320
FXUS63 KDVN 272320
AFDDVN

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

.KEY MESSAGES...

- Active period ahead by this evening through Sunday with several
  rounds of showers/storms.

- Flash Flooding remains a concern for areas that receive
  repeated rounds of thunderstorms tonight/Sunday with the
  potential for areas of 2-4 inches of rain. A Flood Watch has
  been issued for southeast IA, west central IL and northeast MO
  where confidence in seeing these rainfall totals is highest.

- Severe weather is also possible, particularly by this evening,
  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 613 PM CDT Sat Apr 27 2024

Frontal supercellular storms have been slowly moving east
northeast in the north, but that process should shut down
through 9 PM.

The south 1/2 to 2/3rds will see a progressive QLCS move east
northeast into the area, with wind and embedded possible QLCS
tornadoes. Hail threats may be decreasing for now. This cluster
of storms will push east more quickly than storms that were
occurring earlier this evening, on the pace of 40-50 mph.

Heavy rainfall remains expected from these storms, and any
repeat/or bookend storm clusters.

A tornado watch is in effect for most areas through Midnight.

&&

.SHORT TERM /THROUGH SUNDAY/...
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 /SUNDAY 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...Speck
LONG TERM...Speck
AVIATION...Ervin