Area Forecast Discussion
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033 FXUS61 KPBZ 010210 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 910 PM EST Tue Feb 28 2017 .SYNOPSIS... A series of disturbances will keep periodic rain in the forecast through tonight before a strong cold front results in strong showers and thunderstorms Wednesday. Wintry weather returns behind the front for the last half of the week. && .NEAR TERM /THROUGH WEDNESDAY/...
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A modest short wave is tracking through downt the Mason-Dixon line this evening with moderate and occasionally heavy showers ahead of it. Some embedded thunder is evident as well generally aroung Morgantown. This short wave is projected to track ENE through the evening hours with deeper moisture likely to remain along and south generally of Latrobe. North of this, very little rain is expected through the evening and early portion of the overnight hours. South of there, periods of moderate rain will be likely with a bit of thunder over the next couple of hours before precipitation ends for a while. As the first wave exits to the east, most areas should temporarily dry out even as warm advection continues. This will keep temperatures from falling much at all and allow dewpoints to stay very high overnight likewise. The more substantial system approaches from the west by morning with 0-6 km shear values already topping 80 kts over Ohio by morning. A pre-frontal wave is likely track through during the morning with categorical PoPs indicated for this as well as a very rapid increase in thunderstorm coverage. Due to the wind field, even with just modest instability, any amount of momentum being channeled to the surface would be likely to result in severe wind gusts. Likewise, the surface front itself will approach for the afternoon. Should we be able to destabilize between the two waves, another round of severe wind gust potential may exist. We will be monitoring this going forward as well as continuing to assess flood potential with successive thunderstorm rounds. Fries
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&& .SHORT TERM /WEDNESDAY NIGHT THROUGH THURSDAY/... Confidence continues to increase for severe thunderstorms to generate along the cold front on Wednesday. This is supported by sufficient low level moisture, strong speed and directional shear, and instability. However, the limiting factor to the coverage of severe weather would be the amount of instability due to cloud cover and precipitation from the previous shortwave. Nonetheless, the other parameters should offset the marginal instability to produce possible strong and damaging winds from a scattered or a solid line of convection along the front. Hodographs and model soundings depicted from latest guidance south of PA suggest a brief tornado cannot be ruled out. After the FROPA, upper troughing, cold advection, and limited lake and terrain enhancement should result in scattered snow showers through Thursday. After temperatures peak on Wednesday around 25 degrees above average, a return to below seasonal average temps are expected through the rest of the period. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... Clipper system which has been well-advertised by the models blows in Thursday night with some light snow. A reinforcing shot of cold air arrives behind the system Friday, as snow showers linger and possibly reenhance Friday afternoon with sharp low- level lapse rates. Accumulation rates may initially struggle with warmish ground, but cannot rule out the eventual need for a winter weather advisory in at least the ridges. Overall snow totals were increased slightly for the 24 hour period. Troughing pattern in the wake of the clipper Saturday transitions to a more zonal/flat ridge pattern for Sunday and Monday, and then a more amplified pattern once again by Tuesday with another trough/front approaching. Mainly dry weather for Saturday may be followed by a weak disturbance on Sunday, and then better precipitation chances thereafter as southwest flow and moisture ramp up again. Below normal temperatures at the start will rise above normal once again by Sunday and continuing into next week. && .AVIATION /02Z WEDNESDAY THROUGH SUNDAY/... MVFR with areas of IFR for the forecast period. Rain this evening will remain mainly over ports from PIT and south. Do not expect restrictions with the evening showers. Increasingly strong flow ahead of developing Great Lakes low pressure will likely lead to a period of low level wind shear overnight. Models are suggesting that a linear convective structure is possible sometime after 08Z, but pinning down more exact timing remains difficult. Have continued with previous thinking of a fairly wide VCTS window at all TAF sites. Winds will also pick up out of the southwest, with gusts between 25 and 35 knots possible into Wednesday afternoon. .OUTLOOK... Widespread restrictions and wind problems can be expected with, and in the wake of, the cold front through tomorrow evening. Periodic restrictions are likely through Friday as cold low pressure crosses the region. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...None. WV...None. && $$

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