Area Forecast Discussion
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000 FXUS61 KPBZ 222152 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 552 PM EDT Thu Jun 22 2017 .SYNOPSIS... Downpours are possible through Friday night with a tropical airmass in place. A cold front sweeping through early Saturday will return comfortable humidity levels by the weekend. && .NEAR TERM /THROUGH FRIDAY/... With 6pm update, primary changes were to timing and coverage of precipitation. Training is occurring with storms across Armstrong and Indiana counties, with multiple flash flood warnings in effect. Elsewhere, rain has generally come to an end for the rest of the afternoon. The other change was to the timing of widespread precipitation moving into the region later tonight. Latest synoptic and high-resolution models all show a slight delay in arrival of rain, and have likewise delayed arrival times by a couple of hours. Previous discussion follows. Showers and storms will continue to ride east - southeast south of the warm front that is draped across northern Pennsylvania. The best instability resides farther south toward the I-70 corridor, however it will take an outflow boundary to trigger any convection due to the lack of synoptic triggers in this region. Any storm will be capable of producing downpours with the amount of low level moisture. The focus shifts to the southwest as a wave brings showers and scattered storms through after midnight. The overall speed of the system will keep the heavy rain threat to a minimum, however a quick inch of rain is possible given what happened this morning over parts of Greene county. Confidence is high enough to go categorical pops after midnight area wide. && .SHORT TERM /FRIDAY NIGHT THROUGH SATURDAY NIGHT/... DOWNPOURS POSSIBLE THROUGH FRIDAY EVENING WITH LEFT OVERS FROM TROPICAL STORM CINDY... For information regarding the threat of high water, please reference the hydrology discussion located near the bottom of the product. The remnants of Cindy pass Friday afternoon and evening. This will bring a widespread area of showers and storms to the region especially south of I-70. There should be not a lot of precipitation around during the morning and early afternoon hours, however with the approach of a the cold front during the afternoon hours this will trigger storms and interact with moisture associated with Cindy. The cold front crosses during the overnight hours Friday night so come daylight Saturday any measurable QPF should be east of the mountains. Clearing will rapidly take place before 15Z then a cu field will develop during the afternoon hours. Humidity levels will be noticeable lower as dewpoints drop into the 50s some 20F lower than today. Benign weather Saturday night with moisture arriving from the northwest ahead of the next upper disturbance. && .LONG TERM /SUNDAY THROUGH THURSDAY/... Highlights: - Cooler weather - No signs of a high water threat Full latitude trough will bring a period of below normal temperatures to the region. Afternoon high temperatures will be running nearly ten degrees below their normal benchmarks Sunday - Tuesday. With the trough axis overhead, scattered showers and perhaps a thunderstorm are possible through mid week, but with low level moisture lacking due to the placement of high pressure southeast of the western Great Lakes. A transitory high pressure takes over at weeks end bringing temperatures back to their normal location and returning dry weather. && .AVIATION /22Z THURSDAY THROUGH TUESDAY/... Scattered MVFR cigs will prevail under increasing moist low levels through the afternoon. Increasing instability and moderate levels of shear will support scattered showers and storms, mainly north along a frontal boundary, with potential impacts to KFKL and KDUJ. A few storms may produce strong gusts but will not make any mention of these conditions unless confidence increases. Otherwise, more notable weather and terminal impacts arrive overnight as moisture associated with remnants of tropical cindy approach and interact with a sagging cold front. Will trend all sites to MVFR, but some guidance suggests lower by midday Friday. Heavy rain will likely lead to brief IFR restrictions at any terminal but again, will not put this in at this time. Wind will remain wsw through the period, with gusts this afternoon with plenty of mixing and again Fri afternoon. .OUTLOOK... Widespread restrictions are likely through Saturday morning with the passage of a cold front. && .HYDROLOGY... A flash flood watch has been issued for areas along and south of interstate 70. A piece of energy crosses tonight and will bring upwards of an inch of rain as it passes. With flash flood guidance in the 3 hour time frame over 1.5 inches outside urban areas /Allegheny and western Westmoreland/. The current thinking is as long as we do not get too much rain this afternoon in one location we should be able to hold the rain overnight. The main concern would be QPF Friday afternoon and evening. Meteorologically values all point to high water issues with PWATS over two inches, warm cloud depths above 13KFT, and a strong low level jet. GEFS M-Climate values are near or at record levels for PWATS on return interval, and climate anomaly. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...Flash Flood Watch from 2 AM EDT Friday through late Friday night for MDZ001. OH...Flash Flood Watch from 2 AM EDT Friday through late Friday night for OHZ057>059-068-069. PA...Flash Flood Watch from 2 AM EDT Friday through late Friday night for PAZ021-029-031-073>076. WV...Flash Flood Watch from 2 AM EDT Friday through late Friday night for WVZ002>004-012-021-509>514. && $$ is the U.S. government's official web portal to all federal, state and local government web resources and services.