Area Forecast Discussion
Issued by NWS Central Illinois

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000
FXUS63 KILX 220417
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1117 PM CDT Mon Jul 21 2014

.DISCUSSION...
ISSUED 850 PM CDT Mon Jul 21 2014

Hazy, warm and humid conditions prevail over a good portion of the
region this evening with the main thunderstorm activity well to our
north across North Dakota and northern Minnesota. Watching a band
of mid level clouds now over Iowa which short term models suggest
may develop into some elevated showers and storms over parts of
Iowa as the low level jet and 850 mb moisture convergence increases
as the night wears on. 00z ILX sounding showing a fairly decent
warm layer in place already around 700 mb with our temperature near
+12 degrees while Davenports was up to +14 degrees C. Most models
suggest any of the elevated storms that do develop out to our west
will be fighting an uphill battle as the 500 mb ridge temporarily
builds east into central Illinois and forecast soundings continue
to show a stought capping inversion in place tomorrow morning. What
activity that is able to develop well out to our west will probably
not make it into western Illinois tomorrow morning so will continue
to keep the forecast dry late tonight into Tuesday morning.

00z surface analysis indicating 75 to 80 degree dew points out over
west central Iowa into Minnesota ahead of the cold front that is
forecast to push across our area tomorrow evening. The pooling of
the higher dew points is expected across our area tomorrow afternoon
and evening just ahead of the boundary. The combination of afternoon
temps in the lower 90s and surface dew points expected to be at
least in the low to mid 70s, our apparent temperatures will soar
into the 97 to 102 degree range by mid afternoon thru the early
evening hours. Since this is the first time we have seen the more
widespread high apparent temps this Summer, in addition to coming
off a stretch of cooler temperatures over the past 3-5 days, will
issue a Special Weather Statement highlighting the threats from
the high heat and humidity levels.

Have made only minor tweaks to the current forecast for the overnight
hours, not enough to warrant an updated ZFP this evening.

&&

.AVIATION...
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 t 10 kts.

Smith
&&


.PREV DISCUSSION...
ISSUED 332 PM CDT Mon Jul 21 2014

SHORT TERM...Tonight through Thursday

Temperatures and dewpoints are up several degrees across central
and Southeast Illinois since 24 hours ago as high pressure builds
into the region along with southerly low level flow.
Forecast/observed soundings show a strong capping inversion around
4000 feet agl keeping scattered cumulus cloud development shallow.
For Tuesday...the inversion remains strong for most of the day as
low level moisture and temperature peak out with heat index values
around 96 to 100 degrees affect the region. In the evening, a cold
front will approach from the north bringing mid-level cooling and
surface convergence to erode the capping inversion. A line of
thunderstorms is likely to move across the region as a result,
affecting areas mainly north of I-72 in the evening and sweeping
across I-70 and areas southward by Wednesday morning. Timing of
the front overnight will reduce the threat of severe thunderstorms
with the line, however CAPE/shear values associated with the system
as it approaches suggest isolated severe wind gusts and hail can`t
be ruled out yet. Cooler and drier high pressure pushes into the
region behind this system for Wednesday and Thursday for highs
generally around 80.

LONG TERM...Friday through Monday

Cool and dry conditions will continue through Friday before a
stronger low pressure system moves over the top of the
ridge...initially bringing warmer and more humid conditions and a
chance for thunderstorms Saturday. By Sunday, the low will help
carve out a deep low pressure trough over the eastern U.S. late in
the weekend and into next week. Timing of precipitation features
headed for the area next weekend is far from certain at this time,
between potential MCS activity early in the weekend and a cold
front late in the weekend. Have broadbrushed this with chance to
slight chance category PoP`s Friday night through Monday.

Onton


&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$







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