Area Forecast Discussion
Issued by NWS Des Moines, IA

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129
FXUS63 KDMX 241748
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
1248 PM CDT Wed May 24 2017

.SHORT TERM.../Today through Tonight/
Issued at 315 AM CDT Wed May 24 2017

A mid/upper level low pressure system is sliding from Iowa down over
Missouri early this morning, and will proceed gradually southeastward
through the forecast period. A large low cloud shield surrounding
the low will similarly be slow to clear out today and tonight,
with lingering light showers affecting central Iowa this morning
before sliding southeast in the afternoon. There is some question
as to whether we will see cellular diurnal shower development
again today, with some of the short range, high- resolution models
indicating this. However, with considerably less broad forcing
for vertical ascent today and no instability expected, have
maintained a largely dry forecast for the afternoon, excepting the
departing light showers in the southeast. High temperatures
should be on par with yesterdays levels given a similar airmass
and overall scenario.

.LONG TERM.../Thursday through Tuesday/
Issued at 315 AM CDT Wed May 24 2017

Thursday through Friday: Confidence Medium to High

Few real issues with various model solutions through Friday though
even in the next few days...consensus between GFS and Euro is not
ideal. With warm air advection returning to the area later on
Thursday and Thursday night...likely that some light showers or an
isolated thunderstorm may occur in zone of advection aloft as the
warmer air moves into the region. This will diminish early Friday
morning with only a slight chance of any redevelopment in the
afternoon on Friday due to a lack of any real surface or upper
level support and ridge of high pressure expected to build into
the area. Given some consistency between the Euro/GFS for
Friday...have kept PoP to a minimum mainly in the morning/afternoon
southeast and trimmed elsewhere in the afternoon. Highs Thursday
into Friday will be milder...with Friday expected to be one of the
warmer days in the next 5 to 7 days. Have increased temps into
the mid to upper 70s with the warmer readings west/south.

Saturday through Tuesday:  Confidence Low to Medium

Still many questions for the weekend into early next week. Models
continue to have difficulties with pattern...namely a near zonal
flow over the mid Mississippi River Valley and a persistent H500
trough over southern Canada which is trending toward digging into
the Great Lakes early next week.  Over the past couple of days the
models have been unsure of if/when the two streams may phase...if at
all. The Euro is trending toward keeping the stream more separated
...while the GFS with its usual more northerly bias is trying to
phase the two streams at various times with each new package run.
Getting more and more difficult to believe much of any contribution
from GFS into the forecast. On Saturday the Euro is drier over
our area than the GFS. Will continue to trend toward the Euro for
the above reasons. Additionally into Sunday and Monday another
pair of northern stream shortwaves identified by both models is
anticipated to drop south/southeast from southern Canada across
Minnesota through Iowa. Consensus between GFS/Euro remains low on
both timing and placement leaving little confidence on most of the
forecast details from Sunday through Tuesday. At least both models
are trending in similar directions for temperatures...with both
lowering H850 temperatures to about 4-6c by Tuesday afternoon.
This would most likely keep the entire area bound in a range from
65 to 72 for afternoon highs...at best...and with any cloud
cover/showers possibly lower. Needless to say the given pattern/model
performance/various possible solutions suggest elements beyond
about 3 days this go around will need further attention.

&&

.AVIATION.../For the 18Z TAFS through 18Z Thursday afternoon/
Issued at 1243 PM CDT Wed May 24 2017

MVFR cigs encompass much of the area early this afternoon.
Isolated showers can also be expected over the east. Cigs will
gradually improve from west to east this afternoon into the early
evening, then widespread VFR. Only potential issue overnight could
be fog development if clearing occurs along with light winds. Fog
is not included at this time but will need to be added if
confidence increases.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

SHORT TERM...Lee
LONG TERM...REV
AVIATION...Donavon



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