FXUS61 KLWX 152054 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 354 PM EST Sat Feb 15 2025 .SYNOPSIS... Low pressure will lift from the mid Mississippi Valley to the St. Lawrence Valley through Sunday. The trailing strong cold front will cross from west to east Sunday afternoon. Arctic high pressure will then build toward the region for the first half of next week before a coastal low possibly impacts the area Wednesday into Thursday. && .NEAR TERM /THROUGH SUNDAY/... Very changeable weather currently and over the next 24 hours with multiple hazards, so mainly summarizing the highlights/changes here. Earlier expansion of the Winter Weather Advisory across northern Maryland was brought about by the period of brief moderate to heavy snow (locally totaling more than an inch) that caused temperatures to wet bulb at or below freezing. As warmer air has moved in aloft, some of these locations remain near 32, so a light glaze of freezing rain is possible. This colder than progged aspect also applied to northern portions of the Potomac Highlands (where the snow band also tracked), but those areas were already under an advisory. However, that does mean an extension could be in order this evening. Elsewhere, areas at or below freezing are more isolated...generally along the ridges as forecast. Flood Watch remains in effect. The latest guidance suggests the highest rain totals will be across Highland, Augusta, Nelson, and Albemarle Counties. The most favorable areas for fog development tonight appear to be east of the Blue Ridge as rain tapers to drizzle overnight. West of the Blue Ridge may remain a bit more mixed and warmer. The main convective fine line is forecast to move through during the late morning/early afternoon when much of the area may remain in the stable wedge airmass. That puts the severe weather risk in question. Either way, lightning will be limited, so it will be important to stay weather aware for changing conditions. Highest confidence in High Wind Warning criteria (58 mph gusts) is in the mountains but did not want to go with a partial upgrade. To the east, there is some uncertainty about how much mixing will occur when the strong winds are aloft (generally along/ahead of the cold front). Behind the cold front, it's a small window to thread the needle between the strong winds aloft, pressure rises, and setting sun. Did add counties across our southern tier to a Wind Advisory. Even if 45-plus mile per hour gusts are isolated, saturated soils could aid in tree damage occurring. Behind the front, precipitation will change to snow in the upslope areas along and west of the Allegheny Front. This snow may be heavy at times as steep lapse rates cool into the DGZ. This snow will also be overlapping with the strongest winds. Therefore, upgraded the favored upslope zones into a Blizzard Warning in lieu of a High Wind Warning. The remainder of the western zones were added to a Winter Weather Advisory for a combination of accumulating and blowing snow. Even though high temperatures will show the mid 50s to mid 60s on Sunday, expect this to be a brief spike in the vicinity of the frontal passage for a lot of areas. Previous discussion: The next system is bringing a prolonged period of unsettled weather to the area through Monday, producing multiple weather hazards locally. At upper levels, a potent shortwave is assuming a positive tilt as it ejects out over the Southern Plains, and then eventually a negative tilt as it progresses northeastward toward the Ohio Valley/Great Lakes on Sunday. Such an evolution is causing an area of low pressure to form over Arkansas, and then rapidly intensify as it tracks northeastward through the Ohio and Saint Lawrence River Valleys tonight into Sunday. A prolonged period of warm advection/overrunning will continue through this evening. A bit of a lull (with some leftover drizzle/fog) will likely occur overnight, before a second round of precipitation moves through on Sunday in association with strong differential cyclonic vorticity advection driven ascent ahead of the upper trough. A strong cold front will move through Sunday afternoon, which may bring another round of scattered showers, with strong cold advection and northwesterly winds ensuing behind the front. Warmer air should move in at the surface across the entire area during the late afternoon/early evening hours. Precipitation should be rain for all tonight through Sunday morning except perhaps on isolated ridges. Winter Weather Advisories remain in effect for for these areas until 7 PM. Again, it's worth emphasizing that this will be an elevation driven event, with little to no impact expected in the valleys. Heavy Rainfall/Flooding: This system is expected to produce a broad one to two inches of precipitation across much of the area. This precipitation will be spread out over a prolonged period of time, so most locations aren't expected to have issues with flooding. The exception will be in the Alleghenies, and then eastward into Augusta County, where a combination of that rainfall and snowmelt could lead to isolated instances of flooding. A Flood Watch remains in effect for those locations this evening through Sunday afternoon. High Winds: As low pressure rapidly deepens and tracks off to our north, strong winds are expected in its wake. The system's cold front will move through the area Sunday afternoon. Given extremely strong pressure rises and a robust LLJ, gusty to damaging winds appear increasingly likely within northwesterly flow behind the front Sunday afternoon into Sunday night across the entire area. The strongest gusts are most likely for a few hours behind the initial frontal passage, though gusty winds (advisory caliber perhaps) may very well linger into Sunday night/Monday. Severe Thunderstorm Threat: Although instability is expected to be rather limited, up to a few hundred J/kg of MLCAPE is progged by some hi-res guidance near and east of I-95 and especially into southern MD right ahead of the cold front Sunday afternoon. This, combined with the very strong forcing and low-level wind fields, results in a marginal (level 1 of 5) threat of both convectively-enhanced damaging wind gusts as well as a brief, isolated tornado. Upslope Snow: Upslope snow is also expected in the Alleghenies behind the front late Sunday afternoon into Sunday night. The current forecast has increased to 4-8 inches of snow from late Sunday afternoon through Monday morning. The combination of high winds and snow will produce near blizzard conditions at times late Sunday afternoon into Monday. && .SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/... On Sunday night, the earlier cold front will continue to race off into the western Atlantic as high pressure builds in the wake. Impressive regional pressure gradients are noted with a 970-mb low near Nova Scotia and a 1030-mb anticyclone across the Missouri Valley. The net gradient formed by these features will maintain a gusty wind field into the night. Model soundings support a reduction in the depth of vertical mixing, but do still show quite a bit of wind in the lowest 1,000 feet. As such, expect westerly winds to gust around 30 to 40 mph overnight, with 45 to 60 mph gusts across higher elevations. These winds will also aid in a continued upslope regime with moderate to heavy snow showers along and west of the Allegheny Front. Whiteout to near blizzard conditions are possible at times. Blizzard Warnings will be issued over Garrett and western portions of Grant and Pendleton counties. Area wide low temperatures are forecast to fall into the mid/upper 20s, accompanied by teens in the mountains. Blustery winds will aid in wind chills falling to near 0 degrees along the Alleghenies. For Monday, the mentioned upslope pattern persists with snow showers continuing through the afternoon hours. Froude numbers rise considerably which suggests there may be some spillover effect into downstream locations. Otherwise, expect mostly sunny skies for locations east of the Alleghenies. Compressional warming from downslope effects should help bring high temperatures into the mid 30s to low 40s (upper teens to 20s across the mountains). Synoptic gradients remain tight enough to keep a blustery wind in the picture for Monday. Afternoon gusts could easily push into the 25 to 40 mph range, locally higher in the terrain. Residual gusty winds should reduce in strength after dark with a cold night ahead. Forecast low temperatures on Monday night will be in the upper teens to mid 20s. The usual cold spot should be along the Allegheny Front where lows in the single digits to mid teens will be more commonplace. && .LONG TERM /TUESDAY THROUGH SATURDAY/... Northwesterly flow will continue to transport below normal temperatures into the area on Tuesday. Dry conditions are expected, with high temperatures in the 30s and lower 40s for most. By Wednesday into Thursday, attention will turn to a potential winter storm. Most guidance has the system's area of low pressure tracking through the Deep South on Wednesday before deepening off the Carolina Coast Wednesday night, and then tracking off toward our northeast on Thursday. Confidence is increasing for snow across the area somewhere during the Wednesday/Thursday time window, with Wednesday afternoon through Thursday morning currently looking like the most favorable time period for snow. What remains in question is just how much snow will fall. While several of the 12z deterministic models depict a significant snowstorm during that time window, ensembles continue to show considerable spread with respect to snow totals, which is to be expected this far out in time. The flow pattern leading up to this event has a lot of moving parts. This weekend's system, the large upper low currently in place over Canada, and an upper trough currently located in the Gulf of Alaska will all influence the upcoming event during the middle of the week. Possibilities at the moment range from a system that largely remains suppressed to our south, with just a couple inches of snow, to a major snowstorm with over a foot of snow. Model guidance should slowly come into better agreement with respect to where we'll lie within that range of possible solutions as we move closer to the event. Dry conditions and below normal temperatures are expected within northwesterly flow on Friday. && .AVIATION /20Z SATURDAY THROUGH THURSDAY/... Rain has overspread the area, and the threat for any wintry precipitation types has ended. Conditions have dropped to MVFR, and ceilings are expected to lower further to IFR/LIFR through tonight. There may be a bit of a lull in rain overnight, which could allow fog to develop, especially across the metro terminals. Another round of rain moves through on Sunday morning, which could be accompanied by heavier convective elements and possibly gustier winds. Behind this band of showers, southerly winds may increase. Ceilings are also likely to improve during this time. More scattered showers could occur along the cold front, but the bigger story will be the wind shift and increase in gusts. Gusts to near 45 knots or even a little higher may be possible Sunday afternoon into Sunday evening, with gusts of 30-35 knots possibly lingering overnight. Timing for Sunday was somewhat generalized in the 18Z TAFs and may be adjusted/refined in later issuances. VFR conditions are expected from late Sunday into Monday/Monday night. The strong wind gusts behind the cold front persist into the night with westerly gusts around 25 to 35 knots possible. Winds turn a bit more west-northwesterly on Monday with afternoon gusts up to around 35 knots. Some spillover snow showers could push east of the Alleghenies, but it remains to be seen if these impact KMRB. Eventually winds slowly decrease into Monday evening/night. VFR conditions and northwesterly winds are expected on Tuesday. Sub- VFR conditions and snow are expected on Wednesday, along with north to northeasterly winds. && .MARINE... Winds will remain east to southeasterly through Sunday morning. With light winds and warm/moist air moving over the cold waters, locally dense marine fog could develop overnight into Sunday morning. Winds will increase to SCA strength or perhaps even brief gale Sunday morning particularly over the mid bay. A line of strong showers and perhaps a thunderstorm could also produce strong wind gusts during the late morning to early afternoon. Then, a strong cold front will move through Sunday afternoon. Gale to even storm force gusts appear likely behind that front Sunday afternoon into Sunday night. Gale Warnings remain in effect for now, but portions may be upgraded to Storm Warnings if confidence increases. Gale conditions continue Sunday night into much of Monday across the area waterways with gusts up to 35 to 40 knots possible. Current Gale Warnings are in effect until 4 PM Monday. Those with plans to be on the water should reconsider given dangerous conditions expected. The strength of west-northwesterly winds drop off into Monday evening and night, but there will likely be a need for Small Craft Advisories during this transition period. SCA conditions will likely linger through much of Tuesday in northwesterly flow. Winds may near low-end SCA levels in north to northeasterly flow on Wednesday. && .HYDROLOGY... Remaining snow pack combined with temps rising to 45-55, dew points into the 40s, and rainfall of one to locally two inches tonight into Sunday results in a risk for flooding. Scattered instances of flooding may result. Overall, the QPF trend has been down the past several cycles, but individual CAMs have stripes of higher 2-3 inch values which could still plausibly cause flooding, especially across Highland and Augusta Counties. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...High Wind Watch from Sunday afternoon through Sunday evening for DCZ001. MD...Gale Warning from 10 AM Sunday to 4 PM EST Monday for MDZ008. High Wind Watch from Sunday afternoon through Sunday evening for MDZ003>006-008-011-013-014-016>018-503>508. Winter Weather Advisory until 7 PM EST this evening for MDZ001- 003>006-501-502-507. Flood Watch from midnight EST tonight through Sunday afternoon for MDZ001-501. Blizzard Warning from 1 PM Sunday to 3 PM EST Monday for MDZ001. Winter Weather Advisory from 1 PM Sunday to 3 PM EST Monday for MDZ501. High Wind Watch from Sunday afternoon through Monday morning for MDZ501-502. VA...High Wind Watch from Sunday afternoon through Sunday evening for VAZ025>031-040-053-054-501-505>508-526-527. Winter Weather Advisory until 7 PM EST this evening for VAZ025>031-036-037-503-504-507-508. Winter Weather Advisory from 1 PM Sunday to 3 PM EST Monday for VAZ503. High Wind Watch from Sunday afternoon through Monday morning for VAZ503-504. Flood Watch through Sunday afternoon for VAZ025-503-504. Wind Advisory from 10 AM to 10 PM EST Sunday for VAZ036>039- 050-051-055>057-502. WV...High Wind Watch from Sunday afternoon through Sunday evening for WVZ050>053-055. Winter Weather Advisory until 7 PM EST this evening for WVZ050>053-055-501>506. Flood Watch from midnight EST tonight through Sunday afternoon for WVZ503. Blizzard Warning from 1 PM Sunday to 3 PM EST Monday for WVZ501-505. Winter Weather Advisory from 1 PM Sunday to 3 PM EST Monday for WVZ503. High Wind Watch from Sunday afternoon through Monday morning for WVZ502>504-506. Flood Watch through Sunday afternoon for WVZ501-502-505-506. MARINE...Gale Warning from 10 AM Sunday to 4 PM EST Monday for ANZ530>543. High Wind Watch from Sunday afternoon through Sunday evening for ANZ530. && $$ SYNOPSIS...ADS NEAR TERM...ADS/DHOF/KJP SHORT TERM...BRO LONG TERM...KJP AVIATION...ADS/BRO/KJP MARINE...ADS/BRO/KJP HYDROLOGY...LWX