919
FXUS63 KFSD 300342
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1042 PM CDT Sun Sep 29 2024

.KEY MESSAGES...

- Hot and dry conditions continue through Monday, with September
  ending as one of the driest and warmest months on record for
  several locations in the Tri-State area.

- Critical fire weather conditions for Monday for areas west of
  the James River. Elevated fire weather conditions for areas to
  the east. Gusty northwest winds to 40 mph possible at times
  through the day, with relative humidity values falling into
  the teens.

- A brief cool down for Tuesday before warming again Wednesday.
  Temperatures will wobble a bit between warmer and cooler for
  the rest of the week.

- Precipitation risks continue to remain minimal through next
  week. With long range projections suggesting below normal
  precipitation into the second week of October.

&&

.DISCUSSION...
Issued at 245 PM CDT Sun Sep 29 2024

CURRENT CONDITIONS: Another warm and sunny day with high
temperatures 15-20 degrees warmer than normal for this time of year.
Once again, there are several sites that are in contention to tying
record highs for the 29th of September. We`re beginning to see the
winds in central South Dakota responding to the tightening SPG
mentioned in the previous discussion. Breezy winds will progress
eastward during the overnight into Monday morning, keeping things
well mixed and lows warmer than they would normally be, in the 50s
east of I-29 and 60s to the west.

MONDAY: The big story for Monday will be the fire weather concerns.
Please see the Fire Weather Discussion for more details on this.
We`ve been talking for a couple days now about the strong cold front
that is expected to move through the area. Model guidance continues
to remain in strong agreement in both track and speed of the frontal
passage. It should be passing through central South Dakota around
mid-morning, though eastern South Dakota and Nebraska around mid-
afternoon, and through western Minnesota and Iowa by mid-evening.
Behind the front winds will become northwesterly around 20-25 mph
with gusts 30-35 mph. Areas west of a line from Huron to Wagner
could see gusts approaching 40 mph. This same area will likely see
their high temperatures peak late in the morning, in the mid 70s.
Along I-29 and east, highs will peak in the mid-afternoon in the low
to mid 80s. Temperatures are expected to fall quickly behind the
front as well as the dew points. Leading to very dry and cool
conditions. Overnight lows are expected to be in the 40s.

TUESDAY-WEDNESDAY: Tuesday will finally feel like fall! Skies will
be mostly sunny and highs will only climb into the 60s, just
slightly cooler than average for this time of year. Very dry
conditions continue as minimum afternoon relative humidity falls to
less than 25% for most of the region. Our fall like weather will be
short lived as high pressure builds in at the surface, and flow
aloft begins to flatten out. As surface high pressure moves to the
east Wednesday, winds will become southerly to southwesterly. This
regime of zonal flow aloft and south-southwesterly winds at the
surface tends to be warm and dry. And we can see that reflected in
the highs for Wednesday afternoon in the upper 70s to mid 80s with
minimum relative humidity remaining less than 25%.

THURSDAY AND BEYOND: This regime is also known to bring through fast
moving, dry fronts. And there is good model agreement that this will
be the case as a weak cold front moves through, dropping highs a bit
into the upper 60s north of I-90, and mid 70s to the south. Thursday
another weak cold front pushes the cooler temperatures further south
with most areas only reaching the upper 60s to low 70s. Saturday
another surface high builds in, turning winds southerly and
bringing WAA to the region, and resulting in another warm day
with highs in the mid 70s to 80s. This pattern repeats Sunday
and into the first half of next week.

Throughout this forecast period, concerns for fire conditions will
increase as fields and ditches continue to dry. There is currently
no indications of wetting rain through mid next week. Help your
local fire and rescue out by avoiding sources of sparks! Don`t
throw lit cigarettes out of your vehicle, ensure any chains are
secured and don`t drag, avoid hot exhausts on dried vegetation,
and report any fires immediately!

&&

.AVIATION /06Z TAFS THROUGH 06Z TUESDAY/...
Issued at 1037 PM CDT Sun Sep 29 2024

VFR conditions through the period, with high clouds focused
along a front passing through Monday. Biggest concern remains
strong and shifting winds through the period - including LLWS
overnight for areas along and west of I-29 where the LLJ
strengthens. Expect south to southeasterly winds to shift to
northwesterly through Monday evening as aforementioned front
moves from west to east over the area. Area of strongest LLWS
will be along and west of the James River, with more marginal
conditions later in the overnight for locations near I-29.
Sustained winds of 10 to 20 knots expected into Monday evening,
with gusts 25 to 35 knots. Strongest winds are expected along
and west of the James River from the late morning through
afternoon. Winds decrease after sunset Monday.

&&

.FIRE WEATHER...
Issued at 245 PM CDT Sun Sep 29 2024

SUNDAY: Mixing heights west of a line from Huron to Wagner are
topping 4000 ft AGL, tapping into stronger winds aloft and mixing
down gusts 20-25 mph with a few 30 mph gusts possible this
afternoon. Minimum relative humidity values west of a line from
Huron to Yankton will drop into the 17-24% range for a few hours
this afternoon. As with the previous discussion, the main threat for
fire remains just to the west of our area of concern, over central
South Dakota. Confidence that winds will be strong enough to need a
fire headline for this afternoon is low, and so have opted out at
this time.

MONDAY: Mixing heights of 5000 ft AGL spread east Monday afternoon.
Winds aloft and at the surface will shift from southerly to
northwesterly as a strong cold front passes through the area mid-
day. Behind the front, winds are expected to be strong, with the
strongest winds west of the James River. Here winds will be
sustained at 20-30 mph, with gusts in the 35-40 mph range. With
minimum relative humidity falling to less than 20%, have issued a
Red Flag Warning for this area. Areas east of here, will also
experience stronger winds and gusts, but confidence is lower that
the winds will meet criteria. However, minimum relative humidity
will fall to less than 25%, and so have issued a Fire Weather Watch
for areas east of the James River.

The GFDI is expected to continue to increase as the lack of
precipitation and warm, breezy days take their toll on drying
vegetation. Percent green is also expected to continue to trend
downward, as the agricultural growing season ends. While the
highest risk for fire currently reside mostly over central South
Dakota, the high fire danger area is expected to move east
through the upcoming week.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...Fire Weather Watch from Monday morning through Monday evening
     for SDZ039-040-054>056-061-062-066-067-070-071.
     Red Flag Warning from 11 AM to 8 PM CDT Monday for SDZ038-050-
     052-053-057>060-063>065-068-069.
MN...Fire Weather Watch from Monday morning through Monday evening
     for MNZ071-072-080-081-089-090-097-098.
IA...Fire Weather Watch from Monday morning through Monday evening
     for IAZ001-002-012-013-020-021-031.
NE...Fire Weather Watch from Monday morning through Monday evening
     for NEZ013-014.

&&

$$

DISCUSSION...AJP
AVIATION...SG
FIRE WEATHER...AJP