Area Forecast Discussion
Issued by NWS Central Illinois
FXUS63 KILX 110804
Area Forecast Discussion
National Weather Service Lincoln IL
304 AM CDT Tue Mar 11 2014
ISSUED 803 AM CDT Tue Mar 11 2014
Mild weather has persisted into early morning in many areas, with
above freezing conditions reported over the entire forecast area,
and some temperatures still near 50 degrees over the southeast.
Surface low pressure is organizing over western Kansas, as a
digging upper trough advances eastward across Idaho and Utah. A
warm front arches northeast from the low to around the I-80
corridor in Iowa, then becomes a cold front as it extends
northeast across Lake Michigan.
Main forecast focus is with the snow accumulations and winter
weather headlines for tonight and early Wednesday. Hopefully this
will be the last time we have to worry about this for the season,
but no guarantees given how the winter has gone so far.
SHORT TERM...Today through Thursday:
Initial concern before the snow is with temperatures today. Will
be a rather sharp temperature gradient as the boundary settles
into central Illinois before becoming stationary this afternoon.
Evening model runs converging on the front reaching the I-72
corridor by late afternoon, and areas to the south will likely
enjoy temperatures reaching the lower 70s.
Strengthening surface low will ride east along the front today.
Most of the models are tracking the low across far southern
Illinois, although the NAM is a bit further north, roughly along
the I-70 corridor. Impressive 700-500 mb omega and steepening
lapse rates overspread the area this evening, adding a convective
concern to the precipitation. Indeed, the latest Day1 SPC outlook
does give 5% chances of severe hail/wind across the southern CWA.
Looking at the soundings, transition from rain to snow should take
place late in the evening across the far north, along the I-55
corridor shortly after midnight, and across the southeast CWA late
in the night. Going with a widespread 2-4 inches from I-72
northward, with some 5-6 inch totals possible around Bloomington,
although convection could definitely throw a wrench into these
projections. Will go ahead and issue a winter weather advisory
along I-72 to Danville, then northward, beginning late this
evening and running through midday Wednesday. In addition, winds
will crank up behind the low and gust from 30-40 mph overnight
into early Wednesday. The wet snow may limit the extent of the
blowing snow potential, but will add some patchy blowing snow
where the heavier snow accumulations are expected.
Quick shot of very cold air is on tap Wednesday night, with teens
for lows, but temperatures rebound back into the 40s on Thursday.
LONG TERM...Friday through Monday:
Gradual cooling trend to take place again during this period, as
upper ridge establishes itself along the West Coast, with a
resulting trough pattern over the Great Lakes north to Hudson Bay.
Longer range models having a bit of difficulty phasing periodic
shortwaves over the central U.S., but would generally support dry
conditions until about Sunday afternoon. Upper pattern should
start becoming more progressive early next week, as the western
ridge breaks down.
ISSUED 1201 AM CDT Tue Mar 11 2014
Next storm starting to develop over the high plains this evening
will impact central Illinois terminals by the end of the valid
period. Diffuse cold front over the upper Midwest will sag
southward into Illinois and become more focused late tonight into
Tuesday. The front should remain nearly stationary through the
region prior to low pressure moving in from the plains. Frontal
position tomorrow will have a big impact on wind direction with
gusty northeast flow developing during the day at KPIA and KBMI.
South of the front, I-72 sites should be southerly into the
evening. There is significant uncertainty in the I-72 corridor if
the front were to sag further south as is suggested by 12z ECMWF.
Strong northeast winds will sweep into all terminals during the
Precipitation is expected to develop quickly Tuesday evening with
coupled jet forcing and resultant strong UVV. Frontogenesis will
be significant and there is some potential for convection as well.
Will indicate this potential by introducing SHRA along I-72 during
the evening. Temperature profiles suggest that precip type will
likely remain liquid through 06z with a changeover during the
early morning hours.
CIGs will be a challenge during the evening as MVFR and possibly
IFR CIGs are likely to the north of the front. Will bring in IFR
CIGs at I-55 terminals and KPIA before the end of the TAF period
based on the expected surface low position.
WINTER WEATHER ADVISORY from 9 pm this evening until 1 pm
Wednesday for ILZ027>031-036>038-040>051-053.