486
FXUS63 KDMX 061137
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
637 AM CDT Sun Oct 6 2024

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

.KEY MESSAGES...

- Elevated Fire Danger today with breezy to gusty wind and very
  dry relative humidity values.
- Cooler today and Monday but still near normal temperatures.
- Perhaps some frost tonight north central and west and a few
  locations may drop to near freezing by early Monday morning.

&&

.DISCUSSION...
Issued at 332 AM CDT Sun Oct 6 2024

The cold front that passed through Iowa late Saturday afternoon and
into the evening is now into Illinois and Missouri. Another boundary
is diving southeast through central Minnesota and southeast South
Dakota. Gusty northwest winds are accompanying that boundary
passage. The boundary should reach the far north central Iowa by 6
am and move across the rest of the area this morning followed by
high pressure moving into western Iowa this afternoon. The cold air
at 850 mb behind the second cold front is noticeable with sub 0C
temperatures moving over central and northern Minnesota and that 0C
line could clip far northeast Iowa this morning before moving off to
the east.

Temperatures will be much cooler than yesterday`s near record highs.
highs today will be in the 60s north to low 70s south. Those values
are actually near current normal high temperatures so while today
and Monday will be the "cool" days in the forecast, it will not be
quite that cool outside of low temperatures tonight. More on that
shortly. Dew points will be much lower today and the combination of
the arrival of high pressure across the west and afternoon mixing
and lowering of dew points, the values should fall into the 20s to
low 30s this afternoon. That will result in relative humidity values
falling into the 20s as a result. The peak wind gusts today are
expected this morning as the boundary passes through then a relaxing
pressure gradient and diminishing mixed layer winds will lead to
diminishing winds by this afternoon. Regarding fire weather, there
will still be a high to very high fire danger despite the peak winds
and lowest relative humidity values not overlapping timeframe. Will
be issuing a Special Weather Statement to highlight the gusty wind
this morning and the potential for any fires to spread rapidly given
the wind and the dry fuels, especially the cropland areas.

The area of high pressure will be centered over western Iowa after
midnight tonight. This should result in good radiational cooling
conditions. Dew point values will be dropping into the mid 20s to
low 30s so the question is how low can temperatures fall.
Temperatures under the high currently are not bottoming out with
temperature and dew points spreads remaining fairly high in the 15
to 20 degree range and there is still several hours for that to
change. Have trended tonights lows colder and have introduced low
temperatures in the 33-35 degree range for parts of north central
Iowa and the Nishnabotna River valley along with other low lying
areas. The challenge tonight is if a 5+ degree temperature and dew
points spread maintain with current forecast lows, then frost will
be sparse. If the spread is not maintained, the most likely lows are
too warm in some areas and some areas may reach freezing or below in
those highlighted areas above. Expect a mix of those two solutions
to occur and it is not entirely out of the equation that
frost/freeze headlines be required tonight.

The forecast remains on track as has been advertised for days now
through the work week this week. The forecast has ZERO pops/chances
for precipitation through Friday. Can`t recall a time that there
were 6 days of ZERO pops across the entire forecast area. Monday
will remain "cool" with northwest flow aloft. That flow will
transition to dry westerly flow with a warming trend with highs in
the 80s returning by Wednesday and perhaps by Tuesday for a few
areas. Monitoring the potential for a system to reach Iowa next
weekend though confidence of anything in that timeframe is low as
guidance remains noisy during that time period though there is
consistency returning in the 7-10 day timeframe of another warm
ridge developing into Iowa.

&&

.AVIATION /12Z TAFS THROUGH 12Z MONDAY/...
Issued at 631 AM CDT Sun Oct 6 2024

Monitoring a large area of MVFR/VFR stratus over central
Minnesota this morning as it drops southeast. Guidance would
suggest this stratus will breakup as it moves towards Iowa and
dry air but gaining confidence that some of the stratus will
reach KMCW and perhaps KALO this morning. Most of the stratus
is near 3.5 kft but there remains a chance that a brief MVFR cig
reaches these sites. Otherwise, VFR conditions will persist. A
boundary will pass across Iowa and bring breezy to gusty
northwest winds to the state. The wind will start to diminish
some this afternoon then will become light overnight.

&&

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

&&

$$

DISCUSSION...Donavon
AVIATION...Donavon