Area Forecast Discussion
Issued by NWS Aberdeen, SD

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FXUS63 KABR 220530 AAC

Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
1130 PM CST Mon Jan 21 2019

Issued at 1125 PM CST Mon Jan 21 2019

See below for an aviation forecast discussion for the 06Z TAFs.

UPDATE Issued at 824 PM CST Mon Jan 21 2019

Issued a winter weather advisory for two things. First thing is
the north central zones where 2 to 4 inches of snow is probable.
Noticed earlier this evening, the McLaughlin webcam had iced over,
so there is also a little bit of freezing precip potential over
this advised area. Second thing is the RAP13 suggests rest of the
CWA never fully saturates (between 850hpa and 500hpa) within the
dgz, at least not until very late tonight/early Tuesday morning
leaving the door open for light snow/flurries to switch over to
freezing drizzle tonight. The 00Z KABR RAOB reveals there is a
dry/unsaturated layer between appx 750hpa and appx 600hpa. Below
750hpa there is a stratus cloud layer with more than 75 percent
of the cloud layer residing between -5C and -10C supercooled
droplets realm supporting freezing p-type. The very bottom of the
stratus layer (a couple hundred feet) tickles ice-nucleation
range of -11C to -14C ice crystals realm supporting frozen
p-type. There are locations within the CWA that the RAP13, fed
through BUFKIT, supports many hours of freezing drizzle p-type
before enough cooling/saturation occurs to switch p-type over to
just plain old snow. So, because of the freezing drizzle noted on
area webcams (including McLaughlin), and the short-range, rapid
update guidance supporting some freezing drizzle over the next
several hours before p-type effectively becomes an all snow
p-type, issued a winter wx advisory for the rest of the CWA for a
mix of light snow accum potential combined with a light ice glaze
potential from freezing drizzle. Updates are out.

UPDATE Issued at 538 PM CST Mon Jan 21 2019

See below for an aviation forecast discussion for the 00Z TAFs.


.SHORT TERM...(This Evening through Tuesday Afternoon)
Issued at 333 PM CST Mon Jan 21 2019

Upper level low pressure trough in Wyoming late this afternoon was
showing expanding cloud tops along with increasing radar returns
into Western South Dakota. All models agree well in lifting this low
pressure trough northeast through the night with snow expanding over
the entire cwa. The latest qpf/wpc guidance numbers show amounts
less than a quarter inch water equivalent. This equates to about 1
to 3 inches of snow with the highest accumulations in north central
South Dakota. As this system moves by on Tuesday, the light snow
will end from northwest to southeast with breezy north winds causing
some blowing snow.

.LONG TERM...(Tuesday Evening through Monday)
Issued at 333 PM CST Mon Jan 21 2019

A few below 0 temperatures will return Tuesday night over the
eastern half of the forecast area. Otherwise, dry weather looks to
be the rule through the day Wednesday. A temporary ridge of high
pressure, extending from the larger western U.S. surface high, will
linger overhead through early Wednesday. At that point, a weak
surface low over southern Manitoba and graze northern ND/MN
Wednesday. While most of the precipitation will stay closer to the
low, a slight chance of snow will be possible Wednesday night.

3 hour pressure change of 6-8mb will sweep northwest to southeast
across the cwa late Wednesday evening through Thursday morning,
before the surface high sets up shop overhead during the afternoon
hours. While forecast models are not quite as strong with the wind
potential, we continued to keep winds higher than guidance. Will not
be surprised if we need to do further increases as the time nears.
Blowing and drifting snow could be a concern. Continue to highlight
the potential for dangerously low wind chills with the cold air
coming in Thursday into Friday morning. Current forecast calls for a
few locations to near -40F wind chill over eastern SD and western MN.

While forecast models continue to show another system for the end of
the weekend, timing is still unknown. Chance pops look reasonable
for Sunday through Monday, mainly over our eastern counties.
Ensembles show a wide range of possibilities beyond Saturday,
resulting in a low confidence forecast.


.AVIATION...(For the 06Z TAFS through 06Z Tuesday Night)
Issued at 1125 PM CST Mon Jan 21 2019

Over the next 12 hours, expect MVFR/IFR to persist, along with
some periods of light to moderate snow, and perhaps a little
freezing drizzle. Gusty northwest winds develop by morning and
continue through Tuesday creating occasionally reduced visibility
in blowing snow. Some improvement is forecast Tuesday afternoon
and evening.


SD...Winter Weather Advisory until 6 AM CST /5 AM MST/ Tuesday for

     Winter Weather Advisory until 9 AM CST /8 AM MST/ Tuesday for

MN...Winter Weather Advisory until 9 AM CST Tuesday for MNZ039-046.



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