Area Forecast Discussion
Issued by NWS Aberdeen, SD

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FXUS63 KABR 280545 AAC

Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
1145 PM CST Sun Nov 27 2016

Issued at 1134 PM CST Sun Nov 27 2016

See the updated aviation discussion below.

UPDATE Issued at 850 PM CST Sun Nov 27 2016

The low pressure system continues to track north into the
northern plains states this evening, with the surface low now
centered over northeast Nebraska/southeast South Dakota.
Precipitation continues across the entire CWA, all in the form of
rain up to this point. Temperatures across the region have held
steady (above freezing) and have begun to gradually increase
across the eastern CWA. Still expecting the rain to change over to
snow around midnight for parts of western and central South
Dakota. No major changes made to the going forecast this evening.


.SHORT TERM...(This Evening through Monday)
Issued at 329 PM CST Sun Nov 27 2016

Forecast challenges still revolve around precipitation types,
amounts, and coverage as this strong low pressure system moves up
into the region tonight and Monday.

Currently, temperatures are in the 30s to around 40 degrees across
the forecast area under a cloudy sky and 10 to 15 mph east-southeast
winds. There is also a broad area of rain lifting north through the
forecast area right now.

Rain will continue to develop and stream northward through the
forecast area this evening. And, there is still a small signal for
convective potential across the eastern forecast zones. However, per
satellite imagery, there is a dry slot headed for this cwa and is
expected to reach the cwa by 06Z. The eastern half of forecast zones
is most likely to experience the dry slot`s effects, which will be
to eliminate the precip-producing mid-atmosphere clouds, in effect,
reducing precipitation chances there to "heavy drizzle" unless
elevated thunderstorms develop within the dry slot. By Monday
morning, the highest qpf (rain) amounts should be over far northeast
South Dakota and west central Minnesota (upwards of a half inch)
with lesser amounts down toward central South Dakota (up to a
quarter inch). Meanwhile the rain should continue falling across the
western half of the CWA between 06Z and 12Z Monday. The expectation
remains that the far western fringe of the precip shield should be
cooling off enough for phase change to snow late tonight and
continuing into Monday mainly across portions of central and north
central South Dakota. The boundary layer on Monday is expected to be
exhibiting similar conditions to the system that moved through prior
to Thanksgiving, namely temperatures ranging from around 30F degrees
to as warm as 35F or 36F degrees and relatively low snow-to-liquid
ratios (certainly warmer than climo SLR`s for late November). This
is going to make it tough to accumulate very much snow late tonight
and on Monday. There could be as much as 1-3 inches of snow accum
potential, but then it`s also possible that up to half of it could
be melting on impact with the ground on Monday, or the p-type could
be changing back to rain during the warmer afternoon hours on
Monday. Models also depict fairly strong 0.5km winds developing
along and west of the MO River valley on Monday. However, given how
wet the snow will be and how warm boundary layer conditions are
expected to be, there isn`t much potential for blowing snow in the
forecast tonight or Monday. As for temperatures tonight and Monday,
not really expecting much more than perhaps a 5 or 6 degree swing
between tonight and Monday (highs and lows in the 30s to low 40s).

Overall, the potential for headline-able hazardous weather tonight
or Monday is rather low at this time. So, the biggest concerns
continue to be highlighted in the Hazardous Weather Outlook and
communicated via Social Media.

.LONG TERM...(Monday night through Sunday)
Issued at 329 PM CST Sun Nov 27 2016

To start out at 00Z Monday, the 500mb low will be over western
SD. The slow moving sfc low will be over southeastern SD Monday
night, and move to far northeastern SD/west central MN by daybreak

Expect the stacked sfc-500mb low to finally exit east Tuesday night,
shifting central and eastern MN. Northwesterly flow will remain
across our area through at least Thursday, if not for the remainder
of the work week. Fcst models are pretty consistent with the overall
pattern through Thursday. Expect several waves rotating around the
low to keep off and on light snow showers going. The timing of these
embedded waves is difficult, as is the details. The ECMWF is faster
to bring cooler air into the region Tuesday night. There could be a
quicker transition to all snow than what we are currently
forecasting Tuesday afternoon/early evening.

While snow totals may be well over 4 inches near the ND border, they
are very long duration on the order of 2.5-3 days. Plus, with
daytime temperatures increasing to at or above freezing through
Tuesday, accumulating snow on area roadways will be more difficult
outside of quick bursts of snow. Will continue to mention
the winter/mixed precipitation in the HWO.

30-40kt wind gusts will remain possible Monday night through into
later Tuesday night mainly west of the MO river, with some patches
of blowing/drifting snow possible once roadways cool. Snow ratios do
indicate that the snow will be closer to 10:1, also hampering some
of the blowing and drifting.

Expect dry weather to return Friday through Sunday. Few changes were
needed to a general blend, as high temperatures stay near seasonal
normal values.


.AVIATION...(For the 06Z TAFS through 06Z Monday Night)
Issued at 1134 PM CST Sun Nov 27 2016

IFR/LIFR CIGS and VSBYS can be expected at all TAF sites through
the period as a low pressure system tracks north and wobbles over
the northern plains states. Many locations are still reporting
rain, but ptype is beginning to gradually change from rain to snow
across parts of north central South Dakota including the KMBG TAF
site. This transition will gradually occur from west to east
across the region as the low tracks north and winds switch around
to the northwest. However, afternoon high temperatures will climb
into the mid to upper 30s again this afternoon, so an all rain or
rain/snow mix possibility does exist before returning to snow
again Monday night. CIGS will remain solidly in IFR/LIFR
categories through the TAF period and VSBYS will be reduced in
heavier snow or when wind combines with snow.




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