Area forecast discussion National Weather Service Pittsburgh PA 1228 PM EDT Monday may 20 2013 Synopsis... the risk for afternoon and evening showers and storms will continue through Tuesday. A better chance for widespread activity on Wednesday...as an upper level disturbance moves through. && Near term /until 6 PM this evening/... a relatively weak flow regime remains entrenched over the forecast area today...with one weak system attempting to move directly into the ridge axis along the East Coast to our south and the main large scale player still back over the Dakotas today. While southerly flow has allowed low level moisture to creep steadily into the area...resulting in dewpoints in the 60s this morning and possibly locally touching 70f in Ohio this afternoon...there is seemingly little to help initiate much in the way of convection. Large scale lift is well off to the west...however convection is managing to initiate this morning in a line from southeastern lower Michigan into central Ohio. Given the moisture and instability profile...it seems unlikely that these thunderstorms would fail to propagate downstream a while...so probability of precipitation/thunder chances have been expanded in Ohio and especially southwestern Pennsylvania. Due to our position relative to the large scale features...mixing seems like it should be most efficient over the northwestern portions of the forecast area. This is Colorado-located with the area of best warm advection at 850 mb...so from Zanesville to Mercer temperatures were increased this afternoon. Elsewhere...the status quo remains with highs in the lower to middle 80s widespread this afternoon. Fries && Short term /6 PM this evening through Wednesday/... any convection that develops today will again dissipate with the loss of daytime heating. Ridge will remain in place through Tuesday. Models continue to promote widespread activity late tonight and again Tuesday afternoon. This seems to be overdone as there is no forcing component or upper level wave to get things rolling. Think the best way to handle the situation is to continue with chance probability of precipitation. Expect a better chance for showers and storms Wednesday as the ridge breaks down as a result of large shortwave trough digging into the upper Midwest. More substantial waves will rotate around this feature and into the upper Ohio Valley by Wednesday afternoon. && Long term /Wednesday night through Sunday/... the district remains in the warm sector for Tuesday night through Wednesday night. Temperatures will remain above normal along with a chance of diurnal showers and thunderstorms. A cold front moving slowly south from the Great Lakes Thursday will bring likely showers and thunderstorms for late Thursday afternoon into Thursday night. Behind the cold front Friday the risk of showers will diminish and temperatures will drop below normal. Dry weather can be expected for Friday night into Sunday with temperatures falling into the 40s for overnight lows Saturday morning. && Aviation /18z Monday through Saturday/... broken cumulus ceilings can be expected through the afternoon with the heating of the day. Ceilings will slowly lift from MVFR to VFR by late afternoon. Just a slight risk of a shower or isolated thunderstorm into this evening...but too small a risk to put into the tafs. Another round of MVFR fog is possible late tonight into Tuesday morning. Outlook.../Tuesday through Friday/... chance for shower/thunderstorms will return Tuesday afternoon and increase through Thursday evening as a cold front aprchs and moves through. Building high pressure and VFR conds expd Friday. && Pbz watches/warnings/advisories... Maryland...none. Ohio...none. PA...none. WV...none. && $$