Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 232332

Area Forecast Discussion
National Weather Service Sioux Falls SD
632 PM CDT Mon Oct 23 2017

.SHORT TERM...(This evening through Wednesday)
Issued at 401 PM CDT Mon Oct 23 2017

Decided to extend the wind advisory for southwest MN and our eastern
section of northwest IA into tonight and Tuesday. Second surge of
cold air advection from 925-850mb moves southward tonight,
increasing dramatically between 03Z and 06Z and continuing through
much of the night. With 40 knots at the top of the mixed layer
across our eastern zones tonight, that will likely be enough to
agitate the winds into advisory criteria, especially noting the
higher terrain areas in southwest MN and northwest IA which lend to
increased winds anyway. That said, there will likely be a drop off
in winds this evening before increasing again overnight. However did
not end the current advisory for our eastern zones for simplicity.
Late tonight and early Tuesday, wind speeds could be below wind
advisory criteria again before deep layer mixing increases them
again in the late morning and afternoon. The question was how far
west to extend tonight and Tuesday`s advisory. Decided against areas
along and west of Interstate 29 as the gradient slackens off on
Tuesday in those locations, as well as the winds aloft. At any rate
it will still be windy for our western zones as the upper trough is
showing a PV surge at the 1.5 pressure level of 500-400mb. Would not
rule out a few hours overnight tonight of reaching advisory wind
speeds for along and west of I 29 at the height of the cold air

Mentioned some sprinkles or light showers for locations generally
along and west of the I 29 corridor for this evening. A vort
filament is advancing eastward coinciding with an 850mb baroclinic
zone. With some temperatures close to their convective temperature
this evening as cold air advection moves in aloft, cannot rule out a
few sprinkles or light showers. Otherwise lows tonight will stay in
the 30s due to mixing, and another windy and well mixed day on
Tuesday will produce highs in the in the upper 40s to mid 50s.

On Wednesday, winds will be reduced and from a southwesterly
direction. Therefore raised high temperatures a category above
superblend highs due to the mixing and favorable wind direction.
Should actually be a pleasant day.

.LONG TERM...(Tuesday night through Monday)
Issued at 401 PM CDT Mon Oct 23 2017

The next strong upper trough moves across this area late Wednesday
night and Thursday. It actually depends on what model you believe
in. The GFS, GEM Global and NAM are all in one camp in showing the
upper trough being very progressive. The ECMWF is not as progressive
and slows the trough passage as it digs southward through the
plains. Taken literally, the ECMWF would give light snow east of the
James River valley late Thursday night and Friday with -6 to -8C at
850mb, and -12 to -14C at 700mb. Southwest MN would receive a couple
of inches of snow with lighter amounts elsewhere. As stated above,
the other models do not back this up, with basically nearly a dry
frontal passage aside from some low pops warranted for light rain or
snow across the eastern reaches of southwest MN. Therefore we
will just keep an eye on this and see which solution ultimately
wins out. But right now the ECMWF is the odd model out.

One thing very certain is Thursday will be another very windy day as
the GFS is showing its PV surge down toward 550mb. Superblend winds
with its bias correction were too low, therefore blended a lot of
MOS winds in with superblend to increase speeds at least into the 25
to 40 mph range. If the ECMWF is correct with its digging upper air
pattern, Friday will also be cold and windy. Raw ECMWF highs on
Friday were only in the mid to upper 30s. But since that solution
was not followed, stayed with superblend highs which themselves are
only in the upper 30s to lower 40s and breezy winds in our eastern
zones of 15 to 30 mph. Highs on Thursday are tricky in how quickly
the cold air advection pours in versus the deep degree of mixing.
Therefore definitely trended to superblend on Thursdays highs also.
After Friday, it does not really warm up too much this weekend
with seasonably cool temperatures continuing. There is a big
question mark in terms of very light rain or snow next Sunday
night in our eastern zones with a lot of model discrepancy by
then. Therefore only low pops are warranted.


.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 630 PM CDT Mon Oct 23 2017

Strong northwest winds will prevail through the TAF period. A
secondary cold front will work through the regou towards midnight
leading to an up-tick in wind speeds. Winds will become
increasingly gusty during the day on Tuesday with mixing drawing
momentum from aloft. With mixing, could also see a scattered
cumulus deck develop.


SD...Wind Advisory until 7 PM CDT this evening for SDZ038>040-050-

MN...Wind Advisory until 7 PM CDT this evening for MNZ098.

     Wind Advisory until 6 PM CDT Tuesday for MNZ071-072-080-081-089-

IA...Wind Advisory until 7 PM CDT this evening for IAZ001-012-020-031.

     Wind Advisory until 6 PM CDT Tuesday for IAZ002-003-013-014-021-

NE...Wind Advisory until 7 PM CDT this evening for NEZ013-014.



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