Area Forecast Discussion
Issued by NWS Sterling, VA

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200 FXUS61 KLWX 181442 AAA AFDLWX Area Forecast Discussion...UPDATED National Weather Service Baltimore MD/Washington DC 1042 AM EDT Fri May 18 2018 .SYNOPSIS...
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A front will remain stationary south of the area through tonight before lifting to the north Saturday afternoon. Another cold front will become stationary across the area during the middle of next week.
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&& .NEAR TERM /THROUGH TONIGHT/...
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Rain/showers have been focused over the far southern part of the CWA right last night and will likely remain that way through much of the day today as the front will move little. However, as southerly flow strengthens tonight and front begins to lift north again, will likely see a new round of rain/showers tonight. Heaviest amounts are expected to remain east of the Blue Ridge where additional rainfall amounts of 1 to 2 inches could fall. It does appear the flood threat has diminished considerably for far western MD and areas west of the Blue Ridge, but won`t be making any changes yet to the flood watch. Did remove the threat of thunder for today and tonight and made precip stratiform for much of the area except southern areas.
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&& .SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... Deep moisture will still be present from the surface to the tropopause Saturday and Saturday night. During this time we will see an increase in both the local area streams and mainstem rivers. Lingering showers will continue on Sunday, as cold front drops through the area from the northwest. High temperatures will be in the low 80`s. The dry pattern will not last too long, as a low pressure system moving across the northeast will drag a cold front across the region late Sunday into Sunday night. && .LONG TERM /MONDAY THROUGH THURSDAY/... Drier conditions are expected on Sunday as a trough axis lifts north and east of our region, but some lingering light showers will be possible. The drier conditions will be short lived as a frontal boundary drops down from the north, increasing shower and thunderstorm activity Monday into Tuesday as the boundary slows and stalls across southern Virginia. Depending on where this boundary stalls will have implications on temperatures and precipitation chances through mid week. For now, will continue advertising chance POPs Mon-Wed. Model guidance is in agreement with keeping the boundary just south of our area, maintaining near normal temperatures with a north northeasterly wind flow off the Atlantic. && .AVIATION /15Z FRIDAY THROUGH TUESDAY/...
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IFR conditions today and tonight in rain with some improvement in cigs tomorrow as front lifts north. Clearing skies Sunday afternoon, with another approaching cold front late Sunday into Monday. Low ceilings will be possible during this period. A chance for some scattered thunderstorms on Monday as Mainly VFR conditions forecast Sunday and Monday with the only threat of sub VFR conditions being a passing shower over the terminals. Winds will be light and favor a southerly trajectory. A frontal boundary will drop southward through the terminals late Monday, before stalling south of the terminals through mid week. A moist easterly flow north of the aforementioned boundary will bring the potential for sub VFR VIS/CIGs through mid week.
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&& .MARINE...
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Strengthening winds late tonight will bring SCA winds to all waters into Saturday. A southerly flow will develop Saturday and Saturday night ahead of an approaching cold front. Flow should be generally light with some gusts Saturday afternoon due to diurnal heating. Winds approaching SCA criteria will be possible on Sunday afternoon as a cold front is exiting the region. Calmer winds expected Monday, but the potential exists for some thunderstorms. Generally sub SCA conditions expected Sunday through Monday with winds remaining light. A frontal boundary will cross the waters late Monday which will help increase shower activity, resulting in the potential for periodic gusty winds.
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&& .HYDROLOGY... Conditions continue to worsen as this slow-evolving hydro event continues. A pretty widespread three inches or more of rain has fallen across the northern half of the forecast area already, with amounts that high more spotty to the south. (Parts of Culpeper and Fauquier Counties haven`t even seen an inch so far.) The evolution is so far going along similar to model projections, with light to moderate rain across the north, and more showery and heavy rain developing this morning to the south. This activity will pivot northward, and it appears will be followed by multiple additional rounds of precipitation. Confidence has increased in the rainfall prolonging into Friday night, and accordingly the Flood Watch was extended through that time. Also, the area has been expanded to include more counties. We still expect another 1 to 3 inches across most areas with 3 to 5 inches in southern Maryland and the Virginia Piedmont between now and Saturday. Streams (including the mainstem Potomac) are already elevated or in flood, so flood potential is high. Forecasts now call for moderate flooding on the mainstem rivers downstream from Point of Rocks and minor flooding at several tributary locations. River Flood Warnings will be in effect for these locations based on a high confidence of at least minor flooding. It should be noted that depending on where heavy rain axes set up during the course of the event, there could be even more significant flooding than we are forecasting and interests near any river should heed warnings and keep themselves and their belongings away from the rivers. && .TIDES/COASTAL FLOODING... An onshore flow will increase today and this will cause anomalies to continue to increase. However, confidence is not high enough for any advisories across the Bay and lower Tidal Potomac River. The persistent onshore flow will continue through Saturday and this will increase the threat of minor tidal flooding for the more sensitive locations starting Saturday morning. Additionally, freshwater inundation will pose a threat to the DC/Alexandria tidal zone, and a Coastal Flood Watch is in effect from Friday through Sunday, with a focus really starting Friday afternoon/evening, for moderate flooding or greater. && .LWX WATCHES/WARNINGS/ADVISORIES...
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DC...Flood Watch through Saturday morning for DCZ001. Coastal Flood Watch from Saturday morning through Sunday afternoon for DCZ001. Coastal Flood Advisory until 6 AM EDT Saturday for DCZ001. MD...Flood Watch through Saturday morning for MDZ003>006-011-013- 014-016>018-501>508. VA...Flood Watch through Saturday morning for VAZ025>031-036>040- 050>057-501>508. Coastal Flood Advisory until 6 AM EDT Saturday for VAZ054. WV...Flood Watch through Saturday morning for WVZ050>053-055- 501>506. MARINE...Small Craft Advisory until 3 AM EDT Saturday for ANZ530>533- 538>541. Small Craft Advisory from 2 PM this afternoon to 8 PM EDT this evening for ANZ534>537-542-543.
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&& $$ SYNOPSIS...KLW NEAR TERM...LFR SHORT TERM...KLW LONG TERM...BKF/KLW AVIATION...LFR MARINE...LFR HYDROLOGY...LWX TIDES/COASTAL FLOODING...LWX

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