Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 132323 AFDCTP Area Forecast Discussion National Weather Service State College PA 623 PM EST Wed Dec 13 2017 .SYNOPSIS... A fast- moving Alberta Clipper type system will move through southern Pennsylvania overnight. A new ridge of high pressure will slide across the region Thursday and Thursday night with cold but mainly dry conditions. A new clipper will move north of the region overnight Friday and Saturday morning with limited moisture. High pressure will build across the area early Sunday with a brief moderating trend. A series of cold fronts will move across the area late Sunday into Wednesday. Windy and colder temperatures will follow for Tuesday into Wednesday. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
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An Alberta Clipper, located over southwest Michigan at 23Z, will streak ESE through southern PA overnight and off to our east by early Thursday. This will bring a period of light to moderate snow over central Pa starting this evening and winding down rapidly right around or shortly before sunrise. An impressive mid level jet streak is progged to dive through the Ohio Valley and just south of the MD border later tonight, placing the region in the favorable left front quadrant of the jet. The low level response will be a strengthening southerly flow and a period of strong warm advection and isentropic lift centered over central and northern PA. As expected with a clipper, model omega/temp time-sections indicate fairly high snow/water ratios. Close to 20:1 expected across northern Pa, where max lift if progged to occur within the best dendritic growth zone. Across the southern counties, indications are for slightly lower ratios with some riming likely based on profiles of temp and lift. Model blended qpf, including contributions from latest HRRR and 18Z runs of the GFS/NAM, support storm total snowfall ranging from less than an inch from Chambersburg and York southward, to around 6 inches across Cambria county. Considered upgrading to an warning for Cambria, but given current lack of impressive upstream snowfall rates, don`t want to issue for just one county that may reach minimal warning criteria. Will monitor upstream radar imagery and latest HRRR updates, leaving door open for a later upgrade.
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&& .SHORT TERM /6 AM THURSDAY MORNING THROUGH 6 PM THURSDAY/... The storm will be winding down rapidly later tonight and should be pretty much over in most areas shortly after sunrise. High pressure will build in during the day leaving little more than some scattered snow showers over NWRN sections and possibly the Laurel highlands. Highs ranging from the teens across the northern tier to around freezing in the far SE will average about 10-15 deg colder than normal. && .LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/... A few snow showers for Thursday evening, then clearing and quite cold conditions for overnight under the center of high pressure. Min temps will vary from the single digits over the NW mtns, to the teens throughout the Susq Valley and Southern Tier. A mid level wind max will drop southeast Friday night and early Saturday. Some snow showers expected, mainly across the west. I did up POPS some. For the first part of the weekend, did lower temperatures some more. Still looking mainly dry later Saturday into the first part of Sunday. A complex pattern will prevail after Sunday, with some energy from the southern branch of the westerlies becoming more active. Moisture from the Gulf of Mexico will be limited, with a ridge in place. Expect colder and more in the way of wind by later Tuesday into Wednesday. Overall, minor changes to the package. && .AVIATION /23Z WEDNESDAY THROUGH MONDAY/... * Cloud/Ceiling info will be missing at KBFD until new part can be installed * Most terminals are VFR as of early afternoon, the exceptions being the usual higher elevation culprits from JST north into Northern Mountains where there remains some residual lake effect snow showers. The near term guidance shows the snow showers over the north dwindling over the next few hours, just in time for a larger area of snow to begin overspreading the western part of the flying area between about 22-00Z. The snow will reach eastern areas before 02Z. Expect the brief improvement this afternoon to deteriorate once again with widespread IFR being the predominant condition overnight. MDT/LNS being on the southern edge of the expected snow shield could waver between MVFR and VFR. The snow will taper off quickly in the pre-dawn hours with rapid improvement setting in as the storm moves east of the area. The higher elevation terminals could remain MVFR for a good part of Thursday, but elsewhere airports should become VFR by mid morning and continue throughout the day. Outlook... Thu-Sat...Scattered snow showers and local restrictions NW/Laurels. Sun-Mon...Mainly VFR. && .CTP WATCHES/WARNINGS/ADVISORIES...
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Winter Weather Advisory until 8 AM EST Thursday for PAZ006-011- 012-018-019-025>028-034-037-041-042-045-046-049>053-056>059. Winter Weather Advisory until 8 AM EST Thursday for PAZ004-005- 010-017-024-033.
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&& $$ SYNOPSIS...La Corte/Martin NEAR TERM...Fitzgerald SHORT TERM...La Corte LONG TERM...Martin AVIATION...La Corte

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