LIX issues Area Forecast Discussion (AFD) at Sep 1, 3:00 PM CDT ...New SHORT TERM, LONG TERM, MARINE...801
FXUS64 KLIX 012000
AFDLIX
Area Forecast Discussion
National Weather Service New Orleans LA
300 PM CDT Sun Sep 1 2024
...New SHORT TERM, LONG TERM, MARINE...
KEY MESSAGES:
1 - After a brief drier period through the first part of the work
week, heavy rain again looks likely Wednesday and Thursday.
While it's too soon to say exactly how much rain will fall
and where, localized flash flooding could become a concern.
Please continue to monitor the forecast for the latest
information regarding this potential threat.
2 - NHC continues to include two disturbances of interest in the
tropical weather outlook. The disturbance in the northwestern
Gulf has only a very low (10%) chance of development before
moving inland on Tuesday and is not expected to have any
additional impact on the local area. The disturbance east of
the leeward islands has a medium (40%) chance of development
later this week as it moves through the Caribbean. This system
poses no immediate threat to the local area but could approach
the southern Gulf in approximately 7 days. Remember that model
forecasts will continue to struggle with this system unless or
until an organized center develops. PLEASE do not focus on any
individual model forecasts and instead follow the latest
updates from official sources.
.SHORT TERM...
(This evening through Monday night)
Issued at 259 PM CDT Sun Sep 1 2024
There has generally been less convective coverage today than
originally anticipated and this increases confidence that tomorrow
will be another somewhat dry day. As the surface trough over the
northwestern Gulf slides a bit farther from the local area and
upper level ridging tries to build into the area, the deep
tropical moisture that has engulfed the local area over the last
several days will be shunted a bit farther southwest. This should
help drop PW values closer to 2" across the area, whereas the PW
has been sitting in the 2.25-2.4" range for the last few days. The
ridging aloft won't be strong enough to completely suppress
convection, but it should be enough to keep showers and storms
more in the isolated to widely scattered category. Have once
again dropped the forecast POPs a bit compared to the previous
forecast and am generally now carrying only 15-20% POPs across
eastern areas with 20-30% POPs across western areas where the
slightly better moisture will be.
With lower rain chances and more sunshine afternoon temperatures
are now forecast to rise into the mid to upper 90s across the
area. NBM dewpoints have been running hot the last several days,
and appear to be a couple degrees to high again tomorrow. Have
adjusted downward by blending in some of the short term consensus
guidance, though there is a fly in the ointment to mention. With
the extra sunshine, dewpoints may rise to the levels the NBM was
suggesting as residual surface moisture from the last few days of
rain evaporates.
If this happens, we'll be bumping up against heat
advisory criteria as the current forecast calls for heat index
values topping out right around 105 degrees in several areas.
&&
.LONG TERM...
(Tuesday through Saturday night)
Issued at 259 PM CDT Sun Sep 1 2024
Tuesday will be a transition day as deeper moisture moves back
into the area from the Gulf and a weak boundary sinks toward the
area. With the upper ridging never really establishing itself over
the area, the combination of the increased moisture and the
focusing mechanism of the surface boundary should result in
scattered to numerous showers and storms, especially during the
afternoon hours.
This weak surface boundary will stall near the coast, providing a
continued focus for showers and storms across the area. At the
same time, a weak inverted surface trough will bring additional
moisture into the area and an upper trough will move into the
middle MS Valley. Latest model guidance continues to suggest
moisture pooling ahead of the upper trough will result in PW
values exceeding 2.5" across much of the area during the
Wed/Thurs time frame, which is right around the daily max observed
value in our sounding climatology for those dates. That being
said, efficient rainfall will be possible. Latest guidance has
backed off just slightly in the storm total precip forecast for
Wed/Thurs now indicating areawide totals of 1-3 inches with a
reasonable upper bounds of closer to 5 inches. However, there are
some members that are still higher and the member maximum values
are generally int he 5-7 inch range.
All this is to say the forecast reasoning hasn't changed much and
the potential for at least locally heavy rainfall still looks
solid for Wednesday and Thursday. WPC continues to highlight the
area with a marginal risk, but given the parameters outlined
above, would not be surprised to see that increase as it gets
closer in time assuming no significant changes to the forecast
itself.
By Friday, the upper trough axis should swing east of the local
area, bringing drier air into the area and potentially forcing a
more defined front through the area by Saturday. Forecast still
calls for a downward trend in POPs by Friday and into Saturday as
a result of the drier air moving in. Depending on the strength of
the front, there could even be some lows int the 60s across
northern areas by Saturday! But let's not get our hopes up too
much this early in the game as a lot could still change.
&&
.AVIATION...
(18Z TAFS)
Issued at 1235 PM CDT Sun Sep 1 2024
VFR conditions will prevail through the period. Latest trends in
both radar data and forecast guidance suggest showers will be more
isolated in nature this afternoon than previously thought. Have
removed tempo groups and left vicinity showers in through the
afternoon at all terminals. Any convection should wane during the
late afternoon into the evening and once convective activity
diminishes, expect conditions to remain quiet through the
remainder of the period. Convection on Monday is expected to be
quite isolated, with probabilities too low to mention in the TAFs
at this time.
&&
.MARINE...
Issued at 259 PM CDT Sun Sep 1 2024
Local area remains on the western periphery of a surface high
centered over the western Atlantic with a weak surface trough over
the northwestern Gulf. This continues to result in persistent
east to southeast surface winds in the 10-15 knot range across the
coastal waters. Monday will see a relative lull in shower and
thunderstorm activity, but expect showers and storms to become
more numerous to widespread again by Tuesday. Wednesday and
Thursday could see more significant impacts as deep tropical
moisture interacting with a weak surface boundary results in
widespread moderate to heavy rain across the coastal waters. These
heavier showers will result in locally higher winds and seas as
well as significantly reduced visibility.
&&
.PRELIMINARY POINT TEMPS/POPS...
MCB 71 92 72 91 / 10 30 10 50
BTR 75 96 76 95 / 10 30 10 40
ASD 73 95 74 92 / 10 20 10 50
MSY 76 93 77 91 / 10 20 10 50
GPT 74 93 75 91 / 10 20 10 60
PQL 74 97 75 94 / 10 20 10 60
&&
.LIX WATCHES/WARNINGS/ADVISORIES...
LA...None.
GM...None.
MS...None.
GM...None.
&&
$$
SHORT TERM...DM
LONG TERM....DM
AVIATION...DM
MARINE...DM
Source:
LIX issues Area Forecast Discussion (AFD) at Sep 1, 3:00 PM CDT ...New SHORT TERM, LONG TERM, MARINE...---------------
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