Area Forecast Discussion
Issued by NWS Aberdeen, SD

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FXUS63 KABR 221732 AAC

Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
1232 PM CDT Sun Apr 22 2018

Issued at 1230 PM CDT Sun Apr 22 2018

See updated aviation discussion below.

UPDATE Issued at 1017 AM CDT Sun Apr 22 2018

The current forecast for today looks good overall. Based on
visible satellite have lowered high temperatures by a few degrees
in Deuel County where significant still exist.


.SHORT TERM...(Today and Tonight)
Issued at 327 AM CDT Sun Apr 22 2018

A southerly breeze and mild temperature are the main forecast
"concerns". Looks like winds could go around to south/southwest at
some point so expect a slightly better degree of mixing compared to
Saturday and as such increased highs another degree or two. Models
show some increased dewpoints, much like the diurnal bump that
occurred yesterday, but given drying soils and negligible
evapotranspiration am concerned this may be overdone and afternoon
humidity could fall below the 30-40 percent range we have
advertised. Mixed winds top out around 20kts as well, and with the
green-up several weeks delayed due to cold soils, fire weather is
the only real concern today. Otherwise, tonight as high pressure
continues to back away from the region and low pressure in central
Canada also moves east, look for winds to slacken this
evening/overnight with favorable radiational conditions.

.LONG TERM...(Monday through Saturday)
Issued at 327 AM CDT Sun Apr 22 2018

Overall, not a whole lot of changes to the extended forecast from
the last couple of shifts. Monday will be a nice day across the area
as the CWA is between a departing high centered over the Great Lakes
(and ridge stretching into southern MN) and a cold front stretching
from northeastern WY through northwestern MN and into Hudson Bay.
Ahead of this front, a thermal ridge will stretch across eastern SD
with 850mb temps in the 7-9C range. With mixing into the 850-800mb
range, highs are expected to be in the mid-upper 60s except over
western Corson county where temperatures will be a little cooler due
to the proximity to the clouds associated with the next system.

That system will move into the area Monday evening as a shortwave
moves out of the northern Rockies and catches up with the cold
front. As was started to be seen last night, there continues to
be some differences between the NAM/GFS and the CMC/ECMWF on
whether the shortwave in the Rockies will remain tied to the
shortwave dropping southeast through Manitoba and into the Great
Lakes. The CMC/ECMWF have been trending more towards separation
and in turn take more of a southeast track while the NAM and
especially the GFS track it more easterly into Tuesday. Looking
at the GEFS plumes for our area, there are two clusters, one
towards the deterministic GFS and another towards the CMC/ECMWF.
The ECMWF EPS probabilities lean a little farther northeast than
the deterministic run, so thinking that keeping the forecast
towards a consensus at this point is the best call and hopefully
there will be better agreement in the next 12-24hrs. That idea
moves the precipitation out of the area by Tuesday evening. In
addition to the larger scale differences, NAM has trended low
level temperatures colder over the far northwest CWA, leading to
the potential for snow. If that pans out, seems like it would be
generally over the north central part of SD, as farther south as
low level temperatures cool there is a loss of ice in the clouds.
But it appears that the NAM is still a little farther east with
the heaviest QPF and the in turn more rapidly cools the lower
levels. CMC/ECMWF thermal profiles would keep the precipitation
as all rain and any snow potential to the west of the area. This
is due to enough low level warm air to keep WBZ heights above
1500ft for all but far northwestern Corson county around 12Z.
Thus, will continue the idea of mainly rain and maybe some mix in
northwest Corson county. Finally, the differences between the two
general solutions also lead to variations in the wind forecast,
as the NAM/GFS idea would produce gusts towards 30kts Monday
night and the CMC/ECMWF would keep winds significantly lower.

After that system, area comes under northwesterly flow aloft and
will see a series of weak shortwaves and cold fronts move through
the area (Wed night and again towards the weekend). Each one should
bring a brief cool down but then quickly rebound to normal or even
slightly above normal highs. With the shortwaves tracking to the
east of the area, should see a gradient in temps with the warmest
values in central SD and coolest towards MN. Continues to look like
dry frontal passages and only a brief period of increasing

There are Fire Wx concerns for Thursday behind the cold front, as
cold air advection will lead to good mixing with gusts towards
30kts. Fortunately temperatures won`t be too warm (50s) but RH
values will fall into the 30 percent range.


.AVIATION...(For the 18Z TAFS through 18Z Monday Afternoon)
Issued at 1230 PM CDT Sun Apr 22 2018

Prevailing VFR conditions are expected for all terminals through
the valid TAF period.




SHORT TERM...Connelly
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