Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 191933 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC Issued by National Weather Service Mount Holly NJ 233 PM EST Mon Nov 19 2018 .SYNOPSIS... A weak area of low pressure over the Ohio Valley will ride along a stationary boundary situated near the Mason Dixon Line tonight, with a cold front crossing the area during the day on Tuesday. Low pressure will move across the northern Great Lakes on Wednesday, pushing a strong cold front through the region Wednesday night. High pressure of Canadian origin will build to our north for the remainder of the work week before another system threatens the area over the weekend. && .NEAR TERM /THROUGH TONIGHT/... Weak low propagating along the front will lift northeast tonight further away from the region. The front will finally begin to make progress through the region as a cold front through the early morning hours. Along and just behind the front, we could see light precipitation, primarily west of the Blue Ridge. With the exception of higher elevations in WV, MD, and VA Highlands, most of the region should remain well above freezing. Thus, if any precipitation occurs, it will be mostly rain. In the higher elevations of the Appalachians however, a rain snow mix changing to all snow is possible. There is limited moisture with this system though, so if any snow accumulation occurs it should be less than one inch, or less than 2 inches along the Allegheny Front. && .SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/... Precipitation will come to an end as the northwesterly flow behind the cold front will lead to dry air advection. The one exception is along the Allegheny Front, where orographic lift could result in lingering light showers. With the cold air advection behind the front, temperatures will be considerably lower than on Monday. Highs will be about 10 to 15 degrees lower than highs on Monday, or about 5 to 10 degrees below normal. On the back side of the low, expect a tight pressure gradient, resulting in northwesterly winds gusting up to 25 mph at times and up to 30 mph along ridge lines. By Tuesday night, winds will start to diminish and skies will clear out. This will set the stage for efficient radiational cooling conditions. Consequently, widespread freezing conditions are expected across the region, with the exception of the urban centers where the temperatures may stay just above freezing. && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... High pressure builds in for Wednesday, continuing a trend of below normal temperatures. A dry, arctic cold front is expected on Thanksgiving. The air behind this front is the coldest of the season so far, with temps likely not getting far from the freezing mark on Thanksgiving Day, and possibly reaching the teens in many areas Thanksgiving night. See the climate section below for a few notes on how rare this cold spell might be, though the midnight temperatures will affect this. Did not make many changes to the grids beyond Thanksgiving as there is still considerable uncertainty with the weekend systems. Many models trended slower with the onset of precipitation, now depicting precipitation not arriving until early Saturday morning. While a later onset would be good news for most of the region, with the chance for precipitation type to be all rain increasing, there remains significant chance of some wintry weather at the onset especially west of the Blue Ridge with the potential for cold air damming. Just how persistent this wintry weather will be is yet to be determined, but anyone with travel plans Friday night into Saturday should keep an eye on evolving forecasts. The low will likely pass us by Sunday and with a more Pacific- type air mass following it, the storm looks likely to do what the system last week did... nudge the coldest air back north of the region and leave some more moderate temperatures over our region for Sunday. Uncertainty regarding the timing of a system quickly following on the first one`s heals makes the forecast for Sunday uncertain, but some rain is possible per the GFS, for example. Other models, notably the ECMWF, allow for more of a gap between the systems, which would make Sunday a fairly decent travel day. Stay tuned... && .AVIATION /19Z MONDAY THROUGH SATURDAY/... VFR with dry conditions is expected at all the terminals through 00Z. A weak area of low pressure will passing along and to the north of the terminals tonight, with MRB serving to see the best chance of MVFR VIS/CIGs due to -SHRA, all other terminals likely to remain VFR and mainly dry. A cold front will cross the terminals early Tuesday with winds shifting out of the northwest. Gusts up to 25 KT will also be possible after 15Z. A stronger but dry cold front will move through the terminals late Wednesday into Wednesday night, maintaining gusty northwest winds with VFR VIS/CIGs prevailing. VFR conditions expected Thursday and Friday as high pressure builds in behind another cold front. Gusty NW winds may be an issue, with gusts likely in the 20-30 knot range. && .MARINE... Winds are expected to remain below Small Craft Advisory conditions through tonight as winds should stay mostly light. A cold front will move through the waters on Tuesday with increasing northwesterly winds expected, thus an SCA goes into effect Tuesday morning and persists for portions of the waters into Tuesday night. A brief lull may be realized Wednesday morning over the waters as the gradient weakens, however another strong cold front is expected to sweep through the waters late Wednesday into Wednesday night bringing solid SCA gusts over the marine district. Small Craft Advisories are likely Thursday and may continue into Friday as another cold front slides across the region. && .CLIMATE... Unseasonably cold weather is looking increasingly likely to briefly take hold of the region on Thanksgiving. Daytime temperatures are likely to stay in the 30s, and it could be the coldest Thanksgiving in over 20 years, depending on the readings at midnight. Here are the benchmark readings to compare this Thanksgiving to: Washington DC area Year High Elapsed 2017 47 1 year 2013 40 5 years 2000 38 18 years 1996 35 22 years 1930 30 88 years The high has not been lower than 30 on Thanksgiving since official temperature record keeping began in 1872. Baltimore MD area Year High Elapsed 2017 44 1 year 2013 38 5 years 2000 37 18 years 1996 33 22 years 1930 31 88 years The high has not been lower than 31 on Thanksgiving since official temperature record keeping began in 1872. Rainfall totals continue to creep upward, with Baltimore setting the annual record already. Here are the current rankings for wettest year on record (through November 18th): Washington DC area (DCA) 1. 61.33 inches (1889) 2. 60.83 inches (2003) 3. 60.09 inches (1878) 4. 58.58 inches (2018) 5. 58.17 inches (1886) Weather records for the Washington DC area have been kept at what is now Ronald Reagan Washington National Airport (DCA) since 1945. Precipitation records observed downtown extend the period of record back to 1871. Baltimore MD area (BWI) 1. 63.18 inches (2018) 2. 62.66 inches (2003) 3. 62.35 inches (1889) 4. 58.98 inches (1979) Weather records for the Baltimore MD area have been kept at what is now Baltimore-Washington International Thurgood Marshall Airport (BWI) since 1950. Precipitation records observed downtown extend the period of record back to 1871. Dulles VA area (IAD) 1. 65.67 inches (2003) 2. 59.17 inches (2018) 3. 59.05 inches (1972) 4. 58.09 inches (1996) 5. 55.43 inches (1979) Weather records have been kept at what is now Washington Dulles International Airport (IAD) since 1960. NOTE: All climate data are considered preliminary until reviewed by the National Centers for Environmental Information (NCEI). && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory from 9 AM Tuesday to 5 AM EST Wednesday for ANZ530>534-537>543. Small Craft Advisory from 9 AM to 6 PM EST Tuesday for ANZ535- 536. && $$ SYNOPSIS...BKF/99 NEAR TERM...BKF/99 SHORT TERM...BKF/99 LONG TERM...RCM/99 AVIATION...BKF/RCM/99 MARINE...BKF/RCM/99 CLIMATE... is the U.S. government's official web portal to all federal, state and local government web resources and services.