Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 160508
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
1208 AM CDT Sat Sep 16 2017

.UPDATE...
Issued at 840 PM CDT Fri Sep 15 2017

Another unseasonably warm day across the region with afternoon
highs ranging from the upper 80s to lower 90s, with Springfield
the hot spot at 92 degrees. Latest surface analysis indicates
a fairly expansive area of high pressure over the eastern U.S.
while the closest frontal boundary was located west of the
Missouri River this evening. Model data suggests a 40-50 kt
low level jet will set up over eastern Nebraska through south
central Minnesota overnight accompanied by some decent 850 mb
theta-e advection supporting scattered convection, which should
translate northeast overnight staying well west of our area.

The boundary should edge further east on Saturday with a repeat
performance with the showers and thunderstorms, although the
initiation zone will be further east into Iowa and parts of
northwest Missouri Saturday night. Some of that activity may
approach far western Illinois by Sunday morning as the cool front
inches its way towards the Mississippi River. Until then, little
change in our area with the unseasonably warm weather expected to
hold through the weekend with widely scattered to scattered
showers and storms possible Sunday as the weakening front settles
slowly southeast across the state.

Other than the usual evening tweaks to the hourly temperatures,
the remainder of the forecast/grids are in great shape, as a
result, no ZFP update will be needed at this time.

&&

.SHORT TERM...(This evening through Saturday)
ISSUED AT 250 PM CDT Fri Sep 15 2017

In the short range, unseasonably warm temperatures around 10
degrees above normal will continue in central and eastern IL
through Saturday...as well as into much of next week. With high
pressure well to our east, and an approaching low pressure system
from the High Plains, a southerly wind flow will increase the next
24 hours. The warm air has already made it here, but moisture will
gradually increase along with a continuation of warm temperatures.

We should have another night of patchy, light fog across southeast
and parts of east central IL with light winds and residual low
level moisture. The rest of the area will be clear with
temperatures in the lower 60s.

As the day progresses on Saturday we will see a gradual increase
in clouds as mid/upper level moisture approaches west central, and
then central IL. Despite an increase in afternoon cloud cover,
temperatures are expected to be similar to today`s readings around
90 degrees in most locations.

.LONG TERM...(Saturday night through Friday)
ISSUED AT 250 PM CDT Fri Sep 15 2017

Overall, the upper level pattern will be largely unchanged through
the long term forecast period due to the influence of Tropical
Storm (soon to be Hurricane) Jose moving across the western
Atlantic in the vicinity of the east coast. This will keep us in a
generally weak southwest flow. The result will be very persistent,
warmer than normal temperatures and an increasingly unsettled
period as our atmosphere eventually moistens.

Many areas in central and southeast IL have not seen any
appreciable rain for nearly three weeks, so the advancing weather
systems will have some fairly stout, deep dry air to overcome.
However, the persistence of the upper level pattern should take
care of this in central IL during the day Sunday and into
southeast IL Sunday night/Monday.

The first main weather system to move into the area will be a
cold front from the Plains, moving into central IL later in the
day Sunday. This front will make very little progress as it
becomes parallel to the upper level flow. This will result in
periods of showers and thunderstorms across the whole forecast
area from later in the day Sunday through Monday night. The clouds
and periods of showers will minimize high temperatures a bit, but
lower to middle 80s will still prevail.

The front is expected to weaken and wash out Tuesday, resulting in
summerlike, scattered convection into midweek as weak shortwaves
move across the area and interact with the warm and relatively
humid airmass. Later Wednesday and especially Thursday the medium
range models are in fairly good agreement that a mid/upper level
ridge axis will develop near us, which should bring a brief break
in the convection. As the ridge axis passes to our east late in
the week, we end up back in a southwest flow - which also means
additional chances for scattered convection and continued warm
temperatures.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1208 AM CDT Sat Sep 16 2017

VFR conditions expected to prevail the next 24 hours. Scattered
diurnal cumulus should form late morning over most areas, fading
off toward sunset. Late in the period, a cold front will be
approaching from the west, but any effects aside from an increase
in high clouds will be after the end of this TAF period.

&&

.ILX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...Smith
SHORT TERM...Miller
LONG TERM...Miller
AVIATION...Geelhart



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