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Forecast Discussion
NWS Omaha/Valley, NE


000
FXUS63 KOAX 171126
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
526 AM CST Fri Jan 17 2020

...Updated Aviation Forecast Discussion...

.DISCUSSION...
Issued at 253 AM CST Fri Jan 17 2020

Today and Tonight

Very challenging forecast setting up today with multiple wintry
precipitation types expected. Existing forecast in overall good
shape, but made minor tweaks to slightly higher snowfall amounts,
but also increased the wind gusts tonight into Saturday.

Snow was already spreading in southeast NE, reaching a line to
Albion to Lincoln to Falls City. This will continue to overspread
the region this morning, with snow covering the entire forecast
area by 12z. Some of the highres models suggest there could still
be an hour of a wintry mix on the front side waiting for full
column saturation. Snow becomes moderate to heavy at times this
morning with visibility down to 1/2 to 3/4 mile. 00z HREF data
suggests snowfall rates could approach 3/4 to 1" per hour for a
few hours at any given location, with 6 hourly amounts 2 to 4" CWA
wide by Noon.

Then the forecast becomes increasingly challenging as a dry slot
moves in aloft this afternoon, which removes ice from the column.
At the same time, surface temperatures continue to warm. We`ll
still see precipitation through the afternoon, but it should
become more of a drizzle or freezing drizzle mix depending on
surface temps and location. For southeast NE, temperatures do
warm to freezing or above, which will help mitigate any potential
icing concerns this afternoon there. Elsewhere, for northeast NE
and western IA, temps could be right around freezing, thus
freezing rain or freezing drizzle could allow for a little more
icing in these areas this afternoon and evening.

The drizzle or freezing drizzle continues early in the evening,
but by then, a cold front will be arriving, sweeping into and
through the area by midnight and beyond. This will bring sharply
colder temps back into the region, which will likely flash freeze
wet road conditions, but also switch drizzle back to snow. Winds
could gust 40 to 55 mph tonight as the arctic air rushes back in,
so this will also create areas of blowing snow or flurries
overnight.

Storm total snowfall will range 2 to 5 inches across the forecast
area, and some of that will melt this afternoon as temperatures
warm with daytime insolation. Icing amounts are forecast from just
a trace to a tenth or two across portions of east central NE and
western IA.

Headline Considerations

A winter weather advisory will remain in effect for all areas
through 12z Saturday, for a variety of winter weather impacts.
Wind gusts could reach 60 mph in northeast NE tonight, so we may
have to consider upgrading to a winter storm warning or high wind
warning for a few counties in that area, but will let the next
forecast shift take another look. Not confidant that we can meet
blizzard criteria of 3 hours of 1/4 mile visibility tonight in
the blowing snow, but it`s something we`ll take a closer look at
too for headline upgrades in northeast NE as well.

WSR88D Issues

KOAX radar remains offline due to a hardware upgrade. Technicians
hoped to have the radar operational Thursday evening, but are
waiting for additional parts Friday morning. Users are advised to
use a regional mosaic for radar data in the local area.

Saturday through Monday

Bitter cold air remains in place across the region with Sunday the
coldest day. Very windy conditions expected Saturday with some
lingering patchy blowing snow, but no additional falling snow.
Temperatures Saturday and Sunday nights in the single digits
above and below zero, with wind chill values 10 to 20 below at
times. Extreme northeast NE and northwest IA may need a wind chill
advisory Sunday morning.

Tuesday through Thursday

Temperatures moderate Tuesday and Wednesday back into the upper
30s to lower 40s. Another weather system could bring a chance of
rain and snow Wednesday. Models however diverge on solutions for
Wednesday night into Thursday. GFS brings another substantial
system into the area, but the EC is farther north and keeps the
area dry, thus forecast confidence is pretty low by day 7.

&&

.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 522 AM CST Fri Jan 17 2020

Snow impacting all three TAF sites at forecast issuance, with MVFR
conditions eventually becoming LIFR this morning. Visibility could
drop to 1/2 mile in moderate snow for a few hours, before
transitioning to freezing drizzle or drizzle by 17-21z. Otherwise,
southeast winds at 15 to 30 mph today. But switching to the
northwest later in the TAF period by 05-08z as an arctic front
arrives, when winds could gust 40-47 knots. Snow amounts ranging
2-5 inches.


&&

.OAX WATCHES/WARNINGS/ADVISORIES...
NE...Winter Weather Advisory until 6 AM CST Saturday for NEZ011-012-
     015>018-030>034-042>045-050>053-065>068-078-088>093.

IA...Winter Weather Advisory until 6 AM CST Saturday for IAZ043-055-
     056-069-079-080-090-091.

&&

$$

DISCUSSION...DeWald
AVIATION...DeWald

NWS OAX Office Area Forecast Discussion



Forecast Discussion
NWS Hastings, NE


000
FXUS63 KGID 171115
AFDGID

AREA FORECAST DISCUSSION
National Weather Service Hastings NE
515 AM CST Fri Jan 17 2020

AVIATION UPDATE...

.SHORT TERM...(Today and tonight)
Issued at 302 AM CST Fri Jan 17 2020

Attention is on the ongoing wintry precip event today...followed by
strong winds tonight.

Patternwise, the central CONUS is in southwest flow aloft ahead of a
progressive, elongated upper trough extending from British Columbia
to the southern Rockies. Strong dynamics are in place with this
approaching system with a 110kt H3 southern jet nosing northeast
across the plains today, with a 100kt jet on the back side of the
trough to the west, driving the system eastward. In presence of
strong isentropic lift (300k surface) ahead of the approaching
western trough, precip developed and expanded north across Kansas
and into Nebraska overnight.

Precip type is a messy wintry mix. Current surface temperatures
across our region are cold...all below freezing ranging 15-25F
north/south across our forecast area. Model forecast soundings in KS
show a warm nose (above freezing temps aloft) around H85...and
with that melting layer in place/surface temps below freezing we
are seeing some freezing rain/sleet and occasionally snow. Farther
north into Neb, temps aloft are colder but with saturation
initially lacking in the dendritic layer, the onset of precip has
been more of a freezing rain/sleet mix prior to a changeover to
snow.

In the isentropic lift, wintry precip is expected (and on track) to
continue to expand north and east from KS across central/eastern Neb
by daybreak, with the brunt of the precip with this system expected
to fall during the pre-dawn and morning hours today. The isentropic
lift continues across our central/eastern area through mid morning
then gradually shifts east of our area (into eastern Neb/KS) around
mid day.

Even after the round of isentropic precip departs, we`ll have
continued chances for precip during the aftn and into tonight in
lift/dynamics as the upper trough crosses our region. Moisture
with this later round of precip is not as great for the
aftn/tonight time frames and subsequently additional precip
totals will not be as high, but precip type remains tricky with
temperatures either side of freezing at the surface (in the aftn) and
we lose dendritic moisture/saturation aloft...causing a
drizzle/freezing drizzle precip type.

Then tonight, frontogenetic forcing along a cold fropa will bring us
one more chance for some snowfall. The fropa will be a noticeable
one, marked by an abrupt wind shift to the NW with wind gusts of
45-55 mph expected for areas along/north of I-80 with gusts 35-45
mph expected farther south. Temps tonight will drop below freezing
and any wet outdoor surfaces will re-freeze.

Headlines...no big changes have been made to the current winter
weather advisory headline other than to bump up the start time for
our northern zones.

Precip amounts...Model QPF has increased for the event and have some
slightly higher snowfall totals...with amounts ranging from around
one-half inch in our western zones to 2-4 inches in our eastern
zones. Ice accumulations of a light glaze to several hundredths of
an inch remain possible.

.LONG TERM...(Saturday through Thursday)
Issued at 302 AM CST Fri Jan 17 2020

Saturday remains cold/windy in the post frontal cold airmass. Aftn
temps are forecast near or above freezing, but it`ll feel much
colder as strong winds create wind chills primarily in the
teens/20s. Look for wind speeds to subside heading into Saturday
evening, then an upper trough deepening in the Upper Midwest
region backs in some cooler air for Sunday.

Monday is shaping up to be the transition day between cooler air to
the east and warmer air to the west. Height rises/upper ridging will
bring a warming trend into the middle of the workweek with a
continuation of dry conditions. A shortwave upper ridge breaks
down around the middle of the workweek with chances for precip
returning to the forecast late Wednesday/Thursday. The GFS
advertises a stronger system than the ECMWF so this will be something
to keep an eye on for next week.

&&

.AVIATION...(For the 12Z KGRI/KEAR TAFS through 12Z Saturday)
Issued at 511 AM CST Fri Jan 17 2020

Expect VRB ceilings and vis this morning as heavier snow bands
transit the area. Surrounding obs range 1/2sm to 5sm in -SN.
Tried to put a range of 1 to 3sm as that seems to the majority of
ob sites. Ceilings are expected to lower to IFR later this
morning, but put a TEMPO in for IFR cigs and vis based on surround
obs variability in ceiling heights.

&&

.GID WATCHES/WARNINGS/ADVISORIES...
NE...Winter Weather Advisory until 6 AM CST Saturday for NEZ039>041-
     046>049-060>064-072>077-082>087.

KS...Winter Weather Advisory until noon CST today for KSZ005>007-
     017>019.

&&

$$

SHORT TERM...Fay
LONG TERM...Fay
AVIATION...Beda

NWS GID Office Area Forecast Discussion