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fxus63 kdvn 191919 

Area forecast discussion
National Weather Service Quad Cities Iowa Illinois
219 PM CDT Sat Oct 19 2019

issued at 216 PM CDT Sat Oct 19 2019

At 18z surface analysis indicated the cold front was situated across
the eastern part of the forecast area with light showers being
observed behind the front through much of the Iowa portion of the
County Warning Area. The rain showers were ongoing associated with a pv anomaly
riding up along the front.


Short term...(this evening through monday)
issued at 216 PM CDT Sat Oct 19 2019

Primary forecast concerns for this period of the forecast
include, fog potential tonight, clouds and temperatures for
Sunday, then storm potential for Sunday night into Monday morning
along with winds on Monday.

The cold front will continue moving east through the remainder of
the day and as the pv anomaly that is providing the forcing for the
showers will move away from the area so expectations is that the
showers will diminish in areal coverage as the day progresses.
Still, many areas will see light rain with light accumulations by
days end.

Tonight, after the cold front pulls away, there will be large scale
subsidence ongoing, but as a surface ridge builds into the forecast
area, thoughts are that moisture will become trapped in the low
levels, contributing to fog or stratus development. With the light
winds expected, feel it will be fog so continue that mention in the
forecast for tonight. Not a for sure scenario though and not
confident on the degree of the fog or potential for dense fog.

Next concern is how the fog/low clouds will diminish on Sunday
and its impact on temperatures. Forecast soundings showing the low
level moisture sticking around through much of the day as
additional, moisture advects into the region from the south ahead
of the next system for Sunday night. If clouds stick around high
temperatures will be impacted so highs could struggle to make it
into the 60s.

Now, moving into Sunday night, the surface low associated with the
impending convection will be over the eastern Dakotas with a
trailing cold front along the Missouri River. There are considerable
timing differences in the models when convection will move into
the area. GFS is faster, which would suggest widespread
precipitation chances needed as early as 06z. NAM is slower, by
about 3-6 hours. At this point used a blend to provide the timing.
Significant deep layer shear will be in place with this amplified
system, with values of 50-85kts. Forecast models do build in a
bit of MUCAPE up into the forecast area, but is limited to under
300 j/kg. Primary area of instability will remain across the
southern half of Missouri into southern Illinois. So, very much a
high shear/Low Cape scenario, but there too much of a spread to
get any strong convection so will continue to watch for chances
for anything severe even though at this point conditions don't
look particularly high.

Convection moves out of the area at some point on Monday, then the
winds will pick up. Did increase winds during the day to 15 to 20
kts sustained, but may still be too low.

Long term...(sunday night through saturday)
issued at 216 PM CDT Sat Oct 19 2019

Monday night: a significant upper level pattern change to a colder
regime will begin as a deep 500 mb closed low settles in over the
Great Lakes region. This will movement will cause a longwave upper
level ridge to build over the Pacific northwest and then over the
inter-mountain west. It will be very windy as air wraps around the
back side of the deep Great Lakes low. At 06z Tuesday, GFS 5k above ground level
winds are 40+ knots over cental and eastern Iowa, northwest
Illinois, and extreme northwest Missouri. This will produce
northwest surface winds of around 20 miles per hour with gusts over 40 miles per hour
possible. There will also be a chance of a few lingering showers.
Low temperatures will be in the low 40s.

Tuesday: blustery northwest winds will continue until the closed 500
mb low over the Great Lakes kicks northeast to south of Hudson Bay.
The wind will diminish by evening as the low moves further north.
Skies will begin to clear as high pressure builds into the region in
between the departing upper low and the next system developing near
Alberta, Canada. High temperatures will only be in the mid 50s with
overnight lows temps in the mid 30s.

Wednesday: a 500mb shortwave trof near Alberta will move southeast
to over the upper plains. This will be the first Alberta clipper of
the season to affect the region. It will be partly sunny as high
pressure builds over the forecast area out ahead of the approaching
clipper. Highs will be in the mid 50s across the north with low 60s
over the south. Overnight low temps will be in the 30s.

Thursday and friday: there will be a chance of showers as the
clipper moves over the upper Mississippi Valley. It is interesting
to note that the 12z Saturday runs of the ECMWF, GFS and Canadian
models all have 850 temps progged to be minus 5 to minus 3 degrees
celsius at 12z Friday morning. Surface temperatures at the same time
will be in the 30s. We will keep an eye on this system as it could
produce the first snow flakes of the season. High temperatures will
be near 50 degrees.

Saturday and beyond: cold regime continues.


Aviation...(for the 18z tafs through 18z Sunday afternoon)
issued at 1257 PM CDT Sat Oct 19 2019

Interesting aviation setup for the next 24 hours with a fairly low
degree of confidence in the outer parts of the period. A cold
front will continue advancing from west to east across eastern
Iowa and into western Illinois over the next 6-9 hours. Rain
showers will accompany the front but will diminish in coverage and
intensity as the day progresses. Clear skies are observed to the
west behind the front, but as surface ridging builds in overnight
and winds become calm, the setup is looking likely for fog
development. The question is will it be MVFR or IFR. Look for
improving conditions through the morning on Sunday, but with the
time of year, wouldn't be surprised to hold onto cloud cover for
much of the day.


issued at 216 PM CDT Sat Oct 19 2019

River levels continue to recede on all area rivers. At this time
precipitation in the forecast through the next week does not look
to be enough to cause new rises so expect river levels to continue
the falling trend.


Dvn watches/warnings/advisories...


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