Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 252317

Area Forecast Discussion
National Weather Service Des Moines IA
617 PM CDT Wed Apr 25 2018

...Updated 00z Aviation Discussion...

.SHORT TERM.../Tonight through Thursday/
Issued at 305 PM CDT Wed Apr 25 2018

The low that brought light precip to the west and south today will
push off and any lingering sprinkles will end across the far
south by 00Z. Weak surface high pressure will then slide southeast
tonight keeping skies clear over Iowa with a light wind. Given
the lack of clouds generally weak northerly flow, I do expect good
radiational cooling tonight so I did knock temps back tonight.
Dewpoints are very low so I do not expect fog.

For Thursday, a slow moving, weak cold front will push across the
state mainly in the afternoon hours. Due to the lack of
moisture...weak if any forcing and very hit or miss
frontogenetical forcing, I really have very low confidence in
seeing any kind of precip, however given that a shortwave will
sweep the region mid to late afternoon into the evening, I do have
token slight chance PoPs for a light shower here or there...mainly
across northern into central Iowa then into east central Iowa late
afternoon. The Gulf continues to be cut off so there will only be
whatever moisture can be wrung out right along and immediately
behind the front. Hi-res models barely have clouds below 10K ft
though so the odds of anything making it to the ground are so
small, I have no qpf for Thursday.

.LONG TERM.../Thursday night through Wednesday/
Issued at 305 PM CDT Wed Apr 25 2018

Thursday night through Saturday will be dry and relatively cool
as a strong and very amplified ridge parks over the Rockies
putting the region in deep northwest flow. Highs during this time
will be in the 50s and 60s with the coolest day being Saturday.

Sunday into Monday the upper ridge migrates into the Upper Midwest
as a deep trough digs into the West. Later Sunday into Monday deep
southwest flow will occur and temps will warm considerably...
especially Monday. Despite cloud cover I think we could even see
our first 80 degree temp with just a little sun. I did try to
account for clouds though and although I raised highs Monday,
using a 50/50 Superblend/CONSRAW blend, I then increased highs a
degree or so more. It will also be breezy Monday with a southwest
wind at 15 to 25 mph.

The other caveat to this scenario is that the Gulf will begin to
open up so moisture will increase as will instability. CAPE
increases to around 2500 J/Kg mainly to the west of Iowa but with
time this does work into Iowa a little bit on Tuesday and
especially on Wednesday. We will see increasing chances for
showers and at least a slight chance for thunderstorms Monday west
and Tuesday west into central with better chances Tuesday night
and Wednesday. Wednesday night the aforementioned deep trough out
West works its way into the region pushing precip chances into
eastern Iowa. Given the time of year and the amount of instability
working in, I would not be surprised to see a severe storm or two
with all the convective chances next week but this is too far out
to consider all the finer details that have to come into
consideration. Until then...after the low chance for light spotty
precip Thursday, seasonal temps and dry going into the weekend
then warmer Sunday/Monday.


.AVIATION.../For the 00Z TAFS through 00Z Thursday evening/
Issued at 616 PM CDT Wed Apr 25 2018

High pressure building in will keep conditions quiet at the
terminals this evening. Slight increases in moisture may introduce
a few high ceilings, but conditions will remain VFR. Winds will be
light and variable through the evening, and will prevail from
southwest shifting northwest into the morning hours.

Ceiling and Visibility Confidence... High
Wind Confidence... Medium-High




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