Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Lincoln Illinois
844 PM CST Fri Nov 28 2014

Update...
issued at 844 PM CST Friday Nov 28 2014

A warm frontal boundary has pushed north of the central Illinois
forecast area with central Illinois now in a region of relatively
mild temperatures in the 30s and steady south winds around 10-15
mph. With still milder temperatures to the south, not expecting
temperatures to drop much overnight. Forecast soundings indicate
saturated conditions below 3000 feet elevation below a deep
temperature inversion, so hazy conditions and patchy fog remain a
possibility mainly Galesburg to Robinson southward where snowmelt
has been most pronounced. Current forecast package is on track
with these features and no significant updates are planned this
evening.

&&

Short term...(tonight)
issued at 310 PM CST Friday Nov 28 2014

Southerly winds gusting over 30 mph at times this afternoon, as
35-40 knot winds around 3000 feet (per radar wind profile) get mixed
down to the surface. This has helped erode much of the snow cover,
with visible satellite imagery showing much of the remaining snow in
areas from Rushville to Jacksonville southeast to Effingham.
Temperatures have reached the upper 30s over most of the forecast
area with some 40s across the far southwest as the snow disappears.

Mid and high clouds continue to stream southeast along the warm
frontal boundary, which was stretching from northwest Iowa across
northern Illinois and central Indiana. Will continue to see periods
of clouds through the night over our area. Despite winds staying up
during the night, have added some patchy fog to the forecast for
tonight due to the snow melt, as forecast soundings are showing a
good inversion around 2000 feet to trap the moisture in place.
Temperatures expected to fall only modestly this evening and then
level off most of the night, as south-southwest low level jet around
925 mb starts to ramp up. Consequently, lows should remain above
freezing.

&&

Long term...(saturday through friday)
issued at 310 PM CST Friday Nov 28 2014

Saturday will see another round of gusty south winds bringing warmer
air into the region. 850mb temps are projected to climb into the
12-14c range, which would support highs well into the 50s in dry
mixing conditions. The increasing moisture could lead to increasing
cloudiness, which would temper how warm the surface temps would
climb. The better chances of enhanced lift in the strong waa flows
looks to be in the southeastern half of our forecast area, where
warm frontogenesis will be a bit more focused. With added lift in
that area, will increase cloud cover in the southeast areas, with less
clouds northwest toward gbg. Southeast areas may even see a few sprinkles at
times, which the NAM and GFS are suggesting with their output of quantitative precipitation forecast
on Saturday. Did not introduce any precip with this update, but did
bump up highs a couple degrees above guidance in most areas, with
less increase in the cloudier east-southeast areas. Highs should reach the mid
50 in most areas, with upper 50s in areas with less clouds.

A strong cold front still looks on track for Sunday, with decent
agreement among the models on frontal passage Sunday afternoon. The
increasing SW low level jet ahead of the front across southeast Illinois will aid
the lift in the pre-frontal circulation, triggering scattered
showers mainly east of I-55, especially in the afternoon. High temps
will likely occur before noon in the northwest half of the area, with
strong northwest winds behind the front bringing a sharp cool down the
remainder of the day. Mid-day highs will range from the upper 40s
near gbg to the low-mid 60s near lwv. The 1040mb Canadian high will
blast into Illinois through Sunday night, pushing temps below freezing by
Monday morning. There is some question to if the precipitation will
continue fall after the temps fall below freezing. With a lack of
ice crystals above the shallow surface moisture, any continued
precipitation would most likely reach the ground as freezing
rain/drizzle instead of snow. That could cause some problems for the
morning commute on Monday, mainly along and just south of the I-70
corridor.

The continued surge of cold air on Monday will keep highs mainly in
the 20s, with some low 30s S of I-70. Some light freezing rain or
rain will be possible Monday morning S of I-70, with diminishing
chances in the afternoon as the front sags away to the southeast.

The cold surface high will slide east across the Great Lakes on
Tuesday, allowing a quick return of southerly winds by Tuesday
afternoon. The warming winds should combine with plenty of sunshine
to help most areas climb above freezing. Wednesday could see
increasing mid and high clouds, but highs are still forecast to
reach the upper 30s north of Peoria and low to mid 40s south.

Differences remain the extended forecast for Wed night through
Friday, but not as dramatic as the last few days.
The GFS continues to develop low pressure in the south Central
Plains and moving the low across Illinois in the Wed-thur time frame.
However, now the European model (ecmwf) is showing a shortwave in the general
vicinity, triggering showers about 18-24 hours after the GFS. The
Canadian Gem is also indicating that shortwave in line with the
European model (ecmwf) timing. We have not altered the precip forecast much, with
slight chances Wed night in the west, and chance pops in most areas
thur and thur night. Slight chances were held into Friday southeast of the
Illinois River. Based on temp profiles, we went with snow chances at night
and rain during the day for now, but this will need refining future
model runs arrive.

&&

Aviation...(for the 00z tafs through 00z Saturday evening)
issued at 507 PM CST Friday Nov 28 2014

Mainly VFR conditions expected for the 24 hour taf forecast
period. Main aviation forecast issues include possibility of fog
developing overnight due to pronounced low level moisture and
melting snow, mainly affecting kspi, and low level wind shear
overnight throughout central Illinois. For fog, hrrr model indicating
widespread 6sm vsby which looks reasonable given steady winds
expected overnight. Could be areas MVFR vsby, but generally should
be in VFR category. Have included MVFR cigs at kspi where snow
melt has been most pronounced. Low level wind shear starting around 06z is due to
40 kt SW jet at 2 kft above ground level providing speed and directional shear
from S sfc winds. With wind profile becoming more unidirectional
during daytime hours, ended low level wind shear at 12-13z. Sfc winds generally
s10-15 kts. Gusts 20-25 kts during afternoon hours.



&&

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

$$

Update...Onton
short term...geelhart
long term...shimon
aviation...Onton

National Weather Service Glossary of Abbreviations