LIX issues Area Forecast Discussion (AFD) at Nov 19, 11:47 AM CST ...NEW UPDATE, AVIATION...925
FXUS64 KLIX 191747 AAB
AFDLIX
Area Forecast Discussion...UPDATED
National Weather Service New Orleans LA
1147 AM CST Tue Nov 19 2024
...NEW UPDATE, AVIATION...
.UPDATE...
Issued at 1147 AM CST Tue Nov 19 2024
A very weak cold front continues to move east across the region
shifting the heavy rain/convection to the east. Rain has left the
landbased zones so was able to cancel the Flood Watch a bit early.
Clearing is starting to peak over the western tier, however, some
convective blow off from the convection over the Gulf is streaming
overhead generally east of the I55 corridor. Eventually these
locations too will clear in time. Overall, outside of ending the
rain a bit earlier than previous forecast, no other major changes
were needed for this mid point update. (Frye)
&&
.SHORT TERM...
(Today through Wednesday)
Issued at 448 AM CST Tue Nov 19 2024
An upper level low is currently racing northeast across the
Central/High Plains and will eventually become absorbed by a broader
trough coming into the country northwest of there. A cold front
appendant to the low extends all the way south to the Gulf of Mexico.
Farther south, a broad upper level ridge is anchored over Florida.
Deep tropical moisture which is actually remnants of Tropical Storm
Sara is surging north across the Gulf and being squeezed between the
trough and ridge. 06Z LIX sounding did a great job capturing this
moisture rich air and measured and ASTOUNDINGLY high (for NOV)
precip water value of nearly 2.5"! A few PW points of reference for
Nov 19th: the 90th percentile is 1.59", average max 1.97", daily max
2.04". Before this morning, the latest ever 2.5" PW was
10/29/20(Hurricane Zeta). The anomalously high PW is why we and WPC
have been hitting the flash flooding potential. However, abundant
moisture is just one piece of the puzzle in terms of flash flooding
and doesn't always guarantee it. Latest radar shows a line of deeper
convection moving east across northwestern portions of the CWA and a
wide swath of moderate/heavy rain moving northeastward across the
southeastern half of the CWA. Storm total accumulation values as of
4am are generally in the 1 to 2" range with a few streaks upwards of
3". Values double that seems right in line over the next few hours
which would put the event right in line with the last several
previous forecasts, which also means a city or 2 could see totals
approaching 8+". Goes without saying location location location in
terms of those impacts. From a severe potential, although there's
sufficient shear and helicity, weak low level lapse rates appear to
have been too much of a hindrance for any appreciable wind gusts to
reach the surface. Conditions to rapidly improve from west of east
through the morning hours as all this convection shifts east.
Although the initial frontal boundary that pushes through will bring
drier air to the local area, cold air mass is still well to the
north. It's not until Tues night/Wed that the broader trough
mentioned above digs south into the lower Mississippi Valley and
sends reinforcing boundary through.
&&
.LONG TERM...
(Wednesday night through Monday)
Issued at 448 AM CST Tue Nov 19 2024
The coldest air of the fall season thus far will usher into the
region as strong high pressure builds south and the trough digs into
the southeastern CONUS. Although temps won't be drastically colder
than CLIMO, they'll be substantially colder than it's been all month
long. Mentioned by previous forecasters, the NBM deterministic low
temps the first 3 post frontal mornings is at or above the 75th
percentile. This isn't surprising considering how warm its been
recently. Knowing those values are bias corrected, went closer to
the 25th-50th percentile for the overnight lows Thurs-Sat morning.
One or 2 of those mornings cold see some frost along/north of I-12.
A moderating temp trend then returns this weekend onward as the
trough ejects eastward and ridge builds in.
&&
.AVIATION...
(18Z TAFS)
Issued at 1147 AM CST Tue Nov 19 2024
Outside of residual MVFR conditions for the eastern terminals and
gusty winds toward the end of the cycle, overall favorable flying
conditions are forecast through the period. Watch the northerly
wind gusts ramping up after 15z behind a strong cold front on
Wednesday where some gusts may approach 30kt, especially NEW off
the lake. (Frye)
&&
.MARINE...
Issued at 448 AM CST Tue Nov 19 2024
Strong onshore flow continues ahead of approaching cold front.
Although recent wind obs are borderline Gale Warning, at least some
of the stronger winds are likely convectively enhanced which means
they should be relatively shorter in duration. Regardless, have
extended the exercise caution headline through the today and evening
period. A lull in advisory wind speeds expected this afternoon and
evening as winds transition from onshore to offshore. Its not until
later tonight that a reinforcing front brings strong offshore winds.
So, decided to put out an SCY to account for the extended duration
small craft winds/seas behind this front.
&&
.PRELIMINARY POINT TEMPS/POPS...
MCB 53 67 36 65 / 0 0 0 0
BTR 57 71 38 69 / 0 0 0 0
ASD 57 73 35 67 / 0 0 0 0
MSY 62 71 48 66 / 0 0 0 0
GPT 59 73 42 66 / 0 0 0 0
PQL 59 78 34 69 / 0 0 0 0
&&
.LIX WATCHES/WARNINGS/ADVISORIES...
LA...Coastal Flood Advisory until noon CST today for LAZ058-060-
066>070-076>078-080-082-084-086-087.
GM...Small Craft Advisory from midnight tonight to 6 AM CST Thursday
for GMZ530-532-534-536-538.
Small Craft Advisory until 6 AM CST Thursday for GMZ550-552-555-
557-570-572-575-577.
MS...Coastal Flood Advisory until noon CST today for MSZ086>088.
GM...Small Craft Advisory from midnight tonight to 6 AM CST Thursday
for GMZ532-534-536-538.
Small Craft Advisory until 6 AM CST Thursday for GMZ552-555-557-
570-572-575-577.
&&
$$
UPDATE...RDF
SHORT TERM...ME
LONG TERM....ME
AVIATION...RDF
MARINE...ME
Source:
LIX issues Area Forecast Discussion (AFD) at Nov 19, 11:47 AM CST ...NEW UPDATE, AVIATION...---------------
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