Dickinson County Courthouse, Spirit Lake, Iowa

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Forecast Discussion

Forecast Discussion for FSD NWS Office

000
FXUS63 KFSD 152350
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
650 PM CDT Mon Apr 15 2024

.KEY MESSAGES...

- Red Flag Warning remains in effect until 8 PM tonight.

- High confidence in rainfall arriving tonight and continuing through
  Wednesday morning. Widespread amounts between 1.0 to 2.5
  inches are expected, with isolated pockets of 3+ inches also
  possible.

- Rainfall rates could exceed 1 inch per hour at times, which
  may result in isolated to scattered flash flooding in urban
  and low lying areas.

- Isolated to scattered severe thunderstorms will be possible tonight
  and Tuesday afternoon. The greatest threat with the strongest
  storms will be large hail, but isolated damaging wind gusts
  and a tornado or two cannot be ruled out.

- More precipitation chances (30%-70%) return Wednesday night into
 Thursday mostly south of I-90.

- The breezy conditions will continue along with more seasonal
  conditions from the midweek into the weekend.

&&

.DISCUSSION...
Issued at 251 PM CDT Mon Apr 15 2024

CURRENT: Dry and breezy conditions continue across the region, with
latest observations showing southeasterly winds gusting between 25
to 35 MPH and temperatures in the 70s. Relative humidity values have
plummeted quite a bit this morning, with values largely in the teens
to lower 20s. As such, the Red Flag warning remains in good shape
and will remain valid until 8 PM.

TONIGHT: Sfc warm front and low pressure lift northeastward across
Nebraska this evening, causing showers and storms to return to the
forecast. Similar to days past, latest CAMs continue to slow the
arrival time ever so slightly, with most supporting initiation along
the Missouri River near/shortly after 7 PM. With a stout LLJ
overhead, have ample bulk layer shear (40+ kts) to work with in
addition to increasing low level moisture. However, latest soundings
still show a decent cap in place, suggesting that most if not all of
these storms will remain elevated in nature. Near 03Z, should see
MLCAPE approach 1000-1500 J/kg along the MO River Valley, with mid
level lapse rates between 7.5-8 degC/km, and DCAPE values near 1000
J/kg. Thus, as highlighted in SPC`s Latest Day 1 Outlook, expect
large hail (2+) to be the primary hazard initially - especially in
the Enhanced Risk (Level 3 of 5). As storms grow further upscale,
upper level forcing begins to wane, so would expect hail size to
lessen to the size of ping pong balls or smaller. Damaging winds in
excess of 50+ MPH and an isolated tornado or two also remain
possible. Given that these storms look to take place during the
evening and overnight period, we strongly encourage you to have a
way to receive warnings in the event that storms become severe!

TUESDAY: Widespread rain chances (>80%) are expected heading into
Tuesday and the aforementioned sfc low moves over NE/SD border.
Easterly winds are expected to remain breezy during this time,
especially along and east of the James River, with gusts between 30
to 45 MPH still possible. May even see some locations east of I-29
approach 50 MPH at times as the SPG tightens overhead. For now, have
opted to forgo any wind headlines. Will allow the coming shifts to
evaluate model trends and issue as necessary - so continue to
monitor for updates. Sfc low pressure moves overhead by Tuesday
afternoon, resulting in some lulls in precipitation thanks to the
dry-slot. While tomorrow`s severe weather threat remains highly
conditional on if we can destabilize again after the morning
convection - latest CAMs do show another line of convection across
NW Iowa and SW Minnesota during the afternoon as the triple point
lifts over the SD/IA border. With the current dynamics in place,
would expected elevated hailers to be the primary hazard again, with
damaging wind gusts and isolated tornadoes being a secondary threat.

Lastly, in regard to rainfall totals, expect widespread amounts
between 1 to 2.5 inches across our area, with isolated pockets of 3+
inches also possible. WPC`s latest Day 1 Outlook has introduced a
Slight Risk (Level 2 of 4) to portions of our area, mainly along and
north of the MO River Valley to I-90. As such, could see rainfall
rates exceed 1 inch per hour at times, which may result in isolated
to scattered flash flooding in urban and low lying areas. Ponding
would be expected in areas elsewhere. River rises are also expected
with locations most at risk of approaching flood stage being smaller
streams/creeks and the upper Little Sioux River between Milford and
Spencer.

WEDNESDAY - THURSDAY: Heading into the extended period, any
lingering precipitation chances will continue to push to the
northeast with the surface low by Wednesday morning. Quieter
conditions will temporarily return from the late morning onwards
as a mid- level ridge moves into the region. However,
northwesterly surface winds will increase as the SPG tightens
with gusts between 30-40 mph expected. This along with lingering
cold air advection aloft will lead to a slightly cooler
conditions compared to the previous day with highs expected to
peak in the mid to upper 50s and lower 60s. Otherwise, more
precipitation chances (30%-70%) will likely return from
Wednesday afternoon into Thursday as a weak mid-level wave
interacts with a developing surface low over Nebraska and
Kansas. While the better rain chances will certainly be south of
I-90, most ensemble guidance continues to show the highest
confidence (50%-80%) along and south of the Hwy-18 corridor with
at least a tenth of QPF or greater expected at time.
Nonetheless, the precipitation chances will likely continue into
the early afternoon hours on Thursday before pushing
southeastwards with the cold front.

FRIDAY - SUNDAY: Looking into the start of the weekend, much
quieter conditions return as broad troughing continues to
progress across the northern plains. Northwesterly surface flow
along with lingering cold air advection (CAA) aloft will
continue to gradually decrease our overall temperatures through
Saturday with daily highs sitting in the upper 40s to low 50s
across the area. Things could potentially begin to trend warmer
from Saturday night onwards as a surface high builds in behind a
departing shortwave. A switch to southerly flow along with
increased warm air advection (WAA) aloft will lead to a gradual
increase in temperatures with highs gradually increasing from
the mid to upper 50s on Sunday to the low to mid 60s by Monday.

&&

.AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/...
Issued at 649 PM CDT Mon Apr 15 2024

Mainly clear skies begin the TAF period. Thunderstorms have
developed across north central Nebraska. These storms will continue
to move off to the northwest and will avoid all TAF sites let alone
the entire area. The low level jet (LLJ) will strengthen this
evening, creating low level wind shear (LLWS) at all TAF sites. The
LLWS will be short lived though, only lasting through the evening
hours as new thunderstorms look to develop along the Missouri River
Valley and push northwards. Winds will remain out of the southeast
with gusts as high as 35-40 knots expected to prevail through the
evening and overnight hours.

As showers and storms look to reach all TAF sites around midnight.
Ceilings will remain at VFR levels at first but will lower to
MVFR/IFR levels by tomorrow morning. The showers and storms will
continue across the entire area through the morning hours before
some partial clearing returns to the area mainly east of I-29.
Showers persist west of the interstate. There could be renewed
thunderstorm development tomorrow afternoon but too uncertain to put
in a TAF as of now. Otherwise the showers will end the TAF period.

&&

.FIRE WEATHER...
Issued at 251 PM CDT Mon Apr 15 2024

Red Flag conditions continue across the region, with latest
observations showing temperatures in the mid to upper 70s with
southeasterly winds gusting between 35 to 45 MPH. Relative humidity
values as a result have plummeted into the teens to lower 20s. Thus,
believe the current headline remain in good shape and will remain
valid until 8 PM. We strongly encourage you to exercise caution with
any activity that may cause a spark, as fires can spread quickly
under these conditions!

&&

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

&&

$$

DISCUSSION...SST/Gumbs
AVIATION...Meyers
FIRE WEATHER...SST

NWS FSD Area Forecast Discussion