Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 180544

Area Forecast Discussion
National Weather Service Lincoln IL
1244 AM CDT Tue Jul 18 2017

Issued at 915 PM CDT Mon Jul 17 2017

Quiet weather is expected across central and southeast Illinois
overnight with high pressure building in and a relatively dry air
mass in place. Expect minimal cloud cover, light/variable winds,
and slightly cooler than normal low temperatures for mid July.
Going forecast is in good shape with only minor hourly tweaks


.SHORT TERM...(This evening through Tuesday)
ISSUED AT 310 PM CDT Mon Jul 17 2017

Will issue an excessive heat watch for CWA from Wednesday
afternoon through early Saturday evening. Highs in the low to mid
90s (upper 90s even possible sw CWA on Thu/Fri). Afternoon heat
indices are likely to peak from 100-110F during each of those 4
afternoons. Heat indices are expected to reach 100-105F over
southern half of CWA on Sunday afternoon so heat headlines may
need to be extended longer there. This will likely be our longest
heat wave of the summer for central and southeast IL.

A frontal boundary extending from Bloomington IN to near
Lawrenceville IL and just south of Flora, could develop an
isolated shower or thunderstorm this afternoon before shifting
south of CWA by 6 pm. Otherwise dry conditions expected tonight
and Tuesday across CWA as weak 1018 mb high pressure settles se
across the Great Lakes and ridges into central IL keeping winds
light. Lows overnight to range from the upper 50s and lower 60s
from I-72 north, to the mid to upper 60s in southeast IL where
airmass is more moist (dewpoints still in the lower 70s from
Charleston/Mattoon south). Highs Tue in the upper 80s to around
90F with warmest readings in western CWA with a fair amount of
sunshine expected across area. Dewpoints in the mid 60s to near
70F Tue afternoon to give afternoon heat indices peaking in low to
mid 90s Tue afternoon, warmest in western CWA.

.LONG TERM...(Tuesday night through Monday)
ISSUED AT 310 PM CDT Mon Jul 17 2017

12Z models continue to expand/build subtropical mid/upper level
ridge into the central and southern US during rest of this week
then starting to be suppressed southward during this weekend into
early next week. Disturbances/MCSs riding over top of upper level
ridge will initially pass north of central IL with hot and humid
conditions prevailing from Wed afternoon into this weekend. One
disturbance gets qpf close to far northern CWA later Tue night and
early Wed morning. Another disturbance/MCS to graze close to far
northern CWA again late Wed night and Thu morning. Feel most of
CWA will stay dry thru mid week though. Yet another one brings
slight pops to northern CWA overnight Thu night into Fri morning
and have 20-30% pops over central and ne CWA on Fri afternoon.
Have small pops over ne 1/3 of CWA Fri night then 20-30% over
areas north of I-70 on Sat afternoon. Better chances of convection
for CWA appear to arrive from Sunday afternoon thru Monday as a
frontal boundary moves thru central IL from late Sunday afternoon
and Sunday night and thru southeast IL on Monday. Temps to cool
closer to normal by next Monday along with heat indices coming
down to 85-95F range next Mon afternoon (highest in southeast IL).


.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1240 AM CDT Tue Jul 18 2017

VFR in most sites, though HRRR has started to develop some fog for
SPI tonight. With only a 2 degree dewpoint depression and calm
winds...putting a tempo in for the predawn hours down to IFR.
Other than that...CU rule for GFS and NAM both hinting at a gap in
a cu leaving out BMI and DEC for some cu development
everywhere else today. Winds light and variable under the ridge
and cirrus.


Excessive Heat Watch from Wednesday afternoon through Saturday
evening for ILZ027>031-036>038-040>057-061>063-066>068-071>073.



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