Area Forecast Discussion
Issued by NWS Pittsburgh, PA
Issued by NWS Pittsburgh, PA
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915 FXUS61 KPBZ 142337 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 737 PM EDT Fri Jun 14 2024 .SYNOPSIS... There is high confidence Sunday will be the start of a particularly dangerous, historic, long- duration heat wave for western Pennsylvania, northern West Virginia, and eastern Ohio. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... KEY MESSAGES: - Severe probability lowering as instability weakens with the loss of daytime heating. - Patchy fog may develop within river valleys, notably south of Pittsburgh. ------------------------------------------------------------------- 630pm update... The main areas of convection will continue to shift south and east of the region ahead of the surface cold front. Lingering passage of the front may still allow for isolated convection as it provides enough lift with up to 1000 J/kg MLCAPE available. Amid approximately 50kts of effective shear, a severe threat (mainly wind and hail) remains possible but decreasing in probability. Instability will continue to decline with the setting sun and should allow for further erosion of the Severe Thunderstorm Watch area this evening. As dry weather and clearing skies develop tonight amid building high pressure, there will be a battle between incoming drier air/mixed wind and radiational cooling/boundary layer moisture. Localized occurrences of fog may develop where the cooling and residual moisture are maximized, likely favoring river valleys south of Pittsburgh. && .SHORT TERM /6 AM SATURDAY MORNING THROUGH SUNDAY NIGHT/... KEY MESSAGES: - Dry weather Saturday and Sunday. - Near normal temperatures Saturday with a jump to 5-10 degrees above normal on Sunday. ------------------------------------------------------------------- Heights rise into Saturday as upper ridging builds and surface high pressure slides in to the north. Temps won`t rebound much in northerly flow in the wake of the boundary and dew points will likely mix out some in the afternoon with a dry boundary layer providing a pretty comfortable day. Upper ridging begins to build stronger making a run at 588-590dm by Sunday to kick off the first day of increasingly hot conditions. Surface high pressure establishes off to our east and southwest flow on the west side of the 850 mb ridge axis will induce warm advection with ensemble 850 temps up to 15-17C. This will support widespread upper 80s with even a 40-70% chance of 90F+ for Pittsburgh south and west. && .LONG TERM /MONDAY THROUGH FRIDAY/... KEY MESSAGES: - High confidence in a dangerous heat wave setting up early next week with major heat impacts possible. ------------------------------------------------------------------- Guidance has been consistent that a potentially-historic ridge will continue to strengthen across much of the central and eastern CONUS into the middle of next week. WPC ensemble clusters are highly consistent through Tuesday, indicating high confidence in the temperature forecast. Near-record breaking heat will build in to start off next week. Significant heat is looking increasingly likely with this anomalously strong ridge from Monday and beyond when major to extreme heat risk is likely. NBM probabilities for high temperatures reaching 95+ degrees continue to go up, and are now widespread 60-90% across the area. These higher probabilities are especially prevalent in lower elevation areas (e.g., river valleys) and urban centers, which tend to be warmer than surrounding areas. In addition, dewpoints are currently forecast to remain in the mid 60s to lower 70s, which would result in high enough humidity levels to support heat indices climbing to, and potentially exceeding, 100 degrees. If dew points do hold toward the lower end of that spectrum, we may be able to make a run at 100 degree air temperatures Monday and beyond (last time at PIT was 7/15/95); NBM probabilities for that threshold are now up to 60% on Tuesday with ~50% chance for the remainder of the week. Only acting to exacerbate the prolonged heat effects will be a 60-80% chance of low temperatures greater than 70 degrees through the end of the week. Heat impacts will need to be closely monitored and headlines may need to be considered. Three out of four clusters maintain at least a 594dm ridge through June 22nd with the one exception being a lower probability solution than the others. Return intervals of these heights dating back to 1979 are just about out of the climatological range. CPC suggests that excessive heat may last through June 24th, indicating the potential for a long-duration excessive heat threat. The last comparable, long-duration heat event was from June 1994. Impacts include heightened heat-related illnesses and potential power grid issues with increased demand. It is strongly encouraged to know where cooling shelters are located and stay hydrated. There may be little relief at night. Gather food, water and medication now. Make a list of friends and family to check on and help them prepare. Strongly consider rescheduling outdoor events. Prolonged exposure to excessive heat was the primary cause of weather-related fatalities in 2023. && .AVIATION /00Z SATURDAY THROUGH WEDNESDAY/... Isolated showers and thunderstorms will slowly move southeast through 04z ahead of the surface cold front. After frontal passage, localized areas of patchy fog may develop where rain reinforced boundary layer moisture. This lends to KMGW and KDUJ as the most plausible but some maintenance of mixed winds and dry advection make it a lower probability occurrence. VFR and dry weather with light northerly wind is likely the rest of the TAF period with building high pressure. .Outlook... High probability for VFR and dry weather through the middle of next week as strong ridging develops aloft. The only variance may come with isolated afternoon convection starting Monday, but upper ridging should suppress coverage and potential initiation. && .PBZ WATCHES/WARNINGS/ADVISORIES... PA...None. OH...None. WV...None. && $$ SYNOPSIS...Milcarek NEAR TERM...Frazier/Milcarek SHORT TERM...MLB/Milcarek LONG TERM...MLB/Milcarek AVIATION...Frazier