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Area forecast discussion 
National Weather Service Lincoln Illinois
858 PM CDT sun Jul 5 2015

issued at 852 PM CDT sun Jul 5 2015

High pressure continues to dominate the weather over our area this
evening and should keep the weather quiet around here through most of
the day on Monday. Still may see some patchy fog/haze late tonight
but whatever does form should quickly dissipate by 7 or 8 am.
Based on 850 temperature forecasts tomorrow afternoon and a gusty south
wind...we should see afternoon temperatures warm some 3 to 6
degrees from what we had today...resulting in highs in the
86 to 90 degree range accompanied by dew points in the low to
middle 70s. That pushes the heat index into the middle to upper 90s
tomorrow afternoon.

A weak frontal boundary located over parts of southern Missouri
combined with an upper level wave to produce some scattered storms
late this afternoon which since have decreased in areal coverage
early this evening. Although this frontal boundary is expected to
wash out later tonight...there may be just enough convergence
along it tomorrow afternoon to combine with moderate instability
to produce some widely scattered storms. However...a larger band
of showers and storms will form along a cold front late tomorrow
afternoon over central Iowa and then track east into western Illinois by
tomorrow evening bringing a better threat for more widespread
shower and thunderstorm activity over the forecast area Monday
night into Tuesday morning.

Current forecast in good shape this other than the
usual tweaks to the early evening other changes
were needed that would warrant a zone forecast product update.


Short term...(tonight)
issued at 302 PM CDT sun Jul 5 2015

Weak high pressure will continue to drift away from the area tonight
as our next frontal system...currently over the western Dakotas...
tracks east into the Midwest late Monday. The extensive cumulus
field should dissipate quickly late this afternoon/early this
evening leaving a mostly clear sky overnight. That combined with a
light wind and abundant low level moisture should lead to some
patchy ground fog across the east and southeast late tonight
although forecast soundings are not as aggressive with the shallow
moisture just off the surface as they have been over the past few
nights...probably due to some decent mixing occurring this afternoon.

Long term...(monday through sunday)
issued at 302 PM CDT sun Jul 5 2015

Cold front slated to press southeast across Iowa during the day Monday and
bring a chance of showers and thunderstorms to the Illinois River valley
by late Monday afternoon. Cold front then spreads southeast across northwest Illinois
Monday evening and reaching near I-55 by 12z/7 am Tuesday likely
spreading showers and thunderstorms southeast into central Illinois Monday night.
The Wabash River valley and areas near the Indiana border may stay
dry most of Monday night. Storm Prediction Center has marginal risk of severe storms northwest
of I-55 late Monday afternoon and Monday evening with slight risk of
severe from Galesburg northwest. Very unstable airmass with convective available potential energy peaking
by late Monday afternoon from 2-4k j/kg though weaker bulk shear of 15-
25 kts. Main severe weather threat will be damaging wind gusts. Also
heavy rain threat Monday night into Tuesday with precipitable water
values near or just above 2 inches.

Cold front pushes into southeast Illinois Tuesday afternoon shifting likely chances
of showers and thunderstorms into areas south of I-72. Storm Prediction Center has
marginal risk of severe southeast of I-70 Tuesday afternoon for thunderstorms
with gusty winds along with heavy rains. Very warm highs in upper
80s to near 90f Monday with humid dewpoints in the lower 70s by Monday
afternoon giving heat indices peaking Monday afternoon in middle to upper
90s. Cooler highs Tuesday in middle to upper 70s central Illinois and lower 80s
southeast of I-70.

Frontal boundary to temporarily stall in southern Illinois just south of
County Warning Area Tuesday night with surface wave ridging along the boundary and
bringing quantitative precipitation forecast back north into southern half of County Warning Area Tuesday night and
across area Wednesday and Wednesday night along with chances of heavy rains

12z medium and extended range forecast models show upper level ridge
over the southeast states during midweek that gradually retrogrades
westward into the High Plains by early next week. This develops an
upper level trough over the the Great Lakes and bring short wave
disturbances southeast into Illinois that interacts with seasonably warm/humid
tropical airmass (dewpoints in upper 60s/lower 70s) to bring daily
chances of showers and thunderstorms from Thursday through Sunday of next
weekend as a frontal boundary meanders across the region. Heavy
rains will be possible in tropical airmass in place over central/southeast
Illinois. Highs in the upper 70s and lower 80s Thursday climb into the low to
middle 80s Friday and middle to upper 80s next weekend. Lows will be close to
dewpoints in the middle 60s to lower 70s.


Aviation...(for the 00z tafs through 00z Monday evening)
issued at 600 PM CDT sun Jul 5 2015

Except for the possibility for a few hours of MVFR visibilities in the
10z-12z time frame due to fog/hz...VFR conditions are expected
through this forecast period.

High pressure will drift slowly away from out area allowing
southerly winds to gradually increase over our area...especially
on Monday. A cold front will settle southeast into the Midwest
late Monday/Monday night bringing a band of showers and storms
close to the Mississippi River by 21z Monday. It appears most
of that activity will remain west of the taf sites so with this
forecast issuance...will only include a thunderstorms in the vicinity at pia aftr 21z with
most of the activity expected to hold off until aftr 00z. Surface
winds will be south-southeast at less than 10 kts tonight and then increase
from the south to between 10 and 15 kts with gusts around 20 kts
by afternoon.


Ilx watches/warnings/advisories...


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

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