Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 171756
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
1256 PM CDT Wed Sep 17 2014

.UPDATE...
ISSUED AT 1025 AM CDT WED SEP 17 2014

Updated the forecast earlier this morning to cancel the dense fog
advisory at 9 am over southeast IL. Also increased cloud cover
today especially over central and sw portion of CWA and added 20%
chance of showers along and sw of Rushville to Springfield and
Taylorville line into early afternoon. Highs in the upper 60s to
around 70F looks on track this afternoon with south to southeast
winds less than 10 mph becoming light and variable.

Small MCS over southern MO is tracking ese into mid MS river
valley today and brunt of its showers and thunderstorms will stay
south of central IL CWA. Just a few showers from Schuyler county
south and tracking ese across sw portion of CWA into early
afternoon. Broken to overcast clouds from 5-10k ft as far ne as
Lacon to Decatur to Olney should break up during the afteroon.
Weak surface high pressure over 1018 mb over IN to drift east
across Ohio river valley this afternoon and be close enough to
central IL to keep winds fairly light. Temperatures currently in
the upper 50s and lower 60s shoudl climb another 10 degrees once
sunshine reappears during the mid/late afternoon.

&&

.SHORT TERM...(Today)
ISSUED AT 237 AM CDT WED SEP 17 2014

Recently issued a Dense Fog Advisory across portions of east-central
and southeast Illinois to account for rapidly expanding dense fog.
This dense fog is forming along a northeast-southwest surface ridge
axis, in an area with near zero surface temperature/dew point
spreads and calm winds. It is not entirely clear how far north and
west of the ridge axis a dense fog threat exists, as winds are dead
calm across most of the forecast area. However, a small
temperature/dew point spread exists north/west of the current Dense
Fog Advisory area, and some mid clouds are beginning to spill across
central Illinois from a short wave moving through the plains. These
factors lead me to believe the current advisory should be sufficient.

Aside from the locally dense morning fog, the only forecast problem
for the day revolves around the precipitation threat (if any) from
the wave moving through the Plains. Some of the model guidance is
suggesting the far southern part of the forecast area may be brushed
by light rainfall later today. However, think these precipitation
forecasts are likely too far north. The model consensus has the vort
max with the short wave staying south of the forecast area, along
with the bulk of the isentropic lift ahead of the wave. These
factors, combined with the dry air mass currently in place, support
continuing with our current dry forecast for today. Temperatures
today are likely to be similar to yesterday`s. While weak low
level warm air advection will be taking place, it is likely to be
offset to some degree by additional cloud cover today.

&&

.LONG TERM...(Tonight through Tuesday)
ISSUED AT 237 AM CDT WED SEP 17 2014

High pressure over the Great Lakes to keep us in a dry east to
northeast flow into Thursday evening. After that, incoming shortwave
from the northwest comes into play. As with the daytime models, the
evening runs have continued the trend that the remnant moisture from
Odile will probably make it about as far as Missouri before shunting
southeast, so the incoming wave never really draws from it. This
lessens the threat of widespread heavy rain. The southeast half of
the CWA will likely remain dry through Saturday, while rain chances
increase across the northwest during the afternoon, and the best
chances occur Saturday night.

Sunday may be a bit of a question mark. The GFS and Canadian models
both have a rather clean frontal passage with lingering rain ending
in the morning. However, the latest ECMWF slows the front as a
surface low forms over Kansas, lingering rain across the south half
of the forecast area into Sunday evening. There may be a bit of a
feedback issue with that solution, so will maintain the dry
conditions by Sunday evening.

Rather large surface high will dominate the Midwest early next week,
with dry conditions for a few days.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
ISSUED AT 1255 PM CDT WED SEP 17 2014

Carried chance of rain showers at SPI until mid afternoon with
vsbys 5-7 miles as isolated showers drift ESE. May need to carry
VCSH at DEC but think brunt of showers will pass sw of Decatur.
Showers and thunderstorms with small MCS over southern MO to track
ESE into mid MS river valley during afternoon and we will be on ne
fringe of this weather system today with some isentropic lift
supporting the isolated showers in our sw counties. Scattered to
broken clouds of 3-5k ft to occur this afternoon along with broken
to mid level clouds around 9k ft and scattered at times along I-74
TAF sites of PIA...BMI and CMI. Clouds should decrease later this
afternoon and early evening leaving fair skies tonight. SSW winds
5-10 kts this afternoon to become light ENE this evening and then
east around 6 kts Thu morning. Have light fog with vsbys 4-6 miles
from 08Z-14Z.

&&

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

&&

$$

UPDATE...07
SHORT TERM...BAK
LONG TERM...GEELHART
AVIATION...07






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