Area Forecast Discussion
Issued by NWS Sterling, VA

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000 FXUS61 KLWX 190859 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 359 AM EST Sun Jan 19 2020 .SYNOPSIS... After a cold front pushes to the east this morning, an expansive area of high pressure will translate eastward from the northern Plains, becoming centered overhead by Wednesday. High pressure will move offshore during the second half of the week, then low pressure will approach from the central United States. && .NEAR TERM /THROUGH TONIGHT/... Low pressure will move eastward today exiting northern New England by this afternoon. A cold front arcing to its southwest will cross the region this morning, ushering in drier air on gusty northwest flow. Wind gusts to around 30 MPH seem likely today, breezy but well shy of Wind Advisory criteria (which is frequent gusts of 46 to 57 MPH for 2 or more hours). Daytime highs today will be warmer than yesterday despite cold air advection aloft due to more sunshine and downsloping effects. Highs in the upper 30s to mid 40s are expected east of the mountains, with 20s and 30s for the higher terrain. Given the low-level wind trajectories and a ribbon of vorticity aloft, scattered snow showers are likely over the Allegheny at times, particularly this afternoon. A few flurries could hop east of the mountains into the I-81 corridor this afternoon as inversion heights briefly rise above the ridge line, but a lack of stronger upper forcing or very steep lapse rates in the low levels should preclude any more substantial snow shower activity east of the higher terrain today. A secondary push of cold, dry air will make its way into the Mid-Atlantic tonight. A few flurries or snow showers are possible near the higher terrain, but drier air will overwhelm the column, so accumulations should be minimal. Low temperatures are expected to drop into the teens and lower 20s tonight as the colder air mass pushes in, and with the steady northwest wind, wind chills likely bottom out in the single digits and teens late tonight into early Monday morning. The higher terrain along the Allegheny Front (generally above 3000 feet elevation) will see lower wind chills dipping as low as -10 F or even a pinch lower, but the brevity and localized nature of the threat precluded the issuance of a Wind Chill Advisory on this shift. && .SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/... Breezy and cold conditions continue Monday with highs only in the lower to perhaps briefly middle 30s expected for much of the area (colder in the higher elevations). The good news is that while winds will not be calm by any means, they will become relatively lighter, especially late Monday into Tuesday, taking a bit of a bite out of the wind chills. Dry air and subsidence associated with building high pressure will lead to nil precipitation chances and very little cloud cover Monday through Tuesday. && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... Nearly vertically stacked ridging will move overhead Wednesday and edge east Thursday, so dry weather can be expected. Daytime temperatures will begin moderating back above normal, although overnight lows will remain chilly (teens/20s) due to favorable radiational cooling. Low pressure will be developing in the central Plains Friday ahead of a digging upper level trough. There`s a small chance some precipitation in the warm advection ahead of this system could sneak in late Friday, but the more likely scenario at this time is a Friday night-Saturday period for most of the precipitation as the surface low moves toward the Great Lakes. There is a low probability some of the western valleys could see some wintry precipitation at the onset, but a warming column and lack of classic cold air damming signature greatly deter these chances. Guidance does seem to be trending more toward a closed low solution that could pass overhead later Saturday. This could lead to greater chances of snow in the Appalachians depending on the system evolution, although confidence is very low given the Day-7 timeframe. && .AVIATION /09Z SUNDAY THROUGH THURSDAY/... IFR/MVFR CIGs have been stubborn for IAD/BWI/MTN/BWI early this morning, but satellite and upstream obs suggest conditions should lift between 10-11Z. Thereafter, VFR is expected through Tuesday with gusty NW flow gusting in excess of 25 kts at times. VFR conditions and light winds are expected with high pressure Wednesday into Thursday. && .MARINE... Gusty northwest winds in the wake of low pressure departing the northeastern U.S. will persist into Tuesday. A Small Craft Advisory expands to all waters from mid morning today through this evening, before the more sheltered tidal Potomac River north of Cobb Island and Baltimore Harbor drop out of the advisory. There will be a secondary push of gusty winds toward daybreak, but for now believed mixing would subside just enough to leave some of these more sheltered waters out of the advisory during the bulk of the overnight. Gusts in excess of 20 knots will likely linger Monday into Tuesday before high pressure builds overhead causing winds to become lighter. Light winds are expected Wednesday and Thursday as high pressure continues to build overhead. && .TIDES/COASTAL FLOODING... South-southwest winds have piled up water in the northern half of the Chesapeake Bay with anomalies exceeding 2 feet from Annapolis northward. A cold front will shift winds this morning, but they will be westerly until veering some tonight. Thus would not expect a sharp drop in water levels, and places like Straits Point and Annapolis could hit at least caution stage again with the upcoming high tide. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...Small Craft Advisory until 6 AM EST Monday for ANZ530>534-537- 539>543. Small Craft Advisory from 9 AM this morning to midnight EST tonight for ANZ535-536-538. && $$ SYNOPSIS...DHOF NEAR TERM...DHOF SHORT TERM...DHOF LONG TERM...ADS AVIATION...ADS/DHOF MARINE...ADS/DHOF TIDES/COASTAL FLOODING...ADS is the U.S. government's official web portal to all federal, state and local government web resources and services.