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Area forecast discussion
National Weather Service Chicago/Romeoville Illinois
218 am CDT sun Apr 20 2014
250 PM...forecast concerns include highs back in the 70s Sunday
and Monday...along with possible lake cooling. Showers along with
a chance of thunderstorms Monday afternoon/evening...additional
showers for the end of the week.
Despite the center of high pressure now over the eastern lakes
and pushing into western Quebec...the gradient remains weak over
Lake Michigan and this is aiding cooler easterly flow with temperatures
along the Illinois Lakeshore only in the 40s. Temperatures warm quickly into
the 60s inland. This easterly flow will slowly turn southeasterly
as the gradient gradually tightens overnight. Lows tonight are a
bit tricky...dewpoints will gradually creep up...perhaps into the
lower 40s by morning. Air aloft will also be warming. Lows may end
up occurring in the late evening or early overnight then become
steady or slowly rise toward morning. But usual cool spots may dip
into the lower 40s.
Sunday will be dry and warmer as highs should easily reach the
lower to middle 70s with some upper 70s possible across parts of
central Illinois. However...the gradient now appears to be just weak
enough for a lake breeze to form from downtown north to the WI/Illinois
state line and it will likely remain right along the shore...
making the temperature forecast difficult. Temperatures could stay in the upper
40s/lower 50s right at the shore line...quickly warming into the
lower 70s just a few miles inland.
A frontal boundary will slowly sag across the northern lakes
tonight into Sunday and then become stationary into Sunday night
as low pressure moves across the upper Midwest and northern Great
Lakes region Monday. Precipitation timing continues to slow and much of
the area should remain dry through daybreak Monday with only the
western third of the County Warning Area potentially seeing some showers Monday
morning. Best chance of showers and perhaps a few thunderstorms
will be along/ahead of a trailing cold Monday afternoon into
Monday evening. With lows only falling back into the 50s Sunday
night/Monday morning...highs on Monday will likely be able to
reach the lower 70s...especially eastern two thirds of the County Warning Area
and bumped temperatures up a few degrees.
A ridge of high pressure will move across the region Tuesday and
Tuesday night allowing for seasonal temperatures along with easterly flow
keeping the Lakeshore areas cooler. As the high departs...a brief
period of showers appear possible Wednesday afternoon into
Wednesday evening as warmer air spreads across the region but this
should be fairly short-lived with the rest of Wednesday night and
the first part of Thursday mostly dry. Temperatures rise back to the middle/
upper 60s Thursday and while winds look fairly breezy...they will
be mainly southerly...so some lake cooling along the Illinois shore will
be possible. The best chance of showers and thunderstorms will be
along/ahead of a cold front later Thursday afternoon into Thursday
//Ord and mdw concerns...updated 06z...
Southeast winds near 10 knots will veer south Sunday morning and
increase slightly...with a few occasional gusts 15-20 knots possible
during the afternoon hours. Dry VFR conditions will continue...
with scattered middle/high clouds increasing and eventually forming a more
solid middle-level deck Sunday night.
//Ord and mdw confidence...updated 06z...
* high confidence all forecast elements.
//outlook for Ord/mdw for 12z Monday-12z Saturday...updated 00z...
Monday...afternoon rain showers likely. Brief MVFR possible.
Tuesday and Wednesday...VFR.
Thursday...chance shra/tsra...mainly at night.
217 am CDT
High pressure ridge axis has moved east of the lake this morning...
while low pressure well to the north was moving from Manitoba into
Ontario. This low will continue east to near James Bay by this
evening...with a cold frontal trough trailing southwest across the
upper Midwest and Central Plains to another low developing over the
southern High Plains. This front will begin to sag across Northern
Lake Michigan later tonight...as a weak low pressure wave lifts
northeast into the Great Lakes region along the trailing cold front.
Low pressure will consolidate and deepen across the central and
eastern lakes region by late Monday as an upper disturbance digs
into the region...with the cold front moving to the east and
southeast of Southern Lake Michigan Monday evening. With the low
deepening off to the east...and a broad area of high pressure
building across the upper Midwest...northerly winds will briefly
increase into the 20-25 knots range across Lake Michigan Monday
night and Tuesday. The surface high pressure ridge will then
spread east across the western lakes region Tuesday night into
Wednesday. Another fairly deep low pressure system will then move
across the northern plains and upper Midwest Wednesday night into
Thursday...with increasing south winds in the 25-30 knots range
developing across Lake Michigan. The low will move across the
northern lakes Thursday with a cold front moving east across the
lake by Thursday night.
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