Area Forecast Discussion
Issued by NWS Omaha/Valley, NE

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FXUS63 KOAX 241732
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
1232 PM CDT Sun Mar 24 2024

.KEY MESSAGES...

- Freezing rain and light snow will lead to slick roads this
  morning northwest of an Omaha to Lincoln line.

- Widespread rain expected today with thunderstorms possible. A
  few could be strong this evening and overnight near the
  Nebraska/Kansas border. Additional strong to isolated severe
  storms will be possible in far eastern Nebraska and southwest
  Iowa Monday afternoon.

- A band of mixed precipitation followed by heavy snow may clip
  portions of northeast Nebraska Monday (40-70% chance of at
  least 4 inches in Knox/Antelope Counties). Combined with wind
  gusts of 35 to 45 mph, whiteout conditions and significant
  travel impacts would be possible.

- A second, slightly lighter band of snow may bring travel
  impacts to areas farther east of the main band Monday evening
  into Tuesday (40-60% chance). Highest chances would be in
  vicinity of Norfolk (within a county or 2).

- Dry weather returns for Wednesday and Thursday with
  temperatures trending back up.

&&

.DISCUSSION...
Issued at 428 AM CDT Sun Mar 24 2024

Early morning analysis showed a large scale trough digging into
the western CONUS while a surface low continued to deepen over
eastern CO. This was inducing strengthening southerly flow and
moisture transport pointing into western/central NE, as well as
warm air advection. This resulted in the development of a band
of showers and few thunderstorms to our west. The moisture
transport will gradually shift eastward into this morning,
bringing widespread precipitation to the area. Model soundings
suggest a majority of the precip should fall as liquid given the
aforementioned warm air advection leading to a bit of a warm
nose aloft. However, any convective elements in the precip could
quickly cool the column and lead to snow/sleet. In addition,
surface temperatures as of 4 AM remained within a few degrees
on either side of freezing, continuing to indicate potential for
freezing rain. Did expand the Winter Weather Advisory slightly
farther south last evening and will need to keep a close eye on
surface and pavement temps this morning for potential additional
expansion. As it stands, expecting up to a tenth of an inch of
ice with perhaps a few tenths of an inch of snow/sleet.
Certainly enough for slick roads and sidewalks.

Expect a break in precip by late this afternoon/early evening,
though we`ll still have plenty of cloud cover which will limit
instability. Still, guidance suggests we could have some MUCAPE
on the order of 500 J/kg this evening as some strong to
potentially severe storms approach from the southwest. They
should generally become disorganized as the push northeast and
out of stronger shear, but steep mid-level lapse rates/an
overall cold environment suggest at least some potential for
hail near the NE/KS border. Also can`t completely rule out some
enhanced wind gusts if some of the stronger cores are able to
bring down the stronger winds aloft. Just the regular gradient
wind gusts are expected to be in the 40-45 mph in that area (a
Wind Advisory has been issued), so it wouldn`t take much of an
increase to lead to some damaging winds. Timing of the greatest
severe weather threat would be around 10 PM to 3 AM.

Tonight into early Monday, the surface low will start to push
northeast out of central KS and into far southeast NE (slightly
slower progression than previous guidance). Cold air will start
to wrap in on the back side in northeast NE and lead to a
changeover from rain to a mix of just about everything
(including some freezing rain) to eventually snow. Guidance
still suggests the heaviest snow will remain to our west, but
the eastern edge of that snow band could clip Knox and Antelope
counties, where a Winter Storm Watch remains in effect. There
still looks like there will be sharp cutoff in snow on that
eastern edge, so confidence remains on the lower side as to just
how much snow we`ll get in our area from this band. For what
it`s worth, 24.00Z HREF guidance suggests only a 10-20% chance
of at least 4" within the watch, but when you factor in larger
scale models, that climbs to 40-70%. Would tend to lean toward
the HREF solution, as that guidance should better resolve small
scale details better, but it the time period in question is
toward the very end of its run. Plus, you only have to go about
a half county to the west to get into that 40-70% range, so just
a tiny change in storm track could lead to a big difference in
snowfall at a given point. All that said, while the heaviest
snow looks to remain to the west, even areas that receive sub-
warning- criteria snow could see significant impacts due to 35
to 45 mph wind gusts and at least near-blizzard conditions. In
fact, HREF guidance would suggest about a 50/50 shot at the
necessary snowfall rates and winds for blizzard conditions (per
some blowing snow research) in the watch area Monday.

Meanwhile, as that heavy snow band flirts with the edge of our
forecast area Monday, guidance suggests some potential for
additional strong to isolated severe thunderstorms in far
eastern NE and southwest IA somewhere in the 2 PM to 8 PM
window. It would be a similar setup to tonight, with steep lapse
rates and a cold environment favoring hail development. In
addition, shear looks sufficient for at least somewhat organized
storms. That said, instability will likely once again be
limited with cloud cover and on and off precip in the area,
though HREF guidance suggests there could be some breaks in the
clouds, yielding some potential for surface based storms and a
damaging wind threat. Finally, any time we see storms this close
to a surface low, there seems to be at least a small tornado
threat. However, hodographs in this case look to be quite
straight which should significantly reduce this threat (less
than 2%).

Guidance also continues to suggest a secondary lighter band of
snow will develop east of the primary heavy band Monday night
into early Tuesday as we get some additional shortwave energy to
push in from the southwest and a bit of a low to mid-level
frontogenesis/frontolysis "couplet" in northeast NE. This time,
the band would be squarely over our area, maybe around the
Norfolk area, but of course, there remains slight differences in
the various pieces of guidance. Tough to say if the snowfall
rates in this band would be heavy enough for blizzard conditions
(at this time, lean toward no), but there would certainly be
enough snow and wind for at least some degree of travel impacts
wherever it does fall. Then to the southeast of that band,
including the Omaha and Lincoln metros, generally expect less
than a 1/2" of snow...maybe just enough to make things slick.

Precip should exit the area by mid-day Tuesday with gusty
northwest winds keeping us cool as temperatures top out in the
upper 20s and 30s. Surface high pressure will also quickly build
in and favor dry conditions, though can`t completely rule out
some flurry/sprinkle/light shower activity Tuesday afternoon
into Wednesday with cyclonic flow aloft remaining in place.
However, with low level dry air working in, this should largely
manifest in the form of lingering cloud cover. Southerly low
level flow should return by Wednesday afternoon as mid level
ridging starts to approach from the west. As a result, expect
warming into the weekend, with highs in the 40s and 50s
Wednesday and 50s and 60s Thursday through Saturday. Should also
note that guidance continues to trend later with our next
precip chances, with consensus holding the next system off until
early next week now.

&&

.AVIATION /18Z TAFS THROUGH 18Z MONDAY/...
Issued at 1224 PM CDT Sun Mar 24 2024

MVFR conditions are in place at KOMA and KLNK while LIFR
conditions persist at KOFK owing to low ceilings, with
visibilities rebounding from this morning. Over the course of
the afternoon, expect wind speeds to ramp up with gusts over 30
kts, the return of rain to all sites after 21/22z and ceilings
to improve to IFR at KOFK while they`ll remain MVFR at KOMA and
KLNK. We could see some rumbles of thunder with some of the
deeper rain showers, but confidence for any one time is low. Latest
model trends indicate that there will be a break in the action
tomorrow morning after 12z, with snow moving into the KOFK
during the evening hours tomorrow.

&&

.OAX WATCHES/WARNINGS/ADVISORIES...
NE...Winter Weather Advisory until 1 PM CDT this afternoon for
     NEZ011-012-016>018.
     Winter Storm Watch from late tonight through Tuesday morning
     for NEZ011-016.
     Wind Advisory until 10 AM CDT Monday for NEZ088>093.
IA...None.

&&

$$

DISCUSSION...CA
AVIATION...Petersen


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