... Isolated snow showers will weaken with a building ridge from the west. Wind chill values overnight into early Saturday morning have prompted headlines for portions of the region. Warmer and dry weather is expected to return Sunday.
NEAR TERM /THROUGH SATURDAY/... GOES-16 Nighttime Microphysics RGB channel, along with radar, depicts lake effect snow showers north of I-80 and a narrow weak snow band extending through Lawrence/Butler/northern Westmoreland county. Based on sfc wind obs and the placement of a building ridge to the west, enhanced low-level convergence within the boundary layer is allow a single narrow snow band to venture further inland from Lake Erie. Based on Hi-res model guidance, snow shower activity should diminish after 05Z as winds shift from the west and we lose the influence of Lake Erie moisture.
Clear conditions, under an Arctic cold airmass (850mb temp from the PIT 00Z measured -21.8 degrees Celsius), will allow early Saturday morning temperatures to stay in the single digits across the region. Wind gusts should subside after dawn with a weakening pressure gradient. However, a Wind Chill Advisory for portions of the region (mainly the ridges) will continue through 12Z with forecasted values ranging between 10 below to 20 below.
By Saturday afternoon, high pressure will reposition over the mid-Atlantic, fostering warm advection within southwest flow. Temperatures will likely continue to be 5 degrees below seasonal averages. However, a significant improvement to the afternoon average high temperature will likely shift by 25 degrees.
SHORT TERM /SATURDAY NIGHT THROUGH MONDAY NIGHT/... The next shortwave trough will approach and pass north of the region through the day Sunday, but meager moisture and limited lift will keep late-day precipitation chances low and focused north and east of Pittsburgh. A period of SW flow ahead of the system (and weak sfc cold front) will continue the area warming trend, with high temperatures 5 to 10 degrees above seasonal averages.
High pressure will quickly return with upper ridging Monday as the trough shifts towards the east coast. Residual cold advection behind the sfc cold front will result in a slightly cooler but still above normal temperature for Monday.
LONG TERM /TUESDAY THROUGH FRIDAY/... Warm advection will return Tuesday as southwest flow strengthens ahead of a northern stream upper trough. Precipitation appears likely to return to the region late in the day ahead of a surface cold front. However, ensembles suggest it will likely be decaying as upper forcing is deflected farther north by the far SE CONUS ridge, meaning precipitation chances will lessen into Wednesday as the front washes out. Expect well above normal temperature ahead of the front with likely little change in airmass after it passes/stalls.
The late Tuesday into late week period remains in flux as it will be dependent on the eventual northeast lifting of a deep trough that will develop around the Four Corners region. The trend pushes its Upper Ohio River Valley impact towards the late week time frame, but potential precipitation could arrive as early as Wednesday. There is a high probability for widespread rain as temperature remains above normal through this period, with timing of the onset/ending of the precipitation one of the more uncertain components.