Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Chicago/Romeoville Illinois
314 am CDT Sat Jul 4 2015
305 am CDT
Other than a slim (about 10%) chance of a shower or storm popping on
the lake breeze late this afternoon...look for warm weather with a
good deal of sunshine today. Rather shallow/weak forcing along the
lake breeze along with very weak instability suggests the threat of
anything popping is low and with the models that do convective
mostly keeping activity over Wisconsin...have opted to keep probability of precipitation
below mentionable levels today. Lake breeze should send knock temperatures
down several degrees by early afternoon along the lake but should
see temperatures reach into the 70s along the lake first before settling
back down to the upper 60s/lower 70s behind the lake breeze.
Slightly warmer Sunday with temperatures likely reaching into the middle-upper
80s and possibly reaching 90 in a few locations...though once again
a weak lake breeze is expected along the Illinois shore knocking
temperatures back several degrees in the afternoon.
305 am CDT
Sunday night through Friday...
southerly winds increase Monday in advance of cold front and could
set the stage for temperatures to reach 90...especially eastern/southern
County Warning Area. Debris cloudiness from sunday's convection is a bit of a wild
card...but if it isnt too extensive then lower 90s would be
attainable. Showers/storms could make it into our northwest County Warning Area by later in
the afternoon...but best chance of storms with the front appears to
be Monday night spreading southeast across County Warning Area. Front should clear
southeast County Warning Area by early-midday Tuesday with some threat of storms
potentially lingering into Tuesday...mainly southeast County Warning Area. Some guidance
continues to indicate that the front will hang up and could be close
enough to provide some threat of showers and storms Wednesday night
Onward...though tendency usually is for these fronts to get shaved
further south than guidance indicates so quite possibly could remain
dry for the remainder of the week following the Monday night/Tuesday
frontal passage. Cooler/less humid conditions expected behind the front with a
return to below average temperatures and even cooler weather near the lake.
//Ord and mdw concerns...updated 06z...
* likely lake breeze wind shift with speeds possibly approaching
High pressure spanning the region will provide dry and VFR
conditions...with only few cumulus/high clouds throughout the forecast
period. Have introduced a wind shift to the east later this
afternoon with lake breeze passage. At this time...speeds should
remain in the 6-8kt range but there is a small chance that speeds
could briefly get into the 8-10kt range with the intial passage.
However...confidence is higher in the lighter speeds.
//Ord and mdw confidence...updated 06z...
* high confidence with VFR conditions.
* High confidence with wind speed/direction and lake breeze wind
shift...medium confidence that speeds stay below 10 knots.
//outlook for Ord/mdw for 12z Sunday-12z Friday...updated 00z...
Sunday...VFR/dry. South winds.
Monday...thunderstorms and rain likely Monday night. Breezy south winds.
Tuesday...chance of morning thunderstorms and rain. Northeast winds.
Wednesday...VFR...chance rain showers/thunderstorms and rain Wednesday night. East winds.
Thursday...slight chance thunderstorms and rain. West-southwest winds.
313 am CDT
High pressure spanning the region will move little today into
tonight...but with a weakening southward moving frontal boundary
expected to push into Northern Lake Michigan this morning.
However...this front will continue to weaken as it moves over the
lake but with the current southerly winds turning more northerly
over the north half. Winds will generally stay southerly across
the south half today...with winds over the entire lake returning
to the south later tonight into Sunday. Southerly speeds will
increase Sunday and Sunday night as a trough of low pressure
approaches from the west. Winds really ramp up on Monday with the
arrival of this system with winds over the open waters...mainly
the north half likely approaching 30kt while the south half stays
in the 15 to 25 knots range. Hazardous winds for small craft appear
possible by midday Monday with speeds increasing into the
afternoon...and with speeds possibly approaching 30kt during this
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