Winter Storm in Nebraska, January 18 to 19, 2023

AREA FORECAST DISCUSSION
National Weather Service Hastings NE
1208 AM CST Wed Jan 18 2023

...AVIATION UPDATE...

.DISCUSSION...(This evening through Tuesday)
Issued at 455 PM CST Tue Jan 17 2023

Key Messages:

* Major winter storm on track to impact the region late tonight
  through Wednesday night.

* Winter Storm Warning has been expanded southeast due to expected
  combination of snow and ice.

* Very difficult - if not impossible - travel conditions are
  likely for many areas, including portions of I-80, for Wednesday
  and Wednesday night.

* Due to significant, heavy snow amounts, travel impacts will
  likely linger well into Thursday, and possibly even Friday for
  rural areas.

Forecast Details:
"Calm before the storm" with cool and cloudy conditions expected
through the evening hours.

The slight southward shift in model snow/ice placement observed
last night has held with today's runs...so any forecast changes
have largely resulted from decr ensemble spread and tightening of
gradients. Forecast adjustments include: an uptick in snow
amounts for NW half of CWA due to decr chances for a wintry mix
and higher ensemble QPF (a slight uptick in snow to liquid ratios
(SLRs) also contributed), a slight incr in ice accretion S/E of
Hastings (due to strong model agreement between EC and HREF), and
about a 5 MPH incr in winds/gusts, esp. Wed eve/night. Overall
timing has not changed much as still expect most areas to be under
the influence of some sort of wintry pcpn by dawn Wed AM, with
heaviest snow/ice rates during the daytime hours.

This event will be a high-end winter system for our forecast
area, and impacts are likely to be felt through at least Thu, and
likely even into Fri for rural areas that receive heavy snow. Our
in-house "Blizzard Severity Index" is a solid 3-3.5 (on scale of
0-5) for areas with heaviest snow. Only missing factors to a more
historic blizzard are 5-10 MPH stronger gusts and colder temps.
More well-known Winter Storm Severity Index (WSSI) is also
impressive, with widespread "Major" impacts from SW to NE Neb.,
and a sizable area of "Moderate" impacts surrounding it.

While the bright colors of the 10-15" of snow in our N/W will
likely "steal the show", want to emphasize that severe travel
impacts will still likely be felt on the SE side of heavy snow,
where sleet and freezing rain could be present with initial wave
of pcpn Wed AM. In fact, some model solutions like NAM (and to
some extent the EC) still argue for a narrow area of overlap of
4-6"+ of snow on top of a tenth to quarter inch of ice.
Considering temps at the onset of pcpn in the upper 20s and a
decent NE breeze, this could support efficient ice accretion and
lead to a solid layer of ice beneath several inches of snow. So
even though neither ice or snow amounts would be "impressive", the
combination of the two could really lead to some hazardous
travel. This is why portions of the remaining Winter Storm Watch
were upgraded to a warning - despite generally sub-warning
snowfall amnts. If ice signal strengthens ANY, then there's a
strong argument for taking the warning another tier of counties
SE.

For the Tri-Cities, Kearney and Grand Island have trended to more
solidly all snow, and thus amnts have incr to the 6-10" range,
with iso higher amnts possible. Hastings is still very near the
transition zone, though most guidance keeps the "best" chcs for
ice just E/SE of town. Interesting to note that current forecast
snow amounts range from 7-9" over NW side of Adams Co., to only
3-4" for the far SE side - illustrating well the sharp gradient
expected in snow amnts. Snow rates will decr gradually from SW to
NE through the eve hrs Wed, but N-NW winds will incr at the same
time and gust 30-35 MPH. This will lead to some blowing and
drifting - esp. open areas - and complicate snow clearing efforts
through Thu AM. Should finally have lighter winds towards Thu
aftn, and hopefully even some sunshine.

Last thing to note with this system is that there's going to be a
real possibility for thunder. Forecast soundings show very steep
lapse rates in the 3-6km level, and these are even co-located with
high saturation. CSI appears to be almost a given, and would not
at all be surprised to see outright CI - which is likely hinted at
by HREF showing decent probs for 1-2"/hr snow rates. Those kinds
of snow rates over any given location for even a short time can
really ramp amnts towards the high end of guidance real quick. So
wouldn't rule out 10-12" for Kearney and Grand Island, and 15-18"
for areas from LXN to ODX.

Spent little to no time in the extended portion of the forecast.
Likely facing an extended period of temps below or well below
average given what looks will be a deep snowpack in place. Have
some minor PoPs in the forecast for various times Fri night into
early next week.

&&

.AVIATION...(For the 06Z KGRI/KEAR TAFS through 06Z Thursday)
Issued at 1151 PM CST Tue Jan 17 2023

A major winter storm is heading into the area and aviation weather
conditions will be very poor for much of the next 24 hours
beginning between 3-5 AM. Our TAF sites should see pretty much
all snow from this event and forecast amounts of 7-10 inches
locally higher seems solid. Ceilings will predominately be IFR to
LIFR with visibility possibly flirting with airport minimums in
heavy snow later this morning and afternoon. Will keep visibility
around 1/2 in the TAF for now, but there will probably be at least
periods of 1/4 mile or less visibility. The snow will start to
diminish after sunset and could see slight improvements in
conditions by late evening. The wind will ramp up through the day
and this evening shifting from northeast to northerly through the
period. Blowing snow and reduced visibility from blowing and
falling snow is likely.

&&

.CLIMATE...
Issued at 501 PM CST Tue Jan 17 2023

-- BOTH total precipitation AND snowfall daily records for Jan.
 18th could be broken on Wednesday at Grand Island/Hastings (our
 two primary long-term climate sites for which we issue formal
 Record Reports). Details follow:

Grand Island:
- current Jan. 18 precip record: 0.41" in 1931
- current Jan.18 snowfall record: 4.1" in 1931

Hastings:
- current Jan. 18 precip record: 0.50" in 1912
- current Jan.18 snowfall record: 2.5" in 1960

&&

.GID WATCHES/WARNINGS/ADVISORIES...
NE...Winter Weather Advisory until midnight CST Wednesday night for
     NEZ087.

     Winter Storm Warning until midnight CST Wednesday night for
     NEZ039>041-046>049-060>064-072>077-082>086.

KS...Winter Weather Advisory until midnight CST Wednesday night for
     KSZ005>007-017>019.

&&

DISCUSSION...Thies
AVIATION...Wesely
CLIMATE...Pfannkuch

Hazardous Weather Outlook
National Weather Service Hastings NE
325 PM CST Tue Jan 17 2023

KSZ005>007-017>019-NEZ039>041-046>049-060>064-072>077-082>087-
181200-
Phillips-Smith-Jewell-Rooks-Osborne-Mitchell-Valley-Greeley-Nance-
Sherman-Howard-Merrick-Polk-Dawson-Buffalo-Hall-Hamilton-York-
Gosper-Phelps-Kearney-Adams-Clay-Fillmore-Furnas-Harlan-Franklin-
Webster-Nuckolls-Thayer-
325 PM CST Tue Jan 17 2023

This Hazardous Weather Outlook is for south central Nebraska and
portions of north central Kansas.

.DAY ONE...Tonight.

A winter storm system will move into the region tonight,
especially after midnight, resulting in accumulating snow and ice
prior to dawn in many locations. Winter Storm Warnings and Winter
Weather Advisories are in effect for the local area beginning at
midnight tonight. Please refer to the latest warning and advisory
products for additional details.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday.

Significant winter weather impacts are expected across the region
on Wednesday. Snowfall amounts will vary considerably, from as a
much as a foot or more of snow across areas northwest of a Dawson
to Greeley county line, to less than 1 inch across portions of
Osborne and Mitchell counties in north central Kansas. However,
counties south and southeast of the Tri Cities, where snowfall is
expected to be lighter, will also be more prone to seeing some
freezing rain and sleet, with up to a quarter of an inch of ice
accumulation possible south of highway 6 and east of highway 281.

Please refer to the latest warning and advisory products for
additional details.

.SPOTTER INFORMATION STATEMENT...

Spotters are encouraged to report snowfall and ice amounts to the
National Weather Service.

&&

More information may be obtained at the following web page:
   https://www.weather.gov/hastings

Rossi/Thies