535 
FXUS63 KFSD 252127
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
327 PM CST Thu Jan 25 2018

.SHORT TERM...(This evening through Friday)
Issued at 324 PM CST Thu Jan 25 2018

Warm advection continues across the region today, with southeast 
winds also bringing additional moisture into the region. Without 
snow, this would be a situation with sunshine and warmer 
temperatures for all. However, the thick snowpack from the winter 
storm earlier this week is cooling the lowest layers of the 
atmosphere causing some areas in southwest Minnesota to remain 
cloudy, with patchy fog lasting into the late afternoon. However, 
temperatures are still reaching above average values with sun
peaking through high clouds elsewhere, with highs in the 30s and 
low 40s.

This evening, patchy fog may re-develop briefly, but after midnight, 
a strengthening surface gradient will increase wind strength and 
cause a subtle shift to more southerly wind direction ahead of an 
approaching upper-level trough. This should minimize the upslope 
component of surface flow relative to the Buffalo Ridge; along with 
deeper mixing, this should reduce chances for dense fog overnight 
into Friday morning.

During Friday morning the shift to southwesterly winds will lead to a 
brief period of downslope wind enhancement for areas on the eastern 
slope of the Buffalo Ridge. Locations such as Marshall, Tracy, and 
Windom, MN, could see gusts into the 30 mph range. The deep 
inversion will prevent even stronger winds from mixing down, then by 
afternoon, winds shift more westerly thus ending downslope 
enhancement. Region-wide, temperatures will be mild, with many 
reaching near 40 by the afternoon.


.LONG TERM...(Friday night through Thursday)
Issued at 324 PM CST Thu Jan 25 2018

The next 7 days looks relatively quiet weather-wise, but there are a 
few periods worth noting:

The longwave upper-level trough that moves through this weekend will 
bring a cool down Saturday night into Sunday. A weak surface front 
associated with an embedded shortwave could bring light snow or at 
least flurries to southwest Minnesota Saturday evening. Minimal 
accumulations are expected for any locations that do see snow, and 
winds will be light. Cooler temperatures that are slightly below 
normal linger through Monday.

Tuesday will bring a building upper-level ridge, and warm air 
advection in the low levels of the atmosphere. Despite models 
showing warmer temperatures into the upper 30s and 40s, there is a 
chance that fog could again keep temperatures cooler than forecast, 
with abundant cloud cover. Models do not resolve these details this 
many days out, but the overall pattern is similar to those that led 
to foggy conditions the last couple days.

Wednesday into Wednesday night another cold front looks to usher in 
a cooler Canadian air. Models keep most of the area dry, but light 
snow does look possible as the front moves through. Nevertheless, 
any snowfall does not look to be impactful, with only light 
accumulations.

The final talking point is a potential large-scale pattern change 
late next week. Models are beginning to show a broadening longwave 
trough over Canada, along with a westward shift in the location of 
the Hudson Bay surface low. This is supported by a strengthening 
northwesterly jet over the Canadian and American Rockies. These 
features are favorable for arctic air surging south out of Canada. 
Exact temperatures are not the focus at this point, but generally 
below average temperatures are looking more likely during the first 
week of February. CPC graphics agree with this analysis, 
highlighting a high chance for below average temperatures during 
this timeframe.


&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1200 PM CST Thu Jan 25 2018

Dense fog is beginning to lift and thin at TAF sites throughout
the region. Patchy fog will remain this afternoon, and then some
expansion in fog is possible again this evening as surface 
temperatures cool. However, later tonight, winds make a subtle 
shift to more southerly and will increase in strength. This 
direction is less favorable for upslope flow in our region, and 
along with enhanced mixing, this should prevent dense fog on 
Friday morning. Also of note, the strong southerly jet just above 
the shallow surface inversion will cause strong southwesterly wind
shear of 35 to 45 kts about 2000 ft AGL overnight. Surface winds 
shift to westerly Friday during the morning hours as a weak cold
front moves through.


&&

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

$$

SHORT TERM...VandenBoogart
LONG TERM...VandenBoogart
AVIATION...VandenBoogart