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000 
FXUS63 KOAX 240504
AFDOAX

Area Forecast Discussion
National Weather Service Omaha/Valley NE
1104 PM CST Thu Feb 23 2017

.UPDATE...
Issued at 922 PM CST Thu Feb 23 2017

Overall going forecast in good shape tonight. Strong ascent
associated with CDPVA in the 700-300 mb layer coupled with weak
static stability to some upright instability has led to an area 
of moderate to occasionally heavy precipitation from northern KS 
into eastern NEb/western IA. Models are consistent that this area
of lift will shift north and east over the next several hours 
with mid-level dry intrusion working into the southern 2/3 of the 
FA. This will likely shut off precipitation for a time overnight.
For precipitation type so far we have seen snow in northeast NEb 
with some moderate accumulations to this point. Within the 
strongly forced band we have seen some thunderstorms with a mix of
hail/sleet and some snow on the northwest edge. 

Late tonight as the mid-level cyclone center works east across 
NEb we will see the deformation band sink to the southeast 
associated with moderately strong thermal advection with 
associated frontogenetic circulation. This should be an all snow 
band as it drops to the southeast with snow moving back into the 
I80 corridor around 09-10Z. The snow is then expected to continue 
in northeast NEb/w-central IA down to the I80 corridor and a bit 
south into Friday afternoon. The precipitation intensity will be 
much lighter late tonight and through the day on Friday as the 
static stability increases as mid-level lapse rates decrease, but 
snow ratios will also be increasing. One concern for accumulations
along the I80 corridor is the increasing sun angle and generally 
light nature to the snow on Friday may limit to some degree the 
impact on roadways, but a good deal of uncertainty remains on how 
that affect the impacts of the storm. This concern is less over
the northern CWA where much of the heavy accumulations will be
overnight. Otherwise snow amounts from previous series of 
forecasts looks on track and no changes to those or the headlines 
are anticipated at this time.

&&

.SHORT TERM...(tonight through Sunday)
Issued at 220 PM CST Thu Feb 23 2017

...Major winter storm still on track to affect the region through
Friday...

Forecast overall remains on track for a major winter storm to
affect the region tonight into Friday. Some complications for the
expected weather include a chance of thunderstorms this evening
across southeast Nebraska and southwest Iowa, which will include a
severe threat with some hail possible. Second compounding factor
will be a changeover from rain to snow, where that initially sets
up, and how fast it moves southeast through time. Northeasterly
winds will continue to increase to 20 to 30 mph through time, with
gusts 30 to 40 mph possible. One of the major changes that we 
have made with the upcoming package is to include a slightly 
faster changeover from rain to snow based pm Rap model trends. 

A couple of notes regarding QPF, the GFS model came in a little 
lower, while the SREF and NAM models perhaps a little higher, 
which both indicate up to 12 inches or more from northern NE 
through northern IA. The ECMWF as not as high, similar to the GFS.
Blending all of that together, combined with input from WPC. 
Overall, forecast snowfall amounts have not changed significantly 
from the previous package. We are still forecasting 6 to 10 inches
for the northern half of the forecast area, from 2 to 5 along and
either side of Interstate 80, and an inch or less in southeast 
Nebraska.

Concerning our current package of winter weather headlines, we 
anticipate no major changes with this package, although we may
adjust the start time of the last group of headlines. We feel the
the overall alignment and message of expected impacts looks good 
with current products in effect. We do have very strong winds 
forecast with this system, and will continue to mention near 
blizzard conditions expected with 1/2 mile visibility along with 
blowing snow and possibly drifting. However, just not confident 
we'll see widespread 1/4 mile visibility for 3+ hours, thus have 
no plans to upgrade any of the area to a blizzard warning at this 
time. 

Snow accumulation rates will be winding down significantly Friday
afternoon, tapering to flurries, and ending altogether before
midnight. Due to recent warmth, soil temperatures are running in
the mid to upper 40s. This will easily be overcome by expected
rates. 

Impacts to travel will eventually develop. Near blizzard
conditions are expected across northeast NE and northwest IA.
Travel may eventually become impossible over parts of of the area. 

Quiet weather expected on Saturday. Another weather system brings
a chance of small snow and rain south of I80 on Sunday, with the
GFS a little more robust than the ECMWF. 

.LONG TERM...(Sunday night through Thursday)
Issued at 220 PM CST Thu Feb 23 2017

Another quick moving weather system moves through the region on
Tuesday. Again, the GFS is more robust with this than the ECMWF,
but we will have a chance of snow and rain in the forecast. And
one more system may graze our northern counties on Wednesday. 

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1052 PM CST Thu Feb 23 2017

Light to occasionally moderate snow will continue overnight at
KOFK with MVFR and IFR conditions expected. We will also see some
blowing snow picking up there overnight and will continue through
Friday. For KLNK/KOMA we have seen a mix of rain/snow and thunder
this evening, but we should see some drying move in over the next
several hours before snow moves back in after 08-09Z. Snow is then
expected at these locations well into Friday with a mix of IFR and
MVFR conditions expected. All sites will become VFR by Friday
evening. 

&&

.OAX WATCHES/WARNINGS/ADVISORIES...
NE...Winter Storm Warning from 3 AM Friday to midnight CST Friday 
     night for NEZ034-044-045.

     Winter Weather Advisory from 3 AM Friday to midnight CST Friday 
     night for NEZ050>053-065>067.

     Winter Storm Warning until midnight CST Friday night for NEZ011-
     012-015>018-030>033-042-043.

IA...Winter Storm Warning from 3 AM Friday to midnight CST Friday 
     night for IAZ043-055.

     Winter Weather Advisory from 3 AM Friday to midnight CST Friday 
     night for IAZ056-069-079.

&&

$$

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