Area Forecast Discussion
Issued by NWS Central Illinois
FXUS63 KILX 070445
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE LINCOLN IL
1145 PM CDT TUE OCT 6 2015
ISSUED AT 823 PM CDT TUE OCT 6 2015
Current package remains on-track.
Still some question as to intensity and coverage of fog late
tonight and early Wednesday. Though moist northeast flow has
diminished as a surface ridge has pushed into Illinois, plenty of
residual moisture remains in the boundary layer. For now will keep
current wording of areas of fog, but will have to monitor trends
closely. latest RAP (23z) is more agressive with fog development
than runs from earlier today.
ISSUED AT 258 PM CDT TUE OCT 6 2015
Low cloud deck has faded over most of the forecast area early this
afternoon, but some stratocumulus lingers especially in west central
Illinois. Main concern is that this will return once again tonight.
The atmosphere has not changed much, as the high pressure axis to
our west only slowly edges eastward. The RAP model, which locked
into the idea of this morning`s low clouds and fog about 24 hours in
advance, shows another expanse of stratus/fog advecting in from the
northeast after about 2 am. Wild card will be with some altocumulus
clouds currently over Wisconsin/Minnesota dropping southeast, which
could slow the redevelopment of the low clouds. Right now, will
focus more on the areas east of I-55 and north of I-70 as more
likely to see some fog late night, although some fog along the
Wabash River in southeast Illinois is a possibility as well.
.LONG TERM...(Wednesday through Tuesday)
ISSUED AT 258 PM CDT TUE OCT 6 2015
Areas of fog from I-55 east and locally dense in spots to lift
during mid morning similar to past 2 mornings. Low clouds to also
break up by late morning with skies becoming partly to mostly sunny
by Wed afternoon with weak surface high pressure ridge of 1018 mb
near IL Wed and Wed night. Warm highs Wed in the upper 70s to near
80F. Lows Wed night in the mid to upper 50s. Could be some patchy
fog in southeast IL later Wed night where surface winds lighter.
Another warm day expected Thu with breezy ssw winds by midday Thu
giving highs in the lower 80s. MAV guidance even going mid 80s in
western CWA from Decatur west but did not go this warm since there
will be increasing cloud cover ahead of approaching cold front along
with chances of showers and thunderstorms NW half of CWA Thu
afternoon, with best chances over the IL river valley. SPC has
marginal risk (5%) of severe storms for hail late Thu afternoon and
early Thu evening over IL river valley. MLCapes peak near 1000 j/kg
late Thu afternoon nw IL and 0-6 km Bulk shear from 35-45 kts. 12Z
models similar in sweeping cold front se acorss central IL during
Thu night with likely chances of showers and a few thunderstorms.
Cold front exits southeast IL early Fri morning with lingering
chances of showers on Friday especially in the morning.
Dry conditions return to central and southeast IL Friday night
through next Tuesday as high pressure from the Pacific NW settles
into IL Saturday and then into the Southeast U.S. early next week.
Temps cool back to near or a bit below normal Friday/Saturday and
then warm back above normal early next week with highs in the mid
70s to lower 80s Sun-Tue. WNW upper level flow takes shape during
1st half of next week which would favor fair and mild conditions,
and favorable for fall harvest. CPC`s day 6-10 day outlook Oct 12-16
has IL in above normal temperatures and below normal precipitation.
.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
ISSUED AT 1145 PM CDT TUE OCT 6 2015
High pressure settling over Illinois tonight has allowed winds to
taper off. Mid-level clouds to the northwest are advecting into
the state as well and are limiting some of the potential for
radiative cooling. latest short-range models, the 03z RAP and 03z
HRRR in particular, still suggest fog development along and east
of U.S. Highway 51. Though the development isn`t as far west as
the past two nights there is more consistency between the models.
Will bring KCMI down to LIFR conditions for a brief time around
sunrise. Vsbys are a bit more questionable at KBMI and KDEC but a
few hours of IFR still seems a good bet. As the clouds develop
southeast, mesoscale models suggest some improvement at KBMI by
11z and KDEC by 12z.
Dew Point spreads are currently higher at KPIA and KSPI as they
have been more influenced by incoming mid-level cloudiness.
Surface high should remain over the state on Wednesday keeping
winds light through the TAF valid period.