Area Forecast Discussion
Issued by NWS Sioux Falls, SD
FXUS63 KFSD 161726
Area Forecast Discussion
National Weather Service Sioux Falls SD
1226 PM CDT Sun Oct 16 2016
Issued at 904 AM CDT Sun Oct 16 2016
Based on current HRRR and RAP output, as well as current trends
off of the VIS satellite now that it is getting light enough to
look at it, decided to extend the dense fog advisory into Buena
Vista and Ida counties in northwest Iowa, as well as Yankton
county in southeast SD. There are indications that the dense fog
could drift northward into Hutchinson and Turner counties also.
However did not put them in a headline for now as am a bit
concerned about mixing potential late this morning helping to
scour the worst of the fog out in those areas. But would not rule
out some dense fog in Hutchinson and Turner at least in the
southern areas. Also extended the headline until noon.
.SHORT TERM...(Today and Tonight)
Issued at 427 AM CDT Sun Oct 16 2016
Complex forecast ahead through the next 24 hours, mainly due to
impact of lower clouds and fog. Frontal boundary which passed
through the area yesterday has slowed/stalled just south of the CWA,
with near-surface moisture pooled near boundary. Fog and low clouds
have spread back into parts of northwest Iowa after 06z across Ida
County and neighboring areas. Light near-surface flow starting to
lose its slight northerly component and thus has shown signs of
pulling a bit more rapidly west and northwest over the last hour or
so. Earlier issued a dense fog advisory through into mid-morning for
areas near/east of Sioux City, but behavior of high-resolution
solutions would suggest will need to expand north/west from this
sooner rather than later, taking severely reduced visibility and
very low ceilings all the way to KMHE and even north of there by mid
morning. Even if fog begins to dissipate, the strong inversion will
mean considerable low clouds which will wedge across much of the CWA
except the far west, and take much of the day to expand to the far
east around KMJQ and KMWM. Some significant concerns that
persistence of fog and lower clouds will have a stronger impact on
high temperatures, but profiles indicate that will have at least
upper 60s to lower 70s even under clouds.
Otherwise, warm advection across the far western CWA producing a few
light echoes on radar west of K9V9. So very dry below deck of mid to
high clouds that have not bothered to add even any sprinkles as weak
lift forcing builds east/northeast toward KBKX through the morning.
Strong surface gradient will increase south to southeast winds,
which could reach gusts to 30 to 35 mph west of I-29 during the
midday and afternoon. With humidity levels somewhat higher, fire
danger will remain restrained, with caveat of harvesting activities
having a heightened risk.
NAM is by far most aggressive with development of some instability
by very late afternoon and especially early evening across parts of
SW MN. Most other solutions indicate that moisture will remain
largely below the strong inversion, and useful only for stratus and
perhaps as moisture deepens toward evening of a couple of sprinkles
as again find a small bit of positive area in profile below the
inversion. Will keep some lower pops mainly parts of SW MN and NW
IA during the evening, but indications are anything more organized
or significant is likely to develop just north/east of our CWA
across Minnesota was wave moves past the area during the early
Frontal boundary associated with stronger wave north of the area
tonight will drop southeast, and result may be an attempt to do the
fog and low clouds thing all over again. Have included some post-
midnight areas of fog mainly southeast of a KMWM to KYKN line.
Mid-level frontogenesis increases by late tonight along areas toward
KHON, but again appears quite dry below any mid cloud deck to
preclude any mention of precipitation.
.LONG TERM...(Monday through Saturday)
Issued at 427 AM CDT Sun Oct 16 2016
Monday will be a warm day as a wave passes and cooler air begins to
work south. Ahead of this front winds will be mainly less than 15 mph
and temperatures will warm into the 70s. Some warmer readings and
slightly breezier conditions will be likely along the Missouri River
into south central SD where readings closer to 80 will be possible.
Monday night into Tuesday some marginal saturation aloft and mid
level thermal band will provide a threat for showers. Will keep the
chances along and north of Interstate 90 with the better chances in
southwest Minnesota. Monday night northwest winds may become a bit
breezy but models have been a bit off on timing of this boundary so
how long the breezier conditions continue into Tuesday is a bit up
in the air. Needless to say winds do not appear as though they will
be as strong as previously thought. Highs Tuesday should top out in
the mid to upper 60s.
Wednesday will see a reinforcing shot of cooler air as an upper
level wave passes to the south. Will maintain some lower chances for
rainfall south of Interstate 90 but not anticipating too much in the
way of weather. Otherwise with the cooler air highs Wednesday will
be a bit below normal while highs Thursday will be another 5 degrees
or so cooler.
Made some modifications to temperatures Friday and Saturday. The
inherited temperatures seemed to cool and were likely a remnant from
the deep low that the GFS had on previous runs across eastern Iowa
into Illinois. If the latest EC and GFS verify Friday and Saturday
will likely be another 5 to 10 degrees warmer than forecast,
especially Friday. Far enough out that it is not realistic to go
that much warmer given timing and placement problems in the models.
At this time not anticipating any precipitation potential Friday and
.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1221 PM CDT Sun Oct 16 2016
This afternoon, there will be lower end MVFR to upper end IFR
conditions very near and on the KSUX TAF site which will
negatively impact aviation. In addition, the stratus could
certainly move northward later this afternoon producing some
temporary MVFR ceilings at KHON, and lower end MVFR to IFR at
KFSD. Tonight, the KFSD and KSUX TAF sites are most concerning.
There are indications that as the mid level wave moves eastward
tonight, that low ceilings could scour out at these TAF sites.
However as the associated surface boundary tries to move eastward,
it will hang up and basically stall out in our forecast area
leaving a mass of residual low level moisture to contend with.
Therefore am very concerned about fog development at KFSD, and
even more acute conditions at KSUX. If the fog becomes thick
enough, it of course will create its own LIFR ceilings. The
details in exact confidence are not overly high, but it is
definitely a concern. VFR should then return by late morning