Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 182006 AFDCTP Area Forecast Discussion National Weather Service State College PA 306 PM EST Mon Feb 18 2019 .SYNOPSIS... Colder air aloft pushed into the region today, bringing snow showers with an additional coating of snow across the northern and western mountains of the state. A large area of high pressure over the northern Plains States will move southeast and become centered over the state late Tuesday. A deep trough of low pressure over the Rockies and Southwest U.S. will eject a piece of moisture laden energy across the Southern Mississippi and Tennessee Valleys Tuesday and Tuesday night. This moisture will ride up and over the dome of colder air in place across the Northeast U.S. and bring snow then a wintry mix of precipitation for Wednesday into Wednesday night. Mainly dry and milder air will follow for the end of the week. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/... Colder air moving in aloft in the wake of the weak storm that brought some light snow accumulations (followed by a coating of ice from freezing rain) late Sunday into early this morning, will bring a light additional coating of snow across the northern and western mtns of the state through late this afternoon (where mean cloud- layer temps were in the warmer half of the DGZ thermal ribbon - generally between -12 and -15C). Elsewhere, just some flurries fly across the Central Ridge and Valley region of the state. skies will be mainly OVC through the afternoon, followed by gradual clearing early tonight across the Lower and Mid Susq Valley, and partial clearing late tonight over the remainder of the Forecast Area. 1930Z Temps are right around forecast max values - in the low to mid 20s across the northern tier counties, the upper 20s to lower 30s along the Allegheny, and upper 30s to low 40s in the SE. Northwest winds will continue to gust into the upper teens and mid 20s (KTS) into this evening before veering about 20-30 degrees and decreasing by 5 kts or so late tonight and early Tuesday. && .SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/... Much of the area will be clear by Tuesday morning, though RAP soundings indicate that some patchy thin and low stratocu are possible across the Northern Mtns of PA. The Center of a sprawling area of high pressure covering the NErn half of the CONUS will be centered over New York and PA. However, low pressure will gather over the lower MS Valley Late Tuesday and Tuesday night with a strong southerly flow of WAA and Gulf Moisture out ahead of it, leading to a rapidly blossoming area of Precip across Tennessee and Lower/Mid Ohio River Valleys. The leading edge of this precipitation shield (in the form of snow) will move quickly up the OH River Valley and should start in the Laurels up to a few hours before sunrise Wednesday, and spread north and east to the Central Mtns and Susq Valley between 11-14Z. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... Uncertainty is very high at this point as to the evolution of precip type and the QPF over PA on Wed. GEFS and SREF plumes play out a QPF range from just a tenth or so to many inches. The temps also range wildly. The GFS warms everyone in Central PA up to plain rain during the day, while the NAM and EC keep it much colder. Will keep mentioning the storm in the HWO, but not enough confidence in many aspects to post a watch. Most likely place to get the worst impacts will be along and S of the PA Turnpike. Prev... For Wed, low pressure lifting northeast across the Great Lakes will result in some snow, given warm advection. By late morning and early afternoon, looks like sleet and freezing rain would mix with the snow. This based on thickness coming up fast, as the system is weaker and faster than the one we had last week. Thus did not hit the snow real hard, and did not want to go too high on ice. This in part due to QPF on NAM across the far south was looking too high. Other models have the .25 inch line just brushing the far south. Hard to see much more than .25 in any 6 hour period. The NAM had .75 inches across the south in a 6 hour window. This event looks like the event last week, most of the precipitation would be east of the area by Midnight. For most of the period from Thursday into at least early Saturday, not a lot going on. I did cut back on POPS and weather where I could. Temperatures borderline, so used a mix of rain and snow. Main question is if a deep low will form and lift across the lower Great Lakes on Sunday. For now, went close to the superblend. EC and GFS runs not close. GFS has much weaker systems. If EC was to verify, Monday would be the first real windy day of the late Winter, early Spring season. && .AVIATION /20Z MONDAY THROUGH SATURDAY/... MVFR Cigs will continue into this evening across much of the Central and Western parts of the CWA, with areas of IFR Cigs and MVFR VSBYS in snow showers across portions of the NW mtns and Laurel Highlands. Model soundings indicate there will be lingering MVFR stratocu across the mountains of central Pa, while downsloping flow yields a return to VFR conditions in the Susquehanna Valley from KIPT south through KMDT/KLNS. Southeast of a KAOO to KSEG and KAVP line, sky cover will be generally BKN in the VFR - 3500-4500 FT AGL range along with widespread VFR VSBYS. A moderately tight pressure gradient behind the departing storm will produce gusty west-northwest winds for the rest of today across southern PA. Bufkit soundings support gusts ranging from 27-34KTS from KJST to KMDT and KLNS through about 01Z Tuesday, before winds and gusts decrease by 5-10 KTS. Outlook... Tue...VFR. Wed...Snow to a Wintry mix. Thu...AM light freezing rain/low cigs possible. Fri...No sig wx expected. && .CTP WATCHES/WARNINGS/ADVISORIES... Winter Storm Watch from Wednesday morning through Thursday morning for PAZ058. Winter Storm Watch from late Tuesday night through late Wednesday night for PAZ024>026-033>036. Winter Storm Watch from Wednesday morning through Thursday morning for PAZ027-028-056-057-059-063>066. && $$ SYNOPSIS...Lambert NEAR TERM...Lambert SHORT TERM...Lambert LONG TERM...Dangelo/Martin AVIATION...Lambert

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