000
FXUS63 KFSD 141113
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
613 AM CDT Sun Apr 14 2024

.KEY MESSAGES...

- Summer heat brings highs in the 70s and 80s through Monday,
  much warmer than normal for mid April. Near critical fire
  weather conditions return Monday across the region with
  southeast winds gusting 30 to 45 mph.

- High confidence in rainfall arriving Monday night and
  continuing into Wednesday. Area average rainfall totals are
  expected to reach between 0.50" and 2.00" by Wednesday morning
  with isolated pockets of over 2 inches.

- Isolated to scattered severe thunderstorms are possible with
  showers and storm activity Monday night and Tuesday. 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.

- Cooler, breezy conditions are expected from Wednesday through
  Friday.

&&

.DISCUSSION...
Issued at 438 AM CDT Sun Apr 14 2024

TODAY AND TONIGHT: Expect excellent weather for outdoor activities
today with summer-like heat, abundant sunshine, and lighter winds.
Northwest flow aloft ahead of a strong upper ridge will keep
temperatures a bit cooler aloft and at the surface than Saturday.
Expect highs to range from the mid 70s in southwest MN to the low to
mid 80s near the U.S. Highway 20 corridor.

Low humidity will bring elevated fire danger again this afternoon,
but winds will be notably weaker than Saturday so critical fire
weather conditions are not expected. Portions of northwest IA and
southwest MN may see gusts in the 20s this morning, but gradient
winds will weaken this afternoon as a surface high slides by to our
north with gusts only up to 20 mph. Mostly clear skies and quiet
weather continue tonight with lows in the 40s to lower 50s. Did
maintain a low (<30%) chance for scattered high based showers and
storms in central SD for early Monday morning. This comes as a weak
ridge-riding shortwave slides north through the central Dakotas and
into eastern ND/northeast SD, but the northeastward track coupled
with low level dry air should bring little if any rain to south
central and southeast SD.

MONDAY: Ahead of a strong upper trough sliding east through the
Rockies, broad warm air advection brings another summery, breezy
day. Increasing gradient winds coupled with mixing into a
southwesterly low level jet means southeast winds sustained at 15 to
25 mph. Trimmed back NBM gusts a bit to yield gusts peaking in the
30s to lower 40s Monday afternoon. With winds around 40 kts at the
top of the mixed layer in model profiles, cannot rule out an
occasional gust near advisory criteria (45 mph) Monday afternoon.

The main during the day still looks to be gusty winds and elevated
fire danger. Though there is some uncertainty in the northernmost
extent, a warm front will lift north through the day, likely
reaching somewhere in the forecast area and increasing dew points.
Went with a warmer, drier solution than the NBM given recent trends,
which brings humidity levels into the 20s. Will need to monitor low
level moisture trends closely to determine whether critical fire
conditions will be met Monday afternoon, mainly east of the James
River Valley.

MONDAY NIGHT: Attention turns to severe weather threat Monday night
into Tuesday. However, upper level support for convective
development gets more difficult to come by the further northeast you
go in the Plains, especially as 00z guidance has slowed the ejection
of the upper low into the Plains with the Euro/GFS favoring slightly
slow, southern solution compared to the NAM. Model profiles along
the MO River Monday evening suggest a skinny elevated CAPE profile
which remains capped through at least 5 PM. Chances for showers and
thunderstorms do increase considerably Monday night as the low level
jet ramps up and the sfc low slowly ejects, with the latest guidance
favoring convective initiation in two areas, 1) in the warm sector
likely in south central SD and northern, central, or eastern NE and
2) further west near the inverted sfc trough extended north from the
CO Front Range into the Black Hills.

Weak mid to upper level winds (25-40 kts at 700-300mb) resulting in
modest deep layer shear and more stable air with poor low level
moisture (dew points mainly in the 40s and 50s) make it more
difficult to initiate or support severe storms the further northeast
you go. This would favor the greatest severe threat being along the
MO River and mostly south of I-90 with scattered multicells tracking
northeast into the areas south of I-90. Though there is an isolated
tornado or damaging wind threat, the main threat with the strongest
storms will be large hail with elevated storms and steep mid level
lapse rates. With the warm front lifting north and upper low
eventually ejecting into the Plains, coverage of showers and storms
should increase overnight, though severe threat may be more isolated.

TUESDAY: Though there are differences in the track, guidance
supports the upper low ejecting into the High Plains somewhere from
the NE Panhandle to north central KS by 12z Tuesday. This means
continued periods of scattered showers and storms throughout the
day. Tuesday will be windy as gradient winds increase ahead of the
sfc low advancing into eastern NE, as well as notably cooler with
highs mainly in the 60s. Skinny CAPE profiles develop during
daylight hours Tuesday with storms more likely to be elevated the
further north you go, but low level moisture should wrap in as the
sfc low approaches, yielding dew points at least in the 50s and
potential for surface based storms south of I-90. Low confidence in
timing the severe weather threat on Tuesday (i.e., morning vs
afternoon), but it should only extend into the early evening as the
sfc low tracks east of the area and we stabilize by mid evening.
Stronger deep layer shear (40-50 kts) than Monday will also aid
continued severe weather threat.

Despite severe weather threat winding down by Tuesday evening and
dry slotting potentially giving some breaks in rain, additional wrap
around/deformation-induced rain is expected on the back end of the
system Tuesday night through early Wednesday. With multiple rounds
of rain, confidence is increasing that many areas will see
widespread beneficial rains. By Wednesday mid day, there is a high
(70-90%) chance of > 1" of rain for areas near and east of I-29 with
a moderate-high (50-80%) chance of > 1" west of I-29. Isolated
pockets of 2-3+ inches are certainly possible by Wednesday as well,
especially considering storms will be able to tap into precipitable
water values at the top 3% of ensemble guidance for this time of
year.

WEDNESDAY AND BEYOND: High confidence in cooler, more seasonal
spring weather for the second half of the week as a northern
stream upper low settles near the Canadian border with the
Northern Plains. Confidence in rain chances is low as zonal flow
aloft could bring occasional weak waves through.

&&

.AVIATION /12Z TAFS THROUGH 12Z MONDAY/...
Issued at 611 AM CDT Sun Apr 14 2024

VFR conditions will prevail through the period. Light north
winds will turn northeast today with gusts up to 20 kts, veering
easterly this evening.

&&

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

&&

$$

DISCUSSION...BP
AVIATION...BP