Heavy Rain Threat Late Sunday and Monday Morning

A very moisture rich air mass will be pulled northward Sunday night, bringing with it a threat for heavy rainfall as far north as central Wisconsin.


Drizzle and light showers continue Sunday evening ahead of a warm front that stretches from near the Iowa/Missouri border into western Illinois and south of Romeoville.  North of the front temperatures are just shy of 40 degrees, but south of the warm front temperatures are in the upper 40's to mid 50's.  Dew point temperatures are also fairly high reaching 50 degrees as well!  That's an extremely high dew point temperature for mid-January!

The warm front will continue to lift northward through the overnight Sunday, most likely reaching northern Illinois mid-day Monday.  Temperatures won't get quite as warm as what they are to the south, but highs could spike close to 50 degrees following the rain Monday morning.

Rain showers are beginning to increase in coverage to the southwest, ahead of an approaching mid level low pressure system - or what we refer to as a 'shortwave'.  This shortwave will help push the front northward, but also allow the showers now over Missouri and Arkansas to continue to expand northeast.  The overall coverage of the rain will increase over northern Illinois around Midnight, lasting through early Monday morning.


Strong winds in the lowest level of the atmosphere will also help sustain rain, and even bring a little elevated instability northward.  This increases the chance for a thunderstorm or two by Monday morning.


Rainfall totals could be close to an inch, and possibly higher with any thunderstorms, by Monday evening!  Localized and minor flooding is possible as the ground is still frozen.

Low pressure will move closer to central Illinois by Monday afternoon.  As it does, there could be enough instability to produce a couple stronger thunderstorms over parts of western and central Illinois early Monday afternoon.  The Storm Prediction Center does have that area highlighted with a 'marginal' risk for strong thunderstorms Monday.


The cold front passes Monday evening with temperatures falling below freezing by Monday night.  Most of the moisture will be gone, but there may be enough lift in the atmosphere to allow for a slushy accumulation of snow Monday night into Tuesday morning.