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Area forecast discussion 
National Weather Service Lincoln Illinois
328 am CDT Monday Jul 6 2015

Short term...(today)
issued at 328 am CDT Monday Jul 6 2015

Cold front currently extending from Minnesota to western Kansas will
approach from the northwest today...reaching the Mississippi River
by early evening. Models continue to suggest most of the associated
convection will be immediately along/behind the boundary with very
little occurring ahead of the front in the warm sector. Low to middle
70s dewpoints will advect into the area on southwesterly winds of 10
to 15 miles per hour...resulting in afternoon SBCAPE values of 2500 to
3500j/kg. Despite the strong instability...wind fields aloft will
remain quite weak as shown by meager 0-6km bulk shear of only 15 to
20 knots. Several high-res models are showing isolated convection
developing ahead of the front across the western kilx County Warning Area this
afternoon...as well as along the remnants of an old frontal boundary
lifting northward from southern Illinois. Have therefore included
slight chance probability of precipitation along/southwest of a Henry...to Lincoln...to
Olney line during the middle and late afternoon. Due to ample sunshine
and southwesterly winds...high temperatures will climb into the
upper 80s to around 90 degrees.

&&

Long term...(tonight through sunday)
issued at 328 am CDT Monday Jul 6 2015

00z July 6 models are in relatively good agreement with frontal passage
tonight into Tuesday...although the NAM is now about 6-12 hours
slower than the GFS/Gem/ECMWF. Have therefore ignored the NAM as a
slow outlier in favor of the model consensus. Front will reach the
I-55 corridor by 12z Tuesday...then will settle south of I-70 by Tuesday
evening. With front arriving after dark...daytime instability will
be waning...so severe weather risk appears minimal. Latest day 1
convective outlook from Storm Prediction Center places areas northwest of the Illinois
River in a slight risk...with the main threat being strong wind
gusts. Given precipitable water values climbing to around 2 inches
and overall slow storm movement...greatest threat may actually be
localized flash flooding from the stronger storms across the western
kilx County Warning Area during the evening hours. Several high-res models are
suggesting the storms will steadily dissipate as they push eastward
overnight...so think the window of opportunity for possible severe
weather/flash flooding will be small. Have therefore adjusted probability of precipitation
to feature categorical in the Illinois River valley...tapering down
to chance along/east of the I-57 corridor.

As has been the case for the past several model runs...it appears
the front will sink far enough south to give the northern County Warning Area a
break in precipitation chances Tuesday afternoon and night. In fact...if
the 00z European model (ecmwf) verifies...nearly the entire area may be dry Tuesday
night. At this point...think front will stall along the Ohio River
as it becomes parallel to the upper-level flow late Tuesday. As
such...will continue rain chances across the southern two-thirds of
the County Warning Area...with dry conditions developing along/north of a Canton to
Minonk line Tuesday afternoon and night. Wave of low pressure will
develop over northern Texas along the trailing end of the front on
Tuesday...then will track northeastward across central Illinois
Wednesday night. As the low approaches...the front will lift back
northward and rain will overspread the entire area. Have raised
probability of precipitation to likely Wednesday and Wednesday night...during which time
locally heavy rainfall will be likely. Will have to keep an eye on
the track of the low and the expected quantitative precipitation forecast...as a Flash Flood Watch
may be needed across parts of the area.

Once the wave passes to the northeast...forcing for additional
precipitation will diminish on Thursday. However...with the frontal
boundary remaining in the vicinity...chance probability of precipitation will continue to be
warranted. Another upper-level wave will track along the persistent
boundary Thursday night into Friday morning...bringing another round
of showers and thunderstorms mainly to the northern half of the County Warning Area
at that time.

After that...models have come into better agreement with the
evolving upper-level pattern late this week into early next week.
All solutions show the southeast Continental U.S. Upper ridge gradually
shifting westward and establishing itself over the Desert Southwest
by early next week. As the ridge transitions westward across the
area...upper heights will temporarily rise Friday through
Sunday...pushing the main storm track northward into the upper
Midwest and Great Lakes. As a result...am expecting hot and dry
weather Saturday and Sunday. As the ridge shifts further west...a
deep trough will dig downstream across the Great Lakes/Midwest
next week. Both the GFS and European model (ecmwf) show a corresponding cold front
dropping into the area by Monday...bringing the next chance for
rain and markedly cooler weather.

&&

Aviation...(for the 06z tafs through 06z Monday night)
issued at 1105 PM CDT sun Jul 5 2015

Will have the potential for a brief period of MVFR visibilities in fog/haze
in the 09z-12z time frame overnight...otherwise...VFR conditions
are expected through this forecast period. After that...the threat
for scattered showers and thunderstorms will increase from west to
east Monday night along a cold front. Coverage still in question
with several convective allowing models suggesting some isolated
storms developing after 20z over parts of central Illinois well
ahead of the main cluster of storms along the cold front to our
west. At this point will continue with thunderstorms in the vicinity aftr 20z at pia and
spi and hold off at the other sites for now. We will see some
scattered cumulus develop again late tomorrow morning into the
afternoon hours with bases of 3000-4000 feet. Surface winds will
be from a light southeast direction tonight and then pick up in
speed from the south on Monday with speeds in the 10 to 15 knots
range by afternoon with gusts around 20 kts at times...especially
during the afternoon. South winds of 10 to 15 kts are expected
tomorrow evening.



&&

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

$$

Short term...Barnes
long term...Barnes
aviation...Smith

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