Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 121836 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 136 PM EST Thu Jan 12 2017 .SYNOPSIS... A cold front will approach from the northwest today. The front will cross the region early Friday. The front will stall to the south and a few waves of low pressure will ride eastward along the front over the weekend into early next week. && .NEAR TERM /THROUGH FRIDAY/... Deep southwest flow is in place across the region this afternoon ahead of an approaching cold front from the northwest. Seeing partly to mostly cloudy skies with breaks of sun in the high clouds aloft. Temperatures have responded nicely with widespread 60s to near 70F out there right now. Will see these rise a few more degrees with highs in the upper 60s to low 70s. Cold front will then progress southeastward towards the region tonight, crossing between midnight and sunrise Friday morning. Precip associated with the front will be lessening as it approaches, so showers likely across the higher terrain and in western areas, with only a few light showers possible (20%) as it crosses the rest of the region. After a very mild evening, temperatures will drop post-front, with 40s to low 50s by morning from north to south. Before the front, may be a few patchy areas of fog, but winds should preclude more widespread development. Strong high pressure (1040mb+) will then build into the Great Lakes eastward to New England on Friday and Friday evening. This will induce low level northerly flow. Still expecting plenty of high clouds with baroclinic zone nearby. Highs mid 40s to mid 50s. && .SHORT TERM /FRIDAY NIGHT THROUGH SATURDAY NIGHT/... Waves of moisture will then move towards the region along the stalled frontal boundary that will be positioned to the south Friday night. As surface high holds over New England through Sunday, will see continual northerly surface flow with cold air damming, feeding in low level cold air into the region. This will set the stage for a prolonged light mixed precip event from Friday night through Saturday, and into Sunday morning. Most widespread and organized area of precip will overspread the region after midnight from west to east Friday night, encompassing the entire area during the Saturday morning hours. Forecast is highly temperature dependent with low level cold air funneling in from the north with weak warm air advection occurring aloft. General trend should be a start with light snow/sleet, transitioning over to sleet/freezing rain from southwest to northeast. By Saturday afternoon/evening, precipitation should generally have tapered off to a either a very light sleet/freezing rain (possibly some snow north) or drizzle/freezing drizzle. This very light precip is expected to continue through Saturday night and into Sunday morning. While event will be long in duration, precip amounts will be light, and precip is not expected to be falling continually during entire timeframe. Total snow/sleet amounts expected to be a dusting to less than one inch for most locations, except around one inch or slightly higher where snow can hang on the longest across northern Maryland and West Virginia. Ice accumulations will be a trace to a tenth of an inch for most of the area, with one to two tenths possible possible across portions of western Maryland and down into portions of West Virginia, especially along the Allegheny Front. There is some concern for higher precipitation amounts due to upslope flow in these areas, but have held off on Winter Storm Watch for now due to uncertainty. Lowest snow/ice threat from central VA and into southern MD. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... Strong high pressure centers over the Great Lakes on Sunday while a stationary front stalls to our south, setting northerly flow over our region. Precipitation is possible near the front as it pushes south, which could bring precipitation to our region, but guidance is not in agreement in p-types... and even if we will have any precipitation at all. The front will lift north as a warm front late on Sunday or Monday with winds becoming southerly behind it and upper level ridging building in. Another warming trend is expected Tuesday into Wednesday with high temperatures reaching the 50s and 60s. A cold front approaches from the west and weakens over our area, followed by a low pressure system that will push northeast from the Gulf states increasing the PoPs sometime Wednesday night into Thursday. && .AVIATION /18Z THURSDAY THROUGH TUESDAY/... VFR through the rest of today with gusty southwest winds and high clouds. As frontal boundary moves across the region later tonight and early Friday morning, may see a brief period of MVFR ceilings, but have left out of TAFs for now due to expected limited coverage and uncertainty. There may also be a few areas of patchy fog before the frontal passage, but winds should limit coverage. As front passes, winds will turn to the north. Front will stall south of the region Friday through Sunday with light northerly flow expected to continue. VFR expected Friday, but lower sub-VFR ceilings/visibilities likely developing later Friday night and through at least Saturday night with areas of light mixed precip and icing concerns. Sub-VFR conditions possible as frontal boundary stalls near our area Sunday, bringing some precipitation with it. Wintry mix possible early in the day but details are still uncertain. The front lifts north late Sunday into Monday and dry conditions follow behind it into Tuesday. && .MARINE... Gusty southwest winds continue today and this evening with Small Craft Advisory in effect. A few gusts nearing Gale are possible, but will be brief and isolated. Winds weaken and turn northerly overnight and into early Friday morning as front crosses the region. Another Small Craft Advisory is in effect on Friday for all waters and into Friday night for the lower Chesapeake and Potomac as northerly winds increase behind the front. Sub-SCA conditions will then return later Friday night through at least Saturday night. Frontal boundary stalls near our area Sunday, bringing some precipitation with it. Wintry mix possible early in the day but details are still uncertain. The front lifts north late Sunday into Monday and dry conditions follow behind it into Tuesday. Winds will be light, so not expecting small craft advisory conditions Sunday into Tuesday. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory until 3 AM EST Friday for ANZ530>534- 536>541-543. Small Craft Advisory from 8 AM to 6 PM EST Friday for ANZ530>532-535-536-538>541. Small Craft Advisory until 10 PM EST this evening for ANZ535- 542. Small Craft Advisory from 8 AM Friday to 1 AM EST Saturday for ANZ533-534-537-542-543. && $$ SYNOPSIS...MM NEAR TERM...MM SHORT TERM...MM LONG TERM...IMR AVIATION...MM/IMR MARINE...MM/IMR

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