re: February 2019 Cold blast and southern snow discussion thread

Thanks.

WAFB getting in on the action now predicting snow Tuesday morning for Baton Rouge

This solution looks WAY more like a snow potential than some other models on the previous pages.
Anytime the snow is predicted from the outset, not a rain first/ change over to snow solution, it is more likely.

However, the big question should be the precipitation total. These Arctic fronts tend to dry out things, therefore I can't imagine a lot of precipitation with the system on Tuesday.

NWS Lake Charles discussion this morning (Lake Charles has domain over Alexandria)

quote:

---

This morning`s surface analysis indicates a 1024 hPa high pressure
extends across the northern Gulf Coast. A weak surface trough was
noted over Central Texas along the periphery of the surface high.
This surface trough is forecast to move southeastward throughout
today. This trough could provide enough forcing for ascent to
support isolated rain showers, particularly across the Piney
Woods, later today. However, given the weak nature of the surface
system and only marginal upper level support, I elected to leave
the short term consensus blend "silent" (<14%) PoPs in the
forecast for today. The dry conditions and near to slightly above
normal temperatures are expected to continue through Monday as
high pressure remains in place over the region

A more significant weather system is expected for our region
early next week as an upper level trough digs into the northern
Plains. This will support the development of a strong cold front
which is expected to move through the region Monday night through
Tuesday morning. Forecast model soundings indicate that there will
be a 3-6 hour period where the temperature profile could be
supportive of some snow. However, this will coincide with the time
period that precipitation is exiting the region and the
atmospheric column dries. Therefore, leaned closer to the GFS
solution with the potential for snow to mix in with the rain late
Monday night into Tuesday morning resulting in little to no
accumulation. Confidence in the likelihood or lack thereof for any
snow accumulation will increase as the event gets closer.

The more significant impact from this system will be much colder
temperatures during the second half of next week. Model guidance
is forecasting 850 hPa standardized anomalies of -1 to -2 sigma
over the region during the middle part of next week. The coldest
temperatures are expected Tuesday night into Wednesday morning,
when several hours of below freezing temperatures are expected. A
hard freeze will also be possible across portions of Central
Louisiana. Below normal temperatures are expected to continue
through Friday when the next shortwave trough is forecast to
approach the region. Long term guidance currently has a fair
amount of spread in the location and timing of this shortwave.
Therefore, only carried slight chance to chance PoPs from Thursday
through Saturday based on the uncertainty in the upper level
pattern during this time frame.

---

ETA: and here's what Shreveport is saying

quote:

---

LONG TERM.../Monday through Friday/

NW flow aloft will remain dominant over the Srn Plains/Lower MS
Valley Monday, ahead of the next longwave trough that will begin to
amplify as it digs SE into the Srn Plains and Ark-La-Tex region
Monday night. Low level moisture return will not deepen sufficiently
until Monday afternoon ahead of the associated arctic front, which
will begin entering the I-30 corridor of NE TX/SW AR by mid to late
afternoon. The WSW low level flow ahead of the front will yield
above normal temps across the region Monday afternoon, before
quickly falling with the fropa Monday night. There still is pretty
good agreement amongst the ECMWF/GFS/NAM with the placement of the
front at 00Z Tuesday, extending from near the TYR/GGG areas NE to
just S of TXK to ELD, although the GFS has trended a bit faster its
run 24 hrs ago with the progression of the front from late afternoon
through the overnight hours. In any case, all of the medium range
guidance has trended a bit faster with the cold air spilling SE in
wake of the fropa Monday night, even as areas of SHRA develop near
and behind the front where large scale forcing will be centered
ahead of the primary trough axis. With the faster intrusion of the
colder subfreezing sfc air and aloft, it`s becoming more apparent
that there will be a transition to a mixed wintry precipitation
consisting of brief period of sleet before a changeover to light
snow before the larger wedge of drier air behind the front spills
SE quickly tapering the precip from NW to SE late.

Have trended the forecast as such, maintaining likely pops mainly SE
of I-30 Monday evening, with the changeover expected to commence by
mid to late evening along/NW of the I-30 corridor before
transitioning over to IP/-SN after 06Z for the remainder of the
region. There remains discrepancies though amongst the medium range
progs with how fast the near/subfreezing air will surge SE late
Monday night, as well as how much later the deeper moisture
lyr/forcing within the dendritic growth zone will linger before the
deeper wedge of dry air sweeps in. For this forecast, have trended
with up a half inch of snow accumulations over Scntrl AR and extreme
Nrn LA, with lesser (dusting) amounts elsewhere. Also concerned of
the potential for any lingering puddles from the earlier rains
Monday evening which may result in patchy ice developing on elevated
objects such as bridges and overpasses even after the precipitation
ends and the subfreezing temps settling in (faster than the models
depicted Friday morning). Given the sharply positive and progressive
tilt with this system, any wintry precipitation will have exited the
region by daybreak Tuesday, with temps struggling to reach 40
degrees areawide once arctic high pressure settles into the Srn
Plains. The air begin this front will be quite dry, with temps
plummeting quickly Tuesday night as the sfc ridge shifts E over the
region. The only saving grace for a prolonged period of subfreezing
temps may be an increasing cirrus shield which will round the base
of the longwave trough Tuesday night, although temps may need to be
adjusted lower in later forecasts should this not materialize.

Temps will gradually moderate Wednesday as a light Srly low level
flow returns on the backside of the retreating sfc ridge to our E.
The GFS continues to advertise another cold front backdooring SW
into the area Wednesday night/Thursday, but not quite buying this
yet as neither the ECMWF nor Canadian suggest this. But in any case,
below normal temps will continue areawide through the remainder of
the extended. A shortwave is progged by the ECMWF to traverse ESE
across Cntrl TX/Srn and Cntrl LA Thursday which may yield a few
isolated -SHRA over Deep E TX/Ncntrl LA, which may extend a bit NE
into more of E TX/N LA/extreme Srn AR late in the day. Have
introduced slight chance pops for these areas, with additional
development possible Friday as another shortwave impulse is progged
to drop SE into the region. Attm, it appears that any precip that
develops late in the week will remain liquid, although this will be
closer monitored in future forecasts as sfc temps are expected to
fall to near/slightly below freezing during the overnight hours.
/15/

---

Seeing snow in the forecast on the north shore now on Tuesday

GFS just playing with us now (this is out in fantasy land)

quote:

---

I wonder how long the school systems will wait to determine what to do. This looks like it could be a transportation issue for some depending on the location and the timing.

---

The buses have the same tires in every state. The road crews will do the same thing for a light dusting as they do in all states, nothing.

But don't worry the threat of a snowflake will ensue panic and they'll close the day before

The odds of anything other than rain falling still aren't great here, much less accumulating significantly. Jackson, MS probably needs to think about it. Baton Rouge and south Louisiana? Not really.