Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 201942
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
242 PM CDT Mon Oct 20 2014

.SHORT TERM...(Tonight)
ISSUED AT 242 PM CDT MON OCT 20 2014

Weak low pressure over the Great Lakes this afternoon with a weak
boundary trailing out behind it through Central and Southeastern
Illinois.  Forecast for the overnight rather quiet with
northwesterly flow continuing, though the winds may be variable at
times, becoming light after sunset.  Dry air filtering into the CWA
as the overnight cools should keep the RH just sub saturation.  This
in concert with winds at or above 5kt or so...fog issues are not
expected.  However, another wave making its way into the larger
scale trof from nrn MN is keeping a lobe of lower clouds a bit
further out to the west.  This particular area is expected to dive
southeast in the overnight hours...while the rest of the system
pulls out to the east on the synoptic scale.  The NAM is keeping the
llvls far more significant and brushing ILX northeast with the edge
of the more substantial cloud cover.  Remaining models not really
holding onto as much.  Sat imagery also shows a slow erosion of the
western edge of the clouds...as well as the HRRR supporting the
clouds staying to the north and northeast.  It may be close, but
leaving the overnight mostly clear and lows dipping into the low to
mid 40s.


&&

.LONG TERM...(Tuesday through Monday)
ISSUED AT 242 PM CDT MON OCT 20 2014

As the 500 mb wave cuts off over the eastern Great Lakes tomorrow,
the northeast CWA will be on the southwest fringe of better
moist/cyclonic flow, and will be close to strato-cu deck.  Most
high-res models keep thicker cloud cover to our east and will
continue to trend forecast that way.  Regardless, highs will be
several degrees below normal, ranging from the mid 50s northeast to
low 60 in the south/southwest.

Wednesday and Thursday...Surface and and upper level ridging shift across
the Midwest ahead of the next upper level weakness moving into the
northern Plains.  This will provide clear/dry and seasonably cool
weather.  As the next system shifts into the upper Midwest, showers
should overspread Iowa and Missouri early Thursday.  However as the
dynamics with this feature shift east of the Mississippi River it
will encounter increasingly dry air and surface/upper ridging.  As a
result most of the shower activity is expected to decay during the
afternoon/evening as it shifts through the northern half of the
CWA.  Slight chance pops will cover this possibility.

Friday through Monday...Medium range guidance/ensembles show good
agreement that a pronounced warming trend will affect the region.
This will result from troughs affecting the west and east coasts,
allowing upper ridging to build across the central U.S., and drawing
up a thermal ridge from the southern Plains, pushing 850 mb temps to
+12-16 C this weekend.  Friday will see some moderation with
readings returning near to slightly above normal.  In a rarity for
early fall, highs on Saturday and Sunday are progged to be 10-15
degrees above normal without strong winds aiding in low level warm
advection, due to high pressure in the vicinity.  If the GFS is
correct, southerly flow will increase later Sunday in tightening
gradient ahead of the next low pressure complex in the Plains.  As
this system shifts east it will bring the next chance of rain to the
region for early next week. Considerable uncertainty exists at
that range, with the 12z ECMWF depicting a much weaker system.


&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
ISSUED AT 1237 PM CDT MON OCT 20 2014

Northwesterly flow today with clear skies becoming more northerly
by morning. Light and somewhat variable in the overnight. Some
moisture in the low levels may develop into some sct clouds...with
more bkn deck to the north and northeast. Some concern that the
shortwave over the upper Midwest would dive into the region and
threaten ILX terminals with a more bkn deck. NAM is the only one
showing enough moisture to cover CMI and BMI...other models drier,
including the HRRR. For now, will maintain the SCT mention, though
later issuances may require a bkn deck for CMI and BMI.


&&

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

$$

SHORT TERM...HJS
LONG TERM...25
AVIATION...HJS






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