Scientific Forecaster Discussion
fxus63 kfsd 121113
Area forecast discussion
National Weather Service Sioux Falls South Dakota
513 am CST Tue Nov 12 2019
Short term...(today through wednesday)
issued at 215 am CST Tue Nov 12 2019
Clear skies, light winds, and an anomalously cold air mass for early
November is leading to very cold temperatures this morning. Several
locations below zero with most areas hovering just above zero. The
main concerns in the forecast are focused around precipitation
chances Tuesday night into Wednesday.
Today: strong low level warm advection will commence after
daybreak, as low level winds turn southwesterly. Soundings suggest
mixing up to around 900 mb this afternoon, where a Stout layer of
winds around 30 knots prevails. Gusts this afternoon approaching
30 knots will promote some warming, with temperatures in south
central South Dakota in the 40s. Further east, we'll really struggle to
reach the middle to upper 20s. Throwing in a gusty wind, and wind
chill values through the day only reach the single digits.
Tonight-wednesday: persistent mixing through the night along with
increasing cloud cover will prevent any extreme fall in temperatures
tonight. A shortwave approaching the area after midnight will induce
a risk for precipitation after 3am. Models still struggling to
resolve low level moisture and warm nose with this shortwave. With
the broad and somewhat unfocused lift with the shortwave, the result
is model quantitative precipitation forecast all over the place. That said, this could be a good
setup for a 1-3 hour period of a wintry mix of freezing rain, sleet,
and rain during the onset of precipitation prior to daybreak
Wednesday. The favored area for this would be along and south of I-
90. This idea is supported by ensemble plumes from the gefs and
sref which show sharp increases in probabilities for mixed
precipitation as you travel from Sioux Falls towards Sioux City.
The 00z href probabilities also place the chance for measurable
freezing rain at 40 to 50 percent.
It should be noted that 00z models have trended temperatures
upwards within the warm nose, and that latest nbm guidance is
trending warmer, but i've still had to make some manual adjustments
to introduce additional precipitation types (perhaps not far
enough). Colder air does filter in quickly by mid-morning, which
should turn precipitation to snow. Accumulations will be light
regardless with this system, and as temperatures rise into the mid
30s by mid-day melting should take place.
Long term...(thursday through monday)
issued at 215 am CST Tue Nov 12 2019
Thursday-saturday: quiet and continued cool temperatures persist
through the end of the week and into the upcoming weekend.
Temperatures do rise each day a few degrees, eventually ending up
near normal values by Saturday. No changes made to this period of
Sunday-monday: models in good agreement that a positively tilted
upper trough passes through the region Saturday night and Sunday.
Moisture will be rather limited with this system, so not
anticipating much in the way of quantitative precipitation forecast. With temperatures warming, a
rain/snow mixture could be possible.
Aviation...(for the 12z tafs through 12z Wednesday morning)
issued at 511 am CST Tue Nov 12 2019
VFR conditions likely through the daytime hours of Tuesday. Winds
will increase substantially over Sioux Falls and Sioux City
today, gusts to near 30 knots at times. Clouds will gradually
lower overnight, after a brief period of low level wind shear near Sioux City.
Precipitation chances may arrive at the very end of the taf,
however will leave out at this time and indicate lowering