Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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FXUS63 KOAX 201128
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
528 AM CST Sat Jan 20 2018

.SHORT TERM...(Today through Monday)
Issued at 329 AM CST Sat Jan 20 2018

Winter storm still on track to affect the Plains Sunday into Monday.
And northeast Nebraska continues to be targeted for substantial
snowfall, with a wintry mix expected in much of the rest of eastern
Nebraska and southwest Iowa.

Model forecasts continue to be in fairly decent agreement in regards
to track of surface and upper low pressure centers, taking both
through southwest Kansas Sunday afternoon into southeast Nebraska
and southwest Iowa Monday morning, placing central through northeast
Nebraska in favorable heavy snow quadrant of system. However there
are discrepancies to the east and southeast on amount and timing
of saturation of atmosphere, which will play a big role on
precipitation types and amounts.

Mid level storm system was moving onto the northern California coast
this morning, and will track across Four Corners region tonight
before swinging into the Plains Sunday and Monday. Increasing and
diffluent flow ahead of it will deepen surface low in southwest
Colorado today, leading to northward low level theta-e advection
through eastern Kansas into southeast Nebraska and southwest Iowa.
Already seeing low clouds expanding north in eastern Kansas, and
expect arrival in our CWA later this morning. This increase in
clouds will play havoc with temperature forecast today, however
attendant moisture increase should push highs into the 40s despite
cloud cover. Areas of drizzle are likely later today and tonight as
low level moisture deepens under weak lift caused by mid level
diffluent flow. Northward expansion of drizzle and surface
temperatures at time of occurrence are tricky given competing
influences of moisture advection from the south and low level
northeast winds drawing cooler air into the area. We currently have
temperatures just below freezing near and north of Interstate 80
where some freezing drizzle could occur for a time tonight before
temperatures rise above freezing Sunday morning.

Northeast Nebraska could see a slightly longer period of freezing
drizzle as temperatures struggle to climb through the morning.
However by afternoon expect temps above freezing so drizzle should
be the predominant type until main storm system arrives late in the
day.

Strong frontogenetical forcing is expected to overspread northeast
Nebraska by early Sunday evening when saturation of atmosphere will
foster ice formation in dendritic temperature range. Once snow
begins there, we should see a prolonged period of moderate snows as
Q-vector forcing overrides the area into Monday. Specific humidity
calculations in the 290-295K theta layer suggest snow amounts
could easily top 6 inches overnight, with a few more inches
possible during the day Monday, mainly northwest of a Columbus to
Wayne line.

Farther to the southeast things are not as clear given proximity to
mid level low center and dry air wrapping into the system. The most
likely scenario will be for periods of mid level saturation
providing seeder ice crystals for occasional snow, interspersed with
periods of drizzle or freezing drizzle when mid level dry air is
predominant. Thus snow and ice accumulations will be difficult to
nail down as we head toward I-80 in Nebraska and much of southwest
Iowa. A gradual change to snow will occur as system drifts to the
east on Monday and saturated trowal region of storm gives most areas
some accumulating snows, but probably only on the order of an
inch or two.

Strong winds will also be impactful to travel with this system, and
could create near-blizzard conditions, especially in northeast
Nebraska where the heaviest snow is expected. North winds on the
order of 25 to 35 mph are likely Sunday night in northeast Nebraska,
then across all of eastern Nebraska and into southwest Iowa during
the day Monday. Thus even with the lighter snow accumulations,
blowing snow reducing visibilities can be expected.

Will maintain our current configuration of the Winter Storm Watch,
but have extended it through Monday afternoon as snow will be a bit
slower to end and winds will remain an impact through the day.

.LONG TERM...(Monday night through Friday)
Issued at 329 AM CST Sat Jan 20 2018

After lingering light snow works through eastern Nebraska and
southwest Iowa Monday night, the rest of the week offers a potential
warming trend.

Light snow on back side of exiting storm system will likely drop
some minor accumulations in far eastern Nebraska and southwest Iowa
Monday evening. But by Tuesday morning, we should see decreasing
clouds. The coldest air will follow system to the east rather
quickly, so no dramatic cooling is forecast for Tuesday. However
amount of snow cover will certainly affect temperatures. Still
expect highs to recover to the 30s except for the deepest expected
snowpack in northeast Nebraska.

Otherwise, upper level pattern will transition from northwesterly
flow on Tuesday to a building ridge by Thursday, ahead of
approaching storm system slated for Saturday arrival. Potential
warming will be characterized by 850 temperatures rising above 0C by
Wednesday evening, and approaching 5C or so by Thursday and Friday.
Thus highs in the 40s by Thursday and Friday seem reasonable.

&&

.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 508 AM CST Sat Jan 20 2018

Deteriorating conditions are expected beginning this evening.
Increasing low level moisture is expected through the day as sfc
low pressure strengthens near wrn KS. With influx of moisture from
the south, expect KOMA/KLNK to go to MVFR/IFR by early evening and
prevail the remainder of the fcst pd. As for KOFK, VFR conditions
will prevail before MVFR vsbys move in late this evening.


&&

.OAX WATCHES/WARNINGS/ADVISORIES...
NE...Winter Storm Watch from Sunday afternoon through Monday
     afternoon for NEZ011-012-015>018-030>033-042-043-050-065.

IA...None.
&&

$$

SHORT TERM...Dergan
LONG TERM...Dergan
AVIATION...DEE



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