Flooding in Minnesota, April 11 to 25, 2023

Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
1220 AM CDT Wed Apr 12 2023

.UPDATE...
Issued at 928 PM CDT Tue Apr 11 2023

Plenty of weather "goings-on" round here today. Pierre and
Mobridge smashed high temperature records today. One of them was a
record over 110 years old!

Was able to expire the Red Flag Warning ~45 minutes ago. Still
seeing area streams, creeks and rivers coming up into flood stage
this evening. And, if they're not in flood stage, some of them are
working toward or through action stage.

Also, noting the downslope wind event is underway, with SDDOT site
Peever recently reporting a gust up to 50 mph. Wind Advisory for
the downslope wind corridor in the lee of the Praire Coteau
continues.

No other changes planned to the tonight period.

UPDATE Issued at 621 PM CDT Tue Apr 11 2023

See below for an aviation forecast discussion for the 00Z TAFs.

&&

.SHORT TERM...(This Evening through Wednesday Night)
Issued at 134 PM CDT Tue Apr 11 2023

Key Messages:
* Red Flag Warning conditions continue into the evening hours over
  south central SD.
* Strong downslope winds on the east side of the Prairie Coteau
  tonight.
* Snow melt continuing over northeast SD for the next couple of
  days.

An anomalous upper ridge (18Z NAEFS 500mb heights over SD are max of
the 3-week climo period surrounding this date) has led to warm
temperatures across area, but especially in the snow free locations.
As of 1pm, the snow free areas have risen into the 70s and 80s,
while the snow covered areas in northeast SD are in the 40s and
lower 50s. These warmer temperatures have been aided by good mixing
(up to 750-700mb over the snow free areas) with the ample sunshine
and SSW winds. Red Flag conditions are occurring over the snow free
areas of south central SD, with RH values between 15-20% and gusts
up to 30-35mph from obs as of 1pm. Don't expect too much change in
the conditions for the next few hours, other than the RH values
falling a little more with the warming temps this afternoon.

The increasing winds today are associated with an tightening
pressure gradient ahead of a 997mb low located near the
MT/Saskatchewan border. That low will lift northeast tonight and
Wednesday, with additional support from a shortwave rounding the
upper ridge over central Canada. But as that occurs, it will sweep a
cold front southeast across the region late tonight into Wednesday
morning. As that front approaches, it will help increase the
gradient across the area and with a intensifying low level jet (up
to 50-55kts), expect another period of downslope winds on the east
side of the Prairie Coteau. With the strength of the winds aloft,
thinking we'll easily hit advisory criteria and wouldn't be
surprised to see a few gusts over the high wind warning level. Thus,
will issue a wind advisory for the favored downslope areas of
Roberts/Grant/Deuel counties for this evening and then bring it to
an end as the front moves through towards morning.

For the rest of the area, no clouds are expected with the front and
the main item of note will be the eventual shift of winds to a
northerly direction during the day on Wednesday. This will keep the
winds off the snowpack for the northern areas and lead to another
day of sharp differences between the snow and no-snow areas. Based
on the way that today has been trending, do wonder if the forecast
highs are a touch high in the James River valley near Aberdeen and
wouldn't be surprised if we stay in the 40s. For the snow free
areas, expect highs to be above normal again, but some areas will be
a good 10-15 degrees colder than this afternoon.

Finally for Wednesday night, the cold front looks to stall over
southeastern SD or northwest IA Wed afternoon/evening and then stay
in place Wednesday night. Meanwhile, the upper trough that is off
the Pac NW this afternoon will be moving into NV and models are
indicating a weak shortwave or two ejecting northeast across the
area. With limited moisture in the low/mid levels of the atmosphere,
don't expect any significant precipitation from these initial
shortwave, but felt that continuing the slight chances (15-24%) was
reasonable. Did include a slight chance of thunder too, based on the
steep lapse rates (8.5-9C/km) between 650-500mb.

.LONG TERM...(Thursday through Tuesday)
Issued at 134 PM CDT Tue Apr 11 2023

An upper level trough will be the dominant weather feature during
the extended portion of the forecast. The period begins on Thursday
with an inverted surface trough, stalled front over the eastern CWA
with model guidance suggesting 300 to 700 J/kg of MU-cape. An
increasing LLJ Thursday night may cause isolated thunderstorms over
the far eastern CWA, despite the little buoyancy. By Friday, the
first surface low should be east of the CWA with cooler,
northwesterly flow over much of the region. With decent upper level
support, the CWA could see additional showers on Friday.

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday Night)
Issued at 1219 AM CDT Wed Apr 12 2023

Terminals KABR,KATY,KPIR,KMBG

VFR conditions are forecast to prevail at all sites through the
period. An approaching cold front is keeping low level winds up,
thus LLWS is still in the TAFs tonight. Then as the front moves
through, winds will shift around to a northerly direction on
Wednesday. AMD NOT SKED has been appended to KATY due to a comms
outage.

&&

.ABR WATCHES/WARNINGS/ADVISORIES...
SD...Wind Advisory until 5 AM CDT early this morning for SDZ008-021-
     023.

MN...None.
&&

UPDATE...Dorn
SHORT TERM...SRF
LONG TERM...Parkin
AVIATION...Wise

Hazardous Weather Outlook...UPDATED
National Weather Service Aberdeen SD
146 PM CDT Tue Apr 11 2023

MNZ039-046-SDZ003>007-009>011-015>020-022-033>037-121200-
Traverse-Big Stone-Corson-Campbell-McPherson-Brown-Marshall-Walworth-
Edmunds-Day-Dewey-Potter-Faulk-Spink-Clark-Codington-Hamlin-Stanley-
Sully-Hughes-Hyde-Hand-
146 PM CDT Tue Apr 11 2023 /1246 PM MDT Tue Apr 11 2023/

This Hazardous Weather Outlook is for west central Minnesota,
central South Dakota, north central South Dakota and northeast
South Dakota.

.DAY ONE...This afternoon and tonight.

No hazardous weather is expected at this time.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday.

Increase snowmelt will lead to rising river levels along the Big
Sioux and James Rivers through the end of the week.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time.

SDZ045-048-051-121200-
Jones-Lyman-Buffalo-
146 PM CDT Tue Apr 11 2023

This Hazardous Weather Outlook is for central South Dakota.

.DAY ONE...This afternoon and tonight.

Very high grassland fire danger is expected through early evening as
relative humidity values remain in the 10 to 20 percent range and
winds gust as high as 35 mph.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday.

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time.

SDZ008-021-023-121200-
Roberts-Grant-Deuel-
146 PM CDT Tue Apr 11 2023

This Hazardous Weather Outlook is for northeast South Dakota.

.DAY ONE...This afternoon and tonight.

Southwesterly downslope winds up to 50 mph are expected on the
eastern side of the Prairie Coteau tonight.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday.

No hazardous weather is expected at this time.

.SPOTTER INFORMATION STATEMENT...

Spotter activation is not expected at this time.

SRF