Marine Weather and Tide Forecast for Chester Hill, PA

KEY MESSAGES
1) A milder night tonight across the Western Half of the CWA, but up to several deg F cooler than last night from the Susquehanna Valley east

2) Heat risk late week

3) Increased chcs for rain/possible drought relief

DISCUSSION
KEY MESSAGE 1: A milder night tonight across the Western Half of the CWA, but up to several deg F cooler than last night from the Susquehanna Valley east

High clouds will increase/thicken-up from the west overnight, followed by a bump up in PWAT values by 3-4 tenths of an inch during the predawn hours of Tuesday. This will help to keep temps a few to several deg milder than recent nights there.

Over the Susq Valley and points east, a layer of stratocu was created by a favorable llvl (mean 925-850) trajectory of moisture off the Western Atl, then north across the Chesapeake Bay. The flow in this layer will gradually veer to the SW by midnight, leading to the continued steady erosion of the cloud deck. This earlier cloud cover helped to keep temps down by a few deg F relative to surrounding areas that had more sun. This opposite trend in sky cover between our eastern and western CWA will lead to cooler mins (by some 5-8 deg F) across the Susq Valley and points east.

Mins will range from the low to mid 50s in the east to the upper 50s and low 60s across the Central and Western Mtns.

KEY MESSAGE 2: Heat risk late week

Heat risk seems to have plateaued and perhaps is on the way down. Reasons against widespread heat advisory-level numbers are the anticipated clouds and ocnl rain/thunderstorms. These would serve to keep temps down. Consensus among most of our neighboring offices was to nudge the temps down a little. But, dewpoints may rise a little to balance, and come up with HI/AppT numbers close to what we have running. In any case, the changes did not remove all the risk. We may just want to tone-down the message a little due to the recent trends in clouds/precip chcs.

KEY MESSAGE 3: Increased chcs for rain/possible drought relief

The ridge overhead will be broken down quickly by energy and moisture coming from the west. We may have 4-5 straight days (starting late tomorrow/Tues) when some locations in Central PA could have rain each day. That would be mostly-welcome news for the region. The long-term drought conditions in the S/E could then be improved, and any higher-than-nil fire danger risk (currently only in the NW/ANF) could also be helped to become better.

Despite the multiple days of rain chcs and thunder, SPC has the next 5 days in only the "general thunder" category (and outside mentionable worry-levels for days 4-5), but time will tell if the severe risk increases as the events grow nearer. Friday does look like a pretty good chc for strong to severe storms as good height falls with the advance of a strong upper low/trough are in store.

AVIATION /02Z TUESDAY THROUGH SATURDAY/
Low end MVFR stratocumulus deck that was over east-central PA much of the day has been eroding this evening. Anticyclonic flow around the departing high will bring drier, land-modified air (PWATs mainly between 0.50-0.75") across the eastern 2/3rds of the Commonwealth overnight. A moisture gradient will set up along the Alleghenies, with PWATs around 1.50" just westward where high pressure influence has been weaker.

The warm/moist air will continue creeping eastward as the high pressure loses influence over our area, with even a few showers (coverage <30%) possible across our western terminals (primarily KBFD/KJST/KAOO/KUNV) between 09Z-18Z Tue. Flight restrictions are not expected with these showers, though briefly steady rain may occur given the moisture in place. Lightning may also be possible, especially heading into the afternoon, though the tall/skinny low-CAPE (<500 J/kg) profile will favor rainfall efficiency over lightning production. Rain chances will increases into Tue night.

Outlook...

Tue...VFR favored outside of isolated morning fog. Restrictions possible in -SHRA/-TSRA late.

Wed-Sat...Restrictions possible in -SHRA/-TSRA.

CTP WATCHES/WARNINGS/ADVISORIES
None.