Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 250010

Area Forecast Discussion
National Weather Service Des Moines IA
610 PM CST Fri Nov 24 2017

Issued at 540 PM CST Fri Nov 24 2017

Potent upper level shortwave continues to pivot across the upper
Midwest early this evening...nicely depicted on GOES-16 WV
imagery. Even with the relatively dry air at low levels...some
precip did reach the ground per north-central Iowa METARs and
regional webcams. Tail end of the line of showers will move
across Butler/Bremer/Blackhawk counties over the next hour or two
with dry conditions expected across the forecast area the
remainder of the overnight. Decent 3-hrly sfc pressure rises of
3-5mb continue behind the sfc will see a brief resurgence
in wind speeds and gusts until about 10pm.

Finally numerous record high temperatures were set
today...including 70F at KDSM and 66F at KALO. Please see Record
Event Reports (RERs) for more details.


.SHORT TERM.../Tonight through Saturday/
Issued at 253 PM CST Fri Nov 24 2017

All concerns in this period will be near term associated with the
approaching system and associated trough and weak frontal
passage. A potent short wave/PV anomaly continues to push from
the eastern Dakotas into MN. The lift out ahead isn`t phased well
with 1-3km thermodynamic QG forcing just exiting the south and
east with sharp subsidence behind. Higher aloft the more
kinematically driving forcing immediately ahead of the short wave
is moving through the Upper MS Valley. With subsidence and dry air
below 3km there isn`t much hope of precip reaching the ground
this far south, so nothing more than sprinkles far north.

Winds will be another concern, but very short lived. Steep low
level lapse rates and mixing have developed behind the trough and
ahead of a surface pressure rise center over northeast NE at 19z.
Wind gusts in these areas, include into our far western
forecast area, have reached 35-45kts and are expected to dampen
slightly before diminishing even further approaching sunset. Thus
30-40kt gusts would mainly affect the northwest third of the
forecast area through 4-5pm. The winds will subside by early
evening with mostly clear skies through the night as further
drying and subsidence settles in.

.LONG TERM.../Saturday night through Friday/
Issued at 253 PM CST Fri Nov 24 2017

The two primary concerns through next week will be temp and
precip trends with the system around Monday, and then precip
trends into midweek. The period will begin with upper level
ridging advancing into the Plains with return flow Sun into Mon.
Warm advection Sun will be moisture starved with no precip. The
following system Monday should be fairly similar to today`s. The
thermal ridge axis through Iowa will boost temps well above normal
again Mon, although not to the same extent as today. Record highs
are higher as well. The trough will came through during the night
and the thermodynamic and kinematic forcing will be deep and
coupled, but equally moisture deficient. Thus the passage of this
system will be dry as well.

The next concern will be a closed low advancing through the Plains
into Wed. Models have finally come into better run to run
agreement with this feature and suggest a track somewhere from MO
into southern IA. This coupled shot of warm/theta-e advection and
divergence/DPVA will bring chances for rain or showers around Wed.
Models are in good agreement to end the period with some form of
a long wave trough developing to the west and moving through the
central CONUS. This will be with a considerably dry airmass too so
the forecast remains dry through the end of the next work week
with lowering heights dropping temps back to normal.


.AVIATION.../For the 00Z TAFS through 00Z Saturday evening/
Issued at 540 PM CST Fri Nov 24 2017

A frontal passage continues to move sewd through Iowa this
evening. While most terminals will remain dry with VFR
conditions...a few light showers will be possible at KALO thru
01Z. The other concern will be wind gusts behind the trough
passage this evening...with NW winds of 15 to 25kts...with a few
gusts as high as 30kts. The gusts should gradually subside after
03z. VFR conditions and lighter NW winds are anticipated on




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