Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 191718

Area Forecast Discussion
National Weather Service Lincoln IL
Issued by National Weather Service CHICAGO IL
1218 PM CDT Mon Mar 19 2018

Issued at 1057 AM CDT Mon Mar 19 2018

Only a couple of minor tweaks to going forecast today, namely to
lower cloud coverage for the next couple hours and to raise max
temps by a couple of degrees in a few spots.

Mid-morning satellite imagery depicts a compact short wave feature
over southeast KS/southwest MO, with it`s associated surface low
pressure center analyzed just north of Joplin MO. Extensive cloud
shield was located just upstream of the ILX cwa, with generally
thinner cirrus especially north of I-72. With at least partial
sunshine, temps have warmed quickly into the low-mid 50`s in most
areas as of 11 am, with upper 40`s across the far north in the
Galesburg-Bloomington-Danville areas. Based on current trends, 925
mb temp progs of roughly +5C north to near +7C south this
afternoon, and expectation that thicker opaque cloud cover will
still hold off a few hours, bumped temps just a bit in spots
(largely mid-50`s). Otherwise, remainder of forecast appears on
track with rain spreading across areas mainly south of I-72 later
this afternoon.


.SHORT TERM...(Today and tonight)
ISSUED AT 322 AM CDT Mon Mar 19 2018

Vigorous short-wave trough evident on 07z/2am water vapor imagery
over the Oklahoma panhandle will track eastward today...eventually
spreading rain northward into parts of central Illinois. Latest
radar mosaic shows showers/thunderstorms immediately along/ahead
of the wave across eastern Kansas/Oklahoma, with a band of light
rain likely associated with an upper-level warm front stretching
from Kansas City southeastward to Paducah. This band of rain has
been lifting slowly northward over the past few hours, but has
been gradually dissipating as it encounters dry E/NE boundary
layer flow across Illinois. All high-res model guidance completely
dissipates the band before it can reach the KILX CWA: therefore,
have opted to go with a dry forecast across the board through
midday. As the short-wave and its associated surface low approach,
stronger synoptic lift will support additional showers this
afternoon. Model solutions vary somewhat, but consensus focuses
best rain chances across the SE late this afternoon. Have carried
categorical PoPs along/south of an Effingham to Robinson line
accordingly...with PoPs tapering to just slight chance as far
north as a Paris line. Further north,
dry conditions are expected to prevail through the entire day.
High temperatures will mainly be in the middle 50s, except across
the S/SE where clouds and showers will keep readings in the lower
50s. As surface low pressure tracks into southern Kentucky, light
rain will persist across the southern half of the CWA through the
evening before gradually tapering off overnight. With low
temperatures expected to drop into the upper 20s and lower 30s,
any lingering rain may mix with or change to snow across the far
SE late tonight: however, little or no accumulation will occur.

.LONG TERM...(Tuesday through Sunday)
ISSUED AT 322 AM CDT Mon Mar 19 2018

Additional short-wave energy dropping southeastward out of the
Northern Plains will re-enforce the prevailing upper trough over
the Ohio River Valley and cause secondary cyclogenesis over
eastern Kentucky on Tuesday. This will keep precip chances alive
across southern Indiana and perhaps as far west as southeast
Illinois. While strongest lift and deepest moisture will be
focused further east in closer proximity to the surface low, will
continue to feature low chance PoPs along/south of I-70 through
Tuesday evening. Elsewhere around central Illinois, mostly cloudy
and cool weather is expected with highs only in the lower 40s.
Another cool/dry day will be on tap for Wednesday as high pressure
builds into the region. Despite a good deal of sunshine, highs
will remain below normal for this time of year in the middle 40s.

The Ohio River Valley trough will shift eastward by the end of the
week as weak upper ridging builds into the Midwest. As heights
rise, temperatures will return to near normal in the 50s Thursday
through Sunday. Rain chances will return to the picture as well,
with the 00z Mar 19 models still showing some minor discrepancies
with the next approaching system. All models track a surface low
into the region on Saturday...with the GFS being the furthest
south with the low over southern Illinois by 18z Sat...and the GEM
being furthest north with the low over eastern Iowa. Despite the
N/S spread in track solutions, consensus suggests strongest lift
and best precip chances will develop Friday afternoon through
Saturday afternoon. Main issues arise with potential warm
advection precip well ahead of the system late Thursday into
Friday morning. GFS continues to be aggressive with this precip
while the GEM/ECMWF are going mostly dry. Given presence of
surface ridge extending from southern Canada to the Gulf Coast on
Thursday, deep-layer moisture form the Gulf of Mexico will
essentially be cut off. Therefore, tend to favor the drier
GEM/ECMWF. Will therefore limit PoPs to low chance at best
Thursday night and Friday morning. Once precip begins in earnest
by late Friday through Saturday, the atmosphere will be warm
enough to support all rain. Depending on the exact track of the
low, thunderstorms may be possible as well. Given track
uncertainty, kept thunder out of the forecast until better model
consistency is achieved.


.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1218 PM CDT Mon Mar 19 2018

Primary aviation concern is with gusty east to northeast winds
approaching 30 kts at times this afternoon, and an area of rain
which will spread across areas along/south of an SPI-DEC line.

Mid-high VFR clouds were spreading into central and southern IL
from the west at midday, in association with an area of low
pressure over southwest Missouri. VFR ceilings will lower to the
6000-8000 ft range by late afternoon for SPI and DEC, while
remaining generally above 15 kft for terminals farther north. Rain
will also spread across southern IL during the afternoon, and will
likely come close to the SPI/DEC areas. Dry east-northeast low
level flow will likely result in a sharp cutoff to the rain along
the northern periphery, and at this time have maintained just a
VCSH mention for SPI/DEC, but could foresee potentially having to
add a period of VFR rain at those locations if precip extends
farther north. Rain should pull off to the southeast of SPI/DEC by
mid-late evening.

Otherwise, strong surface pressure falls were developing into
southern IL ahead of the approaching low, helping to tighten up
the pressure gradient and increasing wind speeds. Forecast
soundings support east-northeast sustained speeds in the 15-20 kt
range with gusts 25-30 kt this afternoon and early evening,
gradually decreasing and becoming more northeasterly overnight.
Winds will continue to slowly diminish from the north-northeast
Tuesday morning.




LONG TERM...Barnes
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