Area Forecast Discussion
Issued by NWS Hastings, NE

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FXUS63 KGID 152359
AFDGID

Area Forecast Discussion
National Weather Service Hastings NE
559 PM CST Sun Jan 15 2017

.SHORT TERM...(This evening through Monday night)
Issued 431 PM CST Sun Jan 15 2017

Another busy day trying to keep up with short-term trends on the
ongoing/continuing winter storm. While the overall-expectations
have really not changed much over the past 24 hours (and overall
ice/snow accumulation totals have remained fairly consistent for
over 24 hours now), there is and always has been a decent degree
of uncertainty with this system regarding whether the impacts are
truly "major" (such as widespread powerline/tree damage) or more
of nuisance (such as mainly just travel issues and limited power
issues). Part of this uncertainty arises from the fact that
temperatures hovering only near-to-slightly below freezing may not
be allowing ice accretion to reach optimum levels that you might
see if surface temps were perhaps only 2-4 degrees colder on
average. So, for those expecting truly "major" impacts from this
storm, you may or may not see them, but as anybody knows it only
takes a minimal amount of ice to cause treacherous travel on
untreated roads. These next 12-18 hours will go a long way in
determining how "memorable" or "forgettable" this storm ends up
being, but in coordination with surrounding offices have opted to
allow all Ice Storm/Winter Storm Warnings to continue riding "as-
is" for now.

Of all Warnings currently in effect, the Winter Storm Warning in
northern/western counties may be the most uncertain of all as far
as truly verifying high-end impacts, as ice accumulations appear
to remain fairly minimal compared to farther southeast and the snow
potential for Monday has trended downward into only the 1-2"
range. However, already this morning we had at least a few
significant accidents along I-80 in the Winter Storm Warning area
just from minimal icing, so we are in no hurry to "downgrade" any
counties at this time.

Taking a look at the current/recent weather as of 4PM: Overall
it`s been a somewhat hard day to get a handle on the severity/lack
thereof of icing. While the vast majority of the CWA has now seen
at least a light icing by now (the far northern edges of the CWA
will finally see light freezing rain move in over the next few
hours), treated primary roads seem to be only "partially ice
covered" for the most part this afternoon as temps have warmed a
few degrees since this morning, when there were a few "higher
profile" accidents that we are aware of, especially along I-80 in
Buffalo county. We have had several reports of ice accumulation up
to around one-eighth of an inch, but not really anything so far
causing truly major travel or power line issues. Clearly, the
majority of liquid precipitation equivalent so far today (perhaps
pushing 30-40+ hundredths of an inch) has targeted our southern
zones in KS, while most Nebraska areas have seen 15 hundredths of
an inch or less of total precip so far. In the mid-upper levels,
the parent/primary disturbance of interest is churning across far
southwest TX, with our varied batches of mainly light precip
streaming from south-to-north across our CWA a result of low-mid
level warm air warm advection and diffluence aloft. Precipitation
type today, as best we can tell, has been freezing rain/drizzle
for the vast majority of the area, although low-mid level temps
appear to be getting more conducive for some sleet especially far
west. Temps are currently near-30 most all areas.

Now quickly going through the highlights of these next 36 hours...

This evening/tonight:
Various models (NAM/GFS/ECMWF) have come into excellent agreement
on the track of the parent mid-level low/vort max, taking it to
the central border area of OK/KS by daybreak. While it will not be
constant or overly-heavy in most areas, various "waves" of mainly
light freezing rain/sleet will continue overspreading the CWA
from south-to-north. Another 1-2 tenths of an inch (at least) of
ice accrual is likely overnight mainly within the southeast half
of the CWA, with northwest areas seeing a little more in the way
of light sleet (ice pellets). Low temps will drop only a few
degrees at best from daytime highs, mainly upper 20s. Although
still fairly light, winds will start to gradually increase toward
10 MPH sustained out of the north-northeast late in the night.

Monday daytime:
The daylight hours will likely feature the overall heaviest/most
concentrated precipitation bands of the entire event. This is
largely due to large-scale forcing increasing as the mid level
vort max tracks just to our south-southeast toward the KS/MO/NE
border area as the day wears on, along with a closely associated
surface low underneath the nearly vertically-stacked system.
Overall, expect worse conditions Monday than today given this
increase in frontogenetical forcing/precip intensity. Once again,
most of this precipitation should fall either as freezing rain
and/or sleet, with freezing rain most favored in eastern/southern
counties. Meanwhile, colder air aloft will gradually work in from
the west as the day goes on, finally changing some precipitation
(especially along the back edge of the main deformation band) to
actual snow or at least a sleet/snow mix, with perhaps as much as
1-2" of snow in western zones. One of the biggest questions
involves surface temperatures, as they could warm just enough
around freezing to again prevent truly significant daytime ice
accumulation/impacts, especially in our far southeast counties. If
warming is limited and freezing rain remains the predominant type
in our KS zones, the current Warning expiration time of Noon may
need extended, and next few shifts will have to consider this.
Also of greater concern tomorrow will be increasing northerly winds
as the main low pressure system passes by. Although still not
expecting truly strong winds, sustained speeds of 15-20 MPH and
gusts to at least 25 MPH are looking more likely, which could put
added stress on power line issues.

Monday evening/night:
Various models agree that the vast majority of precipitation
should be over with by sunset. as the main system quickly departs
along the IA/MO border by sunset. However, at least a brief period
of mainly light snow or a snow/sleet mix could persist into the
evening before largely ending by midnight. For now, have not
extended any light precip mention beyond midnight but it could be
a close call. Fortunately, winds are actually expected to decrease
slightly as the night wears on, with gust potential back under 15
MPH by late in the night. There could be some clearing mainly west
while clouds hold firmer east. Low temps are aimed teens northwest
to mid-20s far southeast.

.LONG TERM...(Tuesday through Sunday)

Issued at 431 PM CST Sun Jan 15 2017

Like yesterday, did not devote much time delving into the latter 5
days of the official forecast given the copious attention given to
these first 36 hours. Fortunately, there does not appear to be
anything "major" going on, especially Tuesday-Thursday.

Briefly summarizing:
Little change made from previous forecast. The best news for most
folks is that we are looking at fairly decent warm-up to at least
slightly above average levels.

Temperature summary:
Although am admittedly a little skeptical about how quickly we
warm up, there is plenty of evidence per both the GFS and ECMWF
that westerly-to-southerly low level flow will give things a nice
boost to well-above freezing, especially on Wednesday-Thursday.
High temps Tuesday are aimed into the mid-30s to low-40s range,
with highs then aimed well into the 40s to low-50s Wednesday-
Friday before easing back a few degrees next weekend more into the
low-mid 40s, but of course this is still above-normal if it
verifies. Overnight lows generally 20s to around 30s most nights.

Precipitation summary:
While there is fairly high confidence that Tuesday-Thursday
remains dry as the only halfway decent mid level wave of note is
currently expected to pass at least slightly to our south, the
forecast then becomes littered with several 20-30 percent chances
for rain and/or snow during the entire Friday-Sunday time frame.
By no means will it precipitate on each one of these days nights,
but largely because the primary models (GFS/ECMWF) are not in
great agreement with each other in the timing/position of the next
series of waves lifting into the Central CONUS from the west-
southwest, these low PoPs are included each day as at least one of
these two models shows that "something" could be around at almost
any given time. At least for now, we are not overly concerned with
these precip chances as potential amounts look pretty low and the
temperature regime is generally warmer as mentioned above. That
being said, in the coming days we will have to dive a little
deeper just in case a light wintry mix (freezing rain/sleet) may
be lurking in there somewhere instead of just rain/snow.

&&

.AVIATION...(For the 00Z KGRI/KEAR TAFS through 00Z Monday evening)
Issued at 557 PM CST Sun Jan 15 2017

Freezing rain will be the main precipitation type through this
forecast, with maybe some sleet. There could be a transition to
snow very late in the forecast, but should not amount to much.
Expect wind to finally pick up more toward the end of the forecast
as the upper level system causing the inclement weather moves out.
Continued LIFR visibility for most of the forecast if not all, and
visibility could be quite variable depending on how heavy the
precipiation is.

&&

.GID WATCHES/WARNINGS/ADVISORIES...
NE...Ice Storm Warning until midnight CST Monday night for NEZ041-048-
     049-062>064-074>077-083>087.

     Winter Storm Warning until midnight CST Monday night for NEZ039-
     040-046-047-060-061-072-073-082.

KS...Ice Storm Warning until noon CST Monday for KSZ005>007-017>019.

&&

$$

SHORT TERM...Pfannkuch
LONG TERM...Pfannkuch
AVIATION...Heinlein



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