Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 130428

Area Forecast Discussion
National Weather Service Des Moines IA
1128 PM CDT Mon Mar 12 2018

...Updated for 06z Aviation Discussion...

.SHORT TERM.../Tonight through Tuesday/
Issued at 321 PM CDT Mon Mar 12 2018

Large area of high pressure situated off to the west of the state
with generally northerly flow aloft coming off a high-amplitude
ridge in place across the western US. The northerly flow keeps a
cooler air mass in place across the forecast area, with dry
conditions expected. A weak shortwave trough embedded in the
cyclonic northerly flow aloft will move through tonight into Tuesday
and is expected to bring some high clouds to the area. Therefore
kept Tuesday temps a bit cooler or similar to today with slight
cooling aloft and the addition of some slight cloud cover. Overall
though quiet, dry and cool conditions expected through Tuesday

.LONG TERM.../Tuesday night through Monday/
Issued at 321 PM CDT Mon Mar 12 2018

Models are definitely trending cooler on our warm up this week.
Overall the upper ridge is now being flattened/broken down as it
shifts out of the Rockies into the Plains and Upper Midwest.
Wednesday could potentially be the warmest day of the week with a
surface high shifting to the southeast bringing return flow to at
least southern and central Iowa.  A cold front will be positioned
near northern Iowa which will wash out as it sinks south but may
impact temps across northern Iowa.

For Thursday and Friday the Euro and Canadian models are similar in
that they both hold onto the idea that the ridge will amplify as it
moves into us but over us but they also both push a strong low into
Colorado and Kansas.  the GFS flattens the ridge over us, primarily
due to a strong shortwave dropping down the backside of a Great
Lakes low.  The Euro and Canadian also both develop a surface low
and frontal boundary from Kansas into Missouri.  The GFS is further
south and east with this surface low and front. Even if the upper
ridge does occur like the Euro and Canadian models suggest, the
surface low and boundary would suggest a lot of cloud cover and
potentially an earlier onset to precip which would hamper temps. The
GFS would suggest less precip but still enough cloud cover to hamper
temps.  As for precip...if the Euro were to be closer to what
happens, precip would not be all rain because colder air would get
pulled in on the backside of the low changing the precip to at
minimum, a rain/snow mix with some possibility of changing over to
all snow if enough cold air were to work in.  This would be only for
a few hours overnight then temps warm enough to change back ptype
back to rain Friday morning.

The remainder of the long term has a high level of uncertainty
because models are just all over the place with the a shortwave
impacting the region from Friday night through Saturday night. Since
the Euro is stronger with that low development on Thursday/Friday it
brings it across IA/MO as a decent shortwave and surface low while
the GFS builds a ridge back over the region.  The Canadian is really
different trying to build a ridge and taking the low into the
Northern Plains.  The Euro would keep precip over us while the GFS
and Canadian would mean a dry day Friday into Saturday.  With
confidence low, I kept the forecast of persistence going but made
some adjustments. This means we continue with chance PoPs over the
area Friday night into Saturday morning but I did remove PoPs
the rest of Saturday and Saturday night.

The discontinuity continues for Sunday into Monday but all models
suggest a surface low in the area and enough forcing to have chance
PoPs in the forecast.  Timing and location are in question as are
ptype but at this point, Sunday night/Monday morning would see a
rain/snow mix or possibly all snow across northern portions of the
forecast area with rain south.  Precip would be all rain by Monday
afternoon.  Despite cooler highs now being forecast for late week,
we should still highs in the 40s and 50s with lows in the mid 20s
north to near 40 south.


.AVIATION.../For the 06Z TAFS through 06Z Tuesday night/
Issued at 1129 PM CDT Mon Mar 12 2018

High confidence in VFR conditions prevailing at all terminals
through the TAF period. Winds from the north-northwest and
northwest will increase mid to late morning before subsiding
Tuesday evening.




SHORT TERM...Beerends
AVIATION...Ansorge is the U.S. government's official web portal to all federal, state and local government web resources and services.