Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 230022 AFDCTP Area Forecast Discussion National Weather Service State College PA 722 PM EST Mon Jan 22 2018 .SYNOPSIS... A potent area of low pressure moving across the Great Lakes will push a trailing cold front through the Commonwealth on Tuesday. Temperatures will stay above normal into early Tuesday, before falling back to near or slightly below normal Wednesday and Thursday. Dry weather is expected for the second half of the week. The temperatures will rebound to above normals by the weekend. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/... Regional radar mosaic at 23Z shows light precip associated with WAA and 850mb baroclinic zone lifting north of the state, while band of showers associated with approaching cold front remain to the west. Latest HRRR and earlier HREFV2 indicate showers will overspread the Allegheny Plateau between 02Z-04Z, then reach the Susq Valley by 06Z-07Z. A marginally unstable air mass, combined with strong forcing along cold front, could produce some briefly heavy downpours and thunder late tonight. Based on latest operational model output, and earlier ensembles, will maintain POPS of near 100 pct tonight. 23Z surface analysis shows quasi-stationary front remains hung up along the spine of the Appalachians with little movement anticipated overnight. Based on this, and low dewpoint depressions, will go with nearly steady temperatures overnight. Have added mention of patchy fog across the northeast portion of the forecast area this evening based on current observations. However, arrival of rain and an increasing breeze should scour out the fog in the valley locations late tonight. && .SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/... Model consensus pushes the cold(occluded) front through the eastern half of the forecast area between 12Z-15Z. Will maintain a near 100 pct chance of showers and possible thunder in this area early in the day, then rapidly lower POPS as drier air works in behind the front. Breaking clouds expected by afternoon over the eastern half of the forecast area, as surface ridging builds into the region. However, upslope flow is likely to cause stratocu to linger over the Alleghenies and passage of upper low across the eastern Grt Lks is likely to spread snow showers into the northwest mountains late in the day. && .LONG TERM /TUESDAY NIGHT THROUGH MONDAY/... Cold front and low pressure system will be lifting into New England by Tue night, with secondary front bringing colder air back into PA - along with snow showers in western sections that will taper off by Wed night (after only amounting to an inch or two). Breezy winds up to 30 mph will also impact central PA during that time as temperatures fall back to seasonal levels. Thu and Fri will be cooler as high pressure moves across the region. Eastern areas especially will see chilly mornings as dry air/low dewpoints associated with the high will be in place. Progressive pattern will bring moderating temperatures back for the weekend ahead of another low pressure area. Chances for rain increase heading into Sunday, followed by a return of cooler weather and snow showers behind a cold front Monday. && .AVIATION /00Z TUESDAY THROUGH SATURDAY/...
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Wind speed will increase aloft as a strong low level jet noses in and intensifies over PA. SSW wind at 2-3kft will peak around 55KT late tonight. A cold front will push through around sunrise in the W, and early aftn in the E. There will be occasional SHRA through the night, and the wind will be generally light through the night. IFR will likely be limited to inside the showers. There is a very small chance of TS in the area overnight, and in the SE Tues before 18Z. Have not mentioned it in the TAF yet due to low confidence of occurrence. Expect the LLWS to not go away until CFROPA, then mechanical mixing will make it very gusty on Tues. The highest gusts will be at JST. Cold air will turn the lingering SHRA over the W in the aftn to SHSN. SCT SHSN will then continue over the high terrain of the west into Wed. Outlook... Wed...AM shsn possible w mtns. Thu-Sat...No sig wx expected.
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&& .HYDROLOGY... After coordination with local officials, some concern does still exist for minor flooding along and near the Susq between York Haven and Safe Harbor. Therefore, the Flood Watch for this area has been extended into Tuesday afternoon. Due to the mild temperatures, there is a potential for ice movement, but there will also be deterioration/thinning of the ice through time. All locations along rivers and streams that have significant ice buildup should monitor water levels closely. The anticipated rainfall totals of 0.5 to 1.0 inches over the next 48 hrs is much less than we had a few days ago, and the ice is less pervasive/extensive due to our relatively mild temps (versus the period leading up to our previous significant rainfall). So, no other areas will be placed into Flood Watch at this time. && .CTP WATCHES/WARNINGS/ADVISORIES... Flood Watch through Tuesday afternoon for PAZ065-066. && $$ SYNOPSIS...Dangelo NEAR TERM...Fitzgerald SHORT TERM...Dangelo/Fitzgerald LONG TERM...Lambert/RXR AVIATION...Dangelo/Tyburski HYDROLOGY...Ross

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