Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 140453

Area Forecast Discussion
National Weather Service Sioux Falls SD
1053 PM CST Tue Feb 13 2018

.SHORT TERM...(This evening through Wednesday)
Issued at 257 PM CST Tue Feb 13 2018

Breezy southerly winds and sunny skies have boosted temperatures
this afternoon over readings this time yesterday although widespread
snow cover have somewhat dampened the overall warm up. This low
level southerly flow and persistent warm air advection should keep
overnight low temperatures from falling too low, generally in the
mid teens to low 20s. There is still some indication in the high
resolution guidance of fog potential overnight, and given moisture
advection and some snowmelt due to the sun today, went ahead and
added patchy mention. Confidence in its occurrence and extent is
low though.

For Valentine`s Day, the region sits on the northern edge of the jet
stream with an elongated string of mid level waves moving from west
to east across the region. The moisture profile aloft is much too
dry to be concerned with any precipitation chances and in turn,
expect a good deal of sunshine through much of the day Wednesday. By
the afternoon hours, 925 mb temperatures sit in the +2 to +9 C range
which should translate to above normal temperatures with many
locations rising into the upper 30s to low 40s for highs.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 257 PM CST Tue Feb 13 2018

Our warm up will be short lived as an upper level trough pivots
through the western CONUS and drives a cold front through the region
by Wednesday night and Thursday. With strong cold air advection
behind this front, expect breezy to gusty northerly winds Thursday
and Thursday night and have bumped winds closer to CONSMOS over the
populated guidance. With overnight lows also plunging back near
zero, could run into some wind chill concerns. Additionally, could
see some light snow along the mid level baroclinic zone ahead of an
incoming PV anomaly. This precipitation seems to be primarily
focused across our northwestern half CWA and any accumulations
should be light (under 1 inch).

By Friday, we are back under our all to familiar northwest flow
aloft with temperatures below normal, generally in the upper teens
to mid 20s...a bit warmer across south central SD. The roller
coaster ride of temperatures continues though as low level winds
shift back out of the south and drive some warmer temperatures
into the region in time for the weekend. Some of the 12z guidance
is advertising a quick moving wave which could dent this warmth
for Saturday and could even be accompanied by some light
precipitation. This is not well supported by the ensembles and
thus some uncertainty exists. Sunday is still expected to be near
or above normal in regards to high temperatures.

Models continue to struggle with the evolution of the western
trough for early next week with the ECMWF more amplified than the
other deterministic models and GFS Ensemble. This evolution and
the overall flow will be important for any sensible weather and
thus will stick with blended guidance until model agreement is


.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 1053 PM CST Tue Feb 13 2018

Patchy MVFR to localized IFR visibility in fog is possible tonight
through mid-morning Wednesday. Confidence in the favored location
for development tonight is low, so will have minimal mention in
the TAFs at this time.

Any fog tonight should diminish after 15Z, but mild temperatures
leading to snowmelt Wednesday, and light winds Wednesday night,
could result in more extensive fog development beginning near the
end of this TAF period, mainly across northwest Iowa. Confidence
in the timing of development is moderate, so may introduce MVFR
visibility in KSUX late in the TAF period.

Some models indicate a potential for low level wind shear south of
I-90 during the day Wednesday as westerly flow increases atop a
strong inversion maintained by these models. However, current
thinking is the inversion will not be as robust as these models
indicate, and thus will not have any mention of low level wind
shear. Pilots will still want to be aware of a gradual increase in
wind speeds through the lowest 1-2kft.




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