Area Forecast Discussion
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000 FXUS61 KPBZ 230922 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 522 AM EDT SAT JUL 23 2016 .SYNOPSIS... Hot and humid weather is forecast for into early next week along with intervals of scattered thunderstorms. && .NEAR TERM /THROUGH TONIGHT/...
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A bit of a weak surface wave will move across the northern portions of the area today, bringing in a bit of drier boundary layer air behind it. In general, even ahead of it, the atmosphere outside of the boundary layer is rather moisture starved, so shower and thunderstorm chances will remain very low and relegated only to the southern half of the area during the maximum in diurnal instability with only modest mid-cloud development apparent at this hour. Interestingly enough, increased mixing right along the surface trough as well as locally increasing warm advection with it with bring a corridor of warmer 850 mb air to the northern half of the CWA today. This combined with lowering dewpoints may allow for actual higher temperatures across portions of the northern CWA than farther south. However, as dewpoints fall toward 60F, this will not translate into heat index values. Farther south, a bit more moisture in the column combined with some cumulus development and more insolation being eaten up by latent heating should keep temperatures from running up much above the lower 90s. However, dewpoints will remain elevated throughout the day and likely into the lower 70s during maximum heating. This will create a period of the day with dewpoints in the upper 90s to near 100F, especially in eastern Ohio. The heat advisory previous issued has been continued for this. As the surface boundary settles to the southwestern portion of the area tonight, northeasterly flow should bring drier air deeper into the CWA. This should allow for a wider diurnal temperature fall basically everywhere north of I-70 primarily due to a lower dewpoint and strong radiational cooling. It does seem, though, that this boundary layer drying will be fleeting as low level flow will already be trending from northeasterly to southerly by sunrise Sunday. Fries
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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 /09Z SATURDAY THROUGH WEDNESDAY/...
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Some local MVFR fog is possible this morning, however a mid-cloud deck seems to have developed over much of the area, resulting in wider dewpoint depressions than even a few hours ago. This cloud inhibit much in the way of fog development before sunrise, thus the fog forecast is not confident. Whatever fog does develop should rapidly clear with sunrise, allowing for VFR conditions at all sites on Saturday. Fries .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... MD...None. OH...Heat Advisory from noon today to 8 PM EDT this evening FOR OHZ048-057>059-068-069. PA...None. WV...Heat Advisory from noon today to 8 PM EDT this evening FOR WVZ004-012. && $$ is the U.S. government's official web portal to all federal, state and local government web resources and services.