Interesting read on a possible snowstorm this weekend...

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hardyjim
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Interesting read on a possible snowstorm this weekend...

Post by hardyjim » Mon Dec 16, 2013 10:38 am

Forecasters discussion-


Mostly dry into Thursday...then becoming unsettled with increasing
risk of a major winter storm near or over area this weekend.

Overview...initialization and verification once again good on
synoptic scale and with kinematic fields. Bl relative humidity issues and snow pack
feedback again are fair to poor with most solutions too dry in bl.
Run to run variance and inter model continuity supports a 70/30 mix
of Gem-NH/hi res European model (ecmwf) and UKMET with GFS. This supports our much
discussed weekend winter event to pull further north as suggested in
past 3 days of afd/S. Expect the 06z...GFS run to pull north in a
belated fashion. As discussed over past 72 hours...this type of
upper low tends to pull further north than solutions have shown
the past 24-36 hours. Large scale tools of pw/S...forcing and
duration support the weekend system will produce a large area of
4-10+ inches of snow in or near our County Warning Area. As discussed previous
days...jet magnitude on solutions are even more ominous with
170-210 knots right rear over area...coupled with left front over
area. This clearly shows major moisture physics and phasing issue.
We continue with increasing concerns of the reliability of all
solutions.

Comment...the model run to run problems are part of the model
instability issues routinely discussed. There is a reason in the
"forecast funnel" process we talk about a top down large scale to
small evolution. This is solely due to latent heat processes.
Remember high level jet streak principle are always less impacted
and using conceptual models...will aid the decision maker. This
weekend event will be much better clarified the next 12-24 hours.
Don/T be surprised of a need to raise winter concerns greatly.
<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>>>>>>
This is similar to the November severe weather event that was all
of a sudden "obvious" about 60-72 hours out. Its all related to
the thermodynamic issues with the models (entropy...enthalpy...Gibbs
free energy mainly).

<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<>>>>>>>>>>>>>>>>>>

Saturday and Sunday...have low probability of precipitation which appear are too low by
20-30+ percent or more due to over Reliance on 00z GFS. Temperatures
may need raising 2-5 degrees also. This is the time period the
winter storm could affect the region. Inclined major changes will
happen by day shift as GFS probably trends wetter with north shift
of storm track. Will mention winter storm risks in the hazardous
weather outlook. Possibly the weather story product. Remember...all
the other solutions are further north with system in a manner that
is typical with type of winter event.


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TimMAz6
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Post by TimMAz6 » Mon Dec 16, 2013 7:03 pm

OK......what does that mean? :D Tell me the numbers!!
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hardyjim
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Post by hardyjim » Wed Dec 18, 2013 7:15 am

heres what they said today...looks like an Arctic dump after this too but short lived...at least in its initial intensity..



This weekend...potent winter storm continues to look ominous for
portions of the dvn County Warning Area. Strong energy diving along the West Coast
will phase with the upper low and get ejected out into the Southern
Plains on Saturday and then into the Ohio Valley on Sunday. A 70
knot low level jet will transport copious moisture from the Gulf and
overrun the stalled front to our south. The coupled jet structure
that we have discussed previously is still depicted. Initially the
precipitation should begin as a mix of freezing rain...snow and sleet
in our southern County Warning Area on Saturday spreading northward as the day
progresses...but in the form of snow with the colder air in place.
Careful perusal of the forecast soundings all across the County Warning Area was
needed. The heaviest precipitation is expected Saturday night into
Sunday. While there may still be a mix of snow and sleet in our far
southeast Saturday evening the bulk of this event will be moderate
to possibly heavy snow...except our far northwest County Warning Area where snow will be
light. The deformation zone will linger on Sunday with more
accumulations. Strong winds should also develop on the back side of
the system which may hamper travel on the weekend just before
Christmas. Colder air to follow the passage of this winter storm.


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TerdalFarm
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Post by TerdalFarm » Wed Dec 18, 2013 7:49 am

The NWS office here in Tulsa, Oklahoma, is also unsure:
http://www.srh.noaa.gov/graphicast.php?site=tsa&gc=1

Might be freezing rain changing to snow like the last one, or maybe just a cold rain followed by some snow.

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hardyjim
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Post by hardyjim » Wed Dec 18, 2013 1:19 pm

Today's


Looks like a fun storm....





A winter storm appears likely to impact the Midwest...including the
dvn County Warning Area Saturday afternoon through Sunday afternoon.

The surface boundary will continue to drift east Friday before a
storm develops along the front in Texas Saturday. A strong cut off
low will become phased with northern stream energy to create
cyclogenesis over the Midwest...with a surface low track with
intensification from about 1000mb to 988mb during a 24 hour period
as it GOES northeast over Saint Louis to near South Bend Indiana.
This is the so called...Golden path...for deformation zone snows
over our County Warning Area. Thermally...we are not in Arctic air...but appear cold
enough for sleet in the southeast Saturday afternoon to snow central
and northwest at onset. All locations via cold advection and intense
dynamics should switch to moderate to heavy snow Saturday evening
into early Sunday...with increasing surface winds especially after
midnight into Sunday. Moderate to heavy snow should continue
Sunday through early afternoon before dynamics shift northeast
ending the snow event. All told...this appears to be a storm capable
of high end winter storm impacts...with amounts over 6 inches
likely. I will not issue a watch on this shift...as it is just too
early in the time line. However...should it look to have the same or
greater potential tonight or tomorrow...a watch issuance is very
much likely.

The winds aloft and surface pressures forecast do not appear to meet
criteria for an expected blizzard via pattern recognition from local
studies. That said...again...this storm does appear to fit into the
category of a higher end winter storm with both heavy snow and
notable wind expected from Saturday night through Sunday afternoon.

It should also be said that Saturday itself should not be a
hazardous day prior to snow and sleet moving in from the south
during the middle to very late afternoon. From the quadrant cities on
north...it is likely be to a dry day with no interruption to
seasonal shopping and travel. The far more challenging/dangerous
time period is Saturday night and Sunday...when snow and blowing
snow will likely rule the landscape in our region.

Temperatures throughout the forecast period are a blend of model
guidance...but as we go forward...it seems likely that Sunday night
and Monday night may need to be lowered to well below zero given the
likelihood of fresh snow cover.

Beyond...there are some indications of a weak clipper towards
Christmas day...with fairly cold conditions lingering through late
December.









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