Flash Flood Warning 25, NWS New Orleans, LA

Area Forecast Discussion
National Weather Service New Orleans LA
354 AM CDT Mon Jun 19 2023

...New SHORT TERM, LONG TERM, AVIATION, MARINE...

.SHORT TERM...
(Today through Tuesday)
Issued at 343 AM CDT Mon Jun 19 2023

How long can NW to westerly upper flow continue. This is quite
impressive as far as longevity goes. Some, eventhough slight,
changes to the new normal of this NW flow will be noticed starting
today in that this troughing providing MCS production will move
farther south. At the moment, this troughiness is oriented east-west
from central TX through central LA into southern Miss. The subtle
change is occurring at this time and can best be seen at H7 and H3
levels. Looking at H7, the flattened high that spans from northern
Mexico east to southern FL will begin to move its western ridge
northward. The whole thing would like to move north but the standing
upper trough that has been over the eastern CONUS will remain pretty
much where it is and not allowing the center of this stacked high to
move over our area. But the interaction between the mid level trough
and mid level ridging will cause the trough between these two
features to orient itself from NW to SE from the Red River Valley to
near Shreveport to near Baton Rouge due to the high ridging NW. The
best way to see this is in heights of the H7 level, particularly the
319dam(decameter) height. This will now allow sh/ts to break out
along this corridor and some training could begin to occur as this
trough will be stalled with neither system wanting to give ground.
No difference in intensity of storms either as severe storms and
very heavy rainfall will continue to be the norm with this daily
activity. The highest potential of training looks to be Tuesday as
a frontal boundary slows to a crawl as it nears the area.

&&

.LONG TERM...
(Tuesday night through Sunday)
Issued at 343 AM CDT Mon Jun 19 2023

The stacked nature of these features(high and low) will also be
reflected at the sfc and will begin to send a front, although very
weak, into the area by Tuesday night into Wed. This will be a slow
process though. And while this boundary transits the area slowly,
training of storms could occur Tuesday and again Wed. These could
also last well into the evening hours each day. The front looks to
be over the gulf before stalling late Wed. This will take most of
this activity to that area as well. Dew pt temps look to cool back
to the upper 60s lower 70s by Wed night and temps look to cool also
into the lower 70s north(maybe even a 69F for MCB) to mid/upper 70s
south by Wed night. Another dry air surge will move in Fri keeping
storms over the coastal areas and offshore. This dry air surge will
be from the last short wave moving through the base of the upper
trough allowing this feature to begin moving north then NE. The
migration of this upper low looks to start late Wed night into
Thursday. But the main shift northward occurs as this short wave
moves to the east side of the trough Thu night into Friday. This
will cause the dew pt gradient to begin shifting to the NW bringing
back the deep moisture by the weekend. An easterly wave will move
through the gulf over the weekend providing moisture with a more
normal summer distribution of sh/ts. But the H7 high will have
ridged into the area as the upper trough departs, a hostile
environment will remain over the gulf as this easterly wave moves
through. Now, the good part of this is 2 fold. The first is less
severe storms by late Wed into Thu and possibly Fri, but we will
take this a day at a time. The second is the heat wave may get
broken and could be as early as Tuesday. The conditions will be
similar Tue but sine the trough will be over the area, it will bring
a lot more cloud cover keeping temps lower and as the relativly dry
air moves in, it could also keep the heat wave down Wed through
Friday. Maybe the Heat advisory now and again but the excessive heat
warnings may be going away at least for a short while. By the way,
the only normal thing in this fcast is the easterly wave for this
time of year. We get heat waves in June, but it is not common to see
them to this degree this early, these usually come in July and
August. And NW flow this long is insane. And eventually, the H7 high
will plant itself right over our area by next week. But that's a
ways out still. This migration of the stacked high over Mexico is
quite normal as it should eventually find itself over the SW. And it
is this process that causes the NAMS(North American Monsoon System)
to occur as it bings deep moisture out of the Pacific into the SW on
the western periphery of the high. This is a normal process as well
and if it carries out like it should, then this heat will eventually
subside here and move west until the stacked high moves east, which
is normally does in late July/August. This high may be a lot more
expansive for this time of year, which is something worth looking
into.

&&

.AVIATION...
(12Z TAFS)
Issued at 343 AM CDT Mon Jun 19 2023

Anticipate cloud bases to lift to FL025-035 by late this morning.
IFR with any TSRA that moves over any terminal. The highest chances
of this will be along and north of a line from BTR to MSY to PQL
during the daylight hours and along and south of this line by early
evening through late evening.

Wind gusts in excess of 20 knots likely at most terminals from about
15z through sunset.

&&

.MARINE...
Issued at 343 AM CDT Mon Jun 19 2023

A broad ridge of surface high pressure centered over the southern
and eastern Gulf will continue to produce southwest flow of 10 to 20
knots over the coastal waters through Tuesday. Heading into
Wednesday and Thursday, a weak frontal boundary will slip into the
waters and stall. This will lead to weak northerly and easterly flow
of 10 knots or less during this period time. By the end of the week,
the boundary is expected to weaken and move NW, and a return to
prevailing onshore flow of 10 to 15 knots is expected as the surface
ridge over the southern and eastern Gulf once again becomes more
dominant.

&&

.PRELIMINARY POINT TEMPS/POPS...
MCB  93  72  91  69 /  40  40  70  40
BTR  98  78  95  75 /  30  40  60  50
ASD  95  75  93  73 /  60  50  80  50
MSY  96  78  94  76 /  50  50  70  50
GPT  92  74  90  72 /  80  40  80  60
PQL  91  72  91  70 /  90  30  70  60

&&

.LIX WATCHES/WARNINGS/ADVISORIES...
LA...Excessive Heat Warning from 11 AM this morning to 7 PM CDT this
     evening for LAZ034>037-039-046>048-056>060-064>071-076>090.

GM...None.
MS...Heat Advisory from 11 AM this morning to 7 PM CDT this evening
     for MSZ068>071-077-083>088.

GM...None.
&&

SHORT TERM...TE
LONG TERM....TE
AVIATION...TE
MARINE...TE