Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 272059

Area Forecast Discussion
National Weather Service Sioux Falls SD
359 PM CDT FRI MAY 27 2016

.SHORT TERM...(This evening through Saturday)
Issued at 359 PM CDT Fri May 27 2016

Upper trough is currently extending from southwest Neb to central
KS, and will lift northeastward squarely across the forecast area
very late tonight and Saturday. The is evidenced by both the middle
and upper level QG forcing vectors. In the near term, isolated
skittish showers and thunderstorms will be a threat through about
sunset due to persistent thetae advection. But overall between 7pm
and midnight, the weather should actually be pretty quiet this
evening as the heating wanes. Later tonight ahead of the
aforementioned upper trough, thetae advection increases again and
lingers through the day Saturday as the trough moves through. Some
low level frontogenesis is maximized close to the I 29 corridor late
tonight and Saturday just to the north and west of surface low
pressure also edging northeastward. On the backside of this low,
thetae ridging is pretty persistent, so would not rule out pockets
of heavy rainfall, especially noting light mid level winds,
generally throughout the eastern half of our area east of the James
River valley. That said, the warm cloud depth is relatively shallow
and the low level dew points are not excessively high. So not
expecting widespread heavy rainfall, but as mentioned, localized
moderate to heavy rainfall is quite possible late tonight and
Saturday before all is said and done.

Soundings are exhibiting thin cape by late tonight and Saturday with
not a huge amount of instability. In fact conditions become fairly
stable by Saturday afternoon. Therefore not expecting anything in
terms of severe weather, but it will be wet perhaps knocking a lot
of outdoor activities out of action on Saturday. Lows tonight will
mainly be in the upper 50s, followed by highs on Saturday a couple
of degrees either side of 70.

.LONG TERM...(Saturday night through Friday)
Issued at 359 PM CDT Fri May 27 2016

Upper wave exits to our east Saturday evening, leaving generally dry
conditions for Sunday as shortwave ridging moves over the region.
This should make Sunday the nicest day of the holiday weekend, with
mostly sunny skies, light winds, and highs near 80.

Unfortunately, this will change for Memorial Day. Models still not
in complete agreement on timing/location of fine details. However,
broad consensus shows mid-upper level trough approaching from the
west, with a weak warm front lifting north into the forecast area
during the day. With moisture pooling near/south of the boundary,
and timing of the upper support, felt comfortable bumping pops into
likely range over northwest Iowa by Monday afternoon. Higher precip
chances will then continue along/east of Interstate 29 Monday night
into Tuesday, although by Tuesday the upper pattern becomes much
more muddled as models begin to suffer from apparent convective
feedback. As for severe threat during this time, increasing moisture
and high temperatures again pushing 80 degrees will allow for modest
instability Monday. However, deep layer shear less than impressive
across our forecast area Monday/Monday night, and thus think severe
threat will be minimal.

GEM/ECMWF appear to be in better agreement through the longer range
portion of the forecast, swinging an upper trough slowly eastward
near the Canadian border Wednesday, then lagging said trough over
Ontario through the end of the week while an upper ridge builds over
the Rockies. Drier air works into our forecast area around the south
side of this system, resulting in little if any precip chance for
Wednesday through Friday. GFS, on the other hand, develops stronger
trough which gets cutoff over the central Plains by Thursday, with
periods of showers and/or thunderstorms as shortwaves rotate around
the low. Will hang on to some of the low pops from consensus blend
through this period for now...but given that this solution is an
outlier even among many of the GFS ensemble members, feel the latter
half of the week more likely to be dry. Temperatures will be cooler,
with highs generally in the 70s and lows in the lower to mid 50s.


.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1232 PM CDT Fri May 27 2016

The near term will be highlighted by lower end VFR to MVFR
ceilings. There is a risk of an isolated thunderstorm near KHON
into early this afternoon. By late this afternoon and this
evening, the various nam and gfs moisture fields are suggesting
primarily VFR conditions. However beginning at midnight, a
disturbance will move northward, likely producing a round of
thunderstorms at KSUX and KFSD for a few hours. This could
certainly bring conditions down into the MVFR category with
pockets of moderate to heavy rainfall. For now, left this kind of
activity out of the KHON TAF site as it appears it may remain east
of there. From 12Z to 18Z Saturday, stability begins to increase.
Most of the rainfall should be north of KSUX, impacting the KFSD
and KHON taf sites. However left TSRA out of these two sites for
Saturday morning but with plenty of MVFR conditions.


.FSD Watches/Warnings/Advisories...


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