009
FXUS63 KDMX 170911
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
411 AM CDT Mon Jun 17 2024

.KEY MESSAGES...

- Warm south and cooler with a few storms north today.

- Warm with heat index values in the 90s to near 100 south today
  and most of the area on Tuesday.

- Boundary stalls over Iowa Tuesday night into early Thursday. A
  few severe storms and heavy rain are possible in vicinity of
  the boundary.

&&

.DISCUSSION...
Issued at 409 AM CDT Mon Jun 17 2024

Surface boundary is still lingering over north central and northwest
Iowa early this morning as it remains stretched between Ontario low
pressure and an eastern Colorado low. Storms have fired on the cool
side of the boundary along the nose of the low level jet and along a
ribbon of strong theta-e advection overrunning the surface boundary.
As previously expected, cool thunderstorm outflow is moving
southeast and likely will push the surface boundary south this
morning before eroding and the boundary lifts back north by this
afternoon. A few storms will likely bubble along the gust front as
it moves into parts of central Iowa this morning while the main area
of storms will remain over northwest into north central Iowa. There
remains the potential for a strip of heavy rain in the
Emmett/Kossuth/Palo Alto county areas. In addition, enough
instability exists for a few severe storms with strong winds or
marginally severe hail to occur yet this morning. As of 4 am, a
few severe gusts have been recorded including 60 mph at the
Estherville ASOS.

The boundary will be the problem of the week as it lifts north into
Minnesota tonight then will settle slowly southeast on Tuesday
reaching the northwest forecast area Tuesday evening. The boundary
will eventually stall over central Iowa Wed/Wed night before lifting
north again on Thursday. The boundary timing and location will have
several implications regarding temperatures and precipitation
chances.

As has been discussed the past few days, the eastern CONUS sub-
tropical high will expand northward today while a short wave moves
east into Montana. This will amplify the southwest flow across Iowa
and much of the upper Midwest. This is what will help drive the
boundary back north later today. High temperatures today are again
going to be problematic forecast wise first due to the
aforementioned gust front and how far south it will get. Some anvil
cirrus may overspread parts of the warm sector this morning but the
anvil steering winds are mostly to the northeast. Thermal profiles
in the warm sector continue to suggest that the NBM remains too warm
for much of the area today and Tuesday and continue to back highs
down to near the 50th percentile NBM which is a few degrees cooler
than the NBM and not as impacted by the warm bias correction that is
influencing the main NBM. Highs in the low 90s are expected,
possibly a few mid 90s given the warmer start to the day and dew
points may mix down a bit more than Sunday. Heat index values though
should mostly remain below 100.

Much of tonight and Tuesday should remain dry as the boundary moves
north. Thunderstorm chances will be in the area Tuesday night
through Thursday. The mean storm motions during this period will be
mostly parallel to the boundary which may bring the potential for
training of storms and heavy rainfall. A tropical system over the
western Gulf will be pushing a tremendous amount of moisture into
Texas into Wednesday night but that moisture will be somewhat
blocked due to the the expanded ridging into the mid-Mississippi
River Vally by the eastern CONUS sub-tropical high. There will still
be an abundance of moisture over Iowa with PWAT values of 1.75 to 2
inches. The main threat may transition to heavy rain as the deep
layer shear along the boundary is weak and not supportive of
organized storms. Friday should be mostly quiet followed by more
active weather next weekend as the main upper level system finally
lifts out and a pattern change commences.

&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 1149 PM CDT Sun Jun 16 2024

Thunderstorms will move across South Dakota and Minnesota
overnight but remain largely north of Iowa. Toward Monday
morning, however, some storms may bleed into northern Iowa and
impact MCW at times with MVFR ceilings/visibilities, so have
included a mention there. Otherwise, VFR conditions will prevail
through the TAF period and beyond.

&&

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

&&

$$

DISCUSSION...Donavon
AVIATION...Lee