Area Forecast Discussion
Issued by NWS Central Illinois

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000
FXUS63 KILX 280406
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1106 PM CDT Sat Sep 27 2014

.UPDATE...
ISSUED AT 832 PM CDT SAT SEP 27 2014

Quiet weather pattern to hold into at least Wednesday with
pleasantly warm days and comfortably cool nights. Satellite
data indicating the band of cirrus that was over our area was
starting to shift north and east of our area this evening. The
combination of a clear sky and nearly calm wind may bring some
patchy fog to low lying areas and in river valleys by Sunday
morning. Any ground fog we see early Sunday should quickly
dissipate leaving a mostly sunny sky for the remainder of the day
with temperatures about the same as what we saw today, in the low
to mid 80s most areas. Forecast soundings indicate temperatures
from 925-850 mb cool a degree or two tomorrow, but that should be
offset by less cloud cover and a dry topsoil.

Have made some minor adjustments to our early evening temperatures
and cloud cover and bumped afternoon highs up a bit for Sunday. The
updated ZFP should be out by 900 pm.

&&

.SHORT TERM...(Tonight)
ISSUED AT 238 PM CDT SAT SEP 27 2014

A weak 580 dm 500 mb low spinning over nw IA will stay over western
IA through Sunday morning, and then starting drifting se into MO and
sw IL by Sunday evening. Isolated convection associated with this
feature will stay west and south of central IL tonight & Sunday.
Few cumulus clouds this afternoon especially over western IL will
dissipate at sunset, with patches of mid/high clouds drifting
northward across central IL into Sunday. A 1026 mb surface high
pressure ridge over the Great Lakes region will stay near IL through
Monday, and continue fair weather with light ENE winds into Sunday.
Dewpoints currently averaging in the mid 50s, and lows overnight will
be close to these readings with lower 50s by Danville and Paris.
Patchy shallow ground fog will develop near river valleys again
during overnight (IL and Wabash rivers) and dissipate by 830 am
Sunday.

&&

.LONG TERM...(Sunday through Saturday)
ISSUED AT 238 PM CDT SAT SEP 27 2014

Models in good agreement in evolving longwave ridge over Central
North America into a ridge west/trough east pattern by the end of
the forecast period. Although there are still some detail
differences, particularly with respect to timing, models are in
better agreement in the extended period than yesterday.

Cut-off upper low over middle Missouri Valley embedded under the
ridge will gradually become absorbed back into the northern stream
before moving across the Midwest as a weak open wave Sunday Night
and Monday.  Moisture should be quite limited and lift is weak
suggesting that an increase in cloudiness will likely be the major
impact with any precip staying to our northeast.  Weak cold advection behind
the system may bring slightly cooler temperatures to the area on
Tuesday, but with 850 temps remaining generally in the 11-15C range,
the mercury should remain above seasonal normals.

Energy now over Sierra Nevada will slowly eat away at ridge through
midweek and as surface ridge retracts into the northeast, Gulf of
Mexico should open enabling moisture flow to increase prior to the
incoming wave.  Latest model suites are in better agreement today
with timing of precip onset with operational models keeping forecast
area dry until late Wednesday Night.  Frontal passage looks to be
Thursday Night with showers lingering behind the front until the
passage of the main trough axis Friday.  This seems reasonable given
the cool 500 mb temps in the trough with 12z GFS indicating as low
as -25C over the area at 00z Friday evening.

Latest model runs suggest moderate instability will be in place just
ahead of the boundary Thursday evening and given the significant
shear expected with GFS forecasted 40kt+ 850 mb winds at 00z
Thursday Evening may have some stronger storms. Later forecasts will
need to monitor this potential closely.

Strong cold advection behind the front is also now more consistent
between the operational models with drops of 10C over a 24 hour
period Thursday Night and Friday. MOS Guidance from 12z GFS and 00z
ECMWF are beginning to show this drop below normal for the end of
next week and will be reflected in forecasted temps.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
ISSUED AT 1100 PM CDT SAT SEP 27 2014

Main forecast concern will be in the 09z-12z time frame with the
potential for some brief MVFR vsbys in fog. Will continue to carry
a brief period of MVFR vsbys (~5SM) early Sunday morning with the
higher probability for some patchy fog acrs the west where late
evening temp-dew point spreads were the lowest compared with the
observations sites east. Whatever fog we do see early in the
morning should dissipate by 13z with VFR conditions for the
remainder of the forecast period. Surface winds will remain light
easterly tonight and Sunday with speeds of 3 to 7 kts.

&&

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

$$

UPDATE...Smith
SHORT TERM...07
LONG TERM...Barker
AVIATION...Smith



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