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Area forecast discussion 
National Weather Service Lincoln Illinois
1144 PM CDT Thu Sep 18 2014

issued at 859 PM CDT Thursday Sep 18 2014

Surface high pressure centered northeast of Lake Huron will
continue to shift southeastward across New England over the next
day pushing light dry east to southeast surface winds
through central Illinois. As a result, there will be few or no
clouds, just a few cumulus buildups in the late morning and
afternoon. Comparison of surface dewpoints with forecast lows
tonight indicates fog will be possible overnight, however steady
light winds will mitigate formation in most areas. Best locations
for fog formation still appear to be along the Illinois River and
perhaps the Wabash River so have made minor updates to forecast to
target these areas for fog overnight. Otherwise, forecast of lows
in the upper 40s to near 50 still looks good and no further
updates needed this evening.


Short term...(tonight)
issued at 248 PM CDT Thursday Sep 18 2014

1026 mb Canadian high pressure just north of Michigan will settle southeast
into New England by midday Friday. Aloft, northwest flow persists,
with any active short waves in the near term expected to stay south
of the forecast area. A few cumulus clouds especially in our SW County Warning Area
this afternoon will dissipate at Sundown leaving clear skies
tonight and east winds will become light again near 5 mph after
sunset. Patchy shallow ground fog to develop again overnight
especially near rivers like the Illinois River and lift by mid Friday
morning. Fog should be more limited than the past 2 nights with
wind speeds a bit higher. Similar mav/met guidance lows in the
upper 40s to near 50f looks on track with some mid 40s in parts of
east central Illinois where dewpoints currently in low to mid 40s.


Long term...(friday through thursday)
issued at 248 PM CDT Thursday Sep 18 2014

High pressure centered over the Great Lakes will continue to provide
dry conditions all the way back into Illinois through early Saturday
morning. Warmer conditions are expected for Friday as southerly
winds develop behind the departing high pressure. The thermal ridge
in the 850-700 mb layer will initially surge northward into Iowa
and SW Wisconsin, before sliding east into Illinois for Saturday.
That will result in highs reaching the upper 70s on Friday and
lower 80s on Saturday.

The 12z model suite continues to show a cold frontal passage on
Saturday afternoon into Sat night. We still expect a dry morning on
Saturday with storms erupting during the afternoon, mainly northwest
of I-55 through 6 PM. Instability parameters continue to look
favorable for thunderstorm development, especially during the
daylight hours northwest of Lincoln. Storm Prediction Center has only a 5% risk for severe in
that area, and no widespread severe weather is anticipated. The main
threat would be for strong wind gusts with the deeper convection.

As the front progresses to the southeast Sat evening, storm chances will
expand to I-70 through midnight, then southeast of I-70 after midnight.
Depending on how much the front slows down Saturday night, we could
see a few showers/storms lingering mainly southeast of I-70 Sunday morning.

Beyond that, high pressure will return to dominate the weather from
Monday through at least midweek and possibly the rest of the week.
Dry and cooler than normal conditions will be the rule during that
period. A warming trend could begin on Thursday, as highs climb
into the mid to upper 70s again.


Aviation...(for the 06z tafs through 06z Friday night)
issued at 1144 PM CDT Thursday Sep 18 2014

Mainly VFR conditions are expected for the next 24 hours across
central IL, although local IFR/MVFR visibilities in patchy shallow
fog are possible until around 12z. Fog most likely along River
Valley areas, including kpia. Clear skies expected except for
few-sct040 from 15z-23z. Winds e3-7 kts veering to S-se7-12 kts
after 14z.


Ilx watches/warnings/advisories...


short term...07
long term...shimon

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