Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 260450

Area Forecast Discussion
1150 PM CDT Wed Mar 25 2015


Showers continue to expand overhead and upstream in response to
the arrival of the right entrance region of an upper-level jet
streak over the Great Lakes. These showers should continue to
spread across the forecast area for the next several hours.
Attention also remains focused on the threat for more vigorous
convection impacting the area as low pressure from the central
Plains tracks northeast into the Ohio River Valley. The surface
frontal boundary the low is tracking along is still well to our
south, with the effective boundary generally being pushed even
further south by outflow from storms currently along the front.

While the overall scenario has not changed much from what was
expected earlier today, the latest trends suggest the threat for
thunderstorms and heavy rainfall is mainly to the south of the
forecast area (especially south of central IL). So, have updated
forecast for the expected overnight trends, pushing the thunder
threat further south and reducing the expected rainfall overall.


.SHORT TERM...(Tonight)

18z/1pm surface analysis shows 1007mb low over the Texas panhandle,
with nearly stationary frontal boundary extending northeastward into
the Ohio River Valley.  To the north of the front, another overcast
and cool day is underway across central Illinois with temperatures
hovering in the 40s.  Meanwhile south of the boundary, readings have
risen well into the 70s from the southern tip of Illinois to the
Gulf Coast.  As a vigorous short-wave trough evident on water vapor
imagery over Colorado/New Mexico ejects eastward and interacts with
the low, thunderstorms are expected to become widespread across the
Ozarks this afternoon.  Latest radar mosaic already shows convection
expanding across southern Missouri and expect this trend to continue
over the next several hours.  All models have slowed the northward
progression of precip into the area this evening, with the latest
Rapid Refresh keeping much of the rain W/SW of the KILX CWA until
closer to midnight.  The exception may be the development of a few
scattered showers along an advancing trough axis across the northern
CWA earlier in the evening.  Have adjusted PoPs to account for the
slower arrival of precip, with the best rain chances focused from
late evening through the overnight hours.  Will carry categorical
PoPs along/south of I-72, diminishing to just chance from the Peoria
area northward.  As expected, the 12z Mar 25 models have shifted the
low track a bit further south, now taking it along/just north of the
Ohio River.  This decreases the chance for strong thunderstorms
across the far southern CWA tonight, but keeps the threat for heavy
rainfall alive.  Latest QPF guidance still suggests 1 to 2 inches
of rain along/south of I-70, with higher amounts in excess of 2 inches
further south toward I-64.  Based on upstream convective trends and
the presence of a warm/moist airmass just south of the boundary,
think these amounts seem reasonable.  The heavy rainfall tonight
into Thursday morning will likely result in renewed flooding on many
creeks and streams across southeast Illinois: however, rainfall
rates will not be high enough to produce widespread flash flooding.
As a result, have opted not to issue a Flood Watch across the
southeast, but will instead re-issue the ongoing SPS.


.LONG TERM...(Thursday through Wednesday)

Given the slower approach of the precipitation tonight, it will also
be slower to depart Thursday morning.  Model consensus places the
surface low near Louisville, Kentucky by 12z, with rain continuing
across the E/SE CWA at that time.  Have bumped PoPs up to likely
along/south of I-70 through mid-morning accordingly.  As the low
pulls further away, showers will come to an end by midday followed
by clearing skies from west to east during the afternoon.  High
temperatures will once again be on the cool side, mainly reaching
the middle to upper 40s.

The cool/dry weather pattern will continue through Saturday as a
deep upper trough develops over the Great Lakes.  Numerous weak
waves will drop through the region within the prevailing
northwesterly flow regime Thursday night through Saturday: however,
none of them will significantly impact the weather across central
Illinois.  The first feature is expected to track across Missouri
Thursday night, while a second wave will follow a similar path
Friday night into early Saturday.  End result will be dry conditions
with much below normal temps in the 40s both Friday and

A weak frontal boundary will swing through the Midwest on Sunday,
bringing clouds and perhaps a few showers.  Moisture will be
limited, so will only include low chance PoPs at this time.  After
that, the Great Lakes upper low will gradually shift eastward,
allowing a ridge to build across the central CONUS.  Rising upper
level heights will lead to a pronounced warming trend, with
temperatures returning to the 60s by Tuesday.


.AVIATION...(For the 06Z TAFS through 06Z Thursday night)

Showers have been across most of the central Illinois terminals
for much of the evening, except KPIA and until very recently KBMI.
The rainfall has been lighter than anticipated, and this has
helped hold conditions generally in the VFR or MVFR category. While
CIGS/VSBYS could degrade a bit more over the next few hours until
the rain pulls out, kept conditions pretty steady through the
night. Then, have VFR conditions area wide after sunrise Thursday
morning. Northwesterly winds should prevail through the period,
becoming gusty at times during the daytime hours Thursday.




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