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FXUS61 KPBZ 041338 AFDPBZ

Area Forecast Discussion National Weather Service Pittsburgh PA 838 AM EST Mon Dec 4 2023

SYNOPSIS
A crossing upper level disturbance will maintain scattered rain and snow showers across the region today, north of Interstate 70. Low pressure will bring more widespread rain and snow to the region Tuesday and Tuesday night. Generally dry weather will return by Thursday under a ridge of high pressure.

NEAR TERM /UNTIL 6 PM THIS EVENING/
Isolated to scattered showers are expected to continue today as a shortwave trough tracks from the Midwest to the Upper Ohio Valley region. Critical thicknesses and 850mb temperatures indicate the rain will mix with or change to snow especially for areas north of I 80, though surface temperatures should be too warm for any accumulation. Some limited lake enhancement is also possible north of I 80 late this afternoon as the boundary layer flow veers to the WNW, though the lake surface-850mb temperature differential is marginal at 13 deg C. High temperatures should return to more seasonable levels today.

SHORT TERM /6 PM THIS EVENING THROUGH WEDNESDAY NIGHT/
Scattered rain and snow showers should taper off tonight as the shortwave exits, and ridging builds in ahead of the next trough across the Midwest.

The next shortwave, and its associated weakening surface low, will advance eastward Tuesday, spreading rain and snow across much of the region through the day. Model soundings and critical thicknesses indicate mainly snow will fall for areas north of PIT, with a mix of rain and snow to the south. The exception will be the Laurel Highlands and the higher terrain of WV, where all snow is expected. Daytime accumulations are expected to be minimal for most locations, though the higher terrain areas could see up to an inch.

The shortwave trough is progged to cross the region Tuesday night, with any rain/snow mix transitioning to all snow with loss of boundary layer heating, and cold advection aloft. The boundary layer flow is progged to the west, then north Tuesday night into Wednesday morning. While this will result in orographic lift for additional snow in the ridges, the direction is not optimal for maximum lift. Still, these areas are likely to see 1 to locally 3 inches of snow through Wednesday, with 3-5 across eastern Tucker county WV. Will continue to headline this in the Hazardous Weather Outlook. Current probabilities for 6 inches of snow or greater are at 30% in the NBM, with slightly lower probs from WPC.

The snow should end over much of the area by Wednesday morning as the upper trough exits the area, though areas generally S-E of PIT, could see snow linger into the morning with those areas in closer proximity to the trough. Additional terrain enhancement is likely Wednesday morning as well. Dry weather should return later Wednesday and Wednesday night as a ridge of surface high pressure builds across the region.

LONG TERM /THURSDAY THROUGH SUNDAY/
A less amplified, quasi zonal flow is expected across the area Thursday and Friday, with dry weather expected. More clouds are expected on Thursday as warm advection begins.

A deepening trough is then progged to track east from the Central CONUS by the weekend, as a surface low develops across the Midwest/Mississippi Valley region. Increasing moisture and ascent in southwest flow should result in rain chances returning Saturday, increasing on Sunday, as the trough and surface low further approaches the region. Uncertainty remain in the exact details in the development and track of the low, though current model ensembles indicate it near the Lower Great Lakes/Upper Ohio Valley region on Sunday.

Temperatures will warm though much of the period, reaching 5 to 10 degrees above average by the weekend.

AVIATION /13Z MONDAY THROUGH FRIDAY/
Cold air advection will maintain high MVFR / low VFR stratocu cigs through the day. The boundary layer looks just deep enough to support isolated light snow or rain, which will vary given current cloud top temperatures right around -8 to -10C.
Increasing upper cloud coverage should result in any isolated precipitation leaning more towards flurries during the afternoon hours.

A crossing shortwave will increase chances for light snow mainly north of KPIT later this afternoon and evening, but impacts will be minimal. Probabilities of IFR cigs are less than 20%.

OUTLOOK
Periodic restrictions will continue through Wednesday as cold air returns. Snow shower chances increase for DUJ/FKL Monday afternoon as winds shift from the northwest and cold low-lvl moisture overspreads areas downstream of Lake Erie. Elsewhere, the chance of rain or a rain/snow mix remains with a slightly warmer boundary layer.

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

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