Area Forecast Discussion
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000 FXUS61 KPBZ 111933 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 233 PM EST Mon Dec 11 2017 .SYNOPSIS... Much colder weather arrives Tuesday along with snow. Heavy lake effect snow showers will be possible through mid- week. Another system early Thursday could bring a light accumulation. A brief warmup this weekend. && .NEAR TERM /THROUGH TONIGHT/...
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Cloud will continue to increase ahead of the approaching low pressure system this evening. Given thermal profile any precip in the warm sector will fall as snow so no ptype concerns. Snow will begin around 9Z in northwest PA. Any accumulation prior to 12Z Tuesday will be less than an inch.
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&& .SHORT TERM /TUESDAY THROUGH THURSDAY NIGHT/...
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Snow Amounts: Forecast still on track for the first significant lake event of the season. Eq levels extend up to 11KFT while steep low level lapse rates intersect a favorable thermal profile within the dendritic growth zone. Given flow off the lake, high resolution CAM models agree with recent events of a snow band extending into northern parts of Venango and Clarion counties Tuesday night then retreating into Forest county Wednesday morning. This is where highest snowfall totals are predicted. Counties to the east and west have been placed under a winter weather advisory given boundary flow not being favorable for heavy lake effect. If the wind changes by 20 degrees then we will need to revisit current advisories. The double fetch will allow bands to extend all the way into the Laurel mountains where winter weather advisories were issued. Higher snowfall totals are expected in southwest PA than the mountains of northern WV and western MD due to flow and moisture depth. Most of the snow that accumulates in the mountains of Garrett, Tucker, and Preston will occur Tuesday during the day with the front. There could be near zero visibility with squalls in the this region during the 15z-18z time frame along the baroclinic zone. Snowfall amounts where adjusted a little lower for tonight, otherwise little if any changes through Wednesday. Winds: As low pressure deepens off to our east winds will pick Tuesday night into Wednesday. Mixing heights support gusts close to 40 mph. Can not rule out higher speeds on the ridge tops during the early morning hours Wednesday. Elsewhere in the lower elevations speeds will stay at most in the lower to mid 30s. Wind Chills: Arctic air and northwest winds will bring sub zero wind chills over a good chunk of the region Tuesday evening through Wednesday morning. Lowest values will be in the mountains as they fall between -10 to -15 degrees. This has prompted a wind chill advisory which was bundled up within the winter weather advisory /criteria -10 to -24F/ for Preston, Tucker, and Garrett counties. Next System: 12Z NCEP suite still portrays a weak low pressure system tracking south of Interstate 70 Wednesday night into Thursday morning. What warm advection exists on the front of the system won`t be enough to keep ptype anything other than snow. If this track holds locations that don`t receive much in the way of snowfall /eastern Ohio, northern WV outside the mountains, and southwest Pennsylvania/ could see a quick coating of 1-2 inches around the morning rush hour. This has been highlighted in the hazardous weather outlook given impact level and first snow of the season for aforementioned locations. In the higher terrain, snow amounts may be high enough to warrant a winter weather advisory.
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&& .LONG TERM /FRIDAY THROUGH MONDAY/...
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Highlights: - Snow showers lingering Friday - Temps creeping back to normal - Next weather system Sunday Mid level trough sweeps through Friday, however with westerly flow and it not being that strong, do not expect much additional snow accumulation. The mountains of western Maryland and northern West Virginia could see a light accumulation during the day given position of dendritic layer and moisture depth extending around 10KFT. H5 heights build as transitory ridge crosses the region. A short break in the active weather pattern Saturday. With a little sunshine despite increase mid and upper level clouds. Temperatures should climb into the 40s for the first time in several days save for locations which will have snow cover as they remain in the 30s. Low pressure crosses through the western Great Lakes spreading moisture from the southwest. Thermal profiles and projected onset time have ptype not being an issue at thus juncture. If precip starts earlier there could be a wintry mix, but plenty of time to resolve this as its six days down the road.
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&& .AVIATION /19Z MONDAY THROUGH SATURDAY/... Conditions should improve to VFR for a time this afternoon, ahead of the next system, which will makes it`s approach tonight. Expect conditions to deteriorate in light snow north of PIT early, followed by some restrictions further south as the arctic front passes. Kept similar timing for precip onset and restrictions - around 08-12z with greatest confidence in prolonged IFR at KFKL and KDUJ but brief IFR visibility conditions possible elsewhere. Expect some improvement later Tuesday outside of the terminals impacted by lake-enhanced snow but general MVFR should prevail. Southerly flow will continue until the passage of the front overnight/tomorrow with a return to wnw flow with gusts to near 30kts. .Outlook... Periodic restrictions in snow showers and northwest flow will continue through Wednesday. Another system will bring another round of snow and restrictions to many of the terminals Thursday. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...Winter Weather Advisory from 7 AM Tuesday to 7 AM EST Wednesday for MDZ001. OH...None. PA...Winter Weather Advisory from 7 AM Tuesday to 1 PM EST Wednesday for PAZ007-016. Lake Effect Snow Warning from 7 AM Tuesday to 1 PM EST Wednesday for PAZ008-009-015. Winter Weather Advisory from 7 AM Tuesday to 7 AM EST Wednesday for PAZ023-074-076. WV...Winter Weather Advisory from 7 AM Tuesday to 7 AM EST Wednesday for WVZ510>514. && $$

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