Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 200812 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 312 AM EST Mon Nov 20 2017 .SYNOPSIS... High pressure will build to our south through tonight. The high will move offshore Tuesday and a cold front will pass through Tuesday night into Wednesday. High pressure will build back overhead later Wednesday through Thanksgiving Day. The high will build to our south for Friday and Saturday before a cold front moves through Saturday night. && .NEAR TERM /THROUGH TONIGHT/... Upper-level trough overhead early this morning is beginning to shift to our east while surface high pressure builds to the south. Rising heights will continue to cause any stratocu along the mountains and northern portions of the CWA to dissipate throughout this morning. Plenty of sunshine is expected this afternoon and it will turn out a bit milder this afternoon...but temps will still be below average for this time of year. Max temps will range from the upper 30s along the ridges of the Allegheny Highlands...to the mid and upper 40s in northern Maryland...to the middle 50s in central Virginia. The high will remain to the south tonight. A weak shortwave in a southwest flow aloft may bring a few high clouds...but dry conditions will persist. Min temps will range from the mid and upper 20s in the colder valleys to the mid and upper 30s in downtown Washington and Baltimore. && .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/... High pressure will shift offshore Tuesday while a cold front moves through the Great Lakes. A southwest flow in between these systems will allow for milder conditions. Max temps will be in the upper 50s to lower 60s across most locations. There will be some high clouds in a southwest flow aloft...but the cloud deck should be thin enough for a partly to mostly sunny sky much of the day. The cold front will approach our area from the north and west Tuesday evening before passing through overnight Tuesday into early Wednesday morning. There will be separation between the lift associated with the cold front and deeper moisture to our south and east. Latest guidance shows that some of this moisture can get drawn up into the front...bringing the chance for showers. The best chance for showers will be across eastern areas where moisture has a better chance to move in before the frontal passage. Any showers early Wednesday morning should dissipate as the cold front moves off to the south and east. A northwest flow will cause chillier conditions despite increasing sunshine. High pressure will settle overhead and it will turn out dry and cold. Did also want to note that a few snow showers are possible along and west of the Allegheny Front Tuesday night into early Wednesday. However...as discussed earlier moisture should be limited so any accumulation would be light. && .LONG TERM /THURSDAY THROUGH SUNDAY/... Longwave western US ridging and east coast troughing will continue to dominate the weather pattern over the United States through the holiday weekend. While no significant storm systems are currently forecast, several upper level impulses will move through the large-scale troughing. Sprawling surface high pressure is expected to be in place on Thanksgiving Day from the southern Plains extending northeastward through the Appalachians. At the same time, weak shortwave energy in both the northern and southern branches of the jet stream will be moving towards the east coast and may lead to surface cyclogensis off the southeastern US coastline. At this time, the surface ridging and flow aloft is expected to keep anything that can develop well to our south and east, leading to a dry and uneventful weather forecast for Thanksgiving Day. Surface ridging is expected to persist into Friday as well, keeping the forecast dry. By Friday night and Saturday, a more potent northern stream system will move into the upper Midwest, with its associated cold front barrelling towards the Mid-Atlantic Saturday night. Once again, southern stream energy will be present as well near the southeastern states, and the potential exists for surface cyclogenesis to occur. At this time, fast flow aloft and orientation of upper level trough suggests that a track well offshore is favored. However, chances for rain showers increase, either with the offshore low or with the cold front itself. Following the front Sunday, blustery and colder conditions are likely, along with the potential for snow showers over the higher terrain. Temperatures will start out below normal on Thanksgiving (40s), moderate back towards normal or even a bit above for Friday and Saturday (50s), before falling back below for Sunday (40s). && .AVIATION /08Z MONDAY THROUGH FRIDAY/... West to northwest winds are gusting around 20 to 25 knots early this morning due to cold advection and a weak pressure surge. Do think that there can be a break in the gusts for a few hours between about 09 and 12z as the surge weakens a bit...but confidence is low. Winds will gradually turn to the west this morning and southwest this afternoon. Gusts around 15 to 20 knots this morning should gradually dissipate this afternoon. VFR conditions will persist for tonight through Tuesday. Southwest winds Tuesday will gust around 20 knots in the afternoon. A cold front will pass through Tuesday night into early Wednesday. A few showers are possible along with subVFR cigs. The best chance for this will be across the eastern terminals. VFR conditions will return behind the cold front for later Wednesday through Wednesday night. VFR and light winds expected Thursday and Friday with surface high pressure && .MARINE... West to northwest winds early this morning will gradually turn to the west later this morning and southwest this afternoon. Wind gusts should gradually diminish throughout the day. Will continue with a Small Craft Advisory for the waters through mid-morning and for the Bay and lower Tidal Potomac River through this afternoon. The SCA may be able to be cancelled early across the middle portions of the Bay and lower Tidal Potomac River this afternoon. High pressure to our south tonight will move offshore Tuesday. South to southwest winds will increase during this time ahead of the next cold front. A Small Craft Advisory is in effect for the middle portion of the Bay and lower Tidal Potomac River tonight and for all the waters Tuesday. The SCA may need to be extended into Tuesday evening for portions of the waters. A cold front will pass through the waters late Tuesday night into Wednesday morning. Northwest winds will pick up behind the front and an SCA may be needed for portions of the waters later Wednesday into Wednesday night. Sub-SCA conditions expected Thursday and Friday with surface high pressure. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory until 6 PM EST this evening for ANZ530>534-537>543. Small Craft Advisory from 9 PM this evening to 6 PM EST Tuesday for ANZ531>534-537-539>541-543. Small Craft Advisory from 10 AM to 6 PM EST Tuesday for ANZ530- 535-536-538-542. Small Craft Advisory until 10 AM EST this morning for ANZ535- 536. && $$ SYNOPSIS...BJL NEAR TERM...BJL SHORT TERM...BJL LONG TERM...MM AVIATION...BJL/MM MARINE...BJL/MM

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