149 FXUS61 KPBZ 041321 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 921 AM EDT Mon Sep 4 2023 .SYNOPSIS... A heat wave is expected early this week. Heat indices may push well into the mid-90s. A trend toward seasonable temperature with unsettled weather is expected thereafter. && .NEAR TERM /THROUGH TONIGHT/... 7am update... Forecast is largely on track, and only made very minor updates to sky cover and temperatures. Did tweak afternoon highs up a degree or so based on current trends, so a few more locations may reach 90 degrees than we had previously. Previous Discussion: Eastern CONUS ridging will amplify across the Great Lakes tonight into tonight. The result will be seasonably hot temperatures 10+ degrees above normal for the next several days. With dew points pushing 70 degrees, sticky/muggy conditions are expected for Labor Day with heat indices in the low-to-mid 90s. High temperatures above 90F will mainly be confided to the river valleys and urban corridors this afternoon. While probabilities of nearing Heat Advisory criteria (AptT of 100F) are near-zero, we want to remind everyone to practice heat safety if outside this Labor Day. Overnight temperatures will provide little relief as morning lows dip only into the mid/upper 60s. Continued low-level moisture may foster the development of at least patchy areas of dense fog. && .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/... Continued eastern CONUS ridge building with axis directly overhead means Tuesday will likely be the warmest day of the week. Most of the forecast area outside of the Laurel highlands and ridges have a high probability of reaching 90F. Afternoon dewpoints are expected to be a degree or two higher than today on Tuesday, pushing heat indices into the mid/upper 90s. Wednesday will be more of the same, though likely a degree or two cooler than Tuesday in most places. The potential limiting factors on Wed maxima are the extent of upper-level cloud coverage ahead of a late-week trough and the degree of height falls that could reduce the ridge amplitude. Adjusted Wed highs down a couple degrees closer to the NBM mean consistent with previous shifts. Localized heat indices may reach 100F within the City of Pittsburgh Tuesday and Wednesday due to the urban heat island. This does not meet criterion for a widespread heat advisory, but impacts are still possible in a targeted area. We will continue to message extreme heat concerns in the HWO and may need a localized advisory near Pittsburgh at some point. Tuesday and Wednesday nights will continue to be warm, with lows in the upper 60s to near 70. && .LONG TERM /THURSDAY THROUGH SUN River valley fog, which developed overnight due to radiational cooling and low-lvl moisture will dissolve in the next hour. Otherwise, no major changes have been made to this forecast period.DAY/... Confidence is growing in the chance for thunderstorms Wed night as low pressure crosses the Great Lakes. Cold frontal timing on Thu is still uncertain: afternoon arrival would increase severe weather potential. Despite the uncertainty, a cold front is forecast to pass through the Upper Ohio Valley on Thu. The timing of its passage and strength of cold advection introduces some uncertainty in Thu high temperature, but the range of realistic possibilities is almost entirely below heat threshold no matter the timing. This passage will also introduce a sizable chance for precipitation. Intermittent passing shortwave troughs through the weekend around weak ern-CONUS troughing will increase precipitation chances, and stave off any chances of continued heat. && .AVIATION /13Z MONDAY THROUGH FRIDAY/... MVFR conditions will be brief at MGW due to river valley fog early this morning. Otherwise, VFR conditions will prevail the rest of the afternoon/evening for all terminals under high pressure. Winds will be directed from the west/southwest as the ridge amplifies. Based on Hi-Res soundings and cloud coverage statistics, there is a potential for cu field to develop late morning through early afternoon with diurnal heating. Fog is once again possible early Tuesday morning. Models are currently focusing reduced vis conditions north of PIT and within the river valleys between 09Z and 13Z. .OUTLOOK... NBM suggests isolated restrictions early Wednesday and Thursday morning. Precipitation chances may return late Wednesday into Thursday with a passing disturbance. && .CLIMATE... Record highs temps could be tied or broken at two climate sites on Tuesday, Sept 5th: New Philadelphia,OH (PHD): Record is 92F/2018; forecasted high is 91F. Wheeling,WV (HLG): Record is 92F/2018; forecasted high is 91F. && .PBZ WATCHES/WARNINGS/ADVISORIES... PA...None. OH...None. WV...None. && $$ SYNOPSIS...Hefferan NEAR TERM...Rackley/CL SHORT TERM...Rackley LONG TERM...Kramar/Rackley AVIATION...Hefferan CLIMATE...PBZ Staff