Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 261723

Area Forecast Discussion
1223 PM CDT Thu Mar 26 2015


Clearing line was roughly along I-55 as of 9 am. Upper
trough is still coming in from the west, about to reach the
Mississippi Valley, with associated cold trough likely to cause
some stratocumulus development over the forecast area this
afternoon as well. Still some lingering light rain south of I-70,
and upstream ups have shown a brief switch to mixed precip or snow
as it comes to an end. Latest short-range model guidance has this
out of the area by midday.

Updated zones/grids have been sent, mainly for timing of the
clearing and the precipitation exit. Little changes needed to
temperatures or winds.


.SHORT TERM...(Today)

Drier and colder air is quickly entraining into the northern edge of
the system. Pockets of light rain or no rain are developing in the
precipitation shield over central and southeast IL. By sunrise, we
may have a majority of our area under dry conditions. Will keep a
ribbon of likely PoPs toward Lawrenceville at 12Z, but quickly
shrink the coverage and level of PoPs with each hour after 12Z, with
no precip included in our counties at 18Z.

The other concern this morning is for a chance at some snow flakes
developing on the northern edge of precip as the cold air aloft
pushes into the area on gusty north winds. Forecast soundings
indicate that wet-bulb temps will drop below 0C though the entire
air column except for right near the ground after 12Z. Granted, dry
air will also accompany that colder trend, so precip will be
shutting down as the potential for change to snow occurs. Therefore,
will only include a mention of snow in the narrow band of slight
chance PoPs on the northern fringes of our precip forecast each hour
this morning.

High temps will not climb much above morning lows today due to the
persistent cold advection through the day, despite decreasing clouds
from NW to SE as we head into the afternoon. High temps will
generally remain in the mid to upper 40s, with gusty north winds
adding some chill to the air.


.LONG TERM...(Tonight through Wednesday)

A quiet and chilly weather pattern will take shape tonight through
Saturday across central and southeast IL as strong upper level trof
digs into the Great Lakes and Ohio river valley late this week. One
short wave will dive SE across MO tonight with another short wave
pushing SE across NE MO Fri night. Also have short wave translating
through the Great Lakes region next few days. Central IL will be
in between these features with closest one bringing chance of
flurries to areas near IN border Friday morning. Lows tonight will
be 25-30F. Chilly highs Friday in the upper 30s and lower 40s with
coolest readings from I-74 NE. Cold lows Friday night in the upper
teens and lower 20s as 1030 mb Canadian high pressure settles SE
into WI and ridging south into IL by dawn Sat. One more short wave
dives southward across eastern IL by midday Sat before upper level
trof pulls further east of IL. Another chilly day Sat despite a fair
amount of sunshine with highs 40-45F and coolest in east central IL.

Canadian high pressure shifts SE into the central Appalachians by
dawn Sunday with return southerly flow developing over IL and
starting a warm up. Lows Sat night of 25-30F and highs Sunday in the
low to mid 50s with some upper level ridging into IL by Sunday morning.
00Z models continue to trend slower with 996 mb low pressure moving
east to Lake Superior by sunset Sunday and dragging a cold front SE
toward the IL river. Have 20-30% chance of light rain showers Sunday
especially by afternoon over central IL as clouds increase while dry
in southeast IL. Have 20-30% chance of light rain showers Sunday
night mainly Sunday evening as cold front passes through. This
system does not have much moisture to work with so any rainfall
amounts should be less than a tenth inch.

Upper level flow become more zonal during 1st half of next week
returning milder temperatures to IL. Weak Pacific high pressure
settles into the mid MS river valley Monday returning dry weather
and mostly sunny skies with milder highs in the upper 50s and lower
60s. Weak low pressure moves across southern WI and southern Lake MI
Monday night and brings isolated light rain showers to areas north
of I-74. Quiet weather Tue and even milder highs in the 60s. Another
fairly strong low pressure moves east to near Lake Superior by
sunset next Wed and brings a cold front into central IL Wed evening.
This to return chances of showers Wed and Wed night and perhaps
isolated thunderstorms in southwest CWA. Mild highs in the 60s again
on Wed ahead of cold front, then turning a bit cooler next Thu
behind cold front with highs in the lower 60s.


.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)

Initial concern will be with some brief MVFR periods around KCMI
and possibly KDEC early this afternoon. Have seen some ceilings
around 2000 feet at nearby airports since about 16Z at times, but
general trend will be for the lower clouds there to diminish with
time. Some clouds around 2500 feet are also developing over north
central Illinois as a trough of cold air moves into the area, and
these may reach down to KBMI. As an upper wave swings southeast
through the Great Lakes tonight, a more solid deck of
stratocumulus clouds will likely drop southward across northern
Illinois, with some enhancement from Lake Michigan possible. Have
added some MVFR ceilings for KCMI late tonight and Friday morning,
and kept them in low VFR range at KBMI. Further west, cloudiness
should largely be in the middle levels of the atmosphere. Gusty
winds this afternoon will diminish as sunset approaches, but some
winds over 10 knots likely again by late Friday morning.




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