Area Forecast Discussion
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000 FXUS61 KPBZ 241519 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 1119 AM EDT SUN JUL 24 2016 .SYNOPSIS... Hot and humid conditions will continue. The best chance for showers and thunderstorms will return on Monday with the passage of a weak cold front. Above normal temperatures continue through the week...however they should stay in the 80s. && .NEAR TERM /THROUGH MONDAY/... Showers and thunderstorms over northern Ohio will hold together as they move into an unstable airmass as noted by SPC meso-analysis time lapse charts. This is consistent with new NAM and recent runs from HI-RES convective allowing models. As a result, increased pops to high chance and lower likely /45-60%/ for areas mainly north of the heat advisory. The northern tier of counties contained in the heat advisory could see a brief downpour and period of clouds. However, with several hours of daytime in its wake opted not to change anything with the headline. Previous discussion below... A thunderstorm complex over Michigan will continue to advect east-southeastward in response to a pocket of cooler mid level air. Steering winds across lower MI are westerly then back northwest over Lake Erie. This will carry what remains of the complex over our area this afternoon. This creates two forecast challenges: 1) Thunderstorm coverage. The aforementioned areas of storms crossing lower MI will be the trigger and focus by early afternoon. The 12Z raob for PIT has a cap around 750mb which will erode later today. With dewpoints climbing near 70F and afternoon temps in the 90s, plenty of energy to tap if storms get going. DCAPE values around 1.0 kjkg-1 support the main threat being wet microbursts and brief heavy rain. Storm motion vectors are around 20kts, so if areas get hit more than once a flood threat does exist. HI-RES models and HRRR experimental bring a line of showers and storms commencing around 18z in NW PA and 22z in the far SERN part of our area. 2) Temperatures. Temperatures are already pushing 90F and a modified sounding yields convective temps in the upper 80s. If any place experiences a period of rain, it is still possible for them to reach our forecast high. This was observed Saturday over parts of the area, where rain and clouds did not stop the thermometer from reaching the lower to mid 90s before the day was done. Another record high temperature could be set for Zanesville (3 in 4 days) this afternoon along with a few other sites. This information is contained within the climate sub header found below. && .SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY/... A sweeping cold front will bisect the forecast area Monday night, as the parent upper-level low shifts into the eastern Great Lakes. The boundary will be slow to sag south of the area, prolonging shower and thunderstorm chances into midday Tuesday. By Tuesday afternoon, surface high pressure and drier air will invade from the north and quell rain chances north of I-70. Wednesday is expected to be mostly dry, with the exception coming in the ridges where the elevated heat source could generate a few showers or thunderstorms. Relief from the recent high dewpoints will finally come with fresh air behind the front. Dewpoints will drop precipitously into the low to mid 60s by Tuesday afternoon, and upper 50s to low 60s by Wednesday. Despite temperatures holding above average, the lower dewpoints will feel much more comfortable than the current air mass. TAX && .LONG TERM /WEDNESDAY NIGHT THROUGH SATURDAY/... Highlights: - Continued above normal temperatures - Best shot at rain arrives Thursday night into Friday Overall no real change to synoptic pattern for much of the week as a broad H5 anticyclone dominates the southern 2/3rds of the CONUS. Our mid level height values will fall a few decameters, but not enough to usher in temps where they should be for this time of year. Based on H8 temps not see a stretch of 90F+ weather like this weekend. However, would not be surprised for eastern Ohio to be right around 90F for daytime highs most of the week. Baroclinic zone that crosses Monday night weakens and washes out over the central Appalachians Tuesday as flow become parallel to the boundary and it encounters increased subsidence. In its wake, slightly cooler weather than what we have experienced takes hold for mid week. By weeks end, another shortwave trough traverses the region sweeping a cold front through. Timing differences reside with ECMWF and GEFS, but ECMWF keeps the recent summer trend going of shortwaves passing outside peak heating hours. GFS opts for a Friday afternoon passage. Either way, the next shot of widespread precipitation appears to be Thursday night into Friday. Zonal flow re-establishes for the weekend with temperatures near the climo average of lower to mid 80s. && .AVIATION /15Z SUNDAY THROUGH THURSDAY/... Medium to high confidence forecast. IFR fog at AGC will lift by 13z owing to VFR much like remainder of the terminals through early afternoon. Daytime heating combining with the thunderstorm complex crossing the periphery of the H5 ridge in MI as of 1130Z will lead to scattered thunderstorms this afternoon. While the actual probability of a airport being directly impacted is low continue with just CB mention. Diurnal cumulus clouds around 4KFT will develop by midday and persist through sunset. Overnight mid and high clouds shall keep widespread ifr fog from developing...however if an airport experiences a shower or storm this afternoon then the chance of IFR fog increases. .OUTLOOK /SUNDAY THROUGH THURSDAY/... Restrictions will be possible Monday with the approach and passage of a weak cold front. && .CLIMATE... Hot temperatures across the region today may approach record levels at some sites. Here are a few selected records and forecasts... Site Forecast Record Year Pittsburgh Int`l Airport 94 98 1934 New Philadelphia 97 94 1999 Morgantown 95 93 1987 Zanesville 96 95 1999 && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...Heat Advisory until 8 PM EDT this evening FOR OHZ039>041- 048>050-057>059-068-069. PA...Heat Advisory until 8 PM EDT this evening FOR PAZ020-021-029- 031-073-075. WV...Heat Advisory until 8 PM EDT this evening FOR WVZ001>004-012- 021-509. && $$ synopsis...fries/98 aviation...98 near term...98 short long term...98 climate...fries is the U.S. government's official web portal to all federal, state and local government web resources and services.