Lake County SKYWARN

NWS Area Forecast Discussion

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Area Forecast Discussion
National Weather Service Chicago/Romeoville Illinois
410 AM CDT Friday April 18 2008

.Discussion,
407 AM CDT

The low over Missouri will move slowly into eastern Iowa by midnight
Saturday morning.  Precipitation will be slow moving into the county warning area
of north central Illinois, northeast Illinois and northwest
Indiana.  Will leave a chance of rain for this afternoon using
probability of around 30 percent.  Will forecast occasional rain
for tonight for most of the county warning area except for the far east.  We expect
most of the rain will be over the whole county warning area by Saturday morning.
the GFS model was used beyond 24 hours.  The locally run WRF ARW
and the short range ensemble forecast were very close in the low
forecast for Friday evening.  The low center was 100 miles north in
eastern Iowa than the sref.  But our local model is just one
solution of the forecast equations, not a test of a set of
solutions and our domains and boundary adjustments are different.
the forecast temperature fields were close enough so will use a
blend of the two for the forecast up to 24 hours.

Most of the rain will occur on Saturday.  For the two days the
storm total precipitation is forecast will range from .57 inches
in western ogle and lee counties to .25 inches in valparaiso and
fowler Indiana.  The long meridional trough over the Plains states
will move east into the Ohio Valley where the 500 MB low is
expected to become closed over southern Ohio and kentucky.  We
expect this to occur Sunday.  The largest height falls were over
Texas at 00 UTC Friday.  Large wind shears from 850 to 700 MB were
noted over Texas and Oklahoma.  This shows the trough will become
deeper as it begins to tilt to the east.  The GFS model shows this.
the high temperatures will be in the 60s today and in the upper
50s Saturday.  Then back into the middle 60s.  Another low will move
into the great Plains and the wind over Illinois is forecast to
become southeast to south by Monday.  We will forecast the high in
the 70s for Monday.

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