491
FXUS63 KABR 180941
AFDABR

Area Forecast Discussion
National Weather Service Aberdeen SD
441 AM CDT Wed Sep 18 2024

.KEY MESSAGES...

- A Slight Risk(level 2 of 5) has been posted for far northeast
  South Dakota and west central Minnesota today into tonight. The
  main threats that will accompany the strongest storms will be
  damaging winds and large hail with a smaller threat for an
  isolated tornado.

- Very warm temperatures, gusty winds and a much drier air mass
  combine to produce critical fire weather conditions across central
  South Dakota this afternoon. A Red Flag Warning has been posted
  for areas along and west of the Missouri River.

- Above normal temperatures will continue through Friday with more
  seasonal temperatures for the weekend and next week.

- Showers and storms for the weekend (20-40% chance for moisture).

&&

.SHORT TERM /TODAY THROUGH THURSDAY AFTERNOON/...
Issued at 439 AM CDT Wed Sep 18 2024

A vigorous area of low pressure at the sfc and aloft centered just
west of our region will continue to deliver unsettled weather in two
fold today across our forecast area. Severe weather potential will
exist in our east while critical fire weather conditions will
develop this afternoon across our west. These two situations will
comprise the bulk of the forecast challenges in the short range.

Early this morning, currently seeing a broken line of convection
pushing northward across our eastern forecast zones, mainly along and
east of the James Valley. More widespread convection is developing
south of our areas in southeast SD Meanwhile, light to moderate
showers continue to stream north across parts of central South
Dakota. Anticipate this will remain the pattern going through the
remainder of the pre-dawn hours into the mid morning hours. That
well organized low pressure system is progged to shift north-
northeast across eastern MT and western ND today. This continues to
put our forecast area in the warm sector. Sfc dew point temperatures
in the mid to upper 60s across our eastern zones will be in place.
As daytime readings warm through the 70s into the 80s during the
afternoon, a narrow ribbon of instability develops across our east.
MLCAPE values of 1000-2000 J/kg, 0-6 km deep layer shear of 30-40
kts and steep low level lapse rates will be in place across these
areas. As a sfc trough or dry-line shifts east toward this area, we
should see robust convection develop along the instability axis. The
strongest storms will be capable of producing damaging winds, large
hail and an isolated tornado. SPC has highlighted our far eastern
zones with a Slight Risk(level 2 of 5) for severe weather with an
encompassing Marginal Risk(level 1 of 5) west of the basically
between the James River and I-29. Main time frame of concern for our
area looks to be from mid afternoon through mid evening based off of
CAM solutions.

The other concern today will be on critical fire weather conditions
developing across our western zones. The set up will be very
favorable for a much drier air mass to advect into central South
Dakota this afternoon. The showers currently over that area should
be long gone by this afternoon. Southerly winds will initially turn
gusty by mid morning and then further increase and turn
southwesterly during the afternoon. Gusts are anticipated to top out
between 35-45 mph. Bufkit soundings across the area do indicate
favorable conditions for much stronger winds and dry air aloft will
mix down efficiently across areas along and west of the Missouri
River. Warming temperatures approaching the mid 80s to near 90
degrees will drive relative humidity values down into the 15-25
percent range. With the status of fuels at a critical level for most
of our West River zones, have decided to issue a Red Flag Warning
for those zones and for Hughes County as well.

&&

.LONG TERM /THURSDAY EVENING THROUGH TUESDAY/...
Issued at 439 AM CDT Wed Sep 18 2024

Will start the extended with a trough over the Dakotas (an extension
of an upper low over Canada) and a cut off low over California.
Zonal flow aloft for Friday, with a slight trend from a weak trough
to a weak ridge during the day should support dry conditions with
overnight 850mb cold advection shifting towards warm advection by
the afternoon. This results in a `brief` warmup Friday. A shortwave
rounding the base of the upper low in Canada, with an associated
surface cold front, will cause temperatures to drop for Saturday.
High pressure that follows will also deflect precipitation farther
south in comparison to previous model runs, as the 4-Corners cut off
loops back up and re-integrates into the mean flow, and supports a
Colorado low type system. Still a lot of uncertainty with respect to
the track/timing of this system, though the EC/GFS deterministic
members are fairly similar with the Canadian the outlier. Clusters
from 12Z are likewise indicating poor confidence overall with little
tendency for the ensembles to follow their deterministic member. 12Z
and 18Z GEFS QPF plumes mainly point to a few outliers that bring
significant moisture this far north, whereas farther south (HON
particularly) shows a more even distribution in outcomes, which I
would interpret as that the NBM will probably trend drier over the
next few model runs as the system approaches, barring the system
coming out of the Rockies farther north than is currently progged.
Will stick with NBM POPs for now, which are still only in the 20-40%
range with a noted drop in percentages up in north central South
Dakota. Duration is also notably longer in the GFS and 12Z EC vs the
Canadian and most recent EC lowering POPs confidence as well. Not
much confidence in temperatures thereafter either with the NBM
running about an 8C to 10C in the 25th/75th percentiles for
highs/lows next week.

&&

.AVIATION /06Z TAFS THROUGH 06Z WEDNESDAY/...
Issued at 1240 AM CDT Wed Sep 18 2024

Terminals KABR,KATY,KPIR,KMBG

VFR conditions are forecast through the TAF period. Still some low-
level wind shear to deal with tonight at KABR/KATY and have included
mention of this in the TAFs. Will also be watching scattered showers
and thunderstorms moving across central SD to start the period,
possibly affecting KPIR/KMBG. This activity will move east through
the night and eventually could affect KABR/KATY. Breezy/gusty
southerly winds will continue through the period.

&&

.ABR WATCHES/WARNINGS/ADVISORIES...
SD...Red Flag Warning from 1 PM CDT /noon MDT/ this afternoon to 9 PM
     CDT /8 PM MDT/ this evening for SDZ003-015-033-035-045-048.

MN...None.
&&

$$

SHORT TERM...Vipond
LONG TERM...Connelly
AVIATION...TMT/Vipond