Marine Weather and Tide Forecast for West Alexander, PA

NEAR TERM /THROUGH TONIGHT/
KEY MESSAGES:

- Seasonable to slightly above average temperature this afternoon with eroding stratus - A dry cold front is expected to cross overnight and increase cloud cover.
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Subsidence from upper ridging will continue to aid in the erosion of a staunch stratus layer through this evening.
Increased insolation will aid early cloud-clearing locations to reach high temperature around 5 degrees above the daily average while locations seeing a later onset of sunshine trending closer to near (or slightly below) the daily average. Diurnally-driven cumulus behind the eroding cloud deck is expected to clear around sunset.

A cold front draped across south central MI towards Toronto (Canada) is expected to drop SSE through the overnight period.
Limited moisture within the atmospheric column and meager lift should ensure dry conditions but cold advection should allow the increase in stratocumulus development in the post-frontal environment. This cloud cover and later arrival of cooler air means overnight low temperature remains near to slightly above the daily average.

SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/
KEY MESSAGES:

- High confidence in dry conditions - Frost/freeze conditions appear increasingly likely Wednesday night and Thursday night ----------------------------------------------------------------

There is high confidence in dry conditions persisting Wednesday and Thursday as the local area remains under an area of northwest flow, sandwiched between a broad upper ridge over the central CONUS and a deepening longwave trough over the western Atlantic. Cooler air will filter into the area in response to the amplifying pattern, with high temperatures each afternoon returning to near seasonal levels (low 60s for the Pittsburgh area). As the surface high shifts eastward and centers more over the lower Great Lakes, we will see drier air and calming winds which should result in very efficient nighttime radiational cooling.

A frost/freeze remains possible both Wednesday and Thursday nights.
The most likely areas to experience frost will be north and east of Pittsburgh, where NBM probabilities are near 100 percent for low temperatures dropping to 36F or lower (a decent proxy for frost formation in situations like this). Elsewhere across eastern OH, northern WV, and southwestern PA, locations outside of the immediate Ohio River valley generally see frost probabilities ranging from 40 to 60 percent. With respect to freeze conditions, NBM probabilities for low temperatures at or below 32F are as much as 60-90% for areas north and east of Pittsburgh and the Laurel Highlands. Therefore, expect some combination of frost/freeze headlines Wednesday night.

There are higher probabilities for frost/freeze conditions across a larger portion of the area Thursday night, but any headlines for that period will be dictated by the expanse and magnitude of frost/freeze conditions Wednesday night, as the growing season may end for many locations on Thursday.

LONG TERM /FRIDAY THROUGH MONDAY/
KEY MESSAGES:

- Above average temperatures return Friday into the weekend - Rain chances increasing late this weekend

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The central CONUS ridge shifts eastward Friday through the weekend, centering over the local area early Saturday and over the eastern seaboard on Sunday as an upstream trough deepens over the upper Midwest and Great Lakes. Mostly dry conditions can be expected to start the period, though guidance does suggest a low chance for decaying rain showers to make their way across mainly the northern half of the area Friday night into early Saturday morning. However, confidence in this occuring remains low as ensembles are currently in a rather significant disagreement regarding the magnitude of dry air below 700mb and thus the amount of sub-cloud evaporation. The current NBM mean maintains low (20-30%) PoPs north of I-70 which seems reasonable at this time given the uncertainty. Regardless, if precipitation occurs it would be very light, with even the LREF 90th percentile topping out at only a tenth of an inch of total rainfall during that period (and primarily focused north of Pittsburgh).

As the central CONUS trough continues to advance eastward, it pushes the upper ridge out over the western Atlantic, returning the local area to unsettled weather and increasing chances for showers and thunderstorms Saturday night through Sunday night. Current ensemble guidance indicates 24-hour totals generally ranging from 0.25" to 0.75" across the region within the 25th to 75th percentile range.
However, there continues to be some outlying members that indicate a non-zero chance for higher amounts approaching 1.0 to 1.25 inches in some locations.

Temperatures trend warmer Friday through Sunday, climbing back above seasonal normals with the warmest day looking to be Saturday as highs climb into the low to mid 70s. A cold front on Sunday brings temperatures back down to near seasonal levels to start next week.

AVIATION /18Z TUESDAY THROUGH SUNDAY/
Northwest to southeast erosion of the MVFR stratus will continue through this evening due to subsidence aloft. Scattered to briefly broken low VFR/high MVFR remains possible behind the eroding stratus in conjunction with diurnal heating, but duration of broken cig conditions are likely to be short-lived.
Confidence is high all terminals will return to VFR by 00z, with occasionally gusty NNE wind (15-20kts during the afternoon)
subsiding.

A dry cold front will drop SSE through the region between 05z-14z Wednesday, with impacts mainly tied to the spread of cig restrictions. Model guidance remains varied on the coverage of any post-frontal cloud deck (formed via cold advection and weak moisture influx from Lake Erie) as well as exact heights. Given prior stratus struggles of broader model consensus, TAFs are trended towards HRRR probabilities that suggest 50-90% of at least MVFR cigs (with highest confidence at KMGW due to moisture convergence/upslope flow with higher terrain); probabilities remain elevated for stratus to be IFR or lower but confidence is not high enough at the moment given 12z model data is still finalizing.

Dry advection and subsidence will erode any MVFR stratus by Wednesday afternoon (80-90% confidence of VFR by 18z). There is potential for a stray sprinkle/drizzle due to warm advection aloft but a dry mid-level layer creates a too low probability of it reaching the ground.

OUTLOOK
Surface high pressure with height rises aloft favor VFR into Saturday morning before a series of shortwaves ahead of the next cold front bring increased rain and restriction chances.

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