Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 180631 AFDCTP Area Forecast Discussion National Weather Service State College PA 231 AM EDT Tue Jul 18 2017 .SYNOPSIS...
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A stalled front will remain hung up over the northwest part of the state tonight and Tuesday. Another front will move down from the north and stall over the region for the latter half of the week.
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&& .NEAR TERM /UNTIL 6 AM THIS MORNING/...
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Based on 06Z radar loop, have will remove mention of showers for the rest of the night. However, can`t completely rule out an isolated shower early this morning along corridor of highest PWATs running roughly along I-81. Biggest story early this morning will be the fog, which has already developed in the valleys of northern Pa. A calm wind and wet ground should promote developing valley fog across much of the remainder of central Pa toward dawn. Temps expected to dip into the mid 50s by dawn across the northwest mountains, where drier air has seeped in behind stalled cold front. Elsewhere, will be a warm and muggy night with mins in the 60s.
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&& .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM WEDNESDAY/...
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Scattered diurnally-driven thunderstorms will flare up again Tuesday afternoon along and south of stalled front. However, weak shear indicates storms will be of the pulse variety with little threat of organized severe weather. FFG values are running quite low across portions of the Susq Valley, but PWATS not particularly high Tuesday, so feel threat of flash flooding is fairly low. Have bumped max temps upward slightly based on GEFS mean 850 temps, which support highs from the low 80s across the high terrain of the Alleghenies, to near 90F in southern valleys.
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&& .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... Weak surface ridging and partial clearing should result in areas of fog Tuesday night into Wednesday morning. Wednesday into Wednesday night still looks like the driest 12-24hr stretch during the long term period. 17/12z medium range models depict a general east-southeast shift of the upper level ridge initially centered over the Central U.S. Fast west-northwest flow aloft on the northern periphery of the upper ridge will reside over the area into the weekend. The evolution of convection-producing waves within this belt of westerlies is depicted differently within various models and specifics such as timing and location will depend on details not well resolved until the very short term time frame. That said, the later periods will show a broadbrushed, redundant 30-50 percent POP with refinements expected at closer ranges. The other concern is for a period of hot/humid conditions across the Lower Susquehanna Valley with blended guidance showing at least 2 days of 90+F max temps with max heat index potential approaching 100F. The heat risk was added to the HWO. The hot temperatures should be eroded from the NW with time as the frontal boundary gradually sinks to the south in response to mean troughing developing late in the period. && .AVIATION /06Z TUESDAY THROUGH SATURDAY/... A weak frontal boundary will linger across the central mountains tonight before drifting east and dissipating on Tuesday. Convection this evening consolidated around a nearly stationary weak frontal boundary stretched across central PA - aided by a humid airmass in place. By 02z with loss of heating, most of the convection has dissipated, though isolated stronger storms will persist through ~04z near KJST-KAOO. Outside of very local restrictions around TSRA, conditions are primarily VFR across central PA. But as night progresses, fog looks to become an issue - primarily where rain has fallen, but also in the northern valleys. GLAMP and NAM are hitting the fog hard tonight at many terminals, but that looks overdone. Did mention fog just about everywhere, but with only brief forays into IFR at some sites just before sunrise. Scattered thunderstorms will fire again during the day on Tues over SE half of CWA (east of weak frontal boundary). .OUTLOOK... Wed...No sig wx. Thu...Sct TSRA impacts, mainly NW half. Fri-Sat...No sig wx. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Dangelo NEAR TERM...Fitzgerald SHORT TERM...Fitzgerald/Lambert LONG TERM...Steinbugl AVIATION...RXR

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