Wx Infinity Forums

For the Beaumont/ Port Arthur Area...I have this...

Here is the NAM 12Z...

tireman4 wrote:This is a reference page for the Skew T that was posted.

That's right. The balloon confirmed that the atmospheric profile matched the left image (snow). As I posted elsewhere:

Sleet occurs when precipitation encounters an above-freezing layer on its way down, followed by a layer of sub-freezing air. The rain freezes into sleet pellets and that's what we see at the surface. Without that warm layer (warm nose, because it looks like a nose on the sounding), the precip starts as snow and remains snow all the way down. That's what the Houston sounding indicates. The main question now is how deep will the surface above-freezing layer be. Currently, this above-freezing layer near the surface is about 2500 ft thick. Snow will start to melt as it encounters this above-freezing layer. A thick enough layer will result in all the snow melting before it reaches the ground. A little thinner and the snow partially melts before reaching the ground. This would result in snow pellets (rather than flakes). However, if the freezing level drops, as models are predicting, then the snow would reach the ground tonight. Surface temperatures would be above freezing, but the snow could accumulate on chilled surfaces, like cars. Streets would remain too warm.

18z NAM is more bullish.

And there's the cut off line just south of my house, again. Yawn.

18z NAM 3km brings heavy snow into Harris and Montgomery counties late tonight.

18Z NAM 12km keeps light to moderate snow in Montgomery and Harris for 6-8 hours.

Sooo.. when will the winter advisories for our CWA be issued

davidiowx wrote:Sooo.. when will the winter advisories for our CWA be issued

If any, within the next hour.

Sharp cut off somewhere between 99/Parkway and hwy 105 on most models. Very close call for Monty county, but should still see something in the air. Hopefully...

The 18Z U of H sounding was sent to the Houston/Galveston NWS office. I've been in contact with Dan Reilly over there. It does look like the rain will change to snow tonight. The 18Z NAM snow totals map (below) is impressive, but I suspect it isn't taking into consideration the warm ground and the melting that will occur in the above-freezing layer near the surface. Still, I'm very confident we'll see snowflakes tonight. Best times still look like from 8pm or so through about sunrise.

Looks like the 18Z NAM is swinging some stronger vorticity thru the area around Midnight which I'm guessing is related to the uptick in intensity we are seeing on this run.

sau27 wrote:Looks like the 18Z NAM is swinging some stronger vorticity thru the area around Midnight which I'm guessing is related to the uptick in intensity we are seeing on this run.

Yes, that's the main upper-level disturbance rotating across our area. With even colder air aloft, it's a perfect setup for snow - with the exception of the slightly above freezing surface temps...

wxman57 wrote:

sau27 wrote:Looks like the 18Z NAM is swinging some stronger vorticity thru the area around Midnight which I'm guessing is related to the uptick in intensity we are seeing on this run.

Yes, that's the main upper-level disturbance rotating across our area. With even colder air aloft, it's a perfect setup for snow - with the exception of the slightly above freezing surface temps...

Those who set up under the heavier bands, especially north of I-10, could see temps drop quickly to (around) freezing, right?

wxman57 wrote:

sau27 wrote:Looks like the 18Z NAM is swinging some stronger vorticity thru the area around Midnight which I'm guessing is related to the uptick in intensity we are seeing on this run.

Yes, that's the main upper-level disturbance rotating across our area. With even colder air aloft, it's a perfect setup for snow - with the exception of the slightly above freezing surface temps...

Never thought I'd see this kind of snow optimism from Wxman. Its fantastic

Looking at model data it looks like between 04z-6z will be prime time for snow as the additional shortwave rotates through and moisture spreads further north. Interesting to see how far north precip has spread. All the way up to the DFW area.

A nod to Paul Lewis.


000
FXUS64 KHGX 071756
AFDHGX

Area Forecast Discussion
National Weather Service Houston/Galveston TX
1156 AM CST Thu Dec 7 2017

.AVIATION...
VFR conditions should persist for the next 24-36 hours - with the
exception of near any moderate precip where cigs may fall into
MVFR territory for a time.

Plume of moisture & precip paralleling the coast will continue
thru the day. Metro airports northward will probably see some
intermittent breaks in the precip (and it may be totally done this
afternoon north of CXO). Despite the possibility of some isolated
sleet/snow mixed in with the rain, above freezing surface
conditions will keep impacts virtually nil into the evening.

Later this evening and overnight, we should see another band of
precip develop and parallel the coast. This timing will also
correspond to when even colder upper level conditions favor a
transition to snow being the more prevailing wx type. Again...ground
temps should be above freezing so not expecting accumulations
there, but can`t rule out a dusting on stationary metal objects
etc. Forecast soundings south of the metro area actually show the
more favorable, and slightly longer duration, of the more
favorable conditions for this. Think precip will taper off north-
to-south around 7z IAH to 14z GLS. 47

&&

.OTHER...
NWS Houston/Galveston would like to acknowledge the forecaster
that issued the previous (and his last) discussion below. He`s
been involved with all aspects of this office for the past 23
years. "PL-40" has worked and forecasted the most memorable
floods & severe/tropical/fire/winter/hazmat events this area has
seen during that time period. His fingerprints are left on
virtually every program here...most recently the climate program.
We truly appreciate his service!

There must be a policy of never using forecaster names in the discussions, so long Paul Lewis.

I hate to Grinch it up, but it's just going to be very cold rain with possible slick spots on stop signs and street signs. Nothing to get excited about.

Cromagnum wrote:I hate to Grinch it up, but it's just going to be very cold rain with possible slick spots on stop signs and street signs. Nothing to get excited about.

This is not supported by the soundings, now it probably won't stick but there should be flakes falling.