Area Forecast Discussion
Issued by NWS New Orleans/Baton Rouge, LA
FXUS64 KLIX 271303
Area Forecast Discussion
National Weather Service New Orleans LA
803 AM CDT WED JUL 27 2016
The balloon this morning was released about 30 minutes ahead of a
line of tropical showers. Those showers may produce gusts to
around 30 kts as they track east... maybe a bit higher over marine
areas. PW is still high at 2.3 inches. Interesting wind profile
compared to yesterday. Winds are southwest to 500 mb then become
light and eventually northeast above 250 mb. The area is under
the backside of the upper low to the west and south of the weak
surface circulation in the northeast part of the state. As
mentioned below heavy rainfall is still possible in this
environment... just see the activity along the southwest
Louisiana coast this morning.
.PREV DISCUSSION... /issued 353 AM CDT WED JUL 27 2016/
An upper level low currently parked over Louisiana will slowly
drift to the north today and tonight. As the low pulls to the
north of the area, rain chances should begin to diminish tonight.
However, a very high moisture content airmass will remain in place
today which should result in numerous showers and thunderstorms
redeveloping as the atmosphere destabilizes from daytime heating.
Have kept in a POP of 60 to 70 percent to reflect this risk
through the afternoon hours. Temperatures should also be slightly
cooler than average due to the rainfall and cloud cover with highs
only climbing into the upper 80s. Given the high mixing ratios of
16 to 18 g/kg and PW values in excess of 2.25 inches, rainfall
processes will be highly efficient. Thus, some locally heavy
rainfall could occur over isolated areas with some places seeing
rainfall in excess of 3 inches today. Some street flooding issues
could arise where this heavy rainfall occurs. Convection should
turn more scattered this evening and then turn even more isolated
during the overnight hours as the strongest forcing lifts well
north of the forecast area.
Thursday through Saturday will see a continued region of lower
pressure aloft and weak forcing linger across the Lower
Mississippi Valley. Atmospheric moisture content will also drop
off a bit, but mixing ratios should remain between 12 and 14 g/kg
and PW values of 2 to 2.25 inches will remain in place. As a
result, rainfall chances should remain slightly higher than
normal, and this is reflected by the 50 percent POP in place each
day. Shower and thunderstorm development will be largely driven by
the diurnal cycle with the highest rainfall chances from late
morning through the afternoon hours when the atmosphere is most
unstable. Temperatures will warm slightly with daytime highs
climbing back into the lower 90s for the latter part of the week.
Heading into next week, the forecast area will remain sandwiched
between two upper level ridges. One ridge will strengthen over the
central and southern Plains and the other ridge will remain parked
over the western Atlantic and the eastern Gulf. With weak
troughing aloft still in place, there will be little in the way to
inhibit convective potential each day. Temperatures will rise into
the lower 90s each afternoon, and there will be ample instability
for any convection to tap into. The main driver of how much
convective coverage occurs will once again be the amount of
available moisture in the atmospheric column. With that in mind,
it looks like ample atmospheric moisture will remain in place
throughout the extended period. Precipitable water values will
remain above 2 inches and mixing ratios will be above normal near
14 to 16 g/kg. Given these conditions, have kept in POP of around
50 percent for both Sunday through Tuesday for the late morning
and afternoon hours. Coverage should turn more isolated each night
as overall instability decreases.
Band of showers and a few ts located north of a line from HUM to MSY
to ASD should remain in roughly the same location for much of today
before moving north after noon. Will keep shra prevailing for all
terminals north of the aforementioned line. Showers with isolated ts
can be expected as well south of this line but timing should be
later in the day. Some low ceilings around 015 to 020 will give way
to much higher cover around 120 by afternoon. Conditions will
improve through tonight.
As the weak surface low moves farther inland winds and seas will
gradually improve through the day. The large Atlantic surface
high has already started to ridge into the northern gulf this
morning. This will continue to be the trend through the next
several days. Nocturnal showers and thunderstorms will continue to
form each night but will not be as numerous as the last few days.
Waterspout activity will also decrease in numbers. The next system
to move over the gulf will be an upper low currently located at
about 26N58W. There are two upper lows within that vicinity but
the one located at that lat/lon will be the dominant one that
makes its way around the Atlantic ridge and affects the northern
gulf by Tuesday.
DSS code: Green.
Decision Support Services (DSS) Code Legend
Green = No weather impacts that require action.
Blue = Long-fused watch, warning, or advisory in effect or
high visibility event.
Yellow = Heightened impacts with short-fused watch, warning
or advisory issuances; radar support.
Orange = High Impacts; Slight to Moderate risk severe; nearby
tropical events; HazMat or other large episodes.
Red = Full engagement for Moderate risk of severe and/or
direct tropical threats; Events of National Significance.
.PRELIMINARY POINT TEMPS/POPS...
MCB 87 72 92 73 / 70 50 40 30
BTR 88 73 92 73 / 70 50 40 30
ASD 89 76 91 77 / 60 40 30 20
MSY 89 77 92 78 / 60 40 30 20
GPT 89 78 90 78 / 60 40 30 20
PQL 89 77 91 77 / 60 40 30 20