Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 232358

Area Forecast Discussion
National Weather Service Sioux Falls SD
658 PM CDT Sun Oct 23 2016

.SHORT TERM...(This evening through Monday)
Issued at 258 PM CDT Sun Oct 23 2016

The stratus to the north will be the main challenge tonight into
Monday. Confidence on what will happen not real high but starting to
lean a little closer to the Nam and WRF/NMM output. These 3 models
are the only ones that are handling the current stratus to the north
decently. This will obviously cause big differences in the aviation
categories as well as high temperatures Monday. The Nam/NMM/WRF
highs are about 5 to 10 degrees cooler than the GFS and EC output
and have leaned towards the cooler high temperatures, but not
completely in that direction since confidence is not as high as it
could be. Lows tonight may also be affected if stratus moves in from
the northeast so a little leary that the forecast going out could be
bit on the cool side, especially north and east of a Huron to Ida
Grove line.

.LONG TERM...(Monday night through Sunday)
Issued at 258 PM CDT Sun Oct 23 2016

Starting with Monday night...The initial theta e advection is weaker
than was showing yesterday, and the chance of any light showers
seems correspondingly smaller. Some of the higher resolution
models,such as the nmm, namnest and namdng show an area of very
light rain...or drizzle...developing toward northwest IA and extreme
northeast NE in the hours before 12Z Tuesday. The namdng shows a more
significant area of light rain just to the north of the HON to BKX
area, and since the loaded guidance pops show slight chance into our
far north, will go with this. With only 20 percent pops would like
to see more solid indications of rain to add to the southeast, and
since low level moisture progs, even on the sometimes RH wild NAM,
do not show decent saturation, will keep mention out of that
southeast corner through 12Z Tuesday.

The short wave representing the main weather feature for this week
is still generally being handled consistently by the models. The main
difference from before is a weaker thermal and theta e gradient and
weaker winds spreading ahead of the system, with the best support
coming with the dynamic system coming through Tuesday night. the
best rainfall therefore looks to be in and near northwest Iowa where
the dynamics, moisture advection, and thermal support will all be
enhanced by the wave. So, we are looking at showers increasing
steadily over the area Tuesday, especially over Interstate 29 and
east where pops will be likely to unqualified. Then as the system
comes across the southern end Tuesday night, the best rain should
produce storm totals of an inch to an inch and a half over
northwest Iowa and into the Jackson Minnesota area. Instability
surging into the area from the south should bring some thunder tot
he southern part of the area, with thunderstorms possibly becoming
numerous for a while late Tuesday and Tuesday evening around Sioux
City to Storm Lake. The instability and wind fields look well below
the threat level for severe storms however.

Temperatures Tuesday will be held to the 50s and lower 60s by
clouds and possible rain. As the system moves east of the area
Wednesday, any lingering light rain or showers in southwest MN and
northwest IA will end, and clouds will decrease from the west. The
strength of the surface low will be limited, and adding that the low
will be moving out fairly quickly. Northwesterly winds should not be
strong enough to get breezy. A modest cool inflow will keep high
temperatures Wednesday similar to Tuesday, 50s to lower 60s.

The rest of the forecast period, Thursday through Sunday, should be
mostly dry with near to a little above normal temperatures. A little
warming late in the week and some cooling behind a cold front over
the weekend should be modest, with temperatures neither getting real
warm nor dipping below normal. The GFS and EC are somewhat different
in their solutions. The GFS bringing a Rockies wave over the
developing ridge and passing it east and southeast of the northern
plains, suggesting dry through the weekend. The EC brings a wave
across further south into the area, suggesting a chance of showers
about Saturday. Guidance pops look like the best compromise for now,
with a slight chance of showers centered over southwest Minnesota
early Saturday. Will go with that.


.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 648 PM CDT Sun Oct 23 2016

Still a possibility of some stratus leaking southward from east
central Minnesota and northeast South Dakota late evening through
the overnight. Models are split on how far south this layer may will leave out of TAF sites for now. With lighter
winds...patchy shallow fog will also be possible if the stratus
does hold north.




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