Area Forecast Discussion
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193 FXUS61 KPBZ 101503 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 1003 AM EST Sat Dec 10 2016 .SYNOPSIS... Cold air will remain in place in advance of the next system that will affect the area later tonight through Monday with snow, rain, and the potential of a wintry mix before much colder air arrives late in the week. && .NEAR TERM /THROUGH TONIGHT/...
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Visibilities north of I-80 have lowered below a mile at times this morning as a band of lake snow continues to advance westward as it weakens. Have nudged up POPs and snow amounts across northern Mercer and Venango before flow turns and snow showers end this afternoon. Remainder unchanged. As a weak shortwave flies by the region this morning scattered snow showers and flurries will continue into early afternoon. Only a fresh coating if that is expected. Dry and cold this afternoon and evening as a small bubble of high pressure crosses the upper Ohio valley. A warm front will approach ahead of low pressure developing in the nations mid section overnight, with light snow moving into areas mainly north of I-70 overnight. With dry low levels to overcome at the onset, only very light accumulation expected by daybreak.
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&& .SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... A complex weather scenario will unfold over the latter part of the weekend, stretching into Monday. While there are still some unknowns with this system, confidence in several features including the warm trend is growing. Increasing southerly flow on the back of the surface high will shift the warm advection snow band northward Sunday. Models still differ on just how far north this band gets, with the NAM bullish on fully clearing the northern periphery, which seems a bit hasty, given the strongest southerly flow is still well back to the west. Regardless, most operational models show a carved out warm sector drawn into the area, so PoPs south and east have been trimmed accordingly. The result is categorical light snow continuing north of Pittsburgh Sunday afternoon, while what lingering precipitation that exists south of Pittsburgh transitions to a rain/snow mix as the warm push begins. By Sunday night, the nearly stacked low will move through the Great Lakes. The center of the low this far west favors strong warm advection overnight into Monday. Pushed by a stout low-level jet in the warm sector, 800-900mb temperatures will increase quickly. Surface temperatures will gradually warm through the pre-dawn hours, but will lag behind the warming mid-levels. The result will be a relatively complex precipitation type forecast. Current forecast calls for pure rain making it to Pittsburgh by the morning rush, rain/snow north to I-80, and snow persisting north of that. Southeasterly flow near the ridges will hold the cold air in the eastern facing slopes, ultimately favoring a freezing rain or sleet profile before flow veers southerly. Given the recent warm trend seen in the models, will carry just a chance of freezing rain, and hold off on any FZRA headlines. In terms of snowfall, the best estimate for totals from Saturday night through Monday morning is still about 4-6 inches north of I-80 in PA, with only an inch or two across Pittsburgh. Length of snowfall duration and melting of accumulating snow will preclude any snow related headlines at this time. The warm push continues well into Monday, transitioning all precipitation south of I-80 over to rain. This should quickly cut into any laying snow that had accumulated in the previous 24hrs. Strong moisture transport along the trailing cold front will bolster rain efficiency through Monday afternoon. Will continue to carry categorical PoPs with the frontal passage. Showers will taper down Monday evening as the front clears our eastern edge and upper-level moisture evacuates. A mostly west wind behind the cold front will be detrimental to any continued lake-effect or upslope snow, but enough low-level moisture could maintain patchy drizzle. && .LONG TERM /TUESDAY THROUGH FRIDAY/... High pressure in the wake of the early week system will continue the dry trend through Tuesday. An arctic cold front will re- enforce the cold west-northwest flow Tuesday night. Dry high pressure at the surface will cut-off any moisture feed along the front, thus limiting precipitation potential with it`s passage. Another shot of cold then comes with a passing shortwave trough Wednesday night. All told, by Thursday temperatures will be well- below average with high temperatures expected to be 5-10 degrees below our average lows. Next best chance of widespread precipitation comes with a system next early next weekend. At this point, models showing fairly good agreement with the developing stages. Temperatures will begin to moderate by the weekend as the upper- level flow amplifies ahead of this next system. && .AVIATION /15Z SATURDAY THROUGH WEDNESDAY/... Lake effect snow bands will continue to impact KFKL and KDUJ into the dawn hours. Elsewhere, MVFR cigs will gradually improve to VFR today as drier air arrives from the SW. The next system will roll into the area tonight with snow overspreading all sites near the end of the TAF valid period. .OUTLOOK... Widespread restrictions are likely Sunday and Monday, and again Wednesday, with crossing areas of low pressure. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...None. WV...None. && $$

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