Area Forecast Discussion
Issued by NWS Pittsburgh, PA

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301 FXUS61 KPBZ 171945 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 345 PM EDT Fri May 17 2024 .SYNOPSIS...
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Unsettled weather continues through Saturday with periodic showers and a few thunderstorms. Near to above normal temperatures will continue. Dry weather returns by Sunday afternoon, and continues into early next week with a warmup.
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&& .NEAR TERM /THROUGH TONIGHT/...
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KEY MESSAGES: - Showers and a few thunderstorms will continue into the evening as a trough passes. - Localized heavy rainfall totals and water issues are possible, and rotating cells will need to be monitored. _____________________________________________________________ Steady rain coverage has waned somewhat as the pattern has taken on more of a convective look. A couple of low-topped supercells have managed to form, taking advantage of modest but sufficient levels of 0-3km CAPE and shear from a low-level boundary, creating a few funnel cloud reports. Showers, and a thunderstorm or two, will remain possible this evening as a shortwave trough axis crosses. Any further severe potential looks limited to these low-topped, short-term rotations that could drop a very brief tornado. The storms are too short to produce large hail, and there is not much potential for straight-line wind from these storms either. We also need to continue to monitor the heavy rain/isolated flash flooding potential, although the more scattered nature of the storms will help to mitigate this to some degrees.
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&& .SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/...
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KEY MESSAGES: - Shower chances continue along with above normal temperatures. _______________________________________________ The upper trough will continue to slowly sag to the east Saturday afternoon and evening. Forcing overall becomes more diffuse, and thus more scattered activity is foreseen. Activity will be a bit more concentrated along the ridges though, as some left entrance region jet dynamics skim the region. Severe chances remain negligible, and the heavy rainfall threat overall will be lower. The majority of the CWA should dry out Saturday night as the trough departs and ridging expands over the Ohio Valley. Still, a few showers may linger in the ridges to the southeast of Pittsburgh into Sunday morning, thanks to lingering moisture and easterly flow. Sunday afternoon and night will feature a relative lack of clouds as the upper ridge settles in and surface high pressure takes control. Temperatures will nudge a bit higher in the sun, with readings in the mid 70s to around 80 fairly widespread, around 5 degrees above average.
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&& .LONG TERM /MONDAY THROUGH THURSDAY/...
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KEY MESSAGES: - Ridging should result in dry and warmer weather into early next week. - Rain chances return for Wednesday and Thursday, with some potential for strong thunderstorms.. ____________________________________________________________ A dry forecast continues for Monday and into Tuesday as ensembles largely agree on 500mb ridging and surface high pressure. The rising heights will lead to increasing warmth; temperatures may climb well into the 80s by Tuesday, levels last seen early in May. The ensembles start to diverge a bit on the handling of the next shortwave trough, which crosses the northern/central Plains and into the Great Lakes during the Wednesday to Friday period. Cluster analysis shows some strength and timing differences with this wave, with GEFS generally more in favor of a slower, weaker wave than many of the ENS members. These differences point to different scenarios regarding rainfall amounts and severe weather chances. Still, given the warmth and potential instability ahead of the system, along with increased shear, we will certainly need to watch for the chance of impactful thunderstorms. Indeed, both CIPS and CSU machine-learning guidance point to severe potential on Wednesday and Thursday. In any case, PoPs in the 50-70 percent range as suggested by the NBM are justified. Temperatures will remain above normal, but will likely be muted by Thursday given clouds/rain and a possible cold frontal passage. By Friday, scattered showers may remain in a continued troughing pattern and moisture in low-level northwest flow. Temperatures may be closer to seasonable levels by this point.
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&& .AVIATION /18Z FRIDAY THROUGH WEDNESDAY/...
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A scattering in - Near-normal high temperatures and above-normal low temperatures can be expected. the precipitation shield and cloud deck is now noted working into eastern Ohio this afternoon as slightly drier air intrudes from the west. Some CIG recovery is expected into the early afternoon based on upstream obs and hi res guidance save FKL and DUJ which are favored to remain MVFR. Precipitation coverage will take on more of an isolated to scattered nature this afternoon, though with that we`ll see increasing thunder probabilities. Confidence in coverage and exact timing of a thunderstorm at any site remains low at this time, but any that do see a heavier shower/thunderstorm could experience a brief drop in both CIG and VIS to as low as IFR. Outside of the scattered showers, conditions should remain low end VFR/high end MVFR with increasing probabilities for MVFR after 23z. By the overnight hours, all sites should see MVFR to IFR conditions with a 70-90% confidence. With lingering low level moisture from earlier rainfall, low confidence chances for fog increase after 06z; the wrinkle is a passing wave that will likely reinvigorate showers after midnight, with best chances south and east of Pittsburgh, which may result in more stratus formation than fog formation. MVFR conditions will be slow to erode Saturday morning with probability for MVFR CIGs remaining 60+% through 16z but will slowly begin to see improvement from the west. .Outlook... Upper trough passage to the south Saturday will maintain SHRA/TS chances focused south of KPIT. VFR and dry weather become high probabilities Sunday into Monday under the influence of high pressure.
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&& .PBZ WATCHES/WARNINGS/ADVISORIES... PA...None. OH...None. WV...None. && $$ SYNOPSIS...CL NEAR TERM...CL SHORT TERM...CL LONG TERM...CL AVIATION...MLB