Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Chicago/Romeoville Illinois
309 am CDT Monday Oct 20 2014
152 PM CDT
visible imagery this afternoon indicates a thin cirrus shield over
the region...with some enhancement to the cloud cover across
Wisconsin ahead of a frontal boundary that is pushing from west to
east across the western Great Lakes. Surface ridge has drifted southeast
of the forecast area...which has allowed low level flow to turn
southwesterly. Between the next ridge of high pressure and the
departing ridge...weak troughing will slide east across the upper
Midwest/Great Lakes. This has produced a bump in the gradient and
resulted in breezy conds this afternoon from a good mixed layer.
Guidance has slowed the arrival of the frontal boundary
slightly...but there remains some consistency that the
moisture/precipitation will be displaced to the northeast of the forecast
area through the overnight period. Temperatures tonight will be warmer than
the prior night with lows generally in the low/middle 40s.
Monday through Thursday...
500mb trough axis will continue to pivot east of the region by
midday Monday...however there does appear to be some wrap around
moisture trying to slide south across the lake and may produce some
sprinkles/light rain for northwest in. Have maintained a dry forecast
for northeast Illinois...however late Monday evening a few spotty showers could
sneak into the Chicago metropolitan area into Tuesday morning. Otherwise expect
the far western forecast area to remain dry. Then broad
anti-cyclonic flow arrives and is expected to remain in place through
the second half of the week. Temperatures Monday will likely be the warmest in
the upper 50s to low 60s...then cooling into the low/middle 50s for
Tue/Wed/thur. With high pressure poised to be overhead Tuesday
ngt-Wed-ngt...lows in many areas could easily dip into the middle 30s.
Friday through next weekend...
ensembles continue with the rather benign pattern into the weekend.
Trough digs into the southwest Continental U.S....but is prognosticated to weaken by
Sat/sun. High amplitude ridging over the central Continental U.S. Will
gradually weaken late in the week...however current guidance
suggests the dry pattern will persist into at least Sat. Temperatures will
steadily return to near seasonal conds with highs around 60 to the low
60s by the weekend.
//Ord and mdw concerns...updated 06z...
* southwest winds become west this morning...northwest this
afternoon then north/northeast late this afternoon. Cms
A cold front will move across the terminals later this morning...
shifting southwesterly winds to the west/northwest by middle morning
and then to the northwest by early afternoon. Speeds 10-12kts with
a few higher gusts to start will diminish some by sunrise then
increase again to 10-12kts this afternoon. As the front continues
east this afternoon...the gradient becomes a bit weaker over the
southern end of Lake Michigan. This will likely allow winds to
shift to the north/northeast by late afternoon. Confidence in
speeds is a bit lower...with prevailing speeds likely to be just
Middle clouds will shift east early this morning with lower VFR...
3-5kft ceilings over the northern lakes moving south across the area
later this morning and continuing into this evening with some
potential for high MVFR ceilings...especially south of the lake
affecting gyy. Cms
//Ord and mdw confidence...updated 06z...
High for winds through middle morning...then medium for direction and
timing changes this afternoon/evening. Cms
//outlook for Ord/mdw for 12z Tuesday-12z Sunday...updated 00z...
Tuesday...VFR. Breezy northeast winds.
Wednesday...VFR. East winds.
Thursday through Saturday...VFR. Light west to southwest winds.
309 am...low pressure over the Upper Peninsula of Michigan will
move southeast today and tonight reaching the middle Atlantic on
Tuesday. A trailing cold front will move across Lake Michigan this
morning. Southwest winds will turn northwest this morning then
north this evening. The gradient remains fairly tight across the
southern third or so of the lake...with gusts to 30kt possible for
a few more hours. High pressure will build across Ontario today
and tonight as it strengthens. While the center of this high will
move east into Quebec Tuesday night...a ridge will extend south
across the western lakes tonight and Tuesday...then move across
the lake Wednesday. The gradient will tighten between this
approaching ridge and the departing low with northerly winds
increasing to 30 knots this evening and remaining there until Tuesday
afternoon...as the ridge slowly works east. Cms
Lm...Small Craft Advisory...nearshore waters until 7 am Monday.
Small Craft Advisory...lmz740-lmz741-lmz742-lmz743-lmz744-
lmz745...10 PM Monday to 7 am Wednesday.
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