Area Forecast Discussion
Issued by NWS Sterling, VA
Issued by NWS Sterling, VA
275 FXUS61 KLWX 221431 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 931 AM EST Fri Nov 22 2024 .SYNOPSIS... Chilly temperatures, accumulating mountain snow, and windy conditions look to continue through tonight as low pressure meanders across the northern Mid-Atlantic region. The upper-level low will kick off the New England coast and toward the Canadian Maritimes Saturday allowing high pressure to briefly return for the latter half of the weekend. Another front pushes through the region Monday with high pressure Tuesday into Wednesday. A more potent front and low pressure system look to arrive for the Thanksgiving holiday period. && .NEAR TERM /THROUGH TONIGHT/... A Blizzard Warning has been issued for western Grant and western Pendleton Counties due to the expectation of persistent visibility below 1/4 mile, frequent wind gusts over 35 mph, and heavy falling and blowing snow. Travel will be very difficult to impossible in these areas. Near blizzard conditions are possible over Garrett County MD and northwestern Highland County VA. Otherwise, Winter Storm Warnings remain in effect across the Allegheny Front, with Winter Weather Advisories for western Mineral/extreme western Allegany counties through tonight. Accumulating upslope snow will lead to continued travel disruptions, especially along the I-68 and US-219 corridors. Upper-level low pressure will meander around the northern Mid- Atlantic today before slowly kicking toward the New England coast late tonight into early Saturday morning. A strong piece of shortwave energy will pivot around the low later this morning and into the afternoon hours delivering a reinforcing shot of cold air (H850 temps running -2-6 degrees C), gusty winds, and an enhanced period of upslope mountain snow. The steadiest and heaviest upslope mountain snow shower activity looks to occur later this morning through the early evening hours. This is when the strongest piece of shortwave energy pivots through as the cutoff upper low progresses north and east toward New England. Latest deterministic and ensemble guidance continues to advertise snowfall rates of 1-2"/hr with persistent banding/squalls working over the warning/advisory areas. Snowfall accumulations so far as of 3AM this morning range between 1 to 4 inches across the western slopes of the Allegheny Mountains. An additional 6 to 12 inches of snow is forecast today through Saturday morning with locally heavier amounts above 3000 feet. Storm total snow when it`s all said and done, will range between 12-18 inches for locations above 2500 feet with 2 to 6 inches at elevations above 1500 feet (i.e Frostburg/Cumberland, MD south toward Keyser/Franklin, WV). Outside of the significant snow accumulations, blowing and drifting will be a problem. Brief whiteout conditions are expected at times over the warning and advisory locations as winds increase this afternoon into Saturday morning with the shortwave pivoting through. Gusts up to 50 mph are likely over the higher ridges with 30 to 40 mph gusts in the high valley floors below. This will yield wind chills in the teens and 20s across the mountains today into Saturday. Locations above 3500 feet will likely see wind chills in the single digits. Areas east of the Alleghenies, will also pick up their first snowflakes of the season. A band of rain/snow showers look to push south by mid-morning into late afternoon. The highest confidence for snow appears to be along and north of I-66/US-50 with temperatures hovering between 32 and 37 degrees. Locations such as the Catoctins and Parr`s Ridge in north-central MD could see as much as 1 to 3 inches of snow today as the deformation axis wraps around the low pivoting nearby. Most other locations across central Maryland into northeast Maryland near the PA/MD line will receive a coating to as much as 2 inches. Highest confidence for accumulations on grassy surfaces will be from a line that extends from northwest Cecil/Harford counties back west toward northern Baltimore/Carroll/Frederick counties. Wind gusts of 25 to 35 mph are expected later this afternoon into tonight. Wind Advisories are in effect for the crest of the Blue Ridge and downslope areas of the Potomac Highlands for gusts up to 50 mph at times. High temperatures will range from below freezing over the mountains to mid to upper 40s and low 50s further east. Lows tonight into Saturday morning will fall into the 30s and 40s. && .SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... Snow shower activity will begin to decrease Saturday morning into Saturday midday as the shortwave trough kicks east and the upper level low exits off coastal New England. A period of freezing rain or drizzle is possible early to mid Saturday morning along the higher elevations of the Allegheny Front as deeper moisture vacates halting ice crystal formation. A few one hundredths of ice accumulation are expected with up to a tenth of an inch toward Big Savage Mountain and Spruce Knob. By Saturday afternoon, the shortwave will pivot east allowing heights to rise. Meanwhile, surface high pressure will slide in from the Tennessee River Valley and central Appalachians allowing conditions to slowly improve. With incoming high pressure to the south and a departing shortwave/upper level low pressure system to the northeast expect windy conditions to continue. Sustained northwesterly winds of around 20 to 30 mph are expected, with gusts up to 40 mph, mainly on the ridges and over the open waters. Temperatures warm back above freezing in the mountains Saturday with upper 40s and low to mid 50s further east toward the metro areas. Lows Saturday night will fall back into the mid to upper 30s outside the mountains. High pressure briefly returns to the area Sunday before pushing off the southeast U.S coast Monday. Dry conditions are expected as a result along with moderating temperatures. Highs Sunday will push into the low to mid 50s with 40s over the mountains. Lows Sunday night will fall into 30s. && .LONG TERM /MONDAY THROUGH THURSDAY/... On Monday, weak ridging briefly builds in aloft as one upper trough exits to the east and another approaches from the west. Mostly dry conditions are expected as a result, but as the second trough moves in, some upslope precip (in the form of rain, likely too warm for snow) will be possible, with the greatest chances for the Alleghenies Monday night into Tuesday morning. Subsidence behind the upper trough and surface high pressure will likely yield dry conditions Tuesday into Wednesday. The latter half of the week then demands attention, as guidance consistently suggests a low developing over the central Plains and tracking east to the Mid-Atlantic, and potentially along the coast as a Nor`easter. The timing and strength of this low is still highly uncertain this far out, but another round of snow is possible for the Alleghenies, and possibly east of the mountains as well. && .AVIATION /15Z FRIDAY THROUGH TUESDAY/... Prevailing VFR conditions are expected at most terminals through Sunday. Some brief periods of MVFR are possible, especially later this morning into the late evening as a potent piece of upper-level energy pivots through. Brief IFR is even possible at KBWI/KMTN. A few showers with perhaps a few wet snowflakes or even a little graupel are possible at KBWI, KMRB, KHGR, KOKV, KIAD, and KFDK this morning into this afternoon (16Z-21Z/10am-4pm). Any frozen precipitation will quickly change to rain later this afternoon before dissipating tonight. Significant snow accumulations will remain west of KCBE. Wind will be the biggest impact to aviation today through Saturday. Expect sustained speeds of 10 to 20 kts during the day and nighttime hours with gusts 20 to 30 kts each afternoon/evening. Highest winds look to occur this evening into early Saturday morning. West to northwest winds will decrease slowly Sunday with gusts running 15 to 20 kts. VFR conditions are expected Monday and Tuesday. Southerly winds around 5-10 knots on Monday will gradually increase and then turn WNW behind a mostly dry frontal passage on Tuesday. Gusty winds 10- 15 knots are possible Tuesday afternoon. Sub-VFR conditions remain possible for middle of next week as another low pressure system impacts the region. && .MARINE... High end SCAs are expected to continue through Saturday night with frequent gusts of 20 to 30 kts expected across all waters. Gale force gusts are likely over the open waters of the bay and lower tidal Potomac late this afternoon into early Saturday morning as winds surge behind a departing shortwave trough. Winds are slow to taper Sunday with SCAs likely continue across most of the waters with gusts up to 20 kts. Winds over the waters become southerly on Monday, with the potential for southerly channeling in the afternoon. Winds increase and turn WSW Monday night as a dry cold front approaches, and could reach SCA criteria. SCA conditions could continue into Tuesday with gusty WNW winds behind the front. && .LWX WATCHES/WARNINGS/ADVISORIES... DC...None. MD...Winter Storm Warning until 3 AM EST Saturday for MDZ001. Winter Weather Advisory until 6 PM EST this evening for MDZ501. VA...Winter Storm Warning until 6 AM EST Saturday for VAZ503. Wind Advisory until 6 AM EST Saturday for VAZ503-504-507-508. WV...Winter Weather Advisory until 6 PM EST this evening for WVZ503. Wind Advisory until 6 AM EST Saturday for WVZ506. Blizzard Warning until 6 AM EST Saturday for WVZ501-505. MARINE...Small Craft Advisory until 7 PM EST Saturday for ANZ530-535- 536-538. Small Craft Advisory until 4 PM EST this afternoon for ANZ531>534-537-539>543. Small Craft Advisory from 7 AM to 7 PM EST Saturday for ANZ531>534-537-539>543. Gale Warning from 4 PM this afternoon to 7 AM EST Saturday for ANZ531>534-537-539>543. && $$ SYNOPSIS...DHOF/EST NEAR TERM...DHOF/EST SHORT TERM...DHOF/EST LONG TERM...CAS AVIATION...DHOF/CAS MARINE...DHOF/CAS/EST