Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 181132
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
632 AM CDT Sat Mar 18 2017

.SHORT TERM.../Today through Tonight/
Issued at 328 AM CDT Sat Mar 18 2017

Stratus clouds over the northeastern part of Iowa will gradually
clear today as a zone of high pressure moves across the state. A
stream of higher level clouds will also pass over much of the state
which will filter the sunshine, but overall provide for ample
sunshine. While cold air advection will be waning today, bumped up
high temperatures a degree or two over the north as highs yesterday
were a bit too low over those areas. Over central Iowa, this will
mean high temperatures within several degrees of their mid-March
climatological normals. Winds from the northwest may still be a bit
brisk this morning, but will weaken as the high moves across the
state. As the high slides off to the east late today and tonight,
winds will respond and become from the southeast. This will allow
for warm air advection to commence ahead of a warm front approaching
from the west late tonight.

.LONG TERM.../Sunday through Friday/
Issued at 328 AM CDT Sat Mar 18 2017

Sunday through Wednesday.  Confidence Medium to High.

Little change to Sunday forecast other than potential for a few more
clouds by later in the afternoon southeast.  This may cap highs
there while the western areas warm up more quickly in the afternoon
hours. The southwest half is most likely to see highs in the 60s
with the northeast still in the 50s. As per the previous forecasts
an inverted trough and weak low with an increasing low level jet
will focus instability aloft over the southeast in the early
evening and late evening hours in the southeast. Over the
southeast especially there is increasing elevated cape in the
evening hours through just after midnight Monday morning. This
would be the most favored area for any thunderstorm development. A
strong surface inversion is forecast and this will limit any
severe threat to hail. The low level jet responsible for the
thunderstorm chances will move southeast of the area prior to 12z
with high pressure building into the area on Monday. Temperatures
on Monday will remain mild with highs in the 50s to 60s across the
region. By Tuesday upslope lift over the the High Plains is
expected to create an area of rain and snow over South Dakota and
northern Nebraska. With steering currents forcing the
precipitation back toward Iowa...some light rain may make it into
southwest/west areas by Tuesday. Confidence remains low to medium
with regard to the coverage at this time. As flow over the Plains
returns to more southerly...increasing moisture over Nebraska and
western Iowa may result in additional light showers by Wednesday
afternoon/evening. Wednesday will generally be cooler with 40s to
lower 50s and more clouds over the region.

Thursday through Friday.  Confidence Low to Medium.

Still a fair amount of uncertainty with the near end of week system.
There will however...be plenty of clouds toward the end of the week
as the pattern becomes more active. Both the GFS and Euro are
slightly slower with the arrival of the main wave into Friday...
though some warm air advection and moisture arrives in advance of
the main system late Wednesday night and on Thursday. Initially
there may be a mixture of rain/snow prior to sufficient warm air
advection taking over and keeping all of the precipitation liquid
later on Thursday. With the slightly slower arrival...some questions
remain about the timing of any initial thunder. With limited
confidence for Thunder as early as Thursday... will leave out for
now.  Continued warm air and moisture return into late Thursday
through Friday should increase the chances for thunder over the
area. Though wind fields do increase through the column with time
Thursday night and Friday...the strongest winds at this point are
not collocated in height over our area...though there is slightly
better alignment southeast of Iowa...especially later on Friday.
The first wave will track into the region late Thursday night
into Friday with overrunning rain and possible thunder spreading
northeast into northern Iowa. Highs Thursday will likely reach the
50s over much of the region with lows Thursday night in the 40s
to 50s. With the warm sector fully into the area Friday...highs
may reach the 50s to lower 70s across the south or southeast then
cool into the late afternoon. A second southern stream system
tracking northeast thorugh the main trough will offer the another
chance for precipitation and that appears to over about the
southeast on Friday evening prior the the system pulling east and
cold air advection following the passage of the storm.

&&

.AVIATION.../For the 12Z TAFS through 12Z Sunday morning/
Issued at 632 AM CDT Sat Mar 18 2017

Stratus clouds stretch from north central Iowa into southeast Iowa
this morning with MVFR ceilings at all but KDSM. There may be a
brief period of IFR ceilings with that most likely at KMCW this
morning. Thereafter, conditions will gradually improve into VFR
by later this morning at KFOD and KOTM and by early to mid
afternoon at KMCW and KALO as the clouds break and clear from west
to east. Winds will remain a bit gusty this morning, but high
pressure will move across the state today and this will foster
decreasing winds throughout the day. Winds will become from the
southeast tonight as the high slides east with VFR conditions
prevailing through the end of the TAF period.

&&

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

$$

SHORT TERM...Ansorge
LONG TERM...REV
AVIATION...Ansorge



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