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

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
000
FXUS64 KLIX 220840
AFDLIX

Area Forecast Discussion
National Weather Service New Orleans LA
340 AM CDT Fri Sep 22 2017

.SHORT TERM...

The region will remain placed squarely between an upper level
ridge of high pressure extending from Texas northeast across the
Midwest and an upper level low pressure system over the eastern
Gulf and Southeastern states today and tomorrow. This pattern
will keep a bit more subsidence and slightly greater convective
inhibition in place over northwestern zones while southeastern
zones will see a bit more forcing and omega. In the low levels, a
seabreeze cycle will continue to dominate. As a result, the most
likely areas for convective development today and tomorrow will
be generally along and south of the I-10 corridor where the
combination of moisture convergence along the seabreeze front and
slightly more lift should produce scattered showers and
thunderstorms. The convection should tend to fire up when peak
heating occurs from mid- afternoon into the late afternoon hours,
and have the highest POP during this period. Temperatures will
remain above normal as cloud development should occur later than
normal and convective coverage somewhat below climatological
norms today and tomorrow.

By Sunday, the upper level low is expected to push westward and
become directly centered over the forecast area. As this occurs,
increasing vorticity and lift in the upper levels will overspread
the entire region. Additionally, a surge of increased mid-level
moisture will also advect in from the east, and this will push
precipitable water values above normal by Sunday afternoon. Given
this, expect to see greater convective coverage by Sunday
afternoon, and have placed POP values of 40 to 50 percent in the
forecast for most of the area. The increase in cloud cover and
convection should allow temperatures to fall back to more normal
levels of late September in the middle to upper 80s.

.LONG TERM...

There will be little change in the overall weather regime from
Sunday into Monday, and expect to see similar conditions to those
on Sunday. Above normal PW values and ample forcing aloft will
support another day of 40 to 50 percent POP and near normal
temperatures.

Tuesday will see rapid change as the upper level low over the area
rapidly weakens and shifts back to the east of the region. Strong
negative vorticity advection and upper level ridging will develop
across the Gulf South in response to the departing upper level
low. Strong subsidence throughout the atmospheric column and
strong dry air advection will begin to take hold on Tuesday, and
really come to bear by Wednesday and Thursday. Tuesday should be a
day of transition overall with enough lingering moisture over the
area to spark off some scattered showers and thunderstorms along
the seabreeze front in the afternoon. Have a 20 to 30 percent
chance of rain to reflect this risk. Temperatures will warm
slightly, but should be fairly close to seasonal norms on Tuesday.
However, both the GFS and ECMWF indicate that the upper level
ridge will be very strong across the region both Wednesday and
Thursday. Strong convective inhibition will be in place, and do
not expect to see even much in the way of cloud development both
days. With a sinking airmass in place, temperatures will easily
climb well above normal in the lower 90s both Tuesday and
Wednesday afternoons. At night, the dry air in place should allow
temperatures to fall into the middle to upper 60s at most spots.
The weak boundary layer winds and still relatively high dewpoints
in the low levels should allow for some fog formation Tuesday
through Thursday nights.

&&

.AVIATION...

Most terminals are in VFR status currently but expect a few to begin
to see VSBYS drop bringing a couple down to MVFR in BR around 12z.
Any light fog should quickly dissipate after sunrise with all
terminals expected to be in VFR status through this evening. The
exception will be brief impacts from isolated to scattered SHRA/TSRA
that are expected mainly in the 19z to 00z period with the higher
probability of occurrence expected at KGPT, KASD and KHUM. 22/TD

&&

.MARINE...

A large ridge of high pressure covering most of the eastern U.S. is
expected to persist through early next week. A weak pressure
gradient with mostly light winds of 5 to 10 knots and low wave
heights/seas is expected again today into tonight across the lakes,
sounds and coastal waters.

The pressure gradient is expected to tighten somewhat Saturday into
Sunday as minor low level/surface wave features in the easterlies
(inverted troughs) move west across the northern Gulf. This pattern
will push easterly winds up into the 10 to 15 knots range across
most waters with seas building up to around 3 feet over much of the
coastal waters. High pressure is then expected to rebuild back into
the central Gulf coast region again Monday through Wednesday which
will result in a return to lighter winds and flatter seas. 22/TD

&&

.DECISION SUPPORT...

DSS code: Green.
Deployed: None.
Activation: None.
Activities: None.

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  92  70  90  69 /  20  20  20  10
BTR  92  71  91  70 /  20  20  20  10
ASD  90  70  89  71 /  30  20  20  20
MSY  91  75  89  75 /  20  20  20  10
GPT  89  71  88  72 /  30  20  20  30
PQL  89  69  89  70 /  30  10  20  30

&&

.LIX WATCHES/WARNINGS/ADVISORIES...
LA...None.
GM...None.
MS...None.
GM...None.
&&

$$

32



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.