Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 201723

Area Forecast Discussion
National Weather Service Lincoln IL
1223 PM CDT Tue Mar 20 2018

Issued at 1040 AM CDT Tue Mar 20 2018

Will be updating the gridded forecast shortly to beef up the winds
a bit for the rest of the morning and into the afternoon and
adjust the weather trends in southeast IL.

The latest water vapor satellite loop indicated an upper
circulation pivoting eastward across extreme southern IL. Spotty
light precipitation was associated with the upper low across
parts of southeast IL late this morning. However, as the
circulation shifts to the upper wind fields will be backing from
the NE to NNW. This will allow the far western edge of a newly
developing precipitation shield to extend back across southeast
and east central IL late this afternoon and especially this
evening. Much of the precipitation will be in the form of rain,
but we are expecting a mix with and shift to light snow in far
southeast IL overnight before ending.

The rest of the area will be quite chilly for the first day of
spring with highs only in the 40-45 range and wind chills in the
lower 30s.


.SHORT TERM...(Today and tonight)
ISSUED AT 339 AM CDT Tue Mar 20 2018

08z/3am radar imagery continues to show light precipitation across
portions of east-central and southeast Illinois...primarily along
and southeast of a Shelbyville to Paris line. The precip has
mainly been in the form of rain: however, evaporational cooling
along the northern edge of the precip shield allowed a period of
wet snow to develop from west-central Indiana into the far eastern
KILX CWA around Paris. In fact, 1.3 inches of snow was reported
between Paris and Danville earlier tonight. High-res model
guidance suggests a rain/snow mix will continue to be possible
along the northern edge of the remaining precip for the balance of
the night, with little or no additional snow accumulation. While
radar trends clearly show a diminishing trend, the HRRR suggests
some very light precip may linger across the far SE CWA through
early morning. Have therefore lingered slight chance PoPs from
Flora to Lawrenceville through 14z/9am.

A short-wave trough evident on latest water vapor imagery over the
Ozarks will track eastward today, leading to surface cyclogenesis
across eastern Kentucky. As a result, light precipitation
associated with the developing low will retrograde westward,
spilling back into the SE CWA by mid to late afternoon. Have
included chance PoPs for light rain as far west as a Martinsville
to Flora line accordingly. Elsewhere around the area, after some
morning sunshine, skies will become mostly cloudy this afternoon
with high temperatures only in the lower 40s. In addition, brisk
northerly winds gusting to 25mph will create wind-chills in the
20s and 30s. A few rain showers will linger across the SE into
this evening, followed by dry conditions across the board
overnight. Low temperatures will bottom out in the upper 20s and
lower 30s.

.LONG TERM...(Wednesday through Monday)
ISSUED AT 339 AM CDT Tue Mar 20 2018

Cool/dry weather will be on tap for Wednesday with highs once
again below normal for this time of year in the middle 40s. Once
surface high pressure shifts east of the region, an increasing
southerly flow will help boost temps back into the lower 50s by
Thursday. 00z Mar 22 models all develop a warm frontal boundary
just S/SW of Illinois on Thursday, with a weak short-wave
interacting with the boundary to produce a period of light rain
Thursday afternoon/evening. GFS has been showing this solution for
the past several runs, and now the ECMWF/GEM have followed suit.
The exact placement of the rain band remains in question, but
based on GFS, have included low chance PoPs along/southwest of a
Galesburg to Mattoon line.

After that, a milder and more unsettled pattern will prevail
through early next week. Model agreement is poor at this point, so
forecast confidence beyond Thursday is low. The next significant
storm system is slated to pass through the region Friday night
into Saturday, with model consensus keeping the low track south of
central Illinois. Best precip chances will likely focus during
that time, with dry weather returning by Sunday.


.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1223 PM CDT Tue Mar 20 2018

VFR conditions will prevail through the TAF period the next 24
hours in central Illinois. The main concern for this afternoon and
early this evening will be gusty north to north-northeast winds
caused by a strengthening low pressure center moving up the west
side of the Appalachians toward the upper Ohio River valley.

This low pressure area, combined with shortwave energy from the
upper Midwest dropping into the mean upper trough axis, will keep
clouds over the forecast area through tonight and into Wednesday
morning. The best upper forcing is expected to be well to the
southeast and east, so the clouds will remain in the VFR category.
As the low rapidly shifts eastward, a clearing trend is expected
by mid-morning Wednesday, along with lighter wind speeds.




LONG TERM...Barnes
AVIATION...Miller is the U.S. government's official web portal to all federal, state and local government web resources and services.