Area Forecast Discussion
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000 FXUS61 KPBZ 171151 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 751 AM EDT Thu Aug 17 2017 .SYNOPSIS... Rain is likely with a cold front later today and into Friday. Temperatures will stay warm through the weekend. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Updated PoPs and associated fields to account for current radar trends. Shower and thunderstorm chances will gradually increase in eastern Ohio through this afternoon as the warm front drags through the area. Previous discussion below... The quasi-stationary boundary over Southern Ohio will be pushed northward as a warm front this morning, by a rather vigorous shortwave that will move across Northern Ohio, reaching Northwestern Pennsylvania by early this afternoon. This will eventually place the entire area well into the warm sector, and pump up humidity levels. With the late morning wave, models are keeping most of the activity to the north, closer to its path, while south of this, convection looks to be more scattered or isolated. There will be some limiting factors to storm development and intensity that will need to be closely watched today. The main one, at least through the afternoon, will be the very warm air aloft, which will provide a cap on the atmosphere. In addition, cloud cover associated with the morning wave, will work to limit sunshine, and readings may fall short of forecasted convective temperatures. If the cap is strong enough, cloud cover could decrease as the afternoon progresses. This will all need to be closely watched today. By late this afternoon and into the early evening, the aforementioned shortwave will be moving rapidly over North- Central Pennsylvania. Another, weaker shortwave trough, will move into my Ohio counties by early evening. Models are redeveloping convection ahead of this second wave, moving it eastward during the remainder of the evening hours. At this time, it appears the NAM is struggling with convective feedback, due to an over amplification of the omega field and by trying to develop a cool pool aloft with the wave, which does not seem to be realistic. Additionally, the NAM may be overdoing the PWAT values for today, but I do think, with dewpoints pushing toward or into the 70s, heavy downpours will be a concern. The good news is that the pattern will be progressive, with forecasted storm motion of 20 to 24kts, so individual cells should be moving quickly.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH SATURDAY/... Shortwave trough will be east of the area shortly after midnight. Once the large scale ascension moves east, and diurnal stabilization overtakes the atmosphere, expect the activity to not only move east, but also weaken. Will keep in the risk for showers/storms overnight, with the higher PoPs drifting eastward with the exiting wave. Lingering showers are possible Friday morning, although the coverage is questionable, as the best lift will be well to the northeast and well to the southwest of the region. It`s likely that models are filling showers in through the entire trough axis, which would focus the activity over the southeastern quadrant of the area. As afternoon approaches, the trough axis will shift southeastward toward the Mid-Atlantic region, which should bring an end to the risk of showers, save for the far southeastern ridges. The cold front will finally begin to cross the area late Friday afternoon reaching Northern West Virgina by late evening. By this time, the best lift will be southeast of the area as will be the deep moisture. Because of this, have decided to leave FROPA dry, but this will likely need to be further investigated in future model runs. Cooler air will overspread the area Friday night and Saturday. A strong shortwave trough will cross the region late Saturday afternoon and evening. Have decided to go with slight to low chance PoPs with this feature, as there will likely be another surface boundary accompanying the upper level wave. && .LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/... Broad high pressure will build across the region for the end of the weekend into the beginning of the work week. A cold front should then bring a chance of rain back to the region for Tuesday and Wednesday. Temperatures will remain near average, building into the middle of next week. && .AVIATION /12Z THURSDAY THROUGH MONDAY/...
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Warm front associated with northeastward tracking low pressure will result in some scattered showers and thunderstorms today. Latest hi res guidance has a few showers in the vicinity of ZZV by 10am but most of the activity appears to be much later. Kept the mention of VCTS late this afternoon at all terminals with deteriorating conditions anticipated with the approach of a more potent shortwave late. Wind will be out of the sw under 10kts. .Outlook... Restrictions are likely through Fri morning as the cold front crosses.
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&& .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...None. WV...None. && $$ is the U.S. government's official web portal to all federal, state and local government web resources and services.