Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 182037
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
237 PM CST Sun Feb 18 2018

.SHORT TERM...(This evening through Monday)
ISSUED AT 237 PM CST Sun Feb 18 2018

Decent amounts of sunshine are occurring this afternoon despite
the periods of thicker cirrus. This will be the last sunshine for
a few days, as a significant wet pattern sets up over the region.
Upper low currently over western Washington will open up and dig
southward overnight, which will give us more of a southwest flow
and much warmer temperatures. Latest surface map shows low
pressure in eastern South Dakota, with a trailing cold front back
into the central Rockies. This will push toward the Mississippi
Valley, before taking more of a southwest-northeast orientation.
The Gulf is open for business as we get a steady moisture stream
northward, with dew points progged to rise through the 40s over
our area as early as after midnight. Rapid development of showers
is favored by most of the models late this evening, with the high-
res models focusing more of a southwest-northeast axis of rain on
Monday. Will continue with categorical PoP`s late tonight through
Monday in most areas, although areas south of I-70 may see some
breaks during the afternoon.

Aside from the extreme northern CWA, where snow is still melting,
most of the forecast area should reach the mid 60s on Monday. This
time last year was very warm and resulted in many record highs,
though a few may occur this year.


&&

.LONG TERM...(Monday night through Sunday)
ISSUED AT 237 PM CST Sun Feb 18 2018

Gulf flow will continue to pump the moisture up here, with PWAT
values around 1.5 inches persisting through early Tuesday. Latest
guidance off all the major models shows 3-5 inch rain potential
through the middle of the week, though the exact axis varies
slightly. With a good portion of the forecast area now in drought
conditions, we can take some water initially. However, the flood
threat will increase with time, especially on area rivers and
streams (see Hydrology section below). Will hold off on any flood
watches at the moment, but this may need to be considered over the
next day or so.

The cold front with this storm system will finally start moving in
Tuesday afternoon and evening, and should be south of our area by
early Wednesday. After Tuesday highs in the 60s to mid 70s,
attention shifts back to a temporary return to winter. Model
soundings show a significant warm nose of 5-7C lingering near 850
mb behind the front, suggesting a period of freezing rain and
sleet along and west of I-55 as the precipitation tapers off. This
will be followed by a secondary surge of precipitation later
Wednesday into Wednesday night, as a fast moving wave moves in
from the southwest. With the warm nose lingering into early
Thursday, another round of freezing or mixed precip is possible.
Latest GFS and European models focus two areas of precipitation,
one with the wave itself and one riding more along the lingering
boundary to our south, so there is more uncertainty with the PoP`s
in this time frame. Will still add the mention of mixed precip at
this time, though.

Longer range models are in better agreement with the late week
system, as the upper pattern goes back to the one currently
setting up over the CONUS. Right now, the higher precipitation
axis is projected more over the southern third of Illinois, but
there`s plenty of time for that to change. Will keep some very
high PoP`s mentioned in the southeast CWA as a result.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1119 AM CST Sun Feb 18 2018

Main concerns with this TAF set will be after 00Z. Initially, only
high clouds streaming through. However, ceilings will be steadily
lowering this evening as a storm system begins to approach from
the west. MVFR conditions expected to develop toward 06Z or so as
the lower levels of the atmosphere moisten up, and rain develops.
IFR ceilings will become widespread before 12Z and persist the
remainder of the period.

The low level jet will significant ramp up this evening, with the
approach of this system. Have kept the LLWS mention at all sites
as a result.


&&

.HYDROLOGY...
Issued at 237 PM CST Sun Feb 18 2018

With a good portion of the forecast area now in moderate drought,
the rain will initially be able to soak into the soil. However,
the northern CWA still has several inches of frost depth. This
should erode quickly with the warm temperatures Monday and
Tuesday. With time, the extended rain periods will begin to run
off more into area rivers and streams. Latest significant river
flood outlooks from NCRFC and OHRFC highlight the increasing
risk of rivers reaching moderate flood stage over our area.
Flooding is forecast to develop on the Little Wabash River as
early as Tuesday morning, and other rivers are likely to follow.
Additional rains late week in parts of the area will help keep
river levels high into next weekend. People with river interests
should monitor the latest projections closely.

&&

.CLIMATE...
Issued at 237 PM CST Sun Feb 18 2018

Record highs Monday and Tuesday:

                           Monday           Tuesday
Bloomington                70/1930          68/2017
Champaign                  68/2017          71/2017
Decatur                    66/1930          70/2017
Lincoln                    71/1930          74/2017
Olney                      72/1930          70/1930
Peoria                     71/1930          74/2017
Springfield                71/2017          76/2017

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...Geelhart
LONG TERM...Geelhart
AVIATION...Geelhart
HYDROLOGY...Geelhart
CLIMATE...Geelhart


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