Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 270841

Area Forecast Discussion
National Weather Service Sioux Falls SD
341 AM CDT Sun May 27 2018

.SHORT TERM...(Today and Tonight)
Issued at 338 AM CDT Sun May 27 2018

The obvious story in the short term is the likely record breaking
heat for Sunday. Just how hot we will get is still up in the air.
Temperatures aloft will be a bit warmer than Saturday and, thanks to
lee pressure falls to our west, we`ll have a bit of a pressure
gradient set up and breezy southerly winds as well, particularly
west of the James River. These two facts would together suggest a
recipe for rising above guidance values into the triple digits in
some spots. The complicating factor will be the potential for cirrus
- currently widespread to our west - and just how optically thick
any cirrus will be. Have opted to stay near consensus in our west in
deference to the cirrus. Spots in northwest Iowa - including Sioux
City, Le Mars, and Storm Lake - were pushed just above consensus as
I don`t think cloud cover will be as much of an issue there and
guidance has continued to trend upward. While we are borderline with
respect to our local criteria for a Heat Advisory, have gone ahead
and issued one for many of our eastern zones where there will be
less of a breeze to provide a respite from the heat. It is also
awfully early in the year to have this kind of heat and many people
may be outdoors for the holiday weekend.

With the heat, there is a small but non-zero chance of a couple pop
up isolated storms. Not confident enough to put anything mentionable
into the forecast, so limited any PoPs to 14 percent.

.LONG TERM...(Monday through Saturday)
Issued at 338 AM CDT Sun May 27 2018

More active weather begins to occur starting Monday as the western
trough begins to translate eastward. First shortwave to impact our
zones will hold off until Monday night as it approaches from the
southwest. We`ll have plenty of potential instability to work with
but capping looks to be a significant issue - particularly east of
the James River, with the GFS and NAM both showing an inversion
around 700mb even as lift increases ahead of the wave. Additionally,
shear profiles are rather unidirectional east of the James River.
The best chances for organized convection will thus remain in our
west, with damaging wind as the main concern.

Precipitation chances continue throughout Tuesday as the main wave
approaches. Progged parameters and soundings suggest much of the
region could see severe weather during Tuesday and Tuesday night.
However, given the convection expected in our western zones and to
our north Monday night, still quite a bit of uncertainty in how the
mesoscale features will shake out and if the convective potential
can truly be realized as clouds may be widespread throughout the day.

Wednesday will see a brief respite from the heat with highs only
about 10 degrees above normal. With another trough digging in to the
west by Thursday, upper level flow will remain amplified and another
ridge will build in Thursday and Friday. Spectral deterministic and
ensemble guidance has trended toward a more amplified ridge on these
dates so have followed this trend and pushed highs above consensus.
Luckily this next trough looks to be more progressive than the
previous pattern and chances for showers and storms - and perhaps
temperatures closer to normal - return by the weekend.


.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1032 PM CDT Sat May 26 2018

VFR conditions are expected through the period. Gusty south
winds to 25 knots are possible Sunday afternoon across south-
central South Dakota, impacting KHON terminal.


SD...Heat Advisory from 1 PM this afternoon to 7 PM CDT this evening
     for SDZ062-066>071.

MN...Heat Advisory from 1 PM this afternoon to 7 PM CDT this evening
     for MNZ071-072-080-081-089-090-097-098.

IA...Heat Advisory from 1 PM this afternoon to 7 PM CDT this evening
     for IAZ001>003-012>014-020>022-031-032.

NE...Heat Advisory from 1 PM this afternoon to 7 PM CDT this evening
     for NEZ013-014.



SHORT TERM...Ferguson
LONG TERM...Ferguson
AVIATION...05 is the U.S. government's official web portal to all federal, state and local government web resources and services.