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000
FXUS63 KDVN 151102
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
602 AM CDT Mon Apr 15 2024

.KEY MESSAGES...

- One last quiet day is on tap today before chances of showers
  and thunderstorms increase this evening, lasting into Tuesday
  morning, some of which could be strong.

- Strong to severe thunderstorms are likely for Tuesday
  afternoon and evening, with very large hail and a few
  tornadoes possible.

- Expect a cooldown for the latter part of the week, with
  temperatures returning to near seasonal averages. A few chilly
  nights are expected by next weekend.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 444 AM CDT Mon Apr 15 2024

The final day of our quiet stretch of weather has arrived, with calm
conditions before a more active pattern takes shape tonight. Lots of
sunshine is expected, with high temperatures in the middle 70s north
to the lower 80s south with east winds around 10 to 15 mph - good
conditions to make any last minute preparations for the upcoming
active period.

Speaking of, the system that will bring our widespread chances of
showers and thunderstorms Tuesday will start to move across the
central Plains region this evening into Tuesday morning. For
tonight, we are focused on a warm air advection regime that will
move into our area tonight. CAMs have indicated convective
initiation to be a bit later than previously forecast, with any
activity that develops along the warm front and area of
enhanced convergence to develop around or after midnight
tonight. Soundings still indicate that convection will be more
elevated in nature, capable of large hail, given most-unstable
CAPE values on the order of 500 to 1500 J/kg per various global
models and the HREF ensemble mean. Storm initiation appears to
be most likely over eastern Iowa. SPC has maintained the
Marginal Risk, or level 1 out of 5, for this large hail
threat for areas along and west of a Belle Plaine, IA to
Macomb, IL line. This is just the appetizer for the main show
Tuesday PM. More details on that below...

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...
Issued at 444 AM CDT Mon Apr 15 2024

Guidance has continued to show very good run to run consistency on
the evolution of the area of low pressure that will bring our
widespread chances of strong to severe storms Tuesday, which progs a
cut-off upper-level low translating eastward just north of the Four
Corners region by this afternoon. Surface low pressure will develop
via lee cyclogenesis, and confidence is very high it will move
northeastward towards the eastern NE/southeast SD/western IA region
by Tuesday evening per both the GEFS and ECMWF ensemble low tracks.
This system continues to have strong dynamics with it, given a
central pressure ~990 mb, which per the NAEFS is in the bottom one
percent of climatology. Additionally, a 110+ kt upper-level jet and
a 40 to 50 kt low-level jet will both be impinging on the warm
sector in our area as the surface low approaches on Tuesday. Surface-
based instability appears to be low to moderate, with values
per the HREF of 500 to 1500 J/kg. However, the kinematic fields
of this system remains quite impressive, with clockwise-curved
low-level hodographs and 0-1 km SRH values of between 200 to
400 m2/s2 off the HREF, so lots of streamwise vorticity to tap
into. Moreover, the Sig Tor Parameter is also indicated to be
around 1 to 3, with perhaps a few isolated values exceeding 4.
For context, a majority of significant tornadoes (EF2 or
greater) have been associated with STP values greater than 1
within an hour of tornado occurrence. So, not only could we be
dealing with at least a few tornadoes with this system, but some
of which could be strong. With that said, how the Tuesday PM
severe weather plays out will depend on how things go with
tonight`s convection. If there is ample clearing/destabilization
in the wake of the morning convection, then that would increase
the severe weather threat on Tuesday, but if there is more cloud
debris and less clearing, then this could tamper the severe
threat for Tuesday. So, we will be watching tonight`s activity
closely to see what influence it has on Tuesday`s severe threat.
SPC has expanded the Enhanced Risk, or level 3 out of 5,
northeastward, now including areas along and south of a Vinton,
IA to Bettendorf, IA to Nekoma, IL line. To top this all off,
there is also the potential for heavy rainfall with this
activity, with Pwat values between 1 to 1.5 inches. This is
above 98 percent of climatology per the NAEFS Pwat anomalies. In
total, between 1 to 2 inches of total rainfall is likely, with
perhaps a few isolated areas receiving over 2 inches of
rainfall. Although the rainfall amounts are expected to the
their heaviest over northeastern Iowa, where ongoing D3
drought is located, the concern for flash flooding will be with
urban areas and other areas of poor drainage.

Tuesday night and Wednesday will remain active as the area of low
pressure gradually moves off to the northeast. Chances of showers
and storms will remain with us, but the threat for severe weather
looks to wane late Tuesday and Wednesday as the stronger jet
dynamics shunts off to the east. Eventually, dry conditions will
return for the second half of the week. There may be another
shortwave to move through on Thursday and bring another round of
showers to our area.

As the Tuesday/Wednesday system departs, expect a return to more
seasonal temperatures by Thursday, with highs in the middle to upper
50s and lower 60s. A couple of chilly nights are possible for next
weekend, with lows in the 30s across the area.

&&

.AVIATION /12Z TAFS THROUGH 12Z TUESDAY/...
Issued at 558 AM CDT Mon Apr 15 2024

VFR conditions are expected throughout the TAF period. Today will be
our final day in a stretch of very quiet conditions before a warm
front lifts through the area late tonight into Tuesday morning,
bringing increasing chances of showers and thunderstorms.
Northeasterly winds at the start of the forecast period will
gradually turn more from the east by late this morning through
the afternoon. Stronger east winds are expected to develop this
evening and overnight, with gusts 20 to 30kts.

&&

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

&&

$$

SHORT TERM...Schultz
LONG TERM...Schultz
AVIATION...Schultz