511
FXUS63 KABR 011903
AFDABR

Area Forecast Discussion
National Weather Service Aberdeen SD
203 PM CDT Wed May 1 2024

.KEY MESSAGES...

- Rain showers over mainly south central SD will expand across the rest
  of central to northeastern SD this evening, before diminishing west
  to east Thursday. Rain totals through Thursday will range from a
  0.05 to near 0.5"(highest over north central SD).

- Active pattern continues in the extended period, with at least two
  systems affecting the region. The first (Friday afternoon and
  night) will quickly move through the southeast half of SD and bring
  generally light rainfall (0.1" or less). The next system will be
  larger and prolonged, lasting from Sunday night and potentially into
  Tuesday. Rainfall amounts may exceed 0.5" during that event (50%
  chance) and there may be a few thunderstorms on Monday (20% chance).

- Near to below normal temperatures Friday and Saturday, warming to
  above normal Sunday and Monday.

&&

.SHORT TERM /THIS EVENING THROUGH THURSDAY NIGHT/...
Issued at 203 PM CDT Wed May 1 2024

The weather map early this afternoon shows the surface ridge that
had dominated our area this morning shifting into western MN. There
is a trough of low pressure extending from the main surface low over
southeastern CO to another over western SD. A third low was moving
in from Canada/northern MT. Winds out of the south are beginning to
take hold across areas east of the MO River. Surface winds will
shift out of the southeast tonight as the CO low moves to central
KS/OK by 12Z Thursday and northern lows join forces over western ND
Thursday morning into the early afternoon hours.

Moisture pushing north into the area, and the assistance by embedded
waves in the southwesterly flow at 500mb, will help bring a return
of showers to mainly central SD. This moisture return is a bit
faster than previously expected, with the main focus being across
central SD this afternoon. There are 2 main areas of precipitation,
over north central SD and our southeastern Counties, with not much
in between (on the order of 0.02" through midnight). The trend is
for the northern system to become more dominant across our area,
with 0.l2-0.5" of rain over Dewey, Corson, and Campbell Counties
(highest over western Corson County).

Cooler air will remain in place, with 850mb temperatures staying in
the single digits above 0C through at least 12Z Friday. A few
readings just below 0C will be possible over north central SD right
around 12Z Friday. Highs will remain in the mid 50s to low 60s, with
lows mainly in the upper 30s to low 40s.

Rain shower chances will continue to diminish Thursday afternoon
into Thursday night as a cold front drags across the forecast area,
extending from the surface low over southern Manitoba/far
northeastern ND late Thursday night.

&&

.LONG TERM /FRIDAY THROUGH WEDNESDAY/...
Issued at 203 PM CDT Wed May 1 2024

The start of the long term period (Friday) will continue the trend
over the last couple of days, with a brief period of dry weather
before another period of showers (Friday night). A surface low
centered along the US/Canadian border of ND/MN at the start of the
period will gradually lift northeast. Meanwhile, there will be upper
jet support across southeast half of SD on Friday night, as a jet
streak rounds the base of the upper ridge axis along the MT/ND/SD/WY
border. This will also be supported by a nice area of mid-level warm
air advection and q-vector convergence. All of these features come
together over southeast SD and having rainfall chances of 30-50% to
the southeast of Pierre/Aberdeen seems reasonable at this time. In
addition, instability is extremely limited (MUCAPE values <100
J/kg), so we don`t expect any thunder at this time. With the best
forcing to the southeast of our CWA, precipitation amounts look to
be light where rain occurs and between a Trace and maybe 0.10" (only
30% probability of 0.1" from Watertown to Chamberlain).

Behind the Friday night precipitation, the upper trough departs to
the east on Saturday and high pressure builds over the area. That
will quickly lead to the clouds departing and start a rain free
weekend. While temps will warm up slightly on Saturday (60s), we`ll
see a jump up on Sunday (into the 70s), as the upper ridge axis
moves over the area and southeasterly winds increase ahead of the
next developing surface low in the lee of the northern Rockies. Will
need to keep an eye on wind gusts in central SD on Sunday afternoon,
as they could be nearing advisory levels.

The previously mentioned developing surface low is tied to a deep
upper trough moving into the western CONUS on Saturday night.
Ensemble clusters still showing a decent amount of variability on
how they`re handling this upper trough as it moves into the northern
Plains. This leads to increased uncertainty in the exact details, as
it influences both the intensity and how long the upper wave lingers
into early next week. Despite that, the main two takeaways are that
measurable (0.01") rain chances remain high during this period (60-
80% values) and will continue to see gusty winds into Mon/Tues (NBM
probabilities of gusts exceeding 34kts/39mph are 50-95% for both
Mon/Tues). As for rainfall amounts, 24 hour probabilities of 0.5" or
more are 35-55% for the Monday and Monday night period. Right now,
any excessive rainfall amounts don`t seem too likely at this point,
with 48hr rainfall probabilities of 1" of rain staying below 25%.
That`s likely driven by the limited convection potential, even with
the wrapped up low (somewhere in the 980-995mb range), as joint
probabilities of sfc CAPE > 500 J/kg and 0-6km Shear > 30kts are
between 5-30% depending on the cluster. That being said, there is
some MUCAPE (500-1300 J/kg) on the leading phase of low/precip on
Monday afternoon. That matches up with the elevated NBM CWASP
values/percentiles at that time, although values are around rough
Marginal risk values (50-64). Finally, this stronger and wrapped up
low is what`s leading to the increased winds for early next week,
although wind speed/direction for Tuesday depend on where the
surface low is located.

&&

.AVIATION /18Z TAFS THROUGH 18Z THURSDAY/...
Issued at 1226 PM CDT Wed May 1 2024

Terminals KABR,KATY,KPIR,KMBG

VFR conditions will remain until after 06Z, when incoming rain
helps bring ceilings down to MVFR conditions. Expect mainly MVFR
ceilings at all locations by around daybreak Thursday, most likely
at MBG where more steady rain is forecast. Conditions will improve
west (PIR/MBG back to VFR around 18Z) to east (ABR and then ATY
later in the afternoon) on Thursday.


&&

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

$$

SHORT TERM...KF
LONG TERM...SRF
AVIATION...KF