Scientific Forecaster Discussion
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Area forecast discussion
National Weather Service Omaha/valley NE
530 am CST Wed Dec 11 2019
..updated aviation forecast discussion...
issued at 252 am CST Wed Dec 11 2019
temperatures will slowly moderate into Friday with another Arctic
intrusion forecast this weekend. Best precipitation chances will
be Friday afternoon into evening (rain->snow transition), and
Sunday night into Monday (likely all snow).
Today and tonight:
a shortwave trough over the upper MS valley early this morning
will continue east-southeast into the Great Lakes today in
response to the progression of an upstream perturbation from the
Canadian rockies into the northern plains. In the low levels,
early morning surface analysis placed weak surface low near ksux
with a trailing cold front stretching westward across northern NE.
That boundary will advance south through our area this morning
before stalling across northern Kansas. By this afternoon, a deepening
Lee cyclone over the northern High Plains will begin to draw that
boundary back north into our area as a warm front.
Given the anticipated movement of the surface boundary mentioned
above, we expect the warmest afternoon temperatures (e.G., Around
40) near the Kansas border with lower to mid 20s across our northern
Another weak surface low will track east along the South Dakota-NE border
tonight with strengthening south winds ahead of it supporting some
boundary-layer mixing with lows mainly in the 20s.
Thursday and Thursday night:
a quasi-zonal flow regime in the mid levels will promote the
development of a surface Lee trough over the High Plains. That
pattern evolution will support the advection of a warmer low-
level air mass into the region with afternoon temperatures ranging
from the mid to upper 30s north to mid to upper 40s south.
The low-level warm advection pattern will persist into Thursday
night, supporting the development of a light snow band across the
northern plains. The southern extension of that feature could
glance our northern counties where we will include low pops.
Friday and Friday night:
latest model data continue to suggest mid-level trough
amplification from the Great Plains into MS valley with another
surge of Arctic air spilling south through the north-central
states. The arrival of the front into our area remains uncertain
with the current best guess being on Friday. So, while we will
indicate highs in the 40s and 50s, those numbers could end up
being too high if the arrival of the front is sooner. Further,
there is a relatively consistent model signal that a shield of
light precipitation will trail the surface front, and move into
the area during the afternoon and evening hours. Precipitation
type will be a function of low-level thermodynamic profiles, but
for now, it appears that a rain->mix->snow transition is the most
Saturday and Saturday night:
notably colder temperatures are expected owing to the passage of
the Arctic front. Highs will be in the teens and 20s with lows in
the single digits.
Sunday and monday:
a subtropical-branch shortwave trough is forecast to amplify over
the southern rockies and Southern Plains before tracking into the
mid MS valley. This will be a system to watch as some model
solutions suggest the northern extension of the associated
precipitation shield (which would be snow) overspreading our area
in the Sunday night-Monday timeframe. Temperatures will remain
Tuesday and wednesday:
building mid-level heights and a westerly, downslope wind
component in the low levels would suggest dry conditions with
Aviation...(for the 12z tafs through 12z Thursday morning)
issued at 526 am CST Wed Dec 11 2019
VFR conditions will prevail for the forecast period. Winds will
shift clockwise from the northwest and become predominately
southeasterly by 21z. Low level wind shear will likely be a
concern at the end of the taf period.