Scattered storms expect on Sunday and Monday ahead of an unsettled weather week in Pittsburgh
After a hot and humid Saturday with air temperatures reaching 90 degrees, Sunday begins warm and humid as well, with temperatures in the low 70s and dew points in the low 70s.
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A weak shortwave trough is moving through Ohio early this morning and will move into Western Pennsylvania as daytime heating increases. This will lead to a scattering of showers and storms beginning as early as noon once temperatures hit around 80 degrees or so.
The highest coverage of rain and storms is expected to mainly occur east of I-79, with the Laurel Highlands and a few of our I-80 counties being convective hot spots. Strong microburst winds upwards up to 60mph and localized flash flooding may occur with some storms, but the overall greatest potential for flash flooding will be in central Pennsylvania by late afternoon and early evening.
A weak cold front will move into our northwest counties later this evening and tonight before eventually dissolving across the area. This boundary will carry a low chance for isolated to scattered showers through the overnight hours with temperatures falling into the mid 60s to near 70.
The biggest change to the short-term forecast involves increasing rain chances late tonight and Monday for a large portion of Western Pennsylvania.
A thunderstorm complex that formed in Kansas and Oklahoma has left a remnant area of mid-level spin, and this spin is stronger than what has been modeled over the last few days. This area of spin will get caught in the upper-level flow and drift toward the Ohio Valley by Monday morning and provide the lift needed for more showers and storms from mid-morning Monday through late afternoon.
The highest coverage appears to set up along the I-70 corridor and south toward I-6,8 with locally heavy downpours and isolated flash flooding possible.
Once this system passes Monday evening into Monday night, skies will clear and winds will be very light. This, combined with high levels of relative humidity near the ground, could set us up for some patchy dense fog Tuesday morning. The fog will mix out through the morning on Tuesday with partly to mostly sunny skies and very warm temperatures with highs in the mid to upper 80s.
The pattern does look to turn unsettled by Wednesday afternoon through the end of the week as a surge of deep low-level moisture returns from the southwest. This, combined with several disturbances, will trigger waves of showers and storms Wednesday evening through Friday.
At the moment, Wednesday evening and Friday appear to have the highest chances for precipitation. Locally heavy rain, isolated flash flooding, and a few severe storms cannot be ruled out as well.
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