318
FXUS63 KABR 200819
AFDABR

Area Forecast Discussion
National Weather Service Aberdeen SD
319 AM CDT Mon May 20 2024

.KEY MESSAGES...

- Another round of rain showers and weak thunderstorms are possible
  mid morning through this evening (20-50%).

- A strong system will spread a swath of precipitation (40-100%)
  across the forecast area Tuesday into Wednesday. Total rainfall
  amounts will range from a few hundredths of an inch across north
  central SD up to 1 to 2 inches over far northeastern SD into west
  central MN.

- Another shot at moisture during the Thursday - Friday timeframe.

- Generally at or below normal temperatures are expected for the
  next several days.

&&

.SHORT TERM /TODAY THROUGH TUESDAY AFTERNOON/...
Issued at 319 AM CDT Mon May 20 2024

As of 3AM skies are partly cloudy with some low stratus hanging over
parts of central to south central SD with temps in the 50s across
the CWA. The low pressure system that brought showers and
thunderstorms yesterday continues to push east, with the center of
the low forecasted to be along the SD/MN border by 12Z, with the
cold front trailing southwest. The upper level longwave trough
continues to deepen over the western CONUS, becoming positive tilted
through the day, leaving the Northern Plains on the PVA side of it
with southwest flow between 40-50kts. Weak embedded shortwave energy
from this will move into the area this afternoon/evening as a
surface trough sets up over central and western SD this morning into
the afternoon. Through the day as well a Colorado surface low will
be forming. With this shortwave energy, CAMs indicate rain showers
will move in from the southwest, over south central SD, mid morning
or so and spread northeastward over the CWA through the day. A few
thunderstorms possible this afternoon, mainly for our southern CWA,
but no severe weather is expected as instability is very low north
of this. NBM shows this trend well with pops 20-50% through this
evening.

Our attention then turns to Tuesday which will be quite wet for some
areas, as the ensembles seem consistent and agree on the longwave
trough swinging more east with another embedded shortwave moving
southwest to northeast, ahead of main trough, over the
Central/Northern Plains. The 850mb-surface Colorado low is
forecasted to be over ~NE/KS area by 12Z Tuesday. The low will track
northeast into MN by Tuesday evening, deepening along the way. Areas
east of the Mo River will be on the northern then northwest side of
the low with the deformation zone (Trowel area) east of the James
River into MN where moderate to sometimes heavy rain is possible.
This trowel area will shift northeast Tuesday evening, with the
extreme eastern CWA on the northwest side of the low. Latest Cams
show the precip moving in late tonight/early Tuesday from the
south/southwest to northeast over the CWA. NBM handles this pretty
well with 30-90% pops, lowest northwest of the Mo River, between 06-
12Z Tuesday. Between 12Z-00Z Wed, pops range from 50-97%, highest
from south central to northeastern SD/western MN.

NAEFS` PWAT values look to be 90% above climo over our extreme
southeastern CWA with values ranging from 1-1.25" in this area
(which is in the highest 90 percentile and above per sounding
climo). EC EFI QPF is quite impressive with values of 0.7-0.9 from
south/southeastern SD into northeastern SD/western MN for Tuesday
with a shift of tails ranging from 1-2, highest east of the James
River. So this helps increase confidence on excessive rain possible
for this area. Due to this, the WPC has put parts of northeastern SD
through southeastern SD in a marginal risk (at least 5%) for
excessive rainfall. There is sharp cutoff in rainfall amounts west
of here and with the latest WPC forecast shows the higher QPF
shifting more east and southeast than previous run. However, GEFS
Plumes still keeps QPF between 1-2" over our extreme eastern CWA.
With this, probability of 24hr QPF>0.50" ending at 00Z Wed is 50-
90%, highest over extreme northeastern SD through southeastern
SD/western MN. Areas northwest of the Mo River have 20% or less
chance. Prob of QPF>1" is 65 to 80% from Sisseton southwest through
Huron and east of here. Additional QPF possible beyond the short
term into Wed. Any wobble in the low will affect rainfall totals and
if the low pushes further west/northwest or vice versa with impact
QPF.

Highs will be cool today with winds out of the north ranging from
the mid 60s to the lower 70s and lows in the mid 40s to the lower to
mid 50s. Even Cooler temps for Tuesday ranging in the mid 50s to the
mid 60s.

&&

.LONG TERM /TUESDAY EVENING THROUGH SUNDAY/...
Issued at 319 AM CDT Mon May 20 2024

Colorado low will be in the departing phase by the time the extended
period opens. 1/2km winds on the backside gradient also start out at
around 40-45kts, though that really tight gradient extends to about
the James valley before weakening, and this is also really only
during the 00-06Z portion of Wednesday. Thereafter, we have a weak
pressure pattern and a weak wave embedded with southwest flow aloft.
Not much moisture with this mid level wave, just additional cloud
cover through the day.

Winds shift to southeast by Wednesday night in response to the next
wave moving into the Rockies with a lee low in central Wyoming. This
surface low lifts into western South Dakota/southeast North Dakota
Thursday evening, however the track/timing thereafter is still up
for debate with each of the 3 main deterministic models taking a
different route.  There will be a surge of mild air out ahead of
this feature, with temperatures Thursday up close to average. With
the pattern dominated by a trough across the northwest north central
CONUS...this will be about the only day, with the rest of the
timeframe below normal for the majority of the extended.

&&

.AVIATION /06Z TAFS THROUGH 06Z MONDAY/...
Issued at 1221 AM CDT Mon May 20 2024

Terminals KABR,KATY,KPIR,KMBG

VFR conditions expected through the TAF period at all sites,
besides KATY where MVFR cigs are forecasted between 10-18Z today.
For KMBG/KPIR winds will be out of the northwest/north with gusts
between 15-20kts this afternoon. Rain showers possible again this
afternoon over south central SD and spreading northeastward
through the evening with chances increasing overnight.


&&

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

$$

SHORT TERM...MMM
LONG TERM...Connelly
AVIATION...MMM