Area Forecast Discussion
Issued by NWS Aberdeen, SD

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FXUS63 KABR 210902

Area Forecast Discussion
National Weather Service Aberdeen SD
402 AM CDT Thu Sep 21 2017

.SHORT TERM...(Today through Saturday Afternoon)
Issued at 402 AM CDT Thu Sep 21 2017

High pressure is already well to our east, situated over western
Lake Superior and eastern MN. We`re already looking to our south and
west at the next weather maker. Southerly flow has already returned,
and 850mb winds will be at 40-50kts from mid morning through at
least early afternoon. This will help usher in much warmer air as a
warm front pushes north across eastern SD. Highs today will end up 6-
12F warmer than yesterday, topping out in the 80s for most.

Tonight will be the start of an extended period with a sfc trough
set up across eastern SD, that will continue into at least Saturday
afternoon. As a result, there will be a significant temperature
gradient northwest to southeast, which will be most noticable Friday
afternoon with highs in the low 60s over Corson County, to the mid
and upper 80s over Grant and Deuel Counties. The main concern will
not only be a focus for significant rain, with over 2 inches of rain
expected through Monday, but also the return of severe weather. Will
continue the mention of strong to severe thunderstorms in the HWO,
but may also touch upon the significant rainfall over our
southeastern counties. High amplitude southwest flow continues at
500mb, as the low stretching from the Pacific Northwest to south
central Canada forms a cut off low over the interior west that
slowly sinks across NV by Saturday. Taking a look at the sfc
features, the trough will set up from northeastern Co to south
central SD to northwestern MN by 06Z Friday. Fcst models show
impressive consistency with placement of the sfc low moving up the
trough Friday afternoon, with the low between

Most solutions paint some precip over our far northeastern counties
after 06Z Friday. There is still plenty of uncertaintly, even with
dewpoints in the mid 60s and incrreasing low level jet closer to
daybreak Friday. Add daytime heating to the mix, and Friday
afternoon-evening may get interesting over far eastern SD and
western MN.

.LONG TERM...(Saturday Evening through Wednesday)
Issued at 402 AM CDT Thu Sep 21 2017

The models show great agreement in the Saturday night through
Wednesday time period with the large scale upper level flow along
with the surface features. An abnormally large upper level low
pressure area will be over the southwest U.S. on Saturday night.
Several short waves will eject from this low pressure area until the
low pressure area itself opens up as it kicks out and northeast
across the Northern Plains through Monday night into Tuesday. At the
surface, a nearly stationary front will situated from southwest to
northeast just to the east of our CWA. Therefore, with the
interaction of this boundary and short waves aloft, good chances of
showers/storms are expected across most of the CWA from Saturday
night into Monday. Tuesday and Wednesday look to be dry at this time
as surface high pressure settles over our region.

With prevailing surface winds from the north through most of the
long term along with cloud cover and rainfall, temperatures will be
cooler than normal. Highs will be mostly in the mid 50s to the lower
60s from Sunday through Tuesday with a little warmer conditions for
Wednesday in the 60s. Would not be surprised if Sunday and Monday
were even cooler for highs with these conditions.


.AVIATION...(For the 06Z TAFS through 06Z Thursday Night)
Issued at 1239 AM CDT Thu Sep 21 2017

The forecast currently calls for prevailing VFR conditions at
all four terminals through late Thursday evening. Low level wind
shear should be developing between 1000ft and 2000ft agl within the
next couple of hours at KPIR/KMBG and persisting into Thursday
morning before being mixed out. The low level jet responsible for
generating this wind shear is expected to expand as far east as the
KABR terminal for a few hours prior to sunrise before being mixed
out. Also, there could be a few elevated thunderstorms developing
over northeast South Dakota into west central MN Thursday night.
Will not include in the TAFs this go around, but TS may be needed in
the KABR and/or KATY TAF within the next couple of issuances.




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