277 FXUS61 KCTP 200159 AFDCTP Area Forecast Discussion National Weather Service State College PA 859 PM EST Wed Jan 19 2022 .SYNOPSIS... A cold front will push SE through the state late tonight. A band of rain and snow will develop along and just north of the front across southern PA late tonight and Thursday morning and change to all snow as colder air quickly moves into the region. Very low wind chills are expected Friday and Saturday mornings. A developing low off of the East Coast should stay just far enough to the east to spare Central PA any snowfall Friday night and Saturday. After that, a deep upper level trough is likely to set up over the northeastern CONUS, with an Alberta Clipper potentially affecting the area early next week. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/... Mid evening update. A small area of precipitation on radar just south of Pittsburgh. Another area over eastern VA. Nothing yet in the area between these. Will continue to monitor. With salt on the roads from recent days and little runoff from snow melt today, current products cover situation well. Main issue would be falling temperatures acorss the south late, in the area that gets the snow. Northern and central areas may see little accumulation of anything. Early evening update. Rain and snow still a ways out, and temperatures a bit warmer than fcst. Moon just coming up outside the office as of 715 PM. Made some adjustments. Afternoon discussion below. A rather nice afternoon with partly to mostly cloudy skies, above normal temps in the upper 30s and mid 40s and a moderately gusty SW wind across the Western Mtns preceded a cold front that was stretched along the north shore of Lake Erie. Generally weak radar reflectivity returns south of this front were in the form of virga for now with the mean llvl T/TD spread AOA 10F. This arctic cold front will move into the NW zones around dusk and reach southern PA around/shortly after midnight. At the same time, strengthening uvvel associated with the approaching right entrance region of a rather strong 100-110 kt upper jet stretched across SW Ontario and the St. Lawrence Valley will migrate east and blossom and area of FGEN forced rain/wet snow which will change to mainly snow and become focused across our southern zones late tonight and Thur morning. Snowfall amounts will be quite elevation dependent southern PA during the early to mid morning hours before surface temps fall to below freezing in all areas around or shortly after sunrise. Although snowfall amounts shouldn't;t be greater than 2-3 inches in most places in southern PA, the timing of the precip and strength of the LLVL cold advection will likely cause signif impact for the morning commute across much of the southern half of PA. Even as far north as I-80, an expected coating to one inch could lead to icy roads, or black ice on untreated surfaces, which may be messaged with a SPS later tonight as the potential for that type of weather/impact becomes clearer. A Wint Weather Advisory is in effect across the Lower Susq Region from 07-16Z Thu. Min temps will be at 12Z Thu and will range from 10F across the NW to 30-32F SE. && .SHORT TERM /6 AM THURSDAY MORNING THROUGH FRIDAY/... The cold air is coming in at low levels and is quite dry. This will limit any action off the lakes. Also activity across southern PA will tend to move out rather fast, as dry air works into the area at low levels. For late Thursday into Friday, wind chill values will be low, but on the edge for an advisory. If winds are less, then it just ends up being cold based mainly on temperature. Earlier discussion below. The coldest air mass of the season will spill into the region later Thursday. However, dry arctic air, low/shallow inversion heights and a 340 degree boundary layer flow argue for little if any lake effect snow. Perhaps just scattered flurries across the northwest mountains and Laurels. The next problem is that the mins Thursday night will be sub- zero over the north and west thanks to clearing and the CAA. 8H temps get near -20C in the far NW. This will be the first time <=0F in the CWA this winter. The wind will still be in the 10-15MPH range for the first half of the night, and 5-10MPH later at night. These numbers are good enough to get us down near -15F wind chills in the nrn mtns. We'll probably need a WC advy for Fri morning (and perhaps, but not as likely) Sat morning. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... Dry air will tend to lower chance for snow from any southern systems early this weekend. There is still a small chance across far southern PA, so will leave keep this in the fcst. With the cold air not being very deep, low temperatures will likely be on the cold side, as winds will likely drop off at night, given lack of clouds and snow on the ground. After I run forecast builder, will take a second look at things and may end up adjusting low temperatures some. Earlier discussion below. Below normal temperatures look to remain in place across central PA this weekend through most of next week as large scale troughing remains resilient across Ontario and Quebec. Most guidance keeps a low pressure center far enough out to sea for Friday into Saturday, so that there are no effects for Central PA. However, a fair number of ECENS and GEFS members track the low close enough to produce some light snow across southeast PA Friday night into Saturday morning. Odds still favor dry weather at this time, but continue to mention a low chance of snow across the far southeastern counties, particularly Lancaster County. Aforementioned cyclonic flow looks to bring several shots of northern stream energy and renewed cold temperatures next week. The first of these appears to arrive Sunday into Monday, with snow mainly impacting the Alleghenies and Laurel Highlands. Another arrives by midweek, followed by a third for late week. Will have to monitor associated surface lows with the latter two systems as they currently look to move off to our southeast. Still a great deal of uncertainty at this time in how much these may play into our sensible weather. && .AVIATION /02Z THURSDAY THROUGH MONDAY/... Ceilings are lowering ahead of the approaching cold front. Current virga falling from the higher, mid cloud deck across the NW will transition to scattered to numerous rain and snow showers moving from northwest to southeast. Precipitation is currently nearing the western-most airfields as of 00Z Thursday. Latest guidance shows the scattered showers transitioning into a more stratiform band of rain/wet snow as it enters the Lower Susq Valley after midnight tonight, then all snow for 4-6 hours Thursday morning with IFR to LIFR conditions at MDT and LNS. Elsewhere, the initial light wintry mix will be transitioning to a period of snow overnight with VFR and MVFR cigs lowering to MVFR ad IFR. Expect all airfields (except BFD) to improve to VFR my mid-afternoon on Thursday. Outlook... Thu...Snow showers in west airspace overnight. Rain/snow mix in the southeast through the morning hours. Reductions to IFR likely. Improving to VFR by mid-afternoon. Fri...Chance snow showers NW and South. Sat-Sun...Mainly dry, but a chance of snow showers at times. && .CTP WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory from 2 AM to 11 AM EST Thursday for PAZ036-057-059-063>066. && $$ SYNOPSIS...Lambert/Martin NEAR TERM...Lambert/Martin SHORT TERM...Lambert/Dangelo/Martin LONG TERM...Guseman/Fitzgerald/Martin AVIATION...Gutierrez