Ottumwa, Iowa 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

078
FXUS63 KDMX 211751
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1151 AM CST Thu Nov 21 2024

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

.KEY MESSAGES...

- Cold and blustery conditions again today, this time with the
  strongest winds over eastern Iowa. Wind gusts over 40 mph
  possible in the east.

- Winds diminish into the weekend, with dry conditions and
  slightly warmer temperatures Saturday and Sunday.

- Cold air returns to start out next week.

&&

.DISCUSSION...
Issued at 332 AM CST Thu Nov 21 2024

Surface low pressure in the Great Lakes region has begun to deepen
and will eventually drop south and then east around the backside of
the upper level closed low through the day today. With the upper low
tracking away from the area at the same time, the surface low will
primarily remain over Lake Michigan and east of the area. However,
while it may initially sound unimportant to us in Iowa, strong
pressure gradients associated with this low will stretch into the
eastern portions of Iowa today, keeping conditions breezy on
Thursday. Wind gusts of 30 to 40 mph will be likely, with some in
the eastern portions of the area potentially reaching 40 to 45 mph.
That being said, with the lack of any strong CAA to help mix winds
down and cloud cover inhibiting  thermal mixing, the boundary layer
will become shallower through the day, limiting the magnitude of
winds able to be mixed down. Therefore, while 850mb winds are quite
strong (50+ kts) over eastern Iowa, expecting us to only mix out to
~925 mb or 900 mb, which shows a more modest 35 to 40 kts aloft.

The winds calm down quite a bit after Thursday, as the upper low
departs east and a brief period of surface high pressure and upper
ridging sets in on Friday. This high pressure sticks around through
Friday night before another weak wave approaches into the weekend,
flipping flow to be more southerly and introducing warm air
advection back to the state. Temperatures respond some on Saturday
but more significantly on Sunday as highs reach the upper 40s north
to upper 50s south. While there will be some weak moisture transport
present at the low and mid levels, these two moisture streams never
really phase well enough with each other to saturate the entire
column, therefore producing cloud cover in the low- and mid- levels
but keeping the surface dry on Saturday and Sunday.

Temperatures then plunge Sunday night into Monday as cold air
punches into the region on the backside of this wave. This will
cause highs to fall back down into the low to mid 30s to start out
the week, and appear to stay that way for much of next week as a
primarily zonal flow pattern sets up in the upper levels. With this
more neutral pattern in place through the week, guidance is
struggling with how different waves will impact the overall pattern.
This has resulted in quite the spread in solutions as we look ahead
to the Thanksgiving holiday, with either a deepening trough, weak
shortwave or neutral northwest flow, all being possible outcomes
with varying impacts from the deterministic models. Some
experimental AI solutions even show ridging developing through the
same period. Taking a trip to ensemble land does help to consolidate
these varying solutions, showing the primarily zonal pattern through
the first half of the week transition to steady height falls into
the latter part of next week. Provided there is moisture present,
this would suggest some chances for precipitation around the
holiday, including snowfall. Of course, this is all a week or more
out and these solutions can and will change between now and then.
But given it being one of the bigger travel weeks of the year, its
worth at least keeping an eye on until we get closer and guidance
becomes a bit more reliable.

&&

.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 1137 AM CST Thu Nov 21 2024

Stratus has eroded across much of central Iowa quicker than
anticipated this morning with generally scattered MVFR ceilings
around. Expect a few mainly eastern sites (KMCW, KALO) may do a
bit of bouncing between Sct-Bkn MVFR ceilings, but trends
suggest at least MVFR conditions will return to eastern sites
(KMCW/KALO/KOTM) by later this afternoon into evening. The
caveat is timing uncertainty remains quite high with guidance
not handling the current clearing/VFR conditions well, so
updates may be needed in time especially for the onset of any
Bkn-Ovc cloud cover. Although pockets of IFR ceilings may
return, confidence is less than 50% and probabilities in time
for sub IFR conditions are transient enough in nature to
preclude IFR impacts at this time. Some models hint there could
be fog development north or west, but have not included any fog
either with guidance highly variable in impacts in space and
time. Otherwise, gusty winds out of the northwest continue this
afternoon with gusts up to around 30-35 knots. Winds will
gradually diminish through the evening and overnight hours west
to east.


&&

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

&&

$$

DISCUSSION...Dodson
AVIATION...KCM