Area Forecast Discussion
Issued by NWS Central Illinois

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546
FXUS63 KILX 222015
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
315 PM CDT Wed Mar 22 2017

.SHORT TERM...(This evening through Thursday)
ISSUED AT 315 PM CDT Wed Mar 22 2017

19z/2pm surface analysis shows 1039mb high centered over the Great
Lakes, with cool/dry northeasterly flow noted across central
Illinois.  As the high edges eastward, mid/high clouds currently
across Iowa/Missouri will gradually spread into the area tonight.
Skies will initially start out mostly clear during the early
evening, but will then become overcast overnight.  Low
temperatures will be coldest across the northeast KILX CWA around
Paris and Danville, where skies will remain clear longest and
readings will drop into the upper 20s.  The warmest lows in the
middle 30s will be focused across the southwest CWA where clouds
will increase soonest.

As the high moves further away from the region and boundary layer
winds veer more southerly, warm air advection will increase markedly
on Thursday.  Models continue to produce light QPF across parts of
the area: however, boundary layer airmass will initially be quite
dry, so think they may be too fast spreading precip eastward.  As
such, have kept locations east of I-55 dry through the morning
hours.  Have focused highest PoPs in the Illinois River Valley
Thursday afternoon, with dry conditions expected through the entire
day south of I-70.  High temperatures will top out in the lower to
middle 50s.

&&

.LONG TERM...(Thursday night through Wednesday)
ISSUED AT 315 PM CDT Wed Mar 22 2017

Vigorous short-wave trough noted on latest water vapor imagery off
the coast of southern California will cross the Rockies, inducing
surface cyclogenesis over eastern Colorado Thursday night.  As has
been the case with the past several model runs, 12z Mar 22 models
continue to show the short-wave closing off at 500mb...resulting in
a slower eastward progression of the wave and its associated surface
low.  As a result, confidence is growing that any precip associated
with the slowly approaching system will hold off until Friday night.
Ahead of the wave, partial sunshine and southerly winds will help
boost high temperatures well into the 70s on Friday.  All models
suggest precip will arrive across the Illinois River Valley Friday
evening...then spread across the remainder of the area overnight.
GFS MUCAPE values remain negligible, so have opted to only mention
isolated thunder with the initial wave of precip.  As the system
comes overhead, MUCAPEs increase to 500-1000J/kg and mid-level lapse
rates steepen by Saturday afternoon, warranting an increased thunder
threat.  Will maintain high PoPs and thunder chances throughout the
day and into Saturday evening...before rain chances gradually
decrease from southwest to northeast across the area on Sunday.

After a brief lull in the rain chances Sunday night, the next
southern stream system will quickly spread showers back into the
area on Monday.  This feature has trended south with the past few
model runs, so have concentrated highest PoPs and isolated
thunder mention across the southern CWA.  After that,
considerable model spread exists for the end of the period...so
forecast confidence is low beyond Monday.  At this time, it
appears Tuesday will be a dry day before another system approaches
by the middle/end of next week.  Timing of that system is very
much in doubt, with the GFS delaying it until next Friday...while
the ECMWF/GEM are both more aggressive with its eastward progress
as early as Wednesday.  Will only carry slight chance PoPs for
Wednesday until better model agreement is achieved.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1245 PM CDT Wed Mar 22 2017

VFR forecast for the region with high pressure dominating the map.
Easterly winds today slowly veering around to more southeasterly
by tomorrow morning. Scattered cirrus slowly transitioning to more
of a broken midlevel cloud, likely thin, later in the evening and
through the overnight, as a shortwave traverses the area.


&&

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

$$

SHORT TERM...Barnes
LONG TERM...Barnes
AVIATION...HJS



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