084
FXUS63 KDVN 280305 AAB
AFDDVN

Area Forecast Discussion...UPDATED
National Weather Service Quad Cities IA IL
1005 PM CDT Sat Apr 27 2024

.KEY MESSAGES...

- Active period continues into the overnight and also into
  Sunday.

- Flash flooding remains a concern overnight into Sunday morning
  for areas that will have received repeated rounds of storms
  south of I-80, and this is where a Flood Watch continues.

- Scattered severe weather remains possible, mainly well south
  of I-80 overnight, but also into Sunday although prior
  convection may have an impact on the magnitude/timing/location
  of severe weather Sunday PM.

- Unsettled weather continues through next week, with periodic rain
  chances.

&&

.UPDATE...
Issued at 1002 PM CDT Sat Apr 27 2024

The primary expectations for the forecast largely continue on
track as we head into the overnight hours. An isolated severe
risk continues, and a potential for a developing flash flood
threat in mainly the Flood Watch area will be something we have
to monitor closely with regenerating thunderstorms.

A mesoscale convective vortex (MCV) near the Iowa/Wisconsin/
Illinois border region will continue to shift northeast through
midnight, dragging a somewhat decaying line of thunderstorms
eastward in the zone along/north of I-80. An associated cold
pool from the storms` longevity should help continue to push
this too east of the CWA. Further south and southwest of our
area too, a low-level jet of 45-50 kt as observed on upstream
profilers in western Missouri will support isentropic lift
along/north of the outflow-modified boundary. This will likely
result in storms in central/northern Missouri to continue to
thrive with even new development possible to the west of these,
all of which will likely clip or advance over the southern CWA.
It may depend on cold pool magnitude that develops with this
convection in Missouri, as there already is an ongoing meso-high
in southeast Iowa "shoving" things along. If that is sufficient
enough of a push, it may take the brunt of the severe threat
mainly south or just clip the southern tier. Severe winds are
the main threat, but cannot rule out a brief tornado threat
given still high values of low-level CAPE, especially ahead of
the outflow boundary.

Of greater concern is the training storms in the southern CWA
in a high moisture transport environment. Looping the radar in
Missouri shows some attempts at backbuilding, and RAP forecast
Corfidi vector do become 5-10 kt across the far south between
05Z-09Z. Similarly, if the cold pool development is sufficient,
it may propagate the heaviest rainfall rates along too and just
south/southeast of the CWA, but confidence in that occurring is
low at this time and the threat still very much includes our
south. Given the wet conditions in this area from Friday (1-1.5
inches) and already this evening (additional 0.5-0.75 inches),
this area is primed for a flash flood risk if 1+ inch per hour
rates set up for 2-3 hours.

&&

.SHORT TERM /THROUGH MONDAY/...
Issued at 140 PM CDT Sat Apr 27 2024

Late morning surface analysis shows a surface low centered
across eastern Minnesota and western Wisconsin, with a cold
front draped to its south across east central Iowa and northwest
Missouri. Off to our southwest, another surface low with a
warm front and dry line was centered over the Oklahoma
panhandle, with storms ongoing along this and ahead of a
shortwave in the same location. This shortwave will progress
northeast over the next few hours, and will be the driver of our
weather over the next couple of hours.

The overall forecast remains on track for the area, with shower and
storm coverage expected to increase over the next few hours. The
first round should be focused along the stalled cold front draped
across east central Iowa as we destabilize and reach our
convective temperature in the upper 70s. Latest CAMs focus the
threat mainly along and northwest of the HWY 151 corridor. Ample
0-6km shear and steep mid-level lapse rates pushing CAPEs
around 1000-2000 J/kg may lead to storms capable of large hail
initially.

The second round of storms will come this evening as the
aforementioned shortwave rides the front and drives additional
lift across the area. A renewed LLJ will also ensure ample lift
and increased vertical shear. There remains some uncertainty as
to where storms will initiate and track, which is likely tied to
early PM convection and how much it stabilizes that warm sector
air in eastern Iowa. Regardless, HREF ensembles continue to
paint areas mainly south of Interstate 80 with high POPs. Severe
storms will also be possible with mainly a large hail and
damaging wind threat with near straight hodographs and cold pool
dynamics in play. While low, can`t rule out a tornado threat in
the QLCS and with any remnant boundaries from early PM storms.
Look for this threat to wane by midnight, with concerns turning
more towards a heavy rain/flash flood risk.

Speaking of which, we will need to keep a close eye on flash
flooding potential with these storms. LLJ will advect in a rather
robust PWAT feed across the region with values approaching 1.75" by
midnight. Where storms do train, latest CAMs show QPF by Sunday
morning approaching 2-4 inches. This looks to be favored mainly
in southeast Iowa, west central Illinois and northeast Missouri,
where a Flood Watch is now in effect through Sunday morning.

Heading into Sunday, scattered showers and storms will persist
through the morning and early afternoon, with a renewed round of
more widespread linear showers and storms expected by the
evening ahead of another robust shortwave ejecting out of the
Rockies. There is potential for this activity to become severe,
with the Storm Predication Center advertising a Level 1 to 2
risk for the area. The primary threats with storms will be
damaging winds and large hail, with a secondary tornado threat
if low-level shear can materialize.

&&

.LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
Issued at 140 PM CDT Sat Apr 27 2024

Post cold front passage, we will be in for a dry start to the
week with high pressure moving across the central Plains and
mid-Mississippi River Valley. By mid to late week, a renewed
round of showers and storms is expected for the area as a trough
in the Rockies ejects several shortwaves across the Plains and
Midwest.

&&

.AVIATION /00Z TAFS THROUGH 00Z SUNDAY/...
Issued at 613 PM CDT Sat Apr 27 2024

A stormy period will be in place this evening, with
thunderstorms widespread before 06Z in eastern Iowa and
northwest Illinois. Winds will potentially exceed 40 kts along
and south of Interstate 80 through 04z.

Otherwise, thunder may become more sporadic overnight, with
rain and mvfr cigs continuing. Sunday, a gradual improvement to
higher MVFR to low VFR is expected, with another round of storms
moving in during the afternoon from west to east.

&&

.DVN WATCHES/WARNINGS/ADVISORIES...
IA...Flood Watch through Sunday morning for IAZ087>089-098-099.
IL...Flood Watch through Sunday morning for ILZ025-026-034-035.
MO...Flood Watch through Sunday morning for MOZ009-010.

&&

$$

UPDATE...Ervin
SHORT TERM...Friedlein
LONG TERM...Speck
AVIATION...Ervin