Area Forecast Discussion
Issued by NWS Chicago, IL

Home | Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
FXUS63 KLOT 191007

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

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.



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.



For the 06Z TAFs...

Main forecast concerns center around vsby trends through
daybreak, timing of arrival of rain late this afternoon/early this
evening and timing of arrival of IFR/LIFR later this evening into
Friday morning. Clearing skies have led to some visibility
reduction across the area. Cirrus clouds to the south have started
to make a more northward push and look to move across the
terminals helping to limit vsby reduction or allow for improvement
into the wee hours of the morning. With that in mind have made
some adjustments to the vsby and sky cover through the overnight
with a lowering chance for major vsby reduction.

Winds will turn southerly then southeasterly into the afternoon
with clouds thickening as low pressure approaches from the
southwest. Rain will move into the area late in the afternoon or
very early in the evening and eventually bring IFR cigs and vsby
with LIFR possible. Timing of this may need to be tweaked but have
good confidence in the trend and that IFR may not occur out the
gate with the rainfall. Thunder will also be possible. Low
conditions look to continue into Friday morning.



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.






WWW.YOUTUBE.COM/NWSCHICAGO is the U.S. government's official web portal to all federal, state and local government web resources and services.