685
FXUS63 KDVN 191952
AFDDVN

Area Forecast Discussion
National Weather Service Quad Cities IA IL
252 PM CDT Sun May 19 2024

.KEY MESSAGES...

- A Marginal or level 1 out of 5 risk for severe storms is in
  place tonight with large hail and lightning being the main
  threat.

- Active weather will continue through the period as we are
  more in a mid summer pattern than mid spring.

- Severe weather is possible Monday through Tuesday. An
  enhanced risk for severe weather is forecast for Tuesday.

&&

.SHORT TERM /THROUGH TONIGHT/...
Issued at 252 PM CDT Sun May 19 2024

A frontal boundary sits to our south across northern Missouri into
central Illinois. Regional radar shows scattered showers and storms
moving northeastward across central Iowa. Another area of showers
and storms is currently moving into eastern Nebraska. Temperatures
at 1 PM range from 73 degrees at Dubuque to 84 degrees at Keokuk.

At 500 MB, a shortwave trough over the Pacific Northwest is forecast
to dig southeastward and reinforce troughing over the southwestern
US. This will result in southwesterly flow aloft from the
Southwestern US into the Great Lakes. Showers and storms to our west
are associated with a shortwave trough that is lifting into the area
now through this evening. Have been watching moisture recover across
the area over the last few hours with most unstable CAPE building
northward but ranging from 500 to 1000 J/KG with deep layer of 30 to
40 knots across the area. Models continue to show further
destabilization across the area with 500 to 1500 J/KG from north to
south across the area. Expect showers and storms to develop across
the area as we warm further with isolated to scattered showers and
expect these to exit northwest Illinois by  03 to 06 UTC.

In the wake of this wave, models continue to show fast moving
shortwave ridging that will build into the area. There are still
some slight timing differences between the models which lends lower
confidence in the amount of drying time there will be as another
stronger shortwave trough will be quickly on its heals as a 30 to 40
knots low level jet across central Iowa veers into the area prior to
12 UTC as the stronger lift associated with the approaching
shortwave spreads into the area. This will lead to the development
of showers and storms late in the period. Model soundings show a
strong low level inversion leading to elevated storms. The primary
threat from these storms will be hail and lightning. I have tried to
adjust chances of showers and storms to account for this but expect
the chances for showers and storms to remain west of the Mississippi
River tonight. Low temperatures on Monday morning will be in the
60s.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...
Issued at 252 PM CDT Sun May 19 2024

Active pattern with a mid-summer like pattern is expected to
last through most of the period as a stalled out boundary
resides just south of the CWA Monday through Wednesday. This
boundary will separate the area between Tds in the 40-50s, to
the more robust deep moist Tds in the 60s and 70s to the south.
A series of weak waves and possibly MCVs/convective induced
waves/ move over the boundary Monday morning and afternoon. A
strong synoptic wave, with better shear is expected to approach
the area into Tuesday. At the same time a deepening surface low
with this wave will help to bring this boundary north as a warm
front Tuesday. This will bring higher Tds into the area ahead
of the wave and along with increased shear. Then the boundary
is sent south again as a cold front later Tuesday. After this
point, there are questions about where the boundary will be and
additional chances for thunderstorms.

Monday: Guidance has trended towards a strong wave associated
with a MCV from tonights convection across the Plains. An
initial wave of showers and storms will move through the area in
the afternoon, possibly leaving some OFBs for convection later.
There is a good chance much of the area will see high temps
before this convection then cool into the 70s because trying to
reach 80 again in the late afternoon. Destabilization in the
afternoon, mainly along and east of the Mississippi River will
coincide with the better shear associated with the vortmax.
CAMs have showers and storms form shortly after 18z and move off
to the east. Looking at shear, guidance is rather weak,
especially in the GFS which is faster with the wave. Depending
on timing of this wave, could see better shear co-located with
the better forcing and CAPE across our east. There will be a
threat of damaging winds with a secondary threat of large hail
and tornadoes.

Tuesday: This continues to look like a big severe weather day
across the region. The warm front will move north bringing the
area into the warm sector. CAMs have convection moving through
mid to late morning. In summer, this would kill our PM severe
chances, however, the strong synoptic wave will continue to
bring CAPE into the area. Thunderstorms are expected to
redevelop west of the area. At first, 0-6km shear vectors
perpendicular to the forcing will favor supercells. The 12z
NAMnest depicts this evolution well with the line of supercells
just west of the CWA at 00z Wed. All hazards are possible with
these initial cells. With weak upper level flow, these cells
will quickly turn into a line. Strong LLJ will result in a long
lived QLCS. 0-3km shear vectors are orientated and strong enough
for mesovort development and areas of enhanced wind gusts. After
00z, surface winds veer and there becomes less curvature in the
low level hodos, suggesting the tornado threat is waning. If
winds stay backed or back due to the storm, then a tornado
threat would be possible after 00z as the line moves into our
area. In addition, some heavy rainfall will be
possible with this event, with PWs around 1.5 to 1.7 inches,
which would be above the 90th percentile for this time of year.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1236 PM CDT Sun May 19 2024

A difficult TAF forecast for this period. An area of showers and
storms is approaching I-35 and weakening in central Iowa. Have
moved showers into CID around 21 UTC and then move it eastward
to KDBQ, KMLI, and KBRL by 00 UTC then exit this area of showers
prior to 06 UTC. Expect periods of MVFR visibilities in
showers. Left thunderstorms out of the TAFs for now but they are
possible. There will be a quiet period with high pressure
overhead and a return to VFR conditions. A second round of
showers and storms will move into the area by 12 UTC and linger
through the morning hours. Again, MVFR ceilings and visibilities
are possible with these storms as well. East winds around 5 MPH
will slowly turn to the south through 12 UTC on Monday and
increase to 10 to 15 knots.

&&

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

&&

$$

SHORT TERM...Cousins
LONG TERM...Gibbs
AVIATION...Cousins