Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 191204
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
604 AM CST Thu Jan 19 2017

.SHORT TERM...
255 AM CST

Through tonight...

Early morning water vapor imagery reveals a highly amplified
pattern across the country with the jet stream originating in
central Mexico and oriented north-northeast into the Midwest.
While this is resulting in an unseasonably warm airmass over the
region, it will also be transporting an unusual amount of moisture
into the area through the day today. PWats are expected to tag 1.0
inch across portions of the forecast area this afternoon and
evening which would represent near max values per observed upper
air climatology from ILX/DVN and around 300 percent of the normal
value for this time of year. As a closed upper low currently over
the Oklahoma/Texas panhandle region lifts towards the Upper
Midwest this evening and tonight, expect precip chances to
increase from the south through the afternoon and should peak
across northern Illinois and northwest Indiana this evening and
overnight. Storm total QPF amounts of half to three quarters of an
inch are generally expected, with the highest amounts across the
eastern half of the CWA. In addition, models continue to advertise
100-200 J/kg MUCAPE overspreading the CWA which will support
widely scattered embedded thunderstorms and locally higher
rainfall totals. With recent rainfall already causing flooding
issues, ice jams on portions of the Rock River, and numerous area
streams and rivers either already in flood or near bankfull, there
is obvious concern for additional flooding to occur as we receive
new rainfall on top of still frozen sub-soil conditions. For now,
have opted to issue an SPS to highlight the threat, but those with
hydro interests should keep a close eye on updates to river
forecasts over the next couple days.

Deubelbeiss

&&

.LONG TERM...
255 AM CST

Friday through Wednesday...

Active weather continues throughout the extended forecast with a
series of waves moving across the country resulting in periodic
chances for precipitation. We should see a brief lull in rain
during the day Friday as our upper low departs northeast of the
area and weak mid/upper ridging builds overhead. Meanwhile,
another wave is progged to round the base of the longwave trough
over the Central Plains early Friday and lift into the Upper
Midwest Friday night into Saturday. Continue to carry a chance for
rain with this wave but the better chances and amounts are still
focused to our west. 850 mb temps are still expected to peak in
the 6-8C range early Saturday out ahead of the trough and
afternoon highs are still expected to top out in the mid 50s. A
stronger upper wave/cutoff low is progged to undercut the region
late in the weekend and lift across the Appalachians early next
week. Temperatures are expected to moderate some as northwest flow
develops behind this low and there will be periodic chances for
precip as an inverted trough slowly rotates through the area.
Models seem to be in better agreement at least on the track of the
500 mb low through Monday, though timing differences persist, and
solutions begin to diverge more significantly beyond Monday.

Deubelbeiss

&&

.AVIATION...
For the 12Z TAFs...

Main forecast concerns/challenges this period are with reduced
vis in fog and low ceilings this morning, rain with possible
thunderstorms this evening, and then reduced vis and low ceilings
returning tonight.

The lower ceilings and reduced vis this morning are primarily
impacting DPA and ORD, with the other terminals only seeing minor
reductions in visibility. Expect these similar conditions to
impact DPA and ORD through the morning, with improving conditions
expected by midday. After a window of better conditions early this
afternoon, expect conditions to begin deteriorating once again
late this afternoon. This will first be observed with the area of
rain that will likely approach the terminals this afternoon.
Initial push may be light but do expect steadier rain to continue
for most of the evening. Have not included any mention of thunder
for this evening as confidence is low with timing/duration.
However, do feel fairly confident that scattered thunderstorms
will move across the area this evening, with later forecasts
possibly noting this in the forecast. Low ceilings will return
once again later today/tonight and have maintained similar trends
with the TAFs. However, do think LIFR will return and have
included this in the TAFs. Some guidance supporting earlier timing
for low ceilings later today and will need to monitor this
possible earlier arrival. Other than the rain ending early Friday
morning, don`t anticipate conditions to change much through the
end of the forecast period.

Rodriguez

&&

.MARINE...
401 AM CST

Generally quiet conditions expected across the lake at this time.
High pressure will exit to the east today, and allow for a weak
low to lift up the Mississippi river today. However, it is
expected to dissipate as it moves north. Another low is forecast
to form over the Plains Friday night and reach Minnesota Saturday
night, with a stronger low expected to form over the southern
Plains Saturday night. However, neither systems expected to bring
any significant winds across the lake during this time.

Rodriguez

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...NONE.
IN...NONE.
LM...NONE.
&&

$$

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