Area Forecast Discussion
Issued by NWS Central Illinois

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FXUS63 KILX 292006
AFDILX

Area Forecast Discussion
National Weather Service Lincoln IL
306 PM CDT FRI APR 29 2016

.SHORT TERM...(Tonight)
ISSUED AT 303 PM CDT Fri Apr 29 2016

18z/1pm surface analysis shows stationary frontal boundary extending
from West Virginia southwestward to an area of low pressure over the
Texas panhandle.  As a vigorous upper low noted on the latest water
vapor imagery over northern New Mexico pivots northeastward, the
front will get a push northward tonight.  Rain will eventually
spread into central Illinois ahead of the front: however, the models
remain in poor agreement as to how fast this process will occur. The
NAM continues to be the most aggressive in spreading rain across
much of central Illinois by midnight, while both the GFS and Rapid
Refresh tend to hold it back until later tonight. While the upper
low appears rather progressive, a dry E/NE low-level flow north of
the front will likely impede the initial northward progress of
precip.  As such, prefer the slower GFS/Rapid Refresh consensus in
the short-term.  Have therefore cut back PoPs during the evening to
go with a dry forecast along/north of a Rushville...to Lincoln...to
Paris line.  Showers will then overspread the entire area from the
southwest after midnight, with locations along/north of I-74
remaining dry until close to dawn Saturday.  Forecast soundings show
modest elevated instability developing late, so have included
isolated thunder south of I-74.  Overnight low temperatures will
range from the upper 40s north, to the middle 50s south of I-70.

&&

.LONG TERM...(Saturday through Friday)
ISSUED AT 303 PM CDT Fri Apr 29 2016

Still looks like a rather wet weekend in central and eastern IL as a
potent upper level low and cyclonic surface system works its way
into the Midwest from the southern Plains. Fairly strong
isentropic lift is expected to develop along I-70 tonight, and
work its way northward Saturday morning. Moderate low level
moisture transport will bring seasonally high precipitable water
values northward, resulting in total precipitation in the 1.00 to
1.50" range across most of the forecast area by late Saturday
night. MUCAPES in the 100-200 range indicate the potential for
some embedded, elevated thunderstorms in the precipitation shield
Saturday morning and early afternoon.

The potential for strong/severe storms south of I-70 later
Saturday will be dependent on the amount of partial clearing and
atmospheric recovery/instability that can develop in the wake of
the rain. Could see scattered strong t-storms as far north as a
SPI-DEC-Paris line toward evening and overnight, with scattered
showers elsewhere as the surface low tracks through south central
IL.

Should see quite a few showers and isolated t-storms in the forecast
area Sunday as the upper level low/cold pool moves across central
and eastern IL. The presence of plenty of clouds and periods of rain
will keep temperatures on the cool side Sunday with highs only in
the 55-60 range west of the IL River, and generally in the 60s to
east.

The GFS and European models both indicate that as upper ridging
builds rapidly into the Canadian Rockies, a series of shortwaves
will drop into the Midwest from the north. The models have timing
differences with these, particularly by midweek. The result will be
a slight chance/isolated showers in central IL Monday, with more
uncertainty as to the next chance mid-week and again late in the
week. With a faster, longitudinal flow anticipated, will side
more with the quicker GFS and go with low chance PoPs in eastern
IL Wednesday, and central IL later Friday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1244 PM CDT Fri Apr 29 2016

MVFR ceilings persist at the central Illinois terminals early this
afternoon: however the HRRR continues to suggest these will
scatter over the next 2-3 hours. Have noted a gradual thinning of
the low clouds on visible satellite, so will follow the HRRR and
scatter the ceilings between 21z and 22z. A high overcast from
convective blowoff upstream will remain through the late
afternoon and evening, before clouds once again begin lowering
tonight as a warm front lifts northward into the area. Models
still disagree as to how quickly the lower clouds and precip will
return, with the NAM being the fastest. Based on a continued dry
E/NE low-level flow north of the front, think the slower GFS/Rapid
Refresh is the way to go. As such, have delayed IFR ceilings and
predominant rain until 09z at KSPI and 12z at the I-74 terminals.
Modest elevated instability suggests the potential for a few
embedded thunderstorms, so have included VCTS between 12z and 18z
as the initial surge of warm advection precip moves through. Winds
will be from the northeast at 5 to 10kt early this afternoon, then
will veer to the southeast and increase to between 15 and 20kt by
Saturday morning.


&&

.ILX Watches/Warnings/Advisories...
NONE.
&&

$$

SHORT TERM...Barnes
LONG TERM...Miller
AVIATION...Barnes



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