620
FXUS63 KABR 081720 AAC
AFDABR

Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
1120 AM CST Fri Nov 8 2024

.KEY MESSAGES...

- Dry conditions are expected tonight and Friday.

- Rain will move in over south central SD late tonight and spread northward
  over the forecast area through Saturday before tapering off
  Saturday night.

- Rainfall amounts are forecasted to range from a few hundredths
  of an inch over northeastern SD into western MN, to one quarter
  of an inch over south central SD.

- Generally temperatures will remain a few degrees above average
  over the next several days.

&&

.UPDATE...
Issued at 1019 AM CST Fri Nov 8 2024

The forecast in on track this morning. No major changes are
planned.

&&

.SHORT TERM /TODAY THROUGH SATURDAY AFTERNOON/...
Issued at 338 AM CST Fri Nov 8 2024

As of 330am, skies were mainly clear with light winds. This is
leading to radiational cooling as temps have tanked in the upper
20s to the upper 30s, lowest over the James River Valley. For
today, HREF along with GEFS/ENS agree on a split flow pattern as a
large cutoff low will center itself over southern Colorado and
New Mexico by 12Z and its surface low over north central Texas.
The northern stream consists of a ridging pattern over the
Northern Plains into the Rockies. At the surface, high pressure
will be dominant keeping the area dry for today into this evening
with light winds. Later on in the evening through tonight, the
high moves out of the area as this cutoff low tracks northeast and
surface low tracks northward, with the center of the upper system
over eastern Colorado/western KS by 12Z Saturday. ENS is just a
tad bit westward with its center of the low than GEFS and HREF
mean at this point in time. This results in the surface low a bit
west, over western KS, per EC and more central KS per GEFS.
Through the rest of Saturday, the surface low will continue its
track northeast with the center of the low forecasted to be over
eastern NE/western IA by 00Z Sunday. ENS is still just slightly
west with the center of the low.

The overall system has seemed to slow down on moisture entering the
CWA since the previous run as a few of the HREF members (HRW-NSSL,
NAM Nest, HRW FV3) are first to show precip moving in over south
central SD close to midnight along with the latest NBM run. Luckily
temps stay above freezing so rain will be the main Ptype. Rain will
then surge northward over the CWA through the day Saturday into
Saturday evening. Grids reflect this indicating at 20-85% chance of
pops from 06-12Z, highest over south central SD. Pops increase to 60-
95% between 12Z-00Z highest again over central to south central SD.
With this setup, the CWA will be positioned north of the occluded
low, with models at 500-700mb indicating we get an enhancement of
warmer air aloft being pushed northward and around the low
(deformation zone), mainly over central to southern SD being on this
northern extent of the deformation zone where we have the highest
pops. With return flow ahead of the low, HREF PWAT values increase
northward and over the CWA to about to 0.7-0.9 inches Saturday
morning, highest over central SD in this zone. Both NAEFS and GEFS
PWAT values (0.75") run about 97.5-99.5% above climo relative to the
10/30 to 11/20 1979-2009 CFSR climo. These values push northward
over ND/north central SD by midday as this enhanced zone of moisture
also tracks northward with the track of the low.

Even though this system looks beastly, it really is not going to be
a big rain producer. QPF through 00Z Sunday per WPC super ensemble
spread mean runs from 0.10" over KATY, 0.11" over KABR, and up to
0.20" at KPIR with equal spreads above and below this mean. The
highest (90 percentile) QPF runs around 0.40" up to around a half
inch over south central SD. HREF ensemble`s mean for QPF is a couple
hundredths over northeastern CWA to 0.20" over south central SD,
which is close to what`s in the grids currently. 90th percentile for
this time period runs 0.25-0.40" over central SD. Latest NBM is a
bit higher than HREF/WPC from about 0.07 up to 0.52", highest over
south central SD with the 75th percentile up to 0.75" over south
central SD. The 90th percentile is about 0.6 to possibly an inch,
highest over Jones County. EC EFI does highlight values of 0.5 to
0.8 for QPF, highest over central SD for Saturday.

&&

.LONG TERM /SATURDAY EVENING THROUGH THURSDAY/...
Issued at 338 AM CST Fri Nov 8 2024

When the period opens Saturday evening at 6 pm CST, an
occluded/stacked low is over Nebraska, headed for southern
Minnesota. Behind the system on Sunday, short-wave ridging sets up
briefly. After a couple of days where low amplitude fluctuations
happen between short-wave ridging and troffing, models depict the
development/movement of a somewhat higher amplitude longwave trof
across the western (Monday) into central (Tuesday night/Wednesday)
portions of the CONUS before a large upper level ridge builds over
the region at the end of the period.

The probability of 0.10in of precipitation Saturday night has just
about vanished, down to less than 15%. The probability of measurable
(0.01in) precipitation during the first half of Saturday night is
still around 20 to 60%, but really drops off after midnight Sunday.
Looking at the sounding output of the NAM and GFS in BUFKIT, there
is a drizzle/fog signal showing up for several hours Saturday night
throughout the region until the upper low begins to shift away from
the area. Might be worth an addition to the forecast in the near
future, if BUFKIT soundings continue to suggest 1-3km deep lower
atmospheric stratus layer with weak lift as mid/high
cloud/saturation disappears. With the mid-week longwave trofpa,
there could be some measurable precipitation to monitor for.
Ensembles output remains unenthused, while some of the deterministic
GSM output this morning suggests the PVA/WAA side of the trof could
generate some light precipitation across far eastern South Dakota
before all the forcing/lift support shifts east of the region.

The low level thermal advection pattern throughout the entire period
could be characterized as rollercoaster-ish. Strong low level WAA is
progged for Sunday, behind the departing upper low. The general
consensus is for 925hpa temps to warm up to ~6 to 8C across the far
eastern forecast zones, while the western two-thirds of zones warm
to ~9 to 13C. So, high temperatures warming into the 60s over
central South Dakota certainly seems reasonable, assuming mid/high
cloudcover doesn`t show up/mess up daytime
heating/insolation/mixing. One of these early week low amplitude
shortwave trofs is progged to push a dry cold fropa through the CWA
Sunday night, making Monday a rather chilly day. Looks like another
quick WAA response in the boundary layer on Tuesday before another
cold fropa Tuesday night/Wednesday brings the brisk back. Low level
WAA is progged for Thursday, though. No snow on the ground, either,
so these quick fluctuations in temperatures/advection are more
believable/do-able. Pointing back to the previous forecaster`s
mention about 25th-75th percentile spread, it`s still there Tuesday
onward. But, within that somewhat higher spread there is still this
"up/down" signal in day to day temperature regime changes based on
the rapid-fire pace of warm/cold frontal passage in the out periods.

&&

.AVIATION /18Z TAFS THROUGH 18Z SATURDAY/...
Issued at 1119 AM CST Fri Nov 8 2024

Terminals KABR,KATY,KPIR,KMBG

VFR conditions will deteriorate on Saturday as light rain moves
in. Cigs will fall to MVFR with occasional vsby reduction to MVFR
in heavier showers.

&&

.ABR WATCHES/WARNINGS/ADVISORIES...
SD...None.
MN...None.
&&

$$

UPDATE...Wise
SHORT TERM...MMM
LONG TERM...Dorn
AVIATION...Wise