Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 200352

Area Forecast Discussion
National Weather Service Sioux Falls SD
1052 PM CDT Sat May 19 2018

.SHORT TERM...(This evening through Sunday)
Issued at 337 PM CDT Sat May 19 2018

The strong upper-level trough over eastern Colorado has finally made
some progress and started to move northeast into Nebraska and
Iowa. Ahead of the main trough, a vortex max has lifting northward
into the area, bringing a line of showers along the Missouri
River and portions of northwest Iowa. The trend of precipitation
remaining along and south of I-90 remains valid as northern stream
and drier air aloft will continue to enable or weaken any
precipitation potential further north. In fact, CAMS and model
soundings indicate this line of steady showers will gradually
progress northward before becoming more scattered late tonight
into Sunday. Given mostly cloudy skies and weak instability,
thunderstorms seems unlikely across the area.

There could be a break in precipitation during the overnight hours,
specially in northwest Iowa, while the main upper trough approaches
the area early Sunday morning. This will bring period of showers in
evening and overnight hours, mainly along and east of I-29. In fact,
model soundings suggest better moisture and forcing with this round
of showers. Again with weak instability prevailing, looks to be
sporadic/scattered showers. Temperature-wise, Sunday will remain
slightly cooler due to mostly cloudy skies and north winds. Areas
across east-central SD could see some sunshine through the day,
therefore highs could reach the upper 60s to near 70.

.LONG TERM...(Sunday night through Saturday)
Issued at 337 PM CDT Sat May 19 2018

Behind this system, the work week looks warmer with multiple
chances of showers and thunderstorms. There will be a brief lull
in precipitation on Monday as an upper ridge builds over the
region; however unsettled conditions and warmer temperatures will
return Tuesday into the end of the week. Zonal to northwest flow
aloft will bring multiple impulses of energy, supporting chances
of showers and thunderstorms. With warmer temperatures and
increase in dew point values, models indicate an increase in
moisture and instability along with increasing precipitation
chances. As expected with this type of synoptic pattern aloft,
there is a lot of uncertainty in timing and coverage of
precipitation. At this point, better chances for precipitation
arrives Thursday night into Saturday, where models have some
agreement in a system moving through from the Northern Plains.


.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1043 PM CDT Sat May 19 2018

A tale of three terminals for the upcoming TAF period as the
region sees the back edge of a large area of MVFR ceilings
associated with an upper disturbance persist through Sunday. HON
looks to be VFR through the period. FSD has the toughest forecast
with the edge of the MVFR ceilings expected to be somewhere in the
vicinity. Have gone with the pessimistic outlook for now, thinking
the nighttime hours will bring a slight reduction in ceiling
heights to the MVFR level before recovering to low end VFR during
the day Sunday. SUX will be stuck in MVFR for the majority of the
period, with spotty showers expected overnight.




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