... A dry and seasonable weekend will give way to increasing rain chance for Monday.
NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... 1125 PM Update: Increased near term POPs north of Pittburgh as radar coverage show rain showers, tied to a shortwave trough crossing the lower Great Lakes, crossing the area. Otherwise, previous forecast remains valid.
Previous Forecast... An encroaching longwave trough/weak cold front will cross the region overnight with lack of mid level moisture and instability inhibiting overall precip chance. Nevertheless, an isolated to scattered, light, and brief potential shower will accompany the system as the crossing mid level thermal trough deepens the mixing layer and sufficiently improves the relative moisture depth. An evening update was issued to better account for this potential as per upstream radar returns and obs.
Increased subsidence via building high pressure will end the potential in the predawn of Saturday. Passage of the trough/front will likely drop morning lows to near the average values.
SHORT TERM /6 AM SATURDAY MORNING THROUGH SUNDAY/... Dry and seasonable conditions are anticipated for Saturday as cold advection neutralizes with building high pressure in response to deepening low pressure in split flow developing over the central Plains. Subsidence and dry advection should erode cloud cover from west to east as the day progresses. Benign and warmer weather can be expected Sunday as the ridge amplifies in response to a further deepening of the southern Plains closed low.
LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... Models indicate the phasing of a northern stream shortwave with the aforemention southern stream low on Monday. Moisture return and broad forcing for ascent thus support categorical pcpn probs for monday with warm advection on the eastern flank of that trough supporting rain and near average highs. Rapid sfc low progression and mid level dry slotting are likely to prevent problematic rainfall amounts.
This process is still forecast to result in development of a closed low pressure system over the Mid and Upper Ohio Valley Monday night and Tuesday as the northern stream redevelops northward. As of today, ECMWF and GFS are in agreement that mid level dry slotting on Monday and a low track west and then north of the area by Tuesday, with sustained mid level frontogenesis on the northern flank, do not favor snow amounts beyond advisory level. Cold, moist wrap-around late Monday night and early Tuesday may support that couple inches of accumulating snow, so this potential was mentioned in the HWO as per advisory potential.
Cold northwesterly flow in the wake of the departing system will likely support continued chance for snow showers through Thursday.