Area Forecast Discussion
Issued by NWS Sterling, VA

Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
-- Remove Highlighting --
-- Discussion containing changed information from previous version are highlighted. --
000 FXUS61 KLWX 170844 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 344 AM EST Sun Dec 17 2017 .SYNOPSIS...
-- Changed Discussion --
A weak backdoor frontal boundary will hover near the area today, lifting northward as a warm front tonight into Monday. An upper level disturbance will approach the area from the southwest later this afternoon and evening. A cold front is slated to cross the region Tuesday evening with high pressure building overhead for the remainder of the work week.
-- End Changed Discussion --
&& .NEAR TERM /THROUGH TONIGHT/...
-- Changed Discussion --
Mostly clear skies prevailing early this morning under calm winds across the region. The clear skies have allowed temperatures to radiate nicely with temperatures generally in the 20s, and near the freezing mark in the city centers. A weak frontal boundary resides across PA, bringing an increase in cloud coverage over that region. This frontal boundary will sneak slowly southward today, before lifting northward as a warm front by this evening as a shortwave approaches the region from the southwest. High pressure off the southeast coast today will continue to slowly drift eastward over the western Atlantic, maintaining generally light southerly winds across the area and near normal temperatures in the mid to upper 40s. The aforementioned shortwave that will approach from the southwest today will bring an increase in cloud coverage by this afternoon, as well as an increase in low level moisture. Model guidance in good agreement with some showers developing across the area by this evening, but they will remain light. Expecting liquid precipitation with these showers as temperatures at the surface and aloft will generally be above freezing. A few ice pellets could mix in over our northern zones near the Mason Dixon and the Allegheny Front, resulting in little to no impacts. Temperatures overnight will fall in to the low to mid 30s.
-- End Changed Discussion --
&& .SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/...
-- Changed Discussion --
Weak high pressure will build over the area on Monday with some light showers possible along the Allegheny Front with minimal accumulations expected. Overall dry conditions and moderating temperatures expected for the region Monday and Monday night. Highs on Monday will top out in the low to middle 50s and settle down to in the upper 30s to near 40 degrees Monday night. Another mild day on tap on Tuesday with highs approaching 60 degrees with a southwest flow. A surface trough and associated cold front will cross the region overnight Tuesday, trending a little later than previous guidance. Not much fanfare in the way of precipitation as this front approaches, mainly upslope rain/snow shower across our far western mountains as winds turn northwesterly in its wake. Temperatures Tuesday night will remain above average from the middle 30s to near 40 degrees in the cities.
-- End Changed Discussion --
&& .LONG TERM /WEDNESDAY THROUGH SATURDAY/...
-- Changed Discussion --
Southern stream shortwave energy will be undercutting the forecast area Wednesday into Wednesday night. Some timing and placement discrepancies linger with respect to this wave, but the consensus seems to be converging on a solution that keeps most of the forcing south of the area...which precludes the need to identify specific precipitation type(s). A consensus approach suggests that lows will be below freezing, but thermally that should occur after any precip falls (if there were any). Will allow for a slight freezing chance in the database to maintain a pinch of consistency, but latest trends suggest this won`t be a factor. In the wake of this disturbance, believe that there will be a dry period, as a ridge of high pressure builds from the north. That should encompass at least Thursday and Thu night. Beyond that, the problem becomes timing. A fairly well defined frontal system, attendant to a relatively strong northern stream low, will arrive by/around Saturday. Potentially a warm front will be crossing first, somewhere in the late Friday/Friday night time frame. Temperatures will be key in determining precip type...particularly at night. Will lean toward the warm side...not just to simplify the weather forecast, but also that is in line with the latest blended guidance. Anticipate future runs will vary as guidance seeks a solution that can be locked in.
-- End Changed Discussion --
&& .AVIATION /07Z SUNDAY THROUGH THURSDAY/...
-- Changed Discussion --
Predominate VFR conditions are expected across the terminals through Monday night under a light wind flow regime. A weak upper level disturbance may spark a few showers late Sunday afternoon and evening, but at worse, only brief reductions in VIS/CIGs expected along and north of MRB/BWI/MTN. VFR conditions continue on Tuesday with a mostly dry cold front expected to cross the terminals overnight Tuesday. VFR flight conditions anticipated Wed-Thu.
-- End Changed Discussion --
&& .MARINE...
-- Changed Discussion --
With high pressure in control over the southeastern U.S., light winds will prevail across the waters through Monday night. A cold front will approach from the west on Tuesday, increasing winds out of the southwest, but expected to remain below SCA criteria. A cold front will push through the area overnight Tuesday, increasing winds out of the northwest. SCA conditions likely in the wake of the frontal passage. Winds should remain below critical thresholds Wed-Thu. Northwest flow will be decreasing Wed. While the deterministic gust forecast will be no higher than 15 kt, some guidance sources suggest Small Craft Advisories may extend into Wed. As high pressure builds Thu, flow should become light.
-- End Changed Discussion --
&& .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...None. VA...None. WV...None. MARINE...None. && $$ SYNOPSIS...BKF NEAR TERM...BKF SHORT TERM...BKF LONG TERM...HTS AVIATION...BKF/HTS MARINE...BKF/HTS

USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.