LIX issues Area Forecast Discussion (AFD) at Jan 20, 11:38 PM CST ...New AVIATION...
033
FXUS64 KLIX 210538
AFDLIX
Area Forecast Discussion
National Weather Service New Orleans LA
1138 PM CST Mon Jan 20 2025
...New AVIATION...
.SHORT TERM...
(This evening through Tuesday night)
Issued at 338 PM CST Mon Jan 20 2025
...POTENTIALLY HISTORIC WINTER STORM AND DANGEROUSLY COLD WIND
CHILLS WILL BEGIN TONIGHT... ALL PREPARATIONS SHOULD BE RUSHED TO
COMPLETION...
KEY MESSAGES: 1. Near record-breaking snowfall is likely across
portions of southeast Louisiana and coastal Mississippi. The axis of
highest snowfall totals has continued to shift southward toward the
I-10/12 corridor, but exact totals still remain uncertain beyond a
margin of 3 to 7 inches.
2. Travel should be avoided at all costs beginning overnight tonight
and continuing through Tuesday and into Wednesday due to
treacherous road conditions from snow and ice after it refreezes
on Wednesday morning.
3. Dangerous wind chills and hard freezes will put both people,
plants, pets, and pipes in jeopardy. Wrap pipes, wear layers and
cover skin from the cold air, bring pets and/or plants indoors or
prepare a warm shelter, and check on friends and family, especially
the elderly.
It is looking increasingly likely that the New Orleans and Baton
Rouge Metro areas will see historic snowfall totals that have been
not been observed since at least 1963, if not 1895. Incorporation
of the highest resolution CAM guidance and trends in the NBM and
suppression of surface trough due to observed drier and colder air
mass could result in further adjustments southward in the axis of
highest snowfall totals. At this time, it's likely that the
I-10/12 corridor sees totals between 3 to 7 inches with locally
higher amount targeted within the anticipated frontogenetic band
of heavier snowfall rates where we have the strongest forcing for
ascent. As such, it is advised to not travel on Tuesday and be
prepared to shelter in place in the event roads remain too
hazardous to drive due to refreezing of snow into ice on Wednesday
as well. This also means we could have a sharper cut off for the
highest snowfall totals, especially north of the I-12 corridor in
southwest Mississippi than what is currently advertised based on
current trends.
Additional alterations to this forecast package focused on
transition of precipitation types on the coast occurring earlier
and becoming more strictly snow Tuesday morning and increased
snowfall totals for coastal Louisiana where the Winter Storm
Warning was expanded to in the prior update due to the trend in a
slightly more suppressed surface trough. Since there will be less
time spent in transition in precip type from freezing rain to
sleet to snow along coastal Louisiana tonight, it is less likely
that ice accumulations will exceed 0.25" anywhere within the CWA.
Anomalously dry and cold conditions continue tighten their grip
across the Gulf Coast in association with a strong high pressure
system providing the first shot of cold air across eastern CONUS.
This has allowed a much drier and colder air mass than even what
was originally forecast to advect into the area with dew points
temperatures in the single digits along and north of the I-10/12
corridor, and in the low 10s south of the lake. Behind the surface
trough passage on Tuesday, another strong high pressure system
will descend out of the northern Great Plains with an even
stronger shot of arctic air. This in combination with the fresh
snowfall covering most areas will allow temperatures to crash into
the 10s to low 20s Tuesday night with wind chills in the single
digits to low teens. As such, the Extreme Cold Watch has been
upgraded to a Warning. This night in particular will be one of the
coldest we have seen in this area in several years and will
present a serious threat to people, pipes, pets, and plants. Not
much reprieve is anticipated on Wednesday either as temperatures
barely get above freezing, with help from higher reflectance of
solar radiation from the snowpack. With another hard freeze
Wednesday night, we will likely struggle to melt off the deep
snowfall quickly and could see some of it last into Thursday which
could present hazards for ice on roads.
&&
.LONG TERM...
(Thursday through Sunday night)
Issued at 338 PM CST Mon Jan 20 2025
Another northern stream shortwave trough and an associated front
will slide through the area on Thursday, but this system will be
moisture starved. The end result will be an increase in northerly
winds on Thursday, but with PWATS around 0.25 inches, there will be
no cloud development associated with this system. Temperatures will
also start off very cold with values in the teens and lower 20s as a
lingering snowpack across the area allows for strong radiational
cooling Wednesday night. However, some warming is expected on
Thursday as the heart of the 925mb thermal trough axis starts to
shift to the east. The snowpack will begin to melt, but it will
take some time. With this snowpack reflecting back some of the
thermal energy, temperatures will be cooler than the atmosphere
would suggest with highs only warming into the low to mid 40s. This
will still help melt much of the snow, but some will be left as we
move into Thursday night. Thus, a refreeze is expected to take place
as temperatures fall back into the 20s, and there will continue to
be travel concerns, especially on elevated roadways and bridges
into Friday morning.
The big melt will finally occur on Friday as a surface high becomes
centered over the area and temperatures continue to gradually warm.
The combination of more bare ground and strong solar insolation will
quickly melt any lingering snowpack, and this is reflected by
temperatures forecast to rise closer to 50 degrees Friday afternoon.
As negative vorticity advection increases in response to a deep
layer ridge axis building over the area Friday night into Saturday,
mid-level temperatures will warm dramatically. A fairly sharp low
level temperature inversion will develop Friday night as strong
radiational cooling once again occurs, and this will push overnight
lows into the upper 20s and lower 30s, but this is expected to be
the final night of freezing temperatures in the extended period.
Saturday will see continued warming as strong subsidence and warming
aloft continues with highs warming closer to average in the mid to
upper 50s.
Saturday night through Sunday night will see the ridge axis shift to
the east, and a deep layer southwesterly flow regime will develop
over the area. A fast moving southern stream vorticity max will
slide into the area on the back of this southwesterly flow. In
advance of this system, a surge of moisture will advect into the
region Saturday night with PWATS increasing by around an inch. This
will be sufficient moisture to support scattered shower activity as
the fast moving vort max moves through Sunday into Sunday night, and
have included chance PoP of 30 to 50 percent in the forecast.
Fortunately, little in the way of instability will be in place due
to weak mid-level lapse rates. Have opted to not include a mention
of thunderstorms in the forecast for Sunday. Warm air advection
will also occur over this time period with highs climbing into the
60s and even lower 70s Sunday afternoon. Lows will be near average
Saturday night, and should rise to above average levels on Sunday
night. PG
&&
.AVIATION...
(06Z TAFS)
Issued at 1134 PM CST Mon Jan 20 2025
A mix of very light sleet and rain has been reported over the past
couple of hours as moisture continues to build down from aloft.
Temperatures are above freezing still, so no accumulation on
surfaces has started yet. However, as the temperature drops and
humidity increases after 09z, more snow will begin to develop at
the terminals. The snow will turn intense after 12z with periods
of heavier snow occurring between 15z and 22z. After 22z, drier
air will begin to push in from the northwest and improving
conditions are expected to develop between 22z and 00z at BTR and
HDC and between 00z and 03z at HUM, MSY, HDC, NEW, ASD, and GPT.
All snow should end by 03z with a return to VFR conditions at all
of the terminals by 06z. Winds will remain gusty from the north at
all of the terminals as the low pressure system producing the snow
passes to the south. PG
&&
.AVIATION...
(00Z TAFS)
Issued at 530 PM CST Mon Jan 20 2025
VFR conditions will continue through around 09z, but conditions
will begin to degrade after 09z as a band of light to moderate
snow starts to develop at the terminals. At HUM, the precipitation
will be a mix of sleet and snow between 09z and 14z. After 14z, a
band of heavier snow is expected to develop over the terminals and
then persist through around 22z to 00z. Snow will reduce
visibilities to IFR or lower from 15z through 22z. The snow will
begin to ease after 00z with only some flurries lingering at MSY,
NEW, HUM, and GPT through 06z. North winds will also be strong
with frequent gusts over 20 knots at all of the terminals. PG
&&
.MARINE...
Issued at 338 PM CST Mon Jan 20 2025
Hazardous seas and winds will be present for small crafts through
Wednesday morning. Northeasterly winds of 15 to 20 knots are already
ongoing and will continue to buildto 25 to 35 knots with gusts
upwards of 40 knots in the outer coastal waters (gale conditions) on
Tuesday as surface the low moves east through the central to
northern gulf. Gradual decrease of winds and seas will start
Wednesday, but small crafts should exercise caution through the
remainder of the week.
&&
.PRELIMINARY POINT TEMPS/POPS...
MCB 21 30 12 39 / 50 80 0 0
BTR 26 33 15 39 / 70 90 0 0
ASD 25 33 17 41 / 50 90 10 0
MSY 28 34 24 37 / 50 100 20 0
GPT 25 32 17 39 / 40 90 20 0
PQL 25 36 18 42 / 40 90 30 0
&&
.LIX WATCHES/WARNINGS/ADVISORIES...
LA...Cold Weather Advisory until 6 PM CST Tuesday for LAZ034>037-039-
046>048-056>060-064>071-076>090.
Winter Storm Warning until midnight CST Tuesday night for
LAZ034>037-039-046>048-056>060-064>071-076>090.
Extreme Cold Warning from 6 PM Tuesday to 9 AM CST Wednesday for
LAZ034>037-039-046>048-056>060-064>071-076>090.
GM...Small Craft Advisory until midnight CST Tuesday night for GMZ530-
532-534-536-538-557.
Small Craft Advisory until 6 AM CST Tuesday for GMZ550-552-555-
570-572-575-577.
Gale Warning from 6 AM Tuesday to midnight CST Tuesday night for
GMZ550-552-555-570-572-575-577.
MS...Cold Weather Advisory until 6 PM CST Tuesday for MSZ068>071-077-
083>088.
Winter Storm Warning until midnight CST Tuesday night for
MSZ068>071-077-083>088.
Extreme Cold Warning from 6 PM Tuesday to 9 AM CST Wednesday for
MSZ068>071-077-083>088.
GM...Small Craft Advisory until midnight CST Tuesday night for GMZ532-
534-536-538-557.
Small Craft Advisory until 6 AM CST Tuesday for GMZ552-555-570-
572-575-577.
Gale Warning from 6 AM Tuesday to midnight CST Tuesday night for
GMZ552-555-570-572-575-577.
&&
$$
SHORT TERM...TJS
LONG TERM....PG
AVIATION...PG
MARINE...TJS
Source: LIX issues Area Forecast Discussion (AFD) at Jan 20, 11:38 PM CST ...New AVIATION... (https://mesonet.agron.iastate.edu/p.php?pid=202501210538-KLIX-FXUS64-AFDLIX)
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