965
FXUS63 KABR 021738
AFDABR

Area Forecast Discussion
National Weather Service Aberdeen SD
1238 PM CDT Thu May 2 2024

.KEY MESSAGES...

- Light rain showers lingering through the day with some clearing
  from west to east. Clearing will result in destabilization, enough
  to generate scattered weak thunderstorms (30% coverage). Only
  hazard would be lightning and small hail.

- Next shot at moisture comes mid-day Friday. Probability of 1/4"
  moisture is only 20-40% along and south of a line from Pierre to
  Watertown.

- Much larger system looks to affect the region on Monday, with
  widespread moderate rainfall. Threat for severe weather still
  appears low at this time (higher across NE/KS/OK), but will continue
  to monitor trends.

&&

.UPDATE...
Issued at 1239 PM CDT Thu May 2 2024

A slightly slower exit of rain and clouds has been noted.
Otherwise, the forecast looks to be on track. We`ll continue to
watch this afternoon as the area of clearing continues over
central SD for the potential for some cumulus development and a
few thunderstorms.

&&

.SHORT TERM /TODAY THROUGH FRIDAY AFTERNOON/...
Issued at 340 AM CDT Thu May 2 2024

Weak low pressure over North Dakota and a second system to the south
is responsible for shower activity and cloud cover across the state
along with stable easterly low level flow. As we move through the
day, there is only a slow progression of POPs and low clouds
eastwards. BUFKIT profiles and CAMS suggest that once we see
clearing as low level winds become westerly, the atmosphere will
destabilize enough for shower/weak thunderstorm development. NBM
25th/75th percentiles range from 100-600j/kg. BUFKIT profiles depict
skinny CAPE with westerly unidirectional flow and nearly all the
convection falling below 0C. That translates into potential for
thunder and small hail given how cold it is aloft, but otherwise not
a severe weather risk.

Another period of dry weather develops during the overnight hours
before the next southwest flow wave brings moisture back to the CWA
for Friday.  Again, just another round of mid level warm advection
to support these showers, with a cold front already having undercut
this band of moisture as the low develops to the south. Probability
of 1/4" moisture is only 20-40% along and south of a line from
Pierre to Watertown.

&&

.LONG TERM /FRIDAY EVENING THROUGH WEDNESDAY/...
Issued at 340 AM CDT Thu May 2 2024

Period starts off Friday night with yet another shortwave crossing
the Northern Plains, along with a 100 kt upper level jet max shown
on the 00Z EC deterministic run. Models continue to bring the
northern fringe of precipitation from south central SD up though
northeast SD into western MN. It appears north central SD may miss
out entirely on this Friday night wave of precipitation. Models
continue to suggest this will be a fairly light precip event, with
GEFS/GEPS/ENS QPF means all below 0.50in. It`s not until we get into
the higher end model scenarios (90th percentile) where potential QPF
exceeds 0.50in on the Grand Ensemble across the southeast CWA. No
real instability to speak of either, so just looking at a general
light rainfall Friday night, with the highest chances (40-60%)
stretching from the southwest CWA into the southeast CWA.

Models then show surface high pressure building into the region on
Saturday, with clearing skies and light winds. Aloft, upper ridging
begins moving in by Sunday. So, actually looking at a pretty nice
weekend (albeit breezy/windy on Sunday) with highs rising into the
upper 60s to low 70s by Sunday.

Focus then shifts to the potentially larger and stronger low
pressure system moving in on Monday. All four clusters off the
cluster analysis feature an upper trough across the northern Rockies
into the High Plains/Northern Plains Day 5 into Day 6. As expected,
there are some differences noted in the amplitude of the 500mb wave,
but all basically feature a negatively tilted trough moving into the
region. This gives fairly high confidence in precipitation affecting
a somewhat large coverage of the Northern Plains. We start to get
some instability working northward as well during the day Monday,
although GEFS/GEPS/ENS mean CAPE values are all still below 1000
J/KG. As for any severe weather threat with this large system coming
out, joint probabilities for CAPE>500 J/KG, CIN>-25 J/KG, and 0-
500mb bulk shear>30 kts are still only about 5-15% (Grand Ensemble)
across the CWA, with much higher values well south into the Central
Plains. This seems to line up with the recently released Day 5
severe weather outlook, highlighting an area from Nebraska southward
into Kansas/Oklahoma. CIPS analogs for Day 5 (Monday) 24-hr probs
for severe does bring the 10% contour up into southeast SD, but not
into the ABR CWA. Will be watching these trends over the coming days
to see if any of these features nudge northward at all.

&&

.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 1239 PM CDT Thu May 2 2024

Terminals KABR,KATY,KPIR,KMBG

Varied weather conditions are in place to start the forecast as
the surface trough remains from north central to southeastern SD
and slowly exits est. PIR has moved out of the steady clouds
impacting the rest of the TAF locations to the east. Conditions
range from VFR at PIR/MBG to MVFR to borderline IFR conditions at
ABR/ATY. Look for improving conditions west to east through the
daytime hours, with the potential for VCTS at MBG and to a lesser
extent at ABR.

&&

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

$$

UPDATE...KF
SHORT TERM...Connelly
LONG TERM...TMT
AVIATION...KF