Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 231957

Area Forecast Discussion
257 PM CDT Thu Oct 23 2014

.SHORT TERM...(Tonight)

19z/2pm surface analysis shows weak cold front/trough axis extending
from Minnesota to northern Kansas.  Band of clouds and light showers
accompanies this feature from Missouri northeastward into Wisconsin,
although showers have been struggling to spread eastward into the
very dry airmass across Illinois.  Forecast soundings suggest
continued top-down moistening this afternoon and evening as 500mb
trough approaches from the west.  Despite decent lift ahead of the
trough, dry airmass will be the main mitigating factor for
widespread precip development.  Will therefore continue to feature
just slight chance PoPs this evening across all locations north of
the I-70 corridor and across the N/NE KILX CWA overnight.  Rainfall
totals will be quite light, amounting to little more than a couple
hundredths of an inch at best.  Due to the clouds, overnight lows
will be quite a but warmer than in recent nights, with readings
remaining in the middle to upper 40s.  Skies may temporarily clear
along/west of the Illinois River late tonight: however, with light
winds and plenty of surface-based moisture in place, think fog
and/or low clouds will develop toward dawn.  Have therefore included
patchy fog mention across the W/NW overnight.  HRRR suggests
widespread fog and lowest visbys will develop further west
along/west of the Mississippi River.


.LONG TERM...(Friday through Thursday)

Initial forecast challenge will be how quickly the low level
moisture/clouds are able to clear out during the day Friday as
forecast soundings not looking very optimistic, at least thru
the morning hours. However, we do see some drying taking place
in the lower levels of the atmosphere in the wake of the shortwave
by late morning/early afternoon. Will keep the clouds and mention
of early morning fog in for a few hours after sunrise and then
forecast a gradual decrease in clouds from northwest to southeast
during the day. Models continue to bring a weak cold front into
our area late Friday night into Saturday with very little moisture
to work, with so will continue with the dry forecast later Friday
night thru Saturday morning. After that, some very nice weather in
store for the area thru Monday evening as upper level ridging
builds across the center of the country in response to a rather
deep trof pushing across the western U.S.

Models in decent agreement with respect to the magnitude of the
trof forecast to push across our area on Tuesday and the timing
of the cold frontal passage and rain chances ahead of it starting
late Monday night with likely POPs most areas on Tuesday. Before
the rain moves in though, some pleasantly warm weather is in store
for the region this weekend with summer-like temperatures on Monday
thanks to a gusty south to southwest wind. Despite the weak cold
frontal passage on Saturday, temperatures on Sunday will only cool
about 5 degrees most areas, but rise well into the 70s on Monday
afternoon with low 80s possible in the southeast. Rain chances will
increase ahead of the low pressure system late Monday night in the
west and over all of our area on Tuesday as the front sweeps across
the area. Strong dynamics aloft with 0-6km shear values of 40-50
kts and models indicating surface dew points climbing to around 60
just ahead of the front. Will have to monitor for the possibility
for strong to severe storms Tuesday afternoon if the models continue
with the slowing trend with the frontal passage.

Rain chances start to decrease from west to east Tuesday evening in the
wake of the storm system with dry weather expected for the remainder
of the period. Temperatures will cool back closer to where they should
be for the end of October.


.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)

Mid/high clouds continue to spread eastward across central
Illinois early this afternoon, while MVFR ceilings remain further
west along/behind a trough axis extending from eastern Iowa into
northern Missouri. As this feature moves slowly eastward, clouds
will lower later this afternoon into the evening and a few light
showers will be possible. HRRR guidance suggests low clouds will
stay west of the central Illinois terminals until this evening,
with MVFR ceilings arriving at KPIA by 01z then further east to
KCMI by 08z. Based on 12z NAM forecast soundings and latest HRRR,
think clearing late tonight into Friday morning will be much
slower than previously expected. While skies may temporarily clear
along/west of the Illinois late tonight, light winds/ample low-level
moisture will lead to fog and low cloud re-development. End result
will be overcast conditions until mid-morning Friday at the earliest.




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