619
FXUS63 KDVN 301042
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
542 AM CDT Tue Apr 30 2024

...Updated for 12z Aviation...

.KEY MESSAGES...

- Active forecast remains through the long term, with near daily
  chances for precipitation beginning tonight.

- Temperatures will remain above normal through midweek,
  trending towards normal for the end of the week.

&&

.SHORT TERM /THROUGH WEDNESDAY/...
Issued at 254 AM CDT Tue Apr 30 2024

A sprawling high pressure system at the surface was leading to
a tranquil and cool early morning. An ideal radiational setup
with light winds and generally clear skies has allowed
temperatures to drop into the 40s across much of the area, with
some areas down near 40 in the river valleys and drainage locations
north. Far south areas were still around 50 or the lower 50s.

Today should be largely quiet and very nice as it features a good
recovery on temperatures aided by mixing and solar insolation
leading to gusty southerly winds to 30 mph by afternoon. Mixing
above 850 hPa and temps of 12C-14C brought to surface dry
adiabatically yields highs from the mid 70s to lower 80s.
Attention by this afternoon will shift to our west as a mid
level wave ejects into the Northern Plains. Increasing forcing
atop moisture advection in the low levels ahead of a deepening
surface low and cold front will foster convection initially
across parts of SD/MN/IA/NE, eventually zippering down the cold
front into KS/MO while shifting east. Strong deep layer shear
40-50+ kts and very steep lapse rates of 8c/km will support
Supercells with large/very large hail and damaging winds with
this convection to our west. The challenge for our area is
how far east does the instability axis translate and whether
these severe storms can maintain some of their strength while
entering eastern Iowa and northern Missouri this evening.
In general the CAMs support a weakening trend as the convection
enters the service area and likely begins to outpace the
instability. 00z HREF ensemble paintball 4 hr max 2-5km UH
>150 m2/s2 shows clustering to our west and brings it close to
eastern Iowa before quickly waning 02z-05z. Latest few runs of
the RAP however, show there is likely to be enough 0-1km
instability (500-1000 j/kg) amidst strong 0-3km shear 40+ kts to
maintain a severe threat into eastern Iowa with these cells.
Proxy soundings show some low level CINH developing by the time
the storms arrive, but lots of dry air sub-cloud and strong wind
fields will still yield a concern for damaging wind gusts being
the primary threat. Steep lapse rates around 7.5c/km and the
strong shear will make hail also a threat. Agree with SPC
expanding the Slight risk into portions of eastern Iowa and far
northeast Missouri. The convection should further weaken
approaching the Mississippi River heading into late evening and
N Illinois through early overnight, but still have a gusty
wind/small hail threat. Thereafter, the rest of the overnight
looks to turn quiet once again.

Wednesday looks to be largely quiet and beautiful with surface
high pressure once again in control. Highs look to be in the
70s. Warm advection will kick in during the afternoon leading
to increasing cloudiness.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
Issued at 254 AM CDT Tue Apr 30 2024

The upper pattern becomes active once again with strengthening
isentropic ascent by Wednesday evening/overnight fostering an
increase in PoPs. A developing warm front well to our south
will make this mainly a threat for locally heavy rainfall with
any repetitive convection.

After that system, we will start to see a potent wave deepen over
the Rockies mid-late week. We will see a few leading impulses pass
through the area, leading to persistent showers/storms for the
remainder of the week. This will be a wet period, with the potential
to see quite a bit of rain. With recent rains and more forecast,
some rises along area rivers are expected. The parent wave
developing is the one that has our attention though. Although, there
is plenty of uncertainty with this, as well as major timing
differences amongst guidance. Although, all long term guidance shows
this system. If this wave deepens enough and we get that negative
tilt upon arrival, this will bring the potential for strong to
severe storms late in the week. Although, it is too soon to say for
sure. WPC is highlighting our area in the risk for Excessive
Rainfall from midweek through the end of the week, as they are
currently forecasting between 1-3+ inches of rain by the week`s end
for some. Thus, flash flooding will be possible, as well as rises
along area rivers. So, just be mindful and stay up to date on our
forecasts!

&&

.AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 535 AM CDT Tue Apr 30 2024

Shallow fog impacting KCID will quickly dissipate with sunrise.
Surface high pressure is set to move off by this afternoon. Light
winds will turn southerly and become gusty at 15-25 kt this
afternoon, ahead of low pressure deepening in the Northern Plains.
Mid level warm advection could lead to a few high based showers
developing into portions of eastern Iowa by mid to late afternoon.
Low coverage and minimal impacts, as mainly sprinkles if anything
due to dry sub-cloud air, precludes any mention. Can`t rule out
though some locally higher gusts in/near the virga or sprinkles.
Otherwise, a line of storms is expected to develop to our west
later this afternoon ahead of a cold front and move into eastern Iowa
this evening, while gradually weakening. Before doing so, there
is the potential for gusty winds and hail to accompany the storms,
particularly at KCID and KBRL which appear to have the better chances
for strong storms. Ahead of the convection a transitory period of
LLWS is possible this evening 02z-05z with the nocturnal LLJ ramping
up. Conditions will likely drop to MVFR to local IFR (visibility)
in the strongest storms. Winds will veer to westerly overnight with
the passage of a cold front.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...None.
IL...None.
MO...None.

&&

$$

SHORT TERM...McClure
LONG TERM...Ervin/McClure
AVIATION...McClure