Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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642
FXUS63 KFSD 180454
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1054 PM CST Tue Jan 17 2017

.SHORT TERM...(This evening through Wednesday)
Issued at 343 PM CST Tue Jan 17 2017

Been a long struggle, but finally behind strong exiting wave, have
eroded a majority of lower clouds and flushed fog in areas west of
Highway 71.  Airmass has struggled to modify much at all across
northwest Iowa away from the Missouri River with strong inversion
remaining due to ice on the ground.  As a result, the largest
challenge tonight is whether fog will redevelop tonight, or will the
predominant westerly flow and shallowing nature of moist profile
overrule.  Have gone along with the general idea of the hi-res model
solutions which after a couple hours early this evening, will allow
at least some areas of fog to develop across northwest Iowa, which
will expand for a time and focus toward the southwesterly upslope
side of the Buffalo ridge.  Eventually, a slightly strengthening
southwesterly surface gradient should minimize fog threat later into
the night.  As we work through the evening, favorable off surface
wind direction (WSW) along with sharp inversion should allow for
overnight stronger wind enhancement downstream of the Buffalo ridge,
but with weaker surface gradient and stronger surface inversion with
snowcover than typical, will likely get a lot more variation in
wind speed over distance and time.

On Wednesday, will take a page from the current weather playbook and
favor much warmer readings than most guidance and in most areas.
Most likely to be well into the 40s to lower 50s is the relatively
snow free zone along and south of I-90 in south central toward
southeast SD.  Will have some concern with those areas which likely
have some accumulated ice remaining on surfaces, which could take a
bit off the potential warming, namely KYKN area eastward toward
northeast NE and northwest IA.  Otherwise, probably a bit quick on
expecting too much threat for lower clouds spreading northward,
perhaps late day at best toward the lower Missouri valley/northwest
Iowa.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 343 PM CST Tue Jan 17 2017

The warming trend continues by the middle of the week as southerly
flow bring more moist and warm air into the area. A weak shortwave
will approach from the Central Plains, but it will only bring an
increase in low level moisture. Given that the dendritic layer is
not saturated,looks like this system will only produce stratus
and drizzle Thursday night into Friday. Cloudy skies will prevail,
thus increased lows 1 to 2 degrees for almost all areas. The only
exception falls in areas along the Missouri River, where the edge
of the cloud deck will be located.

A mild but dreary Friday is expected with drizzle during the day and
then, a chance for rain/snow with the arrival of a surface low
system late Friday night into Saturday. As the system moves north
into the area, decent lifting mechanism will be in place with
isentropic lifting on the 295K resulting in deeper saturation-
including in the dendritic layer.  Given the fact that temperatures
will be above freezing,and thermal profiles suggest a warm surface
layer, most of the precipitation will fall as cold rain.

Next chance for increased precipitation will occur by the beginning
of the work week as an upper level trough slides northward into the
area. At this point, there is inconsistency with the models in terms
of timing and track. The ECMWF is quicker than the GFS, with the low
arriving by late Tuesday afternoon, while the GFS puts the system
near the CWA on late Wednesday morning. For now, left SuperBlend
as is until timing becomes more evident.

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1052 PM CST Tue Jan 17 2017

Mainly VFR conditions expected through the TAF period. Models
suggest that some patchy MVFR or IFR fog may redevelop after 06z
for areas along and east of I-29, but will quickly lift late
tonight through around daybreak Wednesday as drier southwest flow
steadily decreases the low level moisture.


&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...None.
MN...None.
IA...None.
NE...None.
&&

$$

SHORT TERM...Chapman
LONG TERM...05/BT
AVIATION...



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