Marine Weather and Tide Forecast for Murrysville, PA

KEY MESSAGES
1) Above normal temperature this afternoon prior to a cold frontal passage; light rain turns into light snow with pockets of freezing drizzle overnight into Wednesday, most prevalent in the eastern ridges.

2) Widespread precipitation favored Sunday with low track dictating rain versus wintry mix threats and ensuing impacts on area river ice.

DISCUSSION
KEY MESSAGE 1...
The melt is on as subtle height rises and a breezy southwest flow have spurred temperatures and dewpoints across the region to their highest values in nearly a month. Temperatures near and south of the city have pushed into the upper 40s and low 50s and should continue climbing under largely clear skies. PIT hasn't cracked freezing since 1/22 and hasn't reached 50 degrees since 1/13. Melting of area snowpack will continue through the day today.

A cold front currently across lower Michigan and far southern Ontario is set cross the region this evening and overnight. Lift generated by the front and a mid-level shortwave will be enough to generate light rain ahead of the boundary, but precip intensity will remain rather light owing to a lack of overall moisture. Much of the area is expected to measure precipitation in the low hundredths and probabilities for even a tenth of an inch don't crest above 40% outside of the Preston and Tucker Co.
ridges.

Cold advection with residual upper level support can maintain light post-frontal showers as rain/drizzle slowly transitions to snow/flurries. With initially weak cold advection, this transition is expected to be gradual and could result in several hours of freezing drizzle due to a lack of ice nuclei with cloud top temperatures largely less than -10C. This period is expected to be longest along the eastern ridges, where freezing drizzle could accumulate a light glaze to a few hundredths. To cover this threat, a Winter Weather Advisory has been issued for the ridges of Indiana to Tucker County from 3AM to 3PM Wednesday. Cloud top temperatures are expected to cool more quickly further north and thus freezing drizzle may be more short-lived further north.

Post-frontal northwest flow will also support light lake enhanced and upslope flow driven snow showers favoring western PA and the WV high terrain. These showers could linger into Thursday morning, resulting in generally less than 1" of accumulation but low probabilities for 1-3" of snow remain in the upslope locations of the Laurel Highlands.

Outside of precipitation impacts, the only other potential impact for this period is the re-freezing of any snowmelt Tuesday night into Wednesday morning on untreated surfaces.
Fortunately, this risk looks lower (but non-zero), as temperature falls are expected to be quite gradual and breezy conditions will promote some level of evaporation.

KEY MESSAGE 2...

Ensembles continue to point towards the late weekend period for our next impactful precipitation event. This is driven by a shortwave aloft kicking eastward from the Four Corners Region and sliding through the Southeast and southern Mid-Atlantic.
Ensembles and their clusters disagree greatly on timing, position, depth and orientation of the eventual trough and this makes discussion of the forecast for this time period rather low confidence.

Some ensembles bury this wave and associated surface low across the Southeast and Carolina coasts (largely GEFS driven), while others develop a more Nor'easter look to them and carrying precipitation further north (largely Euro driven). As such expected QPF values in the 10-90th percentiles (trying to highlight a reasonable lower end dry solution and a reasonable higher end wetter solution) run the gambit from nothing to near an inch of rain in Pittsburgh.

The most likely scenario remains that the lowest levels warm enough for much of the precipitation to fall as rain (after an initial short period of wet bulbing featuring wet snow). Impacts from snow look minimal and thus overall impacts are largely tied to QPF, dewpoints and temperatures influence on snowmelt and river ice thawing/breakup. Higher values of each lead to an increased risk of ice breakup and the potential for ice jamming and associated flooding. As previously stated it remains too early to say the degree of ice breakup we will see but the mention of it remains important.

There remains a small contingent of models (roughly 10-15%)
with earlier precipitation onset and/or more staunch cooler surface air that results in a period of freezing rain which would necessitate winter headlines near the WV terrain. Once again, it remains early to commit either way and we will keep a close eye on future forecast developments.

AVIATION /00Z WEDNESDAY THROUGH SUNDAY/
KEY MESSAGES...

1) Deterioration to MVFR with light rain possible this evening with a cold front passage

2) MVFR/IFR ceilings persist into Wednesday

3) Light snow possible on Wednesday, best chance for restrictions at FKL/DUJ/LBE

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Just ahead of a passing cold front, low clouds have quickly developed this evening with ceilings dropping to MVFR beneath them. Some light rain showers will be possible in the 00Z to 03Z timeframe along and ahead of the boundary as it sags south across the area. Highest precip chance will be for MGW and LBE, though can't rule out some showers for PIT and surrounding SW PA terminals, so have included a TEMPO group for just a couple hours ahead of and along the FROPA. Precipitation should end immediately following the frontal passage, and hi res guidance suggests a brief period of cig improvement as well with the low clouds scattering beneath thicker mid-level coverage. That'll be short lived as post-frontal low-level cold advection in stout northwest flow reinforces a MVFR low stratus deck overnight.
With that, some light rain/snow chances will once again be introduced primarily for FKL/DUJ with lake enhancement from a now only partially frozen Lake Erie.

Temperatures drop below freezing by early Wednesday morning with the precip type then all snow. A short period of freezing drizzle will be possible very early, primarily in the ridges east of LBE/MGW. Low-end MVFR ceilings prevail through Wednesday as moisture remains trapped beneath a subsidence inversion.
Expect light snow showers to persist with saturated low-levels extending just into the DGZ.

Outlook...
MVFR cigs linger into Thursday under cold NW flow and crossing upper disturbances. VFR returns late Thursday through Saturday under high pressure.

PBZ WATCHES/WARNINGS/ADVISORIES
PA...Winter Weather Advisory from 3 AM to 3 PM EST Wednesday for PAZ074-076-078.
OH...None.
WV...Winter Weather Advisory from 3 AM to 3 PM EST Wednesday for WVZ510>514.