Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 180205
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
905 PM CDT Fri Mar 17 2017

.UPDATE...
Issued at 855 PM CDT Fri Mar 17 2017

Northwesterly winds and mostly clear skies north of the mid and
high level clouds that are settling over the southern half of the
state. However, the clearing will be short lived as low clouds
under a deep upper level low begin to settle into the region.
After midnight, expect the low clouds to creep south into Central
Illinois. HRRR/NAM/RAP have differing solutions as to how far
south the clouds will settle...which will do little to impact
overnight lows as northwesterly winds will continue to push cooler
air into the region. No major updates are anticipated at this
time.

&&

.SHORT TERM...(This evening through Saturday)
ISSUED AT 254 PM CDT Fri Mar 17 2017

Cold front has entered the northwest part of the forecast area early
this afternoon, and was roughly along the Illinois River at 2 pm.
Some nice clearing has taken place west of it, and temperatures have
quickly risen into the lower 60s from Galesburg to Jacksonville and
was even near 70 toward Quincy. Eastern CWA remains socked in and
temperatures were only in the mid 40s.

Much of the forecast area is expected to be clear by sunset.
However, stratocumulus clouds over the upper Mississippi Valley have
started to sink across the Iowa/Minnesota border. 925 mb humidity
plots off the RAP model suggest this reaching the northern part of
the CWA mid to late evening, and encompassing a good part of it by
morning, as an upper low tracks southeast across the western Great
Lakes region. Not going quite that fast yet in the gridded forecast,
but will bring mostly cloudy skies to the I-74 corridor toward
midnight and over the rest of the forecast area early Saturday
morning. This should diminish from west to east as the upper low
pulls away. Temperatures tomorrow should be fairly similar to
today`s cloudy areas, but some 50s will be possible if the clouds
move out fast enough.

.LONG TERM...(Saturday night through Friday)
ISSUED AT 254 PM CDT Fri Mar 17 2017

The last half of the weekend will start out with high pressure
shifting east of Illinois, and a southerly flow developing. 850mb
temperatures will climb steadily from 00z/7pm Saturday through
Sunday night. That will result in high temps on Sunday climbing into
the mid to upper 50s, with lows Sunday night remaining in the mid to
upper 40s. The low temps will be held on the mild side by a blanket
of clouds and increasing chances of rain and storms after midnight.
The SPC Day 3 outlook indicates a Marginal Risk for our counties
west of I-55 for Sunday night through 12z/7am Monday. This appears
reasonable due to GFS MUCAPE values in the 600-1000J/kg range on
the nose of a developing low-level jet streak late Sunday night.

The storm chances will be shifted slightly southward on Monday as a
cold frontal boundary drops southeast across Illinois. The slower
forward speed of the frontal passage may lower the potential of a
continued severe threat into Monday, but rain chances will continue
through the day southeast of the Illinois River, in the vicinity of
the stalling front.

Rain chances should generally come to an end on Tuesday as the front
progresses toward the Ohio River Valley. We will carry just some
slight chances of rain in our far southern tier of counties, due to
the close proximity of the front just to our south.

High pressure moving from south central Canada into the Great Lakes
will provide dry and seasonable temperatures for Tuesday night
through Wednesday night. Rain chances increase again on Thursday,
as a warm front lifts through Illinois. On Friday, a cold front
will approach Illinois, helping to trigger another round of rain
and a few thunderstorms.

&&

.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 701 PM CDT Fri Mar 17 2017

Low pressure sliding across the Great Lakes this evening pushing
clouds into the nrn ILX terminals...PIA and BMI most likely to see
cloud cover as a result. Timing of the clouds vary from
08-12z...and the HRRR is far lower into the MVFR cat than the
RAP13 at closer to 8000ft. Have pushed the forecast closer to the
HRRR for PIA and BMI due to current cigs north of IL.
Northwesterly winds throughout...staying up overnight to limit fog
development. Expect scattering out tomorrow afternoon.


&&

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

$$

UPDATE...HJS
SHORT TERM...Geelhart
LONG TERM...Shimon
AVIATION...HJS



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