Hamlin, Iowa Weather Forecast Discussion

242
FXUS63 KDMX 161108
AFDDMX
Area Forecast Discussion
National Weather Service Des Moines IA
608 AM CDT Tue Sep 16 2025
...Updated for the 12z Aviation Discussion...
.KEY MESSAGES...
- Today will be the warmest day over the next week with highs in the
  80s to near 90 degrees. Temperatures begin to trend downward
  starting Wednesday through late this week.
- 20-30% chance of isolated to scattered showers and
  thunderstorms with chances highest this afternoon. Severe
  weather is not forecast, but weak funnel clouds are possible
  from developing storms with gusty winds up to 40 to 45 mph are
  possible from decaying storms.
- Extended period of rain and storm chances over Iowa Wednesday through
  Friday that linger into this weekend. It will not rain during
  this entire period, but rain is likely each day in at least
  some portion of the state.
&&
.UPDATE...
Issued at 323 AM CDT Tue Sep 16 2025
Upper level pattern is taking on an omega block as seen on GOES-East
water vapor imagery early this morning. There is the closed low
spinning over the Carolinas with the other closed low over the
northern Rockies with a ridge of high pressure wedged between
the two. Iowa will largely be under the influence of the tilted
ridge axis today, which is just off to our east and pointed into
the western Great Lakes. Forecast soundings are indicative of
this ridge with wind speeds below 500mb less than 10 knots. With
the ridge in place, there is little in the way of forcing with
it remaining subtle at best. While forecast soundings have once
again backed off of the convective temperatures being breached,
the capping is weak enough such that peaking heating should be
able to aid in the development of isolated to perhaps scattered
thunderstorms, mainly this afternoon and early this evening.
The weak flow means that severe weather is not a concern today;
however, gusty winds from weakening storms and the funnel cloud
potential still remains. Soundings show an inverted V signature
with dry low levels and downdraft CAPE values over 1000 J/kg.
Convective allowing models are picking up on the gusty outflow
winds up to 40 to 45 mph as storms decay. For the funnel cloud
potential, the non-supercell tornado parameter on this run of
the RAP is not noteworthy and LCLs are a bit higher. That said,
examination of soundings show that the 0-3km CAPE will exceed
150 J/kg with a degree of enhanced stretching potential as well.
Thus, considering all the ingredients in this weak flow regime,
will need to be monitoring for weak funnel clouds during the
cumulus/storm growth phase. Temperatures will be similar if not
perhaps a degree or so lower compared to yesterday with the
850mb temperatures remaining largely unchanged so it will be a
warm and humid day for outdoor activities.
As storms dissipate early this evening, the closed low over the
northern Rockies will slowly begin to trek towards the upper
Mississippi River Valley through late this week passing over it
sometime this weekend. The trend with this feature has certainly
been a slowing down of its progression over the last 24 to 48 hours.
With this low sitting and spinning west of Iowa through Friday,
waves of low level theta-e advection will be paired with a steady,
modest QG convergence. This will result in limited sunshine and
conditions that will turn more seasonal late this week.
Further, chances for showers and storms will increase over the
state given this forcing. Those chances will initially be highest
over western Iowa compared to eastern Iowa on Wednesday into
Thursday before spreading more across the state Thursday night
into Friday. Severe weather continues to look unlikely given the
weak shear. While precipitable water values will be 150 to 175%
of normal with seasonally high warm cloud depths at times and
thus could lead to locally heavy rainfall, antecedent dry
conditions per USGS streamflows, NASA SPoRT relative soil
moisture percentiles, and National Water Model high magnitude
flows forced by the GFS or NBM are not alarming on a broad scale.
Showers and storms may linger into this weekend dependent on
how quickly or slow the closed low finally moves east of the
region.
&&
.DISCUSSION...
Issued at 137 PM CDT Mon Sep 15 2025
At 500 MB, the large high pressure ridge that dominated the
Midwest over the weekend has been pushed a bit further eastward,
and now stretches from the southern High Plains northeastward
into the Great Lakes region. Iowa is still beneath the western
periphery of the ridge and temperatures remain well above
normal. However, a broad low pressure trough has carved out over
the northern High Plains and Rockies, with one lobe moving over
the Dakotas today. It was the approach of this trough that
shunted the ridge eastward and has provided a return of some
showers and thunderstorms today, as well as somewhat mitigating
the seasonally impressive heat of the past couple days.
As the 500 MB lobe of vorticity over the Dakotas today moves up
into Canada tonight, in its wake Iowa will lie beneath light
southwesterly flow between the larger trough well to our
northwest and the elongated ridge just to our southeast. The
result will be persistent, light southeasterly surface flow,
broad and nebulous forcing for ascent, ample available moisture,
and low coverage (20-30%) rain chances primarily tied to diurnal
heating with a maximum in the afternoon and evening today and
Tuesday. With very weak flow/shear and no strong forcing severe
weather is not anticipated, however, on Tuesday
afternoon/evening most model solutions depict strong 0-3 KM CAPE
of around 200-250 J/kg along with enhanced stretching
potential, signaling some potential for weak funnel clouds that
we will continue to assess tonight and tomorrow. Also, with the
main 500 MB ridge axis having moved east of us and some cloud
cover associated with scattered showers and storms, temperatures
will be held a bit more in check Tuesday with highs generally
ranging in the upper 80s and a few 90 degree readings very
similar to today. While this is below the levels seen last
weekend, it is still well above normal and combined with
dewpoints in the low to mid-60s, will still feel warm and humid
for most outdoor interests.
On Wednesday and Thursday the approaching 500 MB trough will
slow up and gradually close off, with the resulting low spinning
over the High Plains for a couple of days before finally pushing
across Iowa and Minnesota sometime roughly around Saturday. This
will bring several days of somewhat cooler, generally cloudy
weather in the latter half of the week, along with higher rain
and thunderstorm chances. Appropriately, PoPs steadily increase
from west to east around Wednesday with 40-70% rain chances in
parts of our forecast area between Wednesday and Friday or so.
The synoptic set-up does not favor significant severe weather
chances, however given the degree of atmospheric moisture and
weak steering flow/slow storm motions, locally heavy rainfall
will be possible. Very dry antecedent conditions are in place
which will mitigate any flooding concerns, however if high-
rainfall rate storms happen to affect a flood-prone area or any
location receives multiple rounds of heavy rainfall over those
few days, then some localized impacts could be possible. The
Weather Prediction Center has included a Marginal Risk of
flooding in Iowa accordingly.
The 500 MB trough will move off to our east around the latter
half of the weekend, but it appears another trough will deepen
over the central U.S. in the early part of next week. There is
considerable model variability in the solutions for that system,
but it is likely to result in continuing rain chances and a lack
of significant warming during that time.
&&
.AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/...
Issued at 608 AM CDT Tue Sep 16 2025
This aviation period is not without its uncertainty despite
official forecast showing VFR conditions. Once again today,
there will be the potential for isolated showers and storms to
develop. Chances are highest at 20 to near 30% from late this
morning through late this afternoon. However, confidence in
which location may see one continues to be too low to include at
any terminal. So, will be monitoring for AMD. Any shower or
storm that does form may produce gusty winds as the storm
dissipates.
&&
.DMX WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
UPDATE...Ansorge
DISCUSSION...Lee
AVIATION...Ansorge

NWS DMX Office Area Forecast Discussion