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000
FXUS63 KFSD 151134
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
634 AM CDT Mon Apr 15 2024

.KEY MESSAGES...

- Highs in the 70s and 80s for today. Warm temperatures in
  combination with dry fuels, low relative humidity values, and
  gusty southeast winds have prompted a Red Flag Warning for
  most of the region this afternoon.

- High confidence in rainfall tonight and continuing into
  Wednesday morning. Widespread rainfall totals of around a half
  an inch are expected. Areas of northwestern Iowa and
  southwestern Minnesota have a high (>80%) chance of seeing an
  inch or more. Isolated pockets of over 2 inches are also
  possible.

- Isolated to scattered severe thunderstorms are possible
  tonight and Tuesday morning. The greatest threat with the
  strongest storms will be large hail, isolated damaging wind
  gusts. While the threat for tornadoes is low, they cannot be
  ruled out.

- Cooler temperatures and breezy conditions are expected
  Wednesday through Friday.

&&

.DISCUSSION...
Issued at 352 AM CDT Mon Apr 15 2024

TODAY (Monday): Water vapor imagery shows our ridge for today as
well as a low pressure system spinning over the southwest region of
the U.S.. This ridge along with broad WAA and a 40-50 kt LLJ will
result in warm and breezy conditions this afternoon. Winds will be
out of the southeast, and given the good mixing of the past few
days, expect this trend to continue. This will result in gusts in
the 35-40mph range with a few 45 mph gusts mixed in. The strongest
gusts will be along and west of I-29. East of I-29 winds will be
slightly tamer, in the 25-30 mph range. Some areas of central South
Dakota may have gusts approaching wind advisory criteria, and so
this will need to be monitored as the afternoon unfolds.
Temperatures will range from the 70s to the low 80s with warmer
temperatures as you move south. Very dry air will be in place over
the region this afternoon, resulting in falling dew points and
relative humidity (RH) dipping into the teen to low 20 percent
range. Latest trend in the short term guidance indicates a faster
decline in RH as well as lower minimums. As such, have decided to
upgrade our Fire Weather Watch to a Red Flag Warning. More on this
in the Fire Weather Discussion below.

TONIGHT: The CAMS continue to show the slowing trend mentioned in
the previous discussion. Current runs indicate convective initiation
beginning in our southern counties along the Missouri River around 8-
9pm. Bulk shear in the 0-6km layer has held steady in this set of
model runs at around 40 kts. But soundings continue to indicate we
will be capped in the low levels. 700-500 mb lapse rates are
sufficiently steep, in the 7.5-8 deg C range. However, the best
instability remains to the south. At the surface, SBCIN is in the
100+ J/kg range, which along with the strong cap will likely inhibit
surface based convection. However, there will be around 500 J/kg of
MUCAPE, which supports that if convection does initialize, it will
likely be elevated. The greatest threat with this environmental set
up will be large hail up to around 1.5 inches, with a secondary
threat of damaging wind gusts in excess of 50 mph, and an isolated
tornado or two.

TUESDAY: Strong winds continue into the overnight hours as the SPG
tightens ahead of the approaching surface low out of northern
Colorado. Stronger winds will move east with the low into Iowa and
Minnesota by late morning. Winds are expected to decrease by Tuesday
afternoon as the low overtakes the area.

Mid Tuesday morning, CAMS guidance indicates another line of
thunderstorms developing along the warm front over northwestern Iowa
and southwestern Minnesota. Mid-level lapse rates are expected to
weaken, but remain robust enough to again support the formation of
large hail and damaging winds. This stronger line of storms is
expected to quickly move out of the area to the northeast.

CAA will follow as the low moves to the northeast, and temper highs
for Tuesday into the 50s to low 60s. Short term guidance has come
into good agreement on track, but there is still the possibility
that it could wobble north or south a bit more in the coming 24
hours. Currently, guidance suggests a lull in rain Tuesday
afternoon as the dry slot moves over southeastern South Dakota,
northwestern Iowa, and into southwestern Minnesota. On the
backside in the deformation zone, rain will redevelop and
continue through late Tuesday, into early Wednesday morning
before tapering off. Plentiful QPF is present within this
system. As a result, most areas will see at least a half inch of
rain. Ensemble guidance shows a 70-90% probability for areas
east of I-29 to see 1 inch or more. With this in mind, isolated
pockets of 2-3 inches are possible, especially over northwestern
Iowa.

WEDNESDAY AND BEYOND: Mostly zonal flow aloft and northerly winds at
the surface will keep temperatures a little closer to normal for
this time of year, in the 50s with lows in the 20s to 30s. Another
round of showers looks possible for Thursday, however model guidance
is in low agreement at this time, and therefore confidence is
low.

&&

.AVIATION /12Z TAFS THROUGH 12Z TUESDAY/...
Issued at 634 AM CDT Mon Apr 15 2024

Today will begin with VFR ceilings prevailing. Winds will increase
out of the southeast to 15-20 kts sustained with gusts 25-35 kts.
Occasional gusts of 40 kts are not out of the question as a
strong low pressure system approaches out of Colorado/Nebraska
late this afternoon. Clouds will move in followed by widespread
showers and thunderstorms. Some of these thunderstorms could be
strong to severe, producing up to 1.5 inch hail, and damaging
wind gusts. Though the chance is low, cannot rule out a brief
tornado or two as well. As the storms move in, expect ceilings
to decrease to MVFR with periods of IFR under stronger
thunderstorms. A few hours of LLWS is possible at all sites
between 16.03Z and 16.07Z. Showers and thunderstorms continue
past this TAF period into late Tuesday evening before tapering
off early Wednesday morning.

&&

.FIRE WEATHER...
Issued at 433 AM CDT Mon Apr 15 2024

Very High fire danger is expected across the region today. Winds
will be out of the southeast sustained at 20-25 mph with gusts 35-40
mph. A few 45 mph gusts are not out of the question. Highs today
will be in the upper 70s to low 80s, with relative humidity dipping
into the upper teens to low 20 percent. Considering the cured fuels
and lack of green up at this point in time, have decided to upgrade
the Fire Weather Watch to a Red Flag Warning for portions of
southeastern South Dakota, northeastern Nebraska, northwestern Iowa,
and southwestern Minnesota. Please, use caution with any activity
that may cause sparks, as fires will spread quickly. Report any
fires that do start immediately.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...Red Flag Warning from 11 AM this morning to 8 PM CDT this
     evening for SDZ038>040-052>071.
MN...Red Flag Warning from 11 AM this morning to 8 PM CDT this
     evening for MNZ071-072-080-081-089-090-097-098.
IA...Red Flag Warning from 11 AM this morning to 8 PM CDT this
     evening for IAZ001>003-012>014-020>022-031-032.
NE...Red Flag Warning from 11 AM this morning to 8 PM CDT this
     evening for NEZ013-014.

&&

$$

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