Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Chicago/Romeoville Illinois
1057 am CDT Thursday Mar 13 2014
338 am CDT
A progressive pattern will continue to provide varying temperatures
over the coming days but little in the way of significant
precipitation through the weekend. Friday and Saturday should see
generally seasonable temperatures...with Sunday and Monday cooling
off again before another milder but possibly wetter period next week.
Winds turn south by middle to late morning today and despite increasing
cloudiness...should support warming about ten degrees above
yesterdays highs. The timing of a cold front passage on Friday is
somewhat uncertain and poses a challenge for the high temperature
forecast on that day. Elected to trend slightly cooler overall
given hints of an earlier frontal passage. Also maintained a 10 degree spread
from north where the diurnal trend flattens earlier to south which
will have more time to warm up. Lack of sufficient moisture along
this boundary will limit precipitation chances as the front moves
A ridge building over the upper Midwest behind the front Saturday
will provide calm winds or light northerly flow over the area with
plenty of middle March sunshine...so temperatures overall Saturday
should not be too much cooler than Friday. Northeast flow off the
lake Saturday night might normally support some lake effect snow in
northeast Illinois...but am not going to introduce more than slight
chance probability of precipitation given how the relative lack of open water may limit
Saturday night and Sunday a low pressure system sliding to our south
was previously expected to bring in another chance of snow. With
the strong ridge now expected to remain in place over the Great
Lakes...this low is appearing more likely to support some late
winter severe weather along the Gulf Coast together with a tight
pressure gradient over the local area. Our resulting cloud cover
and strong north to northeast winds will keep both Sunday and Monday
quite a bit cooler than the start of the weekend.
Deterministic models begin to diverge quite a bit after Sunday...but
the GFS and European model (ecmwf) both show the next low pressure system moving out
of the northern plains into the Midwest late Monday into Tuesday.
At this point the two models as well as the GFS ensemble all have
the low center passing north of the local area...keeping US on the
relatively milder and mostly rain side Tuesday and Wednesday.
//Ord and mdw concerns...updated 16z...
* S to SW winds gusting to around 20 knots this afternoon and early Friday
High pressure will move east of the terminals this morning. Winds
have turned light southerly and will continue to increase in speed
through the morning with gusts into the 18-20kts possible this
afternoon. Gusts will diminish this evening then redevelop after
midnight as the gradient tightens. Prevailing winds will remain
generally in the 190-220 range but begin to turn more westerly
toward daybreak Friday.
An area of 3-4kft clouds has begun to shift southeast and away
from the terminals across east central Illinois. An area of middle
clouds...5-8kft will spread across the area later this morning.
There remains a small potential for few/scattered MVFR level clouds
around 2kft and have maintained scattered mention but confidence
is low. Otherwise...expect VFR through the period. Cms
//Ord and mdw confidence...updated 16z...
* high confidence in all other forecast elements.
//outlook for Ord/mdw for 00z Saturday-12z Thursday...updated 12z...
* Friday night...dry/VFR.
* Saturday...dry/VFR. Wind shift to northeast in the afternoon.
* Sunday...gusty northeast winds possible.
* Tuesday...chance of rain/snow. MVFR possible.
* Wednesday...slight chance of rain/snow. MVFR possible.
316 am...a ridge of high pressure over the lakes region early
this morning will move southeast today. Southwesterly winds will
quickly increase during the middle/late morning as low pressure moves
southeast from Manitoba today to Lake Superior by Friday morning.
As the gradient tightens...expect 30kts over much of the northern
two thirds of the lake. This will move east to Quebec on Friday
with a trailing cold front moving across the region.
A large area of high pressure will move south from Canada Saturday
across the lakes region Saturday night and Sunday...moving east to
New England Sunday night. This will turn winds northeast over Lake
Michigan Saturday afternoon into Saturday night. As low pressure
moves east across the southern U.S. The gradient will tighten and
a period of 30kts is possible Saturday night into Sunday morning
before the gradient begins to weaken and speeds/gusts diminish.
There remains quite a bit of uncertainty regarding the track...
timing and strengthen of low pressure moving across the plains
Monday/Monday night and then across the lakes region Tuesday.
Current grids/forecast shows southerly winds developing Monday...
shifting westerly Tuesday into Tuesday night. Changes to the
current directions and speeds are likely as trends emerge with
this system. Cms
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