Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 230145 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 945 PM EDT Mon May 22 2017 .SYNOPSIS... A cold front is crossing the region this evening. High pressure will briefly return overnight 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. && .NEAR TERM /THROUGH TUESDAY/... Cold front is currently near the Blue Ridge but only slowly moving eastward. Have slight chance POPs til late evening for anything the front initiates, but at this points odds favor nothing more tonight. If the front makes it through the area overnight, 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. && .SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY NIGHT/... Tuesday`s forecast remains very tricky due to a gap between the synoptic and mesoscale models handling low pressure development along the front to our southeast. Previous shift 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. && .LONG TERM /THURSDAY THROUGH MONDAY/... 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. && .AVIATION /02Z TUESDAY THROUGH SATURDAY/... VFR to high MVFR currently, with lower clouds lingering in spots. Some patchy fog may develop overnight, most likely affecting MTN and BWI. No additional precip expected through early Tuesday. Tuesday forecast remains uncertain with guidance spread in position of low pressure and moderate rainfall. Continued to hedge toward a more optimistic solution of MVFR for now except at CHO, 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. && .MARINE... Winds remain less than 10 kt. Southerly flow will become west/northwest overnight with a cold frontal passage. No further showers expected overnight. The pressure gradient will tighten Tuesday as low pressure moves up the coast. Have kept 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. && .TIDES/COASTAL FLOODING... 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. && .LWX WATCHES/WARNINGS/ADVISORIES... 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. && $$ SYNOPSIS...ADS/RCM NEAR TERM...ADS/RCM SHORT TERM...ADS/RCM LONG TERM...KLW AVIATION...ADS/KLW/RCM MARINE...ADS/KLW/RCM TIDES/COASTAL FLOODING...ADS

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