Area Forecast Discussion
Issued by NWS Aberdeen, SD

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FXUS63 KABR 201747 AAB

Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
1247 PM CDT Thu Apr 20 2017

Issued at 1241 PM CDT Thu Apr 20 2017

Have been steadily increasing sky cover across the western CWA
over the past few hours as daytime heating has increased the
stratocumulus field back to the west. Forecast highs for today
appear on track for the time being and only minor changes made
there. Otherwise, will be assessing fog potential for tonight
along with timing the departure of cloud cover. Aviation
discussion has also been updated below for the 18Z TAFs.


.SHORT TERM...(Today through Saturday Afternoon)
Issued at 348 AM CDT Thu Apr 20 2017

Light returns are hanging on in parts of the northern CWA this
morning, with stratus covering much of the Dakotas. The slow moving
upper low, with a trough extending upstream/back to the northwest
suggests we will struggle to see any sunshine and what does make it
through will only support additional low level clouds. Thus, have
lowered highs, particularly across the James valley and Sisseton
hills region to low 50s.

A weak upper ridge begins to move into the region this
evening/overnight. Drying aloft is noted in NAM BUFKIT profiles. The
question is how quickly does low stratus dissipate/advect away. On
the western edge, where sunshine destabilization has lead to
stratocumulus, this should be rapidly in the evening. It may take
a bit longer in the James valley and Sisseton hills regions
however. Despite this, a lack of mixing and ample low level
moisture will result in fog development with an induced high
pressure overhead. The degree of coverage and intensity of the fog
is the uncertain part of this forecast, so will limit coverage to
areas and keep dense wording out for now.

Also lowered lows for the tonight period to follow the trend of
cooler highs today. The lack of daytime heating and loss of cloud
cover will result in temperatures plummeting this evening. Given
readings in the 20s a few nights ago, there is no need to mention
frost until we begin to experience a much milder string of weather.
That will have to wait for the weekend if not longer, with Canadian
high pressure dominating the rest of the forecast and 850mb
temperatures stuck between +1 and +4C Friday. Saturday offers
slightly better mixing and thus highs in the mid/upper 60s.

.LONG TERM...(Saturday Evening through Wednesday)
Issued at 348 AM CDT Thu Apr 20 2017

The early part of the extended period will be fairly quiet with high
pressure in place Saturday night. The high gets pushed east on
Sunday by an approaching low pressure system, which looks to track
across the state Sunday night and Monday, bringing the next chance
for precipitation to the area. High pressure begins to nose in from
the north late Monday night and Tuesday, bringing a respite in the
precipitation. Another system moves in at the tail end of the
period, bringing another chance for precipitation Tuesday night and
Wednesday. Little to no instability associated with either system,
so will keep precipitation mention as rain showers. Subzero 850 MB
and 925 MB temperatures both Tuesday night and Wednesday night may
allow for the precipitation to mix with or change over to light snow
for a while, mainly during the late overnight hours.

Sunday will be the warmest day of the period with decent WAA ahead
of the approaching lows. Highs will be in the mid 60s to lower 70s.
Near normal temperatures in the 60s on Monday will then make way for
cooler air due to more cloud cover and potential precipitation, with
highs in the 50s Tuesday and Wednesday. Overnight lows will
generally be in the 30s, with the exception of a warmer night in the
40s Sunday night.


.AVIATION...(For the 18Z TAFS through 18Z Friday Afternoon)
Issued at 1241 PM CDT Thu Apr 20 2017

BKN-OVC MVFR CIGs will remain in place over all TAF sites early
this afternoon, with a gradual shift to lower end VFR CIGs later
this afternoon. Expecting skies to gradually clear overnight, with
potential for FG/BR to settle in as winds go light and variable.
VFR conditions will prevail on Friday after any morning FG/BR




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