Wednesday, September 30, 2015
Pumpkins, Scarecrows and High Pressure Systems
Fall is finally here! Just a few days ago Madison was seeing lots of warm moist air coming up from the Gulf of Mexico which was keeping our late September in the mid to upper 70s with high humidity. However, since then, a strong high pressure system has moved into the area causing cooler but dry temperatures in the Midwest. Great fall hiking weather is expected all week with highs of 60 and lows of 40. The first weekend in October will be free of precipitation and mostly sunny, perfect for autumn activities.
High temperatures will remain in the uppers 50s and low 60s due to a high pressure system (1030 mb) currently located in northern Wisconsin. The system is not likely to move out of the area anytime this week because it is situated between a strong low pressure system to the east and a high pressure wind to the north in Ontario/Quebec. The combination of these two features and the fact that the great lakes region is located below the left jet entry region will produce lots of upper level convergence and in so, downward vertical motion. Low temperatures at night are expected to drop to the low 40’s but not low enough for frost to form. Dry air from the north will cause the lowest dew points in the afternoon by boundary layer mixing. Surface winds are expected to increase over the weekend due to the strong pressure gradient across southern Wisconsin, which is expected to intensify.