Steady Warmup to Follow Near-Record Cold

After experiencing sub-freezing temperatures early Saturday morning, a steady warmup through this next week could have us spending several consecutive days in the 70’s.

Temperatures spent over five hours at or below freezing in the overnight hours from Friday into Saturday with a minimum temperature of 29 degrees recorded in Rockford. This ties the years 1980 and 1983 for the second coldest temperature recorded on a May 9^th on record. However, temperatures managed to warm into the low 60’s just over twelve hours later.

As of Saturday evening, a low pressure system is approaching from the northwest with its cold front expected to push through the Stateline overnight. With the storm’s cold front, triple point, and low pressure center all forecast to pass near the Stateline, continuous thick cloud cover and rainfall is expected to last through Sunday evening. Cold northwesterly winds, along with the rainfall, cloudy skies, and strong low-mid level troughing, will make it difficult for temperatures to escape the 40’s on Sunday. In fact, temperatures are once again forecast to approach freezing in the predawn hours of Monday.

 

A lack of temperature advection on Monday means temperatures will rely mostly on diabatic heating from the sun so cloud cover and low level moisture will be key factors. However, lots of sunshine and a dry atmosphere should allow temperatures to heat up at a good pace through the first half of the day. Temperatures are expected to top out in the lower to middle 50’s on Monday.

A shift northward in the mid-level jet and slight ridging in the low levels will allow for some low to mid-level warm air advection. This, in conjunction with mostly sunny skies and more dry conditions near the surface, should pull our temperatures into the upper 50’s, possibly even lower 60’s, by Tuesday.

Strong moisture advection through the day on Wednesday will collide with areas of enhanced mid-level vorticity brought on by a shortwave disturbance to provide a chance for some rain showers in the late afternoon or early evening. Southerly flow will cause our warming trend to continue but enhanced cloud cover and additional moisture in the low levels will likely keep our temperatures in the lower to middle 60’s.

 

Come Thursday, a system of low pressure moves through central Iowa propagating northeastward. As the system drags its warm front over the Stateline, temperatures are expected to reach the 70’s. All the while, a chance for rain through the day will turn into a chance for thunderstorms in the evening. As is expected, lapse rates rise in the warm sector with added vorticity and additional moisture which produce a favorable environment for thunderstorms. CAPE values are expected to exceed 1000J/kg and an elevated LFC shouldn’t be much of a problem with steep low level lapse rates. Although, with an elongated vertical CAPE profile, a relatively weak shear profile, widespread severe thunderstorms are not expected at this time but a few strong to severe thunderstorms are possible.