Area Forecast Discussion
Issued by NWS Aberdeen, SD

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FXUS63 KABR 261738

Area Forecast Discussion
National Weather Service Aberdeen SD
1138 AM CST Sat Nov 26 2016

Issued at 528 AM CST Sat Nov 26 2016

See updated aviation discussion below.


.SHORT TERM...(Today through Monday Afternoon)
Issued at 204 AM CST Sat Nov 26 2016

Generally quiet weather IS expected for the first 24-36 hours of
the forecast, as an upper ridge slides east across the area. This
will lead to another day of above normal temperatures across SD.
Highs today are a little tricky, as there are a couple features
that will influence values. First over the east, there are some
pockets of lingering snow cover, which like yesterday will likely
keep values in the lower 40s. Second is the gradually dissipating
high clouds today which will weaken the sun`s influence at an
already low sun angle. Third is the weak winds in the boundary
layer due to the area being between a high in Colorado and
Arkansas and a low in far northern Saskatchewan. These weak winds
(generally less than 9kts up through 850mb) will make it difficult
to tap into the anomalous 850mb temperatures around 9C (nearing
90th percentile for KABR at this time of year). That being said,
still think there will be enough mixing to push highs up 1-5
degrees from yesterday, especially over Central SD. That produces
highs in the lower 40s over the east to the low-mid 50s over
central SD.

The dry weather will continue into Sunday morning before an upper
trough currently nearing the northern California coast will move
into the central CONUS. This upper trough will lead to a
persistent period of unsettled weather through much of the
upcoming work week as it slowly makes its way east. As the
leading shortwave quickly moves into Colorado on Sunday morning,
a surface low will develop in the lee of the Rockies and rapidly
move northeast and intensify. Models are still continuing to show
a strong low around 980mb over east-northeast SD by 06Z Monday.
If that pans out, KABR may set a new November record low SLP per
records kept at WPC (current KABR record is 986.8mb set in Nov
1961). That signal is also shown in both the NAEFS CFSR
climatology and GEFS M-Climate data where they are both
indicating values SLP outside what has been seen in the last 30
years and GEFS reforecasts. In addition, 850mb heights are around
4 standard deviations below climo on Monday afternoon, although
850 temperatures are near normal. Those anomalously low SLP
values will continue through the first half of the work week as
the low stalls around the SD/ND/MN border.

Since we have established that this will be an abnormal event,
what impact will it have on the area. First, will see a push of
moderate rain moving through eastern SD late Sunday afternoon
into Sunday night as the shortwave, surface low, and decent
mid-level WAA/Q-Vector divergence move through. Since the warm
air will be in place, expect this to occur as all rain and where
the heaviest precipitation occurs over the eastern half of the
CWA. Some indications of convective elements (50-100j/kg of
MUCAPE, pocket of 6-6.5C/km 700-500mb lapse rates and Showalter
values around 0 to -1) to the rain along and just to the east of
the surface low on Sunday night. Did opt to add in a mention of
thunder for the SE part of the CWA. Over the far western CWA
(mainly towards the Missouri River) the upper level moisture and
forcing is limited, but thermal profiles would support a
transition to snow overnight. That transition will continue to
move eastward through Monday morning as the 850/700mb lows stall
over the Northern Plains. That will likely continue to feed
moisture around the low and into the area for Monday and much of
the first half of next week. Thus, expect fairly steady light snow
for much of the area on Monday. Overall, expect the impact of the
snow through Monday to be limited due to surface temperatures
staying in the low to potentially even mid 30s (likely limiting
accumulations on roads). Could see some rain/snow mix over
southern and northeastern portions of the CWA hanging on for much
of the day as wetbulb0 heights stay around 1000-1500ft (if dry
slot doesn`t move over that area).

.LONG TERM...(Monday Evening through Friday)
Issued at 204 AM CST Sat Nov 26 2016

A fairly strong upper level trough will be over the region when the
extended period begins. The main low with this trough will spin over
the Northern Plains through much of the period, weakening Thursday
night and Friday.

At the surface, a strong low pressure system will be centered
somewhere over the eastern Dakotas, depending on which model you
look at. The low center will shift off to the east over Minnesota on
Tuesday, then looks to spin there for a couple of days, keeping at
least light precipitation over the CWA from Monday night into the
day Thursday. At this time, temperatures looks warm enough early in
the period for the precipitation to be rain or a rain/snow mix
Monday evening and again during the day Tuesday, then cooler air
gets wrapped in and keeps it all snow Tuesday night into Thursday.
Overall, it looks to be an long lived event of light precipitation,
with snow amounts from Monday evening through the day Thursday only
accumulating a total of 2 to 4 inches. The Thursday night through
Saturday period looks to be dry as the system finally exits to the
east and high pressure settles in over the region.

Temperatures will be right around normal through the period, with
highs in the 30s and overnight lows in the upper teens and 20s.


.AVIATION...(For the 18Z TAFS through 18Z Sunday Afternoon)
Issued at 1136 AM CST Sat Nov 26 2016

VFR ceilings and vis will remain through the day today. Patchy
fog will be possible tonight, mainly over our east for ABR and ATY
where the light winds remain. Rain will be approaching from the
south Sunday, by stay mainly south of the TAF sites through 18Z.




LONG TERM...Parkin
AVIATION...KF is the U.S. government's official web portal to all federal, state and local government web resources and services.