Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 250434
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1134 PM CDT Thu Sep 24 2020

...Updated 06z Aviation...

.DISCUSSION.../Tonight through Thursday/
Issued at 238 PM CDT Thu Sep 24 2020

Overview...Mainly dry and warm conditions will persist through
Saturday before cooler air and below normal conditions settle into
the state by early next week. The highest chance for rainfall
will be on Sunday over portions of southern Iowa, but overall rain
chances remain slim. Tuesday still looks to be on the brisk side,
but not as strong as previously forecast.

Details...Showers and thunderstorms passed over northeastern Iowa
this morning and early this afternoon as a compact shortwave dips
southeastward into the Ohio Valley. Low clouds were draped back over
central Iowa and were slowly pulling away to the east. While winds
over northern Iowa may switch to the north for a period later today,
winds will become from the south on Friday and turn breezy. It will
be rather warm for late September and in some places several degrees
away from record highs as temperatures peak well into the 80s.
Dewpoints into the low 60s across much of central Iowa should help
to offset an otherwise critical fire weather day. That said, with
dry antecedent conditions and the warm, breezy conditions, it is
also not an ideal day for any burning.

The front that has been advertised for Saturday is delayed and will
arrive late Saturday. This will result in much higher temperatures
than yesterday`s forecast, but similar to this morning`s forecast
for Saturday afternoon. A lead jet will pass north of the state and
much of the QG convergence will also pass north as well. Any chances
of rain look displaced well to the northeast of our forecast area
with soundings showing insufficient moisture. However, another area
of QG convergence will pass over southern Iowa as the lead jet lifts
toward Lake Superior with a stronger, 125kt jet digging towards the
area Saturday night into Sunday. The favorable jet dynamics along
with QG convergence and moistening mid-levels should provide a
period of showers early Sunday into Sunday afternoon over portions
of the state. There does remain dry air in the low levels, but there
is support for light rainfall in the GFS/CMC/ECMWF deterministic and
GFS/ECMWF ensemble members as well through Sunday afternoon and
evening over parts of southern Iowa.

The stronger jet will help to carve out a longwave trough over the
central US with the GFS lifting the longwave trough poleward some
toward midweek while the ECMWF remains persistent with a shortwave
dropping into the base of the longwave trough and closing off a low.
These differences may result in slightly better chances for rainfall
from the ECMWF, but remained with model blend into next week. This
offers low end, mainly daytime showers focused over portions of our
eastern forecast area and eastern Iowa through midweek. Next week
will also be below normal with temperatures by midweek struggling to
reach 60 degrees. As for winds, Tuesday still looks to be the
breeziest with gusty winds, but not to the level that yesterday`s
00z/12z cycle was indicating.

&&

.AVIATION.../For the 06Z TAFS through 06Z Friday night/
Issued at 1133 PM CDT Thu Sep 24 2020

VFR conditions will prevail through the TAF period. Winds will
shift to southerly overnight and increase tomorrow morning at all
sites. Winds will remain breezy for much of the day Friday.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

DISCUSSION...Ansorge
AVIATION...Carter


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