Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 150737 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 337 AM EDT Mon Oct 15 2018 .SYNOPSIS... A warm front will lift through the region this morning, followed by a cold front crossing southeastward from the Great Lakes this evening. A wave of low pressure will pass offshore to the south near the Virginia/North Carolina border Tuesday night, followed by a secondary cold front moving southward by late Wednesday. High pressure will build eastward from the Ohio Valley into the Mid- Atlantic Thursday, then pull offshore Friday as a cold front approaches from the west. && .NEAR TERM /THROUGH TONIGHT/... As an area of low pressure lifts northeastward from the Great Lakes and into southeast Canada, a warm front will lift northward across the region this morning, with the area residing in the warm sector by the afternoon. The attendant cold front will then push eastward and cross during the afternoon and evening hours, clearing south of the area by early Tuesday morning. In addition to patchy drizzle and some low stratus, an initial area of rain showers will push northeastward and across the region early this morning. Following this, there will likely be a lull period during the late morning and early afternoon where any showers will be isolated to scattered at best. As the cold front then begins its approach, showers will again increase in coverage during the mid to late afternoon, especially across eastern West Virginia and northern/western Maryland. As the cold front crosses later this evening, showers will then increase across the DC/Baltimore metro areas. The low level wind field is actually quite strong, and there will likely be just enough instability for a line of gusty showers and possibly an isolated tstorm to develop along the frontal boundary from DC east and northeast. Mostly cloudy skies are expected today, although some breaks of sun will likely be seen across portions of central VA and southern MD. Highs today will reach into the 70s. With the aforementioned low level wind field, south to southwest winds will increase and some gusts 20-25 mph are likely, with up to 35-45 mph along the higher elevations of the Allegheny Front. High pressure will then begin to move into the region overnight, and gusty northwest winds will develop behind the front, with gusts up to 30 mph early Tuesday morning. Showers will end from northwest to southeast by Tuesday morning. Upslope areas of the Allegheny Front and southeast MD will be the last to see precip end. Lows in the 40s/50s. && .SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/... The front will stall well south of the region across the Carolinas on Tuesday with a ridge of high pressure overhead. With fast southwest flow aloft, there will still likely be high clouds around, but conditions will be dry. Highs in the upper 50s to low 60s. A wave of low pressure will develop along the frontal boundary Tuesday night and move quickly out to sea by Wednesday morning. The effects will remain primarily southeast of the region but a few showers may make into southern Maryland. Lows in the 40s to around 50F. As that system departs, a dry but potent cold front will cross the region on Wednesday. This will lead to the development of gusty northwest winds heralding the arrival of cooler temperatures by Wednesday night/Thursday. Highs Wednesday in the 50s/60s with downslope flow, but a much cooler night expected Wednesday night with lows in the 30s/40s. && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... Transient mid/upper ridging will pivot west to east over the Mid- Atlantic as surface high pressure builds in from the Ohio Valley Thursday into Friday. Dry weather with highs in the 50s to lower 60s are expected (about 10 degrees below normal). Northwest breezes gradually relax through the day Thursday as high pressure moves closer and the gradient relaxes. Winds should go calm Thursday night as the surface high moves overhead, and it may be one of the coldest nights so far this season. This is especially true if high clouds streaming in ahead of the next approaching trough hold off until near dawn, resulting in ideal radiational cooling conditions. Clouds will increase Friday, and there is a low probability of some showers creeping across the mountains by day`s end as a cold front begins encroaching on the area from the west. Guidance is in generally good agreement on the front crossing sometime Saturday. While there will only be about 24 hours of return flow resulting in limited moisture, at least some periods of showers seem plausible during this time. A strong autumn high will follow in its wake resulting in breezy conditions behind the front and a reinforcing of cool temperatures. Some upslope snow showers are possible over the higher terrain as well during the second half of the weekend. && .AVIATION /08Z MONDAY THROUGH FRIDAY/... MVFR conditions are expected to start the day today with stratus and showers/drizzle as a warm front crosses the region. Improvement to VFR is likely by the afternoon, but additional showers will then traverse the terminals later this afternoon and evening. South to southwest winds up to 20 knots are expected today, with potential for localized higher gusts in showers this evening. Winds then abruptly turn northwest following a cold frontal passage later this evening and tonight with gusts to about 25 knots. Primarily VFR is expected following this frontal passage through at least Wednesday night. Additional gusty northwest winds are likely Wednesday. Mainly VFR Thu-Fri. NW flow could be gusty (20-25 kts) Thu AM, then becoming light as high pressure builds overhead late Thu into Fri. && .MARINE... SCA is in effect for portions of the Chesapeake Bay and lower Tidal Potomac this morning in strengthening south to southwest flow. This expands to all waters by this afternoon. As a cold front crosses the waters this evening, showers with localized higher gusts are possible, and Special Marine Warnings may be necessary. Behind the front, an abrupt shift to northwest winds are expected with widespread gusts 20-30 knots. A SCA is in effect into Tuesday morning, with winds weakening Tuesday afternoon. Another cold front will approach Tuesday night and winds will increase again out of the southwest and SCA conditions become possible. The front will cross Wednesday morning and SCA conditions are likely in strengthening northwest winds Wednesday and Wednesday night. Northwest flow ahead of high pressure building in from the Ohio Valley may still be strong enough to result in SCA gusts over the waters through at least Thursday morning. Winds should go light by Thursday night into Friday as the high moves overhead. && .TIDES/COASTAL FLOODING... Anomalies will remain a bit elevated through tonight before northwest flow begins to drain water out of the Chesapeake Bay. Flooding is not currently forecast, however, as the higher of the next two high tide cycles (astronomically) is this evening after winds turn northwest and anomalies begin to decrease. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory until 10 AM EDT Tuesday for ANZ530-531- 539-540. Small Craft Advisory from noon today to 10 AM EDT Tuesday for ANZ535-536-538. Small Craft Advisory until noon EDT Tuesday for ANZ542. Small Craft Advisory until noon EDT Tuesday for ANZ532>534-537- 541-543. && $$ SYNOPSIS...DHOF NEAR TERM...MM SHORT TERM...MM LONG TERM...DHOF AVIATION...MM/DHOF MARINE...MM/DHOF TIDES/COASTAL FLOODING...DHOF

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