Area Forecast Discussion
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FXUS63 KILX 270001

Area Forecast Discussion
601 PM CST Wed Nov 26 2014

.SHORT TERM...(Tonight)

Vigorous Clipper system continues to dive southeast, with the center
northwest of St. Louis at mid afternoon. Light snow struggled to
move in initially with the drier air in place, but has made some
good progress this afternoon, and had reached Decatur and Effingham
by 3 pm. Visibility in the snow area has consistently been in the 1
to 2 mile range. Recent grid updates have limited the rain/snow
mix potential to only areas south of I-70 over the next couple
hours, and latest observations would suggest that perhaps only
Lawrenceville area would have this concern as temperatures there
have reached near 40.

Short-range models in good agreement with moving the system
southeast along the Mississippi River through this evening. Areas
north of I-74 still likely to see little of the action beyond some
flurries, as the northeast flow will be establishing itself with the
passage of the low. Have continued the light snow over most of the
remainder of the CWA into mid evening, quickly diminishing to
flurries from northwest to southeast late. Overall amounts still
looking on the light side, around an inch or so from near Rushville
southeast through Springfield toward Vandalia.


.LONG TERM...(Thursday through Wednesday)

Weakening clipper system should be well off to our southeast by
Thursday morning with our area under the influence of low level
cold advection thru most of the day. Forecast soundings continue
to hold on to the low level moisture into at least the early
afternoon hours before high pressure settles in from the northwest
by late in the day. This should result in a decrease in cloud cover
from northwest to southeast during the afternoon with temperatures
struggling through the 20s. Look for a fairly quick drop off in temps
tomorrow evening as the high shifts across the area with return flow
setting up over western IL after midnight, which should put a halt
to the temp fall across the west. A gusty south wind should help
bring warmer air back into the area on Friday with afternoon
temperatures in the 40 to 45 degree range. Forecast 850 temps by
Saturday afternoon in the +12 to +14 degree C range which should
translate to 50s for afternoon highs. With a slower trend continuing
in models for our next frontal passage on Sunday, most of our area
will enjoy mild temperatures with low 60s possible over southeast
Illinois Sunday afternoon.

Main forecast concern will be later Sunday and especially Sunday
night as models suggest some low chance POPs across at least our
east and far southeast as the front and low level cold air tracks
southeast. Not a lot of Gulf moisture will be available in our area
ahead of the front thru Sunday evening but as the boundary shifts
south of the area late Sunday night/Monday morning, we will have
to watch for the development of some light rain or drizzle with
overnight lows expected to drop into the low to mid 30s. For now,
will hold on to slight chance to chance POPs over central thru
southeast IL on Sunday ahead of the boundary with precip chances
getting shunted south with the front late Sunday night into Monday
morning. Most of the forecast soundings not showing much if any
ice crystals in the upper portion of the clouds Sunday night so
drizzle or even freezing drizzle along the northern edge of the
precip shield may need to be added in future forecasts for Sunday
night into early Monday morning.

After another setback with temps on Monday in the wake of the
upper wave and attendant cold front that slips to our southeast,
warmer temperatures will return on Tuesday and hold thru the
remainder of the extended period as the upper flow transitions
more into a zonal flow thru much of next week. Significant model
spread really shows up after Tuesday with respect to shortwave
energy that had been parked out near the California coast over the
the weekend, which is forecast to eject across the Rockies and into
the Plains on Wednesday. The GFS is at least a day and a half faster
than the ECMWF with the wave as most of the guidance starts to show
POPs as early as late Tuesday night into Wednesday over the forecast
area, whereas the ECMWF speed would indicate rain chances holding
off until later Thursday into Friday. With more of a zonal flow
forecast across the lower 48 thru most of next week, would think the
quicker solution would be the way to go midweek and beyond. Will
indicate chance POPs starting on Wednesday with temperatures averaging
out close to or above normal after Monday.


.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)

Clipper system/low pressure center just south of KUIN will
continue to produce light snow and IFR conditions in west central
and parts of central IL through at least 03z - particularly at
KSPI. As the low weakens and scoots southeast into southern
Illinois during the evening, a brief period of freezing drizzle
may accompany the light snow before it dissipates.

There is a sharp cutoff in the snow and the low ceilings...mainly
along I-74...which includes KPIA, KBMI and KCMI. These locations
will have highly variable conditions with ceilings mainly in the
MVFR category, but with brief periods of VFR early this evening.

The GFS model wants to break up the clouds around or shortly after
daybreak Thursday. However, upstream observations and the presence
of moisture in the lowest few thousand feet of the atmosphere
should keep MVFR ceilings in place across all of central and
eastern IL through the morning and at least the early afternoon.
Could be some break in the clouds by late afternoon, but will
address that in future TAF issuances.




SHORT TERM...Geelhart
AVIATION...Miller is the U.S. government's official web portal to all federal, state and local government web resources and services.