Area Forecast Discussion
Issued by NWS New Orleans/Baton Rouge, LA

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FXUS64 KLIX 031452
AFDLIX

Area Forecast Discussion
National Weather Service New Orleans LA
952 AM CDT Wed Jun 3 2020

.UPDATE...
Have issued a Flash Flood Watch in the name of prudence to get ahead on
the messaging for what should be a long duration heavy rainfall episode.
Efficient rains are expected, and probably already underway in the New
Orleans metro area, at this time. We are using the NBM 90 Percent exceedence
values over the 7 day period, which paints 10-12 inch accumulations over
the SE half of the CWA. Localized amounts, particularly on banding that may
eventually develop, could double the amounts. Products have been updated to
include headlines.

&&

.PREV DISCUSSION... /issued 535 AM CDT Wed Jun 3 2020/

SHORT TERM...

Summer pattern will continue as a strong Bermuda high will pull
moisture into the area throughout the remainder of the week. PW
values will range upwards of 1.80 inches thus heavy downpours are
possible each and every day. In the meantime...a weak shortwave
will move over Arkansas and portions over Louisiana today bringing
POPS into likely categories today. A strong upper level ridge
will continue to build over the western Plains on Thursday and
Friday. Weak upper level troughing will linger through the mid-
south regions of central Tennessee and into north/central
Mississippi through Friday. The combination of the trough axis
lingering to the north along with high PW values a continuation
of scattered to numerous showers and thunderstorms are expected
through Friday. All eyes will turn to Tropical Storm Cristobal by
late Friday and Saturday. The storm is expected to stall and
drift slowly into the Yucatan of Mexico...late Thursday and into
Friday morning given the weak steering currents. Depending on how
long and far inland the storm gets into Mexico could be a huge
player as to whether it holds a defined circulation.
Regardless...with land friction the wind field will likely spread
out in diameter. As ridge amplifies over the Plains and trough
digs into the lower midwest and midsouth region by late Friday and
Saturday the system is expected to begin turning northward. The
trough is expected to dig far enough south to begin to pull the
system northward by the upcoming weekend. Depending on timing...as
trough moves off the eastern seaboard on Sunday the system could
slide under the ridge and take a more northwesterly turn towards
southeast Texas. As a result...a faster northward movement would
likely bring it much farther east. Regardless...heavy bands of
rain are likely to be focused on the eastern side of the center
given the likelihood of a not fully organized early season
Tropical system.

LONG TERM...

The extended is going to be highly dependent on a low confidence
forecast of Tropical Storm Cristobal. Some things that appear to
be more certain: heavy rainfall potential will be on the increase
with each passing day as the deeper moisture channel streaming
from the circulation is squarely over LA and southern MS. Some of
the rainfall would be beneficial in mitigating drought conditions
but don`t need too much of a good thing. Spring tides will also be
in place and will become augmented by deeper fetched onshore flow
and tightening pressure gradient to produce a coastal flood
threat. This will likely warrant a Coastal Flood Advisory for less
than 3 feet of inundation by the weekend, possibly replaced by
some type of warning thereafter. Again depending on future track
and intensity of Cristobal.

AVIATION...

UPDATED 0500Z...

No significant impacts expected overnight tonight, with primarily
VFR conditions expected through 10-12Z. Some periodic MVFR
conditions can be possible with lower CIG`s, and perhaps limited
flight CAT`s for KMCB with light surface fog and/or low CIG`s.
Short-range guidance is in good agreement that nocturnal/early
morning showers and few thunderstorms may develop, with much more
coverage expected mid/late morning today for all locations. Main
threats with any shower or storm today will be temporary
reductions in visibility due to heavy rain, gusty, erratic
downdraft winds and dangerous lightning. KLG

MARINE...

Steady onshore flow at moderate levels initially will be
increasing over subsequent days with the evolution and future
track of Tropical Storm Cristobal. Wave model guidance shows
packet swell generation emanating northward in the 12 to 14 second
period ranges Saturday and Sunday. This will produce steep waves
running 12 to 16 feet, primarily swell. Wind forecast will be
dependent on future track but currently showing increase to high
end SCA, if not gale/storm force by Sunday afternoon.

DECISION SUPPORT...

Code: Yellow
Activities: Monitoring T.S. Cristobal
            Critical DSS site support
            Flash Flood Watch

&&

.PRELIMINARY POINT TEMPS/POPS...
MCB  86  71  87  71 /  70  50  60  10
BTR  88  71  89  71 /  60  40  50  10
ASD  88  71  88  71 /  60  30  50  10
MSY  87  74  87  74 /  60  30  50  10
GPT  83  73  85  73 /  60  30  50  20
PQL  86  70  88  70 /  60  30  50  20

&&

.LIX WATCHES/WARNINGS/ADVISORIES...
LA...Flood Watch through Tuesday morning for LAZ034>037-039-040-
     046>050-056>072.

GM...None.
MS...Flood Watch through Tuesday morning for MSZ077-080>082.

GM...None.
&&

$$

24/RR


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