Area Forecast Discussion
Issued by NWS Aberdeen, SD

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FXUS63 KABR 181745 AAC

Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
1245 PM CDT Thu May 18 2017

Issued at 1239 PM CDT Thu May 18 2017

Aviation discussion updated below for 18Z TAFs.

UPDATE Issued at 1018 AM CDT Thu May 18 2017

Winds are gusting in the 20 to 30 mph range across most of the
CWA, which was a tad higher than what was in the grids earlier
this morning. Have therefore increased wind speeds a touch through
the morning and afternoon, but we should then see a slight
downward trend by early evening. Otherwise, seeing some nice
clearing in the James valley westward into central SD, so adjusted
sky cover accordingly. Current high temps appear on track and no
changes made there for the time being.


.SHORT TERM...(Today through Saturday Afternoon)
Issued at 347 AM CDT Thu May 18 2017

Lingering light rain across eastern SD/western MN this morning, with
a persistent pressure gradient from north to south around 10mb
resulting in gusty north winds. Trowal moisture and the gradient
both weaken, however mixed winds in NAM BUFKIT soundings will
continue to generate breezy conditions today. For temperatures - We
are getting a ribbon of low clouds clearing out across western
counties this morning, and despite high clouds on the increase
associated with the next system, most of the area should see enough
filtered sun to get us into the upper 50s for highs.

It will be a tricky temperature forecast for tonight. There is the
outside possibility of frost, however the scenario doesn`t look
favorable.  First, model guidance does have quite a bit of high
clouds as the next upper low rotates into Colorado.  NAM BUFKIT
soundings support CIGS of 10-15kft becoming more widespread as the
overnight hours progress. High pressure over northern North Dakota
with a lee low over Texas will generate a north south pressure
gradient of 8mb, keeping winds from decoupling completely. Thus,
while I did go a tad below guidance - into the mid 30s to around 40,
I opted not to mention frost in the forecast.

Northeast to easterly flow shows up in BUFKIT soundings as a very
dry near surface layer. Overtop of that we should see elevated
moisture and periods of lift associated with isentropic ascent
pinwheel northwards. This dry layer will gradually erode, and it
looks like a prolonged period of precipitation chances as the upper
low is slow to move, lingering through most of Saturday. GEFS plumes
show quite a range across most cities in the CWA - with around a
half inch of spread. Mobridge is the lower end outlier with a lower
range in GEFS outcomes and a mean around a quarter inch, while
Watertown will see a higher range of outcomes and a mean around 1

Loose threads - While precipitation on Friday/Saturday is expected
to be almost all rain, profiles in both the GFS and NAM are quite
cold. The NAM is notably colder than the GFS in the low levels -
which explains the spotty but not irrelevant accumulations. Lately I
have not had much confidence in NAM outcomes at this time range based
on a few experiences last winter and early spring. West river seems
to be the prime target for more widespread light accumulations, with
both the GFS/NAM and several SREF members showing a sharp drop off
along the western CWA border. Thus, I would not be surprised if a
few spots see snow mixing in with rain just about anywhere within
the CWA, and and cant rule out a few spots receiving some sloppy
light accumulations.

Based off NAM/GFS 925mb temperatures, and limited diurnal heating -
expect limited temperature range for the latter half of the short
term, with highs some 20 degrees below climo, and lows about 10
degrees below climo.

.LONG TERM...(Saturday Evening through Wednesday)
Issued at 347 AM CDT Thu May 18 2017

The long wave flow still appears as if it will transition to a
positive PNA (Pacific North American) western conus
ridge and east conus trof...during the forecast time period.

Often times a positive PNA pattern can lead to mostly dry conditions
over the ABR cwa. However, this time around mid level temps will
remain quite cool, and with daily diabatic heating, low to mid level
lapse rates steepen up quite a bit in the afternoon and early
evening. So, one could argue for diurnal showers just about every
afternoon. However, with fairly scant available moisture, will rely
more on a couple mid level waves before mentioning pcpn in the
forecast. One decent looking pv anomaly comes through Monday, and
another on Thursday. Have reserved those time periods for the
highest pops.

Temperatures should generally average out around normal.


.AVIATION...(For the 18Z TAFS through 18Z Friday Afternoon)
Issued at 1239 PM CDT Thu May 18 2017

MVFR CIGs continue at KATY but look to be clearing out and/or
becoming SCT VFR later this afternoon. Otherwise, VFR conditions
will prevail through the rest of the afternoon and overnight
hours. Mid and high level clouds will gradually increase from the
south tonight as a storm system approaches. By Friday morning, low
end VFR CIGs are expected at KPIR, with -RA moving in also. By mid
morning, expect CIGs to go MVFR with -RA continuing.




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