.AVIATION /12Z SUNDAY THROUGH THURSDAY/...
Flight categories and LLWS will improve from west to east 
through 18Z as a cold front crosses the Commonwealth, with
MUCAPE values along the front still below 100-250 J/kg,
keeping certainty/likelihood in thunder below 30%. The latest 
LAMP provides high confidence (80%) in prevailing VFR across 
most sites after 18Z, with an exception being the Allegheny 
Plateau (KBFD/KJST). MVFR ceilings are moderately likely 
(50-60%) to persist here as low- level moisture lingers upwind 
of the Alleghenies, though the modeled ceiling heights are on 
the borderline of MVFR (around 2500 ft). One scenario in which 
VFR could verify is if gusty post-frontal winds mix drier air 
from aloft into the boundary layer, allowing for ceilings to 
rise above MVFR thresholds. Conversely, factors such as 
orographic lift from upslope westerly winds at KJST, and 
positioning downwind of the Great Lakes at KBFD, might keep the 
boundary layer moistened enough for MVFR. 

The more complex evolution through 18Z is across our eastern 
terminals (KIPT/KMDT/KLNS), where a maritime air mass associated
with a backdoor cold front has led to ceiling restrictions 
ranging from IFR (KIPT) to LIFR (KMDT/KLNS). While the primary 
cold front may bring IFR restrictions from heavier rain showers,
conditions will trend toward MVFR to VFR as the front scours 
out the wedge of cool moist air. Looking more closely at the 
Lower Susquehanna Valley (KMDT/KLNS), Nighttime Microphysics 
satellite imagery shows the leading edge of the low stratus deck
becoming diffuse and slowly drifting northeast as southerly 
return flow builds in the warm sector, with nearby terminal York
Airport (KTHV) jumping from IFR to VFR at 09:30Z. The 06Z 3km 
NAM has handled the progression of this feature best so far, and
suggests that the low clouds at KMDT/KLNS will mix out around 
12Z. Looking at KIPT, the airport should rise above IFR by 13Z 
as post-frontal westerly winds scour out the maritime air mass.

Otherwise, mainly dry conditions are expected after 18Z as the 
cold front moves offshore, with an exception being our Allegheny
Plateau terminals (KBFD/KJST). A shortwave will be moving 
across the Ohio Valley this afternoon, which with cooling 850 mb
temperatures and daytime heating with low-level moisture in the
wake of the cold front, will steepen low-level lapse rates and 
support scattered upslope and lake-effect rain/snow showers.

Outlook...

Mon...Breezy and cooler with MVFR N/W and VFR elsewhere, with 
scattered rain/snow showers possible.

Tue...Mainly VFR with a few rain/show showers.

Wed-Thu...VFR.

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