Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 202359 AFDCTP Area Forecast Discussion National Weather Service State College PA 759 PM EDT Tue Jun 20 2017 .SYNOPSIS... Weak high pressure will slide south of the commonwealth through Wednesday afternoon. Weak upper air disturbances will produce isolated showers across the northwest late tonight and over the rest of central PA on Wednesday afternoon, although most of the time with be fair and dry. A deep upper level trough will approach the region later this week and draw a plume of deep tropical moisture north from the Gulf Coast region. This will bring increasing showers and thunderstorms back to the state from late Thursday into early Saturday. Drier and cooler conditions will return later Sunday into next Monday. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... Visible imagery at 2330Z showing some vertical development to the cumulus across northern Pa. Will maintain a slight chance of a shower in this area until around sunset. After sunset, expect skies to become clear across much of central Pa. However, a potent shortwave diving southeast across the Grt Lks will push a band of weakening showers into northwest PA after about 03Z. Based on upstream lightning data and model CAPEs, will leave tsra out of the forecast for now, but can`t completely rule out a rumble or two over the northwest mountains around midnight. A blend of latest model data support overnight POPs from around 50 pct across Warren county, to around 20 pct across the rest of the northern mountains and <10 pct south of I-80. Mins shortly after sunrise Wed will vary from the low 50s over parts of the northwest mountains, to the low 60s across the Lower Susq Valley. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH 6 PM WEDNESDAY/... Models indicate shortwave will sweep eastward across central Pa between 12Z-16Z, accompanied by isolated/scattered showers, mainly along the I-80 corridor. A push of low PWAT air in it`s wake should result in a dry afternoon across northern Pa. However, diurnal heating will lead to some modest CAPEs across the southern counties, leading to isolated/scattered showers and a slight chance of thunder in the afternoon over that part of the state. Well mixed soundings and mean 850mb temps between 12-14C should translate to max temps from the low 70s across the highest terrain of the Alleghenies, to the low and mid 80s across the southeast counties. && .LONG TERM /WEDNESDAY NIGHT THROUGH TUESDAY/... The medium range flow pattern looks to be mainly dominated by a broad quasi-zonal flow between the subtropical ridge off the SERN US and a broad low over SRN Canada. After a couple of days with comfortable humidity, dewpoints and the corresponding chances for rain will start to creep up Thursday. GEFS shows the PWAT creeping up above normal during the day Thursday as the flow turns SWLY and of a warm front approaches from the Gr Lakes. By Friday the tropical airmass will have re-established itself with dewpoints well up into the 60s and lower 70s over the entire region making for a sticky end of the work week. Friday is also the trickiest part of the extended rain-wise as moisture from newly minted Tropical Storm Cindy in the Gulf gets funneled up the west side of the SERN upper ridge. The question remains how far north this moisture can get before being shunted east under the fast quasi-zonal flow over the northern US. As it stands, it looks like the best chance for widespread showers/thunderstorms will be during the day Friday into Friday night. The 12Z guidance suggests the heaviest rains stay south of our forecast area, but being days away yet, need to be monitored. The GEFS brings drier air in by early Saturday and even shows some below normal PWAT air in place by Sunday. The zonal flow is forecast to become more cyclonic during the weekend, which warrants the mention of small chance POPs, but less humid with just some spotty pop-up showers. By early next week there is disagreement between the broad cyclonic flow aloft in the GFS/GEFS and a stronger upper trough/low advertised in the ECMWF for later Monday into Tuesday. As of this cycle we are keeping an optimistic forecast to start next week. After a couple of warmer than normal days early in the period, temperatures are forecast to return to slightly below normal by the weekend lasting into next week. && .AVIATION /00Z WEDNESDAY THROUGH SUNDAY/... Mostly VFR through tonight. A few showers/isolated tstorm possible this afternoon over the NW mtns in proximity to a trough brushing that region. Outside of the isolated tstorm risk around BFD, biggest impact today will be breezy westerly winds increasing to around 15 mph with gusts to 25 mph. These diminish to 8 mph or less by early evening. .OUTLOOK... Wed...Mostly VFR conditions. Isold to sct SHRA poss mainly central and north Thu...Sct SHRA and Iso TSRA N. Fri...Cig restrictions poss west. SHRA likely / chance TSRA. Sat...Chance for SHRA/TSRA south. Restrictions poss early. Sun...Improving conds...mainly VFR. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Dangelo/DeVoir NEAR TERM...Fitzgerald SHORT TERM...DeVoir/Fitzgerald LONG TERM...La Corte AVIATION...DeVoir/RXR

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