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Area forecast discussion 
National Weather Service Hastings NE
1146 am CST Monday Dec 22 2014

issued at 1103 am CST Monday Dec 22 2014

Sent an update to the forecast to increase high temperatures a few
degrees as with a few peeks of sunshine...good mixing and strong
winds...the temperature curve was a little behind this morning.
Evenso...with 20-25 miles per hour will still feel like a rather
cool day. In addition to the change to forecast temperatures today...also
tweaked cloud cover as well as delayed timing of precipitation this
evening/overnight a few hours per latest model guidance.


Short term...(today and tonight)
issued at 358 am CST Monday Dec 22 2014

Bit of a messy upper level pattern in place across the northern/Central
Plains...which in general sits under the influence of a broad
trough axis extending south out of between ridging
over the east/west coasts. This pattern has embedded
of which is making its way across the area...bringing scattered
precipitation. Currently...outside of the eastern fringes of the
County Warning Area...isnt a lot going on. At the surface...seeing the cold front
/at least the wind shift/ starting to work its way into western
portions of the County Warning Area...while srly winds remain in place across
central/eastern portions. As expected...temperatures have remained above
freezing overnight...with 3 am observation ranging from the middle 30s to middle
40s...allowing what precipitation is falling to do so as liquid. Seeing
some brief patchy fog develop in areas where winds drop off prior
to the passage of the have that mention going in the
forecast the rest of this morning.

The main story through the short term period of today and tonight
remains with precipitation chances associated with shortwave energy
sliding into the area. Models in decent agreement showing this
first disturbance not really pushing out of the area today...with
time becoming phased in with additional energy sliding
S/se...developing into a more closed circulation by this evening.
Agreement with its placement at 00z this evening isnt too
bad...its elongated feature centered roughly over the central
South Dakota/ND border...with an axis extending S/southeast into northwestern MO. Getting
into the evening/overnight hours...even this close to the period
models continue to show some differences...leading to overall
lower confidence in the forecast. While most models show the low
remaining elongated with a lobe of energy rotating with it...the
GFS is a bit further east than others with the low by sunrise
Tuesday /over eastern IA/...others are more over scentral Iowa. It is
also quicker with bringing in snow wrapping around the backside.
With others a touch slower/west...forecast is trended more that
way...which resulted in some changes to the forecast.

For the daytime hours today...kept some probability of precipitation in across the entire
County Warning Area for this morning...but short term/hires models suggest part of
the day /like late morning through middle afternoon/ may not see did trend probability of precipitation back. Have some higher probability of precipitation starting to
work their way in from the north mainly later in the day with that
low becoming a bit more organized...with the question lingering
how fast the colder air works in and brings a change over to snow.
At this point...kept a rain/snow mix confined to the north /roughly
along and north of Highway 92/...with rain south of there. This will be
something for the day shift to keep a close eye on...if anything
moves in before 00z. As mentioned above confidence isnt the
highest...that GOES for temperatures as well. Am sticking to the
more pessimistic side of things...with not seeing a notable
increase in temperatures through the day...and have near 40 in the north
to middle/upper 40s in the south. Some models suggest we could get a
few degrees higher than currently forecast. Behind the
front...nwrly winds build in...and has been the case for a few
days now...models/guidance showing breezy conditions developing
from west to east through the day...with speeds reaching into the
15 to 25 miles per hour range with higher gusts.

For this evening/tonight...have higher probability of precipitation building south as that
upper level low gradually does the same...with the better
chances remaining across SC Nebraska. Do have a rain/snow mix lingering in
the evening in southern areas...but should quickly transition over to
all snow and remain that way through the rest of the overnight.
Better/more widespread chances for snow look to hold off until
Tuesday...which is a change from previous models. There is some
suggestion that especially prior to 06z tonight...locations south of i80
may see little/if anything. Didnt go quite that far north...but do
have the far southern portions of the County Warning Area dry until after 06z. With
models showing less in the way of quantitative precipitation forecast during the overnight
hours...did trend the forecast quantitative precipitation forecast/snowfall back a bit...with
totals generally in the half to 1 inch range across SC Nebraska...a few
tenths across NC Kansas. The breezy conditions look to continue
overnight...though we may see a brief period in the evening with
speeds tapered...before picking up again later with models showing
a reinforcing front moving through...tightening up the pressure
gradient across the area...along with a stronger corridor of winds
aloft starting to work their way in from the N/NW. These winds
combined with what snow falls could result in less than ideal
conditions...especially during that 06-12z Tuesday period.

Long term...(tuesday through sunday)
issued at 358 am CST Monday Dec 22 2014

Guidance suggests an upper tropospheric longwave trough axis will
extend from south-central Canada to the Southern Plains to start
the long-term forecast period at 12z Tuesday. This trough axis
is currently expected to linger over the central Continental U.S. Tuesday
into Tuesday night before moving east into the Mississippi Valley
and eventually the eastern Continental U.S. By late in the week. Upper
tropospheric ridging is then expected to build into the central
Continental U.S. Wednesday and Thursday before another upper tropospheric
trough axis approaches from the west late Thursday through
Saturday...and eventually clearing our area on Sunday.

Starting with the first trough axis Tuesday into Tuesday this time it appears the primary axis of upper
tropospheric thermal axis ahead of the trough axis will reside
east of our area by 12z Tuesday. That said...guidance also
suggests a closed low...near 700mb...embedded within the trough
axis...will be noted over Iowa. During the day Tuesday...a lobe of
locally enhanced vorticity is expected to swing south and then
southeast along the west/southwestern periphery of the closed low.
DPVA and resultant Omega ahead of this lobe appears as though it
will be sufficient...along with tropospheric moisture...for
precipitation production across much of our area during the day
Tuesday. At this time it appears any Omega in association with
this lobe of energy should clear our area by 00z Wednesday...thus
confining any precipitation across our area to the day Tuesday.

Taking an even-average of the NAM...operational GFS and ec
presents liquid precipitation amounts of ~0.10" during the day
Tuesday...which slightly undercuts wpc guidance but not by much.
Forecast proximity soundings from across the County Warning Area...per the NAM and
operational GFS...suggest the lower troposphere will remain
supportive of snow through the morning hours. This should remain
true across our north/northwestern County Warning Area during the afternoon hours
as well...but there are some signals that enough lower
tropospheric warming could take place by Tuesday afternoon across
our south/southeastern County Warning Area to support more or a rain and snow mix.
An even-average of the NAM and operational GFS suggests snow-water
ratios of ~11:1 will be realized...which is just a touch below wpc
guidance of 12-13:1. Went ahead with snow-water ratios of around
11:1 Tuesday well as Tuesday afternoon across our
north/northwestern County Warning Area. For Tuesday afternoon across our
south/southeast...went ahead with ratios closer to 7:1 to account
for the potential mix of snow and rain. Given all this...snow
accumulation of around a half inch to as high as about an inch is
currently forecast during the day Tuesday. This
accumulation...along with accumulation from Monday night into
early Tuesday morning...should provide storm-total snow
accumulation of one to perhaps two inches.

In addition to the anticipated snowfall on increasing
boundary-layer pressure gradient is also expected to promote a
period of strong wind across much of the County Warning Area...with guidance
currently suggesting our west/northwestern County Warning Area will observe the
strongest wind...sustained at around 23kts with gusts near 30kts.
Given this...will continue to highlight the potential for
restricted visibility in blowing snow on Tuesday.

An overall lack in Omega should promote dry conditions to our area
Tuesday night through Wednesday night. Heading into the day
Thursday...and more so Thursday night and Friday...guidance
suggests Omega ahead of the aforementioned second upper
tropospheric trough axis will be sufficient for precipitation
production across portions of the region. Confidence on when and
where exactly this precipitation will occur remains somewhat
low...with the ec suggesting light precipitation will be realized
over our west/northwest County Warning Area by late Thursday....and more over our
north/northwestern County Warning Area during the day Friday. The operational GFS
on the other hand is somewhat slower and slightly farther
northwest in the track of the storm system. Nonetheless...there
appears at least a chance for measurable light precipitation
across portions of the County Warning Area Thursday into Friday and as a
result...went ahead with 20-30% probability of precipitation across portions of the
area...with the highest probability of precipitation relegated to our northwestern County Warning Area
where Omega is currently expected to be strongest. Obviously
trends will need to be closely monitored as this ties in with the
Holiday but at this time...this appears to be a low-impact event
of perhaps some light snow.

Persistent southerly boundary-layer flow and resultant thermal
advection should provide a subtle warming trend Tuesday through
Thursday...with highs starting in the low to middle 30s on Tuesday
but climbing into the upper 30s to middle 40s by Thursday. The
passage of a boundary-layer baroclinic zone Thursday afternoon or
night is then expected to allow a cooler air mass into the
region...with highs falling back into the 30s for the most part to
finish the forecast period. Overnight lows in the 20s are
currently forecast for the most part Tuesday night through
Thursday night...with lows in the teens then expected to finish
the forecast period.


Aviation...(for the 18z kgri/kear tafs through 18z Tuesday afternoon)
issued at 1103 am CST Monday Dec 22 2014

Mainly VFR conditions are expected for the next 6 hours or so as
ceilings have lifted behind this mornings front. Evenso...expect
generally overcast skies with ceilings near or above 6kft through
around 23/01z. Thereafter...ceilings will lower and MVFR or lower
ceilings/visibilities are expected the remainder of the period as a
secondary cold front and some light snow traverse the local area
overnight/Tuesday. In addition to lowering ceilings...winds are not
expected to relax much overnight as the associated surface low
begins to organize and become negatively tilted late this
afternoon through the overnight hours. As a result...expect breezy
northwesterly winds through the period...potentially gusting to
near 25 kts or higher later this afternoon...and again during the
day on Tuesday...with potentially lower visibilities possible in light


Gid watches/warnings/advisories...


short term...adp
long term...Bryant

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