Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 212353
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
653 PM CDT Mon Apr 21 2014

.DISCUSSION...
ISSUED 256 PM CDT Mon Apr 21 2014

Much as anticipated, scattered showers and isolated thunderstorms
are spreading across central and southeast Illinois today,
associated with the passage of a weak frontal system.
Precipitation chances end later tonight as the system pushes east
of the area. Then, primary forecast concerns turn to precipitation
chances with a stronger system for Thursday, as well as with a
more uncertain weather pattern to start next week.

SHORT TERM...Tonight through Thursday:

Given the current speed of the system, the precipitation threat
across the forecast area should end by shortly after midnight
tonight, with fairly rapid clearing expected in its wake.

The cooler air filtering in behind today`s system will drop
temperatures back closer to normal for Tuesday and Wednesday
(highs in the 60s). Quiet weather is expected for this period as
well as upper/surface ridging build across the area.

A stronger system than today`s is still on track for
Thursday/Thursday night, although the severe weather threat with
this system still does not appear to be very high. Instability is
likely to be rather low (CAPE values AOB 1000 j/kg), but bulk
shear will be better (on the order of 40 kts). Some of the guidance
still suggests we may see precipitation as early as late
Wednesday afternoon/Wednesday night in the pre-system warm
advection regime, but the most favored area for this precipitation
remains north of the forecast area. However, the strong WAA will
boost temperatures will above normal once again, with highs in the
70s in many areas.

LONG TERM...Friday through Monday:

Cooler temperatures begin to spill into the area Friday behind
Thursday`s system, but quiet weather is anticipated. From
Saturday, and especially Sunday, through the end of the period,
the forecast details become especially murky. While there is
general agreement that a Rex block will develop during the period,
the specific placement of the ridge and trofs is problematic at
best. The GFS and Canadian models have consistently kept our area
under the influence of the upper ridge and sprawling/dry surface
high, while the ECMWF has consistently pushed the upper low more
quickly beneath the ridge position. These differences suggest that
either an extended dry period (GFS/Canadian) or extended wet
period (ECMWF) is possible. Obviously, this is not very helpful,
and the considerable ensemble spread within each specific model is
not helpful either. So, given the considerable uncertainty,
keeping pops to the drier side of 50/50 seems to be the best bet.
Hopefully the models will sort out their differences soon with
respect to the expected blocking pattern.

Bak

&&

.AVIATION...
ISSUED 653 PM CDT Mon Apr 21 2014

VFR conditions will prevail at all sites next 24hrs. All sites
will be overcast with clouds around 6-8kft this evening. Showers
will still be around the area too so will have each site with
VCSH. The showers will continue for about 2-4 hours from west to
east. Once the pcpn moves through, clouds will lift back to around
20kft, high cirrus. Once the front comes through, skies will
become clear and will last that way rest of the night and into
tomorrow morning. Winds will be west to southwest this evening and
then become westerly as the front pushes through. The front will
be broad, so a quick change to the northwest will not occur. Then
around midnight, winds will switch to more northerly and continue
that way through tomorrow. Speeds will be less than 10kts this
evening, but then pick up overnight and then become a little gusty
tomorrow.

Auten
&&

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

$$







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