000
FXUS63 KABR 240530 AAC
AFDABR

Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
1230 AM CDT Sat Jul 24 2021

.UPDATE...
Issued at 1226 AM CDT Sat Jul 24 2021

Updated aviation discussion below.

UPDATE Issued at 914 PM CDT Fri Jul 23 2021

Scattered thunderstorms have occurred across both the northern and
southern parts of the CWA this evening, and a Severe Thunderstorm
Watch remains in effect until 2 AM for a good portion of the CWA.
No changes made to winds or temperatures at this time.

&&

.SHORT TERM...(This Evening through Saturday Night)
Issued at 351 PM CDT Fri Jul 23 2021

The main challenges through the period involve severe thunderstorm
potential this afternoon/evening and elevated fire weather danger on
Saturday.

As an upper trough continues to advance east into the Northern
Plains, stronger flow aloft continues to encroach on the forecast
area. As such, deep layer shear has increased, with effective bulk
shear values of 30 to 45 knots. Within the flow are a couple subtle
shortwaves, which increase the likelihood for thunderstorm
initiation/maintenance. At the sfc, there are two main areas of
focus for potential initiation: a sfc trough which extends from
south central to north central/northeastern SD, and a frontal
boundary that extends from central ND towards eastern WY. Convection
may initiate on either late this afternoon and evening, but coverage
remains in question as these forcing mechanisms are fairly weak. Any
storms that do develop have a very moist environment to work with,
especially to the east of the sfc trough (dewpoints in the 70s).
Steepening mid-level lapse rates, inverted-v soundings and large
DCAPE all favor a wind threat, and a cluster/supercell storm mode
makes hail a potential threat as well. There may be pockets of
storms during different times and at different locations given the
set-up, through the evening hours.

By Saturday, the passing front will usher in much drier air on
northwest winds, by about 20 degrees plus dewpoint-wise. Minimum
afternoon RH values will be in the teens to mid 20s percent. Deep
mixing due to the dry airmass in unidirectional flow raises
questions about how strong the wind will get. This will determine
how elevated the grassland fire danger will be. Guidance points
towards the strongest 700-500mb winds being across the north and
northeastern CWA, with gusts perhaps up to 25 mph or better at
times. Temperatures remain above average as well, with highs in the
90s.

.LONG TERM...(Sunday through Friday)
Issued at 351 PM CDT Fri Jul 23 2021

Pattern through the period features northwest zonal flow with riding
upstream initially. Sunday will feature a subtle feature at 500mb,
more or less a speed maximum in the flow with a mid level warm
advection push. Tenuous moisture may be enough to generate mid level
convection but with a dry layer below 10kft and just a few hundred
j/kg elevated/skinny CAPE I really don`t see how any of that works
out to much more than a few sprinkles/hundredths of moisture. The
ridge upstream slowly amplifies through the start of the work week,
becoming the main headline as it features 500mb heights nearing 2
standard deviations above climo and 700mb temperatures around +16C.
Monday/Tuesday/Wednesday looks to be the hottest period, with the
passage of a backdoor front to undercut the warmer air aloft late
Wednesday through the degree/timing of relief it provides is too far
out to qualify as something we can forecast well at this point. Back
to the Monday - Wednesday time period, model dewpoints increase into
the 60s, and lows will stall at around 70, so heat impacts will be a
concern to keep an eye on. The ridge retreats back to the west for
the latter half of the work week and we`re back into a northwest
flow regime with stronger flow aloft. As for moisture chances under
that regime, well the blended guidance does suggest some options but
at these timescales I really don`t feel confident advertising quite
as much moisture as there isn`t much for continuity between
these fast moving, subtle systems.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday Night)
Issued at 1226 AM CDT Sat Jul 24 2021

Terminals KABR,KATY,KPIR,KMBG

Scattered thunderstorms will track across the eastern half of the
area through the early overnight hours, likely exiting the region by
09Z. Periods of IFR/MVFR vsbys will be possible with the storms.
After the storms exit the area, VFR conditions will prevail for the
rest of the overnight period and through the day Saturday.

&&

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

$$

UPDATE...SD
SHORT TERM...Lueck
LONG TERM...Connelly
AVIATION...SD