Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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FXUS63 KFSD 252029

Area Forecast Discussion
National Weather Service Sioux Falls SD
329 PM CDT Tue Oct 25 2016

.SHORT TERM...(This evening through Wednesday)
Issued at 330 PM CDT Tue Oct 25 2016

Afternoon water vapor loop showing a somewhat disjointed full
latitude trough moving out of the Rockies this afternoon, with
energy centers across western North Dakota and another stretching
center pushing into the central high plains.  Each has induced an
areas of surface low pressure, more broad on the northern front and
somewhat more supported toward western Kansas.  Much of the area has
been quiet through the day with a few showers brushing along the
Highway 14 corridor during the later morning, but more or less has
been generally a lot of cloudiness with just a few breaks here and
there concentrated around the Missouri river valley. Temps have
responded well to even limited sunshine warming into the lower to
mid 60s, while mainly 50s under thicker shroud of clouds. On either
front, these temps are far from those required for diurnal
convective initiation, which is well-capped yet at this point by a
warmer and unstable layer for areas north of the warm front crawling
northward toward I-80 where readings have reached the 70s and
approaching 80 in some spots.

High resolution models have been quite good with showing the delay
to precip onset through the bulk of the day, and have been fairly
consistent run to run in location despite a bit of continued slowing.
Will see the convection across parts of northern/central South
Dakota begin to sink southward toward the northern CWA.  By very
late afternoon, the warm advective wing could start to initiate a
rogue elevated shower or thunderstorm across northwestern Iowa
toward eastern portions of southwest Minnesota. Gradually, deeper
lift forcing with the northern mid level trough will increase as
trough starts to dig toward Minnesota this evening, with an increase
in the leading warm advection which should initiate a more
widespread coverage of convection by early to mid evening through
areas near/east of I-29. Overall, shear with even fairly weak flow
is decent for a 1-2km AGL elevated parcel, reaching 25 to 35 knots
in the 2-5km layer. Elevated mixed layer yielding a fairly thin
instability profile with a magnitude from 500-800 J/kg, not
excessive by any means. Any of a very small severe threat would
likely be limited to the early to mid evening hours mainly across
parts of northwest Iowa, would remain fairly isolated, as well as
one-dimensional in terms of a marginal large hail threat. The most
significant rainfall is likely to be across parts of SW Minnesota
into NW Iowa, averaging a half inch to inch near/east of Highway 59.

On Wednesday, the main surface wave will continue to wind up and
trek eastward across Iowa. An inverted trough will extend back into
the heart of the CWA, and likely that a widespread mass of lower
clouds will plague most of the CWA into midday before some mixing
along the dissipating trough axis starts a better erosion process.
Maintained a small area of light shower threat early in the day
before larger scale subsidence/cold advection ceases any residual
lift with departing trough in shallow moist layer. Clouds may be
hard to eliminate from parts of southwest Minnesota and northwest
Iowa even by late afternoon. As a result, with the smaller area of
cooler air wrapping in behind the area of low pressure along with
the abundance of clouds, there should be a fairly large difference
in afternoon temps, from 40s in parts of southwest Minnesota to mid
60s in south central SD.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 330 PM CDT Tue Oct 25 2016

There really is not much of a significant weather threat for our
area for the Wednesday night through Tuesday period. It looks like
dry weather will be the rule, with upper ridging and warming late
this week followed by weekend cooling behind a front, then a start
to warming again Monday, but another wave could stop the warming by

There is a question of patchy fog potential Wednesday night in the
eastern part of our area, mainly northwest Iowa. For much of the
night winds will be light, but some lingering clouds from the
previous system, and the start of a warming flow before daybreak
Thursday, appear to minimize the threat, and have decided to leave
fog mention out.

Have gone with the guidance mention of a minimal chance of showers
far north...Huron SD to Brookings SD to Marshall MN with the cold
front Saturday...and another low mention with a westerly wave Sunday
night and Monday, again mainly north and northeast. But overall, as
mentioned above, dry weather should be the rule. Lift and thermal
support with the weak systems should be very modest, and there does
not appear to be any decent moisture advection in the cards.

The strongest winds appear to be getting to the breezy levels in the
east on a warm Friday just ahead of the weekend cold front, with
some fire weather concerns if moisture levels go low enough. The
cooling winds Saturday should be modest. Currently looking modest
winds early next week could turn out a bit stronger if future runs
strengthen the modest wave currently depicted for Monday.

Temperatures will continue to run at or above normal. The warmest
day looks to be Friday, with plenty of 70s likely, while 50s north
to 60s south looks to be the coolest for the weekend and possibly
next Tuesday. When we are in the last week of October and going to
the first day of November, and there are no freezing temperatures in
the forecast, it is definitely mild.


.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1250 PM CDT Tue Oct 25 2016

Disturbance pushing out of the Rockies will increase lift across
the area late today, and perhaps some spottier precipitation
favoring areas toward KHON late afternoon is expected to begin to
break out in a more widespread fashion within 00z-03z window
closer to and east of the I-29 corridor. Ceilings will become more
widespread and lower from the lower end VFR into the MVFR range as
precipitation develops. Gradually, low pressure winding up south
of the area will draw back the lower clouds south and westward
toward location of inverted trough across the far western/southern
CWA through the latter half of the night. This inverted trough
will linger back through the James Valley through the morning, and
to the east will be a bit of a struggle to work out of the lower
clouds, outside some mixing of drier air aloft to raise or break
ceilings along the weakening boundary.




SHORT TERM...Chapman
AVIATION...Chapman is the U.S. government's official web portal to all federal, state and local government web resources and services.