Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 240321
AFDILX

Area Forecast Discussion
NATIONAL WEATHER SERVICE LINCOLN IL
921 PM CST Fri Jan 23 2015

.UPDATE...
ISSUED AT 917 PM CST FRI JAN 23 2015
Weak surface ridge and mostly clear skies slowly giving way to
some AC moving across the Midwest from the northwest. Forecast on
track as some warmer air advects into the region. No major updates
to the forecast anticipated other than some small adjustments to
the hourly grids.

&&

.SHORT TERM...(Tonight)
ISSUED AT 247 PM CST FRI JAN 23 2015

Clearing line from the morning stratocumulus deck was unable to make
any further eastward progress, so the clouds decided to dissolve in
place instead. 2 pm visible satellite imagery showing most areas
west of I-55 now mostly sunny, with the clouds rapidly eroding on
the western flank of what`s left. The clear skies won`t last too
long though, as mid-level cloud deck ahead of the next frontal
boundary is already in southeast Iowa. The boundary itself is still
back across eastern Nebraska through the Minneapolis area, and will
be moving through our forecast area between midnight and sunrise.
However, no precipitation is expected with it. Lows across the
forecast area should fall into the upper 20s.

&&

.LONG TERM...(Saturday through Friday)
ISSUED AT 247 PM CST FRI JAN 23 2015

By and large, the forecast period will be dominated by a ridge
west/trof east pattern across North America, a pattern that has been
pretty common of late. The fast moving northwest upper-level flow
that has been over the forecast area has had numerous, mainly weak,
impulses embedded within it traveling over or in our vicinity. Most
of these waves lately, and those expected over the next several
days, have been too weak and/or moisture starved to produce much
precipitation locally. This trend should continue to be the case for
most of the days of this forecast. However, a more significant
clipper system still appears on track to impact the area late
Saturday night into Sunday night. This system is our primary
forecast concern today.

A weak upper/surface trof will move across the area later
tonight/early Saturday, but it is only expected to be accompanied by
an increase in cloud cover. This cloud cover is currently evident
upstream from the Great Lakes into the central Plains.

The timing of the main clipper is pretty well agreed upon, and has
been for a few days now, with the primary precipitation risk
occurring late Saturday night/early Sunday Morning into Sunday
afternoon. However, the track of the system continues to exhibit
considerable model spread, as well as run-to-run variability. The
overall model trend had been toward a more northerly track until
about 24 hours ago, but now the trend is back toward the south. The
northern track would have resulted in minimal precipitation risk for
the forecast area, with the bulk of it falling in the form of rain.
The more southern track, most pronounced in the latest run of the
GFS, would support more widespread precipitation locally, with at
least the northern portion of the forecast area in line for some
accumulating snow. Forecast confidence in the details with this
system remains low considering the variability/inconsistency.
However, given the trends of the past 24 hours, have boosted PoPs
into the Likely category for much of the forecast area on Sunday,
and added some light snow accumulation across the north. If the
models lock into a more southern solution, one that takes the
clipper just south of the forecast area like the current GFS,
temperatures will need to be lowered, PoPs raised, and snow amounts
boosted. For now, will be conservative with the changes until the
ultimate outcome is a little more clear.

For the remainder of the period, mostly quiet weather is expected. A
weak wave is most likely to impact the area Monday and again by
Thursday. However, these disturbances appear too weak to carry
mentionable precipitation at this time. Temperatures through the end
of the next work week should be at or above normal. The coolest
readings are likely Monday/Tuesday behind the main clipper, and
again Friday behind Thursday`s disturbance.

&&

.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
ISSUED AT 554 PM CST FRI JAN 23 2015

Some minor adjustments to the trend to VFR for ILX terminals this
late in the day. As the low clouds pull away... midlevels move in
from the NW. Mid level and southwesterly sfc winds through the
overnight until approach of a boundary/trof will bring back in the
low clouds. Models struggling somewhat in producing signif cloud
cover, although the soundings reflect the moisture. Without the
boundary, may have been a little less pessimistic. For now, will
maintain the BKN MVFR until cloud development/high res models can
offer a different solution. Winds more nwrly behind the boundary
tomorrow.


&&

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

$$

UPDATE...HJS
SHORT TERM...Geelhart
LONG TERM...Bak
AVIATION...HJS





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