Area Forecast Discussion
Issued by NWS Central Illinois

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000
FXUS63 KILX 200833
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
333 AM CDT Wed Aug 20 2014

.SHORT TERM...(Today and tonight)
ISSUED AT 333 AM CDT WED AUG 20 2014

Storms have developed along a boundary in northeast MO and southeast
IA early this morning. These storms should move into western and
southwest IL in the next several hours. These could get into western
parts of the CWA so will have some chance pops in the west this
morning. However, all models seem to indicate this area will not
travel very far and should dissipate during the morning hours. The
associated boundary will then slowly lift northeast as a warm front
through the CWA, and though convergence along this boundary will be
weak, some isolated showers or thunderstorms will remain possible in
the early afternoon. By late afternoon and into the evening and
overnight hours, the warm front will remain across the central part
of the CWA so the chance of showers and thunderstorms will continue
during the evening and overnight hours.

Temperatures will be a few degrees warmer than yesterday, with some
areas in the west and south getting to around 90. Overnight lows
will also be warmer as most of the CWA will be in the warm sector
overnight.


&&

.LONG TERM...(Thursday through Tuesday)
ISSUED AT 333 AM CDT WED AUG 20 2014

Position of the boundary after lifting through the FA today and
tonight will have a signif impact on the location of the showers and
thunderstorms. Though most recent models are lifting the boundary
further to the northeast, some chance pops Thurs and slight chance
pops remain in place at least over the northeastern portions of the
CWA from Thursday night through Friday night. Pops increasing
somewhat for Saturday as models are collapsing the ridge somewhat as
a wave moves over the ridge and into the Ohio River Valley.  Though
the precip chances are scattered at best and low confidence...the
models have been very persistent with the very hot temperatures for
some summer like conditions that are well above normal for this time
of year. Models have also shown consistency with  850 mb temps in
the 19-25C range through Sunday.  This will drive the temps into the
upper 80s/lower 90s with heat indices in the upper 90s/low 100s.
Forecast dwpts into the low to mid 70s may be over representing llvl
RH enhancement from widespread precip in the models that may not
quite come to fruition as widespread.  Todays heat indices are more
borderline for Heat Advisory criteria...but far more likely to see
from Thursday into Sunday with subsequent forecasts, should the
trend continue. Into the extended, day 7/just into day 8, models
actually beginning to diverge into a solution to break down the
ridge with an upper system pushing a return of precip in for Tues
night into Wed.


&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
ISSUED AT 1145 PM CDT TUE AUG 19 2014

Skies clear across the TAF sites late this evening, but will see
some increase in clouds from the west late. Main concern is with
potential for fog. Latest short-range guidance suggesting the
KSPI-KCMI corridor most at risk for significant fog, as a weak
frontal boundary is draped in that area and dew points are pooling
along it. However, the increase in clouds near KSPI may help
mitigate the fog from getting out of control. The RAP model is
fairly robust with widespread dense fog affecting all the TAF
sites, but the HRRR has it more patchy within the KPIA/KSPI/KBMI
triangle. Right now, will go with a TEMPO period of 1SM at the
southern TAF sites and keep it a little higher further north,
where the air is a bit drier. Will also need to watch for
convection developing along the front in northern Missouri over
the next few hours. General thought is that this should stay
southwest of KSPI and will not mention at this time.

In the longer range of the TAF, concern is with timing of
convection late Wednesday afternoon and evening. NAM is faster and
much further south with storms moving through as early as 19-21Z,
while the latest GFS favors the evening hours, with other guidance
much more widely scattered but in the evening. Will favor the
later time frames with VCTS mention in the TAFs, although
confidence is somewhat uncertain at this time.


&&

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

$$

SHORT TERM...AUTEN
LONG TERM...HJS
AVIATION...GEELHART





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