000
FXUS63 KDVN 131123
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
623 AM CDT Tue Apr 13 2021

...AVIATION UPDATE...

.SYNOPSIS...
Issued at 315 AM CDT Tue Apr 13 2021

Current water vapor imagery was indicating closed upper low centered
near Duluth MN, while a secondary closed upper system was taking
shape over the northern Intermountain West.  The southern edge of a
large deck of stratocu clouds associated with the low to the north
was wrapping around eastward toward the northwestern CWA. Enough of
a tight pressure gradient from NW-to-SE acrs IA between MN arrowhead
sfc low and western high plains ridge axis to keep 5 to 10+ mPH
winds going acrs the local area. This mixing keeping most temps up
in the upper 30s to low 40s, and there may not be much more drop off
from that through dawn. Thus these conditions not very conducive for
much frost formation this morning unless the winds can decrease
more, which may happen in the far southwest closer to the ridge and
will keep patchy frost in those areas. Otherwise will remove mention
other areas. Cooler than normal and mainly dry wx regime still looks
on tap until maybe Saturday.

&&

.SHORT TERM...(Today and Tonight)
ISSUED AT 315 AM CDT Tue Apr 13 2021

Today...Most of the near term model runs not handling the southwest
extension of the incoming cloud deck mentioned above and will keep
partly to mostly cloud coverage, be a bit more bullish on clouds
north of I-80 and especially Hwy 30 on north for stretches of the
day.  Acrs the southern CWA there may be periodic streaks of mid
clouds and cirrus, but the DVN CWA will generally lie in between wx-
making streams of the closed cyclone gyrating to the north, and
steering southern stream from the southern plains to the southern OH
RVR Valley. Will keep the fcst dry, but there may be a low chance
for an isolated shower in the northern to northeastern CWA this
afternoon in any thick cumulus field enhanced by steep LLVL lapse
rates...better chances to the north acrs MN, far NE IA and into WI.
Back to the steep lapse rates, in cyclonic flow and deep mixing to
make for another blustery day with west winds of 15 to 25 MPH and
gusts to 30 MPH. As a LLVL cold pool continues to advect down acrs
the region out of south central Canada, we will need deep mixing to
at least H85 MB just to get the fcst highs of low to mid 50s. In
areas to the north that have more clouds, several areas may have
trouble getting out of the 40s.

Tonight...Challenge of how cold to go with potential for more clouds
and incoming sfc ridge pressure gradient maintaining winds of 5 to
10 MPH making for marginal frost formation conditions. Feel the
cloud deck along and north of I80 wrapping around the vortex rolling
acrs northern WI, will maintain with maybe just a few breaks, and
the south may still have a few passing wisps of CI off the southern
stream. But the cold advection will still be realized under clouds
and winds of 5-10 MPH, like what is currently going on in upstream
source region airmass acrs southeast SD and southwest MN. Thus it
looks like widespread low to mid 30s still in line, but hopefully
the clouds and winds to prevent some 20s from occurring. Will
advertise the unseasonable cold in the HWO/weather story and still
put patchy to areas of frost in the grids, but hold off of any frost
or freeze headlines for now with uncertainty on the extent. ..12..

.LONG TERM...(Wednesday through Monday)
ISSUED AT 315 AM CDT Tue Apr 13 2021

The upper air pattern through the extended remains dominated by a
very far southern displaced jet stream, resulting in cool, but not
particularly stormy weather over the Midwest. The main threat for
any rainfall will be associated with an upper low forecast to move
out of the Rockies Thursday.  While that should support an increase
in cloud cover for the Friday through Sunday time period, the system
is expected to be far enough south that moisture return should be
held well south of the CWA.

Temperatures will continue to run about 10 degrees below normal
through Thursday, followed by a bit of moderation through the
weekend, as slightly warmer air aloft is forecast. This should
result in highs in the upper 40s Wednesday, with plenty of clouds in
the north half, as well as some diurnally driven sprinkles as the
cold pocket aloft rotates down through that period. By Thursday this
moves out of the area, but we`ll not see a true warmer up, just
moderation. Overnight lows will be cold, but as with the current
night, there is enough potential for cloud cover and continuous
gradient winds that lows in the mid 30s to lower 40s are less
conducive for frost threats.  So, if there`s any good news in this
cool pattern, it`s that tonight`s threat is the main show for any
freezing temperatures.

Friday through Sunday, highs in the upper 50s to lower 60s are
forecast, with lows upper 30s to lower 40s.  Clouds and light
precipitation are possible, but pops are held very low right now,
given the previously mentioned southern track of the system, and
limited if any moisture return at lower levels for the weekend.

Looking beyond into the early week, the upper pattern continues to
be favored for northwest flow and limited moisture. That`s good
news, but will keep us focusing on any freeze/frost potential
through the early 20s of April.

ERVIN

&&

.AVIATION...(For the 12Z TAFS through 12Z Wednesday Morning)
ISSUED AT 621 AM CDT Tue Apr 13 2021

A VFR day with scattered to broken clouds around 4000 ft are
expected today into this evening, with winds westerly at 15 to 25
kts. Tonight, the winds will drop to 5 to 12kts by sunset, and
remain VFR through the night with generally partly cloudy to
mostly clear skies.

&&

.HYDROLOGY...
Issued at 932 PM CDT Mon Apr 12 2021

Runoff from heavy rainfall over the weekend has caused significant
rises, and in some instances flooding along tributary rivers and
portions of the Mississippi River. Most rivers have since crested
and were in the process of receding today, with only a few
exceptions.

The Wapsipinicon River at Dewitt and La Moine River at Colmar are
at Moderate flood stage and are forecast to crest overnight. The
Mississippi River has a flat crest near Illinois City, which will
make its way south with in-bank rises at points downstream over
the next several days. These stages, and latest forecasts, have
been trending a bit lower than previous forecasts. Gladstone now
looks likely to crest below flood stage and the Flood Watch that
was issued Monday was cancelled.

No rain is in the forecast through this week and no additional
flooding is expected.

&&

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

$$

SYNOPSIS...12
SHORT TERM...12
LONG TERM...Ervin
AVIATION...Ervin
HYDROLOGY...Sheets