Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 161725
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1225 PM CDT Tue Sep 16 2014

.UPDATE...
ISSUED AT 1045 AM CDT TUE SEP 16 2014
High pressure building into the region will keep the weather quiet
and rather non-eventful throughout today. Stratus slowly
retreating to the south as cooler air filters in. Temps on track
for highs into the 60s, with mostly sunny across the nrn portions
of the state... and mostly cloudy and slowly clearing in the
southern half. Most cu development should be tempered a bit in the
north by synoptic subsidence. The southern half of the state will
likely see more in the way of cu, as seen on current vis sat
imagery. Very minor adjustments to the hourly grids and no update
anticipated at this time.

&&

.SHORT TERM...(Today)
ISSUED AT 230 AM CDT TUE SEP 16 2014

Quiet weather expected overall today across central and southeast
Illinois. Canadian high pressure and its associated dry air mass will
continue to build into the area today, helping to scour out the low
clouds that currently reside across much of the forecast area. The
low clouds have been clearing slowly from the north as the high
builds in, and the latest trends suggest the clearing should reach
the I-70 corridor by 10 a.m. this morning. Once the skies clear,
mostly sunny skies should be the rule, as forecast soundings and CU
rule suggest diurnal cloud development should be minimal. The
possible exception to the clearing sticking, at least until sunrise,
is the potential for fog/stratus development. This development has
been patchy thus far upstream, and do not expect it to become too
widespread. Temperatures today, as they have been more often than
not lately, will be well below normal with highs mainly in the
mid-upper 60s.

&&

.LONG TERM...(Tonight through Monday)
ISSUED AT 230 AM CDT TUE SEP 16 2014

High pressure building southeast into the Great Lakes to dominate
our weather through Thursday. Latest model guidance continues to
indicate some sort of MCS type activity across Missouri and Kansas
Wednesday into Thursday, sliding along the edge of the upper ridge
that will slowly inch eastward into the Plains. However, the
persistent east/northeast flow over our area should keep this
precipitation at bay.

Significant shortwave will dig as it crosses the Rockies on Friday,
settling into the Mississippi Valley by Sunday morning. Have largely
kept the forecast dry through about midday Saturday, then quickly
increased the PoP`s from west to east during the afternoon and
evening hours, as the front arrives. One significant item of concern
is with the potential for heavy rain. The remnants of tropical
cyclone Odile over Baja California will be spreading into the Desert
Southwest over the next day or so. The latest GFS model continues to
show that a piece of energy and associated moisture from this system
will be drawn northeast into the northern wave, reaching central
Illinois after midnight Saturday night with the potential for a few
inches of rain. The ECMWF and Canadian models are not quite as
generous on this point, but do draw in some of the moisture into the
wave by Saturday morning and produce weekend rainfalls of up to 1.5
inches. Have increased PoP`s Saturday night to around 60% across
most of the forecast area, as confidence increases in the general
rainfall trend over the area. Continued the PoP`s on Sunday east of
I-55, although this should be winding down during the afternoon as
the front exits the area.

A large broad upper trough will persist over the Midwest early next
week in the wake of this system. Latest ECMWF model has
significantly backed down on the amount of cool air with this
system, with 850 mb temperatures on Monday now around +5C rather
than the -2C from the previous run. The GFS lags behind the ECMWF
with bringing the cooler conditions into the area. As a result, have
kept highs in the 70s on Sunday and Monday, with the coolest
conditions just beyond the current forecast period.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
ISSUED AT 1222 PM CDT TUE SEP 16 2014
Light and variable winds throughout the pd under a building sfc
ridge. Main issue becomes the retreat of the stratus in the srn
terminals...OVC in DEC and BKN in both CMI and SPI, hanging close
to the MVFR/VFR break. Per vis sat imagery, the stratus erodes and
is replaced by a blooming cu field almost immediately. Given this
trend...am leaving current conditions until about an hour or two
before sunset as the cu field breaks up. For now, fog mention is
still MVFR, though the lingering llvl moisture in the south will
lend itself to lower vis in the srn terminals should it not be
able to mix out by max heating this afternoon.

&&

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

$$

UPDATE...HJS
SHORT TERM...BAK
LONG TERM...GEELHART
AVIATION...HJS





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