Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 192107 CCA
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
307 PM CDT MON SEP 19 2016

.SHORT TERM...(This evening through Tuesday)
Issued at 306 PM CDT Mon Sep 19 2016

A very pleasant evening ahead as winds go light and gradually turn
to the south. The only thing of interest overnight will be a weak
wave moving across North Dakota which will force the mid level winds
from the west to the southwest. This will bring winds parallel to
the mid level thermal boundary and could cause scattered showers to
develop. Model soundings near highway 14 even hint at a little weak
instability so thunder will not be impossible, but a fairly low
threat so will not include in the forecast. Otherwise with light
winds and a dry air mass lows will cool into the 50 to 55 degree
range in most locations.

This small threat for showers will likely remain to the north of
highway 14, but a few sprinkles, similar to this morning, could creep
towards interstate 90. Southerly winds will increase through the
morning with a few gusts to 25 at times likely. It will be another
warm day with highs in the 80s.

.LONG TERM...(Tuesday night through Monday)
Issued at 306 PM CDT Mon Sep 19 2016

Low pressure aloft will move across the area on Tuesday
afternoon, then another wave will arrive from the southwest late
Tuesday night. This will bring a threat for thunderstorms as the
low level jet focuses on parts of northwest Iowa and southwest
Minnesota. Initially during the late afternoon and evening the
atmosphere looks capped so development might be difficult. The
better chances through the night will likely remain north and east
of the Buffalo Ridge which is on the east edge of the stronger cap
aloft.

The surface boundary begins to become more organized on Wednesday,
mainly over the central parts of SD. A moist northeast flow at the
surface begins to develop over northeast SD on Tuesday night and
slowly works towards highway 14 by mid day. With warmer air likely
to work north through the day as the cooler surface air works south,
once any stratus develops along and behind this front it will be
tough to erode as this warming above the cooler surface air
continues into Thursday. With this boundary around Tuesday through
Friday there will be potential for some larger temperatures swings
as the differences across the boundary are likely to be about 15
degrees.

The thunderstorm threat will remain across areas along and east of
Interstate 29, but as a wave moves into eastern Nebraska Wednesday
afternoon the threat for thunderstorms will increase, with the
better chances from about 23z through 6z. Instability is potentially
very high, 3000 J/kg to 4000 J/kg with somewhat uniform but not
overly strong shear, especially from 3km to 6km. This might support
briefly fairly strong storms.

Higher confidence in stratus on Thursday over a larger area as Nam
and even the too warm and dry GFS both showing a fairly deep stratus
layer around 900mb or so. With a more widespread stratus field along
and north of the boundary dropping south high temperatures will
likely struggle to get out of the 60s. The exception will be
locations south of the boundary, likely from around Yankton to the
Iowa Great Lakes where temperatures could soar to near 80.

The low pressure to the west is acting much differently than
yesterdays runs, so confidence in Friday and Saturday a little low.
Overall looks like normal to above normal temperatures with chances
for thunderstorms.

For Sunday into Monday, luckily at this time the models have trended
away from the potentially very cool pattern early next week. Instead
of leaving upper level low pressure over the northern plains, the
models now shift this upper low into southern Canada which brings
mild westerly flow to the area. There should be a lingering chance
for showers on Sunday otherwise highs both days should be in the
upper 60s to mid 70s with lows from the upper 40s to lower 50s.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1213 PM CDT Mon Sep 19 2016

VFR conditions will prevail through the TAF period. There could be
a few isolated showers near KHON site between 07Z and 11Z, but
ceilings and visibility will remain within the VFR parameters.

&&

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

$$

SHORT TERM...08
LONG TERM...08
AVIATION...JM5



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