FXUS63 KDMX 230907

Area Forecast Discussion
National Weather Service Des Moines IA
407 AM CDT Sun Sep 23 2018

.DISCUSSION.../Today through Saturday/
Issued at 330 AM CDT Sun Sep 23 2018

Not much change to the going forecast. The main focus remains on
precip chances late Monday afternoon through Tuesday. For today
and tonight, zonal to slightly southwest flow aloft will continue.
At the surface, a low over the Northern Plains with an associated
slow moving frontal boundary over MN. Ahead of this low, southerly
flow will bring warmer temps into Iowa for today. Soundings are
dry so not looking at much in the way of cloud cover though there
is some very shallow low level moisture around Ottumwa that may
lead to patchy ground fog very early this morning. Tonight the low
level moisture gets a little deeper but the low level flow will be
greater as well with low level jet developing and shallow mixing
bringing surface winds up to around 10-12kts which would preclude
any fog development.

During the day Monday the surface low over South Dakota will begin
to lift to the northeast and drag a cold front into northwest Iowa
by 00Z. The front will slowly cross the state and reside along a
line from northeast Iowa to south central Iowa by 12Z Tuesday and
exit the state by early afternoon Tuesday. Today`s model runs
diminish the amount of instability across Iowa that they
previously had and given that the front is moving across the state
well after peak heating the diminished instability is reasonable.
Shear however is still sufficient for organized storms...a few of
which could become strong to severe especially in the late
afternoon/early evening hours. Any strong storms would be capable
of hail and strong wind. A marginal risk of severe storms remains
in place for the area and appears reasonable, though the window
for this would be short. PWAT`s are still 1.3 to 1.5 inches so
some stronger storms could still be capable of producing heavy
rainfall, though the setup for heavy rainfall isn`t great.

Models show some lingering chance for precip Tuesday as the upper
trough swings through the state but by late Tuesday the trough
axis will be east of the forecast area and precip chances will be
diminishing in the evening.

There will be a break on Wednesday into Thursday but cooler air
will once again spill into the region so highs will once again
fall into the 60s. Thursday into Friday another deep trough pushes
across the region with another surface low moving across the far
Northern Plains and dropping another cold front through us.
Instability and forcing is far less with this boundary so not
really looking at big precip chances with this and even less
chance for thunderstorms. The GFS is a little more bullish than
the Euro but both show some potential for precip across northern
Iowa Thursday then sagging through the state on Thursday night.

Models really diverge after Friday with the Euro dropping yet
another cold front through the state and another reinforcing shot
of cold air. If the euro is right then we will see showers
Saturday with highs in the lower 60s. The GFS develops a low over
the Plains again bringing a more southerly flow back to the state.
The GFS would suggest a drier Saturday and warmer temps...into the
70s. For now models blends were left in the grids until confidence
improves or model consistency becomes established.


.AVIATION.../For the 06Z TAFS through 06Z Sunday night/
Issued at 1153 PM CDT Sat Sep 22 2018

Potential for patchy fog over southeast Iowa and in vicinity of
KOTM remains the primary aviation concern through the period.
Otherwise, light southeast wind becoming breezy from the south on
Sunday along with mostly clear skies.





NWS DMX Office Area Forecast Discussion