124 FXUS61 KLWX 161830 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 230 PM EDT Wed Apr 16 2025 .SYNOPSIS... High pressure will build into the area through Thursday before moving offshore Thursday night. A warm front will pass through Friday and high pressure to the south will dominate the weather pattern for Saturday. A cold front will pass through late in the weekend before settling to the south early next week. && .NEAR TERM /THROUGH TONIGHT/... An upper-level trough will slowly shift east through this evening while surface high pressure approaches from the Great Lakes. A gusty northwest flow will continue due to a deep mixing layer, but winds will not be as strong as yesterday (weaker wind field and gradient compared to yesterday). Frequent wind gusts around 25 to 35 mph are most likely. The northwest flow will allow for cool conditions for this time of year, with highs ranging from the 40s in the mountains, to the mid and upper 50s across northern Maryland, to the lower and middle 60s in central Virginia. Winds will diminish for most areas around sunset due to the loss of mixing. High pressure will build overhead late tonight, causing winds to become light. The combination of light winds, clear skies, and dry air will provide a good setup for radiational cooling. Therefore, Frost Advisories are in effect for northern Maryland and for most locations west of Interstate 95 where the growing season has started. A Freeze Warning is in effect for the central Shenandoah Valley where winds are expected to completely decouple, allowing for temperatures to drop to around 28 to 32 degrees. && .SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/... High pressure will remain overhead Thursday while heights rise behind the departed upper-level trough. More sunshine is expected with a milder afternoon. The high will slowly move offshore Thursday night and a warm front will pass through the area Friday. Timing of the warm front is a little uncertain, but it does appear that it will pass through most areas to allow for a breezy and much warmer afternoon. Perhaps the boundary may get hung up over northeastern MD for a bit. Friday night will turn out dry and warm with a southerly wind behind the warm front. && .LONG TERM /SATURDAY THROUGH WEDNESDAY/... A very complex flow pattern will evolve across the CONUS during the long term period, leading to much greater than normal forecast uncertainty. Models are in reasonably good agreement that by Saturday morning a positively tilted trough comprised of multiple shortwave disturbances will extend from the Desert Southwest northeastward toward the Upper Midwest. A cold front will reside along the southeastern periphery of this trough, extending from the Southern Plains northeastward through the Mid-Mississippi Valley toward the Great Lakes. Surface high pressure will reside offshore, with upper ridging in place across the Southeast. Such a pattern will favor south to southwesterly flow on Saturday and well above normal temperatures as a result. Current forecasts call for temperatures to reach well into the 80s at lower elevations, with 70s in the mountains. Most of the day should turn out dry, but a few showers and a thunderstorm may approach northern Maryland in the evening. Thereafter, forecast uncertainty increases markedly, with both deterministic models and their respective ensembles showing considerable spread. This spread is illustrated well by comparing the GFS vs the Euro and Canadian. The GFS maintains one coherent trough, which progressively lifts northeastward over time, placing us on the warm side of the system on Sunday, with a strong cold frontal passage and much cooler air following for Monday. On the other hand, the Euro and Canadian break the initially positively tilted trough to our west into two pieces. The northern half of the trough rapidly progresses to our east on Sunday, causing high pressure to build to our north at the surface in its wake, and a back door cold frontal passage to occur, leading to much cooler temperatures on Sunday. The southern half of the trough is left behind as a cutoff upper low over the center of the country, which is subsequently picked up by a trailing trough. Southerly flow out ahead of that system would lead to a warming trend early next week, following cooler conditions on Sunday. To further illustrate the uncertainty, ensemble members from the GEFS, EPS, and GEPS showing considerable spread for Sunday through Tuesday. Along with that, there`s also uncertainty with respect to precipitation. The current forecast calls for low- end chances for showers each day, which seems reasonable given the uncertainty. && .AVIATION /18Z WEDNESDAY THROUGH MONDAY/... Gusty NW winds around 25 to 30 kt are most likely through this afternoon. Winds diminish tonight and shift to a southerly direction Thu and Fri. VFR conditions and south to southwesterly winds are expected on Saturday. Forecast uncertainty increases substantially by Sunday, but most outcomes favor VFR conditions. && .MARINE... High end SCA conditions are expected through 00Z tonight for all of the waters. The SCA continues for the Bay and lower Tidal Potomac River through tonight. Lighter winds are expected Thu into Fri, but southerly winds will pick up later Friday into Friday night and an SCA may be needed. Winds may approach low-end SCA levels in south to southwesterly flow on Saturday. Uncertainty with respect to wind speed and direction increases substantially by Sunday. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...Small Craft Advisory until 6 AM EDT Thursday for MDZ008. Frost Advisory from 2 AM to 9 AM EDT Thursday for MDZ003>006- 008-011-503>508. VA...Frost Advisory from 2 AM to 9 AM EDT Thursday for VAZ028-030- 031-036>040-050-051-053-055-056-501-502-505-506-526-527. Freeze Warning from 2 AM to 10 AM EDT Thursday for VAZ025>027- 029. WV...Frost Advisory from 2 AM to 9 AM EDT Thursday for WVZ051>053. MARINE...Small Craft Advisory until 6 AM EDT Thursday for ANZ530>534- 537-539>541-543. Frost Advisory from 2 AM to 9 AM EDT Thursday for ANZ530. Small Craft Advisory until 8 PM EDT this evening for ANZ535- 536-538-542. && $$ SYNOPSIS...BJL NEAR TERM...BJL SHORT TERM...BRO LONG TERM...KJP AVIATION...BJL/BRO/KJP MARINE...BJL/BRO/KJP