Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 241727
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
1227 PM CDT SAT SEP 24 2016

.SHORT TERM...(Today and Tonight)
Issued at 346 AM CDT Sat Sep 24 2016

An upper level trough presently over the eastern Rockies will push
out onto the Northern Plains for today and tonight, bringing
increasing rain chances to our area during the period. A surface
cold front is currently analyzed through west central SD and NE,
with showers and thunderstorms streaming northward along this
boundary. This front will push into our western zones around late
morning, then slide slowly across the area before exiting very early
on Sunday morning. Good 850 mb moisture transport emanating from the
Gulf of Mexico is streaming northward into the Plains states out
ahead of this boundary, and models in general consensus with
scattered showers and thunderstorms developing through the Missouri
River Valley toward 12Z, then expanding to the north and east and
becoming likely from the eastern James River Valley eastward by
afternoon under moderate QG forcing. Although SPC has the eastern
two thirds in a Marginal Risk for this afternoon, think that the
severe threat is pretty low with CAPE values generally running 1000
J/KG or less and relatively weak unidirectional wind shear. With the
clouds and precipitation highs should settle in the mid 70s to lower
80s.

The front continues its eastward trek tonight, with the better
precipitation chances being east of the Interstate 29 corridor. Do
have a little better upper level support with upper level divergence
increasing due to a jet streak located through eastern SD. With
that, will see and increasing chance of heavy rain over portions of
southwestern MN and northwestern IA in the early evening. Cooler air
will begin to filter into the area behind the boundary, and looking
at lows in the lower to mid 50s overnight.

.LONG TERM...(Sunday through Friday)
Issued at 346 AM CDT Sat Sep 24 2016

Large closed upper level low continues to swing northeast into south
central Canada on Sunday, transitioning the region into cool and
brisk northwest flow. Tight pressure gradient and well mixed
environment will result in gusty northwest surface winds, peaking in
the afternoon.  The strongest winds will push into south central SD
where borderline advisory level conditions may develop. Will need to
watch this area for a potential wind advisory headline. With ample
cool air advection in place, we will also see some stratus filter
southward through the area during the day. While instability is
pretty meager, there may be a few isolated sprinkles or light
showers that pop up, but will leave pops just below mention for the
moment. Highs will be in the 60s.

Northwest upper level flow continues into Monday and Tuesday,
although by Tuesday, ridging to the west does nudge into the western
High Plains. Skies will clear out Sunday night, leading towards
sunny weather on Monday and Tuesday. Brisk northwest winds will
persist on Monday, with the strongest winds shifting into the
eastern half of the region. By Tuesday we start seeing return flow
developing, and winds decreasing in speed. Highs moderate into the
upper 60s to mid 70s on Tuesday.

Latest model runs bring stronger ridging into the Plains for
midweek, a change from model runs 24 hours ago. Seasonally mild
weather can be expected Wednesday and Thursday, with highs in the
70s. Prevailing dry conditions continue. Forecast model patterns
show some interesting differences late week, especially in regards
to the pattern across the eastern US. The GFS and ECMWF both place
the Plains into more of a southwesterly upper flow pattern, but lack
agreement in the timing and track of a wave lifting into the region
Friday/Friday night.  Will leave the low end pops in place for now.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1223 PM CDT Sat Sep 24 2016

18Z TAFs reflect showery conditions this afternoon with embedded
thunderstorms. Rainfall beginning to fill in across eastern
Nebraska at this time, and is heading northward. Therefore it
should affect the TAF sites for awhile this afternoon. VFR
conditions will be mixed with MVFR and possibly even short term
IFR conditions under the rainfall. Otherwise, there will be a
gradual eroding of the cloud cover from west to east through the
evening hours and into the overnight, providing VFR conditions for
a bulk of tonight. Cold air advection stratus clouds will then
move into the western half of the forecast area Sunday morning
providing MVFR cloud cover for KHON and KFSD.

&&

.FSD Watches/Warnings/Advisories...
SD...None.
MN...None.
IA...None.
NE...None.
&&

$$

SHORT TERM...JM
LONG TERM...
AVIATION...MJ


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