Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 181758

Area Forecast Discussion
National Weather Service Lincoln IL
1158 AM CST Mon Feb 18 2019

Issued at 1100 AM CST Mon Feb 18 2019

Dry high pressure building southward into Illinois is providing
northern areas with some much needed sunshine. Areas south of
Rushville to Bloomington look to remain cloudy due to a trough of
low pressure slowly drifting south toward southern Illinois. A few
flurries could linger into early afternoon for areas south of
I-70, but even those chances are low.

In northern areas that see clearing today, residual moisture
above the ground in the 3-4K FT layer could be triggered to
produce diurnal cumulus during any heating from the sun. However,
we went more optimistic with the sky forecast update for the rest
of today and this evening. As a result of the additional sunshine,
have added a couple degrees to the high temps across the north.

The remainder of the forecast appears on track. Updated forecast
info is already available.


.SHORT TERM...(Today and tonight)
ISSUED AT 306 AM CST Mon Feb 18 2019

The main impact in the short term period is this mornings
precipitation impacting portions of central and southeast
Illinois. First update to the forecast was upon arrival. I quickly
glanced over short range models and decided HRRR had the best
handle on timing and location. After 4 hours, HRRR still has a
good handle on advancement of light precipitation.

Light snow flurries continue to fall across north central and
portions of central Illinois early this morning, as a system to
the north slowly slides out of the region. Locations impacted by
flurries will include the I-74 and I-72 corridors through 10z.
I-74 will continue to have flurries throughout the early morning
into mid morning before dissipating toward 16-18z. Locations along
and south of the I-70 corridor could experience some slight
freezing drizzle this morning, as temps are holding near freezing.
This is also expected to diminish during the morning. Winds will
continue to shift from the west to northerly today, with the shift
currently along a Macomb to Bloomington line. Temperatures today
and tonight will remain winter-like, as highs will range from the
mid 20s to mid 30s, and lows will drop to the teens to mid 20s.

.LONG TERM...(Tuesday through Sunday)
ISSUED AT 306 AM CST Mon Feb 18 2019

The main focus tonight was on the low pressure system arriving
Tuesday night, lasting through Wednesday. A few dry days will
move into the area mid week and linger through the end of the work
week. More attention will be placed on this weekend as the week
progresses, but for now, I only focused on the first main system
as it will create possible issues across the Midwest.

Collaboration with LSX, it was decided to break the PoPs into 3
hour segments for a better handle of the arrival and exit of this
system. It appears that we were the only offices around that
decided on this route. After analysis of this technique, it was
not necessary to get a handle of this event. However, it was a
great way to see how small differences can make the progress of a
system more understandable.

Model breakdown had a very consistent time line for arrival and
exit of this system. All of the models used (GFS, Fv3, Canadian,
NAM, and ECMWF) had a dry start in our CWA at 00z Wednesday. They
bring the start of precipitation into the area between 03-06z.
There was agreement of the models that freezing rain would occur
on the rain/snow line, especially with a wide swath of FZRA across
much of the Midwest. As the low core moves from southwest to
northeast across the northern half of Illinois, this will allow
freezing rain to slide from south to north overnight Tuesday into
Wednesday morning. Freezing rain is forecast to fall north of
I-70, with the highest amounts along and north of a SPI-BMI line.
Current calculations suggest the possibility of up to 0.15 inches
of ice accumulation, along with a 1 to 2 inch range of snowfall
across the CWA. These numbers bring totals close to advisory
criteria, however at this time no advisory will be issued to
ensure consistency with the 12z run of models. At that time, if
models continue this trend, an advisory could be issued at
forecaster discretion/impact based, as this event could cause
impacts Wednesday morning. This system will move out of the region
Wednesday night, bringing dry weather back to the region to end
the work week.

Another system will arrive during the weekend, but as previously
stated, more attention will be given to it once the Tuesday system
is ongoing.


.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1158 AM CST Mon Feb 18 2019

A trough of low pressure extending from east to west across
central Illinois will keep MVFR clouds over at least our southern
three TAF sites of SPI, DEC and CMI. PIA and BMI should see some
improvement to VFR by mid to late afternoon, as dry air mixes out
the clouds. Diurnal heating will try to create a re-development of
a cumulus field for PIA and BMI, but those clouds should dissipate
into early evening with loss of heating.

The southern half of Illinois looks to remain cloudy throughout
this TAF period, but MVFR ceilings should at least improve to VFR
this evening.

Winds look to remain northwest through tonight, with periodic
speeds of 10-18KT this afternoon. A variable wind is expected
overnight as wind directions drift through the north to northeast
and eventually settle out from the east after sunrise on Tuesday.




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