Area Forecast Discussion
Issued by NWS Des Moines, IA

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408
FXUS63 KDMX 252035
AFDDMX

AREA FORECAST DISCUSSION
National Weather Service Des Moines IA
335 PM CDT Sun Sep 25 2016

.SHORT TERM.../This evening through Monday/
Issued at 329 PM CDT Sun Sep 25 2016

A cold front has been moving through Iowa today and has brought a
switch to breezy westerly winds and drier air to the state. Dew
points over western Iowa have already fallen into upper 40s to low
50s in contrast to the mid to upper 60 readings along the far east.
A few isolated showers/sprinkles remain possible over the far
southeast forecast area though profiles are drying quickly with any
residual moisture at 10 kft or above. Further north a stratus deck
has dropped into northern Iowa with cigs around 3500 ft. This
stratus will move out of the area this evening then clearing across
the entire area. Winds will diminish overnight and dew points will
continue to fall. Likely to have dew points in the 30s over western
Iowa by Monday morning though the extremely wet ground over the
state will modify this airmass a bit. In addition the west winds
will remain 4 to 8 mph and will help keep temperatures from
bottoming out completely. Low temperatures will be in the 40s most
areas.

.LONG TERM.../Monday night through Sunday/
Issued at 329 PM CDT Sun Sep 25 2016

Little change needed to what will be a fairly benign forecast
period.  An upper level trough will pass across the region tonight
and deepen into a closed low over the Great Lakes on Monday while an
upper level ridge sharpens over the Rockies.  This will put the
Upper Midwest in a North to Northwest flow and with no real waves
expected to top the ridge the forecast problem remains one of
temperatures.  Monday will be cool and quite breezy but as the
models evolve this Great Lakes low they either deepen it and drop it
South or...as the Euro suggests...retrograde it West.  If that
happens then our flow will be more Northerly and our temps will be
too warm.  As it is I went with the coolest blended guidance and
trimmed it some on Tuesday and Wednesday is now looking even cooler
than Tuesday.  If the Euro is right...not only will it be much
cooler Tuesday and Wednesday but there would also be a chance for
some light showers across the East as a vort max rotates around the
upper low generating some light precip as it retrogrades to the
West. At this point it is an outlier and I kept the forecast dry.
Still it will be something to be watched going forward.

For the end of the week the upper ridge over the Rockies shifts into
the Plains and we moderate in temps for Thursday into the weekend to
more seasonal or slightly above seasonal highs.  We will be
continued dry through the period so flooded areas of Iowa will have
a good long period of dry conditions to allow rivers to recede and
areas to dry out.  The Euro still hangs on to this idea of
retrograding the low which by this time is deep in the Ohio Valley
but it`s slamming into a very stout ridge so this seems an unlikely
scenario at this point.  If this solution were to come true...it
would mean an additional chance of precip over the East Saturday
into Saturday night but since I have little confidence in this
solution...I kept the forecast dry.  However...by this time there is
a deepening low moving onto the West Coast so the ridge axis will
begin to shift and push precip chances probably East of the Rockies
but still a long way from Iowa.

&&

.AVIATION.../For the 18Z TAFS through 18Z Monday afternoon/
Issued at 1231 PM CDT Sun Sep 25 2016

The IFR to low MVFR clouds are beginning to push east early this
afternoon. Another region of stratus is moving southeast from
South Dakota and Minnesota. This stratus will have some MVFR cigs
with best potential for impact in northern sites including KMCW.
The cigs will clear overnight with SKC expected by Monday morning. Gusty
west winds will prevail through the afternoon before diminishing
overnight. The winds will become gusty once again by mid Monday
morning.

&&

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

$$

SHORT TERM...Donavon
LONG TERM...FAB
AVIATION...Donavon



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