Area Forecast Discussion
Issued by NWS Aberdeen, SD

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148
FXUS63 KABR 211538
AFDABR

Area Forecast Discussion
National Weather Service Aberdeen SD
1038 AM CDT SAT MAY 21 2016

.UPDATE...
Issued at 1034 AM CDT SAT MAY 21 2016

The current forecast looks good overall. Winds are a bit underdone
today...thus have increased speeds by a few knots. Several
locations are reporting sustained winds in the mid 20 mph range
with gusts exceeding 30 mph.

UPDATE Issued at 703 AM CDT SAT MAY 21 2016

12z aviation discussion updated below.

&&

.SHORT TERM...(Today through Monday Afternoon)
Issued at 402 AM CDT SAT MAY 21 2016

A broad upper trof persists over the pacific northwest while a ridge
dominates the central plains. Over the course of the day the upper
trof will migrate slowly eastwards, which will help increase the
pressure gradient slightly, resulting in continued gusty winds
across the forecast area through the evening.

Tonight, the low level jet redevelops across the Dakotas and
Nebraska, however the increased gradient will result in 850mb winds
increasing into the 40-50kt range. MUCAPE values are lower compared
to previous runs but will still top out around 500j/kg. The reason
for the lower MUCAPE values is that guidance is trending somewhat
slower with surface and upper level features. As the NBL mixes out
late Sunday morning expect convection to weaken/dissipate. The
surface front now looks to make a slow progression into the Missouri
valley during the day. 700mb temperatures will initially run around
+10C, but as the core of the warmest air aloft pushes into eastern
South Dakota, cooler mid level temperatures will allow for
convection to develop along the front. NAM mixed layer dewpoints are
about 5F higher compared to the GFS, however both result in MLCAPE
values between 2500 to 2000j/kg respectively. The farther west
placement of the front compared to previous runs also places storm
development in a more favorable 0-6km shear environment around
40kts, with a mainly unidirectional shear profile. Am more
comfortable adding mention for severe hail under this environment.
Training will also be possible due to the slow frontal movement, and
a north/northeast storm motion, however storm speed of 40 to 50kts
and dry ambient conditions will mitigate most of the flood risk.

The front will continue to move very slowly during the evening and
overnight hours but the low level jet development and orientation
favors a more rapid transition of convection into the eastern CWA
after the loss of daytime heating.  850mb temperatures drop very
little in the post frontal environment, however dewpoints will end
up much lower on weak westerly low level flow.

.LONG TERM...(Monday Evening through Friday)
Issued at 402 AM CDT SAT MAY 21 2016

The models continue to agree well and have been consistent from run
to run with the upper level flow pattern affecting our region in the
long term. Our region remains under southwest flow aloft from Monday
night through Friday. Upper level troughing over California and off
the west coast will send off several short wave troughs through the
week until the trough itself kicks out and into our region Friday
and Friday night. This pattern will result in several chances of
showers and storms through the week. The models then show a large
upper level low pressure area developing over the western U.S. for
the weekend. This will keep the unsettled weather pattern in place
into the weekend. Winds should not be much of an issue as we will be
near the frontal zone. Temperatures should be above normal to begin
the period and then cool back down closer to normal late in the
period.

&&

.AVIATION...(For the 12Z TAFS through 12Z Sunday Morning)
Issued at 703 AM CDT SAT MAY 21 2016

Stratus clouds will stream up from the south affecting PIR and
MBG through today and tonight. The ceilings are expected to be
mvfr/low vfr. ABR and ATY will be vfr through the entire period.
With a tight surface pressure gradient and strong low level mixing
winds...expect windy conditions for the day with southeast winds at
15 to 25 knots with gusts over 30 knots. There is also expected to
be some llws at ABR and ATY later this evening and overnight with
winds up to 45 knots off the surface.


&&

.ABR Watches/Warnings/Advisories...
SD...NONE.
MN...NONE.
&&

$$

UPDATE...SD
SHORT TERM...Connelly
LONG TERM...Mohr
AVIATION...Mohr



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