Area Forecast Discussion
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000 FXUS61 KPBZ 192209 AAA AFDPBZ Area Forecast Discussion...UPDATED National Weather Service Pittsburgh PA 609 PM EDT Wed Apr 19 2017 .SYNOPSIS... A series of low pressure systems will keep periodic rain chances in the forecast through late week. && .NEAR TERM /THROUGH THURSDAY/...
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610pm update...have made adjustments to overnight PoPs in line with latest radar trends and hires model guidance. Leading edge of shortwave trough is crossing Western Lake Erie and is sparking a unorganized line of showers and storms. Shortwave is expected to continue to move east-southeast this evening and then be followed by a more significant wave of energy after midnight. Models are putting more emphasis on the first wave, as far as activity is concerned. Atmosphere ahead of trough is not overly unstable, either at the surface or aloft, but there may be enough shear to allow for, already developed convection, to be maintained through the evening and into the overnight hours. As the surface stabilizes this evening, additional convective development will be dependent on the unstable layer above 5000ft. Have increased the PoPs overnight, creating the timing and location in line with the movement and speed of the two waves tonight. Have also added in the mention of gusty winds and small hail. Confidence in stronger winds is low, but hail is a possibility as the freezing level is reachable and lies within the unstable layer aloft. Temperatures have been updated as well. Previous discussion... Shower activity will increase in coverage this evening as models have been consistent depicting a line of showers/thunderstorms this evening along surface boundary crossing the region from the NW to SE....followed by a MCV which is progged to cross the region later in the evening to several hours after midnight. Instability is expected to be minimal but there is potential for strong wind gusts with storms. Overnight lows will be mild with cloud cover and continued WAA ahead of the approaching cold front.
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&& .SHORT TERM /THURSDAY NIGHT THROUGH FRIDAY/... Showers and Thunderstorms will be possible again on Thursday mainly during the afternoon and evening once/if convective temperatures are achieved which now look to be in the upper 70s. Activity during the day will be largely dependent on instability. Any decent breaks in cloud coverage should be sufficient. The main threat is the potential for strong winds associated with any storms that have a strong enough updraft to push cores above drier air progged to be around 20-25kft. Update the HWO to mention slight risk of damaging winds for western zones. With near 99 percentile PWAT values by that time will need to keep an eye on rain rates. A cold front will cross Thursday night but unfavorable overnight FROPA timing and waning instability should help limit potential for severe storms. The SPC marginal outlook still appears reasonable at this time. Temperatures will return to seasonal levels by Friday. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... A trough from the NE CONUS to the Plains should keep rain chances and cool temps across the area over the weekend as it approaches and crosses the region, and as a surface low tracks to our south. Building ridging should return dry and warmer weather by early next week. && .AVIATION /22Z WEDNESDAY THROUGH MONDAY/... MVFR cigs are beginning to lift to just above 3kft this afternoon. This will likely continue through the evening before deteriorating tonight. A fast moving disturbance will move through the southern Great Lakes tonight, bringing showers and possible thunderstorms, mainly from HLG and north. Expect IFR restrictions beginning with this activity late evening into the overnight. Winds will generally be south 5-10 KTs. .Outlook... Restrictions will be possible Thursday with low pressure and a cold front. Widespread restrictions are possible Saturday and Sunday with strong low pressure. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...None. WV...None. && $$

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