Area Forecast Discussion
Issued by NWS Aberdeen, SD

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FXUS63 KABR 211727 AAC

Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
1227 PM CDT Thu Sep 21 2017

Issued at 1225 PM CDT Thu Sep 21 2017

See updated aviation discussion below.

UPDATE Issued at 1018 AM CDT Thu Sep 21 2017

Current forecast is on track, therefore no changes made at this


.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 noticeable
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.

Most solutions paint some precip over our far northeastern counties
after 06Z Friday. There is still plenty of uncertainty, even with
dewpoints in the mid 60s and increasing 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 18Z TAFS through 18Z Friday Afternoon)
Issued at 1225 PM CDT Thu Sep 21 2017

VFR conditions will prevail across the area through midday Friday.
Scattered showers and thunderstorms are possible across the far
northeastern CWA tonight, but at this time it does not appear that
any TAF sites will be affected.




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