Area Forecast Discussion
Issued by NWS Aberdeen, SD

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FXUS63 KABR 261545 AAA

Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
1045 AM CDT Fri Apr 26 2019

Issued at 1045 AM CDT Fri Apr 26 2019

A waa/frontogenetic band of clouds extending from northwest to
southeast will continue its slow progression across the cwa
through the afternoon. There were weak radar returns with this
possibly producing some light showers/sprinkles. Have in some
small chance pops for this band. Otherwise, made some adjustments
to cloud cover and pops.

UPDATE Issued at 635 AM CDT Fri Apr 26 2019

Aviation discussion updated below for the 12Z TAFs.


.SHORT TERM...(Today through Saturday Afternoon)
Issued at 355 AM CDT Fri Apr 26 2019

Mostly clear skies across the CWA early this morning with light
winds as surface high pressure builds in. Temps are falling through
the 30s for many areas, and expect several areas to be near or below
freezing by sunrise along and west of the James River. As we head
through the day, clouds will gradually increase from west to east,
although expect eastern portions of the CWA to be mostly sunny
through much of the day. Highs will rise into the upper 50s to low
60s for most areas. Interesting to note that this morning there is a
weak band of lift/forcing that scoots northward across western and
central SD. Models are picking up on this and try to generate a few
sprinkles or very light showers as it lifts through. There is
evidence of this beginning right now as mid level clouds are on the
increase in a northwest to southeast oriented band over western SD.
This area of clouds may very well expand northward through central
SD during the morning hours. Have added slight chance POPs to
account for perhaps a sprinkle or light shower as this band of lift
passes through.

Main focus in the short term is tonight through Saturday as a quick
moving, but very potent low pressure system moves east along the
SD/NE border. Increased POPs and snow amounts with this system as
models continue to trend more bullish with QPF and snow. But again,
this will all depend on surface temps and unfortunately this
continues to be a tricky and low confidence forecast. Highest QPF
axis of perhaps in inch or slightly more basically runs along the
Hwy 212 and 14 corridors. Within this band, it`s hard to determine
how much of this will fall as snow. Very impressive amounts of lift
and forcing with this system, as well as the coupled jet structure.
HREF probs of 2"/hr of snow is fairly high. Everything will depend
on if temps can cool quickly enough to turn rain to snow and have it
accumulate for at least a couple hours in order to generate the 3+
inches that are currently forecast. There are suggestions from some
models of 6+ inches, and this is certainly possible if temps cool
quickly enough. Right now, current forecast has a swath of 3 to 6
inches from Dewey county eastward to Deuel county, but would not be
surprised if amounts are higher given a quicker cooling of surface
temps. Also, have a feeling snow will accumulate on grassy surfaces
much better than roads/sidewalks, so have questions on overall
impacts as well. For right now, no headlines given the questions on
impacts and overall low confidence on surface temps tonight. Will
let day shift make the final call. Did make some adjustments to
hourly temps after 06Z tonight to make a quicker hourly temp fall
within the axis of heaviest precip and dynamic cooling. Also, forced
more snow into the forecast at 35 degrees vs 34 degrees, which in
turn gave some higher amounts. Again, a very difficult forecast and
a matter of a couple degrees could make the difference of 6+ inches,
or little to no snow!

System moves out on Saturday, with cool temps in its wake. Generally
stuck with the trend of going cooler than guidance for high temps.
If less snow falls than forecast though, highs on Saturday may need
to be increased a few degrees within the heaviest QPF axis.

.LONG TERM...(Saturday Evening through Thursday)
Issued at 355 AM CDT Fri Apr 26 2019

Overall, the pattern in the long term period is not overly amplified
over the northern plains. There is still good model agreement for an
upper level disturbance moving through the region in west-northwest
flow aloft from late Saturday night through late Sunday evening, and
it could get rather breezy by Sunday evening across parts of central
and north central South Dakota. Off the 00Z guidance tonight, timing
of precipitation chances appeared to be sync`d up mainly when the
thermal profile is warm enough or warming up enough to support
mainly rain in the forecast over the second half of the weekend.
Things dry out on Monday as surface high pressure builds into the
region. Then, the next chance for precipitation starts to ramp up
across the region by early Wednesday morning, and is, again, mainly
showing up (based off the 00Z guidance) as warm/rain p-type within
the waa-forcing region of the next upper level disturbance lifting
east-northeastward out of the Rockies. Those precip chances are
tapering off by Wednesday evening, leaving the rest of the extended
forecast dry, for now. The deterministic low level thermal progs
show the vast majority of the period, Saturday night through Friday,
to be below normal, supported by the latest available NAEFS 850hpa
standardized anomalies running appx 1 to 2 standard deviations below
climo normal through Thursday.


.AVIATION...(For the 12Z TAFS through 12Z Saturday Morning)
Issued at 635 AM CDT Fri Apr 26 2019

VFR conditions will prevail today. During the overnight hours,
RA and SN will spread east across the region with IFR/MVFR CIGs
and/or VSBY becoming likely.




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