Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 212359 AAB
AFDILX

Area Forecast Discussion...UPDATED
National Weather Service Lincoln IL
559 PM CST Tue Feb 21 2017

.SHORT TERM...(This evening through Wednesday)
ISSUED AT 211 PM CST Tue Feb 21 2017

Frontal boundary continues to erode over the area this afternoon,
and is difficult to place on a surface map but is roughly along a
St. Louis to Rantoul line. Showers over the eastern CWA continue to
erode and are largely focused south of I-70. As the upper trough
overhead continues to separate itself from the influence of the low
along the Arkansas/Louisiana border, the precipitation trend will
continue to decrease and rain should be out of southeast Illinois by
mid-evening.

Overnight focus is with fog potential. Still quite a bit of cloud
cover over the forecast area this afternoon, as the northwest flank
ebbs and flows along the Illinois River valley. While clearing is
anticipated west of I-55 this evening, 925-850 mb humidity plots
suggest a more difficult breakup to the east through the night. High-
res models are suggesting two potential areas for development. The
RAP, HRRR, and ARW all advect fog northeast up the Illinois River
valley beginning around midnight, with a secondary low cloud/stratus
surge northward into eastern Illinois. The NAM, GFS and SREF more
favor areas east of I-55 with a shallow moisture profile below 950
mb. Not enough certainty to go with a fog advisory at this point,
but will continue to mention areas of fog after midnight into early
Wednesday morning.

After the fog moves out, another unseasonably warm day expected on
Wednesday, with 850 mb temperatures up to +12 and a nice southwest
wind. Have not made any changes to the high temperature forecast,
going several degrees above guidance with low-mid 70s.

.LONG TERM...(Wednesday night through Tuesday)
ISSUED AT 211 PM CST Tue Feb 21 2017

Strong trough expected to move ashore the west coast on Wednesday
will develop a surface reflection as it clears the Rockies Thursday.
As the low pushes through the central plains a warm front is
expected to develop over central Illinois providing a focus for the
development of showers and thunderstorms by afternoon. As the low
pushes northward during the evening, drier air will overspread much
of the area bringing significant chances of rain south of I-72
temporarily.

Differences in timing of the surface lows passage to our northwest
has distinct implications on Friday`s weather. 12z NAM is fastest of
the deterministic models with moving the surface low into Lake
Superior by Midday and pushing a trailing cold front through the
state Friday morning before moisture and instability can develop. On
the other extreme the 12Z CMC is the slowest with the progression of
the system suggesting much of the state will see a chance of
possibly strong thunderstorms during the afternoon and evening. 12Z
GFS and 00Z ECMWF are relatively similar in bringing the front
across the state during the day with moisture return adequate to
produce a potential for strong, possibly severe winds, over the
eastern half of the state Friday afternoon.

Wrap-around moisture associated with the upper system should bring a
chance of light rain, possibly mixed with snow early west of the
Illinois River, to the northern portion of the region Saturday.
Weak waves in the northwest flow behind the system may again bring a
chance of light precip to the region again Sunday.

Next surge of energy out of the western trough will approach the
area Monday and Monday Night bringing another chance of more
significant rainfall and milder temperatures. Models are very
dissimilar in their evolution, timing, and strength of this initial
wave. Although a period of rain appears likely for the first part of
next week, the details remain uncertain.

Prior to the frontal passage on Friday, 850 temps remain well above
average and will likely bring temperatures 20 to 25 degrees above
normal although tempered from Wednesday`s readings by increased
clouds and scattered precipitation.  A return to near normal
temperatures will occur over the weekend.  Although the majority of
GEFS members bring in milder air into the area ahead of the next
Pacific trough early next week, there is significant spread so there
remains uncertainty with respect to the intensity of the warm-up.

&&

.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 554 PM CST Tue Feb 21 2017

Tricky aviation weather forecast across central Illinois tonight.
A decaying frontal boundary lies just east of the area, and quite
a few mid-high level clouds continue to stream across parts of the
area from an upper-level low over the lower Mississippi Valley.
Some of the high-resolution guidance suggests considerable
stratus/fog developing across the area overnight. However, if the
mid-high level clouds stay in place, the threat should be
mitigated to some degree. Otherwise, wet soils from the rain that
fell earlier today should combine with light winds and clearing
skies to produce the low clouds & fog. Have not hit the terminals
too hard yet, but do have IFR vsbys developing after midnight.
Skies should clear during the day tomorrow.

&&

.CLIMATE...
Issued at 930 AM CST Tue Feb 21 2017

Record Highs / Record Warm Lows - Tuesday Feb 21st...
Peoria........ 69 / 46
Lincoln....... 69 / 45
Springfield... 69 / 48
Champaign..... 67 / 47
Bloomington... 69 / 46
Decatur....... 68 / 48
Danville...... 67 / 50
Galesburg..... 68 / 40
Charleston.... 71 / 52
Effingham..... 73 / 52

Record Highs / Record Warm Lows - Wednesday Feb 22nd...
Peoria........ 71 / 51
Lincoln....... 71 / 52
Springfield... 71 / 53
Champaign..... 69 / 49
Bloomington... 70 / 53
Decatur....... 72 / 51
Danville...... 71 / 54
Galesburg..... 61 / 45
Charleston.... 71 / 52
Effingham..... 74 / 55

Record Highs / Record Warm Lows - Thursday Feb 23rd...
Peoria........ 64 / 49
Lincoln....... 68 / 50
Springfield... 70 / 50
Champaign..... 65 / 50
Bloomington... 66 / 52
Decatur....... 73 / 53
Danville...... 67 / 51
Galesburg..... 65 / 44
Charleston.... 69 / 52
Effingham..... 75 / 54

&&

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

$$

SHORT TERM...Geelhart
LONG TERM...Barker
AVIATION...Bak
CLIMATE...Geelhart


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