Area Forecast Discussion
Issued by NWS State College, PA

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826 FXUS61 KCTP 231133 AFDCTP Area Forecast Discussion National Weather Service State College PA 733 AM EDT Wed Aug 23 2017 .SYNOPSIS... A much cooler and drier air mass is sliding in from Canada this morning. High pressure will control the weather into next week. && .NEAR TERM /UNTIL 7 PM THIS EVENING/... As high clouds peel back, more fog is revealed. The strong sun should dissipate it by 10 am - and then self-destruct into a field of diurnal cu. All the showers should be done over the south. Prev... Cold front sliding through and dewpoints have dropped into the 50s in the north. This dry air will continue to spread south and east this morning and bring a refreshing change. Some fog has begun to form at BFD despite the dewpoint drop as the wind has gone calm. The WNW wind may return there before morning. But, for the time being, The GOES-16/R fog channel difference product is showing the dendritic pattern already showing up as the high clouds slide to the east. I have added fog to the valleys as temps are cold enough. Any sprinkles across the southern tier and far eastern zones should dry up before sunrise. The rest of the day will be fair and mainly dry. After the northern valley fog burns off, some taller cu should develop over far wrn NY and nwrn PA. These diurnal cu could make a sprinkle or two in the N. With such dry air at the surface, I can`t see much actually hitting the ground from 4-5kft cloud bases. Temps will be pretty close to normal in the SE half of the fcst area, but about 3 to 5F below normal in the NW half, especially on the hill tops. && .SHORT TERM /7 PM THIS EVENING THROUGH 6 PM THURSDAY/... Cold air in the form of 8H temps as low as +6C (1-2sigma below normal) will slide across the Great Lakes and settle in for quite a few days. Decoupling to calm air tonight will help maximize radiational cooling and help fog to form in the valleys, but some cloud cover over the west may keep the fog in check. Mins will be 45-60F across the area. A potent short wave trough will push across the Great Lakes Thursday or Thursday night. The NAM is quickest with this feature, but most other models delay the window of best forcing until Thurs night. This feature is strong enough that - even without anything more than meager lake moisture - it could generate an organized area of showers. Due to the timing uncertainty and lack of deep moisture, I have capped the POPs in the low-end chance range (30-40pct) and held mentions to only the NW third/half of the area for later Thursday and Thursday evening. Maxes will be 5-6F lower than Wed values in the m60s-m70s. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... An extended period of early autumn-like weather will continue right through the upcoming weekend as a -2sigma upper trough (and similarly anomalous/cool 850 mb temps) moves over the Great Lakes and NE U.S. 1026-1028 mb SFC High (+2-3 Sigma) over south-central Canada will drift slowly to the Great Lakes by this weekend. GEFS mean 850 mb temps will dip about 2-3 deg C in all locations for Friday-Sunday, leading to max temps averaging 5-10 F below normal (with min temp departures about 10-13F below normal) as a large Canadian High Pressure area pushes SE across the Glakes Region and becomes centered over the NE states. Lows Fri/Sat/Sun mornings with high centered overhead will be dipping into the l-m 40s over the Northern Mountains (and deeper valleys of the Central Mountains) and solidly into the 50s elsewhere. Some of the perennial cold spots near and to the east of KBFD could see readings of 38 or 39F. && .AVIATION /12Z WEDNESDAY THROUGH SUNDAY/... Not a bad morning out. Mainly VFR now, with just some high clouds. Expect winds to kick up at times today. Main change to the 12Z TAF package was to add some fog late tonight and early Thursday morning. Temperatures fcst to drop to fcst dewpoints, and with light winds, would expect some fog. .OUTLOOK... Thu-Sun...No sig wx expected. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Dangelo NEAR TERM...Dangelo SHORT TERM...Dangelo LONG TERM...La Corte/Lambert AVIATION...Martin

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