Tech Disco 10-4-2012

Synopsis

the last bit of warmth will be felt this afternoon and tomorrow afternoon, and then thigns will get dicey as a pair of frontal systems will align with a massive area of cold advection that will completely change the game for this weekend, featuring a threat for some early winter weather. 

Short Term(Tonight through Friday Night)

The feed of warm air via westerly warm advection stemming from a Canadian low pressure system working along southerly advection from a Southeast U.S high will keep us above average in high tempos for today and tomorrow, but Friday afternoon, we'll see some changes. First, the trough axis from the cold front currently draped across eastern Wisconsin and Illinois, will cross through the state between 12z and 18z, however showers will lag behind, beginning to precipitate in NW PA  around 3z Saturday morning, and slowly crossing through and out of centre county around 15z to 18z Saturday afternoon.  His will be the start of the cold advection, for this first front is a part of the larger Canadian low pressure system.

Long Term (Saturday through Monday)

The first cold front mentioned above will bring rain across the state in a NE to SW oriented squall line that will startup after 0z Saturday, and will completely exit by 0z Sunday, but the end of showers will not come until overnight Sunday into Monday. A tight pressure gradient will be draped across the Great Lakes, Ohio Valley and Northeastern U.S. by 0z Sunday, which will be followed by a shortwave trough that will tear up the pressure gradient out near Illinois, slowly developing surface low pressure into a cell that will merge with a warm front from the south to carry a synoptic rain system along the warm side of the low, giving the state showers starting around 12z Sunday and quickly spreading throughout the state by 21z and leaving by sunrise Monday morning. The PVA will lag the low, but there won't be enough to really occlude the low and wrap some precip or lake effect precip as the low clears out, but the NAM and GFS put the 540 dam line through Pittsburgh and Dubois, leaving room for wintry precip if the low can occlude or if the low is repositioned in the future. Either way, High pressure will beign to seep through the steep pressure gradient come Monday, and the surface ridge will slide into our area to kick off next week.