671
FXUS63 KDMX 081125
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
525 AM CST Fri Nov 8 2024

 ...Updated for the 12z Aviation Discussion...

.KEY MESSAGES...

- Pleasant today with highs in the upper 50s to near 60.

- High chances (>80%) for rain Saturday, lingering into Saturday
  night west/north. Rainfall amounts of 0.10" to around 0.25"
  will be common.

&&

.DISCUSSION...
Issued at 232 AM CST Fri Nov 8 2024

Fairly quiet conditions tonight as a broad ridge of surface high
pressure blankets the state. Spurious pockets of fog have been
observed once again, but not as widespread or as dense as
previous nights to this point. A few areas of more notable
visibility restrictions of a mile or less are likely toward
sunrise, but fog will quickly dissipate as we begin to warm this
morning. Today is looking quite pleasant as winds remain on the
lighter side and temperatures top out in the upper 50s to near
60, which is 5 to 10 degrees above average for this time of
year.

A nearly cutoff large upper low currently near the AZ/NM border
kicks northeast across the central Plains on Saturday as it is
absorbed into the mean prevailing flow aloft. The 00z model
suite remains nearly unanimous with a swath of rain showers
passing through in concert with low to mid level thermal forcing
and northward moisture transport. Forecast advertises high
chance PoPs (80%+) translating north and east through the day,
starting in our southwest counties early morning and eventually
arriving north/east by the afternoon. Upper low matures as it
moves into eastern Nebraska by late afternoon with a well
defined dry slot wrapping around the southern periphery of the
system, which will eventually dry out much of the area by mid to
late day. The exception would be portions of western into
northern Iowa which will reside under a decaying mid-level
deformation zone as the upper low begins to occlude, and
support at least scattered light rain shower activity into
Saturday night. The kinematic parameter space is rather
impressive by mid to late Saturday afternoon with the upper low
and surface reflection in a climatologically favored corridor
for cool season severe weather episodes in our area. However,
the deep moisture fetch ahead of this system is interrupted by a
weakness in the surface pressure fields to our south near the
Gulf coast, likely due to influences from Raphael in the GoM.
Fortunately models generate little to no CAPE this far north and
thus any threat of severe weather is expected to stay low.
Overall precip amounts will be on the lighter side with both
GEFS/ECENS showing <10% probs for 0.50" of rain, with
deterministic model guidance showing 0.10" to 0.25" amounts.

Temperatures remain near to above normal Sunday and into early next
week along with dry conditions. A weak shortwave pushes a
somewhat diffuse frontal boundary through the state Monday, but
has little appreciable moisture to work with and will have no
meaningful sensible impact other than a wind shift and passing
mid/high level clouds. Next opportunity for precip arrives
Wednesday as a trough emerges from the western conus. GFS and
Euro show considerable differences wrt to amplitude and
progression of the trough, which has cascading impacts on
probable precip coverage, wind potential, etc. Respective
ensemble data sets do not offer much more clarity and generally
reflect their deterministic counterparts, and thus sticking with
the NBM 30-40% chance for rain is prudent until models start to
exhibit more consensus in the pattern evolution toward the
middle of next week.

&&

.AVIATION /12Z TAFS THROUGH 12Z SATURDAY/...
Issued at 525 AM CST Fri Nov 8 2024

Pockets of visby restrictions from fog this morning is the primary
challenge for the current TAF period. Most observed fog has been
confined to portions of north/east Iowa. ALO has seen intermittent
visby reductions down to 1sm or less at times. Opted to leave in a
TEMPO mention of IFR visby through 14z. Fog coverage has been very
sparse elsewhere, and most model guidance maintains VFR
prevailing conditions.

Any fog coverage will be quick to dissipate after sunrise this
morning, with VFR conditions prevailing through the remainder of the
TAF period.

&&

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

&&

$$

DISCUSSION...Martin
AVIATION...Martin