Area Forecast Discussion
Issued by NWS Aberdeen, SD

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FXUS63 KABR 171750 AAB

Area Forecast Discussion...UPDATED
National Weather Service Aberdeen SD
1250 PM CDT Mon Jul 17 2017

Issued at 1236 PM CDT Mon Jul 17 2017

Made some minor changes to the forecast this morning, mainly to
delay pcpn until 20Z. As of 17Z, the surface trough/frontal
boundary is moving across north central SD. Dew point are slowly
dropping behind the front. Breezy southwesterly winds and high dew
points are ahead of the front. Thunderstorms are still possible
along the fropa later this afternoon as low level lapse rates
steepen. With limited shear and upper level support, the overall
severe threat is marginal. Damaging wind gusts will be the main

UPDATE Issued at 703 AM CDT Mon Jul 17 2017

12z aviation discussion updated below.


.SHORT TERM...(Today through Wednesday Afternoon)
Issued at 416 AM CDT Mon Jul 17 2017

Southwesterly environmental winds will lead to deep mixing today
with the NAM and GFS between 8 and 11kft respectively. We are also
seeing some much higher dewpoint air moving into the area.
Additionally, 850mb temperatures increase to around +28C. Therefore,
will continue the premise of much of the area topping out around
100F. As we anticipate mixing out somewhat, heat index values are
also only around 100. As such, will pass on any heat headlines.

Fire weather is the next threat, as deep mixing yields afternoon
humidity in the 20 and 35 percent range. Mixed winds are also going
to be gusty initially, with a 30-40kt jet overhead mixing out. Mixed
winds thereafter are mainly in the mid 20kt range for gusts. Decided
to elevate fire danger to Very High ahead of the front for today.

For this evening, the front will provide the focus for convection.
Flow through the profile is mainly unidirectional out of the
southwest. CAMs are all fairly consistent with development around 22
and 23Z between Huron and Mobridge areas. MLCAPE values are around
1000 to 1500 j/kg with rather high DCAPE thanks to the height of
convection/depth of dry layer. There should be enough flow within
cloud layer to support storm rotation for a hail threat as well.

Frontal passage will result in more stable conditions with the nose
of high pressure edging out of Canada and North Dakota with dry
conditions tonight. 500mb flow remains zonal, so we expect another
low to move across the area Tuesday. While the periphery of the CWA
will see some MLCAPE, its actually the right entrance region of a
90kt jet to the north that supports additional precipitation.

We also now expect a warm front to set up across the area Wednesday,
though this looks to reside along the southern periphery of the CWA.
This may be an additional focus are for convection. MLCAPE values
are not very high, but there is strong shear.

With the more active pattern Tuesday and Wednesday, it looks like
temperatures will be more seasonal for mid July.

.LONG TERM...(Wednesday Evening through Sunday)
Issued at 416 AM CDT Mon Jul 17 2017

Large upper high pressure area over the southern U.S. will begin the
long term along with an upper low pressure area moving off the
Pacific into southwest Canada. This upper low pressure area moves
across southern Canada and then southeast into the Great Lakes
region into Sunday. This will suppress the southern U.S. high
pressure area with heights rising/upper ridge building across the
western U.S. into Sunday. Therefore, the upper level flow over our
region will transition from west to northwest by Sunday. There will
be several periods of showers/storms from Wednesday night through
Friday night as short waves move over the region and a surface front
moves back and forth. Saturday and Sunday both look to be mainly dry
at this time across our region. Otherwise, temperatures still look
to be near to several degrees above normal mostly in the 80s and
lower 90s from Thursday through Sunday.


.AVIATION...(For the 18Z TAFS through 18Z Tuesday Afternoon)
Issued at 1236 PM CDT Mon Jul 17 2017

A frontal boundary will cross the region today with winds shifting
from the south, to the north behind the front. Thunderstorms are
possible along the front later this afternoon. Some storms may
impact the terminals of KABR and KATY. Damaging winds will be the
main threat.




SHORT TERM...Connelly
AVIATION...SD is the U.S. government's official web portal to all federal, state and local government web resources and services.