Saturday, May 26, 2012

A Blast of Heat on Sunday

A severe thunderstorm with large hail prompted issuance of a severe thunderstorm warning over southeastern Stephenson county before daybreak on Saturday morning.  In addition to the hail, the storm produced a  band of heavy rain as it moved toward the east into Winnebago county.  Some parts of Winnebago county received 1" to 2" of rain from the county line in a relatively narrow band eastward across the central part of the county towards  Rockford, Loves Park, and Machesney Park.  It was much needed rainfall, because it has been very dry this May, but it did come  much too fast, so there was some runoff and street flooding is spots. 

A warm front lies just to the southwest of the Stateline tonight.  It is the dividing line between 50 and 60 degree air to the northeast of the front, and 70 and 80 degree air just to the south of the front.  A thunderstorm complex sweeping across Wisconsin late this afternoon into the early evening pushed an outflow boundary southward across the Stateline dropping temperatures from the 88 degree high in Rockford this afternoon to 68 degrees in a fairly short period of time as the winds switched from the southeast to the northeast, and gusted up to 25 mph.  The effects from that outflow boundary have subsided as of 11 pm, and winds are now light easterly.  There are thunderstorms moving eastward across central Wisconsin tonight, and they will remain well to the north of the Wisconsin/Illinois border.  However, there is a slight chance of showers and thunderstorms overnight as the warm front moves across the area and northward into southern Wisconsin by morning.  Hot weather from the southern and central plains, Mississippi valley will surge northward across the area on Sunday.  The atmosphere will be capped, so no thunderstorm development is expected.  Skies will be mostly sunny, and winds will  be southerly at 10-20 mph.   The hottest temperatures so far this spring are expected on Sunday afternoon reaching 95 degrees.  That will be a new record for the date surpassing the old record of 92 degrees last set in 1978.  Heat indexes during the afternoon will be in the 95 to 100 degree range.  It will be mostly clear and very warm on Sunday night with a low near 72 degrees, a full 20 degrees above the average low of 52 degrees.

Early on Memorial Day a cold front will be stretching from northwestern Wisconsin, across northeastern to southwestern Iowa to northeastern Kansas.  It will be very warm and humid with a southwesterly breeze continuing.  Skies will be partly cloudy, and thunderstorms will be possible in the morning, but more likely in the afternoon as the cold front gets closer.  Some of those thunderstorms have the potential of become severe with damaging winds and large hail.    Showers and thunderstorms will end in the evening with the passage of the cold front. 

It will be sunny, cooler, and less humid on Tuesday as high pressure ridges into the mid west from the northern plains.  Winds will be northwesterly 10 to 15 mph, and it will be a delightful day with highs in the middle 70's.  Skies will be mostly clear on Tuesday night with an overnight low in the low 50's.

On Wednesday it will be partly cloudy and cooler with a northerly breeze.  High temperatures will be below average for a change... only around 67 degrees.  There will be a slight chance of some light showers on Wednesday night, and it will be chilly with temperatures dropping into the upper 40's.

Skies will be partly cloudy on Thursday and Friday with a slight chance of more light rain showers.  It will remain cool with highs in the upper 60's and lows in the middle to upper 40's. 

Temperatures will warm up into the low 70's on Saturday as the pattern becomes more zonal.

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