Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 251951
AFDFSD

AREA FORECAST DISCUSSION
National Weather Service Sioux Falls SD
251 PM CDT Tue Jun 25 2019

.SHORT TERM...(This Evening through Wednesday)
Issued at 212 PM CDT Tue Jun 25 2019

Pleasant but breezy conditions continue across most of the region
this afternoon. These winds will slowly subside this evening a
ridge of high pressure moves through the area.

For tonight, we`ll be watching convection rolling off the Northern
High Plains late this evening and into Wednesday morning. Nearly
all convective allowing model solutions indicate one or more
clusters of storms moving eastward later this evening as low-level
flow begins to back and EML starts to move eastward. Now this
activity should begin to weaken as it slide east along an
advancing corridor of 800-1000 J/KG MUCAPE into central South
Dakota. That said, certainly an increased potential, looking at
soundings, for enhanced winds to persist even as this activity
weakens given very dry sub-cloud layer under high based storms.
Unfortunately, with such low certainty on where activity will
develop and the potential for scattered development along a broad
axis from North Dakota to central Nebraska on the edge of the
advancing EML, have spread a broad 20-30% PoP into Wednesday
morning for most locations.

Continued uncertainty on Wednesday, as we`ll really need to see
where the eventual evolution of overnight convection takes place.
It`s certainly possible that diminishing activity sends out a few
outflow boundaries that could serve as afternoon focus points for
redevelopment in the afternoon. However, a broad EML will advance
northward through the day, and could certainly cap off convection
potential into the evening as shortwave ridging briefly arrives.
Temperatures should climb into the 80s in most areas as warmer and
more humid air starts to lift northward.


.LONG TERM...(Wednesday Night through Tuesday)
Issued at 212 PM CDT Tue Jun 25 2019

Wednesday night: No matter which solution you look at, all
guidance indicates a shortwave will cross the Central Rockies and
move into the Plains either late Wednesday evening (ECMWF) or
after dark (NAM/GFS/CMC). As a large reservoir of CAPE in excess
of 2500 J/KG remains in place by Wednesday evening, it will
certainly be possible to see two areas of redevelopment. One area
will be along any retreating outflow or on the edge of thermal
ridge across SW MN and NW Iowa, and a second area along the High
Plains tied more closely to the shortwave. Both areas will
certainly have the ability to turn severe given pool of
instability, although there is a little more uncertainty with the
activity that tracks east of the Plains late Wednesday night into
Thursday morning. Upgrades in the SPC risks may be possible if
more certainty can be pinned down on locations.

Thursday-Friday: Mid-level heights begin to build quickly on
Thursday, as morning convection slides to the east, and we`ll
begin to head towards our first heat wave of the Summer season.
Temperatures approach 90 in portions of the CWA by Thursday
afternoon, with 90s building east on Friday.

Saturday-Sunday: The peak of this upcoming heat wave will arrive
Saturday and Sunday. Latest guidance pushes temperatures will into
the 90s, and unfortunately, a good setup for high dew points is
arriving. Have bumped up highs a couple degrees with fairly high
expectation of heat headlines for the weekend as heat index values
jump over 100 degrees.

Monday-Wednesday: A bit of disagreement begins in medium range
models to start next week. The GFS indicates falling heights
across south central Canada to start the week, allowing a front to
drop into the region. The ECMWF holds the ridge a bit stronger to
start the week, but then does sink a boundary closer to the
Dakotas by Tuesday. Will not make any adjustments to the forecast
for next week given the uncertainty.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1202 PM CDT Tue Jun 25 2019

VFR conditions expected for the upcoming 12 or more hours. We`ll
monitor thunderstorms across the western Dakotas move towards the
area later tonight, which could impact the terminals. Confidence
too low to include at this point, but further mention in the 00Z
TAF may be possible.


&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...NONE.
MN...NONE.
IA...NONE.
NE...NONE.
&&

$$

SHORT TERM...Dux
LONG TERM...Dux
AVIATION...Dux



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