Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 251738

Area Forecast Discussion
National Weather Service Lincoln IL
1238 PM CDT Mon May 25 2020

Issued at 350 AM CDT Mon May 25 2020

Summer like heat and humidity will continue across central
and southeast Illinois through Thursday. Highs into the 80s are
expected each day through Thursday, along with daily scattered
shower and thunderstorm chances, though there will be plenty of
dry periods each day. Chances of showers and thunderstorms could
linger southeast of I-55 on Friday as a cold front pushes into the
Ohio river valley. Dry, cooler and less humid weather will arrive
by this weekend.


Issued at 1106 AM CDT Mon May 25 2020

Isolated weak showers continue to develop across west central IL
and then in extreme eastern IL and move northeast. Forecast has
good handle on the precip in the west, but is lacking in the east.
Will make some adjustment to this in new update. Remainder of
forecast looks fine for afternoon as main focus across the US will
be a semi-stationary boundary from central IA into KS. As this
boundary slowly moves east today, additional thunderstorms will
develop along and ahead of it in eastern IA and all of MO. Some of
the storms could reach into central IL later this afternoon and
this evening, and some could be strong. Current forecast has good
handle on this, so only update needed is to eastern IL where
scattered showers still occurring. Update will be out shortly.


.SHORT TERM...(Today and tonight)
ISSUED AT 350 AM CDT Mon May 25 2020

Early morning surface map shows weak 1008 mb low pressure over
central MN with a cold front extending thru western IA and central
KS to 1002 mb low pressure in southeast NM. High pressure was over
New England and the mid Atlantic States. A broad southerly flow of
warm/moist air from the gulf of mexico continued into IL. Temps
were in the mid to upper 60s over CWA. Radar mosaic shows a small
cluster of showers just north of Lacon in Marshall county lifting
slowly NNE. A cluster of showers and thunderstorms was over se MO.
Main area of convection was well west of IL over the central and
southern plains.

00Z models continue to show a strengthening upper level
subtropical ridge near the east coast next few day, with strong
588 dm 500 mb high over the mid atlantic states tonight. An upper
level low to remain near north central/NE Texas thru Wed. Surface
front to remain nw of IL thru Wed night. A tropical air mass with
modest instability remains in place over CWA through mid week.
CAPES rise to 1700-3000 j/kg by this afternoon, highest in east
central and se IL by late afternoon. Though wind shear remains
quite weak today through Thu morning. Have best chances of
scattered showers and thunderstorms this afternoon and early
evening with locally heavy rain again possible as precipitable
water values range from 1.5 to 2 inches by afternoon. SPC keeps
marginal risk of severe storms generally west of CWA this
afternoon and evening. Highs today in the mid to upper 80s with
afternoon heat indices peaking in the upper 80s and lower 90s.
Mainly isolated convection after dark tonight and mainly over
western CWA. Muggy lows in the upper 60s much of CWA tonight.

.LONG TERM...(Tuesday through Sunday)
ISSUED AT 350 AM CDT Mon May 25 2020

Strong upper level ridge over the eastern Great Lakes/mid Atlantic
States and into New England Tue/Wed with 590 dm 500 mb high off
the southern New England Coast. Upper level low moves slowly to se
OK or ne Texas by Wed. CAPES peak from 1500-2500 j/kg Tue and Wed
afternoon while wind shear remains weak. Scattered showers and
thunderstorms likely develop Tue afternoon/early /Tue evening and
again Wed especially in afternoon/evening hours. SPC does not have
a marginal risk of our area Tue/Wed, but locally heavy rains
again possible with precipitable water values topping 1.5 inches
both day. Trended highs a few degrees warmer than NBM next few
days, with mid 80s Tue and low to mid 80s Wed.

Likely chances of showers and thunderstorms shift eastward across
CWA during Thu as a cold front pushes into nw IL early Thu and
into se IL Thu evening, with upper level low moving to near the
OK/AR border. Highs Thu in the lower 80s most of area and still
humid. Best chances of showers and some thunderstorms shift se of
I-55 on Friday as cold front pushes se into the Ohio river valley.
Cooler highs Fri in the mid to upper 70s, warmest in southeast IL.
Getting less humid with dewpoints dropping into the mid to upper
50s Fri afternoon in central IL and lower 60s in southeast IL.

Strong upper level ridge builds northward over the Rockies late
this week with broad upper level trof into the Great Lakes. This
puts IL in a nw upper level flow by Fri night and Sat and to bring
a dry and pleasant stretch of weather for the weekend. Highs Sat
in the mid 70s, mid to upper 70s on Sunday and upper 70s to around
80 next Monday. Summer time heat and humidity will likely build
eastward into the area during next work week as strong upper level
ridge shifts eastward. Some convection ridging over top of upper
level ridge this weekend and early next weekend currently appears
to stay north of CWA, but some uncertainty of that depending on
orientation of upper level ridge to our west.


.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1237 PM CDT Mon May 25 2020

Convection has already started to develop across the area,
seemingly along north to south lines. One line is near CMI, while
the second line is west of BMI and DEC, while the last line is
well west of the IL river. Thinking is these will continue this
afternoon and effect all sites at some point in the late afternoon
and into the early evening. So have VCTS at sites when think best
chance of storm near the sites. Possibility of storm at sites
should continue through early evening and then diminish with loss
of heating. Then just cirrus til tomorrow, when another round of
CU develops over the area, affecting each site. Chance for
thunder is there, but not great enough to warrant any mention in
TAFs at this time. Winds will be generally out of the south
through the period with speeds of around 10kts or less.




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