Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 240408

Area Forecast Discussion
National Weather Service Sioux Falls SD
1108 PM CDT Fri Mar 23 2018

Issued at 646 PM CDT Fri Mar 23 2018

Radar filling in dramatically at this time lending confidence to
the winter headlined areas. Southwest MN still looks to run the
biggest risk of accumulating snowfall as the precipitation works
its way eastward during the mid and late evening hours. Will watch
for the possibility of thunder snow in southwest MN and extreme
northwest IA which could really enhance snow rates briefly.
However, indications off of the latest RAP and NAM show elevated
MU CAPE values greatly decreasing between 00Z and 02Z, and remain
in our southern zones across the southern half of the rain shield.

Soundings also indicate that there could be some sleet mixed in
with the rainfall under the higher reflectivity returns this
evening. Interesting how the 12Z simulated comp reflectivity off
of the ARW and NMM are actually quite accurate right now. Both of
their 00Z reflectivity prognosis have the heavier returns very
close to the MO River valley, which is not too far south of where
the current activity is. The HRRR and experimental HRRR have been
struggling with this precip, although the latest HRRR has


.SHORT TERM...(This evening through Saturday)
Issued at 341 PM CDT Fri Mar 23 2018

Forecast broadly remains on track for the CWA. Open wave currently
ejecting off the Rocky Mountains will translate eastward this
afternoon along the nose of an upper jet, bringing broad lift to the
region. This lift will interact with a frontogenetic layer around
850mb to lead to widespread precipitation by 00z. Main source of
uncertainty with the precipitation remains type, as surface
temperatures will be around 32 degrees as precipitation begins.
Temperatures have remained cool into the early part of the afternoon
so am not worried about rain failing to switch over to snow. Snow to
liquid ratios remain low as -12C heights look to be around 15kft,
which supports a wet snow solution. Main tweak to the forecast was
delaying the onset of precipitation and lowering amounts slightly in
deference to the relatively dry easterly flow that is ongoing today.
Snow amounts will remain robust in southwest Minnesota as a quick
changeover to snow is expected. The wild card is potential
convection in southwest Minnesota. Progged soundings show elevated
CAPE at or less than 50 J/kg that is spotty both spatially and
temporally. While the trend has been away from getting convective
snows, will stick with winter storm warning despite borderline snow
amounts, just in case.

Saturday will be cold as cloud cover lingers across the region.
Expect the fresh snowfall over southwest Minnesota to reinforce
their cold bias from the past several weeks.

.LONG TERM...(Saturday night through Friday)
Issued at 341 PM CDT Fri Mar 23 2018

While most of the focus of this forecast update was the impending
snowfall tonight, there is one highlight in the extended period.
Next chance for precip comes courtesy of advection driven lift and
an inverted trough on Monday. Precipitation type looks to be an
issue with this as well, with a warm nose aloft around 850mb and
the layer isn`t always saturated above -10C. This will bring
chances for freezing rain in addition to snow and rain.

The CWA will be affected for the remainder of the extended periods
by large scale troughing aloft, leading to temperatures at or below
normal. Multiple southern stream impulses far to our south will cut
off most of our access to moisture, leaving only scant chances for
precipitation after Tuesday.


.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1106 PM CDT Fri Mar 23 2018

Strong storm system lifting eastward will provide plenty of IFR to
MVFR conditions tonight, with some LIFR ceilings and visibility
under the heavier snowfall areas. MVFR ceilings will last through
the day on Saturday. Late tonight, some light freezing drizzle is
a threat for KFSD lasting through early Saturday as the system
pulls eastward.


SD...Winter Weather Advisory until 10 AM CDT Saturday for SDZ040-056.

MN...Winter Weather Advisory until 10 AM CDT Saturday for MNZ089-097-

     Winter Storm Warning until 10 AM CDT Saturday for MNZ071-072-080-

IA...Winter Weather Advisory until 10 AM CDT Saturday for IAZ002-014.

     Winter Storm Warning until 10 AM CDT Saturday for IAZ003.



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