Scientific Forecaster Discussion
fxus63 koax 130946
Area forecast discussion
National Weather Service Omaha/valley NE
346 am CST Wed Nov 13 2019
..updated forecast discussion...
issued at 330 am CST Wed Nov 13 2019
forecast concerns in the short term will be the extent of
the wintry mix of precipitation and if a Winter Weather Advisory
In coordination with fsd/lbf/dmx will include a few of our northeast
Nebraska and western Iowa counties in a Winter Weather Advisory this
morning for a period of mixed precipitation/light glazing of ice
until the warmer air moves in. See details below.
The 00z oax sounding had some moisture around 2100ft and above 13k
ft with a deep dry layer in between. Water vapor satellite imagery
highlights the mid level moisture associated with the trough over
North Dakota/Montana/Wyoming. A late evening subjective surface map
had the surface warm front lifting into Minnesota with a surface
trough extending across central South Dakota and west central
Nebraska from surface low pressure in North Dakota. Surface
temperatures were variable, in the teens and 20s locally, but much
warmer in the 30s and even 40s closer to the trough. Radar imagery
and 06z metars shows light rain at kphp in southwest South Dakota.
Earlier shifts opted to take a wait and see approach with this light
precipitation event that may produce a light glaze of ice for parts
of northeast Nebraska into western Iowa. With light events the
metwatch and short term evolution will be important. Surface
temperatures will play a big role in the impacts and forecast
soundings still support some freezing rain on the leading edges with
rain/snow/sleet mix possible. The gefs plumes show around 100%
freezing rain prob at sux while the nbm has 80 to 90% and wpc 70 to
80% percent for the area where we have our Winter Weather Advisory.
Wpc/sref guidance has backed off on overall qpf with the event,
however the nbmexp/ec/GFS still have about twice as much as wpc. All
models tend to keep it in the trace to 0.1 of qpf with limited/low
impacts. With our sounding showing dry air to overcome, there is
upper level support that will continue to moisten the atmosphere
from the top down and forecast soundings show the dry air being
overcome at Norfolk after 9am and Oma by noon.
The 06z NAM fcst was too cold with the surface temperatures and the
GFS was better. By 08z...the rap13 was doing better and the href
had the warm air by onl depicted better. Temperatures will
initially start out below freezing, then with the trough passage
warm above freezing. During this window, as precipitation increases
and due to the warm air aloft, the expected precipitation type will
be freezing rain, but also a wintry mix. The 0830z radar showed the
stronger returns just northeast of vtn with rain there; not
initialized well on the hires models. The trend is for light
precipitation to continue east southeast through the morning hours.
After 18z...the below freezing temps are limited to a few of our
western Iowa counties with a mix possible.
As stated earlier...in coordination with fsd/lbf/dmx will include a
few of our northeast Nebraska and western Iowa counties in a Winter
Weather Advisory this morning for a period of mixed
precipitation/light glazing of ice until the warmer air moves in. A
couple of the models shift the accumulating precipitation farther
south where the frontogenesis is expected, thus the temperatures and
precipitation area will need to monitored.
South and southwest winds will shift to the northwest with the
trough passage with temperatures warming up. Highs today in western
Iowa should hold in the 30s with upper 30s to lower 40s for eastern
Tonight through Tuesday...
not as cold and still on the dry side Thursday through Tuesday.
Ridging Thursday and Friday will be followed by a quick longwave
trough passage Saturday night and Sunday morning and a shortwave
in the flow Monday ahead of ridging for Tuesday. Temperatures
will moderate over the next couple of days with near or above
normal temperatures expected into early next week. A quick moving
cold front will pass through Saturday night. The front could
produce a little light precipitation, however most locations
should remain dry. Another front will pass through Monday. Again,
this front may have a little light rain with it, but not much.
Aviation...(for the 06z tafs through 06z Wednesday night)
issued at 1123 PM CST Tue Nov 12 2019
Southerly winds will remain breezy overnight. Low level wind
shear will continue overnight near 50 knots at fl020 at all sites.
A front will move through the area Wednesday morning and will
bring a chance of mixed precipitation to ofk for most of the day.
Additionally, Oma may see a few hours of rain and snow mixed
during the early afternoon. Ceilings are expected to decrease to
MVFR at ofk and Oma Wednesday afternoon, but should begin to
improve Wednesday night. There is a small chance for light
freezing rain and a light icing, especially for a few hours after
the onset of precipitation.
NE...Winter Weather Advisory until 11 am CST this morning for nez011-
Iowa...Winter Weather Advisory until 11 am CST this morning for iaz043.