Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Chicago/Romeoville Illinois
639 am CDT Wednesday Oct 22 2014
310 am CDT
Transition away from the below average temperatures of late to warmer than
average temperatures by this weekend into early next week still on
track...with a couple shots of rain possible.
Any lingering lake cloudiness in NE Illinois early this morning will fade
with 100% sunshine looking likely today. Temperatures should
moderate several degrees over yesterday most areas...though lake
adjacent areas of NE Illinois will still face onshore winds and cooler
temperatures than the remainder of the County Warning Area. Mainly clear skies and light
winds should allow for another chilly night tonight.
Skies will cloud over Thursday leaving our prospects for seeing the
solar eclipse Thursday afternoon dim. Sharp upper trough will
approach from the west Thursday and despite relative lack of
moisture...forcing looks to be strong enough to provide for a decent
shot of showers spreading from west to east Thursday and ending
eastern County Warning Area Thursday evening. Southern extent of this shortwave will
be weakening as it runs into the narrow ridge behind the large
eastern Continental U.S. Upper low. The anticipated gradual weakening of the
trough in our neck of the Woods is reasoning for highest probability of precipitation west
and lower probability of precipitation east...though guidance often weakens these systems
too quickly and have generally gone with higher MOS probability of precipitation for this
Warm advection will ramp up behind this system as upper ridging
briefly builds into the area Friday allowing for moderating temperatures.
The 00z WRF-NAM did have a stronger trough moving through on Friday
with some light quantitative precipitation forecast...but given the global models all much more
muted with this trough with no precipitation have bumped up sky cover a bit
and probability of precipitation up to 10% but kept forecast dry for now.
Pattern will remain quite amplified through the weekend with deep
trough to our NE and upper ridge building into the central Continental U.S..
guidance has trended a bit farther west with the NE Continental U.S. Upper
trough this weekend placing our County Warning Area a bit closer to the cooler air
mass...but still expect highs to make it into the 60s. It now
appears the GFS...ECMWF...and Gem have Monday as our warmest day
with 850mb temperatures prognosticated to be around 1.5 Standard deviations above
average. Given the increasing southerly winds think most of the County Warning Area
stands a decent shot to tag 70f with ensemble maximum temperatures as warm as
the middle to upper 70s. Cold front looks to end our brief stint of
Indian Summer Monday night or Tuesday with showers and possibly some
thunderstorms accompanying the front.
//Ord and mdw concerns...updated 12z...
* MVFR ceilings this morning.
* East winds middle morning through early evening. Cms
3kft ceilings continue to slowly dissipate as they spread north.
Maintained ceilings for a few more hours at Ord/mdw but scattering
should continue over the next few hours.
No change to the winds...starting calm in many locations and light
northwesterly at Ord/mdw. These should shift to the east/southeast
by middle morning then turn more easterly this afternoon with a
possible lake breeze. Prevailing speeds should remain below 10kts.
Winds turn light southeasterly this evening then southerly
//Ord and mdw confidence...updated 12z...
* high for MVFR ceilings this morning...medium for clearing timing.
* High for winds through the period. Cms
//outlook for Ord/mdw for 00z Friday-12z Wednesday...updated 12z...
* Thursday night...chance of rain showers. MVFR possible.
* Friday...dry/VFR. Southwest winds.
* Saturday...dry/VFR. Gusty northwest winds.
* Sunday...dry/VFR. South/southeast winds.
* Monday...slight chance of rain showers. Gusty south/southwest winds.
* Tuesday...chance of rain showers. Strong/gusty westerly winds.
324 am...a large ridge of high pressure extends from Quebec into
the western lakes. This ridge will move east today and tonight and
slowly weaken. Easterly winds will continue to diminish this
morning but wave action...especially across the southwestern part
of the lake will slowly subside this morning. Winds will turn back
southerly tonight and increase on Thursday as the gradient
tightens ahead of an approaching cold front which will then move
across the lake Thursday night as it dissipates. The flow will
turn back southwesterly Friday ahead of another cold front which
will move across the lake Friday night into Saturday morning.
Winds behind this front will increase to 15-25 kts with higher
winds possible over the northern part of the lake. Cms
Lm...Small Craft Advisory...Illinois nearshore waters until 7 am
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