Scientific Forecaster Discussion
fxus64 klch 141804
Area forecast discussion
National Weather Service Lake Charles la
1204 PM CST Sat Dec 14 2019
14/18z taf issuance.
morning fog and low clouds continue to lift/scatter over eastern
portions of the area, with mostly clr skies expected to prevail
through the aftn. Weak high pres sits over the area, resulting in
a generally light and vrbl wind. Expect fog to develop again
tonight, resulting in vsby reductions to MVFR after 06z. Some
locations could see vsbys lower to IFR or LIFR occasionally.
Fog/cigs expected to lift by mid-morning, with winds bcmg
southerly and strengthening as low pres develops over the
Previous discussion... /issued 915 am CST Sat Dec 14 2019/
Dense fog remains in places, but it is dissipating quickly so let
the advisory expire and will just have a clean up of the advisory
at this time.
Previous discussion... /issued 602 am CST Sat Dec 14 2019/
for 12z taf issuance.
sfc obs currently show varying amounts of dense fog across the
forecast area...could continue to see visibilities bounce around a
bit until the fog Burns off and VFR conditions take over by
15z/16z. Thereafter, a lack of good low-level moisture should
maintain VFR conditions through the day. Sfc high pressure
drifting past the region will maintain light veering winds. Fog
guidance is hinting at a repeat of dense fog development
tonight...have tempered this a bit by not going quite so low just
yet to allow later issuances to better address this threat.
Previous discussion... /issued 416 am CST Sat Dec 14 2019/
fog is the story for tonight, as visibilities quickly diminished
late in the evening Friday. A weak surface trough resulted in a
brief westerly wind shift and visibilities marginally improving
for an hour or two here at lch, but the fog has since re-thickened.
Surface observing stations showing at least some visibility
reduction at all land stations, with many below 1/4 mile. With
winds remaining nearly calm, there's been little appreciable
reduction to dew points. This, along with hi-res guidance, leads
to not anticipating any real improvements prior to sunrise. Have
expanded the dense fog advisory to account for lowering visibility
in the remainder of southeast Texas counties as well.
Fog begins to burn off in the hours after sunrise, with a fairly
pleasant day ahead. Dry northwest flow aloft with light winds at
the surface will lead to precipitable water values remaining low, and a dry day
with temps rising into the upper 60s to around 70 for the
afternoon is expected. Flow aloft becomes more zonal overnight
with a warm front expected to surge northward at the surface. Hi-
res guidance indicating maybe some isolated showers will be
possible with this, so kept limited "quiet" pops in the forecast.
Moistening airmass will yield at least some fog potential, but
southerly winds should remain elevated enough to preclude anything
widespread, so opted to not include any mention in the current
forecast weather grids.
By Sunday, a deepening trough over the west Continental U.S. Results in zonal
flow breaking down aloft, and along with continued southerly winds
at the surface, results in a further moistening airmass. Clouds
will be on the increase through the day, but still looking at
temps rising to well above seasonal norms for the day and into
Sunday night / Monday morning.
Aforementioned trough continues to dig into the plains with
surface troughing developing downstream in the arklatex region.
Southerly winds increase with precipitable waters rising to around 1.50" or
higher in the warm sector as a strong cold front begins to advance
towards Louisiana. Pops begin increasing early Monday morning,
with higher pops through the day as the front passes. The current
setup as progged is one Worth monitoring, with the area being
highlighted for a marginal to slight severe risk. Shear and
helicity, especially at the low levels, looks quite impressive in
advance of the front. With instability rising to sufficient
levels, anything that develops ahead of the front in the warm
sector will potentially exhibit supercellular characteristics,
with all severe hazards possible. If convective coverage in the
warm sector becomes too widespread, the overall severe threat
would be a little more limited. With the advertised shear amounts,
severe potential would also be present with cold fropa, with a
wind/spin-up tornado threat along a line of storms. Periods of
moderate rain will also be possible through this, though overall
only expecting around an inch or so of total rainfall, with some
locally higher amounts. A lot of moving pieces, but something to
keep an eye on over the weekend.
Cooler and drier weather takes hold after the front through the
remainder of the week as high pressure builds in. Lows Tuesday
morning will be in the 30s/40s, and even colder the following
days, with lows near or slightly below freezing along and north of
the I-10 corridor Wed/Thu morning. At least something of a brief
warmup and a re-introduction of low end pops appears possible
later Friday and into the weekend as return flow develops on the
periphery of the departing surface high.
some areas of sea fog will be possible through at least mid-
morning, primarily near the coast and in Inland Lakes/bays. A
moderate onshore flow develops Sunday and persists until the
passage of a cold front Monday night into Tuesday. Thunderstorm
chances increase Monday ahead of the front, with a few strong
storms possible. Rain chances diminish behind the front with a
moderate offshore flow developing. Moderate offshore flow persists
through Wednesday, becoming lighter as surface high pressure
becomes more centered over the region for the remainder of the
Preliminary point temps/pops...
aex 67 48 79 63 / 0 10 20 50
lch 69 54 78 66 / 0 10 10 50
lft 68 53 77 65 / 0 10 10 30
bpt 70 57 77 67 / 0 10 10 40