate unless an unmodeled MCV pulls the surface low farther north. With better precipitable water values to our southeast, think heavy rain threat is limited, but areas from Charlottesville to St. Marys could have a period of moderate rain. It is more uncertain how much rain falls in the metros. The low will be progressive though, with any rain ending for most areas Tuesday evening. A closed upper low will be moving south into the Mid-west Wednesday while a sfc low and associated cold front moves eastward across the Ohio Valley. A brief period of subsidence is expected across the Mid- Atlantic Wednesday leading to mostly dry conditions for most of the day. Weak instability and lift increase across the southwest by late afternoon. If current trends hold, widespread rainfall will occur Wednesday night as a boundary lifts northward into the area. There may be some weak instability, resulting in a few rumbles of thunder. Have not strayed too far from model consensus for temperatures. Diurnal ranges will be muted due to clouds and precipitation, with lows in the 50s to lower 60s and highs in the upper 60s to mid 70s.
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&& .LONG TERM /THURSDAY THROUGH MONDAY/...
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A slow-moving low pressure system will allow for the chance for rain showers and a few thunderstorms to linger across the region Thursday into Thursday evening. The chance for rain showers shift to the Mason-Dixon line and adjacent areas Friday as the storm system finally departs northeast into New England. By Friday night and Saturday, weak high pressure will move into the region. Dry conditions and a gusty breeze should ensue. Rain showers develop in the region again for Sunday as the next storm system pivots into the region. Temperatures will be warmer.
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&& .AVIATION /19Z MONDAY THROUGH SATURDAY/...
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Cigs are lifting into the MVFR category at mid afternoon, and are expected to rise to VFR by this evening. A weak cold front will be crossing the area. Scattered showers are possible near the front, and perhaps a thunderstorm, but any impacts would be very local/targeted, so have only included VCSH in the TAF. Tuesday forecast a little uncertain with guidance spread in position of low pressure and moderate rainfall. Have hedged toward a more optimistic solution of MVFR for now, but IFR isn`t out of the question. A break in precipitation is expected Tuesday night through most of Wednesday, although with continued uncertainty of how ceilings will respond. Showers and perhaps a storm are possible Wed night-Thu night as a warm front moves across the terminals. Sub-VFR conditions possible during this time. Ifr conditions Thursday. Winds southwest around 5 knots Thursday. Mvfr conditions Thursday night. Winds becoming west 5 to 10 knots Thursday night. Vfr conditions Friday into Friday night. Winds increasing northwest 10 to 15 knots gusts 20 knots Friday, diminishing to 5 to 10 knots Friday night.
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&& .MARINE...
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Winds have dropped to less than 10 kt. Mixing should be rather poor today in vicinity of showers. Southerly flow will become west/northwest this evening with a cold frontal passage. Will have to monitor the potential of thunderstorms reaching the waters this evening, although it is looking more doubtful that any will reach the waters. The pressure gradient will tighten Tuesday as low pressure moves up the coast. Have raised a Small Craft Advisory for the mid Bay and lower Potomac, where the gradient will be the best. The winds should subside Tuesday night as the low moves away. Low pressure will be moving west of the area Wednesday night into Thursday, lifting a warm front into the area. Southerly flow may reach SCA criteria. No marine hazards Thursday night. Small craft advisories possible Friday. No marine hazards Friday night.
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&& .TIDES/COASTAL FLOODING...
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Anomalies have continued to fall to around 1/2 ft except on the Potomac. Flooding looks unlikely for the next couple cycles at least. However, a coastal low Tuesday provides some uncertainty. Guidance ensembles then diverge substantially through midweek, although increasing water levels look more likely by Wednesday night.
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&& .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory from 2 PM Tuesday to midnight EDT Tuesday night for ANZ533-534-537-543.
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&& $$ SYNOPSIS...ADS NEAR TERM...ADS SHORT TERM...ADS LONG TERM...KLW AVIATION...ADS/KLW MARINE...ADS/KLW TIDES/COASTAL FLOODING...ADS

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