Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus63 kilx 211800 
afdilx

Area forecast discussion
National Weather Service Lincoln Illinois
1200 PM CST Thu Nov 21 2019

Synopsis...
issued at 305 am CST Thu Nov 21 2019

Occasional rain showers associated with a deep low lifting across
the upper Midwest will be in place today, along with windy but
otherwise mild conditions. Winds are expected to gust into the 30
to 40 mph range at times today, with a few sporadic higher gusts
possible, especially early in the day. Precip chances will
diminish behind a cold front that will sweep across central
Illinois this afternoon and evening. Temperatures will top out in
the upper 50s to near 60 today, then fall back into the upper 20s
and 30s tonight. Some showers will linger over portions of east
central and southeast Illinois Friday, but much of central
Illinois will be dry. Temperatures will be cooler Friday with
highs only in the low to mid 40s.

&&

Update...
issued at 1120 am CST Thu Nov 21 2019

The cold front is progressing quickly across the area, and is
producing very limited additional precipitation. While instability
may have been present earlier this morning west of our area, it
was not enough to generate thunder then and is not expected to be
sufficient for any thunder this afternoon. Storm Prediction Center also removed the
general thunder from our cwa, so we have removed any mention of
thunder from our grids the rest of today.

Have lowered the coverage and level of pops for rain the rest of
today into this evening in general. Chances will still be present,
but mainly east of I-55 early this afternoon, diminishing in area
to mainly south of I-72/Danville by mid-afternoon and south of
I-70 by this evening.

The strong winds have been remaining below advisory criteria, and
that should continue this afternoon, based on forecast soundings
and expected momentum Transfer.

Updates this morning were mainly to the pop/wx/thunder forecasts.
Temps look on track, as well as the remainder of the forecast
database.

&&

Short term...(today and tonight)
issued at 305 am CST Thu Nov 21 2019

Early this morning, low pressure is centered just northwest of Des
Moines, Iowa with a broad corridor of strong warm advection set up
across the middle and upper Mississippi Valley. Kilx vwp indicates
50-55 kt winds are in place as low as 2000-3000 ft this morning
helping to transport an unseasonably moist and warm air mass over
the region. The 00z sgf raob indicated pwats in excess of an inch
upstream of US Wednesday evening. The more persistent mid level
moisture convergence will remain focused across northern Illinois
into Wisconsin where the heaviest precip should occur. Meanwhile,
water vapor imagery reveals mid level dry slot wrapping around
the back of the low which poised to wrap across central Illinois
through the morning. This should allow the more broadly occurring
precip shield moving across the area during the predawn hours to
become spotty and more showery as we head into the mid/late
morning and afternoon. Meanwhile, there are currently
thunderstorms occurring across eastern Kansas where the trailing cold
front is located, and near term guidance does continue to indicate
weak MUCAPE values overspreading central Illinois today, so will
keep at least a slight chance mention for thunderstorms. Quarter
to half inch of rain is expected today with some locally higher
amounts where any heavier showers or storms develop.

As mentioned, strong winds aloft are already in place this
morning. Soundings indicate fairly stable conditions near the
surface with the strong mid level warm advection resulting in a
sharp low level inversion. With cloud cover and precip, do not
anticipate mixing to develop ahead of the cold front today, but
still could be some downward momentum Transfer of the higher
winds aloft, especially due to showers. Dvn recently reported 47
mph wind gust as showers overspread the area. Do think a sporadic
few gusts in excess of 45 mph (wind advisory criteria) are
possible, but not sure they'll be prevalent enough to warrant a
Wind Advisory at this time. Meanwhile, mixing does ramp up behind
the cold front as it passes across central Illinois this
afternoon, but models continue to indicate that winds will fairly
quickly diminish behind the front, at least in terms of the
potential for for reaching advisory criteria.

The cold front is progged to pass southeast across the I-70
corridor this evening with dry weather and diminishing winds
spreading in from the northwest. The front does stall near the
Ohio Valley tonight into Friday and waves back north slightly as a
shortwave trough digs across the Midwest tonight. This may result
in some lingering precip mainly along and south of I-70 tonight
into early Friday before precip finally shifts out of the
forecast area entirely behind the shortwave Friday afternoon. The
remainder of Friday should be dry as high pressure builds across
the Midwest. Temperatures will be quite a bit cooler behind the
front, though, with afternoon highs only in the low to mid 40s.

Long term...(friday through wednesday)
issued at 305 am CST Thu Nov 21 2019

As we head into the weekend, models depict a few distinct
shortwaves across the Great Plains and Canadian prairies
Saturday, with varying degrees of interaction indicated by the
models resulting in modest differences in their evolution. The
stronger southernmost wave/closed 500mb low is progged to lift
northeast along the baroclinic zone this weekend with surface low
developing and lifting across portions of the Tennessee and Ohio
valleys. Latest runs of the GFS and European model (ecmwf) indicate that precip on
the left quadrant of this system will impact portions of the local
area. Given the general expected low track, it's possible for
some light snow accumulations to occur in central and east central
Illinois, though a number of details still need to be worked out.

This wave should quickly move through with dry weather back in
place Saturday evening into early next week. Very large
differences between models take hold thereafter, and the forecast
for much of next week contains slight chance and low chance pops
owing to this uncertainty. A couple lows are progged to develop
and move across the region next week, however, given model
differences and poor run to run continuity, confidence in any
details is very low.

&&

Aviation...(for the 18z tafs through 18z Friday afternoon)
issued at 100 PM CST Thu Nov 21 2019

Aviation concerns will initially be tied to gusty southwest winds
and changing wind direction with the cold fropa, as well as
IFR/MVFR clouds. The cold front has reached near I-55 as of 18z,
and will progress quickly past the remaining taf sites. Winds will
be on a steady shift from SW toward northwest this afternoon, with wind
speeds remaining in the 15g30kt range throughout the process.

Forecast soundings are pointing toward any lingering IFR ceilings
improving to MVFR by 20z at all terminal sites. Satellite images
show an expansive area of MVFR clouds extending back to the west and
NW, so clearing to VFR will likely be delayed until after 06z
tonight, if not more toward sunrise on Friday.

&&

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

$$

Update...shimon

National Weather Service Glossary of Abbreviations