Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 220758

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

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.



ISSUED 1105 PM CDT Mon Jul 21 2014

MVFR vsbys possible in ground fog again late tonight, roughly in
the 09z-13z time frame, otherwise, VFR conditions will persist
thru the forecast period. Best threat for fog, at least based on
the latest temp-dew point spreads appears to be along and east
of I-55, which would encompass BMI, DEC and CMI. Latest HRRR
forecast hitting the lower vsbys the hardest from MTO to DEC
to just east of BMI by morning. What fog the does form during
the early morning hours should be gone by 13z most areas. After
that, some mid and high level clouds will track in from the
west but it now appears the showers that models were depicting
earlier this evening out to our west by dawn will stay west of our
TAF sites.

Secondary concern will be in the 00z-06z time frame as a cold
front shifts across the area and TSRA chances along it. At this
time, with such warm temperatures aloft, it appears that
thunderstorm coverage will be too limited at this point. As a
result, will include VCTS at the TAF sites during the time frame
that the front will be moving thru. Surface winds will be out of
the southeast at 5 to 8 kts overnight and then turn into the
south and southwest tomorrow at 12 to 17 kts with an occasional
higher gust during the afternoon. Winds should diminish quickly
towards evening and then gradually turn into more of a southwest
to west direction at 5 to 10 kts.




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