Marine Weather and Tide Forecast for Murrysville, PA

NEAR TERM /UNTIL 6 PM THIS EVENING/
KEY MESSAGES:

- Dense fog possible across southeast OH into nrn WV and western PA this morning - Dry conditions through the afternoon

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Patchy dense fog is likely across eastern OH and slightly encroaching into western PA this morning with clearing skies and light winds. Based off latest nighttime microphysics satellite imagery and available webcams, have issued a Dense Fog Advisory these areas. To the north and east, more localized areas of fog are likely, but not enough in coverage to justify an advisory.
These areas coincide with favorable hydrolapse(s) and MRi values, while areas farther north and east tend to favor low stratus based off latest forecast soundings.

A shortwave ridge transitioning over the region today will result in dry conditions under increasing subsidence. Overall though, heights/thickness will be lower as longwave troughing over the midwest deepens as a jet max dives down the backside of the trough, so daytime highs will top off several degrees lower than observed Friday, but still slightly above normal.

SHORT TERM /6 PM THIS EVENING THROUGH SUNDAY NIGHT/
KEY MESSAGES:

- Rain chances increase tonight into Sunday - Colder with rain mixing with/changing to snow Sunday night ----------------------------------------------------------------

The deepening upper trough is progged to dig across the Upper Midwest and western Great Lakes overnight and Sunday. Meanwhile, surface low pressure will deepen as it tracks up the Ohio River Valley. While there is a minimal chance of brief light rain across northern zones this evening with a weak shortwave, rain chances will substantially ramp up across much of the area Sunday morning as the surface low traverses the eastern Great Lakes and drags its trailing cold front across the region.

Coverage should become more scattered behind the front, but showers will persist as the upper trough continues to deepen and approach from the west. Temperatures drop quickly after midnight Sunday night as rain mixes with and then transitions to snow.
With warm ground temperatures and prior rainfall Sunday, only minor accumulations (a few tenths of an inch) are expected by sunrise on Monday, mainly on grass and elevated surfaces.

LONG TERM /MONDAY THROUGH FRIDAY/
KEY MESSAGES:

- Much colder with snow showers Monday into Tuesday - Accumulation possible mainly north of I-80 and in the ridges - Unsettled Wednesday and Thursday with occasional rain/snow chances mainly north of Pittsburgh - Apparent temperatures in the teens Tuesday morning -------------------------------------------------------------------

Ensembles continue to point towards the longwave trough digging across the eastern CONUS on Monday. Differences remain in the upper patterns between the GEFS and the Euro that would mean different durations of NW flow and thus differing snow accumulations through Tuesday. Despite these differences, the picture remains the same that NW flow will bring scattered to numerous snow showers across portions of the OH Valley.

850mb temperatures are expected to drop to between -8 to -10 deg C by Monday, while Lake Erie temperatures hover around +12 to +14 deg C. Lake and terrain enhancement will be likely Monday into portions of Monday night and possibly early Tuesday before flow backs to the W and the most efficient lake and terrain enhancement is turned north of the region. Mesoscale features (such as a reinforcing surface trough) will greatly affect SFC to 850mb flow and thus the positioning, duration and intensity of any heavier focused lake bands remains low confidence at this time. Despite this, models continue to hint at the likelihood of one or several lake bands yielding enhanced snowfall near and south of Lake Erie. NBM probabilities continue to ebb and flow but currently sit between 40- 50% for advisory level snow north of I-80. These probabilities have remained rather steady for the PA and WV ridges however where probabilities remain between 50-60%. We will continue to monitor the evolution of this system and pattern over the coming forecast periods.

The trough is expected to begin to shift east of the area on Tuesday, as boundary layer flow backs to the SW and snow chances decrease through the day.

Broad upper troughing is then expected to persist across areas from the Upper Midwest into New England. Occasional rain/snow chances will be possible, mainly north of PIT, as individual shortwaves rotate through the trough.

Temperatures are expected to be 15 to 20 degrees below average Monday and Tuesday, before moderating some by mid week.

AVIATION /12Z SATURDAY THROUGH WEDNESDAY/
Skies were clearing from W-E as a shortwave trough exits the region. With low level moisture in place, fog and stratus was developing after the clearing occurs. Expect LIFR to develop initially across Ohio airports, with MVFR further east to PIT/AGC. Additional MVFR stratocu was moving ESE toward the region along a secondary surface trough/cold front. These should move over FKL and DUJ overnight, which should preclude fog formation.

MVFR is expected for most airports north of I-70 today, or north of a ZZV-AFJ-VVS line as this front approaches and stalls across the area. VFR is expected to the south, with scattered cumulus and cirrus above. CIGS should improve to VFR this evening ahead of an approaching shortwave and surface low pressure.

Outlook...
Restrictions are likely Sunday in rain as low pressure crosses the Upper Ohio Valley region. Periodic restrictions and snow showers are then expected Sunday night through Tuesday as a deep upper trough crosses the region, and lake/terrain enhancement occurs. Another crossing trough will maintain restriction potential Wednesday, with rain and snow possible.

PBZ WATCHES/WARNINGS/ADVISORIES
PA...Dense Fog Advisory until 9 AM EST this morning for PAZ029-031.
OH...Dense Fog Advisory until 9 AM EST this morning for OHZ039-040- 048>050-057>059-068-069.
WV...Dense Fog Advisory until 9 AM EST this morning for WVZ001>004- 012-021-509.