Over the past several days, it have been pretty quiet as highs have been in the mid to lower 70s. This September has been an odd one compared to what we typically see in the month of September. The city of Des Moines is on pace for the 3rd warmest September on record, while Mason City is 16th on record. Waterloo and Ottumwa are further down the list as they are on pace for the 26th warmest September on record. This above average warmth will continue into the earlier part of this week. Highs on Monday will range from the upper 70s to lower 80s and highs on Tuesday will be very unseasonal as highs will be in the mid to lower 80s. Wednesday will be our last above average temperature day before a cold front slams through the state on Thursday dropping temperatures and bringing a prolonged period of rainfall . This is where the forecast starts to get interesting.
Over the past few days, we have been keeping our eye on a storm system that could bring significant rainfall and drop temperatures back to below average. This is what we expect to happen. It looks like a longwave 500mb trough will be moving across the Rockies ejecting energy in two or more rounds through southwesterly flow over Iowa. As the leading wave approaches late on Wednesday, a low pressure should develop over Western Kansas. The leading wave will move overhead sometime on Thursday generating showers and thunderstorms, however, the placement is uncertain as much will depend on the location of the low pressure and the front. On Friday, the main 500mb trough will then move overhead clearing everything out to the east by late Saturday. This will bring a prolonged period of rain across the state. However, it is likely that there will be dry periods within this time frame. At this time it is uncertain when those time frames are. Severe weather looks to be a possibility but is uncertain at this time due to all of the uncertainties.
Rainfall totals will be impressive with this storm system. It does appear that rainfall totals could be between a half of an inch to as much as a inch with some locally higher amounts possible. Behind this late week system, much cooler air will surge into the area next weekend. In most areas it will be the coolest weather yet experienced this season. Overall, this is something that we will continue to watch and will bring you further updates on our Facebook page and right here at Iowachase.com.