Area Forecast Discussion
Issued by NWS Aberdeen, SD

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FXUS63 KABR 230531 AAB

Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
1131 PM CST Mon Jan 22 2018

Issued at 531 PM CST Mon Jan 22 2018

No major changes planned for the overnight forecast. Fog will be
the biggest concern across the region.


.SHORT TERM...(This Evening through Tuesday Afternoon)
Issued at 320 PM CST Mon Jan 22 2018

Forecast challenges surround fog potential underneath low stratus
clouds tonight into Tuesday.

Currently, it`s cloudy everywhere but west river. Temperatures are
holding in the 20s underneath clouds, warmer out west over the bare
ground with sunshine. Strongest northerly surface winds of 20 to 30
mph with higher gusts have been and continue to be over in east
central South Dakota (up to around Watertown) and west central
Minnesota (in the Ortonville area). Based off area webcams,
widespread dense fog over the Coteau region and out in parts of
central/north central South Dakota became localized early in the
afternoon, and continues to dissipate this afternoon.

Guidance and short range model solutions point to the cloud cover
sticking around overnight, at least, over the eastern two-thirds of
the forecast area. The portion of the western forecast zones that
has cleared off this afternoon stands a pretty good chance of
fogging or low stratus`ing back in again overnight tonight, per the
RAP13, which has support from other short range guidance. With a
similar synoptic set-up in place again tonight, prior to the wind-
shift to west-northeasterly, figuring fog that forms will have the
potential to become dense quickly. So, have issued a Dense Fog
Advisory for tonight through 18Z Tuesday mainly for north central
South Dakota. With the advent of the next upper circulation moving
into the region from the west-northwest later tonight and Tuesday, a
surface trough/frontal boundary will begin to move into the forecast
area, initially late tonight across north central South Dakota,
turning winds more out of the west-northwest. So, depending on the
timing of that wind shift will determine how long any fog/stratus
can be around late tonight/early Tuesday morning before slowly being
dissipated/advected eastward. Model soundings all show any
cloudcover associated with this upper wave being mid/high clouds, so
no pops/wx/qpf mention in the late tonight or Tuesday grids right
now. Little more than a 5 to 10 degree swing in temperature is
expected with the clouds around overnight and Tuesday.

.LONG TERM...(Tuesday Evening through Monday)
Issued at 320 PM CST Mon Jan 22 2018

At 00Z Wednesday the western third of the nation will be under a
500mb ridge (that will move over our area Wednesday afternoon
through Thursday afternoon). While the main 500mb trough will be
set up over the eastern states, a secondary low over central Canada
will have a trough extending through the Northern and Central
Plains. A weak cold front will be sliding over our eastern counties,
with clouds being the main impact, with no precipitation expected.

Temperatures Wednesday will still be able to top out in the 40s
(unless low stratus clouds keep us cool, as fcst profiles show
plenty of moisture through at least early morning). Low pressure
over southwestern Canada will slowly slide a trough into the Dakotas
Wednesday night, with a warm front setting up just to our south
Thursday morning. The warmest air of this period will move in for
Thursday and Friday, with highs in the upper 30s to mid 40s. The sfc
low is expected to move into western ND (and possibly north central
SD) as early as 06Z Friday. Timing will change, and this will have a
significant impact on daytime highs Friday. It looks to be mainly dry
again (originating from the drier northwest), with moisture staying
above 500mb. Much of the energy and moisture stays over ND and
Canada. But we`ll still get clouds and and stronger winds with a
wind shift. Also, some cooler air able to move in moving from the
northwest as the sfc low shifts across the Red River Valley Friday
morning/early afternoon and cold front exits to our east most likely
by 18Z. The coldest air, 850mb temperatures of -14 to -16C is still
well behind the system over central Alberta/Saskatchewan.

Models continue to indicate a secondary trough/cold front rotating
around the exiting sfc low near James Bay for Saturday afternoon and
evening. While the 00Z GFS had 850mb temperatures fall to -10 to -
17C by 00z Sunday, it`s 12Z rendition was only -5 to -13. Will see
if this trend continues, or if it`s just a glancing blow of cold
air. Otherwise, after a couple of cooler/breezy days, waa and
ridging return for Monday.


.AVIATION...(For the 06Z TAFS through 06Z Tuesday Night)
Issued at 1126 PM CST Mon Jan 22 2018

IFR conditions will persist overnight at all sites as stratus and
fog overspread the region. Conditions will improve from west to
east on Tuesday as the winds shift to the west.


SD...Dense Fog Advisory until noon CST /11 AM MST/ Tuesday for



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