Area Forecast Discussion
Issued by NWS Central Illinois
FXUS63 KILX 110503
Area Forecast Discussion
National Weather Service Lincoln IL
1203 AM CDT Tue Mar 11 2014
ISSUED 852 PM CDT Mon Mar 10 2014
Will be tweaking grids to reflect falling temps faster than the
forecasted curve. Low temps still in line and no ZFP update will
Light winds have allowed temps to fall quickly this evening.
Periods of clouds will oscillate temperature drop the rest of the
night, but LAV still in line with current forecast for lows.
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 evening.
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.
ISSUED 215 PM CDT Mon Mar 10 2014
SHORT TERM...Tonight through Thursday
One more unseasonably warm day on Tuesday, then a return to winter
Tuesday night into Wednesday with moderate snow accumulations across
Main forecast concern continues to revolve around storm system for
Tuesday night into Wednesday morning and snowfall potential across
the north half of the forecast area. Pleasant weather conditions to
hold over the area thru Tuesday afternoon as a cold front slips south
into our area by morning, setting up a rather tight temperature gradient
from north to south. Warmest readings across the far south with
afternoon temperatures approaching 70 degrees, while north of the front,
temperatures will edge into the lower 50s. Still thinking the precipitation
associated with some frontogenetical forcing north of the front tomorrow
will stay north of our area thru the daylight hours. However, conditions
will start to deteriorate later Tuesday evening, especially after midnight
from northwest to southeast.
Latest operational models have trended a bit further north, except
for the ECMWF which is fairly close to its previous run. The SREF and
12z NAM-WRF has a definite trend north with the surface wave, and as
a result, forecast soundings keeping all but our far northwest areas
in rain or a rain/snow mix thru 06z Wednesday. All models depict some
impressive 700-500 mb omega and steep mid level lapse rates during
the evening with a coupled jet structure setting up over or just
to the east of the forecast area late Tuesday evening. The NAM-WRF
also showing some weak instability associated just to the east and
south of the projected low track, which would increase the thunder
threat over the southern third of the forecast area tomorrow evening.
Further north into the colder air, the signal for any slant-wise or
even upright convective elements is there, but not as evident as we
saw in last night`s runs, but any of these mesoscale features can change
on a dime withe each model run. The message here is the threat does
exist for a brief period of convective snows to the northwest of
the low track but this far out, trying to pin point that in the grids
will be tough. Based on the current track of the surface low, snowfall
will range from 2 to 5 inches with locally higher amounts possible
wherever any convection does occurr after midnight tomorrow night.
The band of moderate snow looks to be mainly north of the Interstate
72 late tomorrow night into Wednesday morning. Grids showing a fairly
tight surface pressure fall and rise couplet noted on the NAM-WRF
associated just to the northwest of the track of the low, so winds
of 30-35 mph will be likely across most of the area later Tuesday
evening through Wednesday morning. Still thinking the snow will be
rather wet, at least initially, so widespread blowing and drifting
should not be a major factor, despite the gusty winds. Based on
the projected speed of the system and forecast soundings keeping
it at least a mix until midnight, will hold off any watch for now,
but will highlight the impacts in our HWO and upcoming SPS.
The snow should be winding down late Wednesday morning over our east
with some lingering flurries or sprinkles in the afternoon along
with a return colder weather. However, as is the case many times
in March, temperatures will vary considerably from day to day and that
will be the case starting Thursday as we warm back up quickly into
the lower 40s east to the low to mid 50s west after a cold morning
where early morning lows dip into the teens to lower 20s.
LONG TERM...Friday through Monday
Temperatures will moderate back to or above normal on Friday into
Saturday as we see the upper low that brought us the snow Wednesday
morning quickly shift well off to our east by Friday. Models indicate
several waves tracking mainly to our north early in this forecast
period with not much in the way of moisture or lift close enough to
our area to warrant POPs at this time. However, a rather strong upper
wave will dig sharply to the southeast later in the weekend and this
feature will have a better tap of moisture with it, as a result, precip
chances return later Saturday night through Sunday. Most of the POPs
will be in the slight chance range as model spread with the late
weekend system is still quite large. Temperatures will start a downward
trend on Saturday to where we will be be below normal again as we
head into early next week.