-- Discussion containing changed information from previous version are highlighted. --
960
FXUS63 KABR 231134
AFDABR

Area Forecast Discussion
National Weather Service Aberdeen SD
634 AM CDT Sun Jun 23 2024

.KEY MESSAGES...

- Dry and mild today.

- Increasing heat and humidity for Monday with temperatures in the
90s and dewpoints approaching 70. Heat index values could top out
around 100 degrees in the afternoon mainly across the James valley.

- A few showers and storms will be possible late Monday (marginal
risk or 1 out of 5), otherwise expect dry weather until later in the
work week when a more organized storm system moves into the Northern
Plains.

&&

.SHORT TERM /TODAY THROUGH MONDAY AFTERNOON/...
Issued at 400 AM CDT Sun Jun 23 2024

A couple of small areas of fog evident on satellite, and a quick
look outside shows quite a bit of shallow fog, a consequence of the
moisture from the previous day. For today, we start seeing 700mb
temperatures on the increase, though low level flow is southeasterly
as the gradient tightens across the state (about 10mb east to west)
and 850mb temperatures don`t show much of an advection term.
However, tonight into the first half of the day Monday we see a
rather significant increase, and that matches a peak in 700mb
temperatures of around +16C. That said, a weak low/front crosses
South Dakota through the course of the afternoon, shifting winds to
northwest. This will aid in mixing and allow for highs to jump, but
may similarly shunt the highest humidity to the south. NBM dewpoints
peak at 3pm and then drop (down to the low 60s by the following
morning)...thus really only looking at a 1 day `event` where heat
index values top out around 100F. Fairly confident in dewpoints with
a 3-4 degree range between the 25th and 75th percentiles for
Aberdeen, with a similar range for Huron. The big question is with
highs with Aberdeen/Huron 25th-75th 93-100 degrees and 92-98 degrees
respectively and means of 94. That gets us heat index values
around 100 for a few hours...so with that will go with a heat
advisory for south of Aberdeen where models have the higher
likelihood of exceeding 100 degree heat index values for more than
a few spots and for multiple hours. Back towards Pierre, less
confident, as we see the 25th-75th range in dewpoint start to drop
after 10am, a consequence of the expected weak frontal passage,
so will leave Sully/Hughes/Lyman out for now.

So the next topic is thunderstorm/severe weather potential. Warm
advection elevated convection should be mainly across North Dakota
or maybe down into the Leola hills area, but there is a deep, dry
hot airmass below any elevated storms so thinking is this should end
up being a non-issue. There is limited evidence from CAMS that
convection could develop along the front as it moves into the far
eastern CWA. NBM POPs in this respect, is only about 20% which is
apt for the environment. There is a high amount of CAPE (+4000 J/KG)
and mainly westerly flow, but the warm mid-levels above cloud layer
evident in BUFKIT soundings suggest it will be difficult for
convection to maintain itself. This is however, only though 00Z (see
long term)

&&

.LONG TERM /MONDAY EVENING THROUGH SATURDAY/...
Issued at 400 AM CDT Sun Jun 23 2024

A fairly progressive upper flow pattern will dominate most of this
period. We start off Monday night into Tuesday morning with quasi-
zonal flow across the Dakotas as a mid level wave shifts southeast
out of south central Canada into the western Great Lakes. Mid level
ridging builds back into the region Wednesday into Thursday in
response to an upper trough moving into the PacNW. That will be the
system that guidance progs to track across the northern tier of the
CONUS and into our region toward the end of the week.

Monday night into early Tuesday morning, a trailing sfc cold front
departing our area to the south and east combined with perhaps some
shortwave energy will allow for a few showers and storms to persist.
That activity should be clearing out of the forecast area during the
morning hours. Drier conditions are expected the remainder of the
day through at least Wednesday night as sfc high pressure builds
into the region. That high will drift east of our area on Thursday
setting up return flow as the aforementioned upper trough shifts out
of the PacNW into the Northern Rockies/High Plains. Lee side
troughing induces as a result and we see yet another sfc low
pressure system develop west of our region. That system is progged
to track into the Dakotas on Thursday into Friday and provide us
with a 30-60 percent chance for showers and thunderstorms. Rainfall
looks to be highly variable, as is the case with any convection.
Current NBM progs indicate the probabilities of seeing a quarter of
an inch or more in a 72-hour period ending early Saturday morning
range from around 30-60 percent across the entire forecast area.
Temperatures through the period will start off well above normal
with highs in the 80s to around 90 degrees on Tuesday before cooling
off closer to late June normals in the upper 70s to mid 80s the
remainder of the week.

&&

.AVIATION /12Z TAFS THROUGH 12Z MONDAY/...
-- Changed Discussion --
Issued at 633 AM CDT Sun Jun 23 2024

Terminals KABR,KATY,KPIR,KMBG

VFR conditions for all terminals once the shallow fog in KATY
mixes out.
-- End Changed Discussion --

&&

.ABR WATCHES/WARNINGS/ADVISORIES...
SD...Heat Advisory from 1 PM to 7 PM CDT Monday for SDZ017-018-036-
     037-051.

MN...None.
&&

$$

SHORT TERM...Connelly
LONG TERM...Vipond
AVIATION...Connelly