Norwalk, Iowa 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

706
FXUS63 KDMX 170414
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1114 PM CDT Wed Apr 16 2025

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

.KEY MESSAGES...

- Elevated fire weather conditions through the remainder of this
afternoon; gusty breezes prevail into Thursday

- 20-30% chance of a few storms over southern and eastern Iowa
toward and after sunrise Thursday morning with any activity
diminishing by midday.

- Storm chances increase as high as 60 to 80% north of US 34 late
afternoon into the evening hours. Severe storms possible with main
severe hazard being large hail. Initial storms before and around
sunset west of roughly Highway 169 could have damaging wind gusts
and perhaps a tornado.

- More seasonal temperatures this weekend with renewed shower
  and storm chances Sunday.

&&

.DISCUSSION...
Issued at 200 PM CDT Wed Apr 16 2025

Upper level water vapor imagery shows mid-level ridging pushing into
the state while an upper low is off the California coast with a
shortwave trough over western Canada. Early afternoon visible
satellite imagery has varying degrees of high clouds spread across
Iowa while low level warm air advection is ongoing. Temperatures are
well above normal well into the 60s and 70s this afternoon. Gusty
winds from the southeast are prevailing along with relative humidity
values between 20 and 30% resulting in elevated fire weather
conditions. There have been a handful of fire hotspots - mainly
prescribed burns - detected by satellite through the veil of clouds.
Into tonight, a wave of strong low level theta-e advection in
concert with a 30 knot low level jet develops ahead of a lead
shortwave trough passing over the state. Convective allowing models
(CAMs) are more muted in their signal of convection toward daybreak
Thursday compared to previous runs of the global models. While there
is still a chance of an isolated severe storms or two with large
hail over our southern or eastern forecast area toward daybreak into
Thursday morning (e.g. MPAS suite vs other CAMs), this is less
likely than thought in previous days.

Any ongoing storms are expected to wane in the morning as the low
level jet weakens and an elevated mixed layer (EML) spreads over the
state ahead of surface low pressure moving over eastern Nebraska.
There looks to remain quite a bit of cloud cover at varying levels
per the latest HREF cloud cover guidance. However, if the cloud
cover ends up being less than forecast, forecast temperatures may
need to be boosted as they are near the 25th percentile of the
initial National Blend of Models guidance. The EML should cap off
any storm development in the afternoon until closer to or shortly
before sunset when storms are expected to quickly develop along a
cold front stretched over northwestern Iowa into east central and
southeast Nebraska. Forecast soundings from the 12z HRRR and 9z RAP
show potential for a brief window of surface based storms, but this
is conditional on the boundary layer heating sufficiently to
overcome any lingering inhibition. If surface based storms do form,
there could be 1000 J/kg or more of MLCAPE and the hodographs also
show favorable low level turning for rotating storms (supercells).
However, winds between 500m and 1 to at times 2km show less speed
shear such that this keeps low level storm relative helicity (SRH)
values low. While large hail will be the main severe concern,
damaging wind gusts and a tornado may be possible in this window
around sunset. With the loss of daytime heating coupled with a
restrengthening EML, any surface based storms will transition to
elevated storms. Interestingly, the full hodograph becomes elongated
as the LLJ develops, but with storms transitioning to elevated they
will likely be only realizing more of a linear hodograph. With good
ventilation and steep mid-level lapse rates, the main concern here
would be large hail.

Storms are expected to weaken and lessen in coverage later in the
evening and especially after midnight. While there may be some
lingering showers into Friday morning, the western Canada trough
elongating back into the southwestern US will aid in pushing the
cold front through the area with increasing subsidence and cold air
advection behind it. Additional convection is likely along the
front, but this looks to be just southeast of our forecast area at
this time later Friday afternoon. The cold front will stall south of
the state and should result in dry conditions on Saturday.
Deterministic models agree that a shortwave trough will track over
or near the state late in the weekend. This along with ensemble
means from the various global of the probability of a tenth of an
inch of precipitation point to renewed shower and storm chances
around Sunday.

&&

.AVIATION /06Z TAFS THROUGH 06Z FRIDAY/...
Issued at 1114 PM CDT Wed Apr 16 2025

Expectations have changed little since 00z. VFR conditions are
generally anticipated overnight with nothing beyond patchy mid
and high level cloudiness. A few periods of MVFR visibilities
due to smoke cannot be ruled out, but confidence is insufficient
to mention at any particular location at the moment. There is
some potential for showers east into the early morning hours,
but they should remain VFR. Thunder may briefly occur as well,
but confidence is too low to include until short term trends
note otherwise. At least MVFR stratus is expected to overspread
central IA Thursday as low level moisture increases. Chances for
showers have been introduced Thursday evening. Thunder is
certain possible as well, but has not been mention at this lead
time until confidence increases. Periods of LLWS are also
anticipated south overnight night, and again near KOTM Thursday
evening.

&&

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

&&

$$

DISCUSSION...Ansorge
AVIATION...Small