Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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531
FXUS63 KFSD 192138
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
338 PM CST Thu Jan 19 2017

.SHORT TERM...(This evening through Friday)
Issued at 338 PM CST Thu Jan 19 2017

The main story in the short term is the persistent fog and stratus
threat in the area. A weak mid to upper level low will continue to
wander northward through the Central Plains, bringing a persistent
source of low-level moisture and lighter mild southerly winds into
the area. Soundings continue to show a very strong inversion in the
low levels; a wealth of moisture at low-levels capped by a very warm
and dry layer aloft. The strong inversion will aid development and
persistence to widespread fog, with visibilities expected to drop to
less than a quarter mile in many areas through the overnight hours.
Currently, the lowest visibilities exist along the upslope side of
the Buffalo Ridge, but these low visibilities should become more
widespread in short order this evening. In collaboration with
surrounding offices, a dense fog advisory will be issue from 6pm
Thursday to 10am Friday.

A cloudy and mild Friday is on tap, with a slight chance of
precipitation throughout the day. The low level moisture will deepen
over the nighttime hours, along with a decent lift provided by the
weak trough moving into the region. Although the low level moisture
layer will be increasing tonight, dry air at mid levels will keep
the precipitation risk as drizzle.

Limited change in temperatures are expected due to a thick cloud
layer over the area. This will keep mild temperatures through Friday
and beyond. Tonight`s low will be in the mid to upper 30s with some
areas in the upper 20s in our far west. A mild Friday with highs in
the upper 30s to low 40s.

.LONG TERM...(Friday night through Thursday)
Issued at 338 PM CST Thu Jan 19 2017

Friday night will continue to see a very saturated surface and low
level environment, which will at a minimum keep dreary overcast
conditions but may also be supportive of fog. Added some fog in
during the evening, but as a weak wave lifts into the area
additional saturation aloft will likely lead to some spotty light
rain and light snow. At this time accumulation looks minimal.

Saturday will see the better chances lift to the north and east of
the area but fairly cloudy conditions will persist. mild
temperatures in the 30s will continue.

Precipitation is not expected Sunday as northwest winds and drier
air aloft build in. Mostly cloudy conditions are expected again but
at least a little sunshine will be possible. Highs again the 30s and
possibly some lower 40s.

In the outer periods(Monday through Thursday), Large broad scale
troughing across much of the middle of the United States through the
period. The system moving onto the Plains Monday night into Tuesday
will be the system that will really helps carve out this broad
trough. Still appears to be a pretty strong system which should
bring mainly snow to the area, although a little rain will also be
possible if it gets warm enough at the surface. Aloft, temperatures
support snow and not looking like any kind of an elevated warm layer
will work in which would support mixed precipitation. This system
will be a bit on the slow side so snow chances will continue into
Wednesday. For now will not trust the widespread inch of QPF from
the 12z GFS, especially given the east coast system may slow any
lower level moisture return. It will really come down to placement
and for now believe that the 0z and 12z ECMWF on track a little more
with about a half an inch of QPF with maybe just a northward
adjustment as it appears that we should be able to keep the
environment saturated. At this time not expecting precipitation on
Thursday. Temperatures will be on the normal to a little above
normal side with lows in the 20s and highs in the 30s.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1153 AM CST Thu Jan 19 2017

Visibilities are a bit of a question mark through the TAF period.
However it does appear a low cloud event is setting up for the
forecast period. Hedged the visibilities primarily in the LIFR to
IFR categories. But one thing more certain, is that ceilings
should remain very constant in the LIFR category if upstream
ceilings are any indication. Be aware, especially for tonight,
that VLIFR visibilities of a quarter mile or less could occur.
This is not shown in the TAFs however due to too much uncertainty.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...Dense Fog Advisory until 10 AM CST Friday for SDZ038>040-052>071.

MN...Dense Fog Advisory until 10 AM CST Friday for MNZ071-080-089-090-
     097-098.

IA...Dense Fog Advisory until 10 AM CST Friday for IAZ001>003-012>014-
     020>022-031-032.

NE...Dense Fog Advisory until 10 AM CST Friday for NEZ013-014.

&&

$$

SHORT TERM...05
LONG TERM...08
AVIATION...MJ



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