Scientific Forecaster Discussion
fxus63 kfsd 130501
Area forecast discussion
National Weather Service Sioux Falls South Dakota
1101 PM CST Tue Dec 12 2017
Short term...(this evening through wednesday)
issued at 243 PM CST Tue Dec 12 2017
A series of clippers moving through the northern plains mid-week
will bring a typical mixture of temperature variance, strong winds,
along with light winter precipitation risks. Generally, only minor
deviations to the ongoing forecast through the next 48 hours as
models has remains fairly consistent.
This afternoon and tonight: light southwesterly winds are pushing
warmer air slowly northeast with highs in the 50s in the
southwestern corner of the County Warning Area and temperatures in the middle 30s
over the Buffalo Ridge. Guidance continues to show clipper currently
over Alberta dropping southeast overnight, with sfc low pressure
forming over eastern ND by midnight. Warmer westerly surface flow
will prevent any large drop in overnight lows, and we may see a
quick jump to surface temperatures after midnight and through
daybreak before a weak sfc trough moves through.
Wednesday: as the sfc low track southeast down Interstate 94, the
initial sfc trough will usher in strong winds by daybreak. Low
level flow at the top of the mixed layer will approach 50-55 knots
prior to and after daybreak and continue through the middle of
the day, with surface pressure gradient and downward momentum
Transfer supporting fairly widespread 40 to 50 mph winds through
the day. A Wind Advisory will be issued for the entire forecast
area. Winds can frequently surge ahead faster than model guidance
suggests with these clippers, so have bumped start time a little
earlier to have a bit of wiggle room.
Accompanying the wind will be two areas of light precipitation, one
area tied more directly to the upper jet over eastern and northern
Minnesota, and a second tied more closely to positive vorticity advection from the mid-level
shortwave in central and eastern South Dakota. Thermal profiles support an
area of scattered precipitation lagging behind the strong corridor
of wind, likely in the form of very light rain mixed with a bit of
snow. Moisture profiles are rather disappointing which is likely the
reason for the minimal amount of quantitative precipitation forecast in guidance west of I-29.
Moisture is a little better along the Buffalo Ridge areas through
mid-morning which would support the slightly higher pops. After the
first wave moves through, soundings really dry out, with only a
narrow moist layer along the Buffalo Ridge counties centered around
900 mb. The lack of ice crystals early in the afternoon could
support very light drizzle/sprinkles, but have concerns the depth
and lift within that moisture layer is just too thin to even produce
precipitation. Secondary lift from a southwestward sinking pv layer
could be strong enough for a bit of light snow late in the afternoon
as soundings show a bit more depth to moisture. For temperatures,
have maintained trends towards warmer than normal guidance through
the day. Minimal cold air behind this system, combined with a bit of
a westerly component over snowless ground in the western Dakotas
should allow temperatures to push or linger into the mid 30s well
through the day.
Long term...(wednesday night through tuesday)
issued at 243 PM CST Tue Dec 12 2017
Thursday: a second shortwave begins to enter the area early on
Thursday, tracking over the western Dakotas. The best chance for
any light precipitation will be west of the James River Valley.
Depending on temperatures, some areas could see minor snow
Friday-sunday: models continuing to struggle to come to a common
solution, but the consensus is continuing to show mostly dry
condition and a continuation of warmer temperatures. As flow
becomes more progressive in nature, we'll have shortwave ridging in
the area for Friday. A good southwest wind fetch should bump
temperatures well above normal on Friday. As troughing swings
through the region on Saturday, we'll have a cold front pass
southeastward, but again, minimal moisture and cold air results in
temperatures holding above normal. Sunday will return to westerly
flow and warmer than normal temperatures.
Monday-tuesday: warmer than normal temperatures and a fairly high
likelihood of dry conditions continue as we start out next week.
Aviation...(for the 06z tafs through 06z Wednesday night)
issued at 1056 PM CST Tue Dec 12 2017
Cold front working through the area. Behind the front, winds are
rapidly increasing aloft, and will mix to the surface on
Wednesday. Stratocumulus is expected to develop Wednesday morning
in the 2500-3500 foot range. Strong northwest winds will decrease
South Dakota...Wind Advisory from 6 am to 6 PM CST Wednesday for sdz067-070-071.
Wind Advisory from 4 am to 3 PM CST Wednesday for sdz038-050-052-
Wind Advisory from 6 am to 3 PM CST Wednesday for sdz039-040-
Minnesota...Wind Advisory from 6 am to 6 PM CST Wednesday for mnz072-080-081-
Wind Advisory from 6 am to 3 PM CST Wednesday for mnz071-097.
Iowa...Wind Advisory from 6 am to 6 PM CST Wednesday for iaz001>003-
NE...Wind Advisory from 6 am to 6 PM CST Wednesday for nez013-014.