... Mainly dry weather is expected today under building high pressure. Rain returns tonight and Tuesday with a cold front.
NEAR TERM /UNTIL 6 PM THIS EVENING/... 730am update...Extended freezing fog wording through 14z given additional time needed to heat and mix down drier air, while trimming areas that no longer have fog based on latest satellite imagery. Adjustments were made to morning temperature given strong overnight cooling and lower than anticipated dew point temperature. The rest of the forecast remains on track.
Satellite and surface obs show patchy fog forming in the river valleys this morning with most prevalence across the DUJ area. With temperatures in the 20s, freezing fog will be possible in these isolated spots, and light icing may be possible on elevated surfaces.
Dry and seasonably warm weather is expected today as high pressure crosses the region under zonal flow aloft. Increasing warm/moist advection in advance of approaching low pressure will increase cloud cover through the day. Afternoon temperatures will top out around 5 to 10 degrees above average.
SHORT TERM /6 PM THIS EVENING THROUGH WEDNESDAY/... Low pressure will strengthen over the Great Lakes region tonight with a deepening shortwave trough, crossing north of the area on Tuesday. An associated warm front will lift northwards across the region tonight, with precipitation overspreading the area from the west late tonight/early Tuesday. Rain chances will continue through Tuesday morning with the passage of a cold front.
Strong warm advection should maintain all rain for the Pittsburgh metro and south, with snow mixing into rain for the I-80 corridor at onset. Minor snow accumulations of generally less than an inch late tonight/early Tuesday will be limited to extreme NE zones (Forest/Venango/Clarion/Jefferson) before a transition to all rain areawide later Tuesday morning.
Precip will quickly diminish behind the front Tuesday afternoon, though lingering upslope rain/snow will be possible across the ridges into Wednesday morning. Quick progression of the sfc low and associated fronts will keep QPF amounts relatively light and should preclude flooding potential. Highest rain totals of 0.5 inches will be limited to the I-80 corridor with generally 0.30 for the ridges and 0.25 or less elsewhere.
Warm advection will drive high temperatures to near 50F on Tuesday with cooler and more seasonable temperatures behind the front on Wednesday.
LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/... Sfc high pressure will slowly build across the area and into the SE CONUS through the long term. This will keep mostly dry conditions through the weekend.
A digging upper trough over the Great Lakes will briefly return colder temperature Thursday and Friday before moderating back to near-seasonal average for the weekend.