Area Forecast Discussion
Issued by NWS Pittsburgh, PA
Issued by NWS Pittsburgh, PA
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278 FXUS61 KPBZ 041146 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 746 AM EDT Thu Jul 4 2024 .SYNOPSIS... A series of disturbances will create periods of scattered thunderstorms through Friday, offering low probabilities for localized flash flooding and gusty wind. Dry weather with seasonable temperature will return Saturday into Sunday. && .NEAR TERM /THROUGH TONIGHT/... KEY MESSAGES: - Scattered showers and thunderstorms are possible today, favoring locations along and south of I-70. These storms may pose a localized flash flooding and strong wind threat. - Should not be a washout for your Independence Day plans, but remain weather-aware. ------------------------------------------------------------------- Broad surface high pressure parked over the southeast and upper ridging across the East Coast keep warm and humid conditions in the forecast today. Surface analysis shows a relatively warm and muggy morning underway, with many area temperatures in the mid-70s at 3 AM, and dewpoints sitting near 70F. With high humidity and overcast skies, temperatures will only drop another few degrees by sunrise. Save for patchy morning fog, a relatively quiet morning is in store. Isolated to scattered showers and thunderstorms are expected again today as another weak shortwave crosses the area. After a few isolated morning showers, better chances for rain will be this afternoon and evening, with focus for activity mostly along and south of a stationary boundary lying along the I-70 corridor. For those of us north of I-70, this will mean mainly dry conditions save for a few stray showers and thunderstorms today. Those south of I-70 will see increasing coverage this afternoon and evening, but will still remain scattered to isolated, and shouldn`t be a full afternoon washout. South of I-70, modest instability (around 1000 J/KG), weak lapse rates, and weak forcing should limit concerns for damaging wind and localized flash flooding, but low probabilities remain given near-record PWAT values, enough column shear, and potential for some storm training with parallel storm flow and surface boundary. Any flooding or severe wind threat will be maximized in the afternoon/evening period when surface-based instability will be maximized. These threats will trend down through the evening and overnight. With persistent cloud cover through much of the day, high temperatures will end up nearer to seasonal norms and about 5 degrees cooler than what we saw Wednesday. Increasing coverage of showers and thunderstorms areawide is expected later tonight ahead of the approaching trough, but this should be after [most] firework shows are over (we all have that one neighbor...). Have outdoor holiday plans? We recommend checking in on the radar and forecast every now and then this afternoon in case rain is moving your way. && .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... KEY MESSAGES: - More widespread coverage is expected Friday, with damaging wind and flash flood threats remaining possible. - Dry and more seasonable weather returns on Saturday. ------------------------------------------------------------------- By Friday, a more organized shortwave and surface low pressure crossing the Great Lakes will lift the stationary boundary northward as a warm front, eventually pushing a late-day cold front through the region. Increases in storm motion and lack of parallel boundary flow should temper flash flooding risks. However, the environment will remain similar to today, but with convective coverage expanding to most of the forecast region. The afternoon/evening timeframe remains the most likely period of impact of hazardous weather (primarily damaging wind). Cloud cover and limited insolation/surface destabilization is likely to again be the limiting factor for severe weather, but guidance indicates a more favorable thermodynamic profile for severe weather Friday versus today. More robust breakup of late morning/early afternoon cloud cover than is currently forecast is likely to mean more robust convective development in the afternoon. Passage of the surface cold front and upper shortwave will diminish storm chances Friday night, with dry and seasonable weather returning on Saturday. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... KEY MESSAGES: - High probability for dry weather and slightly above average temperature the rest of the weekend. - Unsettled weather returns Tuesday through at least mid-week. ------------------------------------------------------------------- Confidence remains high in dry weather continuing through the weekend as surface ridging remains over the Ohio Valley and upper troughing persists over the Central Plains. Temperatures should remain near-normal on Sunday, but increasing return flow and warm advection on Monday ahead of the next low pressure system will drive daily highs back above-normal. Ensembles indicate more active weather Tuesday into mid-week as low pressure crosses and upper troughing sets up across the East. && .AVIATION /12Z THURSDAY THROUGH MONDAY/... A mix of cigs kicks off the TAF period as terminals range from IFR to VFR, based primarily on where the heaviest rain fell in the past 12-24 hours. Conditions gradually improve to VFR areawide by late morning or early afternoon. A few isolated showers are ongoing in the PIT/AGC/LBE area and VCSH has been included to start the TAF period to reflect this activity. Elsewhere, scattered shower and thunderstorm activity ramps up this afternoon and evening, though uncertainty remains rather high regarding the coverage and intensity of convection and therefore mostly VCSH/VCTS has been maintained in TAFs. Expect an overall weakening trend in convection after 00Z with instability waning overnight. A weak front stalled across the area will continue to result in generally light and variable winds throughout the period, with the exception of gusts in and around thunderstorms. Restrictions likely return early Friday morning, especially in areas that see rainfall today/tonight. .Outlook... Additional rounds of showers and thunderstorms (with occasional restrictions) are expected episodically through early Sat as a cold front slowly crosses. VFR should return Sun amid high pressure. && .PBZ WATCHES/WARNINGS/ADVISORIES... PA...None. OH...None. WV...None. && $$ SYNOPSIS...Frazier NEAR TERM...Rackley SHORT TERM...Rackley LONG TERM...Rackley/Frazier AVIATION...Cermak/Shallenberger