Area Forecast Discussion
Issued by NWS Sterling, VA

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501 FXUS61 KLWX 130209 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 909 PM EST Thu Jan 12 2017 .SYNOPSIS... A cold 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/... As of 02z, a cold front stretches from near Caribou, through central Pennsylvania, to near Charleston WV. Showers and thunderstorms from this afternoon along the front have weakened, but a solid line has held together as they approach the forecast area. Some leading showers have entered northern Maryland and adjacent eastern West Virginia; have updated forecast to account for scattered showers north of DC through the evening. Guidance still predicts the line will fall apart before entering the area further, which is accepted given the loss of feeble January daytime heating. Temperatures still in the mid 60s. In light of this, have adjusted hourly temperatures, and thus low temperatures, upward. Lows will be warmer than normal highs for this date. Strong high pressure (1040mb+) will 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 THURSDAY/... 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 /02Z FRIDAY THROUGH TUESDAY/... VFR conditions ahead of a cold front. As frontal boundary moves across the region between midnight and dawn, may see a brief period of MVFR ceilings. Like predecessor, have left out of TAFs due to expected limited coverage and uncertainty. 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 tonight with Small Craft Advisory in effect. 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. && .CLIMATE... Two record daily high temperatures were set for January 12th: 70 degrees at BWI (ties record for Baltimore area from 1890) 70 degrees at IAD (breaks record of 63 set in 1995) Record daily warm low temperatures are possible for January 12th: DCA (DC area) record is 47 set in 1890 BWI (Baltimore area) record is 46 set in 1890 IAD (Dulles area) record is 41 set in 2013 && .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...HTS/MM SHORT TERM...MM LONG TERM...IMR AVIATION...HTS/MM/IMR MARINE...HTS/MM/IMR CLIMATE...DH

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