Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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007
FXUS63 KOAX 241800
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
1200 PM CST Tue Jan 24 2017

.SHORT TERM...(today through Thursday)
Issued at 301 AM CST Tue Jan 24 2017

...A significant winter storm will impact the area today into
Wednesday...

Manual 00z upper-air analysis and early-morning water vapor
imagery indicate a substantial mid-level trough stretching from
the far eastern Pacific to spine of the Rocky Mountains.
Pronounced mid and upper-level wind maxima observed within the
basal portion of the trough over the lower CO Valley will eject
northeast into the central and southern Plains, driving the
deepening of an associated mid-level trough and related surface
cyclone over the central Plains today. At the same time, a plume
of steep mid-level lapse rates --best observed by the 00z
soundings at Denver, CO and North Platte, NE-- will advect
east/northeast in the mid MO Valley, conditioning the environment
for robust vertical motion within a frontogenetically forced
precipitation band evolving to the north of the surface cyclone.

Latest short-term model guidance indicates that strengthening
lower to mid-tropospheric warm advection and isentropic upglide
will foster a broadening band of light snow (perhaps mixed with
sleet) this morning from the vicinity of the western KS surface
low northeast into east NE and perhaps west IA. This band will
pivot north into northeast NE and west-central IA by afternoon and
strengthen with time as the steepening mid-level lapse rates
couple with intensifying frontogentical forcing. Embedded upright
convection is not out of the question with periods of moderate to
heavy snow occurring through the afternoon. Farther south across
east-central NE, slightly warmer boundary-layer temperature
profiles will yield a rain-snow mix. Some sleet or graupel is
possible, as is a rumble of thunder.

By tonight, precipitation will change over to all snow from
northwest-to-southeast across the area as cold air deepens on the
backside of the surface cyclone passing to the east. Strengthening
gradient flow in the low levels will promote strong northwest
winds, creating areas of blowing and drifting snow, especially
across northeast NE and west-central IA.

The 00z models continue to converge on a more southern track to
the surface low along with higher QPF within the deformation axis.
As a result, it is reasonable to expect storm-total snowfall
accumulations in excess of a foot along the NE-SD border with as
much as six to eight inches possible along a line from Albion, NE
to Onawa, IA. We, therefore, have included Boone, Madison,
Stanton, Cuming and Burt counties in NE and Monona county in Iowa
to the Winter Storm Warning, and added Saunders and Washington
counties in NE and Harrison and Shelby counties in IA to the
Winter Weather Advisory.

Light snow along with gusty northwest winds will continue
Wednesday before tapering off Wednesday night.

.LONG TERM...(Thursday night through Monday)
Issued at 301 AM CST Tue Jan 24 2017

We will remain in a high-amplitude mid-level pattern through next
weekend, featuring a western U.S. ridge with a downstream trough
over eastern North America. A number of disturbances will
translate from central Canada into the central U.S. during that
time frame. One such impulse is forecast to move into the mid MO
Valley Saturday into Saturday night when a chance for flurries or
light snow will exist. Thereafter, medium-range guidance suggests
that a significant short-wave trough will temporarily dampen the
western U.S. ridge prior to moving through the northern Plains
into upper Great Lakes next Monday/Monday night. These data
indicate that the strongest forcing for ascent and associated
precipitation potential would remain to the north of our area.

The above-mentioned large-scale pattern will favor below normal
temperatures into next weekend. This will especially be the case
in areas that receive more significant snowfall over the next
24-36 hours.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1200 PM CST Tue Jan 24 2017

Snow band associated with H7 frontogenetical forcing lifting
north across northern portions of the CWA, taking with it heavier
IFR/MVFR snow and visibilities. Expect a pause in persistent,
widespread precipitation in the short term, as dry slot associated
with upper/low level system moves across the area. Area sounding
are showing decent mid-level instability, and as large scale
forcing increases with approach of upper level system, may see
increase in convective precipitation, thus introduced a period
of sleet in KOMA TAF, and may do the same for KLNK during
the afternoon hours.

Another round of persistent, widespread snow is expected this
evening and overnight. Maintained previous forecast of IFR/MVFR
visibilities due to SN BR/FG and IFR cigs through 12 utc.

&&

.OAX WATCHES/WARNINGS/ADVISORIES...
NE...Winter Weather Advisory until 9 AM CST Wednesday for NEZ042>045-
     050-051.

     Winter Storm Warning until 9 AM CST Wednesday for NEZ011-012-
     015>018-030>034.

IA...Winter Weather Advisory until 9 AM CST Wednesday for IAZ055-056.

     Winter Storm Warning until 9 AM CST Wednesday for IAZ043.

&&

$$

SHORT TERM...Mead
LONG TERM...Mead
AVIATION...Fortin



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