Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 080900 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 400 AM EST Thu Dec 8 2016 .SYNOPSIS... Cold front moves through the Mid-Atlantic through the day today. High pressure returns to the area Friday into the weekend. Another cold front crosses the area Monday followed by another reinforcing cold front Wednesday. && .NEAR TERM /THROUGH TONIGHT/... Tricky forecast through early morning...Nearly all guidance failed to capture radiational cooling overnight...which allowed many locations to drop below freezing. Having said that, cloud cover has finally arrived and sites are beginning to slowly warm (e.g., IAD went from 29F-33F over last hour). Main question then becomes will...and more importantly where...will any precipitation be through mid-morning as potent jet max approaches the area. High-res guidance continues to show low-end possibility of light precipitation developing a few hours on either side of daybreak. With low wet-bulb zero heights and only a very shallow low level inversion, expectation is that anything that falls would either be snow/rain/drizzle. Question then becomes...what will surface temperatures be where it precipitates. While very low probability...there is a non-zero possibility of some isolated light glaze on area roads (outside of immediate DC/Balt metros) coinciding with rush hour where air/road temperatures are below freezing. Will be watching this very closely to see how things evolve over the next few hours. Overall, best chance of precipitation will be across S MD after sunrise...where plain rain showers are most likely. Any precipitation moves east by midday...with some gusty winds up to 25 mph developing by afternoon. Highs today peak in the M/U40s...before tumbling tonight behind cold front. Westerly flow will promote the development of upslope snow showers beginning overnight. && .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... On Friday...Mid-Atlantic will be sandwiched between Canadian high pressure building into the area from the central CONUS and trough of low pressure departing the NE CONUS...with a strong cold air advection pattern. Thus, expect a blustery and cold day...with wind gusts up to 25-30 mph and highs AOB 40F. Additionally, wind chills expected to be AOB freezing all day. Strong low-level upslope component through a moist layer will allow snow showers to continue Friday into Saturday morning. While low-end advisory level snowfall remains possible...current forecast keeps storm total amounts between 2-3 inches for the entire event (roughly 24 hours). High pressure continues to build overhead Friday night through Saturday night...with cold weather continuing. Lows Saturday and Sunday morning AOB 30F. Highs Saturday similar to Friday...with most places AOB 40F...though winds expected to be lighter as high pressure is overhead by afternoon. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... The long term is a bit active, continuing the recent trend started at the end of November. Starting on Sunday, we have a fast zonal flow aloft. We`ll have a stationary front in the area with perhaps a little overruning precipitation, most likely north of the CWA. Any precipitation that makes it into the CWA may be wintry, at least partly, given a cold atmosphere, but a lot of uncertainty on this. Highs will be chilly, 30s north and 40s further south. The fast zonal flow aloft buckles just slightly as a shortwave moves across the region later on Monday. At the surface, a wave of low pressure will ride across the area, but it looks like it will cross to our north. While the odds of wintry precipitation will still exist Sunday night, by Monday it appears the low pushes a warm front north of the area and most of our CWA will likely end up rain. Highs will rise into the 40s to lower 50s. After a short break Monday night into Tuesday, another disturbance is progged to move late Tuesday and Wednesday next week. By this time however, guidance gets into some significant disagreement, with varying strength of the next trough. GFS has a signficant storm, though we stay on the warm side until it passes, while EC is much weaker with little precip. Either way, we end up cold late next week, but temps middle of next week are highly uncertain. && .AVIATION /09Z THURSDAY THROUGH MONDAY/... VFR conditions tonight with light flow. A cold front crosses the area from the west today with MVFR cigs and rain/snow chances mainly SE of DC metros/southern MD. Gusty NW winds expected this afternoon through Friday...along with the possibility of some low level turbulence. VFR conditions prevail Saturday through Saturday night...with relatively light winds as high pressure builds over the area. Sub VFR possible Sunday night and Monday with another storm system moving through. && .MARINE... Light and variable flow through sunrise under high pressure. A cold front moves through the waters later this morning with west- northwest winds increasing to gusts up to 30 kt through the afternoon. Bumped up current SCA headline a little bit temporally based on BUFKIT soundings and HRRR wind gust output. Thus, SCA now begins at 10 AM for most waters...and 2 PM for southern MD waters. SCA then continues for all waters through Friday and will likely need to be extended for at least a few hours Friday night into Saturday morning. While a few isolated gale force wind gusts are possible late tonight into Friday...most areas should just have solid SCA conditions. Winds begin to diminish Saturday morning as high pressure builds into the area. Relatively light winds Saturday and Saturday night as high pressure resides over the area. Winds may increase Sunday and Monday as another system approaches. && .TIDES/COASTAL FLOODING... Anomalies have increased markedly in the last 12 hours. Flow over the waters was light during this time and we are not near a full or new moon, so best guess is that this may be related to the lowering pressure combined with slosh back. Really, not sure, but bottom line is that we currently expect some very minor flooding at high tide in St. Mary`s county this morning before stronger NW winds start to lower anomalies this afternoon. Elsewhere, think we reach action stage in some spots but should stay below minor, and anomalies as mentioned should drop thereafter. Will need to monitor the other sites however as there will be some spots which come close. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...Coastal Flood Advisory until noon EST today for MDZ017. VA...None. WV...None. MARINE...Small Craft Advisory from 10 AM this morning to 6 PM EST Friday for ANZ530>533-535-536-538>541. Small Craft Advisory from 2 PM this afternoon to 6 PM EST Friday for ANZ534-537-542-543. && $$ SYNOPSIS...MSE NEAR TERM...MSE SHORT TERM...MSE LONG TERM...RCM AVIATION...MSE/RCM MARINE...MSE/RCM TIDES/COASTAL FLOODING...RCM

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