Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 260917
AFDFSD

Area Forecast Discussion
National Weather Service Sioux Falls SD
417 AM CDT Mon Jun 26 2017

.SHORT TERM...(Today and Tonight)
Issued at 417 AM CDT Mon Jun 26 2017

Scattered showers and a few thunderstorms will continue to drift
southeastward across our southern zones through the early morning
hours. There is clearly a vort filament extending across the
forecast area, especially through our eastern zones from north to
south in the morning hours. In addition, mid level QG forcing
is evident from 700-500mb departing northwest IA by 18Z, as well as
surface troughing extending eastward across far northern Nebraska.
As the morning progresses, mid level moisture wanes in our south
ending the rain threat, and surface high pressure oozes southward
keeping the air mass seasonably chilly. Will watch for the formation
of patchy fog as surface dew point depressions are very small early
this morning north of the clearing line. If any fog develops, it
will generally be along and north of I 90. Temperatures will mix to
above 850mb this afternoon, but soundings showing a fair amount of
cumulus popping from the James eastward, therefore highs will mainly
be in the upper 60s to mid 70s.

Not a lot going on tonight. Winds will shift to the southeast and
south, increasing a bit west of the James Valley later tonight.
Preferred bias corrected mos lows which showed a trend of chilly
lows in our east where winds will be the lightest, but milder
readings in our west with the stronger southerly winds.

.LONG TERM...(Tuesday through Sunday)
Issued at 417 AM CDT Mon Jun 26 2017

Main concern within the medium range this morning is the threat for
severe storms on Tuesday night and early Wednesday.

Increasing southerly jet will bring strong south winds to the area
on Tuesday, likely gusting in excess of 30 mph for most locations.
This will bring an increased transport of moisture into the region,
slowest in the east where trajectory remains a bit more out of the
exiting low-level ridge into early evening. With ridging aloft,
push of warmer temperatures and steeper 7-500hPa lapse rates will
keep chances for storms minimized through the day. However, still
will have to watch for a bit more elevated moisture to become
involved, for this could increase threat of a few mid-level
showers/storms during the afternoon as lapse rates in excess of
8C/km push through southeastern SD.  Somewhat limited mixing depth
with warming aloft makes for highs from upper 70s east of I-29 to
perhaps the mid 80s west of the James River.

Likely genesis region for convection will occur across western
portions of SD during the late afternoon into very early evening, in
lee of the Black Hills and along the frontal convergence as wave/jet
begins to punch into the ridge in the high plains. Environment
heading into the evening suggests elevated CAPE from 1500-2000 J/kg,
and the 45-55kt low-level jet stretching out low-levels in fairly
nice turning hodograph. Rooting out useful shear, looks like
effective values of 30-40 kt. As long as storms can work toward a
more elevated nature, should see maximized severe threat for large
hail and damaging wind west of the James Valley through the evening
hours, although the hail size will be increasingly limited by the
warm temperatures aloft as well as likelihood of more linear
structures/competing updrafts developing through the evening as
shear vectors remain aligned main along boundary.  Presence of the
warm and dry layer aloft will likely impede the strongest storm
potential heading eastward toward I-29 and beyond, and shear being
largely line-parallel will also lead to a decreasing threat of
severe wind gusts as likely MCS works eastward. Marginal threat
seems appropriate.

Some convection will likely be lingering into the morning around
northwest IA and southwest MN as low-level jet continues to veer, and
precipitation could come to a slightly more rapid end with effective
outflow boundary progressing along with wave and well ahead of main
synoptic boundary.  With passage of wave, more westerly component
should quiet down convective threat most areas, with perhaps a
limited chance through the afternoon across mainly northwest Iowa as
the boundary of more limited convergence presses through, but fairly
unlikely to modify airmass in wake of overnight/early morning
storms.  Behind the front, readings likely to reach well into the
80s through the western Missouri River corridor.

Boundary will continue to push southward through early Thursday,
south of I-80, but as another wave drops out of the Canadian Rockies
and into the northern plains later Thursday into Thursday night,
this should wander a bit more northward as low pressure organizes to
the south.  While impacts in terms of severe weather are likely to
remain south of the area later Thursday/Thursday night, there should
be an increase in potential for thunderstorms starting later
Thursday afternoon in the Missouri and James River areas, spreading
north and east across the area overnight.

Less confident in the overall pattern from Friday onward, as models
take closed wave through the Northern Plains in some way, shape and
form through Saturday. Run to run continuity could be characterized
as shaky at best. Precipitation is likely overdone Saturday and
Sunday, at least in coverage. Temperatures should start Friday as
the coolest day, then slight day to day warming through Sunday.

&&

.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1047 PM CDT Sun Jun 25 2017

VFR conditions are expected to continue through the TAF period.
Scattered to broken mid clouds streaming southeastward through the
region will bring some spotty light rain showers with isolated
thunder through around daybreak Monday morning. Winds will remain
less than 10 kt.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...None.
MN...None.
IA...None.
NE...None.
&&

$$

SHORT TERM...MJ
LONG TERM...Chapman
AVIATION...



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