Area Forecast Discussion
Issued by NWS Aberdeen, SD

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000
FXUS63 KABR 200818
AFDABR

Area Forecast Discussion
National Weather Service Aberdeen SD
318 AM CDT Fri Apr 20 2018

.SHORT TERM...(Today and Tonight)
Issued at 317 AM CDT Fri Apr 20 2018

Not much change to the overall evolution of the system to our south
(for our area anyway). Already have increasing high clouds, but CAMS
suggest moisture may be somewhat delayed. Will also have to overcome
a decent sub-cloud dry layer evident in BUFKIT soundings and given
weak/elevated lift there may be some virga initially. Temperatures
today/tonight are progged to remain above freezing, with a freezing
level around 3-4kft so precipitation type is just rain.


.LONG TERM...(Saturday through Thursday)
Issued at 317 AM CDT Fri Apr 20 2018

Main feature of the long term forecast is the potent shortwave
moving through the area Monday night into Tuesday, leading to a
decent opportunity for rain over north central SD.

Before that system arrives, will have some lingering showers over
south central SD on the northern edge of the upper low currently
over the southwestern CONUS. This upper low will be moving east out
of Colorado on Saturday. Most of the forcing will be to the south of
the area and even with south-southeasterly flow, there are some
struggles in moistening the lower levels over the eastern half of
SD, thus concerns on if precipitation will occur. Will keep PoPs
confined to the far southwest part of the CWA (Jones/Lyman counties)
and closest to the better forcing. NAM indicating some fog potential
for Saturday morning (and again on Sunday), but since the NAM tends
to overdo the low level moisture and limited rain to aid in
moistening (along with weak low level winds), will keep out of the
forecast. Also for Saturday, expect gusty winds over the northwest
third of the CWA between the surface high ridge extending west from
the Great Lakes and a weak trough over eastern Montana. Mean
momentum transfer values are in the mid 20 kt range and felt that
was reasonable for Corson/Dewey county.

On Sunday, that weak trough from Montana will slowly try to slide
east and move into northwest SD and west/central ND. Models vary on
the eastward extend through Sunday night and in turn the associated
clouds. That will have a potential impact on temperatures, so have
followed a general consensus of models for now (around 60). This
clouds will also impact the wind gusts, with the eastern cwa having
the best opportunity for deeper mixing, but with weaker winds aloft,
expect gusts in the 15-20kt range.

On to the main system for Monday night into Tuesday. Still some
timing differences between CMC/ECMWF and the GFS on how quickly the
precipitation will move through, with the GFS being 6-12 hours
faster.  Even with those differences, models are consistent on
precipitation amounts, with around a half inch of liquid falling
over north central SD. Some hints of convection in the models
(pocket of steeper 700-500mb lapse rates over central-south central
SD), so could see some higher amounts if convection occurs (left
thunder out of the forecast for now with limited elevated CAPE). At
this time, it looks like the precipitation will largely be rain, but
there is a hint in the CMC that there may be some snow mixing in on
the backside. Finally, with the models highlighting a compact low,
there will likely be a 3-6hr period of gusty winds Monday night into
Tuesday morning (near advisory levels).

After the Tuesday system, have a couple of dry fronts pushing
through on Wednesday night and again towards next weekend.  This
trend may not lead to temperatures quite as warm as initially
expected for the end of next week, but it should still end up around
60 degrees.  At this point, there is limited moisture associated
with the fronts as they drop southeast from Canada, so will keep the
forecast dry.


&&

.AVIATION...(For the 06Z TAFS through 06Z Friday Night)
Issued at 1231 AM CDT Fri Apr 20 2018

VFR conditions are expected through most of the TAF valid period.
By late afternoon, some rain showers may be working northward into
the region (mainly affecting KPIR), and after 00Z some sub-VFR cigs
may be developing. Currently, not a lot of confidence in sub-VFR
conditions setting up Friday evening/night. Will continue to
monitor.


&&

.ABR WATCHES/WARNINGS/ADVISORIES...
SD...None.
MN...None.
&&

$$

SHORT TERM...Connelly
LONG TERM...SRF
AVIATION...Dorn



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