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Area forecast discussion...updated
National Weather Service Aberdeen South Dakota
538 am CST Fri Nov 22 2019

issued at 536 am CST Fri Nov 22 2019

See below for an aviation forecast discussion for the 12z tafs.


Short term...(today through Saturday afternoon)
issued at 348 am CST Fri Nov 22 2019

Surface high pressure along with clear skies has allowed
temperatures to fall into the teens early this morning. The surface
high will shift southeast of the area today with increasing
southwesterly winds bringing warmer temps into the County Warning Area. 925 mb temps
are projected to reach the single digits above 0c, which would be
around the 75th percentile. With favorable mixing winds, highs
should reach the mid 30s, in western Minnesota, to the mid 40s, along and
west of the Missouri River. A weak surface trough and mid-level
shortwave will pass through the region tonight. The system will pass
through dry with only a noticeable shift in wind direction to the
northwest. Increasing southwesterly winds will cause a down-slope
wind event between 23-9z Saturday, or until the winds shift to the
northwest. Wind gusts exceeding 45 mph will be possible. A Wind
Advisory could be needed tonight.

Warmer air will move into the region from the northwest on Saturday
with highs reaching the low 40s, in western Minnesota, to the mid
50s, west of the Missouri River. Highs could end up being a bit
warmer due to favorable mixing winds.

Long term...(saturday evening through thursday)
issued at 348 am CST Fri Nov 22 2019

Looks like the flow pattern will showcase a little bit of everything
in the out periods. But at this point, there is limited agreement
amongst deterministic gsm output and enough spread showing up in the
various ensembles output to characterize the extended as having
relatively limited predictability/forecast confidence, especially as
it pertains to the potential for there being any "major" weather
systems between now and December 1.

When the period opens, northwest flow aloft is getting its act
together, developing over the region, including a Canada-sourced
cold frontal passage by Sunday/Sunday night. But, until that front
sweeps southeast through the Dakotas, relatively mild (above climo
normal) air will be in place across the County Warning Area Saturday night and
Sunday. Despite the transient mid-level S/w's, depicted in the
500hpa pattern working down through this fast NW flow sequence, the
forecast remains a dry one through Sunday night.

(Here's where forecast confidence really bottoms out.) By mid-week,
a large longwave trof is supposed to get carved out of the longwave
pattern aloft across the western Continental U.S./West Coast. That is supposed
to translate into a pattern change over this region from dry/cold
northwest flow through Tuesday night to somewhat warmer (and
potentially wet?) Southwest flow aloft by Wednesday night through
Friday. This pattern develops frequently during the cold-season
months, and usually involves the formation of a split flow pattern
which, historically, gsm's have a tougher time "getting right". The
northern branch of the split flow pattern usually introduces high
levels of placement and timing uncertainty (for this cwa) as weather
systems that lift out of the southwestern Continental U.S. Try to lift north
and east across the country's mid-section. While there is some hint
in tonight's 00z gsm's for a weak waa-forced precipitation event
developing across a portion of the Dakotas and Minnesota on
Thanksgiving, right now the forecast confidence in this happening is
low, at best.


Aviation...(for the 12z tafs through 12z Saturday morning)
issued at 536 am CST Fri Nov 22 2019

Other than a few hours of low level wind shear potential this
evening/overnight, VFR skies/vsbys are expected through Friday
night regionwide.


Abr watches/warnings/advisories...
South Dakota...none.


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