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Area forecast discussion 
National Weather Service Lincoln Illinois
1150 PM CDT Sat Oct 3 2015

issued at 905 PM CDT Sat Oct 3 2015

Showers and/or drizzle has been progressing westward into
Illinois. Radar returns and spotter reports confirm drizzle to be
the primary precip type so far this evening, especially along I-55
at 02z. Have added drizzle to the weather grids for the remainder
of the night. Also kept 20 pops going east of the Illinois River as
moderate drizzle was reported at times, which could result in
measurable rainfall.

A blanket of low clouds will minimize the diurnal temp fall the
rest of the night. Temps have already dipped into the upper 40s in
several eastern locations, so will trim a couple degrees there,
and possibly a degree or so farther west.

Northeast wind gusts should diminish after 03z, but sustained
winds will remain 10-16kt the rest of the night.

Updated forecast info will be available shortly.


Short term...(tonight)
issued at 205 PM CDT Sat Oct 3 2015

The long time influence of high pressure has lost ground to the
upper low over the southeastern US, and clouds and low level
moisture are edging into central Illinois throughout today. The
same trend will continue overnight with northeasterly winds. Some
of the gusts will dwindle with decoupling, but the increasing
pressure gradient will keep the sustained winds up. Persistent
cloud cover tonight will keep the temps up a degree or two above
last nights lows. In addition, the enhanced llvl moisture could
result in some light rain, particularly in the extreme east. Not
particularly impressed with the models, as the NAM is even drying
out, but the sprinkles and light rain from this morning were not
previously handled well either in a previously drier air mass.

Long term...(sunday through saturday)
issued at 205 PM CDT Sat Oct 3 2015

Illinois remains in the col between the weakening southeast upper
low and the northern stream for a few more days at mid-levels.
Influence of the low and related strong surface gradient should
diminish early in the week with shortwave ridging developing and
warming temps as 850 temps climb into the double digits c by
Sunday evening and then remain there through at least mid-week.
Models are in reasonable agreement with weakening flow throughout
the atmosphere through Tuesday and should provide generally dry
and slightly above normal temps.

Differences become apparent by Wednesday with the focus on the
amount of phasing between deepening cutoff over Desert Southwest and
the faster northern stream. European model (ecmwf) (00z) kept energy separate and
even retrogrades the upper low back into the Gulf of California by
the end of the week. On the other hand the GFS (06z) kept the
energy moving eastward until it is absorbed back into the northern
flow through a strong shortwave toward the end of the week.
Although there is some spread in the gefs with the upper low
movement, most members are east of the European model (ecmwf) position. The 12z
version of both models are trending toward middle ground. Even
though GFS still has more phasing the overall pattern is much more
in sync.

Implications of the difference are the speed and strength of
northern stream waves - the first of which begins to impact the area
Wednesday night and Thursday. With more phasing, the GFS is slower
and stronger with this initial wave while the European model (ecmwf) progressively
moves it to the mid-Atlantic region by Friday.

Given the better performance of the European model (ecmwf) with the current southeast
U.S. Upper low and the propensity of the atmosphere to cutoff
recently will lean toward the European model (ecmwf) solution this package. This
faster and weaker evolution of the northern stream will likely lead
to weaker warm air advection ahead of the mid-week system and will be undercutting
mex guidance a tad.

Even though the European model (ecmwf) does bring in next wave on Saturday, moisture
appears to be mostly shunted east along the Atlantic Seaboard. The
GFS is strong enough with this next wave to tap some Gulf moisture.
Given the differences evident in model forecasts, will leave
mentionable pops out of Saturday for now.


Aviation...(for the 06z tafs through 06z Sunday night)
issued at 1150 PM CDT Sat Oct 3 2015

IFR cloud ceilings are gradually progressing westward into
Illinois, with IFR conditions already at cmi and near bmi/Dec. Radar
trends have shown a decrease in coverage of precip in the last
couple hours, but a transition to drizzle may be occurring as LCLs
lower. Satellite images indicate we should expect the warm
conveyor belt to continue to funnel a stream of moisture up the
isentropic surfaces the rest of the night and into Sunday morning.
Precip chances will be lower farther west, based on the projected
westward progression of the upper trough. Therefore, have not
included vcsh/-dz in the pia taf. IFR conditions should improve to
MVFR later Sunday morning, with VFR conditions possible after 21z
starting in near the eastern terminal sites.

Northeast wind gusts have generally subsided, but sustained
speeds of 09-15kt will continue overnight. A relaxed surface
pressure gradient will finally develop tomorrow, helping to calm
down the very breezy conditions of the last 4-5 days. Wind
direction will remain northeast, but speeds should remain in the
9-12kt range.


Ilx watches/warnings/advisories...


short term...hjs
long term...Barker

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