Area Forecast Discussion
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196 FXUS61 KPBZ 220418 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 1218 AM EDT Tue May 22 2018 .SYNOPSIS... Active weather through Tuesday night with a series of showers and storms moving through. A dry mid to late week is forecast. Unsettled weather returns the back half of the upcoming holiday weekend. Above normal temperatures are predicted the next seven days. && .NEAR TERM /THROUGH TODAY/...
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Convection has weakened considerably over the past couple of hours as it moved into a generally more stable regime over our CWA. Downward trend in lightning as well as cloud top temperatures match up well with weakening radar returns. Will continue to watch rainfall totals in a couple areas that have received multiple rounds of rain as PWAT remains high and warm cloud depths top 10K feet. However, the isolated nature of truly heavy rainfall rates suggests that excessive rain/flooding will remain a low overall risk. Have updated PoPs to slowly move precipitation across in concert with HRRR runs for the rest of the night, with high likely/categorical values. Upped QPF in some areas as well, and made some minor changes to other grids. Previous Discussion: Cloud forecast is tricky Tuesday through early afternoon because of overnight precipitation and left over residual moisture. If the sky clears and daytime heating occurs another round of showers and storms would move through during the afternoon hours ahead of a mid level piece of energy. These storms could contain gusty winds which may attain severe levels. The marginal risk in the latest SWODY2 as expanded to cover the entire region. Given low confidence in amount of daytime heating this risk level seems appropriate. H7-H5 lapse rates push 6.5Ckm-1 during the afternoon thus if surface instability is present there will be more to tap as air parcels rise. Continued with likely pops for the afternoon hours over all of western Pennsylvania, northern West Virginia, and western Maryland.
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&& .SHORT TERM /TONIGHT THROUGH THURSDAY/... Broken line of showers and thunderstorms should be through the mountains by 3Z owing to dry weather the balance of the night. Any fog development will be confined to northern areas where boundary layer winds shall be lighter. Not to keen on widespread fog development given BUFR soundings still show a fair amount of moisture in the lowest few thousand feet, so decided to leave fog out of the weather grids at this time. High pressure builds down from the eastern Great Lakes Wednesday. With the northerly wind component this will be the coolest day of the next seven, but temperatures still should climb well into the 70s given amount of sunshine and progged 10C temps near the top of the mixing layer. As the surface anticyclone settles on top of the area, Wednesday night into Thursday morning is the best time window for fog potential. We are in the stretch of the longest daylight hours of the year, so confidence is too low for inclusion. Diurnal cumulus develops downwind of Lake Erie Thursday other than that a splendid day with lots of sunshine. Boundary layer temps increase 2C, so daytime highs will be around 5F warmer than Wednesday. && .LONG TERM /THURSDAY NIGHT THROUGH MONDAY/... Highlights: - Dry weather to start - Trouble in the tropics - Wet second half of Memorial Day Weekend High pressure provides dry weather through the first half of Saturday as mid level ridging takes control over the eastern United States. With H5 heights around 582dm and H8 temps around 16C daytime highs should be well into the mid 80s outside of the mountains and perhaps north of I-80. Plenty of sunshine and warm temperatures between H6-H7 will put a cap on any cu from growing into a shower or storm across the higher terrain. The forecast gets messy Saturday afternoon through Memorial Day. A potential tropical system will slowly spin along the Gulf Coast states, while moisture is pumped north from the gulf on the windward side of the Appalachians. This in conjunction with an active jet stream brings several disturbances across during the aforementioned time frame. PWATS peak around 1.7" while warm cloud depths run near 12KFT. This spells potential for heavy rain and potential flooding if an any gets hits repeatedly. Right now, its too hard pinpoint location of showers with embedded thunder so nothing that meets confidence for insertion into the hazardous weather outlook. Severe thunderstorm threat appears low given the amount of clouds forecast. GEFS/GEPS remain in good agreement on the large scale synoptic system outside small location differences near the Gulf Coast. The timing of the shortwave troughs place highest QPF values in the mountains Saturday evening through Memorial Day. NAEFS pwats are in the low end of the probability of extremes using CFSR climo, thus for now do not see a high end event. && .AVIATION /04Z TUESDAY THROUGH SATURDAY/... VFR conditions and dry weather are generally expected into the overnight hours before widespread rain moves in from the west. Ceiling restrictions are not expected until Tuesday morning, and primarily across the north. Widespread visibility restrictions are not expected, although MVFR/IFR conditions could be possible in isolated heavier rain. Isolated thunderstorms will be possible overnight, and again Tuesday afternoon. OUTLOOK... Restrictions in showers/thunderstorms are likely into Tue eve with a crossing cold front. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...None. WV...None. && $$

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