Scientific Forecaster Discussion

Return to Local Conditions & Forecast
Area forecast discussion 
National Weather Service Lincoln Illinois
1155 PM CDT Wed Apr 23 2014

issued 900 PM CDT Wed Apr 23 2014

The initial wave of warm advection rain showers will affect areas
mainly along and north of I-74 the rest of the evening. Precip
amounts will be very light, with a couple hundredths possible.
Most areas that see precip across the north will just see trace
amounts of sprinkles.

Clouds will remain across the area the remainder of the night,
helping to limit the diurnal swing for low temps. Lows should
generally bottom out in the mid to upper 40s, with a few low 40s
possible closer to the Indiana border.

Trends for rain and storms tomorrow appear to be slowing down. We
could see dry conditions for a majority of the day tomorrow, with
areas west of I-55 having the best chances of rain before 6 PM.
Will let the night shift do more complete updates on slowing down
the eastward advance of pops on Thursday, but wanted to at least
mention the observed model trends with the evening update.

Minor updates were done to pop and weather grids for the rest of
the night, along with slightly warmer temps. The latest forecast
info will be available shortly.



issued 1155 PM CDT Wed Apr 23 2014

A break in the precipitation will occur as a tongue of dry air
follows the initial wave of warm advection precip. The warm front
will develop near the Missouri-Illinois border tomorrow morning,
then progress eastward tomorrow afternoon just ahead of the cold
front. A slower trend is being depicted in the 00z models, and
thunder chances will be focused mainly between 23z and 05z from
west to east. There should be a period of steady rains in the warm
sector ahead of the cold front, with thunder chances highest during
that time as well. A thunderstorms in the vicinity was included starting at 23z in pia and
03z at cmi. A tempo for MVFR or possibly IFR may be needed for a
couple hours tomorrow evening.

Winds will increase quickly tomorrow morning, as the nose of an
850mb low level jet advances into western Illinois. Gusts early in the morning may
actually be a few knots higher than the afternoon based on the
strength of the low level jet as depicted in the hopwrf and rap. A few gusts
may top out over 30kt for pia/spi between 14z-16z. Wind directions
will be southeast for the first 12-15 hours of the tafs, then it will
shift toward the south into the afternoon as wind speeds remain
strong in the 18g28kt range. By evening, wind speeds should
subside a bit as the pressure gradient weakens near the cold


Previous discussion...
issued 253 PM CDT Wed Apr 23 2014

Plenty of dry air in place over Illinois early this afternoon, on
the periphery of a high pressure ridge, with dew points in the
upper 20s to lower 30s. Across the southeast half of the forecast
area, clouds have been eroding as they move into the drier air. Area
of showers has been advancing eastward from Iowa. Looks impressive
on radar, but surface observations are showing cloud heights well
over 8000 feet in many cases, indicating not much in the way of
measurable rain is reaching the ground. However, this is enough
that a mention of isolated showers across the northern County Warning Area this
evening is warranted.

The first forecast concern is with the timing of rain over the
next day or so, as this storm system pushes eastward. In the
longer term, the duration of the rain is a concern as we get set
in a rainy pattern for the first half of next week.

Short term...tonight through friday:

Water vapor imagery and upper air analysis showing a deep trough
currently pushing east across The Rockies, and is progged to move
across the Mississippi Valley late Thursday. The dry air at the
lower levels will take some time to saturate, with the forecast
soundings still rather parched below 850 mb at mid afternoon. Have
limited Thursday morning pop's to areas west of I-55 and still
kept them below 50% during the afternoon east of I-57, otherwise
have maintained the categorical pop's over 80% in much of the
forecast area during the afternoon. Best instability looks to be
along and south of I-72 for any thunder, although some low cape's
to around 200 j/kg progged as far north as Peoria, so have kept
some thunder mention that far north. With the system a bit slower,
will mention 80% or higher pop's into the evening across the east
half of the forecast area into the evening. Dry weather then on
tap for Friday.

Long term...Friday night through wednesday:

A cold front will push southward through the region Friday night.
Big question will be where it ends up, as it will likely not be
going anywhere for awhile. Most of the models do have it through
the forecast area by early Saturday, although the European model (ecmwf) and Gem
models linger it more toward the I-72 corridor. Saturday should be
dry. However, the main action will be later in the weekend, as all
the models continue to close off an upper low over the central
rockies. This low will only slowly drift eastward, and will likely
linger in some form into the middle of next week.

Most of Sunday should be fairly decent, with the rain most likely
across the western County Warning Area during the afternoon. After that, rain is
likely on and off, with pop's gradually diminishing Tuesday and
Wednesday as the cutoff low slowly weakens. By this point, as the
core of the colder air settles over the Midwest, temperatures will
be a good 15 or so degrees below normal, with highs Tuesday and
especially Wednesday generally in the 50s.



Ilx watches/warnings/advisories...