Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Sioux Falls South Dakota
1254 PM CDT Thursday Oct 8 2015
issued at 1027 am CDT Thursday Oct 8 2015
Two changes to the forecast today...1) more pessimism with degree
of cloudiness this afternoon and into the evening across the
North/East...and 2) addition of a bit stronger precipitation mention
across the west/south.
Surface frontal zone has pushed through the entire County Warning Area at this
point in the morning...as main upper wave is now pushing through
the northern Great Lakes. Another upstream jet streak digging
across Montana...and this impulse will push east/southeast into
the Central Plains tonight. A fairly broad area of middle level
frontogenesis links the two features...and have seen a scattering
of very light returns across southwest to central South Dakota through the
early morning. Fairly unlikely for measurable precipitation with
a fair degree of drying below the middle layer. Some of this will
likely clip the far southwest County Warning Area middle morning to early afternoon
before slipping southward. Better upper forcing looks to trend
just a bit south of the Missouri River late afternoon and early
evening...and given the continued influx of drying below the middle
deck...will forego adding in any mentionable later day/early
evening probability of precipitation to the lower Missouri Valley at this time.
Otherwise...area of stratus across all but far western North
Dakota and progression has been to encroach into north central and
northeast South Dakota through middle morning. Flow below inversion
starts to take on more of a northerly component and rap/NAM/hrrr
indicate that a fairly distinct layer of lower clouds will likely
become a stronger feature through the afternoon east of the
Missouri Valley...and perhaps well into the evening east of I 29.
Still looking at 20 to 30 knots of wind in mixed layer this
afternoon...so current wind gusts expectations on track. With
abundance of clouds...did notch back high temperatures a bit...or work in
a steadying to slight fall across the North/East during the
afternoon. Many locations mixing behind boundary and should
approach highs prior to advance of stratus field from the north.
Short term...(today and tonight)
issued at 303 am CDT Thursday Oct 8 2015
As the front finishes moving southeastward across the area next few
hours...it is still not completely out that isolated showers or
storms could develop in the lingering instability...and with a few
narrow bands of middle clouds/possibly altocumulus castellanus moving over the
eastern/mainly southeastern part of the area. The hrrr keeps
trying to develop scattered activity but it looks more like
isolated if anything. This should all be out by 12z/7 am CDT.
The area of middle level moisture drifting across western South Dakota
could still bring isolated light showers as it moves southeast...and
this could include the far southwest corner of our area during the
day...so have left the small probability of precipitation in...although there is a case for
going with just sprinkles. The cloud deck of course will reach
somewhat further north/northeast over the area before decent
clearing late in the day and this evening.
Northwest winds will reach the breezy category today with winds
slightly stronger east of the James River than west. Highs will reach
the lower 60s north to the lower 70s southeast...or not too much
warming from the very mild early morning temperatures over the area.
The clearing tonight will be accompanied by decreasing winds. Lows
will be in the upper 30s north to low 40s south...again holding
above frosty levels.
Long term...(friday through wednesday)
issued at 303 am CDT Thursday Oct 8 2015
Rather quiet weather is still expected through the medium and
extended portions of the forecast. Temperatures remain on track to
surpass seasonal normal by 10 or more degrees this weekend...with
very balmy overnight temperatures into early next week.
Only reasonable chance for precipitation would fall on Sunday night
into Monday as a rather strong shortwave zips through the region. A
system cut-off from gom moisture...it will have to rely solely on
moisture it can drag across The Rockies from the Pacific northwest.
For now...prefer the drier GFS over the European model (ecmwf). Both models do
suggest very light rain potential over the northern half of South Dakota
into central Minnesota into Monday morning. Likely the big story for
Monday will be very blustery conditions. Should see sustained
winds push 20-30 miles per hour through the first half of Monday...occasional
gusts could push 40 to 45 miles per hour as we quickly mix out Monday
morning. Have bumped up wind speeds in that portion of the forecast.
Through the middle and end of next week...a continued warm pattern
will persist. Temperatures will continue to average 5 to 10 degrees
above seasonal normals with dry weather anticipated.
Aviation...(for the 18z tafs through 18z Friday afternoon)
issued at 1254 PM CDT Thursday Oct 8 2015
Area of MVFR ceilings across eastern North Dakota and northeast
South Dakota will cycle southeast across the area through the
afternoon and evening...slowly dissipating on the back edge from
west to east through the later afternoon and night. Most certain
for impacts at khon in the immediate term...and kfsd from middle
afternoon through the evening. Ksux would appear to be just
outside a more certain trajectory...and have kept lower clouds
scattered at this time from late afternoon through the early
overnight hours. Otherwise...surface wind gusts will occasionally
attain around 25 knots through the afternoon.