962
FXUS63 KDMX 130432
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1132 PM CDT Fri Jul 12 2024

 ...Updated for the 06z Aviation Discussion...

.KEY MESSAGES...

- Heat continues to build through the weekend, with peak heat
  indices 105F+ south and west Sun and Mon

- Low confidence in convective trends through the weekend, but
  potential increases somewhat with frontal passage Mon night
  into Tue

- Drier with more seasonal temps and lower humidity for the
  latter portions of next week

&&

.DISCUSSION...
Issued at 302 PM CDT Fri Jul 12 2024

The weather pattern over the next several days will be
characterized by a gradual expansion of the broad Rockies upper
ridge a bit farther into the MO Valley which will increase our
heat and humidity, while the northern Plains will see faster
mid/upper level flow and the passage of a few short waves
keeping convection more active there. Our weather will mainly be
dominated by the heat dome through the weekend, but in
sufficient proximity to the active westerlies that confidence in
convective trends is reduced and precip cannot be ruled out.

At the moment this afternoon, cumulus continues to develop
south and west in the peak heating of the day along and south of
the 1.5km moisture gradient. Farther to the west elevated
convective debris lingers across NE associated with the H85/H7
baroclinic zone. Theta-e advection associated with the
baroclinic zone is expected to advanced north and east through
the night ushering in our elevated heat and humidity for the
weekend, and should mainly be dry due to sufficient CINH surface
and aloft. However some models are hinting that the
thermodynamic forcing may align with the better moisture
currently over southern IA so have mentioned some slight chances
there, but as mentioned in the above paragraph confidence in
convective trends is low.

For tomorrow, any nocturnally driven potential should wane with
the primary concern turning to elevated heat and humidity.
Highs 90-95F are anticipated across the southwest half, and with
advection and evapotranspiration boosted dewpoints to above 70F
peak afternoon heat indices are expected to reach 105F+
generally over the southwest half of the area. Thus have issued
a Heat Advisory for those locations. Similar values are expected
Sunday and potentially Monday, but with the aforementioned
convective uncertainty consensus among surrounding offices leads
to taking heat headlines one day at time. While not a strong
trend, convection allowing and parameterized models both suggest
some potential for some nocturnal convection Sat night so have
added a some slight chances through central portions of the
state. Sunday should see very similar heat and humidity
parameters, with heat indices 105F+ southwest half, so another
Heat Advisory could very well be needed depending on overnight
convection and its strength if it occurs.

By Monday the deepening long wave trough which will eventually
end our heat episode should be traversing the northern Plains
with lingering convection from Sunday night dropping through the
Upper MS Valley and possibly entering northeastern IA when
confidence in convective trends begins increasing somewhat with
sharper focusing mechanisms. A cold front is expected to begin
entering northern sections during the afternoon, but MLCINH is
expected to keep much of the convection at bay until low level
jet contributions increase moisture transport and 0-2km
convergence. Effective shear is expected to be moderate at best,
but there will be some severe potential in this window due to
the degree of instability. The most robust convective potential
should end early Tue as the surface front exits the state,
however the NBM suggests weak waves traversing the base of the
long wave trough will still keep chances for showers and a few
storms in the forecast through early Wed.

Once the lingering effects of the departing frontal boundary end
early Wednesday, the remainder of the week should be dry with
seasonal temps and dewpoints, or even a touch below normal. The
model solutions are in good agreement with weak northwest flow
aloft after the Ontario long wave trough passes, but show varied
placement of the associated surface high (northern Plains vs
Great Lakes). However most solutions suggest generally eastern
low level trajectories which would support a more pleasant temp
and dewpoint regime.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 1131 PM CDT Fri Jul 12 2024

VFR conditions are forecast to prevail through the TAF period. TSRA
potential remains quite uncertain, however model guidance suggests
there may be some iso/sct activity early Saturday morning in
southern Iowa, then shifting into northern Iowa by late Saturday
evening. The likelihood of TSRA occurrence at any particular
terminal is low, and thus still held off on any mention in this
TAF issuance.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
Heat Advisory from 1 PM to 8 PM CDT Saturday for IAZ023-
033>035-044>048-057>061-070>075-081>086-092>097.

&&

$$

DISCUSSION...Small
AVIATION...Martin