230
FXUS63 KFSD 180344
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1044 PM CDT Fri May 17 2024

.KEY MESSAGES...

- Isolated thunderstorms may develop late Friday afternoon and
  evening over SW Minnesota and adjacent areas of Iowa and South
  Dakota. Non-severe storms could bring a few reports of hail
  or gusty winds.

- Thunderstorm chances return late Sunday into Monday, with a
  continued uncertain potential for severe weather.

- The highest focus for convection arrives Monday night into
  Tuesday bringing a risk for severe storms to the Tri-State
  area along with widespread potential for 1-2+ inches of
  rainfall. This rainfall could bring some rivers back into
  flooding levels.

- Cooler temperatures but continued unsettled weather remains
  through the rest of next week.

&&

.DISCUSSION...
Issued at 236 PM CDT Fri May 17 2024

THIS AFTERNOON:  A very warm day across the Tri-State area as
temperatures have risen into the  middle and upper 80s in most
areas.  Some areas will likely see a late day surge to 90, as mixing
intensifies.  There remains a narrow tongue of surface dew points in
the lower to middle 50s in the CWA.  With the increased surface
convergence this afternoon, it`s not out of the realm of
possibility to see a few high based thunderstorms form along a
line from near Yankton to Sioux Falls to Marshall/Windom later
today. MLCAPE may approach 500 to 900 J/KG along this line, and
while the severe weather risk is low, given sharpening mid-lvl
lapse rates some small hail or localized wind gusts could be
possible.

TONIGHT:  Lingering isolated thunderstorms may persist through mid-
evening before dissipating.  Additional convection is likely over
the western Dakotas later tonight along an area of low pressure and
surface front.  This front will push eastward overnight with an area
of elevated moisture likely developing into ACCAS overnight as it
moves eastward.  A few high based showers/virga are possible across
most of the Tri-state area through 9am Saturday.   Behind this
front, CAMs all suggest potential for 35 to 45 mph winds moving into
central South Dakota by 3-4am, and the James River valley by 7am.
Winds are expected to weaken as they travel east and the brevity of
higher winds may be too short to issue an advisory for ATTM.

SATURDAY: Breezy west to northwest winds will prevail through
Saturday, though wind gusts will fall into the 20 to 25 mph range by
the afternoon.  Fairly dry air is expected to both advect southeast
and then mix down in the afternoon, and have also favored
temperatures slightly above the NBM in the afternoon.

SUNDAY: High pressure slides through the Tri-State area Saturday
night into Sunday, however broad warm advection and a subtle
shortwave is likely to initiate convection over the Nebraska
Panhandle and western Kansas overnight. Some sort of MCS may
develop and track into eastern Nebraska and northwest Iowa
early Sunday. The GFS/NAM/GEM all remain focused over the
southern counties for heavier rain, while the ECMWF is shifted a
few counties further north. If a larger scale MCS does develop,
it could interrupt moisture and potential for any further north
isolated development across the Dakotas. At this point morning
activity will likely not be severe. We will however had to watch
for some increased potential later in the evening and overnight
though this remains highly uncertain. If further south tracks
of morning activity verify, then more focus towards afternoon
and evening activity develop along a boundary over the western
Dakotas late in the afternoon. This activity would then track
eastward overnight, it would likely continue eastward though a
MUCAPE pool of 1500-2000 J/KG until weakening near the James
River. Could see potential eastward expansion of SPC outlooks
towards the James River Valley and further into the Dakotas.

MONDAY-TUESDAY:  Broad southwesterly flow leads to a very complex
and then potentially wet forecast for a large portion of next week.
By Monday morning a surface front will try to settle into Northwest
Iowa.  A cooler day is likely Monday with lingering clouds, and this
will keep temperatures into the upper 60s to lower 70s.  However,
the pattern setting up would be favorable for sharply increasing
PoPs by Monday evening into Tuesday.  A deeper influx of moisture is
expected to arrive late Monday, pushing PW values towards 1.5".
Wherever the surface boundary falls, only modest inhibition may
exist by the evening, increasing the potential for a few
stronger surface based storms. MLCAPE between 1500-2000 J/KG
along with a modest increase in effective shear towards 35
knots, could produce an increased severe weather risk in the
evening. Greater convection risks develop after dark however as
the LLJ and low-lvl frontal circulation increases, mid-lvl dPVA
develops, and broad upper diffluence from an approaching upper
jet moves into the area. This will produce the potential for a
fairly large area of heavy rainfall potential. GEFS/ECE
probabilities for >1" rain break the 70% range, with
probabilities for >2" of rain already at 20%. Some initial
severe weather risk may continue into the early overnight hours,
mainly due to an elevated hail risk. Both the CSU Machine-
learning probabilities along with the CIPS analogs both support
the potential for further north expansions of the severe weather
outlooks from SPC.

WEDNESDAY-FRIDAY: We`re going to remain quite active through most of
next week as a large trough remains centered over southern Canada.
This trough is going to keep a risk for showers and thunderstorms
nearly every other day into next weekend, along with a drop in
temperatures towards or even slightly below seasonal normals.

&&

.AVIATION /06Z TAFS THROUGH 06Z SUNDAY/...
Issued at 1043 PM CDT Fri May 17 2024

VFR conditions are expected for the TAF period. The low level jet
(LLJ) has strengthened this evening, leading to low level wind shear
(LLWS) across the area which will persist through the overnight
hours. The LLJ will also keep gusty southerly winds through most of
the night with gusts up to 20-30 knots. A cold front currently over
central South Dakota will push eastwards through the area during the
overnight hours. Sprinkles to very light rain showers are possible
but confidence remains too low to put in a TAF. A small period of
stronger gusts up 35-40 knots is expected west of I-29. Winds will
swing to out of the northwest behind the front and remain gusty
through the rest of tomorrow with gusts up to 20-30 knots expected.
Winds will slowly wane through the afternoon and evening hours.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...None.
MN...None.
IA...None.
NE...None.

&&

$$

DISCUSSION...Dux
AVIATION...Meyers