Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 211416 AFDCTP Area Forecast Discussion National Weather Service State College PA 1016 AM EDT Wed Jun 21 2017 .SYNOPSIS...
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An upper air disturbance will will push southeast across the region this afternoon. A deep upper level trough will approach the region from the Northern Plains and Upper Great Lakes later this week and draw a plume of deep tropical moisture north from the Gulf of Mexico. This will bring increasing humidity along with the chance for showers and thunderstorms late Thursday into Saturday. Drier and cooler conditions will return later in the weekend into next week.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Radar shows some isolated showers and even a thunderstorm in spots. Satellite loop shows the sun is breaking out which is leading to mid level lapse rates beginning to steepen as the primary upper trough axis across eastern Ohio drifts over the CWA. RAP shows a tight upper jet streak diving out of the central Gr Lakes with the local area firmly under the left exit (favorable) region of the jet. Forecast model sounding show a nice inverted V signature for this afternoon. SPC has painted much of the CWA with a Marginal Risk for severe storms this afternoon, and this looks quite reasonable given strong deep layer shear, expected lift under the left exit region of the upper level jet and steepening lapse rates under the falling heights aloft. Relatively high convective LCLs/cloud bases will help to produce isolated and brief, strong downburst winds in the 18-23Z window. Basin average rainfall today should stay under 0.20 of an inch. A push of low PWAT air in the wake of this sfc/upper level disturbance should result in a dry afternoon across NW PA. Max temps this afternoon will be in the mid to upper 70s across the mtns, around 80F across the Central Mtns, and near 85F across the Lower Susq Valley.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/... Convection dies down pretty quickly early this evening, and initially mainly clear skies and quickly diminishing wind (combined with wet damp ground from one or two showers/TSRA in many areas) will lead to areas of valley fog during the early- mid morning hours. Lows early Thursday will be on the chilly side and in the 40s across the NW mtns, while the rest of the CWA will see a min temp in the 50s to lower 60s. Thursday starts out partly cloudy and comfortable in the temp and humidity Dept as a bubble of high pressure slides SE and over us for late morning. The low level flow will become swrly during the afternoon and evening hours Thursday, and another flat upper trough (and sfc warm front) will move east across the region and trigger showers and scattered TSRA over the Central and Southern portion of PA. PWATs will increase from below normal and only 15-20 mm this morning, to over 40 mm (or 1-2 sigma) by 00Z Friday just to the west of the approaching warm front. && .LONG TERM /THURSDAY 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. 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 /14Z WEDNESDAY THROUGH SUNDAY/...
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VFR conditions prevail across the flying area as of mid morning. An approaching upper level disturbance will help trigger scattered showers and thunderstorms. Some of the stronger storms will cause brief localized sub VFR conditions, and some of the stronger storms could cause cause wind gusts, mainly this afternoon. The wind will become SW picking up to around 10 mph gusting to 15-20 mph. Any convection will down pretty quickly by early evening, and initially mainly clear skies and quickly diminishing wind will likely lead to areas of valley fog during the overnight hours (mainly where rain falls today). A warm front will approach the region Thursday triggering showers and scattered thunderstorms, mainly over the west and NW during the afternoon. .OUTLOOK... Fri...Cig restrictions likely west. SHRA likely / sct TSRA. Sat...Chance for SHRA/TSRA south. Restrictions poss early. Sun...Mainly VFR. Chc SHRA/TSRA.
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&& .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...La Corte/Lambert NEAR TERM...La Corte/Lambert SHORT TERM...Lambert LONG TERM...La Corte/Lambert AVIATION...La Corte/RXR

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