Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 141744
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
Issued by National Weather Service Omaha/Valley NE
1144 AM CST Tue Feb 14 2017

.SHORT TERM.../Today through Tonight/
Issued at 401 AM CST Tue Feb 14 2017

No Hazardous WX Impacts Expected
Confidence: High

09z Tue water vapor imagery easily picking up two shortwaves north
and NE of Iowa. The first shortwave is propagating primarily
eastward along the Great Lakes. The "impacts" of this shortwave for
Iowa are a shift in wind direction from W/SW to NW as a weak
attendant boundary aligned W-E passes through Iowa. The second
shortwave is more well-defined and is expected to take a track
similar to the first shortwave. Notably colder air is present behind
the attendant boundary...which should arrive in NE IA by around 15z
and make it through the Des Moines metro by 18z-21z. Fcst
models...especially the GFS...are trying to bring some junky low-
level clouds through Iowa with this second fropa. However, 09z Tue
obs in the source region of ND/northern MN do not pick up on low-
level clouds. 850mb temps appear to be similar to Monday...yielding
highs in the mid 40s to low 50s across central to southern IA. Thus,
have nudged guidance temps up slightly in the south to more closely
match general persistence from Monday. There is no support for
precip in the DMX CWA with this fropa.

.LONG TERM.../Wednesday through Monday/
Issued at 401 AM CST Tue Feb 14 2017

No Hazardous WX Impacts Expected
Confidence: High

Wednesday through Thursday morning...
The aforementioned second low is expected to deepen and remain
near Ontario/NE Conus. Meanwhile, a thermal ridge extending well
into Canada will begin to build over the intermountain west.
Through Thursday morning, the region is expected to remain in
CAA/NW flow. Wednesday morning 850 mb temps should be a solid 5 to
10C cooler than Tuesday morning...suggesting mins in the upper
teens across northern Iowa. Fcst soundings, especially in NE IA do
not decouple winds overnight, so expecting 10 to 20kts
overnight...placing wind chills in the single digits north. The
thermal ridge should begin to crash over Iowa around 00z
Thu...causing WAA to spread from west to east and temperatures to
remain nearly steady and slightly increase overnight Wednesday.

Heavy rainfall possible Monday into Tuesday...
Confidence: Low

Thursday afternoon through Monday...
Record to near-record warmth still looks likely during this time
period. Run-to-run consistency has been very good...and if
anything, trends have been in the warmer direction. Overall
consensus is beginning to tighten with 850mb temps in the +12C to
+15C range. Assuming we don`t fully mix out, Des Moines max temps
in the mid 60s would be very reasonable. For Saturday, models
starting to come into a little better focus with sandwiching Iowa
in westerly flow between a cut- off low passing through the
Ozarks, and a somewhat weak shortwave propagating eastward through
southern Canada. Neither of these systems should have mesoscale
impacts on Iowa. 850mb temps fall to the +6C to +9C range... so
warmed temps from pvs fcst closer to persistence and then knocked
5 or so degrees off highs.

WAA then builds Sunday into Monday as models try to resolve our next
chance for precip. Run-to-run and model-to-model consistency not
great with overall synoptic setup. Given timing, will not get into
too much detail...There appears to be a shortwave that will pass
near the Canada/US border and is phased with a low that looks to
propagate eastward through the deep south. Moisture transport into
Iowa may be off the charts as 850mb winds reach and exceed 50 kts
from a wide-open gulf. Thunder and heavy rainfall Monday into
Tuesday cannot be ruled out at this time. 850mb temps look to
remain near +10C...keeping all precip as rain and record to near-
record warmth in the region.

&&

.AVIATION.../For the 18Z TAFS through 18Z Wednesday afternoon/
Issued at 1138 AM CST Tue Feb 14 2017

Continued VFR conditions are forecast at all TAF sites through
Wednesday morning. Strong low pressure moving into the Great Lakes
may spread brief MVFR cigs close to KMCW and KALO for a time this
evening, but expect only scattered conditions at this time.
Otherwise gusty northwest winds to 25kt in northern Iowa will
subside to or below 12kt this evening.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
NE...None.
IA...None.
&&

$$

SHORT TERM...Kotenberg
LONG TERM...Kotenberg
AVIATION...Dergan



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