Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 260828

Area Forecast Discussion
National Weather Service Lincoln IL
328 AM CDT THU MAY 26 2016

.SHORT TERM...(Today)
ISSUED AT 325 AM CDT Thu May 26 2016

The current pattern with a mid level ridge over the east coast and a
trough over the intermountain west progged to progress slightly
eastward through the day, but not enough to provide any clear-
cut answers on thunderstorm distribution through the day. A few
features to note however are the shortwave over western MN/IA
providing some developing organization to convection over that
area in the early morning. This feature should move northeastward
and should move some thunderstorm activity into areas west of I-55
in the early morning hours so have introduced chance thunderstorms.
Although the upper level feature will provide less influence later
in the morning, an outflow boundary should be able to propagate
eastward propagating scattered thunderstorms across the central/SE
IL forecast area to the IN state line by late morning and have
moved the chance thunderstorm area eastward accordingly. Models
suggesting another outflow may clip the northeastern portions of
the forecast area during the afternoon so have included the I-74
corridor through Bloomington-Champaign-Danville with another
period of chance thunderstorms. Otherwise, after the morning
period of convection takes place, generally a slight chance of
thunderstorms included through the day due to forecast uncertainty
in weak triggering mechanisms combined with a moist and unstable
air mass characterized by forecast CAPE of 2000-3000 J/KG.
Marginal 0-6km bulk shear of 20- 30 kts could be enough for a few
strong storms containing gusty winds and hail, and SPC has
outlooked the area from near I-57 westward in a marginal severe
weather risk.

A slight increase in humidity of the air mass today should result in
dewpoints rising to the upper 60s to around 70 during the afternoon
today after starting out in the mid 60s. This combined with highs in
the mid 80s will again feel warm and humid. South winds around 10-12
mph will continue through the day promoted by gradients between
surface high pressure over the southeastern U.S. and general low
pressure over the Plains.


.LONG TERM...(Tonight through Wednesday)
ISSUED AT 325 AM CDT Thu May 26 2016

Upper low currently entering western Arizona should track into
southern Colorado by this evening, before weakening and lifting into
the northern Plains. Precipitation in the short term will continue
to be driven by localized boundaries and weak ripples in the upper
flow ejecting from the east side of the low, so forecast trends
remain uncertain with a wide variety of model solutions. Some
increase in lift is anticipated by Friday as the low ejects into the
Plains, and have mentioned likely PoP`s across mainly the western
half of the forecast area into Friday evening. Air mass in that area
will remain juicy with precipitable water values around 1.8 inches,
so some localized heavier rains are likely with the stronger storms.

The pattern into the holiday weekend will continue to favor
scattered thunderstorms, although chances decrease with time, and
have only mentioned slight chance PoP`s on Memorial Day across the
western half of the area. The upper pattern during this period will
be transitioning more toward a zonal flow for a time, before some
modest ridging takes place early next week as a trough digs
southward across the Rockies. The longer range guidance has some
difficulty resolving the evolution of this trough, with the ECMWF
fairly aggressive at a closed low just north of the North Dakota
border and the GFS with a weaker low back over Wyoming. The former
solution would sweep a cold front through on Thursday, while the
latter has a much weaker frontal passage on Friday. Both solutions
favor at least scattered convection beginning on Tuesday.

Little change in temperatures is on tap, with highs of 80-85 degrees
largely forecast through the extended period. However, the pattern
change would favor some slightly lower dew points as the weekend


.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1150 PM CDT Wed May 25 2016

Believe VFR conditions will prevail through the night and possibly
into tomorrow as well. Question is, will the convection in
northeast MO expand and continue across the state overnight and
into western IL by early tomorrow morning. Short range convection
models indicate that by the time the MCS arrives, it will just be
scattered showers. Even though models are not handling things well
at the moment, this has been the trend last couple of days. So,
though will be bringing in more clouds into the area by morning,
will only have VCSH at all TAF sites in the morning. Next question
then is will there be pcpn during the afternoon tomorrow? Any
outflow boundary form late tonight will probably wash out and the
area could be too cloudy to really get the instability going.
Models always struggle with convective features and due to
uncertainty of boundary location in the afternoon, will keep VCTS
in the TAFs for afternoon and early evening and let later shifts
reevaluate for better location and timing. Winds will be south to
southwest through the period.


.ILX Watches/Warnings/Advisories...


LONG TERM...Geelhart
AVIATION...Auten is the U.S. government's official web portal to all federal, state and local government web resources and services.