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Area forecast discussion 
National Weather Service Lincoln Illinois
1140 am CST Wed Nov 26 2014

Update...
issued at 930 am CST Wednesday Nov 26 2014

Vigorous clipper system continues to drop southeast, with the low
center currently over south central Iowa. Radar echoes continue to
fill in across western Illinois, although these so far are mainly
mid level clouds as there was a fair amount of dry air exhibited
on our morning balloon sounding. The column should start
moistening from the top down fairly quickly in west central
Illinois, and light snow should be ongoing over the southwest County Warning Area
by midday. Some of this area is already up to near freezing and
there may be a mix of rain and snow for a couple hours, but this
should trend toward all snow as evaporative cooling takes place.
Further east, it looks like the main time frame for any snow or
mixed precip will be in the afternoon, so have adjusted the
precipitation trends in the grids. Have also adjusted pop's in the
evening to linger them longer across the southwest half of the
forecast area, but the northeast should dry out as northeast winds
bring drier air back in.

&&

Short term...(today)
issued at 320 am CST Wednesday Nov 26 2014

08z/2am surface chart shows 1010mb low centered just north of Omaha,
with light snow observed as far east as the Des Moines area. 00z
Nov 26 models are consistent with prior runs, showing the low
tracking southeastward into northeast Missouri this afternoon, then
into the lower Ohio River valley by evening. Model quantitative precipitation forecast fields have
come into better agreement, now showing a much more compact area of
precip associated with the wave skirting across mainly the west/SW kilx
County Warning Area today. With so much dry air initially in place, think this
makes sense as precip should be confined to locations immediately
along and to the north of the low track where lift is strongest. As
a result, have continued to hit pops hardest along and southwest of
a Macomb...to Taylorville...to Robinson line. Forecast soundings
support snow as the precip begins by mid to late morning: however,
as surface temperatures rise into the middle to upper 30s this
afternoon, the snow will mix with rain. This will serve to mitigate
potential accumulations, which are still expected to be minimal.
Snowfall amounts of one half to one inch can be expected
along/southwest of a Galesburg to Taylorville line. Further
northeast, have opted to go with a dry forecast along/northeast of a
Bloomington to Paris line.

&&

Long term...(tonight through tuesday)
issued at 320 am CST Wednesday Nov 26 2014

Light snow will linger across much of central and southeast Illinois
this evening, as a trough axis extends northwestward from departing
low pressure in the Ohio River valley. A couple tenths of an inch
will be possible south of I-70 in closer proximity to the actual
low, with only trace amounts further northwest. Any light
snow/flurries will come to an end overnight with cloudy skies
persisting through the night. Still some question as to how quickly
skies will clear on Thursday, with the NAM suggesting clouds hanging
around for much of the day. Given what happened with the clearing
trend yesterday and the presence of plenty of lingering low-level
moisture on forecast soundings, have opted to start the day cloudy,
followed by a gradual west-to-east clearing by afternoon. Will be a
much colder day as well, as the departing clipper system taps
into a very chilly air mass over southern Canada. A glancing blow
of this cold air will result in highs ranging from the middle 20s
north to the middle 30s far south.

The cold air will be short-lived however, as high pressure will
quickly shift east of the region and a strong southerly flow will
develop on Friday. Tight pressure gradient will lead to winds
gusting to between 25 and 30 mph at times, which will help boost
afternoon highs into the 40s. Even warmer weather is expected over
the weekend, as digging upper trough over the northern rockies
induces downstream ridging across the central Continental U.S.. with continued
southerly flow and partial sunshine, temps will soar into the lower
to middle 50s on Saturday and may even reach the lower 60s across
the far southeast County Warning Area on Sunday. As the northern rockies wave tracks
eastward along the northern tier of states, it will gradually push a
cold front into the region early next week. There are still some
model discrepancies concerning timing of frontal passage and any potential
pops, with the latest model solutions delaying the front until late
Sunday. Sprawling high pressure along the Gulf Coast will limit
northward moisture return, so think precip chances along/ahead of
the front will be minimal. Will carry low chance pops across the
central/southern zones Sunday, then across the far south Sunday
night. Front settles southward into the Ohio River valley and
another shot of colder air temporarily arrives on Monday with highs
falling back into the 30s and lower 40s. After that, model
solutions diverge as GFS builds another upper ridge across the
central/eastern Continental U.S. On Tuesday/Wednesday while the European model (ecmwf) shows a
more progressive zonal flow continuing. The latest European model (ecmwf) is much
different than its previous run, so am skeptical to jump on this
solution just yet. As a result, will follow the GFS more closely,
resulting in warmer weather for the middle of next week with
increasing rain chances coming into the picture by Wednesday.

&&

Aviation...(for the 18z tafs through 18z Thursday afternoon)
issued at 1140 am CST Wednesday Nov 26 2014

Area of IFR ceilings has been spreading westward this morning and
had reached the kbmi/kdec areas by midday, with slightly higher
ceilings having just spread into kpia. With a large area of higher
clouds spreading in from the west with a clipper system, am not
anticipating any significant improvement in ceilings in these
areas this afternoon. The greatest impact from the clipper will be
around kspi and points west/south, where light snow is expected to
spread in early this afternoon and reduce visibilities to IFR
levels at times. The bulk of the snow with this system will exit
the taf sites by late evening. While some of the soundings hint at
a brief period of VFR ceilings, lower clouds should dominate into
Thursday morning. East/southeast winds will gradually turn
northeast this evening, then northwest overnight, as the clipper
drops southeast along the Mississippi River.

&&

Ilx watches/warnings/advisories...
none.
&&

$$

Update...geelhart/ejl
short term...Barnes
long term...Barnes
aviation...geelhart

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