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Area Forecast Discussion
Issued by NWS Pittsburgh, PA
Issued by NWS Pittsburgh, PA
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496 FXUS61 KPBZ 111727 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 127 PM EDT Sun Aug 11 2024 .SYNOPSIS... Mostly dry conditions and slightly below-normal temperature are expected through early week. Temperature begins to moderate by mid-week with broad rain chances possible by the end of the week. && .NEAR TERM /THROUGH TONIGHT/... KEY MESSAGES: - Max/Min temperature remain a couple degrees below normal - Chance of showers north of I-80 this afternoon and again tonight ------------------------------------------------------------------- There is high confidence in the weather pattern today and tonight, with a strong upper-level low in vicinity of Toronto, and a jet streak advancing newd to aid in the advance of a weak cold front into the upper Ohio Valley. The jet will advance newd today across the region, fostering enhanced low-level convergence near and north of I-80 during peak heating. A deeply mixed boundary layer and modest moisture within this convergence zone likely will support the development of scattered showers in the 16-18Z timeframe. Owing to the spatial uncertainty in model placement of showers, NBM inherently underplays the PoPs in such situations, so have made some manual adjustment to PoPs this afternoon and again this evening as the upper low`s trough axis advances across Lake Erie and potentially reinvigorates showers overnight in the I-80 corridor. Any showers likely will be gone before sunrise Mon morning, and could amount to little more than 0.1" in localized areas north of I-80. Most areas will remain dry. && .SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/... KEY MESSAGES: - Max/Min temperature remain a couple degrees below normal - Possibility of a shower or two Tuesday afternoon - High confidence in the weather pattern ------------------------------------------------------------------- Thru Tue, there remains high confidence in the weather pattern as ensemble clustering depicts very little deviation from the grand ensemble mean. An amplified mid-level ridge will build across the central CONUS and into Canada as sern-CONUS high pressure remains in place. This pattern leaves the upper Ohio Valley beneath broad nwly flow aloft and building sfc high pressure as the Canadian low weakens and exits. Overall, the pattern is suggestive of general strong heating offset by modest cold advection, diurnal fair-weather cu and deep mixing of the boundary layer. The net result for Mon will be dry weather, nwly sfc wind that may exhibit modest diurnal gustiness, and occasional clouds with daily maxima climbing toward the upper 70s-lower 80s. Tue afternoon may see a weak disturbance advance across the region within this nwly flow aloft, potentially invigorating a few showers. At this time, the probability of showers is low (around 20%), but bears watching for potential increase if moisture return occurs. && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... KEY MESSAGES: - Max/Min temperature closer to normal mid- to late-week timeframe - Rain chances increase late week amid moisture return and greater forecast uncertainty in the weather pattern ------------------------------------------------------------------- Medium confidence remains thru mid-week as the central-CONUS ridge axis shifts ewd, suggesting moderating temperature for the upper Ohio Valley by Wed. Ensemble clustering suggests increasing uncertainty in the weather pattern by Thu as upper-level troughs, progressing ewd from the Pacific NW region, potentially weaken the downstream ridge. By Day 6 (Aug 16), the strength of the lingering ridge is considerably questionable given evidence of a multimodal distribution, as some ensemble members show a more-amplified ridge axis while others depict heights considerably below the ensemble mean. All told, a general evolution of the upper-level pattern toward wnwly flow aloft seems likely by week`s end, supportive of progressive embedded shortwave troughs and greater potential for showers and storms as moisture returns to the region. && .AVIATION /18Z SUNDAY THROUGH FRIDAY/... VFR conditions will continue through the TAF period with high confidence for terminals south of I-80. Here, scattered to broken fair weather cumulus are expected to persist through the afternoon. Deep mixing will allow wind gusts in the 15 to 20 knot range as well, out of the west. North of I-80, at FKL, passage of a shortwave trough, along with marginal moisture, may allow for a few showers this afternoon and evening, with a brief drop to MVFR conditions possible. Best chance will be between 18 to 22Z, handled via TEMPO group. Tonight, the brief shower chances continue at FKL, while most other locations continue to enjoy VFR conditions and decreasing wind, although a few high clouds may stream across the sky. Another round of scattered to broken cumulus is likely by midday Monday, along with light W/NW wind. .Outlook... General VFR is expected through early week as surface high pressure builds under broad upper troughing. && .PBZ WATCHES/WARNINGS/ADVISORIES... PA...None. OH...None. WV...None. && $$ SYNOPSIS...Kramar NEAR TERM...Kramar/MLB SHORT TERM...Kramar LONG TERM...Kramar AVIATION...CL