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Area forecast discussion 
National Weather Service Lincoln Illinois
915 PM CDT Thursday Jul 28 2016

issued at 906 PM CDT Thu Jul 28 2016

Latest short-range model guidance suggests that the bulk of the
shower/storm threat has ended for the forecast area tonight and
into Friday. Given the fact that diurnal instability is weakening,
the weak wave that boosted chances today is now pushing off to the
east, and radar trends are sharply drier in our vicinity, this
seems reasonable. Have updated forecast to go mostly dry into
midday Friday with this thinking in mind.

Other main concern is how extensive low clouds will be across the
area tonight as well as the fog potential. The former could have a
major impact on the latter. While the forecast area is mostly
clear at the moment, satellite loops suggest some low cloud cover
is beginning to bubble up, and this has shown up in a few local
surface observations. Expect this trend will likely continue,
especially across our north (closer to next wave and more
expansive low clouds), although short-range models are less
bullish now on clouds than they were earlier this evening. So,
expecting at least a fair portion of the night will be mostly
clear, and will keep patchy fog going.

Remainder of forecast is in good shape, with only minor tweaks


Short term...(this evening through friday)
issued at 245 PM CDT Thu Jul 28 2016

A cool front moving southeast toward I-55 at mid afternoon will push
into thru eastern Illinois late today and stall out in southeast Illinois
tonight. Had a few reports of funnel clouds over central Illinois since
midday east of the Illinois River, with the most recent report near
Metamora. Isolated to scattered thunderstorms where over much of Illinois
in the tropical airmass over Illinois where dewpoints in the low to mid
70s and temps in the 80s. Most heat index readings were in the
upper 80s and lower 90s, though Springfield had heat index of
98f. Laps convective available potential energy ranged from 1500-3000 j/kg with highest readings
west of I-57. Isolated to scattered thunderstorms will gradually
diminish from west to east during tonight as instability weakens
and front pushes into southeast Illinois. Have patchy fog overnight
until mid morning Friday with light winds and moist low levels.
Hrrr show more widespread fog over eastern Illinois with locally dense
fog possible. Lows overnight range from 65-70f with mildest
readings south of I-70. Highs Friday range from upper 70s NW of Illinois
River, to the mid 80s in southeast Illinois from I-70 south. Another
frontal boundary and a shortwave trof pushing southeast over
central Illinois on Friday to develop chances of thunderstorms and
carried 30-40%. Storm Prediction Center day2 outlook has a marginal risk (5%) along
and south of a Canton to Bloomington line on Friday where
instability will be higher.

Long term...(friday night through thursday)
issued at 245 PM CDT Thu Jul 28 2016

Weak shortwave trof that will affect the area on Friday should start
to shift east of the forecast area Friday night. Still have pops
going Friday night but it appears that most of any convection that
develops during the day Friday will be diurnal in nature and be out
of the area during the evening. After that, the frontal boundary
should push far enough to the south on Saturday to limit the rain
chances to far southern Illinois as weak high pressure settles in
from the northwest. Latest European model (ecmwf) looking drier with this fair
weather system for Saturday and Sunday with the return flow setting
up Sunday night along with pops over southwest Illinois.

Upper level ridging is forecast to build over the region early next
week as a deep trof shifts eastward over the northern rockies. This
should start the heat back up over the area with medium range models
showing varying solutions to how strongly the ridge builds north.
Unfortunately, as has been the case most of this Summer, the ridge
is rather flat and convection has no problem riding the northern
periphery of the ridge and then southeast into the Midwest at least
through the middle portion of the week. This will result in daily
chances for thunderstorms starting Sunday night just ahead of the
warm front, and for the remainder of the period as the model
consensus is rather conservative with any amplification of the
central U.S. Ridge early next week. After our "cool-down" this
weekend, model guidance has most of the area back to or just above
90 Wednesday and Thursday of next week.


Aviation...(for the 00z tafs through 00z Friday evening)
issued at 653 PM CDT Thu Jul 28 2016

A weak cold front will continue to push across central Illinois
tonight, and there will continue to be a low thunderstorm risk
over the next few hours until diurnal instability wanes. Some
guidance suggests significant MVFR/IFR conditions in low
clouds/fog later tonight, but feel this is likely overplayed like
it has been lately. That said, will carry at least a few hours of
MVFR conditions later tonight/early Friday morning. An upper-level
disturbance will bring an additional risk of showers/storms
Friday, but expected coverage and confidence in the details is too
low to carry in terminals at this time.


Ilx watches/warnings/advisories...


short term...07
long term...Smith

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