Area Forecast Discussion
Issued by NWS Aberdeen, SD

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FXUS63 KABR 291718

Area Forecast Discussion
National Weather Service Aberdeen SD
1218 PM CDT Sat Apr 29 2017

Issued at 1215 PM CDT Sat Apr 29 2017

Increasing hourly temperatures west and northwest of PIR, and
decreasing dew points/RH. Otherwise, no significant changes were
made to the ongoing forecast.


.SHORT TERM...(Today through Monday Afternoon)
Issued at 357 AM CDT Sat Apr 29 2017

High pressure will remain in control today keeping conditions dry
with pleasant temperatures, albeit a bit on the cool side and below
normal. Will once again see very low RH values over central SD with
readings likely dropping below 20 percent over north central SD.
Winds look to be around 10 mph or less over areas where RH will be
the lowest. Bumped up highs today a couple degrees based on slightly
warmer temps aloft and comparing conditions to yesterday`s temps.
Will likely be dealing with some high level cloudiness which will
damper temps slightly.

Main focus in the short term will be the storm system moving into
the region on Sunday. Models still showing a strong low pressure
system moving northeast out of the central plains and into IA by 00Z
Monday. Models have shifted the storm track westward just a bit,
bringing more QPF into the James valley and bringing generous
amounts of precip to the entire eastern CWA. Precipitation amounts
of over 1 inch seem likely over the eastern CWA, which is starting
to look like it will include several inches of snow. The column
cools enough by Sunday night as surface temps fall to around 32
degrees. Confidence is increasing in rainfall transitioning to a
heavy, wet snowfall Sunday evening/night and continuing through
Monday morning. Snowfall rates could be quite intense with quick
accumulations especially on grassy areas. Model output of snowfall
continues to vary widely around the Watertown area, but GEFS plumes
are honing in around the 5 inch mark. Current forecast is for around
4 to 6 inches around Watertown and the higher terrain Coteau areas,
but will not be surprised of amounts over 6 inches, especially along
the Coteau ridge line. Debated on a Winter Storm watch, but will
wait for 12Z data to come in to get a better look at thermal
profiles and duration of heavy precip when temps are around 32 to 34
degrees. Want to also see if the westward track is maintained. May
decide yet to issue an SPS to highlight the potential for
significant late season snowfall. What will also be helping aid
snowfall will be the persistent upslope flow into the Coteau thanks
to strong northeast winds blowing perpendicular to the ridge.
Current storm total snow map does have a maxima in this area so am
satisfied with this for the time being.

Storm system looks to get on out of here during the day Monday. It`s
interesting to note that on the back side of this system, temps
aloft warm quickly and there`s already decent warm air advection
kicking in Monday afternoon as the storm departs. There will likely
be a wide range of temps and weather across the CWA Monday, with
cold and snow/rain across the eastern CWA and highs struggling to
reach 40. Meanwhile, central SD will be hovering around 60 degrees
Monday afternoon.

.LONG TERM...(Monday Evening through Friday)
Issued at 357 AM CDT Sat Apr 29 2017

The area of low pressure that will affect eastern portions of the
cwa at the start of the week will exit to the east Monday night.
More shortwave activity on the backside of an upper trough will
bring rain showers to the Missouri River valley Monday night that
will spread east on Tuesday.

Wednesday night and Thursday will see a ridge build in aloft.
Ridging will dominate the latter half of the week until an upper
trough in the northern stream of the jet flattens it late Saturday.
The ridge will allow warmer than average temps to filter into the
region. Highs at the end of the work week are forecast to be in the
upper 60s to lower 70s.


.AVIATION...(For the 18Z TAFS through 18Z Sunday Afternoon)
Issued at 1215 PM CDT Sat Apr 29 2017

VFR ceiling and vis remain. The strongest winds/pressure gradient
remains across our southeast, impacting ATY the most. Expect winds
there to increase through the late afternoon hours out of the
northeast gusting to near 25kts. Otherwise, the main aviation
impact will remain just to our southeast, in the form of MVFR or
lower ceilings that will arrive at ATY after 18Z Sunday.




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