003
FXUS63 KABR 122321 AAA
AFDABR

Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
621 PM CDT Fri Jul 12 2024

.KEY MESSAGES...

- On and off chances for showers and thunderstorms (20-40%
  chances) are possible over the next several days as weak
  disturbances move through the region. Strong to severe storms
  are possible, but likely spotty in coverage.

- Over the weekend, high temperatures will be in the 90s,
  potentially reaching the century mark for some areas on
  Saturday. Heat indices will approach or exceed 100 degrees for
  many areas.

- Temperatures will moderate with lower humidity for the first
  half of next week before readings warm back up toward the end
  of the week.

&&

.UPDATE...
Issued at 618 PM CDT Fri Jul 12 2024

Aviation discussion updated below for the 0Z TAFs.

&&

.SHORT TERM /THIS EVENING THROUGH SATURDAY NIGHT/...
Issued at 323 PM CDT Fri Jul 12 2024

Mostly sunny and hot this afternoon across the CWA, especially along
and west of the James River, where we had earlier issued an SPS
(Special Weather Statement) for heat index values in the mid/upper
90s to around 100 degrees. Latest look at obs does show several
locations in the upper 90s heat indices, especially across central
SD. Even hotter air moves into the region on Saturday as 850mb temps
climb into the mid to upper 20s C by 00Z Sunday for many locations.
Actual air temperatures will be well into the 90s for most areas,
but add to that the dewpoints in the upper 60s to low 70s, and we`ll
see heat indices between 100 and 105 degrees for many areas. Have
therefore issued a Heat Advisory for those areas forecast to meet or
exceed 100 degrees heat index, valid from 18Z Sat to 01Z Sun.

Turning to precipitation chances, it appears there will be some
degree of convective development later this afternoon across the
western Dakotas in vicinity of the surface trough. Some of this
activity may spill into the western CWA counties by early evening.
Rather high cloud bases will promote primarily a strong wind threat.
In fact, DCAPE values are over 1500 J/KG across the western CWA
currently. Rather large dewpoint gradient across western SD, with
40s/50s dewpoints over the far western Dakotas, to near 70 once you
reach the Missouri River. So, overall instability increases
drastically from west to east across western into central SD, but as
this is happening, the cap is strengthening as well. CAMs continue
to show widely scattered in nature activity as things head towards
the western CWA. Will maintain generally 20-30% chances into the
evening hours across the western CWA.

On Saturday, thunderstorm chances are a bit murky as we`ll be
dealing with capping issues, along with potential outflow boundaries
from any morning activity that moves southeast across ND and MN.
Plenty of instability will be in place, as well as a surface trough
moving into the CWA during the afternoon. Impulse aloft is rather
subtle, but could be enough to break the cap into the early evening
hours. Areas of strongest surface heating near the surface boundary
probably will see best potential for convection. Once again will
maintain mainly low chances (20-40%) during the afternoon and
nighttime hours.

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
Issued at 323 PM CDT Fri Jul 12 2024

This period begins with persistent high heat and humid conditions on
Sunday into Monday as the mid level high remains essentially planted
across the Four Corners region of the southwest CONUS. Quasi-zonal
flow aloft across the Northern Plains with embedded mid level waves
will continue to periodically traverse across our region lending to
continued advertisement of 15-30% chances for scattered convection
late in the weekend into early next week. After a more clearly
defined system moves through early next week, sfc high pressure
looks to build in Tuesday and persist through the middle of next
week. This should return cooler and drier conditions to the forecast
area. Temps modify again by late in the period as the high drifts
east and southerly flow draws in warmer and more humid conditions
once again.

The main focus for precipitation chances in this period will be
associated with a deeper upper trough that guidance progs to move
out of south central Canada into the western Great Lakes early next
week. This system will aid in sending south and east a sfc low
pressure system and attendant cold front through our area sometime
on Monday. Anticipate this will be our best window for showers and
thunderstorms in this period. There will be some associated risk for
severe weather with this system, especially east and north(eastern
NODAK/northwestern MN) where more favorable ingredients such as
instability/shear will be present. After that system departs by
Tuesday, a drier air mass will take hold. The aforementioned mid
level high is progged to bump up farther north across the Northern
Rockies/Northern High Plains by the latter half of this period. This
will promote northwesterly flow aloft across our region. Ridge
riding weak s/w energy may crest the ridge and shift across our
region toward the end of the period, but with no deep moisture
available, limited chance for precip seem more likely at this time.

Temperature trends through this period will again start off hot and
rather humid. Daytime highs in the 90s will persist on Sunday with
dew point temperatures in the upper 60s to low 70s. This again could
lead to heat indices around 100 degrees during the afternoon. One
caveat of uncertainty in this being realized is if there will be any
leftover convective debris(cloud cover) that could have a play on
daytime temperature readings. With so much uncertainty still in play
in terms of convection and it`s placement/timing, it`s hard to put a
finger on how hot conditions could get for Sunday and potential need
for additional heat advisory headlines. For now, we`ll stick with
the going trend of high heat and humidity with the thoughts of re-
evaluating the situation as that time draws closer. Temperatures
return closer to normal, if not slightly below normal for the middle
of the week before we warm back up by late week. Ensemble data
suggests increasing probabilities for temperatures reaching or
exceeding 90 degrees once again for central SD by Thu/Fri of next
week.

&&

.AVIATION /00Z TAFS THROUGH 00Z SATURDAY/...
Issued at 618 PM CDT Fri Jul 12 2024

Terminals KABR,KATY,KPIR,KMBG

Prevailing VFR conditions can be expected for all terminals
through the valid TAF period. However, a few stray showers and
thunderstorms may move into central and north central SD this
evening, possibly impacting KMBG and KPIR. Low forecast confidence
with pcpn will prevent the mention of pcpn in TAFS at this time.

&&

.ABR WATCHES/WARNINGS/ADVISORIES...
SD...Heat Advisory from 1 PM CDT /noon MDT/ to 8 PM CDT /7 PM MDT/
     Saturday for SDZ006>008-010-011-017>023-033>037-045-048-051.

MN...Heat Advisory from 1 PM to 8 PM CDT Saturday for MNZ039-046.

&&

$$

UPDATE...SD
SHORT TERM...TMT
LONG TERM...Vipond
AVIATION...SD