Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 211350 AFDCTP Area Forecast Discussion National Weather Service State College PA 950 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/... Today is picky your model for clouds and see which one gets eclipsed. The HRRR is only partly cloud but has more intense clouds where each run develops thunderstorms. So for clouds simply blended the NBM clouds with hourly mesoscale models. Made it blotchy where these models indicated thunderstorms or showers. But lowered amounts verse most of the larger scale models with convective parameterizations would create. Most of the mesoscale guidance implies chance POPS and better and slightly more organized showers/thunderstorms in eastern areas this afternoon. The HREF-V2 and NCAR-3km show this and CAMS are your best forecast. But successive HRRR runs are not as robust. Message is POP showers this afternoon and weak organization in east. So a warmer day more humid than yesterday. && .SHORT TERM /TUESDAY/... Nudged these grids with newer guidance and tried to show increased chance as the sun gets higher in the sky. NCAR EFS and NCEP HREF are at odds for convection timing. NCAR is far faster. Big news is a warm humid day good chance of thunderstorms and strong thunderstorms. And the front will usher in a cool trend. Previous: 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 /14Z MONDAY THROUGH FRIDAY/... 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. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...La Corte NEAR TERM...Grumm SHORT TERM...Grumm/La Corte LONG TERM...La Corte AVIATION...Martin

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