Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 280837

Area Forecast Discussion
National Weather Service Des Moines IA
337 AM CDT Tue Mar 28 2017

.SHORT TERM.../Today through Tonight/
Issued at 337 AM CDT Tue Mar 28 2017

Temperatures, cloud cover, and precipitation onset were the main
focus in the short term. Clearing over the north to northwest has
allowed for temperatures to plummet and for fog to thicken early
this morning. Challenging to decipher how much these temperatures
rebound today before the cloud deck fills back into northern Iowa.
Further south, temperatures have remained fairly steady overnight
and expecting little increase for temperatures today as the
stratus is likely to persist. Thus, lowered maximum temperatures
in the central to southeast portions of the forecast area and
nudged up highs where the clearing is currently located. Banking
on the sun angle and thin cirrus to allow temperatures be the
warmest in the north across the forecast area today.

Delayed the onset of precip until after 06z and just over the far
western portions of the forecast area.  Low confidence much rain
will fall prior to 12z Wednesday east of Interstate 35 with a decent
dry layer b/t 850-500mb to contend against.  Even further west, the
column really doesn`t become completely saturated until close to 12z
per the NAM/GFS BUFR CRL sounding. Have a fairly sharp pop gradient
b/t 06-12z Wednesday from west to east.

.LONG TERM.../Wednesday through Monday/
Issued at 337 AM CDT Tue Mar 28 2017

All systems go for a decent rainfall event on Wednesday into early
Thursday. At the start of the period, will see good isentropic
lift across the state as warm advection persists. Moisture
transport will increase into the state as 850mb lifts northward
toward Iowa. The widespread forcing and associated lift will lead
to deep saturation pushing northward on Wednesday morning with
rain spreading from south to north over the forecast area. Only
concern will be whether or not the far north will see any rain
prior to midday, however even by afternoon, most model solutions
overcome the dry air in the north as moisture continues to stream
northward. Have increased pops to categorical in all areas by
afternoon with near 100 percent in the central and south.

The surface low will approach the southeast corner of the forecast
area on Wednesday night but guidance suggests it should remain to
the southeast of the area. However, some very weak elevated
instability could arrive in the southeast later Wednesday into
Wednesday night with a rumble of thunder. Have opted to forgo the
mention at this point. Otherwise, deformation and decent mid level
forcing will continue to produce precipitation across central into
northeast Iowa overnight Wednesday. At this point, thermal
profiles appear warm enough for primarily rain, although a brief
period of snow cannot be ruled out on Wednesday night in
deformation area should precipitation rates increase enough for
the thermal profile to become nearly isothermal near freezing. GFS
and Euro both show system departing on Thursday with rain ending
by midday. However, NAM lingers system longer through the day but
is likley odd model out. Have continued pops through much of the
day however would anticipate some cutback in subsequent packages
if the drier trends continue.

Quiet conditions are expected from late Thursday into Saturday
morning with ridging nudging into Iowa along with subsidence. Next
system approaches during the later half of the weekend with some
threat of light rainfall, however models are indicating the bulk
of this system may pass south of Iowa. Temperatures will remain
close to seasonal during this time.


.AVIATION.../For the 06Z TAFS through 06Z Tuesday night/
Issued at 1125 PM CDT Mon Mar 27 2017

Confidence increased to medium-high for dense fog to form across
northern tier of Iowa counties, impacting KMCW the most, and
causing reduced vsbys at KFOD and KALO. KMCW may drop to less than
1/2 SM at times from around 10z Tue to 13z Tue. Dense Fog
Advisory likely coming. CIGS to gradually rise after 13z...
Hovering near 3000 and 3500 ft Tue afternoon. With medium
confidence, have pushed most sites into VFR, but will have to
monitor as MVFR could win out.





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