Area Forecast Discussion
Issued by NWS Central Illinois

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000
FXUS63 KILX 301818
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
118 PM CDT SAT APR 30 2016

.UPDATE...
Issued at 1111 AM CDT Sat Apr 30 2016

15z/10am surface map shows 1004mb low just north of Kansas City,
with warm front extending E/SE into far southern Illinois. The low
will only make slow progress eastward today, so much of the KILX
CWA will remain in the cool sector of the system through the day.
12z NAM shows the low tracking to north of St. Louis by 00z, with
the warm front potentially reaching the I-72 corridor. Think this
may be too far north, given the widespread rain that is currently
occurring north of the boundary. Made some updates to the forecast
to lower high temps across the northern half of the KILX CWA and
to adjust hourly PoP trends. Primary rain shield will lift north
of the I-74 corridor by early afternoon, leaving behind only
scattered showers and thunderstorms for the remainder of the
afternoon. Will maintain only chance PoPs late in the day, as
limited instability should keep areal coverage low. Severe threat
appears minimal at this time, and should be focused further
southwest across central/southern Missouri where better
destabilization is likely late this afternoon and evening.

&&

.SHORT TERM...(Today)
ISSUED AT 249 AM CDT Sat Apr 30 2016

An active weather day is setting up across central and southeast
Illinois for today. A vigorous, but weakening, upper-level low is
slowly approaching the Midwest from the central High Plains. To the
east of this circulation, a tropical moisture plume is surging
toward the area in deep southerly flow. Strong WAA/isentropic ascent
will work on this moisture plume and produce an area of showers with
embedded thunder across the forecast area, primarily this morning.

Rainfall coverage should diminish across the area this afternoon,
with additional development at least partially dictated by how far
north the surface warm front pushes. The afternoon position of this
warm front will help determine how much destabilization can occur
during peak diurnal heating. Model agreement in this regard is still
not great, although the forecast afternoon position of the front has
trended north in the past 24 hours in the latest consensus. The main
severe storm threat this afternoon still appears to be south of I-70
where modest instability (1000-2000 j/kg) and bulk shear (30-35 kts)
appear most likely to co-exist. A large N-S spread in high
temperatures appears likely today given the expected afternoon
position of the warm front. Expect daytime highs to range from the
mid 50s north around Galesburg & Lacon, to around 70 south of I-70.

.LONG TERM...(Tonight through Friday)
ISSUED AT 249 AM CDT Sat Apr 30 2016

Most of the forecast focus will be on the period through Sunday
night, as the current storm system works its way through the region.

Surface low expected to track northeast across the region this
evening, reaching northeast Indiana by midnight, although the GFS is
quite a bit slower with this scenario. General thought is that the
steadier showers will be quickly diminishing by this evening,
with a good portion of the overnight hours dry. However, the
remnants of the upper low currently along the Colorado/Kansas
border will move across southern Iowa Sunday morning and across
Illinois in the afternoon, bringing another period of scattered
showers to the area by midday. Have included isolated thunder
mention in the afternoon most areas, as the trough moves overhead.
Any lingering showers should be out of the area around sunset.

Highly amplified pattern expected next week, as upper level ridging
over the western U.S. builds well into British Columbia and Alberta.
Longer range models showing some differences with the extent of the
corresponding upper trough over the eastern half of the CONUS, with
the ECMWF on the deeper side. This would trend toward significantly
cooler conditions over the Midwest during the second half of the
work week. By the end of the week, the upper pattern on both the GFS
and ECMWF models trends toward an omega block type configuration
which would linger the cooler air even longer. Have trended downward
on the temperatures for late in the week, although not as low as the
blended raw model guidance at this point.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 118 PM CDT Sat Apr 30 2016

Area of rain continues to lift steadily northward early this
afternoon, with latest radar imagery now showing it along/north of
the I-74 corridor. Despite an end to the steady rain, IFR ceilings
will persist for the next few hours before ceilings slowly rise
later this afternoon. As winds become more southerly rather than
easterly, HRRR shows ceilings rising into the MVFR category at
KSPI/KDEC/KCMI late this afternoon into the early evening. As low
pressure moves across central Illinois, the IFR ceilings are
expected to advect/develop back southward later this evening
through the overnight hours. In addition, with plenty of low-level
moisture in place and winds becoming light/variable in the
vicinity of the low, fog will be a good bet. Have included visbys
down to around 1/2sm at all sites accordingly. May see scattered
showers/thunder re-develop late this afternoon/evening as per
latest HRRR/NAM guidance, so have included VCTS at all terminals
between 22z and 04z.

&&

.ILX Watches/Warnings/Advisories...
NONE.
&&

$$

UPDATE...Barnes
SHORT TERM...BAK
LONG TERM...Geelhart
AVIATION...Barnes



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