Marine Weather and Tide Forecast for Mercersburg, PA

NEAR TERM /UNTIL 6 PM THIS EVENING/
Variable amounts of strato cu and alto cu were present across the region early today as a result of near sfc Serly flow off the Western Atlantic, and SSWrly flow from the 850 mb level up.

A small llvl jetlet on the eastern side of a much broader LLJ max will move NE across the NW Mtns of PA through about 14Z, which will provide enough focused isent lift over an approaching warm front to bring some fast moving, small showers.

The CWA will then see a several to 6 hour period of dry conditions with some breaks in the cloud cover, before a cold front moves through later this evening and overnight preceded and accompanied by a few more showers and maybe a TSRA (primarily over the Western Mtns - based on timing/available instability of a few to several hundred J/KG of MU CAPE.

Rainfall amounts (accounting for the showers this morning and those later today/tonight) will be mainly less than 0.20 of an inch across the Central Mountains and Susquehanna Valley, while the Laurel Highlands and Northwest Mountains receive between 0.25 and 0.50 of an inch of rainfall today through early tonight.

High temps today will range from around 70F across the Laurel Highlands to about 60F across the Western Poconos and Endless Mtns to the North and East of KIPT.

SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/
The cold front pushes into the NW zones of the CWA this evening and should be through the rest of the CWA by 09Z Tuesday. The lack of instability and CAPE in the early night when it is moving through will mean that the showers will remain meager and sct along the front. Min temps will be mild, esp in the SE due to late passage of cold front. Cold air also not terribly cold, but dry. 8H temps by morning should be near 0C NW but still around 10C SE.

LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/
Thanks to long-wave ridging overhead, a prolonged stretch of days with above average temperatures and no precipitation are likely starting Tuesday night. 850 temps in the double digits above zero will mean mild and even warm temps for most of the period across central PA. The next weather system moves through late in the period on Friday and Friday night. Centralized low pressure over central Quebec will see a cold front draped across southern Canada and across the Great Lakes region. This cold front will extend well into the Ohio and Mississippi valleys. The forcing and moisture along this front will bring a chance for rain and perhaps some storms.

Highs in the 60s and 70s and lows in the 40s and 50s will be trend. Mins should stay above freezing in all of Central PA thru the period, with many nights only dipping into the m50s in the S. Portions of northern PA who have not quite seen grass/flowers takeoff yet should see a burst of green over the next week or two.

AVIATION /12Z MONDAY THROUGH FRIDAY/
VFR conditions expected for the next 6-9 hours followed by a trend toward MVFR. Showers with VCTS will again likely impact KBFD 13-14UTC. Marginal LLWS will dissipate at KBFD by 16Z.
Increasing low level moisture ahead of a warm front will bring low VFR cigs at most TAF sites during the daytime hours.

A cold front advancing into western PA later this evening will bring showers and possibly a thunderstorm to KBFD/KJST. We maintained continuity from the previous cycle with PROB30s to account for potential short duration thunderstorm impacts at these terminals. Very little to no instability is expected downwind of the Allegheny Mtns, so we kept dominant precip type as plain rain showers across the central and eastern TAF sites 23-05UTC. Expect wind shift from 120-180 degrees to 240-280 degrees across the western TAF sites behind the cold front after 22/0000UTC. Post frontal MVFR cigs are probable >60% at KBFD and KJST with higher probs and confidence for MVFR and perhaps even IFR cigs over portions of the east-central airspace in the 00-06Z time frame where llvl moisture briefly pools and flow remains backed along the warm front.

Outlook...

Tue...Early AM low cigs NW, then VFR as clouds lift/dissipate.

Wed-Thu...No sig wx expected.

Fri...Showers developing during the afternoon with restrictions possible.

CTP WATCHES/WARNINGS/ADVISORIES
None.