Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 060950 AFDCTP Area Forecast Discussion National Weather Service State College PA 550 AM EDT Thu Aug 6 2020 .SYNOPSIS...
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A ridge of high pressure will stretch from Michigan to the New England state today and Friday, while a stationary front will be located just south of the Mason-Dixon line. A few weak waves of surface low pressure developing over the Central Appalachians and Delmarva region today and Friday will bring scattered to numerous showers and thunderstorms southeast of I-99 today and Friday. For the weekend, plenty of sunshine and dry weather will precede the arrival of warmer, more humid air and daily thunderstorm chances during the first part of next week.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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A very dry airmass with mainly clear skies and light wind across much of the northern and western mountains was leading to anomalously cool temperatures in the upper 40s to low 50s with areas of valley fog, while a well-defined and persistent jet entrance region over Central PA was leading to large scale lift of the warmer and more unstable airmass across SE PA and points south. This is leading to shield of thick clouds and an area of showers and scattered TSRA (in the Baltimore/D.C. area before daybreak) lifting NE. Several hours of high POPS between 80-100 percent during the mid to late morning hours today across our SE zones will capture this initial weak wave of low pressure, and the associated minor drift nwd of the llvl Quasi Stnry front. Convection-allowing models produce upwards of a quarter to one half inch of rain with the few isolated storms. This shouldn`t be anywhere near enough to cause any flooding issues, even with 3"+ falling on Tuesday in the eastern parts of the CWA. As the jet entrance region weakens and broadens out a bit and shifts a bit further north into central PA this afternoon and early this evening, the large scale weak ascent and areas of sfc- based CAPE of just over 1000 J/KG will support the formation of isolated to scattered SHRA/TSRA further north to near a KIDI t KUNV and KSEG line for this afternoon. Max temps today will be in a fairly tight range (upper 70s to Low 80s) due to the greater amount of clouds in the typically warmer valleys of central and SE PA, and abundant late morning/early afternoon sunshine across much of the Laurel Highlands and Northern Mtns. Winds will be light and mainly from the northeast this morning, then southeast this afternoon.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/...
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Mostly cloudy to overcast skies will be spread across the forecast area tonight with min temps mainly in the mid to upper 60s. Temps across the northern mtns could dip into the upper 50s. The upper trough moving out of the Ohio valley will weaken as it approaches tonight into Fri, but create enough forcing (via the formation of a sharp and compact upper level jet streak) to maintain a weak sfc low over Maryland and keep unsettled weather in the forecast. Went with scattered to numerous showers tonight and scattered showers and tstms Fri afternoon, adding up to about 0.25 to locally 0.50 inch in the Lower Susq, with lesser amounts elsewhere. Max temps Friday will vary form the low to mid 70s over the Northern Mtns to around 80F in the larger metro areas across the Lower Susq Valley.
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&& .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
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High pressure will build in for the weekend, with increasing sunshine and just a slight chance of a stray shower on Saturday. Temps will climb back to a few degrees above normal, with highs in the 80s, but humidity will be on the low side. The longer term will feature a return of warmer weather, with temperatures generally 5-10 degrees above average from Mon through Wed as an upper ridge builds over the Eastern US. Dewpoints climb back to the upper 60s and 70s for Mon and Tue, and perhaps even the mid 70s in the Lower Susq on Tue and Wed. Combined with temps in the upper 80s to near 90, this would mean Heat Index values take a run at the upper 90s to near 100 Tue and Wed afternoon, so long as the low level moisture doesn`t mix out in the afternoon and cause the dewpoint to drop. Boundary layer mixing and entrainment of drier midlevel air was something that was noted on many of the hotter days in July, but a wetter ground and increased moisture flux from vegetation after Isaias may result in the dewpoint remaining elevated during peak heating next week, at least across the Lower Susq. Scattered airmass thunderstorms are possible each afternoon from Mon through Wed. This stretch of weather looks like "typical summer", with no strong fronts or highly anomalous features to speak of, other than increased heat and humidity.
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&& .AVIATION /09Z THURSDAY THROUGH MONDAY/... VFR conditions most of the area. Clouds will spread north into the area from the south across the PA/MD border. Fog is possible across northern valleys for a couple hours near sunrise. A few showers are possible in SE airfields before daybreak and continuing through the day. Don`t expect long- lasting reductions but could see brief cig/vis reductions if a heavy shower moves over an airfield. A few SHRA may pop up over the Laurels/wrn Alleghenies in the aftn, too. But, those will be few and far between. Not expecting much TS, but the highest chc of that will be for MDT and LNS during peak heating but before the minor wave moves to the east of the area. A series of weak low pressure systems will track just south of of our area later this week into the upcoming weekend. Almost everyone will get wet at some point Thurs PM-Fri. High pressure just to our north will then press southward and settle overhead for the weekend. Outlook... Sat-Sun...VFR. AM fog poss nrn valleys. Mon...Mainly VFR with local impacts from sct aftn/eve TS/SHRA. && .CLIMATE... Although the current pattern with below-normal temperatures is not record-setting, a couple stats are worth noting. Low temperatures Thursday morning are expected to be the lowest since late June at a few sites: SITE8/6 FORECAST LOWLAST OCCURRENCE Harrisburg64June 26 (41 days) State College58June 25 (42 days) Bradford46June 17 (50 days) The high at MDT on Thursday is forecast to be 79 degrees. If the temperature fails to reach 80, it will be the first time since June the. The current stretch of 48 days is tied for 5th longest at that site. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Lambert/Banghoff NEAR TERM...Lambert/Banghoff SHORT TERM...Lambert/Banghoff LONG TERM...Colbert/Banghoff AVIATION...Ross CLIMATE...

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