Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 202009

Area Forecast Discussion
National Weather Service Sioux Falls SD
309 PM CDT WED JUL 20 2016

.SHORT TERM...(This evening through Thursday)
Issued at 309 PM CDT Wed Jul 20 2016

A decent looking low level jet is still in place for tonight, but
little else to initiate storms or even high based weak showers,
such as we had early this morning, is apparent. After the exiting
weak short wave to the east, and the weak upper wave bringing higher
clouds west moves on, little upper support is seen, and the best
elevated instability/CAPE of 2000 J/kg or greater appears to stay to
the north and east. So am expecting a convection free night.

Temperatures of course will be quite warm with lows generally in the
mid 70s; certainly warm enough to keep the heat warning going
through the nighttime hours as we have been doing.

Thursday is still likely to be the hottest day of the week overall
in our area. The hottest temperatures of 100 plus still look
destined for our southwest, specifically the Chamberlain area, while
warming in the east brings everybody up at least into the lower
90s, or a few degrees above today in most places. Dew points and
humidity will still be rather high and fuel the excessive heat. The
only cooling factor is the developing boundary which slips into the
area from the northwest during the day, bringing winds to
northeasterly. While cooling from today will be limited, I have
cooled highs at Huron to 100 from a few degrees above, an a little
more cooling than I see could keep them below triple digits.

The strong heating and the arriving boundary could result in
a few storms developing over the southwest corner of the area by late
afternoon and will mention a slight chance for that area.

.LONG TERM...(Thursday night through Wednesday)
Issued at 309 PM CDT Wed Jul 20 2016

Thursday night will see a cool front gradually settle southward
towards the Missouri River during the evening. Isolated
thunderstorms will be possible from south central South Dakota
towards Sioux City through the night but with only a very weak wave
and some concern about capping confidence not overly high.
Instability plenty high to support a severe thunderstorm if a few
can develop but with weak shear it should remain isolated.

Other than a small threat of thunderstorms near the front closer to
Sioux City on Friday, it should be a fairly quiet and warm day.
There is some concern that we will not get quite as warm and humid
as previously expected, but will give it another model run to figure
out what to do with the heat headlines. The area with the highest
chance for losing the heat warning will be southwest Minnesota.

Friday night into Saturday looks like the best chance for showers
and thunderstorms. A slightly stronger wave will move through to the
north which will veer the low level jet to the southwest. This will
bring the deeper moisture and instability back north across the
boundary which should bring a good chance for rain and
thunderstorms. Severe weather will again be possible.

In the outer periods (Sunday through Wednesday), The strong ridging
will have broken down with faster westerlies across the North Dakota
and Canadian border. Sunday into Monday looks quiet as weak upper
level ridging builds across the area. This should be followed by a
decent wave and an increased threat for thunderstorms. The models
are in pretty good agreement in swinging through this wave Tuesday
into Wednesday. Temperatures should be near the seasonal normals.


.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1112 AM CDT Wed Jul 20 2016

VFR through 21/18z. Despite the development of a moderate low
level jet for tonight, other factors such as capping and mid
leveldrying and, for now, lack of a concrete short wave in the
westerly flow should preclude more than the most isolated
-shra/-tsra development. The low level jet has led to examining
low level shear potential in the KFSD and KSUX TAFs, but detailed
examination of model soundings on BUFKIT shows the shear is mostly
unidirectional and fairly broad over the lowest 1-2k feet AGL.
This fits with the depiction of only a broad inversion over these
lower layers, where most LLWS problems are accompanied by sharper
temperature profiles. Have not included LLWS in TAFs for now.


.FSD Watches/Warnings/Advisories...
SD...Excessive Heat Warning until 7 PM CDT Friday for SDZ038>040-050-

MN...Excessive Heat Warning until 7 PM CDT Friday for MNZ071-072-080-

IA...Excessive Heat Warning until 7 PM CDT Friday for IAZ001>003-

NE...Excessive Heat Warning until 7 PM CDT Friday for NEZ013-014.



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