Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 211549

Area Forecast Discussion
National Weather Service Lincoln IL
949 AM CST Tue Feb 21 2017

Issued at 949 AM CST Tue Feb 21 2017

Surface observations show the frontal boundary roughly along a
Springfield to Rantoul line this morning. Radar mosaics showing
the rain mainly from about I-55 eastward this morning, with
another surge moving north across the Ohio River around the
circulation of an upper low over Arkansas. With time, the rain
threat will be concentrated along and south of I-70 under the
influence of this feature. Have updated the rain trends to
increase PoP`s through the afternoon and very early evening across
southeast Illinois, and refined the trends closer to the frontal
boundary. The boundary itself will basically be washing out in
place, so the rains there will be easing up over the next couple
hours. Already seeing a steady erosion along it over the last hour
or so.

Satellite imagery showing the clearing line along the Illinois/Iowa
border this morning. Main question will be how fast this tracks
southeast. The latest RAP humidity layer guidance suggests a
slower progression, and have trended a bit in that direction,
although not as slow as it indicates (with the clearing line
reaching Peoria around 6 pm). Have only made minor changes to the
temperature forecasts, mainly impacting the next couple hours as
the observed trends were below what was forecast.


.SHORT TERM...(Today and tonight)
ISSUED AT 324 AM CST Tue Feb 21 2017

Slow-moving cold front continues to edge eastward early this
morning...with latest surface analysis placing it along the
Mississippi River.  Light to moderate showers are occurring
along/ahead of the boundary, primarily impacting locations along
and west of the I-55 corridor.  Showers will gradually spread
eastward across the remainder of the area, but may not reach the
Indiana border until mid-morning.  The front will tend to
dissipate as it tracks further east, so am expecting areal
coverage of showers to decrease as the day progresses.  Temperature
forecast will be a bit tricky today, as cloud cover and showers
will keep readings down across the E/SE KILX CWA.  With clearing
expected to take place across the west this afternoon, think
warmest highs in the upper 60s to around 70 will occur along/west
of I-55.  Further east where overcast conditions will persist
through the entire day, highs will only reach the lower to middle
60s.  Front will sag into the Ohio River Valley and wash out
tonight, allowing skies to become mostly clear across all but the
far SE where partial cloud cover will linger.  With clearing
skies, light winds, and a very moist boundary layer in
place...think fog will develop overnight.  Fog should become
thickest/most widespread where afternoon mixing will be the
least...generally across the eastern two-thirds of the CWA.

.LONG TERM...(Wednesday through Monday)
ISSUED AT 324 AM CST Tue Feb 21 2017

Fog will gradually dissipate Wednesday morning, with mostly sunny
skies expected by afternoon.  Given abundant sunshine and increasing
southwesterly winds ahead of an approaching boundary, record high
temperatures appear to be a good bet.  Thermal ridge will be in
place across the region...with 850mb temps increasing to 12-14C. As
a result, am expecting afternoon highs to top out in the lower to
middle 70s.  Front will drop southward into central Illinois
Wednesday night, eventually stalling near the I-72 corridor.  A
distinct north-south temperature gradient will develop on
Thursday...with highs ranging from the upper 50s far north around
Galesburg and the lower 70s south of I-70.  Much of the
day should be dry: however, as synoptic lift increases along the
boundary in advance of a potent short-wave ejecting out of the
Rockies, scattered showers will develop during the afternoon.

Low pressure is still expected to develop in the lee of the Rockies
Thursday evening, then track into the southern Great Lakes by Friday
evening.  Minor model discrepancies are still present: however,
consensus shows a strong cold front bisecting central Illinois by
18z Fri.  Given unseasonably warm/moist southerly flow ahead of the
front, the atmosphere will become moderately unstable across east-
central and southeast Illinois...with GFS indicating MUCAPE values
of around 1000J/kg.  In addition...0-6km bulk shear values will
increase to 55-65kt as a powerful mid-level jet approaches from the
west.  Think strong to potentially severe thunderstorms will develop
along/ahead of the front Friday afternoon, mainly along and east of
I-57 where likely PoPs are warranted.  Any storms that fire will
quickly shift into Indiana by early evening, followed by breezy and
sharply colder conditions.  Models continue to suggest wrap-around
moisture will brush the N/NW CWA late Friday night into Saturday
morning.  With temperatures falling into the upper 20s and lower
30s, a period of light snow will be likely...with some minor
accumulations possible along and north of a Canton to Danville line
by Saturday morning.

Cool/more typical mid-February weather will prevail over the
weekend...with highs in the upper 30s and lower 40s on Saturday
rising into the 40s everywhere by Sunday.  The return to normal
will be short-lived however, as zonal flow will allow temps to
warm significantly by early next week.  Unfortunately the warming
trend will also be accompanied by precipitation.  At this time it
appears a brief period of light snow will be possible Monday
morning before temps warm sufficiently for all rain Monday
afternoon into Tuesday.


.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 552 AM CST Tue Feb 21 2017

A cold front will gradually push across central Illinois today,
with variable wind directions for much of the day, as wind speeds
remain less than 10 kt. A band of rain showers will advance
eastward ahead of the front, with rainfall coming to an end from
west to east through the day. Dry conditions should develop at all
TAF sites by early afternoon. As rain comes to an end this
morning, PIA and SPI could see VIS and CIGs dip to IFR or even
LIFR for a brief period. HRRR and RAP forecasts show narrow
channels of low clouds and low vis that could advance eastward
slightly into PIA and SPI areas. Have included a tempo at PIA for
3/4sm BR for now, and will monitor progression of low vis/cigs.
The latest guidance is now showing winds becoming mainly easterly
in the vicinity of the front, as it rotates into a west-east
orientation as it drops into Illinois. There is low confidence in
the wind direction progression over the next 12 hours, but wind
speeds should remain 8 kt or less.

Locally dense fog could affect eastern Illinois later tonight, due
to light winds and residual ground level moisture. DEC and CMI
will have the higher potential of VLIFR fog after 09z.


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




LONG TERM...Barnes
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