Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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000
FXUS63 KDVN 110905
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
305 AM CST Sat Nov 11 2017

.SYNOPSIS...
Issued at 305 AM CST Sat Nov 11 2017

06Z surface data has high pressure over the Great Lakes with a
developing storm system in southeast Colorado. Dew points were in
the teens from the Ohio Valley into the upper Midwest with 20s and
30s across the Plains.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 305 AM CST Sat Nov 11 2017

Quiet and dry conditions will continue through sunrise with
temperatures in the upper 20s to lower 30s.

After sunrise, the dry conditions will continue through mid-day.
Some filtered sunshine may or may not be seen during the morning as
southerly flow pushes temperatures above freezing. Attention then
turns to the afternoon hours.

This afternoon clouds will thicken as southerly flow continues.
Trends with the models continue to show roughly a 5 kft layer of dry
air at the surface as the atmosphere moistens aloft. Starting around
mid afternoon forcing increases across the area which may be enough
to allow some light rain to develop west of the Mississippi.

This evening moisture and forcing will increase across the area
allowing light rain to develop across the entire area. With some dry
air still across the north third of the area, thermal profiles of
the atmosphere suggest the potential for some cooling. However, RAP
trends show the important wet bulb temperature slowly climbing above
freezing both at the surface and aloft. So while there may be some
cooling of the atmospheric column across the north third, the
precipitation should remain in the form of all rain during the
evening hours.

After midnight, nocturnal cooling of the atmosphere should allow a
rain/snow mix to develop over roughly the northeast third of the
area. Ground temperatures have cooled but are still in the 38 to 41
degree range so any mix that develops late tonight is expected to
melt on contact with the ground. However, if the forcing can
strengthen then narrow bands of precipitation could force the
atmosphere to locally cool further and allow a complete change over
to all snow. If this occurs, then grassy areas may see a hint of
white develop prior to sunrise.

.LONG TERM...(Sunday through Friday)
ISSUED AT 305 AM CST Sat Nov 11 2017

Light precipitation will be on-going Sunday morning as the
strengthening upper level shortwave exits to the east. Dry and
continued cool conditions then follow through Monday. An active
zonal flow will then bring a warming trend, returning temperatures
closer to mid November normals for mid to late in the week. Roughly
every 3 days, systems embedded in the flow will bring precipitation,
with the next arriving Tuesday night.

Sunday: There remain minor differences among the operational models
with the timing and strength of the upper level shortwave, shown
passing over the forecast area roughly between 12z and 18z. The GFS,
WRF and CMC all depict a west to east band of light precipitation
centered along the highway 20 corridor under this forcing and along
the deformation axis of a surface low passing through MO into
central IL. The critical question will be the amount of cooling in
the thermal profiles along the northern tier of counties, which
suggests at least a possibility of a rain/snow mix with the
colder/stronger WRF early in the morning. This could lead to at
least a brief period of a wet trace of accumulation in northwest IL
early in the morning. Elsewhere, chance to likely pops are
maintained for light rain in the morning, which will end with the
departing system by early afternoon with temperatures recovering
into the lower 40s.

High pressure passes through Monday for continued cool, but dry
weather. Models are in good agreement with the next system for late
Tuesday into early Wednesday. A low level return flow sets up
Tuesday, warming highs into the lower to mid 50s over at least the
southwest. The main period of forcing passes through Tuesday night,
where pops are now in the likely to categorical range for for rain
showers. Have introduced isolated thunderstorms over the west and
south were the GFS depicts steep mid level lapse rates and modest
convergence along a 30 to 40 kt southwest wind at 850 mb. This will
supply sufficient moisture to support the widespread QPF amounts
over a quarter inch shown in the models.

The next system arriving late in the week remains low confidence,
due to continued poor agreement in the model timing and strength of
the upper level trough. For now, an extended period of chance pops
will run from Thu night through Fri night, which will likely be
narrowed down considerably in time. With daytime temperatures in the
40s and 50s and overnight lows in the 30s, this looks to be another
rain event.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday Night)
ISSUED AT 1114 PM CST Fri Nov 10 2017

A mid cloud deck around 8000 feet will continue for the overnight
in through Saturday. The weak low pressure system bringing the
clouds will move over the region through Sunday morning, and will
eventually bring low clouds, drizzle, and some rain to the region,
but through Saturday afternoon, it should only slowly saturate
the atmosphere from top down, keeping the lower cigs well to the
west. MVFR cigs will likely develop area wide after 00z/11, and
for now, have introduced rain and 3500 to 5000 cigs, with lower
conditions likely after 06Z/12.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...NONE.
IL...NONE.
MO...NONE.
&&

$$

SYNOPSIS...08
SHORT TERM...08
LONG TERM...Sheets
AVIATION...Ervin



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