Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 162332

Area Forecast Discussion
National Weather Service Des Moines IA
630 PM CDT Thu Mar 16 2017

.SHORT TERM.../Tonight through Friday/
Issued at 208 PM CDT Thu Mar 16 2017

As of 20z a ridge axis was in place over the CWA, sandwiched
between a broad, deamplifying trough to the east and a digging
shortwave trough to the west. This shortwave will work to break
down the ridge and push it east. Moisture return in the low level
southerly flow ahead of the shortwave will bring the potential
for fog and stratus late this evening and tonight. The most
favorable area for fog will be over the snowpacked areas of north
central Iowa, with widespread stratus and maybe a few areas of
drizzle to the south. The shortwave rounds the top of the ridge
and dives southeast overnight, which will push a front through the
cwa. Drier air in the northwest wind behind the front will work to
push out some of the low level moisture and clear up most of the
fog and stratus by Friday morning. Breezy, unidirectional winds
tomorrow will promote deep mixing of the boundary layer during the
afternoon hours. This will lead to a uptick in temperatures
despite the northwest flow. Previous MaxT forecast looks on track
with highs ranging from the mid 40s in the north to the mid 60s in
the south.

.LONG TERM.../Friday night through Thursday/
Issued at 208 PM CDT Thu Mar 16 2017

Upper level ridge builds over the central tier of the country
through the weekend, which will keep temperatures above normal.
A shortwave through will move through the Pacific northwest toward
the northern High Plains. Low level winds over the state become
southerly again in response to deepening lee side low pressure,
which will lead to warm temperatures into the 50s and 60s on
Sunday. Showers and thunderstorm chances increase Sunday night as
a front sweeps through. Cannot rule out the possibility of an
isolated strong to severe storm. A stout EML advects eastward with
700-500mb lapse rates of 8C/km or greater, occurring over the top
of a zone of strong theta-e advection. This is supported by the
GFS with MUCAPE values around 1000 J/kg along with 30-40 kts of
deep layer shear.

The shortwave moves east and deepens over the Ohio Valley, which
will keep the area under cool northwest flow aloft through the
first half of the work week. Attention then turns to the next
storm system to impact the area toward the middle to latter half
of next week. Both the GFS/Euro and their ensembles advertise a
a deep low moving through the Four Corners region and into the
Central Plains by Thursday. Although this system looks to remain
somewhat cutoff from the northern stream which will limit the
availability of Arctic air, temperatures look to be just cool
enough to keep wintry precipitation in the conversation for now.


.AVIATION.../For the 00Z TAFS through 00Z Friday evening/
Issued at 630 PM CDT Thu Mar 16 2017

Flight conditions will be variable through the period.  VFR
conditions will become at minimum MVFR but likely IFR as low level
moisture advects into the TAF locations in a warm air regime.  Cigs
will lower and there looks to be about a 4 hour window from 07Z to
11Z or so where fog will be likely over snow pack areas.  Further
South I would not be surprised to see some drizzle as well as MVFR
vsbys in fog.  Winds are expected to diminish ahead of a surface
trough that will move across.  Aft 15Z winds switch around to the NW
and increase.  Aft 18Z most locations will be 18g26kts.




LONG TERM...Martin
AVIATION...FAB is the U.S. government's official web portal to all federal, state and local government web resources and services.