Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 141743
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1243 PM CDT Thu Mar 14 2024

 ...Updated for the 18z Aviation Discussion...

.KEY MESSAGES...

- Areas of showers and storms likely through the morning and
  into the afternoon. Threat of severe weather has decreased.

- Critical fire weather conditions may develop Saturday.

&&

.DISCUSSION...
Issued at 224 AM CDT Thu Mar 14 2024

Overnight radar imagery is full of activity with widespread shower
and thunderstorms stretching from NE/KS and through northern MO into
southern Iowa. This is all associated with an upper shortwave that
has broken off from a large parent upper low closing off over the
western conus. The most intense thunderstorm activity so far
has remained just south of the state within the deeper
instability axis, generally along and south of a surface warm
front. Showers and storms have bled north into southern Iowa,
however stubborn dry air has chewed into progression and
coverage with northerly extent. A few stronger cores remain
possible in far southern Iowa through early morning, posing a
threat for small hail and gusty winds. Rain gauges in the area
suggest up to 0.75" has fallen in a few areas, so pockets of 1"+
amounts are certainly possible before this activity pushes east
later this morning.

Focus for rainfall chances shift further north this morning and
afternoon as a fractured mid-level def zone moves through.
Again, a very dry airmass sitting just off to our north and east
will impinge on the precipitation shield and limit the spatial
extent of appreciable QPF. Still looking at the potential for
0.25" to 0.50+", mainly between Hwy 30 to Hwy 18 and lesser
amounts or even no additional rainfall to the north and south.

Conditions clear out tonight as the dry air spills back south
in the mean northwesterly flow behind the departing wave. While
no precipitation is expected through the weekend, fire weather
concerns crop up Saturday as a front sweeps south through the
state. Deep boundary layer mixing behind the front + dry airmass
should have no problems undercutting NBM dewpoints, which like
most model guidance has exhibited a high bias with dewpoints in
recent days. Taking the 25th percentile of NBM guidance lowers
RH values into the 20% range during the peak heating hours.
Winds near the top of the mixed layer are ~30-35 kts and should
have little trouble transporting to the surface within deeply
mixed, unidirectional northwest flow. Conditions turn cool and
blustery Sunday into Monday as a deep upper low dives into the
Great Lakes and shoves a colder airmass southward into the
region. Wind chills come Monday morning will be in the single
digits and teens, a far cry from the warmth we`ve seen as of
late. The cool spell does not last long as warm air advection
returns by mid-week beneath building heights aloft, sending
temps back above normal with highs in the 60s looking likely.

&&

.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 1236 PM CDT Thu Mar 14 2024

A widespread mix of cigs across Iowa early this afternoon
ranging from IFR to local LIFR over southern Iowa to improving
conditions over northern Iowa with VFR expected at KMCW by early
this afternoon and possibly as far south as KDSM by late
afternoon. An area of rain over central Iowa will slowly
diminish through the afternoon before ending. Cigs will then
improve with VFR expected at most sites by late this evening. A
northeast wind will increase later this afternoon and evening
before diminishing into Thursday.

&&

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

&&

$$

DISCUSSION...Martin
AVIATION...Martin


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