336 FXUS61 KLWX 070848 AFDLWX Area Forecast Discussion National Weather Service Baltimore MD/Washington DC 348 AM EST Fri Feb 7 2020 .SYNOPSIS... Strong low pressure will depart across the Northeast and Canadian Maritimes while rapidly intensifying through tonight. A weaker area of low pressure approaching from the Ohio Valley will cross the area Saturday night. A cold front will follow, possibly stalling near the region through the middle of next week. && .NEAR TERM /THROUGH TONIGHT/... A coastal front extends from north-central Maryland through northern Virginia and into the central Shenandoah Valley early this morning. A strong shortwave from the southern stream along with a coupling upper-level jet has caused low pressure to develop along the coastal front. This low will continue to strengthen as it passes through our area this morning and the low will further intensify as it moves off to the northeast this afternoon. For early this morning, locally dense fog is expected near and northwest of the coastal front. However, an increasing gradient should cause wind to increase and that mixing will cause fog to dissipate between 6 and 8 am for most locations. A potent temperature gradient will also exist overhead this morning, with temps in the 50s for the Washington and Baltimore metro areas into central Virginia and 30s/40s northwest of the coastal front over eastern WV, western MD, and the northern Shenandoah Valley/Potomac Highlands. As the potent shortwave and coupling jet cause low pressure to intensify this morning, this will lead to showers. This is a very potent system and winds are very strong just off the surface. Therefore, a line of showers along the cold front associated with the strengthening low will have to potential to produce gusty to perhaps even locally damaging wind gusts. The best chance for this to occur will be across central Virginia, southern Maryland and near Interstate 95. This is because the warmer surface temps will have eroded the inversion. The most likely timing will be between 7 am and 10 am this morning. On the cold side of the low across the Allegheny and Potomac Highlands into eastern WV, extreme northern VA and north-central and western MD, widespread showers are expected this morning as the low passes by just to the southeast. The deformation zone will also move through these areas, so rain may be locally heavy at times. At the same time, colder air will rapidly be working its way in from the west. There is a higher amount of divergence among the hires guidance, particularly for this occurring within the next 6 hours or so. Therefore, the confidence in the forecast is on the low side. However, it does appear that the low-level temps will be just warm enough for most of the moderate to locally heavy precip through 12z to fall as rain. The one exception would be along/west of the Allegheny Front where precip will change to snow. As precipitation is ending, that change over to snow will progress across the rest of the aforementioned area, with the higher confidence for snow being over the ridge tops. A slushy inch or so of snow is possible over the ridge tops, but the valleys should hold on to just enough warm air for any accumulating snow to be light at best and confined to grassy surfaces. Should the precipitation change over to snow a bit earlier, than accumulating snow would impact most of these areas during the morning commute. Again, confidence is low for this to occur given the reasons mentioned above. For locations along and west of the Allegheny Front, accumulating snow is expected and this will have more of an impact with snow covered and slippery roads. A Winter Weather Advisory remains in effect for western Grant and western Pendleton Counties, and a Special Weather Statement has been issued for western Allegany and western Mineral Counties where we are not categorically confident for 3" of snow in 12 hours, but there will be an impact from accumulating snow this morning. Upslope snow showers will continue this afternoon into this evening for the same areas, and the Winter Weather Advisory continues into this evening. Another concern for today will be strong gradient winds. A strong pressure gradient due to the rapidly intensifying low will cause winds to rapidly strengthen between 12 and 15z across most areas. The Wind Advisory continues for the metro areas, central Maryland, and northern Virginia as well as the Blue Ridge Mountains. Wind gusts around 50 mph are expected across these areas and a wind shift from the south to the west and northwest is expected this morning. Strong cold advection will cause gusty winds to continue through the afternoon, but the gradient may subside during the mid to late afternoon hours causing the gusts to come down just a bit. Blustery and noticeably colder conditions are expected tonight. There will be some upslope snow showers along and west of the Allegheny Front. A few flurries could spill east of the mountains. Min temps will be in the 20s for most areas with lower 30s in downtown Washington and Baltimore. && .SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... Weak high pressure will briefly build to our south for Saturday, and this will allow for dry and seasonable conditions for most areas. Another upper-level disturbance will pass through the area late Saturday into Saturday night. A period of snow or snow and rain is possible, especially late Saturday afternoon into Saturday night near the Allegheny and Potomac Highlands. Farther east, the isentropic lift will be separated from the weak dynamics, so confidence in any precip is low at this time. Light snow accumulations are possible in the Potomac and Allegheny Highlands and perhaps into the Shenandoah Valley and eastern WV, extreme northern VA and western MD. However, confidence in snow accumulation east of the Potomac Highlands is low at this time. Another weak area of high pressure should bring dry conditions to most areas Sunday but this system will move offshore later Sunday and Sunday night. A cold front from the northwest will approach Sunday night and this may trigger some showers overnight, especially across northern and western areas. && .LONG TERM /MONDAY THROUGH THURSDAY/... Long range guidance agrees in the large scale pattern through the long term. However, there is above average uncertainty in smaller scale features. From a hemispheric point-of-view, a strong mid level ridge will nose across the Bering Strait toward the North Pole, nudging a strong Polar low near the Davis Strait/Greenland southward toward the Hudson Bay. Meanwhile, subtropical ridging will continue to build over the Southeast. This leaves the east-central CONUS in fast westerly flow aloft between the competing forces of ridging to the south and troughing to the north. An attendant surface front will likely drape itself near the Mid- Atlantic, but model run-to-run variability has been high on exactly where and when the front ends up. There is cold air available not far to the north, and some ensembles bring this cold air south by the end of the week, but again it will be fighting subtropical ridging to the south. This pattern will likely be one with frustratingly low certainty and high variability until about 48-72 hours prior to any individual disturbance or potential storm system. && .AVIATION /08Z FRIDAY THROUGH TUESDAY/... Low clouds and patchy dense fog will continue early this morning, but cigs and vsbys should gradually improve between 12 and 15Z as winds increase behind a cold front. Showers are expected through mid-morning, and some snow showers may mix in around KMRB right before precipitation ends. There is the potential for a line of showers to produce locally damaging winds around KDCA and KBWI. However, strong west to northwest winds are expected behind the cold front with gusts around 40 knots expected. Winds will gradually diminish later this afternoon through tonight. VFR conditions are expected most of the time Saturday through Sunday night. A brief period of light rain or snow is possible Saturday night, but confidence is low at this time. Sub-VFR is possible early next week, though there is above average uncertainty in timing and placement of a nearby front that could lead to such conditions. This also casts uncertainty in wind direction and speed. && .MARINE... Low pressure will intensify as it passes through our area this morning and the cold front associated with the low is expected to pass through the waters between 13 and 16z. Strong winds will develop during this time and these winds will continue through this afternoon. A Gale Warning is in effect for the waters. A line of showers is also possible with the frontal passage, and Special Marine Warnings may be needed for locally damaging wind gusts. Winds will gradually diminish tonight, but a Small Craft Advisory is in effect for the waters. High pressure will remain to the south of the waters Saturday. Winds may be close to SCA criteria, but confidence is too low for a headline at this time. A weak disturbance will pass through Saturday night and high pressure will briefly return Sunday before moving off to the south and east by Sunday night. Winds may approach SCA criteria Sunday night. Model variability precludes substantial certainty in wind forecast specifics early next week, but in general southwesterly flow should stay generally below Small Craft Advisory criteria. However, if a cold front approaching from the Ohio Valley is a little stronger, the gradient may result in a strong enough wind field for some gusts in excess of 20 knots over at least portions of the waters, particularly on Monday; but again, certainty is low. && .TIDES/COASTAL FLOODING... Water levels remain around or just over 1.5 feet above astronomical predictions early this morning. This would bring several sites near minor flood. With increasing westerly flow today, certainty probably won't be high enough to issue advisories until a few hours before high tide at any individual site given the marginality of the threat, and uncertainty in precisely how and when water levels will react in increasing westerly flow later this morning. The sites with the highest potential to breach minor flood thresholds are DC SW Waterfront (this morning and again late this afternoon), Straits Point (midday) and Annapolis (this afternoon). && .LWX WATCHES/WARNINGS/ADVISORIES... DC...Wind Advisory from 9 AM this morning to 3 PM EST this afternoon for DCZ001. MD...Wind Advisory from 9 AM this morning to 6 PM EST this evening for MDZ004>006-505-507-508. Wind Advisory from 9 AM this morning to 3 PM EST this afternoon for MDZ003-011-013-014-016>018-503-504-506. VA...Wind Advisory from 9 AM this morning to 6 PM EST this evening for VAZ507-508. Wind Advisory from 9 AM this morning to 3 PM EST this afternoon for VAZ052>055-057-505-506. WV...Wind Advisory from 9 AM this morning to 3 PM EST this afternoon for WVZ051>053. Winter Weather Advisory from 7 AM this morning to 10 PM EST this evening for WVZ501-505. MARINE...Small Craft Advisory from 6 PM this evening to 6 AM EST Saturday for ANZ530>543. Gale Warning until 6 PM EST this evening for ANZ530>543. && $$ SYNOPSIS...BJL NEAR TERM...BJL SHORT TERM...BJL LONG TERM...DHOF AVIATION...BJL/DHOF MARINE...BJL/DHOF TIDES/COASTAL FLOODING...DHOF