textproduct: State College

WHAT HAS CHANGED

* Added Northern Centre County to Winter Weather Advisory * Extended end time of Winter Weather Advisory from 7AM to 9AM for the north central mountains

KEY MESSAGES

1) Quick-hitting minor to plowable snow accumulation for later tonight into the Wednesday morning commute

2) Increased uncertainty with snow/mixed precip potential Thursday

3) Mild end to February/meteorological winter -- but does March come in like a lion with another wintry system early next week?

DISCUSSION

KEY MESSAGE 1: Quick-hitting minor to plowable snow accumulation for later tonight into the Wednesday morning commute

A clipper system tracking across the Upper Great Lakes will bring a quick-hitting shot of snow primarily across the western and northern Alleghenies late tonight through Wednesday morning. Warm advection ahead of the surface low will combine with left exit region jet dynamics into favorable DGZ to produce 1-3" totals over the higher terrain with C-1" southeast of I99/I80. Bulk of the accumulating snowfall will likely fall within a 4-8 hour window with light snow/flurries after 12Z Wed across the Allegheny Plateau and Laurel Highlands. The snow and slippery road conditions will impact the Wednesday morning commute in some areas and may result in travel/school delays.

KEY MESSAGE 2: Increased uncertainty with snow/mixed precip potential Thursday

Overall, the 2/24 00Z & 12Z model trends have been bearish on the margin concerning snow/mixed precip potential for Thursday. A southeastward QPF shift in the deterministic GFS, NAM, and ECMWF is quite evident in the 12Z runs with NBM QPF matching closer with AIGFS and WPC to AIGEFS. The uncertainty is likely tied to shortwave differences in the fast quasi-zonal flow and strong temperature gradient across the northern half of the CONUS. POPs and snowfall were reduced via baseline foundational NBM which accounts for the bearish trends and implies lower forecaster confidence. It's not out of the question the southeastward shift reverses in future cycles, but for now the signal is considerably weaker than this time yesterday. KEY MESSAGE 3: Mild end to February/meteorological winter -- but does March come in like a lion with another wintry system early next week?

Regardless of the outcome on Thursday, Friday and Saturday continue to shape up quite well as we close out the month of February/meteorological winter on a nice warming trend. Saturday looks like the warmest day with max temps in the low 40s to mid 50s running +5-10 degrees above the historical average.

But does March come in like a lion? Uncertainty exists regarding the potential for overrunning winter precip early next week as Pacific energy/moisture catches up to retreating arctic high pressure. Stay tuned.

AVIATION /06Z WEDNESDAY THROUGH SUNDAY/

Widespread VFR conditions continue as of 25/06z, with low-level dry air preventing snow aloft from reaching the ground. An exception to this was at KBFD, where IFR conditions were observed between 04z-05z as a band of snow briefly overcame the dry air, with a quick recovery to VFR as the band moved away from the airport.

Nevertheless, gradually lowering ceilings and light snow are still expected to progress west-to-east over the next couple of hours, with snowfall expected across all of the western terminals (BFD/JST/AOO/UNV/IPT) with moderate-to-high (~60-80%) confidence. The main change with this TAF package was to delay the onset of snow by an hour or two, which was based on observational data & recent NAM/HRRR guidance. KBFD and KJST still appear most likely to observe IFR restrictions through the morning due to snow, with the NAM/RGEM suggesting snow showers continuing through at least 15z. An embedded shortwave moving across the Great Lakes later this afternoon/evening might refuel snow showers over KBFD/KIPT, and to a lesser extent, KJST. Additionally, the NAM/GFS show elevated Snow Squall Parameter values over the Allegheny Plateau and Northern Tier between 18z-06z, signaling at the chance for more flight restrictions later today. While the latest HRRR is sparse with snow shower coverage during that time period, other mesoscale guidance (NAM/RGEM/WRFs) reflect this enhanced potential, though timing and coverage remains uncertain.

Some LLWS concerns remain at BFD/JST/AOO over the next 6 hours as a LLJ passes overhead. A secondary area across SE PA (MDT/LNS) will be possible (~30-40%), though mentions in the TAF were left out due to the lower likelihood. Diurnal mixing will allow for wind gusts to mix to the surface in the afternoon, though the core of the LLJ will have pushed east of the region by that time, with 15-25 kt wind gusts expected during the day.

Outlook...

Wed...IFR restrictions most likely in snow showers across KBFD/KJST/KIPT, with MVFR restrictions more likely elsewhere.

Thu...Low potential (~20-30%) for snow showers across southern Pennsylvania. Elsewhere, dry with VFR conditions probable.

Fri-Sat...Dry conditions with VFR probable.

Sun...Low potential (~30%) for snow showers across NW PA. Elsewhere, dry with VFR conditions probable.

CTP WATCHES/WARNINGS/ADVISORIES

Winter Weather Advisory until 1 PM EST this afternoon for PAZ004-005-010-011-017-024-033. Winter Weather Advisory until 9 AM EST this morning for PAZ006- 012-018-037-041-042.