Area Forecast Discussion
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565 FXUS61 KPBZ 231503 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 1103 AM EDT SAT JUL 23 2016 .SYNOPSIS... Hot humid weather is forecast for into early next week along with intervals of scattered thunderstorms. && .NEAR TERM /THROUGH TONIGHT/...
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Weak boundary, indicated mainly from a wind shift in surface obs, is bisecting the CWA this morning. In the vicinity of this boundary some cumulus is starting to develop. This may be the focus for the development in widely scattered thunderstorms today, as is progged by the hi-res models. In addition, the help of a passing shortwave in northwest flow, may further provide lift for a thunderstorm or two. Opted to expand low chance pops a bit further north, based on the model and satellite/surface analysis. Otherwise, most locations should exceed 90 today. Dry air through the entire column is present north in NY where dewpoints are in the upper 50`s. The Buffalo sounding also shows this dry air at both the surface and aloft. This will be advected toward the region as the shortwave trough approaches, which should limit both cloud cover and decrease dewpoints over the northern half of the region this afternoon. While this should bring a break in the humidity, it could also stand that any mixing may bring temperatures up above 90 faster than locations to the south, where the warmer dewpoints and cloud cover remains. Have made little change to temperatures through the afternoon and with the 70 dewpoints likely to hold over our southern counties until late today, have opted to keep the heat advisory as is, as indiceswill still be very near 100. Model guidance suggests that these drier dewpoints will never fully make it across the entire region before southerly flow returns ahead of the next front Sunday. But, this should be sufficient enough to provide a cooler night, for the northern half of the region, than previous nights.
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&& .SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... A passing shortwave ridge aloft will keep the forecast area mostly dry through the afternoon Sunday. Only maintaining a slight chance of showers/thunderstorms during the evening as the ridge axis shifts east and flattens due to a weak wave passing through the southern Great Lakes. Ample low-level moisture will linger, keeping dewpoint temperatures in the mid to upper 60s. This moisture, combined with hot temperatures, will again have heat indices in the mid to upper 90s for most locations west of the Ridges. Only have a few counties flirting with 100, and those counties already have a Heat Advisory for Saturday, so opted to maintain the Sunday HWO mention for now. An upper-level trough will approach from the west Monday, dragging a weak cold front behind it. This will be the impetus for the best chance of rain over the next several days. Mid-level temperatures will remain fairly homogeneous Sunday into Monday, but strong warming at the surface and lingering high dewpoints will fuel instability ahead of the trough Monday afternoon. This, along with modest vertical shear, should be enough for a few strong thunderstorms to develop, but a widespread severe threat is not expected at this time. Model soundings do suggest efficient rain production with any thunderstorms Monday as the warm cloud layer will extend above 10kft and PWATs approaching 2.0", which is well above average. The boundary will sag south of the area Monday night, with gradually declining rain chances into Tuesday morning. tax && .LONG TERM /TUESDAY THROUGH FRIDAY/... A weakening surface boundary will stall just south of the forecast area Tuesday. Models differ slightly on how far north afternoon thunderstorms activate along the boundary Tuesday and Wednesday. Kept slight chance PoPs relegated to south of the Mason-Dixon line Tuesday afternoon, but high pressure building at the surface across our north, results in a mostly dry forecast. Dry weather is expected to last into Thursday morning, as upper-level flow goes zonal. High pressure will start to break down towards the end of next week as broad troughing begins aloft. This will bring periodic showers and thunderstorms back to the forecast through the early part of next weekend. tax && .AVIATION /15Z SATURDAY THROUGH WEDNESDAY/...
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vfr conditions today. In airports from KZZV to KPIT to KLBE and south, there is a chance of an isolated shower after 18Z but will be very widely scattered. .OUTLOOK /SATURDAY THROUGH WEDNESDAY/... Restrictions will be possible late Sunday and Monday with the approach and passage of a weak cold front.
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&& .PBZ WATCHES/WARNINGS/ADVISORIES...
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MD...None. OH...Heat Advisory until 8 PM EDT this evening FOR OHZ048-057>059- 068-069. PA...None. WV...Heat Advisory until 8 PM EDT this evening FOR WVZ004-012.
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&& $$

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