textproduct: State College

WHAT HAS CHANGED

* No major changes from previous forecast

KEY MESSAGES

1) Stratiform rain expected across central PA rest of tonight into Wed.

2) Chillier to end the week with frost/freeze potential returning as early as Wed Night/Thur morning in the northern tier, but more likely Thu night/Fri morning.

DISCUSSION

KEY MESSAGE 1: Stratiform rain expected across central PA tonight into Wed.

Wave of low pressure rides up the advancing cold front tonight and slows things down. A good feed of moisture will continue to spread rain west to east across the CWA late tonight and Wed AM. The front should clear the eastern counties later in the aftn Wed. Before it does so, some convection may form ahead of it. But, a cap around 10kft will try to suppress storms in the SE. Do not expect the storms to become strong, moving east of the area in the middle of the aftn. Some lingering SHRA are possible in the late aftn/eve. Maxes will be 15F colder than Tue thanks to all the clouds and rain.

-------------------------------------------------

KEY MESSAGE 2: Chillier to end the week with frost/freeze potential returning as early as Wed Night in the northern tier, but more likely Thu night.

After the cold front pushes E and S of the CWA on Wed, the sky may clear out well enough in the nrn mtns to allow the temps to drop into the M30s. Some cloud cover is still possible, and the wind is not totally calm until later at night/early Thurs AM. Thus, there is the chc for frost there, but it's not a slam dunk. Thurs night/Fri AM looks better for as high pressure builds behind the front, albeit with its center off to the south. Most guidance puts mins into the 30s over the NW half or more of the CWA Fri AM, with less cloud cover than the night before. Not many pixels of 32F or lower on the MinT grid, but a small (20%) risk is there for someone to have a freeze across the NW. The risk for frost is much more - around 70% for the Allegheny Plateau and Laurel Highlands. So, we'll need to consider frost advy as we near that period. At this point, we're not quite confident enough for any frost/freeze products. We do have it mentioned in the HWO, but may need to expand mentions. After two more weak systems Fri - Sun, we get another cold night Mon night/Tues AM.

AVIATION /12Z WEDNESDAY THROUGH SUNDAY/

Widespread stratiform rain is ramping up across central Pennsylvania this morning, with radar returns across all airfields outside of LNS as of 7A/11Z this morning. Low-level dry air across MDT/LNS could keep precipitation chances minimal through 13Z; however, bulk of model guidance does outline saturation fairly quickly so went ahead and have included rain chances beginning at these airfields at 12Z Wednesday. Current conditions northwest of the area outline LIFR conditions, which tracks well with 50th percentile membership of 00Z HREF ensemble guidance; thus, have trended ceiling in this direction, also blending it GLAMP model guidance which appears to also be running closely with current observations.

Most restrictions in the 12Z TAF package will be ceiling-based based on all model guidance through 00Z Thursday, with high (~80-90%) confidence in widespread MVFR ceilings. Forecast becomes more complicated with respect to our western terminals (all but MDT/LNS) where model guidance has slight disagreement on low-level moisture in play at these airfields. Multiple runs of GLAMP guidance indicates IFR restrictions at BFD/JST so higher confidence (~50-60%) in IFR and below restrictions at these terminals through ~22Z Wednesday; however, LIFR restrictions will also be in play (~30-40% confidence) with timing being the main uncertainty. Based on this have thrown in a TEMPO group for BFD where timing/magnitude of ceiling below 300 ft AGL remains most uncertain while prevailing (FM) groups at JST where this potential looks more robust. Transient periods of IFR are also progged by model guidance at AOO/UNV/MDT but confidence remains lower (~20-30%) at these airfields, thus have limited mentions to SCT/BKN cloud decks in the 14Z-21Z Wednesday timeframe. After 00Z Thursday, widespread VFR conditions are expected to prevail based on a combination of GLAMP/NBM model guidance with the low-level cloud deck slightly eroding into a more SCT-BKN cloud deck, with some clearing across the central mountains (AOO/UNV/IPT) possible based on HREF/NBM model guidance after 08Z Thursday.

Outlook...

Thu-Fri...-SHRA possible, but trending drier.

Sat...Restrictions possible in rain.

Sun...Showers and thunderstorms in the afternoon with restrictions possible.

CTP WATCHES/WARNINGS/ADVISORIES

None.