Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 231139
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
539 AM CST Mon Jan 23 2017

.SHORT TERM...(Today and Tonight)
Issued at 406 AM CST Mon Jan 23 2017

Widespread stratus across the forecast area early this morning will
be sticking around through today as high pressure over the area
begins to move off slowly to the east through this afternoon. Low
pressure over central Rockies will then push into central Plains
late this afternoon through tonight. Inverted trough and mid level
frontal zone expected to set up in the vicinity of I-90 east of the
Missouri River after midnight tonight. Will start with Pops west of
the James River mid to late afternoon, and spread these east through
tonight, with rapid increase in chances toward Tuesday morning as
low starts lifting more northeastward into Nebraska. Western areas
south of I-90 should be warm enough for rain or a rain/snow mix
through early to mid evening if any precipitation gets going, with
only snow for all areas after midnight.

Expect pretty small diurnal temperature changes today due to cloud
cover, except for our southwestern areas where some stronger warm
advection gets going closer to the central Rockies low. Low
temperatures tonight will again stay pretty mild in the upper 20s
with continued warm advection ahead of the low and widespread cloud
cover.

.LONG TERM...(Tuesday through Sunday)
Issued at 406 AM CST Mon Jan 23 2017

Focus remains on the medium range winter storm slated to affect the
region Tuesday into Wednesday. Still some differences among the
models regarding timing/track, primarily with the 23/00Z ECMWF now
trending slower and farther south than its previously consistent
runs.

Tuesday will begin with a surface low beginning to move east out of
the Central Rockies, somewhere near the western KS/NE border (or
possibly farther south, per the latest ECMWF), with a 120-130+kt
upper jet from New Mexico into Missouri as it rounds the base of an
elongated mid-upper level trough. Initially seeing a dry layer below
750mb over eastern portions of the forecast area very early Tuesday,
but this layer quickly saturates as strong isentropic lift develops
across the entire area in the 290-300K layer. Would anticipate a
rapid increase in coverage/intensity of precipitation as it expands
east Tuesday morning, aided by an intensifying mid-level front which
develops from the lower James River Valley into southwest Minnesota
or northwest Iowa by 18Z Tuesday. Again, location of the strongest
frontogenesis varies due to the north-south differences among the
models, with potential placement anywhere from near Highway 20 on
the southern end of the spectrum, to just north of I-90 on the
north end. Similarly, 850mb low placement varies from southwest of
Lincoln NE to near Sioux City IA by 25/00Z.

By Tuesday evening, stronger frontogenetical forcing shifts east of
the forecast area as the upper trough axis nears the Nebraska/Iowa
border, but some indications of a weak TroWAL lagging back across
northwest Iowa. This should provide support for additional moderate
snowfall in this area through Tuesday night, though with the upper
trough slow to exit the area, most of the area will continue to see
at least light accumulations through the night.

Intensity and coverage of snowfall will continue to decrease through
Wednesday as the upper trough pulls away to the east, though could
see spotty flurries/light snow continue into the afternoon east of
the James Valley as a trailing vorticity lobe slides into the back
side of the trough. All in all, continues to look like a broad area
of 4-8" of snowfall across the forecast area, but with uncertainties
in placement of the stronger frontogenesis and resulting potential
for more focused snow bands, coordinated with surrounding offices
and opted to leave Winter Storm Watch in place for now.

With focus on the upcoming storm system, little change was made in
the longer range of the forecast. Continues to look dry beyond
Wednesday, with a cool down for the latter part of the work week.
Potential for some warming again through next weekend, though
temperatures will surely be impacted by the upcoming snowfall.

&&

.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
Issued at 532 AM CST Mon Jan 23 2017

Widespread MVFR ceilings of 1200 to 1500 feet across the region,
with areas of IFR ceilings of 500 to 1000 feet along I-29 will
change little through this morning. VFR visibilities of 6 to 10
miles. Lower ceilings will lift to MVFR for all areas near or
after 18z, with areas along the Missouri River lifting to levels
of 3500 to 5000 feet. Large winter storm system to start moving
east through KS/NE tonight bringing a chance of snow and IFR/MVFR
ceilings and visibilities toward 12z Tuesday.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...Winter Storm Watch from Tuesday morning through Wednesday
     morning for SDZ040-055-056-061-062-066-067-070-071.

     Winter Storm Watch from late tonight through late Tuesday night
     for SDZ038-039-050-052>054-057>060-063>065-068-069.

MN...Winter Storm Watch from Tuesday morning through Wednesday
     morning for MNZ071-072-080-081-089-090-097-098.

IA...Winter Storm Watch from Tuesday morning through Wednesday
     morning for IAZ001>003-012>014-020>022-031-032.

NE...Winter Storm Watch from Tuesday morning through Wednesday
     morning for NEZ013-014.

&&

$$

SHORT TERM...MG
LONG TERM...JH
AVIATION...MG


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