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Area forecast discussion 
National Weather Service Hastings NE
542 am CST Sat Dec 20 2014

Short term...(today and tonight)
issued at 356 am CST Sat Dec 20 2014

Map analysis indicates a weakening upper tropospheric trough axis
moving into the middle-Mississippi Valley and a ridge axis over the
central to northern rockies. Upper tropospheric flow over our area
remains from the northwest as a result...but is fairly weak at
around 40kts near 30000ft above ground level. At the surface an area of high
barometric pressure is noted across the Great Lakes region...with
a trough along the Front Range of The Rockies. Boundary-layer flow
across our area remains from the south to southwest as a result.
Satellite data and surface observations also indicate a band of
stratus extending from northeastern Kansas into eastern Nebraska.
Fog is also noted underneath this stratus shield. Visibility
restriction in this fog is generally in the 3-6sm range through
most locations...with the only exception being along the western
periphery of the stratus shield where visibility restriction of
1/4sm to 1sm is being observed. The western periphery of the
stratus currently extends from near kodx to near kk61 and as a
result...locations generally west of Highway 281 are observing
clear skies and little if any visibility restriction...while
locations farther east are observing visibility restriction of
1/4-1sm with a ceiling of 100-500ft above ground level.

Guidance from the NAM...operational GFS and ec all suggest the
northwesterly upper tropospheric flow over our area will become
quasi-zonal through the next 24 hours as an upper trough axis
begins to develop over the Central Plains by 12z Sunday. Meanwhile
at the surface...the trough along the Front Range is expected to
strengthen somewhat thus allowing for continued south to
southwesterly boundary-layer flow. Given all this...an overall
lack in Omega should prevent measurable precipitation from being
realized across our area through the next 24 hours...and such has
been presented in the forecast.

As for the stratus and fog currently impacting portions of the
area...satellite trends through the past several hours indicate
the cloud deck...as well as the fog...is moving east at 5-10kts.
Assuming this trend persists...the stratus and fog should clear
our area to the east by 15z or 16z. Until that point however...a
thin corridor of dense fog will certainly remain possible along
the western periphery of the cloud deck...primarily along our
extreme eastern County Warning Area and as a result...opted to continue the dense
fog advisory for locations generally east of Highway 281 until
16z.

Looking ahead to tonight...the NAM suggests another round of
stratus could be realized over our east/southeastern County Warning Area as
isentropic upglide and saturation...primarily along the 280-300k
surfaces...commences. The operational GFS is not nearly as robust
with the cloud cover...but given the trends of the past few days
opted to play it safe and increase cloud cover across the
County Warning Area...with the most dense cloud cover residing across our
east/southeastern County Warning Area. There are also some indications...again
primarily from the NAM...of fog development across our
east/southeastern County Warning Area and as a result...went ahead with fog in the
forecast late tonight into Sunday morning across our
east/southeast.

Additional sunshine...when compared to the past several
days...should result in a significant increase in diabatic heating
and warmer temperature readings today when compared to the past
few days...with highs in the 40s to low 50s forecast for the much
of the County Warning Area today. The only exception is across our east/northeast
where cloud cover may linger a bit longer thus helping keep
afternoon temperature readings in the upper 30s. Little change in
the boundary-layer air mass and an anticipated increase in cloud
cover should then provide similar temperature readings tonight
when compared to early this morning...with lows generally in the
20s currently forecast.

Long term...(sunday through friday)
issued at 356 am CST Sat Dec 20 2014

Primary forecast concern revolves around precipitation chances.

The start of the long term period Sunday morning has models in
pretty good agreement with the overall story...showing the area
under generally zonal flow...influenced by a weak trough axis
extending south from the parent low over the ND/can border.
Expecting to see S/southwesterly winds in place...driven by a trough axis
in place through the High Plains. Kept the daytime hours on Sunday
dry...one disturbance is moving out but another is quick on its
heels. Some uncertainty exists as we get into the latter portions
of the day...as some models show the potential for some light
precipitation/light dz building north and possibly clipping the southeastern
corner of the County Warning Area ahead of this next disturbance. Think that
better precipitation chances will hold off until after 00z. Forecast high
temperatures for Sunday remain generally in the 40s.

Sunday night through Tuesday is a messy time frame with periodic
precipitation chances. Models showing another upper level shortwave
disturbance sliding southeast out of wcentral Canada into the
Dakotas...eventually developing into a closed low pressure system
by Monday morning. There is good agreement with models showing not
a lot of eastward movement with this system during the daytime
hours...with the general location over eastern or southern portions of Minnesota.
Monday night into Tuesday...a shortwave disturbance rotating
around this low pushes through the region...while the low is still
hanging around the Minnesota region. This more active portion of the
pattern looks to present the County Warning Area with some precipitation chances...though
models are fairly scattered with the generally light quantitative precipitation forecast...and
disagree some with the timing and location. Thus couldnt go too
high with probability of precipitation...kept things in the 20-30 percent range until
better agreement can be reached between models. Even though we are
getting into the latter parts of the month...models continue to
show the airmass Sunday night into Monday being warm enough to
support mainly rain for precipitation type...though a rain/snow mix in northern
locations not out of the question. A cold front will start working
its way through the area during the day on Monday...with the
colder air working its way in more into Monday night/Tuesday...so
the later portions of the event look to see a switch over to
snow...but things should be winding down...so notable
accumulations are not expected. Behind this frontal passage on
Monday...and continuing into Tuesday...gusty northwest winds are
expected. While speeds in the 15 to 25 miles per hour range are expected
Monday...a tightening pressure gradient along with stronger winds
aloft building is expected to result in winds in the 20 to
possibly 30 miles per hour range. Highs in the 40s expected once again Monday
/though may be reached earlier in the day/...with 30s forecast for
Tuesday.

Looking ahead to the Christmas evening /Wed/ and Christmas day
/thurs/ time frame...expecting dry conditions for Wednesday...with
models in pretty good agreement showing the main upper level
trough axis finally having shifted far enough east to move precipitation
on. Northwesterly upper level flow is expected to be in place
during the daytime hours...becoming more zonal with time Wednesday night
as another upper level disturbance starting to work its way
through The Rockies. West/northwest winds are forecast with speeds around 15
miles per hour...with highs in the middle 30s to middle 40s.

More uncertainty/lower confidence is in place as we get into
Christmas day/night and Friday...as models vary on the evolution
of the next upper level system. The GFS/European model (ecmwf) both keep most of/if
not all of the daytime hours dry...with the ec trying to push some
precipitation into northwestern portions of the County Warning Area by the end of the day. The ec
is showing a stronger system...digging further south into The
Rockies...before pushing out onto the plains Thursday night/Friday
and bringing accumulating snow to the County Warning Area. The GFS shows more of a
northwest flow clipper type system...with the brunt of the lift/quantitative precipitation forecast
sliding across South Dakota/northern Nebraska...barely clipping the northern fringe of the
County Warning Area before quickly sliding east of the County Warning Area early Friday morning.
At this point cant really buy full into either solution...and have
low chance probability of precipitation cwa-wide. Along with probability of precipitation...temperatures may need
adjustment depending on how models trend...as the European model (ecmwf) is also a
much colder solution.

&&

Aviation...(for the 12z kgri/kear tafs through 12z Sunday morning)
issued at 542 am CST Sat Dec 20 2014

VFR conditions currently forecast for kear. Vlifr to start for
kgri...but VFR conditions are also expected at kgri later today.

Stratus...with a base in the 100-500ft above ground level range...persists
across the area generally along and east of a line from kodx...to
kgri and kk61. Visibility restriction to around 1/4sm in fog also
persists generally along the same line from kodx...to kgri and
kk61. Unfortunately...satellite trends and surface observations
through the past hour or so indicate the stratus and fog has
stalled and is no longer moving east as it was earlier this
morning. As a result...it now appears vlifr conditions will
persist at kgri through the first few hours of the taf. As a
result...went ahead with vlifr conditions in the taf for kgri
12-16z...with VFR conditions then forecast 16z Onward. Obviously
this will need to be closely monitored with taf amendments
possible should the stratus decide to move out more quickly or
worse...linger longer than currently expected. As for kear...the
stratus appears safely east for now and thus the VFR forecast.
That said...taf amendments are also possible for kear should the
stratus decide to retrograde west...but it is Worth mentioning
that...at this time...there are no indications the stratus will
move back west this morning. The surface wind at both taf sites
will start fairly light...but eventually become more established
from the south/southwest at 5-10kts later today.

&&

Gid watches/warnings/advisories...
NE...dense fog advisory until 10 am CST this morning for nez039>041-
047-048-062-063-075-076-085-086.

Kansas...dense fog advisory until 10 am CST this morning for ksz007.

&&

$$

Short term...Bryant
long term...adp
aviation...Bryant

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