Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 210706

Area Forecast Discussion
National Weather Service Lincoln IL
206 AM CDT Mon May 21 2018

.SHORT TERM...(Today and tonight)
ISSUED AT 206 AM CDT Mon May 21 2018

A strong short-wave evident in GOES-16 6.95 um and 7.34 um water
vapor bands over mid-Missouri valley is providing support to
convection moving through Illinois. Although instability is
limited, synoptic forcing is stronger than with the waves over the
last few nights and there is more confidence that the
precipitation should hold together into the day. Models in good
agreement with a surface low crossing northern Illinois during the
afternoon and evening. A weak cold front in the wake of the low
should provide some additional forcing as it moves east across the
eastern portion of the state near and after peak heating. 00z
3-km NAM and HRRR suggest that any redevelopment will be
scattered, but the combination of enhanced convergence along front
and diurnal instability may be enough to produce several strong
storms, mainly from I-57 eastward, during the afternoon and
evening. Appears strong winds would be the primary threat given
the unidirectional wind profile and limited instability.

A gradual drop off in rain chances should occur from west to east
Monday as the wave axis moves slowly across the Midwest. Abundant
clouds and scattered precipitation should keep temps from rising
much Monday, particular northwest of the Illinois River, highs
should be near normal for middle/late May.


.LONG TERM...(Tuesday through Sunday)
ISSUED AT 206 AM CDT Mon May 21 2018

Once the wave moves out of the region early Tuesday, much drier air
will advect into the area as high pressure covers much of the Great
Lakes region. Mid-level heights climb significantly through
midweek with 500 mb heights increasing 80 m between Tuesday and
Thursday Morning. This should push sfc temps well into the 80s by
the end of the week.

Remnant energy from the trough currently along the west coast will
move over the ridge and slide down into the Great Lakes toward the
end of the week. Although the major synoptic models have this
general idea, they do differ significantly on the strength of the
wave and how it interacts with a weakness along the northwestern
Gulf of Mexico coast. Depending on the amount of phasing that
occurs, rainfall may be prolonged and potentially heavy over the
Holiday weekend per 18z GFS, but 00z GFS matching up better with
ECMWF which keeps the energy seperated and keeps bulk of Gulf
moisture from interacting with the northern stream wave until after
it has passed the forecast area.  If this model trend continues
there will likely be a period or two of precipitation over the
weekend though probably not a complete washout.


.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1100 PM CDT Sun May 20 2018

Timing of showers and thunderstorms into the forecast area over
the next several hours and affect on cigs and vsbys into the
early morning hours the main forecast concerns this period.
Complex of weakening showers and thunderstorms was tracking
northeast into west central Illinois and should continue to move
across the remainder of the forecast area into the early morning
hours. As the upper wave that is responsible for the precipitation
moves across the area on Monday, showers and low (mainly MVFR)
cigs and vsbys will prevail through the morning with a gradual
improvement in cigs and vsbys expected for the afternoon to low
VFR early in the afternoon, with cigs lifting or even scattering
out towards 00z.

Surface winds will be mostly easterly tonight at 8 to 13 kts with
winds veering into a southerly direction by Monday afternoon with
speeds in the 10 to 15 kt range.




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