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Area Forecast Discussion
Issued by NWS Pittsburgh, PA
Issued by NWS Pittsburgh, PA
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318 FXUS61 KPBZ 131818 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 218 PM EDT Tue Aug 13 2024 .SYNOPSIS... Dry weather with slowly rising temperature is expected through Thursday. Precipitation chances will increase Friday with slow low pressure passage, leading to mainly diurnally driven convection Saturday into early next week. && .NEAR TERM /THROUGH TONIGHT/... KEY MESSAGES: - Mainly dry day with temperatures near seasonal averages. ------------------------------------------------------------------- Weak shortwave movement over surface high pressure across the Upper Ohio River Valley region will yield scattered to occasionally broken afternoon cumulus development and seasonal temperature. Expect another clear sky and seasonably cool night across the region, creating low probability fog potential favoring the river valleys of northwest PA (where surface moisture is slightly more entrenched). && .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... KEY MESSAGES: - Dry weather with slowly rising temperature expected through Thursday. ------------------------------------------------------------------- There is high confidence in surface high pressure slowly traversing the region underneath height rises Wednesday into Thursday. Little variance is likely from forecasted values during this period as dry weather persists and area temperature climbs to and slightly above the daily average. Temperature will peak Thursday afternoon, but degree of heating may be slightly dulled if thicker high cirrus arrives earlier in the day ahead of the next low pressure system. && .LONG TERM /FRIDAY THROUGH MONDAY/... KEY MESSAGES: - Precipitation chances increase Friday into Saturday with slow passage of an upper level trough. - Ensembles favor Great Lakes troughing into early next week that would maintain low probability, diurnally driven convection. ------------------------------------------------------------------- Ensemble synoptic pattern analysis shows relatively minor differences of the progression of an upper level trough towards the Great Lake region starting Friday and lingering into early next week. Broadly speaking, this pattern will promote periodic shower and thunderstorm chances, low probability severe/flash flood threats, and near to slightly below average temperature. The initial wave of showers and thunderstorms are likely to arrive Friday morning ahead of a rotating shortwave through the based of the trough positioned over Minnesota. Mesoscale variability does exist on the influence of the antecedent dry air mass and location of best lift/forcing; these factors will drive precipitation coverage and intensity. Early trends favor some splitting of eastward moving convection lending to higher probabilities south of I-70 and north of the I-80 corridor. More robust convective development is likely late Friday through Saturday as the upper trough positions just west of the area and both the pre-frontal trough and surface cold front swing through. Ensemble means hint at some marginal instability with dry air aloft leading to a low end wind threat Saturday afternoon, but confidence is still low on conditions all aligning properly. Sunday into Monday is likely to feature isolated to scattered diurnally driven convection with the backside of the trough remaining overhead. && .AVIATION /18Z TUESDAY THROUGH SUNDAY/... VFR largely expected through the TAF period with sct-bkn VFR cu possible with a crossing weak shortwave. Cu will dissipate this evening leaving a clear sky and light wind as sfc high pressure remains across the region. Fog development will be possible overnight under this setup. 12Z guidance had continuity with previous runs in hinting at an all or nothing type of setup, but overall decreased probabilities (30-20% chance of both less than 5mi and 0.5mi). Forecast soundings do show a favorable hydrolapse dewpoint depressions should be at or very close to zero.. Forecast confidence will be high later in the afternoon after observing dewpoints when the boundary layer is well mixed and crossover temperatures can be determined. .Outlook... VFR is expected through Thursday under high pressure. Periodic restriction chances return Friday through the weekend with slow moving low pressure. && .PBZ WATCHES/WARNINGS/ADVISORIES... PA...None. OH...None. WV...None. && $$ SYNOPSIS...Frazier NEAR TERM...Frazier SHORT TERM...Frazier LONG TERM...Frazier AVIATION...88