Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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FXUS63 KOAX 091142
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
542 AM CST Fri Dec 9 2016

.SHORT TERM...(today through Sunday)
Issued at 306 AM CST Fri Dec 9 2016

The main forecast concerns center around several small chances for
light snow through the short term. The 00Z upper air analysis
indicated relatively low-amplitude flow over the CONUS with a
broad trough over the eastern third of the country, and west to
northwest flow over the western two-thirds. A 115 kt H25 jet was
noted over the Pacific Northwest associated with some 30-50 m H5
height falls. Downstream over the Plains a strong thermal gradient
existed, mainly over the southern Plains that was evident at H7.
This thermal gradient will be the source of a couple of chances of
light snow as jet segments and associated generally weak shortwave
troughs translate along this high contrast ribbon.

Models are in general agreement today that as the upstream 115 kt
H25 moves into then northern Plains the ageostrophic response will
be low to mid level WAA over northern Neb into SD. This will lead
to increasing clouds over most of the CWA today, and lift may
prove sufficient for some flurries or a brief period of -sn over
the far northwest CWA later this morning and into the early
afternoon. Accumulations are not expected. The tonight period
should be dry over the CWA, but with clouds and southeast winds we
have increased lows most areas to tighten up the diurnal range. As
the current Pacific Northwest height falls move into the northern
Rockies Saturday the central and northern Plains become located in
the right rear entrance of the upper level jet, and although the
static stability on cross sections appears high per EPV >.1, a
frontal circulation is expected to develop given the isentropic
ascent and jet placement. The placement on this band differs in
the models though with the GFS farthest south and the NAM farther
north. At this time given the cross sections where the better
saturation, thermal profile, and lift are juxtaposed appear to be
north and east of our FA. We feel that an initial band of -sn will
likely develop in our northern CWA Saturday morning, but quickly
lift north into MN/SD. We will continue with high pops during this
period with up to around an inch of snow possible in Cedar/Knox
Counties and less south.

This initial band of -sn will lift out of the area and the rest of
Saturday and Saturday night will be dry. Relatively mild
temperatures are expected during this time with the continued
southerly flow and clouds in the area. The previously mentioned
height falls and associated QG forcing will then move through the
CWA on Sunday with an associated cold frontal passage by
afternoon. Again it appears that most if not all of the snow
associated with the shortwave-trough will fall to our north, but
will maintain some chance pops over the northern/eastern CWA
closest to the important mid-level thermal gradient.

.LONG TERM...(Sunday night through Thursday)
Issued at 306 AM CST Fri Dec 9 2016

A continued unsettled pattern is expected through the extended as
a seasonably fast jet continues to extend across the CONUS and a
strong thermal gradient remains in play. Any shortwave trough
riding along this gradient can lead to a period of isentropic
ascent and a period of -sn, and confidence in timing these waves
and associated precipitation is very low currently.

The global models do tend to agree in another strong arctic surge
from Tuesday night into Wednesday /the GFS is certainly stronger
with this than the EC/ and we will include some chance of light
snow with this front. If the GFS were to prove closer to reality
than our forecast temperatures are to warm for Wednesday through
Thursday, but little change to this period was done due to the
uncertainty. The GFS and EC then to some degree want to buckle the
flow toward the end of next week that may lead to some chance of
precipitation, but again uncertainty in precipitation is very low
with confidence in continued cold weather very high.

&&

.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 538 AM CST Fri Dec 9 2016

Area remains under the influence of high pressure at the start of
the period with VFR conditions expected to prevail through the
forecast period at all sites. CIGS however will gradually lower
through the day with cigs around FL050 moving in between 00Z and
06Z.

&&

.OAX WATCHES/WARNINGS/ADVISORIES...
NE...None.
IA...None.
&&

$$

SHORT TERM...Boustead
LONG TERM...Boustead
AVIATION...Fobert


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