Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 220155 AFDCTP Area Forecast Discussion National Weather Service State College PA 955 PM EDT THU JUL 21 2016 .SYNOPSIS... Pennsylvania will be on the northern edge of a subtropical ridge into next week. A couple of weakening cold fronts will pass through the area Friday and again on Saturday. && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
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For the 10 PM update, did cut back on pops some overnight. Left some mention of showers and storms across the north, given rather strong warm advection noted on the 00Z BUF sounding. Earlier discussion below. After a cool start early today, the temperature was 91 degrees here at the office just before 6 PM. However the dewpoints across the area are still mainly in the 50s. No real change made to fcst package this pt. Convection over the central Great Lakes is falling apart as it moves toward NW PA. Left pops for late tonight as is for now. Will continue to look at how second area of storms over WI holds together. Dewpoints rather dry across our area. Most likely will cut pops down on the late evening update. For now will hold as is, still a lot of question to how high dewpoints and CAPE will get late tonight into Friday. Earlier discussion below. High pressure will move off the Mid Atlantic coast today...allowing return sw flow to advect warmer and eventually more humid air into the state. Large scale subsidence and a dry airmass in place will ensure another dry day with abundant sunshine. GEFS mean 8h temps of around 18C will translate to max temps from the mid 80s over the high terrain of the north and west to around 90 in the valleys. The overnight will begin dry before remnant convection from an MCS currently diving through the Central Gr Lakes makes a run at my NWRN zones. We should remain dry through late evening with the chances for rain start to ramp up from midnight onward.
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&& .SHORT TERM /6 AM FRIDAY MORNING THROUGH 6 PM FRIDAY/... Shortwave topping the ridge into the nw flow aloft will advect increasing moisture/instability into the region later tonight and Friday. Ensembles point to an increase in the PWATs ahead of the shortwave and associated weakening cold front. 00Z NCAR ensemble supports the idea of a dying line of thunderstorms working into the nw mountains during the few hours either side of sunrise as the parent shortwave and best large scale forcing pass well north of the state. During the day the weakening cold front will be battling high heights aloft as it drops se into the region. After the early day activity fades, diurnal heating and weak convergence with the dying front will bring the chance for additional showers/thunder mainly during the mid day and afternoon hours and mainly over northern areas. Deterministic guidance shows mid level temperatures on the order of 9-11C which will act as a convective deterrent, limiting the extent of development and doing little to break the recent extended period of widespread dry conditions we have been experiencing. 00Z NCAR ensemble data indicates the best chance for late day thunderstorms will be across northeast PA, closest to trailing shortwave tracking across upstate NY. SPC has placed nearly all of central Pa in a marginal risk area Friday, but with the expected warm mid levels, thinking is that convective activity will be widely scattered with the very far north being most susceptible to a few strong storms. 8h temps rising to near 20C should translate to max temps from the m/u80s over the Alleghenies, to 90-95F elsewhere. The heat, combined with rising dewpoints, should result in widespread heat indices in the 90s. && .LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/... Big story in the extended fcst is expected heat wave lasting into early next week, as axis of subtropical ridge briefly shifts from the plains to the northeast conus. Anomalous upper lvl ridging building over PA should bring hot and mainly dry wx this weekend, as warm temps aloft suppress convection. Next chance of shra/tsra for most of the area comes Monday ahead of shortwave working across the Great Lakes. However, any rainfall Monday is likely to do little to stem the dry pattern we have been in. Latest GEFS mean qpf is up to a half an inch at most. 12Z ECENS/NAEFS mean 8h temps are near 22C Saturday through Monday, indicating the potential of several days in a row with highs in the 90s in the valleys. The hottest temps look to be on Saturday as latest GEFS gives high temperature anomalies in the +4 standard deviation and have slightly backed off on Sunday. Have adjusted Max temperatures accordingly. Heat indices around 100F appear possible by Mon across the Susq Valley, as higher dewpoints are advected into the area. Overnight lows are also a concern as the area doesn`t cool off at night through the weekend with Southern PA lows in the 70s with highest readings Monday morning. Some modest cooling appears likely by Tue/Wed of next week behind weak cold front. However, temps still likely to remain somewhat abv normal within a generally zonal flow. && .AVIATION /02Z FRIDAY THROUGH TUESDAY/... VFR conditions currently exist over the region, and are expected to persist overnight. Convective line just moving over western Lake Erie is rapidly weakening, and expect this line may entirely fizzle before reaching any central PA airfields. Have therefore removed VCTS from KBFD TAF for the overnight. Isolated to widely scattered thunderstorms are possible across the entire airspace Friday into Friday night, but coverage and certainty too low to include in any TAFS at this point. Highest risk would likely be across northern and central areas. OUTLOOK... SAT-SUN...Early morning fog possible...otherwise no sig wx. MON-TUE...Restrictions possible with a chance of SHRA/TSRA. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...La Corte NEAR TERM...La Corte/Martin SHORT TERM...La Corte LONG TERM...Fitzgerald/Ceru AVIATION...Jung

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