The posts in this forum are NOT official forecast and should not be used as such. They are just the opinion of the poster and may or may not be backed by sound meteorological data. They are NOT endorsed by any professional institution or 
December 20, 2004
this Monday morning
"The time is 330 AM this Monday morning. I have 2 items here to intice your
attention.
It's my hope to please both storm lovers, with severe weather, and winter
weather
weenies, (www's), alike in the same week, and that's hard to do in these parts.
This weather I'm alluding to is NOT coming today or tomorrow; this is the
extended
range forecasting objective of mid-to-late this week.
Briefly, storm lovers get the attention first near mid-week this week; winter
weather
weenies get the attention late this week.
I have not gone through the laborious 20-item checklist over severe weather yet
for Wednesday as variable factors are continuously changing and is too soon to
evaluate
with reputable, trusting numbers just yet, but there is enough data I've
reviewed
for 72 hrs out (3 days out), that suggests that you will see another episode of
severe weather warnings get issued for Southeast Louisiana region. I'm not
going
to pour through the aerial extent of this, nor types yet, but I do see all 3
types
of severe weather on the table. Quality of moisture return and temperature
recovery
are a couple negatives, but there are also several good positives that lean
toward
severe weather as well. Since severe weather occurs more times out of the
calendar
year than does wintery weather, I'll have to put storm lovers on hold, for the
moment,
while I tend to the www's right here.
Based ONLY off the 00Z data from a long-range model, shows a continued threat
for
wintery precipitation for Southeast Louisiana region. Many times you've been
seeing
this particular scenario get put on hold, go away, then only to re-appear again
as a re-newed prospect for snow. It has re-newed its vow again. No
cheerleading
here now, nor applause, because as simple as just another short 12-hour run
later,
then things can swap right back to NO SNOW as it had done 24 hours ago. I'll go
over a short listing of items here.
In brief, I review a checklist of about 7 items for snow. In it, more than half
of these items have had their respective criteria met from the model run last
night
for late this week, by Friday. Things begin changing one by one starting
Thursday.
The lowest thickness layers criteria gets met, first. Then, by Friday, the mid-
layer
thickness of 850 to 700 Hpa level get met. All this while H85 temperatures meet
and exceed thresholds, and so too does H7 temperatures as well. For those of
you
who utilize only the traditional, conventional 1000 to 500 HPa thicknesses,
don't!---because
you can get burned! There's much more to this science than a simple inspection
of that rain/snow line! A saturated layer is forecast on area profile soundings
on Friday of this week, at least above the surface. This means that surface
temperatures
could wet-bulb down a third of the way down toward the dewpoint in the lower
layers,
if virga started up, which would better the surface temperatures that'll likely
be struggling to hover near the freezing mark. The freezing levels as shown on
the skew-T vs. Ln P diagrams shows the entire temperature profile to be below
freezing
for Friday. (We'll see about that!) Getting below 32 has been a chore, and
still
hasn't been achieved officially yet, in New Orleans, at the surface! This means
on this 108 to 120 hour forecast, which is a 4 1/2 to 5 day forecast, that given
such a PROPOSED profile, then it would precipitate all as snow; no mix. Gang,
you're
not new to meteorology, and you've been around the block a few times. A 4 1/2
to
5 day forecast is subject to change another 4 more times, so no celebrating or
dancing
on your desks just yet. It is also understood that you come into this
discussion
this morning, accepting the fact that a 4 1/2 to 5 day forecast is BARELY held
together
with bubble gum and barbed wire at best!!! So remember my words here in the
event
it doesn't come to fruition, but don't forget what's about to be said when it
does.
Let me continue with some age old FALSE myths, particularly addressing the
native
New Orleanians here, who are not well-versed with snow:
False Myth #1: The surface temperature has to be 32 degrees F, or lower, in
order
to snow. This is false. Many people have a hard time believing this is false,
unless, you're one who is well-versed with snow situations in northern climates.
Did you know that even wet snow or sleet can still occur with surface
temperatures
as warm as the upper 30's and even lower 40's? This comes with a stiff,
stipulation
though. And it is this...The above freezing temperatures must be CONFINED TO
THE
LOWEST 500 ft of the ground, and the temperature profile must be freezing from
500
ft and above; otherwise all bets are off.
False Myth #2: There must be a surface low in the Gulf of Mexico for snow or
wintry
precipitation to occur here. There doesn't have to be. I've even witnessed
snow
flurries and sleet here in New Orleans--both of which were non-measureable and
occured
a few years ago, and in the '96-'97 winter whereby they sent everyone home for
non-measureable
sleet that occured one winter morning. (What do you mean non-measureable?)
This
means a trace; it doesn't collect on the ground. It's not a necessary
condition;
though, this typically would promote the best ideal situation for accumulating
snows.
Trace amounts that are not visible on the ground and only in the air, melting
upon
reaching the ground, are easier to get here in New Orleans. I've counted at
least
3 times when this occurred in just the 8 years I've taken up residence here.
Once,
non-measureable, trace amounts occurred when I worked for Nash Roberts in the
'96-'97
winter and again on January 1, 2001, and yet a third time on January 2, 2002.
(Why
does nobody remember these times, then?) They don't remember or recall these 3
times because there was NO accumulation on the ground in New Orleans, that's
why.
It was only trace amounts flying in the air, for which you had to be looking
hard
for, and at least in 2 of those 3 events, it occurred at nighttime when everyone
was in bed. These events go unnoticed, unless there are accumulations that rest
on the ground, which is far, far much harder to get here in New Orleans. A
simple
TRACE of snow FLURRIES or sleet are easier to get during any given season.
False Myth #3: The 540 thickness has to be over or to the right of New Orleans
to get wintery precipitation. This is not true either. The entire atmospheric
sounding profile must be inspected to gauge a determinant toward freezing or
frozen
precipitation types.
Heaviest snows w.r.t. a surface low's position can vary quite dramatically,
anywhere
being between 150 miles to 240 miles north of a surface low, with even more
exceptions
to this bounded range given, than ever thought possible. This correlates to
about
roughly 2 to 2.5 degrees of latitude to the LEFT of the track of a surface low.
It also corresponds to about 1.5 degrees to the left of an H85 low.
Well, we could go on and on here, but what's the point, really, with a 5-day
forecast?
The next writing I release to you will be one on severe weather in another day
from
now. Then, if it still continues looking like wintery weather comes to fruition
late this week, then I will once again write on that subject as time draws
nearest.
The more times I have to write this week, then the bigger that either event
looks
to me.
If you'd like to do more read-up on what is meant by thicknesses, then I have an
excellent posting that I composed a couple days ago and have placed it on my
website
there on Saturday for you all to view, which is sitting BENEATH the picture
appearing
there: http://www.home.earthlink.net/~pvamagic It is still there for you to view."
T. Scott Barry
Meteorologist, OU grad. '95
pvamagic@earthlink.net
_________________________________
P.S. Margaret Orr from channel 6 mentioned possibility of frozen precip. also this morning. YIPPEE!!!
