← Previous June 18, 2024 2:14 PM

FXUS63 KDMX 181914
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
214 PM CDT Tue Jun 18 2024

.KEY MESSAGES...

- Storms and Locally Heavy Rains into Wednesday
- Much Cooler Wednesday
- Stalling front & continued wet into Thursday
- Heating up into the weekend/Storms PM Saturday

&&

.DISCUSSION...
Issued at 215 PM CDT Tue Jun 18 2024

.Short Term /Tonight through Wednesday Night/...

Confidence Short Term:  Medium to High

Low pressure trough just west of Iowa this morning, situated in 
eastern South Dakota/northern Nebraska with a trailing cool front 
and adjacent warm fronts over southern MN and north central 
Minnesota. Dew points have pooled into the lower 70s over much of 
Iowa and eastern Nebraska with a large pool of mid to upper 60s from 
Wisconsin south to the Southern Plains.  Aloft, a strong LLJ of 45 
to 50kts continues to pull a large and continuous ribbon of +15C dew 
points into northwest Wisconsin. The sharp low pressure trough lies 
across western Nebraska with much cooler air over the Northern 
Rockies and Pac Northwest. Though we remain capped at H700 with +12 
to +14C temperatures over the region now, by late afternoon and 
evening there will be enough lift/sfc moisture convergence to break 
the cap along the approaching cool front in eastern Nebraska, storms 
will begin to develop quickly into the evening hours. The main 
concern tonight will be damaging wind gusts and locally heavy 
rainfall. The environment will be less supportive of large hail and 
tornadoes, but with the instability there will be a potential for a 
brief funnel or tornado. As for upper level wind fields in this 
event, the bulk of any collocated winds through the column will 
briefly be over northern/northwest Iowa between 00 and 06z. That 
said, any severe into the evening will more likely be pulse reports 
than anything organized to more long lived. Tonight as the boundary 
sags into the area, PWATs will be ramping up to 2 to 2.25 inches 
along and just behind the boundary from around 02z through 12z. Warm 
cloud depths are over 4000m which is more than enough to promote 
efficient rainfall. At this time, the sfc boundary will drift into 
southern Iowa while the H850 boundary remains a little farther north 
toward the I80 corridor. This will likely promote additional showers 
and thunderstorms for much of the day tomorrow. With the mid to 
upper level moisture still pooling along the upper level boundary, 
there will be a risk of repeated moderate rainfall across central to 
southern Iowa. Tonight the main risk appears to be across the north 
and maybe limited to a small section of northern/northeast Iowa 
where there is a risk of localized 2 to +4 inches due to the 
boundary becoming a bit more east west oriented there for a slightly 
longer period of time overnight. With the boundary farther south 
Wednesday, the risk will shift toward central to southern 
Iowa/northern MO during the day and afternoon hours. Tomorrow will 
have little chance for any severe weather. Tomorrow the higher PWATs 
and more efficient warm cloud depths will set up south of I80 into 
MO through Wednesday night. At this time there is not much dynamics 
to sustain any long lived thunderstorms or training storms for 
tomorrow. For the moment given the spread of uncertainty as to 
if/where any persistent storms occur, we will not be issuing any 
headlines for flash flooding. Rather, if it looks more likely over a 
region of the forecast area due to less frontal movement or storm 
propagation tonight or tomorrow, then one will be considered. 
However, the front over southern Iowa/northern Missouri is expected 
to lift north once again and reach northern Iowa by Thursday 
morning. This will likely add to our several day rain totals over 
the region. With the passage of the front overnight, mins will 
settle into the upper 50s to lower 60s northwest, while the central 
to southeast holds onto upper 60s to lower 70s.  Highs tomorrow will 
be considerably cooler; afternoon readings in the lower to mid 70s 
most areas with lower 80s possible in the south. Tomorrow night mins 
will be similar to tonight. 

.Long Term /Thursday through Tuesday/...

Confidence: Medium

As the boundary retreats north into Thursday morning, another round 
of showers/storms can be expected. With the better forcing over 
western/northwest and northern areas, the general focus of any 
heavier rainfall will shift back to northern Iowa and areas north. 
At this time, low pressure is expected to deepen over the High 
Plains and this will likely lift the front farther north into 
Minnesota and out of the region by later Thursday night. As warmer 
air moves back into the region at H700, it will be more difficult to 
see storms building over our area, but late Friday night into 
Saturday there may be a tendency for storms over southern MN to 
build south into the cap. Highs Friday and Saturday will return to 
the 90s for Friday and Saturday before a brief cool down Sunday back 
into the 80s. Both operational medium range models show the system 
that tracked north into MN/southern Canada will drag a cool front 
southeast through Iowa by later Saturday evening. This will lead to 
another round of storms Saturday afternoon/evening across the 
region. At first glance, there appears to be a bit more support for 
organized severe weather with increasing wind fields through the 
column Saturday afternoon and evening. Though currently not 
outlooked, the east and northeast may see an uptick in strength 
during the period. Once the front pulls east we will see a few days 
of much warmer and quieter weather as the H700 cap returns across 
the region. Highs will build back into the lower to mid 90s by 
Monday and Tuesday with additional storms possible Tuesday. 

&&

.AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/...
Issued at 1231 PM CDT Tue Jun 18 2024

Main challenges are wind gusts; especially through 02z and then
coverage of storms next 24 to 48 hours. Thin line of convection
over central to north central areas may impact MCW/FOD with some
scattered storms through 00z. Then expecting more coverage for
the remainder of the period with occasional lower vsby/cigs down
to MVFR as the storms track east southeast through 12z.
Lingering convection will remain for the duration of period aft
12z as upper level boundary stalls; with MVFR conditions still
possible. /rev

&&

.HYDROLOGY...
Issued at 215 PM CDT Tue Jun 18 2024

Rainfall, locally heavy in some areas over the next few days will 
lead to rises on area rivers again. The question is how much the 
rivers will rise. The existing official river forecasts take into 
account only 24 hrs of QPF. Our probabilistic guidance, which 
includes QPF out to as much as 10 days is showing higher river 
stages in many locations and much higher in some locations. One 
location (the West Fork Des Moines River at Estherville) is already 
above flood stage.

Based on the present probabilistic guidance such as the QPF ensemble 
hydrographs, the Hydrologic Ensemble Forecast System (HEFS) and the 
National Water Model (NWM), the most likely scenario is many sites 
reaching action to flood stage (minor flooding) within the next 
week. That being said, even moderate or major flooding is not out of 
the question at some locations (but not the most likely scenario). 
Right now the locations to be the most impacted look to be in the 
Des Moines River basin and its tributaries above Saylorville Lake, 
the Raccoon River basin and the Cedar/Iowa/Winnebago River basin. Of 
course the actual placement, amount and duration of the rainfall 
will be big factors in determining the actual hydrologic
response.

&&

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

&&

$$

DISCUSSION...Donavon
AVIATION...REV
HYDROLOGY...Zogg