Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 170818
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
318 AM CDT Thu Aug 17 2017

.SYNOPSIS...
Issued at 317 AM CDT Thu Aug 17 2017

An mature storm system continues to spin over central MN early this
morning, with the CWA about the see the passage of the cold front.
Mid levels have already seen a dry slot work over the area, and
convection since this has spread over has been very small and
isolated. However, models are showing a bout of lift along the cold
front through sunrise, and that may allow for an increase in
coverage over the Illinois counties.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 317 AM CDT Thu Aug 17 2017

After early morning convection lifts out of the area, the main
question today will be cloud cover. Low clouds wrapping around the
back side of the low are expected to spread east today, and will
likely be overcast for a few hours this morning in the north 1/2,
then remain that way through early afternoon in the far north. The
south should see deeper mixing, and no more than scattered cloud
cover. This figures into the high temperatures forecast, though we
will have a very mild start, weak cold advection and cloud cover
will keep the north in the lower to mid 70s, while deeper mixing and
sunshine to the south will have lower to mid 80s expected.

Tonight, a quiet and mostly clear night is forecast with the system
departing the region. Lows in the upper 50s to lower 60s are
forecast as winds remain 5 to 10 mph from the west overnight.

.LONG TERM...(Friday through Wednesday)
ISSUED AT 317 AM CDT Thu Aug 17 2017

Long term forecast starts with zonal flow before it turns NW as an
upper level wave clips into the area.  Once this moves through the
area, the overall weekend looks dry before a return to zonal flow
brings daily chances of storms are warm moist weather to the area.

Friday...strong CVA at H5 will lead to height falls at the surface
and a subsequent deepening of the H84 low and sfc low across t. he
area.  The last few runs have moved the wave from north of the CWA
to south of the CWA and now a direct hit on the area. Most guidance
agrees on the current predicted location. If this trend holds up we
can expect to see showers and storms Friday afternoon and evening.

If the current guidance is correct on placement we would see a sfc
low moving across the CWA from 00Z Saturday through 06Z Saturday
with strong convergence along the cold front. Surface winds to the
east of the low are out of the east. Deep layer shear near 50 kts
with 0-1km shear near 35 knots suggests rotating updrafts. With this
pattern and subsequent mass fields believe that shear will be
sufficient for organized strong and even severe storms.  H7 temps
are prog to be in the mid single digits. Even though dewpoints are
in the low to mid 60s, strong forcing and shear could lead to severe
storms.  The main limiting factor will be temperatures and
instability during the day.  What is likely to happen is that storms
won`t fire until later in the afternoon early evening on the front.
The main threat from potential severe storms would be large hail.
With the low on top of us we are likely to see strong enough winds
to keep us mixed.  If this occurs we could see severe winds and
possibly tornadoes.

At this time, the uncertainty in track of the H5 upper low will keep
the mention of severe out of the HWO but use strong thunderstorm
wording along with too soon to tell if there will be severe storms.

A quiet weekend with drier and slightly more comfortable temps are
forecast.  Into next week, the forecast skill is low as zonal flow
and mesoscale features will drive the weather.  What happens the
night before will affect what happens the next day.  There will be
storms around into next week, just have low confidence on placement
and timing.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday Night)
ISSUED AT 1129 PM CDT Wed Aug 16 2017

A cool front is passing producing clearing skies. Winds will shift
from the south to the west. After 17/10Z...wraparound low clouds
from a surface low in Minnesota will overspread locations along
and north of I-80 corridor including likely the MLI terminal by
10/14Z with MVFR to higher end IFR conditions lasting until mid to
late PM when skies will clear. The BRL terminal will remain fair.
Winds will be westerly at 10 to 20 mph through the day Thursday
decreasing to 5 to 10 mph in the evening.


&&

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

$$

SYNOPSIS...Ervin
SHORT TERM...Ervin
LONG TERM...Gibbs
AVIATION...Nichols


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