Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Chicago/Romeoville Illinois
1002 PM CDT sun Oct 19 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 03z...
* southwest winds occasionally gusting to around 20 knots through the evening.
* Southwest winds shift northwest Monday morning.
* Scattered-broken low end VFR clouds Monday.
High pressure is off to the east with low pressure moving eastward
across Lake Superior which will keep a steady southwest wind in
place through the evening. Speeds will probably settle slightly
early but expect them to come up a bit as the pressure gradient
tightens. Occasional gusts are also possible. A cool front will
cross the area Monday morning as the low continues east which will
turn winds northwesterly. The gradient will weaken so speeds will
likely hover around 10 knots Monday. Low level moisture is forecast
to increase behind the front...especially Monday afternoon. Expect
that lower end VFR ceilings will move in with scattered-broken coverage.
//Ord and mdw confidence...updated 03z...
* high confidence in wind trends.
* Medium confidence in lower end VFR ceilings Monday.
//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.
324 PM CDT
Low pressure moving through Ontario tonight will drag a cold
front across the lake and tighten the pressure gradient this
evening. Gale force gusts are possible for a time but generally
winds should stay below Gale Warning criteria. A Small Craft
Advisory continues for nearshore waters this evening and through
the early overnight hours due to strong offshore winds...but waves
should not be a big problem until winds turn northwest and then
north by late Monday...increasing again in a gradient between an
approaching high and the slowly departing low. These strong
northerly winds persist through Tuesday after which time the ridge
moves over the lake bringing fairly quiet conditions.
Lm...Small Craft Advisory...nearshore waters
until 3 am Monday.
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