Area Forecast Discussion
Issued by NWS Quad Cities, IA IL

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FXUS63 KDVN 191741
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
1241 PM CDT Wed Sep 19 2018

...18z AVIATION UPDATE...

.SYNOPSIS...
Issued at 332 AM CDT Wed Sep 19 2018

Upper level ridging was centered over the southern plains this
morning with showers and storms over the ridge axis from South
Dakota into Iowa. Convection developed overnight on the nose of the
925mb southerly jet which pushed over a boundary sitting from near
Omaha to Keokuk on the southern edge of the surface high which was
centered over the Great Lakes. A line of showers was nearly
stationary for several hours in southeast Iowa and northeast
Missouri, which radar estimated 1 to 2 inches of rain fell in that
time. These showers and storms have now begun to move eastward into
Illinois. The convection to the west and northwest will be the
concern for today`s forecast.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 332 AM CDT Wed Sep 19 2018

The evolution of the convection now over northwest
into west central Iowa this morning will be the primary concern for
today`s weather. Fog this morning as well as hot temperatures will
be additional focuses for the forecast.

Starting with the fog, visibilities and ceilings have been jumping
around most of the overnight hours as no local areas have observed
any dense fog set in for the night. With light winds, expect lowered
visibilities for through sunrise or a few hours afterwards.

A warm front, which is currently over Missouri into Illinois will
lift north through the forecast area through the day today. There
will be a good focus for convergence on the nose of the low level
jet through the day today, and as the front lifts north, believe
this will generally be north of the forecast area. So, confidence is
higher on the bulk of storms today occurring over the northern part
of the forecast area into Minnesota and Wisconsin. However morning
activity should be across central Iowa into west central Illinois
then will lift northward into the afternoon. Precipitation chances
have trended in this manner for today`s forecast.

Cloud cover and precipitation trends will impact high temperatures
today. Some areas will start out with partly sunny skies, but clouds
should increase as the convection to the west moves eastward. The
greatest amount of cloud cover is likely across Iowa and the
northern half of the forecast area today, but the southern parts of
the area should clear out this afternoon. Have trended high
temperatures down a bit in the northern half of the forecast area
today, where mid to upper 70s are likely. To the south, thinking
highs will reach around 90. Low confidence on forecast dewpoints,
but if they hit the low 70s, heat indices will reach the upper 90s
today in some places.

For tonight, a shortwave trough will round the ridge axis and with a
good moisture feed from the low level jet, think wherever that focus
lies, storms will continue through much of the night. That being
said, there is good model agreement that this will generally be
north of the forecast area. With little to suggest the front will
move south later today and tonight, I think this is a viable
solution which would keep the local area capped overnight. That
being said, could see an outflow boundary push southward into the
area, which could cause some storms to develop into the northern
areas. For this reasoning, kept precipitation chances for areas
mainly north of interstate 80 overnight.

The main concern from storms today and tonight is going to be heavy
rain as precipitable water again sits from 1.75 to 2.00 inches.
Additionally, there looks to be abundant deep layer shear to suggest
a few storms could become organized with wind and hail being
additional threats.

.LONG TERM...(Thursday through Tuesday)
ISSUED AT 332 AM CDT Wed Sep 19 2018

A significant cool down will occur following the passage of the cold
front Thursday night.

Thursday
Assessment...high on well above normal temperatures and strong winds.
Low on rain chances.

Where the nocturnal thunderstorm complex develops Wednesday night
will be the key regarding rain chances for Thursday morning.

Internally, the models suggest the initiation point is northern Iowa
or possibly southern Minnesota with the complex moving east or east
northeast. If the initiation point(s) and track are correct then
Thursday would be dry for the entire area.

However, boundaries produced by the storm complex could move into
the northern half of the area and help generate convection (similar
to Tuesday morning).

Right now the model consensus has slight chance to chance pops
across the northeast half of the area Thursday morning with dry
conditions Thursday afternoon.

Very warm and windy conditions will be seen on Thursday. Cloud cover
from any morning storms may suppress temperatures across the north.
However, temperatures in the low 90s should be achievable across the
south half which could put records at risk. Refer to the climate
section for specific numbers.

Winds Thursday should easily be 20 to 30 mph with higher gusts due
to deep mixing and favorable wind profiles.

Thursday night
Assessment...high confidence on a strong cold front moving through
the area. Medium confidence regarding the severe weather potential.

Thursday night the strong cold front moves through the area with
strong southerly winds ahead of the front. The models for several
days now have indicated the strongest forcing is along and behind
the front.

Right now the model consensus has chance pops for Thursday night.
However, a period of likely or even categorical pops would be
reasonable for a time Thursday night.

The timing of the front does raise questions regarding the overall
severe potential. However, given the energy potential that builds
during the day combined with the strong wind fields one cannot rule
out the possibility of severe storms occurring well after sunset.
Thus the slight risk for areas west of the Mississippi looks
reasonable.

Friday and Friday night
Assessment...high confidence

Breezy and much cooler conditions will be seen across the area on
Friday as colder air pours into the area. Some lingering showers
will be possible for a time Friday morning in the far east and
southeast areas. However, the rest of the area will remain dry.

Chilly conditions will be seen Friday night across the area as high
pressure builds in and winds become light. Widespread 40s are
expected.

Saturday on...

Saturday through Sunday night
Assessment...high confidence

Cool Canadian high pressure will move through the Midwest and into
the Ohio Valley resulting in dry conditions with at or below normal
temperatures.

Monday through Tuesday
Assessment...low to medium confidence

Monday into Tuesday the models diverge on their respective solutions
in terms of specifics.

The ECMWF and to a lesser extent the CMC global have an upper level
disturbance moving through the area Monday/Monday night generating a
round of rain followed by more rain with another significant cold
front on Tuesday.

The GFS has no upper level disturbance on Monday but does push the
first of two cold fronts through the area Monday afternoon/night
followed by the more significant front on Tuesday.

As a result of these differences, the model consensus has slight
chance to chance pops Monday, chance pops Monday night, and slight
chance to chance pops on Tuesday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday Afternoon)
ISSUED AT 1232 PM CDT Wed Sep 19 2018

A weakening complex of showers & storms will bring MVFR/IFR
conditions to KDBQ/KMLI through early afternoon. Behind this,
expect primarily VFR conditions with the exception of KCID/KDBQ
where VCSH will be possible through early evening. Late tonight,
patchy MVFR fog/mist will be possible thanks to recent rainfall
across the region. In addition, showers & storms will be possible
near KDBQ where a PROB30 group is included.

&&

.HYDROLOGY...
Issued at 1152 AM CDT Wed Sep 19 2018

One to three inches of rain has fallen in parts of north central
and northeast Iowa over the past 24-36 hours. The current WPC
rainfall forecast through Thu morning has a 100-150 mile wide
swath of another 1 to 3 inches generally centered on and spanning
along the Iowa/Minnesota border. For this reason, river forecasts
for the Cedar River basin are forecast to rise above flood stage
in the Day4 to Day7 time frame. Due to the uncertainty of amounts
and placement of forecasted rainfall, I have issued new Flood
Watches for the Cedar River at Vinton, Cedar Rapids, and
Conesville. I have also continued the Flood Watch on the Iowa
River at Marengo, which, although delayed 48 hours, still is
forecast to exceed its flood stage early next week.

As for current river flooding on the Lower Mississippi and Rock
rivers, the levels on the Mississippi at Gladstone, Burlington, and
Gregory Landing are expected to drop below their respective flood
stages tonight.  However, the Rock River at Joslin will continue to
slowly fall; reaching its flood stage level Saturday.

&&

.CLIMATE...
ISSUED AT 332 AM CDT Wed Sep 19 2018

Record Highs for September 19...

Moline.........93 in 2013
Cedar Rapids...98 in 1925
Dubuque........94 in 1948
Burlington.....94 in 2013

Record Highs for September 20...

Moline.........94 in 2017
Cedar Rapids...93 in 1931
Dubuque........92 in 1895
Burlington.....93 in 2017

&&

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

$$

SYNOPSIS...Brooks
SHORT TERM...Brooks
LONG TERM...08
AVIATION...Speck
HYDROLOGY...14
CLIMATE...08


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