-- Discussion containing changed information from previous version are highlighted. --
873
FXUS63 KDMX 200451
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1151 PM CDT Wed Jun 19 2024

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

.KEY MESSAGES...

- Retreating front - continued wet into early Thursday
- Heating up into the weekend/Storms Saturday
- Period Showers/storms return Tues/Wed
- Warm & humid conditions persist next week

&&

.DISCUSSION...
Issued at 213 PM CDT Wed Jun 19 2024

.Short Term /Tonight through Thursday Night/...

Confidence Short Term:  Medium to High

After an evening/overnight of welcomed rainfall, we continue with a
lazy boundary from southwest Iowa to northeast Iowa early today. A
weak impulse at H850 is embedded in the flow in north central MO at
12z and will drift north today, resulting in continued showers and
isolated storms mainly near and south of the boundary through
afternoon. Not much has changed with regard to PWATs and warm cloud
depths today. This will result in some heavier showers at times
through 00z, but rainfall amounts are expected to be mainly under a
half inch. Despite the belt of moisture lingering in the south
today, the northwest has cooled and dried enough to prevent much
rainfall. High pressure over the Northern Plains is briefly
providing a short window of dry conditions there. The overall
pattern remains the same. There is a low over Mexico with the
tropical system more/less stuck in the western Gulf. A long fetch of
moisture is being pushed northwest through Texas and eastern
Colorado, somewhat displaced now from yesterdays +15C plume which
was as far north as southern Canada. There is also a large
subtropical high off the east coast which has been keeping storms
from getting east of the Mississippi River and will eventually back
toward the Central Plains over the weekend. As the high moves
northeast tonight, a piece of energy will peel off the Mexico low
and amplify in the Western Plains. This will bring the higher
moisture plume back north and also lift the current lazy front back
into northern Iowa by 12z Thursday. Tonight the strongest forcing,
warm air advection and best frontogenesis is over Nebraska into
northwest Iowa. While the area of showers and storms over
southeast/eastern Iowa becomes more diffuse and weaker through early
evening, an area of storms will gradually become more organized and
widespread over Nebraska between 00 and 06z. Though there are some
minor differences in the operational EC/GFS, there is good consensus
for the overall placement and evolution of Nebraska storms overnight
tonight into Thursday. North of US20 will likely see more storms
than the remainder of the region later tonight into Thursday night
as the front struggles to lift farther north with any outflow
keeping the front somewhat stationary. Current CAMS is suggesting
less than a quarter inch will fall over the north through Friday
sunrise, while both synoptic models are forecasting a range of half
inch to over an inch from north central to northwest areas. Most of
the north`s flash flood guidance remains near 1.5 to 1.75 through the
period, so the risk for any hydro issues remains low other than any
quick 1 to 2 inch amounts that fall in urban locations. Through the
day Thursday, our H700 temperatures respond and warm to near 10C in
the south once again as the higher chances for storms lifts north.
Lows tonight will be fairly mild in the south with mid to upper 60s
expected while the north dips to around 60.  Tomorrow, warm and
humid cnoditions return with mid 70s north where scattered storms
will be more common while the central/south will reach the mid/upper
80s. With the front retreating to southern Minnesota by Friday,
overnight mins Thursday night will range from the mid 60s north to
the lower 70s south.

.Long Term /Friday through Wednesday/...

Confidence: Medium to High

By Friday the eastern CONUS ridge will have backed west enough to
keep the best forcing north/west of the area. A nearly standing wave
over Colorado will continue to transport the +15C moisture plume
north into the Dakotas and Minnesota where moderate to heavy
rainfall and flooding is becoming more apparent. While Iowa will not
be capped at H700, forcing only begins to increase Friday night into
Saturday as the Colorado low finally ejects northeast into northern
MN. There is good consistency in the evolution of the system between
the GFS/EC. This will likely drag a cool front across Iowa Saturday
afternoon. There will be a potential for a cluster of storms to
track into northern Iowa late Friday night, while additional storms
build southwest along the boundary Saturday. Increasing low level
jet Friday night will also help to sustain any storms that fire over
northwest Iowa. This will also be aided by a weak H500 wave
overnight, while another wave accompanies the Saturday convection.
There are some thermal differences on Saturday that complicate any
severe weather forecast at this time. While the GFS is a bit cooler,
the EC is building temperatures at H700 during the day but at the
same time increasing 0-6km bulk shear enough to help in storm
organization. Both models suggest a lack of significant frontal
convergence during the day. All things considered, scattered storms
should occur with a few possibly reaching severe levels. We have a
few more days to parse out the details.  Similar to this go around,
we will see an increase in PWATs to around 2 to 2.25 inches along
the boundary with warm cloud depths above 4000m. This will also
promote efficient rainfall and possibly a quick inch or two in any
of the more organized storms. The front will be east of the region
around 06z Sunday with a break from the rain and heat into Sunday.
For the period Thursday through Saturday, temperatures will be
warming up again into the 80s to lower 90s in the south. Sunday may
see a drop of some 5 to 7 degrees with 70s to mid 80s over the
region. Our current forecast may need a small downward adjustment
for Sunday as we near the weekend. Toward the end of the period, we
will see a gradual building of heights at H500 with nearly steady
H850 temperatures in the lower 20s. This will keep highs in the 80s
to lower 90s; lows in the 60s to lower 70s. There will also be a
tendency to see a few impulses tracking within the flow which will
bring storm chances periodically to the area.

&&

.AVIATION /06Z TAFS THROUGH 06Z FRIDAY/...
-- Changed Discussion --
Issued at 1148 PM CDT Wed Jun 19 2024

No dramatic changes within this TAF issuance. Chances for
thunder remain relatively low, so have limited precipitation
mentions to VCSH mainly in/around KDSM/KOTM/KALO. More pertinent
will be the MVFR/IFR ceiling progression across the area as hi-
res guidance continues to suggest expansion and northward lift
through the period. Have continued to hold back on the most
aggressive (IFR) depictions and kept current prevailing mentions
to MVFR. That will need to be monitored though as there is an
area of IFR ceilings over southern Iowa and northern Missouri,
just uncertain how expansive that will truly become.
-- End Changed Discussion --

&&

.HYDROLOGY...
Issued at 213 PM CDT Wed Jun 19 2024

Not much response from last nights rainfall over the area and today
we have received only light amounts in the south. Will need to
monitor northern Iowa next 3 to 4 days as increasing risk of
moderate or locally heavy rainfall over portions of northwest Iowa;
particularly near the West Fork Des Moines River Basin.  Thursday
and Friday into Saturday may bring sufficient rainfall to push some
areas back into minor flood stage over the weekend.

&&

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

&&

$$

DISCUSSION...REV
AVIATION...Curtis
HYDROLOGY...REV