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FXUS63 KILX 171120

Area Forecast Discussion
National Weather Service Lincoln IL
520 AM CST Sun Nov 17 2019

Issued at 316 AM CST Sun Nov 17 2019

A weak cold front will move across the region today and tonight  
bringing a band of rain that will gradually progress east across 
central Illinois this afternoon through tonight. Temperatures will
warm into the 40s today, then fall back into the low 30s tonight.
A gradual warming trend is expected through the first half of the
week with highs back into the 50s for a few locations Tuesday and
area wide by Wednesday. 


.SHORT TERM...(Today and tonight)
ISSUED AT 316 AM CST Sun Nov 17 2019

Early this morning, a cold front is located from central Iowa 
southwest across south-central Kansas. The front is progged to
shift east across the Mississippi River Valley around mid 
afternoon then across central Illinois this evening and overnight.
The front should shift into Indiana during the early morning 
hours Monday. For today, expect increasing clouds ahead of the 
approaching front, then a band of light rain will be in place 
ahead and along the front as it moves across the area later today.
Precip should begin to spread across the Illinois River Valley by
early to mid this afternoon, with temperatures warm enough for 
precip to be all rain at this point. Precip will exit the eastern 
portions of the CWA during the predawn hours Monday. Even across 
the eastern CWA tonight, most of the precip should fall as liquid,
though couldn't completely rule out a few flakes mixing in east 
of the I-57 corridor late tonight.

.LONG TERM...(Monday through Saturday)
ISSUED AT 316 AM CST Sun Nov 17 2019

Monday should be dry behind the departing cold front as a surface 
ridge builds across central Illinois. Attention does turn quickly 
back to the northwest as a shortwave trough digs towards the
Midwest within the broad northwest flow over the region. 
Unfortunately there remains quite a bit of disagreement on the 
strength and track of this wave as it takes aim on portions of the
mid and upper Mississippi Valley Monday night. The ECMWF and GEM 
bring in a swath of light snow right across central Illinois, so 
have introduced slight chance PoPs, despite the dry solutions from
the NAM and GFS. If the ECMWF does verify, does appear that areas
along and north of the PIA to LWV line would remain snow, though
areas south/southwest do maintain temps aloft just warm enough to 
support rain or a wintry mix. Will have to keep a close eye on 
this time frame given the amount of uncertainty and possibility 
for some light accumulations.

The rest of the day Tuesday and Wednesday appear dry and a bit 
warmer as upper ridge building across the Great Plains shifts east
across the Mississippi Valley. Strong warm advection will drive 
850mb thermal ridge across the local area later in the day 
Wednesday. This should result in temperatures back into the mid to
upper 50s across central Illinois with a few 60 degree readings 
not out of the question.

By Wednesday night, expect low pressure to begin to take shape
over the central Great Plains in response to a lead shortwave 
ejecting out ahead of a deep upper low moving onshore over SoCal. 
Surface low will further deepen as this southern stream shortwave
interacts and phases with a northern stream wave digging across 
the Canadian Prairies into the Upper Midwest Thursday. Expect rain
to overspread the area in advance of the lead wave and attendant 
surface low as broad warm advection overspreads the region and 
helps to saturate the column. Chances for rain will continue into 
the day Thursday as a trailing surface cold front and 
aforementioned northern stream wave push across the area. In 
addition to the precip chances, winds will be something to keep an
eye on Wednesday night into Thursday. The tightening pressure 
gradient associated with the developing low will help to increase 
wind speeds across the region. Isallobaric response will also help
drive strong winds with this system. Moderately strong pressure 
falls of 4-6mb/6hr are progged ahead of the low Wednesday night, 
followed by even stronger pressure rises of 7-11mb/6hr behind the 
cold front Thursday. Soundings from the GFS show a couple windows 
in the vicinity of the front with mean boundary layer momentum 
transfer in excess of 40 kt and top of the channel winds of 
around 50 kt. Certainly could be in the ball park of needing a 
wind advisory barring any big changes in guidance, particularly 
during the day Thursday.

Models indicate more benign weather will return Friday and
Saturday as high pressure builds back across the region. There 
is a low expected to move across the lower Mississippi Valley that
could push precip into southern Illinois, close to our southern 
CWA boundary. Will need to keep an eye on this system, otherwise 
most of the area should be dry and cooler with temperatures back 
into the lower 40s for highs.


.AVIATION...(For the 12Z TAFS through 12Z Monday morning)
Issued at 519 AM CST Sun Nov 17 2019

A cold front will slowly work east across central Illinois today 
and tonight. VFR conditions and south winds are expected out ahead 
of the front much of the day. Ceilings will lower to MVFR and 
precip chances will begin to increase as the front approaches and 
winds veer to the southwest. Winds will veer to the northwest this
evening and overnight behind the front. Conditions may drop to 
IFR or remain low MVFR for a while behind the front as post-
frontal stratus lingers over the region. Can't rule out some 
lingering drizzle behind the front as well, though the better 
chances for precip should diminish.




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