602
FXUS63 KDMX 091925
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
225 PM CDT Sun Jun 9 2024

.KEY MESSAGES...

- Breezy winds decreasing this evening

- Pleasant conditions continue into Monday

- Seasonal warm summertime temperature begins Tuesday

- More active pattern with storm chances at times Tuesday
  through Thursday

&&

.DISCUSSION...
Issued at 225 PM CDT Sun Jun 9 2024

The breakdown in the sprawling, broad trough over southern Canada
into the Northeastern US is in progress as one longwave trough is
now being carved out over northeastern North America with its center
along the Quebec/Ontario province border. Of first influence, this
has kept the overnight and morning convection well south of Iowa
with heavy rainfall and flash flooding over southern Missouri.
Secondly, the resulting surface pressure gradient has been tight
over the Great Lakes stretching into the northeastern third to half
of Iowa this afternoon. This has resulted in breezy to gusty winds
there with winds gusts of 35 to around 40 mph. With the potential
for blowing dust as shown on the Iowa DOT Plainfield camera, did
issue an SPS for these winds and potential, localized visibility
impacts. Temperatures near to below normal and low humidity will
prevail today and Monday as high pressure passes through the region
making for comfortable June conditions.

Tuesday will mark the transition towards a warmer and more active
pattern for the remainder of the work week. The longwave trough over
northeastern North America will depart and at the same time a ridge
will build over the Desert Southwest. This will push higher heights
over Iowa Tuesday through the end of week and perhaps into next
weekend. High temperatures will be above normal reaching well into
the 80s to around 90 degrees during this period. This heat will be
nothing unusual for June with nothing of note on the ECMWF extreme
forecast index or shift of tails. Latest NBM maintains a 70% chance
of reaching or exceeding 90 degrees Thursday afternoon along and
south of Highway 30 across much of Iowa.

Now, the ridging would push farther northward allowing for more
heat, but a parade of shortwave troughs passing over the southern
Canadian prairies will keep the ridge depressed. These shortwaves
will bring several storm opportunities through the week with the
first being early Tuesday with a lead shortwave. These could bring a
few showers or storms to northern Iowa, but time of the day does not
lend itself to an apparent severe risk. As the high departs to the
east, near surface flow will become from the southwest allowing for
the return of richer boundary layer moisture. A cold front tied to a
surface low associated with a northern stream shortwave will be
brought into the area later Tuesday. Appreciable instability and
shear may be along this boundary for a strong storm, but the
shortwave energy is making a glancing pass that may limit widespread
thunderstorm chances or severe weather. Another shortwave moves into
the region later Wednesday and with more instability and higher deep
shear, this could result in organized thunderstorm development. This
seems most likely over northern Iowa closer to the forcing with the
SPC day 4 outlook as well as the Colorado State University`s (CSU)
machine learning random forest outlook placing higher probabilities
over some or all of northwestern or western Iowa. Thursday will
bring a final round of storms and possible severe risk with this
parade of shortwaves, though how much of the state may have storms
will depend on the speed of the cold front. Mid-level lapse rates,
instability, and deep layer shear all look favorable for a severe
risk and here too, SPC and CSU show the highest probabilities over
southern and/or central Iowa. This cold front is currently forecast
to push south of the state Thursday night into Friday and give a
short break from the active pattern. However, waiting off the
southern California and Baja California coast most of the week will
be an upper level closed low, which will finally eject towards the
region late in the week. This could bring a better chance of
thunderstorms on or around Saturday with the shortwave energy
moving closer to or over the state.

Looking at hydrology concerns, while the warm cloud depths and
precipitable water values look to be seasonal to perhaps seasonally
high, QPF amounts at this time horizon do not look concerning
looking at the 100 member ensemble data. Also, with agricultural
crops established with last week`s USDA crop progress showing nearly
all corn planted and 80% emerged with soybeans lagged being about
20%, this will help to absorb and mitigate heavy rainfall concerns.
Rivers are also trending downward allow for some capacity as well.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1230 PM CDT Sun Jun 9 2024

There is high confidence in VFR conditions prevailing through
the period at all terminals. Breezy winds from the northwest
gusting between 20 to around 30 knots will decrease around and
after sunset. Lighter winds will become from the northeast late
in the period.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

DISCUSSION...Ansorge
AVIATION...Ansorge