Marine Weather and Tide Forecast for Thornburg, PA

NEAR TERM /THROUGH TONIGHT/
KEY MESSAGES:

- Continued shower chances today, decreasing in coverage overnight.
- Temperatures remain seasonably cool.
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Broad upper low pressure remains over the Northeast today allowing for cooler northwest flow wrapping in locally. This has set us up for quite a fall-looking and feeling day with lake enhanced cloud coverage and scattered showers. Ascent is broad, transient, and weak, so coverage should be scattered through the afternoon and focus the greatest north of Pittsburgh and in the PA ridges coincident with the best cold advection, lake moisture, and upslope component.

Marginal surface destabilization has occurred early this afternoon according to latest ACARS soundings resultant of the low-level cold advection with subsidence sitting around 800 mb.
The taller showers have been able to reach high enough for some graupel formation with inversion heights around -5C. HRRR/RAP soundings suggest perhaps a bit more growth to the mixed layer in the afternoon, but not much, so the same trend should hold true through the afternoon hours with mostly rain showers and some embedded graupel.

After the loss of heating, chances decrease from southwest to northeast and remaining showers will be confined to orographic forcing and lake moisture. Some drier low-level air looks to work in tonight, but the extent of clearing that's able to result in is still questionable. HRRR data suggests the most likely area to scatter out are the lowlands south of I-80 to northern WV with higher confidence that I-80 and north holds on to clouds. In areas that do clear, patchy fog is possible late with probability favoring northern WV. It'll be a chilly night ahead areawide with lows in the upper 30s to low 40s. Chances of <36F maximize around or just above 40% in the WV ridges and southeast OH where the HRRR suggests clearing being more likely, but elevated wind should help preclude frost development.
Confidence in widespread coverage is low, so will mention in the HWO.

SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/
KEY MESSAGES:

- Lingering showers north Saturday, otherwise dry and cool.
- Slightly warmer and dry Sunday.
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Much like a typical winter regime, showers may tend to hang around a bit longer for the I-80 corridor and higher elevations Saturday with lake and orographic influence, as the upper low draws away. This remains a fairly high confidence period with little variation the 500mb clustered height field. As drier air moves in Saturday, and mixing ensues, cloud coverage is expected to decrease throughout the day northwest of Pittsburgh, along with shower chances. Highs remain around 10 to 15 degree below average with continued cold air aloft.

There is high confidence in at least a brief bout or ridging Sunday as the 500mb low makes its way into the Canadian Maritimes, though there is a slight difference between the 1)
Euro dominated cluster (showing ridging), vs. 2) GEFS dominated cluster (showing a low- amplitude shortwave late Sunday). This may mean the difference between 1) continued dry and slightly warmer weather vs. 2) continued cool highs with some slight shower chances in the I-80 corridor and ridges. Regardless of the outcome, there is high confidence temperatures remain seasonably cool.

LONG TERM /MONDAY THROUGH FRIDAY/
KEY MESSAGES:

- Uncertainty increases in the pattern next week.
- Moderating temperatures, but still slightly below normal is most favored.
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Confidence has increased in a pleasant Memorial day, with highs closer to seasonal normals and precipitation chances >10%. The day may start clearer, with clouds increasing overnight ahead of the next weather system.

Clustered 500mb variance increases Monday into Tuesday with uncertainty as to weather another upstream trough pivots into northern Canada or not. The wettest of all scenarios into Tuesday, with a 50% to 70% chance of >1" has a deeper trough or upper low development in the upper Midwest to south-central Canada, pulling the storm track more northwest. Direr scenarios result from either continued ridging (which would also keep us warmer) or the development of a trough over us, pushing the storm track farther south and keeping us cool. Regardless of the outcome, there is at least a 60% (I-80 and north) to 90% (WV mountains) chance of seeing some rain Tuesday.

Late week will very much depend on the development (or lack thereof)
of the aforementioned eastern tough. Clusters have scenarios from: the trough on or past us (generally cooler and wetter), to the trough weaker and west of us (warmer and wetter), to the trough well into the Canadian Maritimes (drier and warmer). So anything is still on the table. Late week highs could be anywhere from the upper 60s to low 80s.

AVIATION /18Z FRIDAY THROUGH WEDNESDAY/
Isolated to scattered showers, breezy west-northwest winds, and a VFR stratocu deck will persist through the remainder of the afternoon and evening. Areas along and south of a line from BVI-PIT-LBE see clouds scatter out overnight with the loss of daytime heating/mixing, while farther north towards FKL/DUJ the stratocu deck remains in place and ceilings drop back to MVFR.
Winds relax in most areas overnight, though likely don't go calm as the local pressure gradient will still support prevailing west-northwest winds around 5-10 knots.

The cloud deck that lingers north of PIT overnight gradually lifts to VFR levels Saturday morning, while the onset of daytime heating allows another SCT to BKN stratocu or cu deck to form elsewhere farther south. Breezy northwest winds and VFR ceilings then prevail throughout much of the day Saturday.

Outlook...

Sunday through Tuesday will likely remain free of ceiling or visibility restrictions. Low pressure tracking up the Ohio Valley eventually brings rain chances and restrictions back to the area Tuesday night.

PBZ WATCHES/WARNINGS/ADVISORIES
PA...None.
OH...None.
WV...None.