Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 221554

Area Forecast Discussion
National Weather Service Lincoln IL
1054 AM CDT Tue Jul 22 2014

ISSUED 1051 AM CDT Tue Jul 22 2014
Cold front approaching the Midwest but an overnight disturbance to
the northwest brought some showers and thunderstorms down into the
region. IR sat imagery showing warming cloud tops and slowly
weakening thunderstorms on radar as well. Upped some of the pops
over the far west for some rainfall and sct thunder. Diurnal swing
doing well in the forecast... updated a bit for the west with
current conditions. Updates out momentarily.


ISSUED 649 AM CDT Tue Jul 22 2014

A dissipating line of convection approaching from the NW should
continue to weaken over the next few hours, with mainly mid clouds
drifting into central IL from that complex. Some MVFR fog at CMI
will dissipate by 13z as it has the last few mornings. Then VFR
conditions should prevail through the day and into the evening

Storm chances will increase this evening from NW to SE as a cold
front arrives. Storm coverage may be limited by the amount of warm
air in the mid levels of the atmosphere, but if any storms do get
going, they could quickly become strong with winds and hail. VCTS
was included in all TAFs beginning at 01z in PIA and expanding
east to CMI at 03z. There should mainly be a 3-4 hour window of
storm chances for PIA and BMI, but farther east and south the
front may slow down and rotate slightly, keeping storm chances
through 08z-09z for the SPI/DEC/CMI corridor.

Forecast soundings are showing some low level moisture behind the
front possibly creating some MVFR ceilings for late tonight into
Wed morning.

Winds will be S-SW today, with speeds increasing to 12-14kt
sustained by late morning. As the cold front arrives from the NW,
wind speeds should diminish in the vicinity of the front to less
than 10kt, then veer to the W-NW behind the front later this
evening and overnight.


ISSUED 257 AM CDT Tue Jul 22 2014

Clear skies once again across the forecast area early this
morning, with some shallow dense fog mainly along the Indiana
border. An advancing area of mid/high clouds was ahead of the main
frontal boundary, which extends from an MCS in northeast Minnesota
southwest into Nebraska.

Initial forecast concerns involve the heat index across the
northwest CWA today, and rain chances tonight/Wednesday morning.
Longer range, the timing of rain chances through the weekend comes
into play.

SHORT TERM...Today through Wednesday:

2 am surface analysis showing 70-75 degree dew points not too far
away across Iowa and northwest Missouri. Should start to see some
of this coming into the areas along/northwest of the Illinois
River by late morning. With highs in the lower 90s, heat index
values of 100-105 are likely in that area. This is just shy of
advisory criteria, and with some question as to how much the
incoming clouds will affect the temperatures, will hold off on any
advisory for now.

Cold front expected to arrive in the northwest CWA mid to late
evening, and be through nearly all of the forecast area before mid
morning Wednesday. Strength of the cap appears to limit much of
the convection until the front is nearly on top of us. SPC 4km WRF
and ARW models, as well as the NAM, show the best chances of
storms developing over northern Missouri and and perhaps clipping
our far southwest counties as they track southeast. Looks like
best chances for rain in our area should be focused in the 9 pm to
4 am time frame. Rather healthy CAPE`s will be available but shear
will be a little more modest, so severe weather threat is a bit
lower this far south. Think the rain should be limited to areas
along/south of I-70 by morning, and out of the forecast area by

LONG TERM...Thursday through Monday:

Upper ridging expected to amplify across the Rockies through late
week, before being squashed by a strong 500 mb low which will be
coming into the Pacific Northwest beginning on Wednesday. This
should become an open wave late in the weekend by the time it
starts heading our way. Broad trough across the Midwest will bring
much drier conditions late week with temperatures well below
normal, but not as cool as the peak of the last cool spell. More
of a cooling trend will become established next week as a large
upper low settles into the Midwest.

Dry conditions expected Thursday, but an MCS is expected to form
Thursday night to our northwest along the 850 mb thermal gradient
over Iowa, dropping southeast. Thinking this should stay northwest
of our area until the remnants arrive on Friday. Better rain
chances expected with the next MCS Friday night and Saturday, as
the surface warm front becomes pronounced over the area. Sunday
is a little more questionable with rain chances, but some 30%
chances are warranted with the arrival of a cool front.




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