Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 211137 AFDCTP Area Forecast Discussion National Weather Service State College PA 737 AM EDT Mon Aug 21 2017 .SYNOPSIS... High pressure moving off the Mid Atlantic coast will bring a warm and increasingly humid southerly flow to the region into Tuesday. A strong cold front will move through the region late Tuesday and Tuesday night. Cooler and drier conditions will return for the second half of the week. && .NEAR TERM /THROUGH TONIGHT/... Radar shows scattered showers and thunderstorms moving mainly through southern NY with a few trailing smaller cells in McKean county. The HRRR weakens this activity by mid morning as it moves away from the instability. High pressure will slide off the coast and a warm and more humid airmass will return to the region. The shortwave will drift across the area this afternoon providing weak large scale ascent. Models agree in developing a fair amount of CAPE and eastern areas are also expected to see some moderate deep layer shear develop as well. SPC has outlooked our eastern zones with a Marginal Risk which looks entirely reasonable. Convection will tend to decrease quickly after sunset with a warm and muggy night in store ahead of an approaching cold front. The amount of cloudiness today could hamper eclipse viewing as clouds and showers begin to pop up this afternoon. As it stands now, it looks like my SWRN zones will enjoy the least amount of cloudcover. && .SHORT TERM /TUESDAY/... The big weather maker still looks to be a potent late summer cold front that will pass through the region Tuesday evening into early Wednesday. Consensus model timing shows the front just entering NWRN PA by 8PM Tuesday/00Z Wednesday. Models develop just some modest CAPE east of the front over much of central and western PA. The exception is over eastern PA in what appears to be a lee side surface trough feature. The ECMWF/GFS and the ensembles all develop a finger of moderate to strong instability over SERN areas along the coastal plain. Deep level shear is also progged to increase and exceed 35kt. Interesting to note that the GEFS shows very little unstable air from the cold front into central PA and the SREF which paints more CAPE overall, has a distinct minimum of instability over our area during the day into the evening. This suggests there could be a fair amount of pre-frontal cloudiness hindering heating. The whole region is painted under a Slight Risk which seems based more on expected impressive wind fields than model generated instability. Highs are still expected to rise into the 80s, to around 90 over southern areas before the clouds increase ahead of the front. A very humid airmass will make it feel warmer. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... After our surge of heat and humidity, the strong front will bring a noticeably cooler and drier airmass to the region starting midweek and lasting through the end of the week into the weekend. Interesting to note that the deterministic models show 850 temps as cold as 2-3C just north of the Canadian border behind the cold front, a reminder the change in seasons is not all that far away. Chilliest readings look to be the mornings of Fri/Sat/Sun with high centered overhead, dipping lows into the 40s over the Northern Mountains (and deeper valleys of the Central Mountains) and solidly into the 50s elsewhere. && .AVIATION /12Z MONDAY THROUGH FRIDAY/...
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Cluster of showers and storms over southwest NY state lifting northeast. Some adjustment made to the 12Z TAFS. Earlier discussion below. Less weight on fog now, given clouds moving in. Some storms near Lake Erie now. Mid level wind fields may support some strong storms today. Yesterday I was thinking today would be dry. However, strong warm advection may result in some showers and storms later today and early this evening. .OUTLOOK... Tue...Patchy AM fog poss. Late day/evening tsra impacts poss. Wed...Early AM low cigs poss BFD/JST. Thu-Fri...No sig wx expected.
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&& .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...La Corte NEAR TERM...La Corte SHORT TERM...La Corte LONG TERM...La Corte AVIATION...Martin

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