Area Forecast Discussion
Issued by NWS Aberdeen, SD

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FXUS63 KABR 201748 AAC

Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
1248 PM CDT Sat May 20 2017

Issued at 1235 PM CDT Sat May 20 2017

See below for an aviation forecast discussion for the 18Z TAFs.

UPDATE Issued at 1103 AM CDT Sat May 20 2017

Only some minor timing adjustments made to pops/wx for today into
late this evening based off current radar and future hi-res cam
reflectivity forecast. Also, nudged qpf down a bit over the west
and up a bit across the far eastern zones. Not changing all that
much in the max Temp forecast right now for today. Still looks
like warmest readings will be over north central SoDak where less
clouds and little or no precip will occur today. Updates are out.

UPDATE Issued at 623 AM CDT Sat May 20 2017

See updated aviation discussion below.


.SHORT TERM...(Today through Monday Afternoon)
Issued at 355 AM CDT Sat May 20 2017

Today: Light returns showing up on regional radar, however CIGS
remain fairly high and PIR ABR ATY and MBG all have dewpoint
depressions on the order of 10 to 15 degrees. That said, as the low
deepens over Nebraska, flow becomes more easterly and we should
saturate out the low levels. TROWAL moisture will wrap back into
the CWA through the majority of the today period, though the focus is
across eastern South Dakota/western Minnesota, and west river
counties will experience more hit/miss shower activity. High
temperatures in the east are unlikely to budge much today, while
more filtered sun will allow for readings to top 50 out west.

Tonight: It gets complicated. Lets address P-TYPE first. NAM has a
cool bias, however both it and the Canadian suggest some light snow
accumulation as the system treks northeast, with TROWAL moisture
continuing to wrap back into the eastern CWA. Added mention of
Rain/Snow, with the focus over the higher elevations of the Coteau.
This is just a novelty as ground/air temperatures are too warm for
snow to stick. Winds will remain breezy in the eastern CWA as the
surface low moves across Iowa/Minnesota, so despite lows in the 30s,
frost should not be a problem.  Its a different situation in western
and central counties. With such a cool airmass - 925/850mb
temperatures 2 standard deviations below climo - and cloud cover
during the day limiting warming, we expect high temperatures to
struggle into the 50s. The next question will be the degree of
clearing overnight, which is highly uncertain as we lack a well
defined high center. NAM BUFKIT profiles take much of the night to
completely dry out and GFS 500/700/850mb RH also remains high
through the evening and early overnight hours before some gaps of
drier air mix in. Thus, only expecting partial/patchy clearing.
Despite this, the cool start to the evening, along with light
winds supports a threat for patchy frost.

Sunday features continued cool temperatures and breezy northwest
winds but soundings continue to dry out, so mid/late may sunshine
should support highs in the 60s.

Sunday night/Monday: A secondary shortwave drops out of Canada.
With northwest flow, and cooling temperatures aloft - steepening
lapse rates will lead to elevated shower activity. Mixed winds in
BUFKIT soundings top out around 20-30kts.

.LONG TERM...(Monday Evening through Friday)
Issued at 355 AM CDT Sat May 20 2017

A broad mid level trough will be over the region Monday night, with
shortwave energy in the vicinity through Tuesday evening. Ridging
then sets up through Thursday night before the flow becomes
southwesterly and a series of shortwaves track across the region
through the end of the period.

At the surface, high pressure will drop southward over the western
Dakotas Monday night, then shifts eastward through the day Wednesday
ahead of a trough digging down the lee of the Rockies. As the trough
slowly shifts eastward, precipitation chances will increase by late
in the week and continue into the weekend. Instability and shear
appear to be minimal at this time, so will not include thunder and
will keep the precipitation mention as just rain showers.

Temperatures will still be a bit cool on Tuesday, with highs mainly
in the 60s. Will see a return to the 70s mid to late in the week,
with Thursday likely being the warmest day of the period. More cloud
cover and potential precipitation will bring temperatures back down
into the 60s on Saturday. Overnight lows will be mainly in the 40s.


.AVIATION...(For the 18Z TAFS through 18Z Sunday Afternoon)
Issued at 1235 PM CDT Sat May 20 2017

Widespread rain showers broken out into a couple of large blobs
over the region (one over northeast South Dakota right now, and
another over far southeast South Dakota and northwest Iowa) will
continue to spread over portions of central and northeast South
Dakota through the rest of today and during the overnight hours.

KABR and KATY can expect the prevailing conditions to include
light rainfall through at least 06Z tonight before precipitation
begins to taper off/dissipate. And, these two terminals should be
in and out of MVFR/IFR cigs and/or visbies over the next 12 hours
before wholesale improving conditions begin to return.

KPIR will be on the western fringe of precipitation chances
through this afternoon into early this evening before
precipitation chances go away there. It`s possible KPIR could be
flirting with some MVFR cigs for a few hours mainly between late
this afternoon and late this evening. Otherwise, VFR conditions
should prevail there through the TAF valid period.

KMBG will likely remain dry and VFR throughout the TAF valid




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