Scientific Forecaster Discussion
fxus63 koax 072337
Area forecast discussion
National Weather Service Omaha/valley NE
537 PM CST Sat Dec 7 2019
..updated aviation forecast discussion...
issued at 236 PM CST Sat Dec 7 2019
One more mild day to end the weekend before sharply colder air
settles into the region. Some light snow or freezing drizzle could
accompany the initial surge of cold air Monday morning, but the
primary weather story is temperatures swinging back to near 15
degrees below normal for mid week.
Only thin high clouds were left over eastern Nebraska and southwest
Iowa this afternoon, allowing some filtered sun to help warm
temperatures. Southwest winds gusting over 20 mph were a major
contributor to the warming today, with temperatures topping 50
most areas. This setup will continue through the evening before a
weak cold front/wind shift begins to settle into the region early
Sunday morning. That front will wash out during the day, keeping
pressure gradient weak leading to light winds and little mixing.
Thus would expect temperatures to be a few degrees cooler Sunday
afternoon, though light winds and some sunshine should make it
feel just as mild.
Sunday night through tuesday:
Pieces of Arctic airmass are forecast to dive into the plains early
next week as a deep mid level trough extending from Hudson Bay to
northern California rotates into the central and eastern Continental U.S.
Through mid week. The northern and Central Plains through the Great
Lakes and New England will be under this influence at least through
Closer to home, the leading edge of the cold air is expected into
northeast Nebraska Sunday night. Limited layer moisture will be
available with this system, however lift along and behind frontal
zone should be sufficient to squeeze out at least light precipitation
for our area as front swings through the County Warning Area between midnight and
noon. Forecast soundings from the GFS suggest some saturation in
dendritic temperature zone occurring during maximum lift along
frontal zone. However loss of ice crystals behind front may lead to
pockets of freezing drizzle as well. Still, given limited moisture
availability and fast-moving nature of front/lift, expect any snow
and ice accumulations to be minimal, limited to less than a half
inch of snow and maybe a hundredth of an inch of ice in northeast
Nebraska and west central Iowa.
The colder air will affect all areas as 850 temps drop more than 15c
from Sunday afternoon to Monday afternoon. Also, strong north winds
gusting over 30 mph at times Monday will make it feel even colder.
Morning highs in the 20s and 30s are likely on Monday, with steady
or falling afternoon temperatures and wind chills in the single
digits and teens.
A secondary and reinforcing surge of cold air arrives Monday night,
but moisture is even more limited with this front. Thus no
precipitation is expected, but temperatures should remain in the 20s
for Tuesday afternoon.
Wednesday through saturday:
Mid level flow pattern becomes more zonal for the end of the week,
allowing some moderation of temperatures through Saturday. A couple
of shortwaves riding through the plains may bring small chances for
light precipitation Thursday and Friday, but consensus between model
output will have to get better before an increase in confidence and
precipitation chances is warranted. Otherwise the cold
temperatures will continue Wednesday with highs in the 20s, but
moderating toward 40 Thursday through Saturday.
Aviation...(for the 00z tafs through 00z Sunday evening)
issued at 511 PM CST Sat Dec 7 2019
VFR conditions will prevail through the forecast period. Low level wind shear will
will be a factor at all terminals this evening just ahead of a
surface trof currently extending from the eastern Dakotas to