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

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FXUS64 KLIX 251428
AFDLIX

Area Forecast Discussion
National Weather Service New Orleans LA
928 AM CDT SUN SEP 25 2016

.SOUNDING DISCUSSION...

Only subtle changes have occurred over the last couple days, but
the most notable is the mean mid level temperatures in the 700-500
mb layer have cooled to point this morning where the capping
inversion has been basically eliminated resulting in higher lapse
rates throughout most of the troposphere. Precipitable water is
near the seasonal climatology near 1.6". The steep near-surface
inversion eroded when the surface temperature reached 80F and the
elevated low level inversion will be eroded when the surface
temperature reaches about 85F. Sounding projected max temperature
is 92 with a mixing height/mixed layer reaching up to 7-9 kft at
peak heating. The convective temperature is rather high at 90F.
Winds in the lower levels up to 10 kft were mostly southeast to
south averaging 6-12 knots, then mostly varying from northeast to
northwest at light to moderate speeds above 10 kft with the peak
wind 32 knots around 40 kft.

12z balloon info: a successful flight ascending for 127 minutes
reaching a height of 21.4 miles above the ground bursting over
eastern Lake Pontchartrain only about 16 miles south-southwest of
the office.

TD

&&

.PREV DISCUSSION... /issued 415 AM CDT SUN SEP 25 2016/

SHORT TERM...
Upper level ridge that encompasses most of the southeastern United
States is beginning to compress and weaken as a trough is moving
northeast across the high plains. The weakening of the ridge will
allow for scattered convection to develop and become slightly more
widespread today. Surface analysis shows a weak inverted trough
developing over southern Mississippi and Alabama. This correlates
perfectly with the general location where the HRRR suggests
thunderstorms will initiate this afternoon. These storms should move
southwest into the CWA along the MS/LA border before dissipating as
they track across the Florida Parishes. The latest forecast pops
were adjusted to represent expected convection. Those rain chances
are slightly above the previous forecast and what neighboring
offices have. Highs will be about the same as yesterday in the lower
90s which is several degrees above normal.

LONG TERM...
The ridge overhead will continue to suppress Monday which will allow
the trough to the north to dig further south. Rain chances should
remain in the low end change category as the first significant
cold front since last spring approaches the region. A reduction in
500 mb heights will result in high temps struggling to reach 90.

The upper trough will slowly push east while spreading south over
the southeast conus through Thursday. Much cooler and drier air will
surge south across the CWA during those days. Expect fall like
temperatures with highs in the lower to mid 80s and lows in the
upper 50s to lower 60s. These conditions could stretch into the
weekend albeit some air mass modification.

Meffer

AVIATION...

Generally VFR conditions will prevail through Sunday morning. A few
hours of lower cigs and vsbys will be possible around sunrise and
TEMPO groups have been included for the KHUM and KMCB. A sct cu
field is expected between 3 and 4kft by late morning and isolated
convection in the afternoon but too isolated to mention in taf
forecast for now. 18

AVIATION...

General VFR conditions expected all terminals through Monday
morning. KHUM and KMCB may see some localized light fog formation in
areas prone to drainage aspects near daybreak, but should be limited
in extent and duration. Isolated showers and thunderstorms will
occur this afternoon but too isolated to mention in taf
forecast...so will handle within 6 hours. 18

MARINE...

Light winds and low seas in a flat pressure gradient are expected
through Monday. Frontal passage expected into the gulf waters Monday
night to bring a moderate increase in offshore flow as cooler and
drier air builds into the north gulf. The continental high will then
settle over the eastern CONUS and moderate slowly throughout the
week while winds veer to a more easterly flow by mid-week. A
secondary surge may push through the coastal waters on Thursday. 18

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  93  71  91  67 /  30  20  30  20
BTR  92  72  91  69 /  20  20  30  20
ASD  92  73  91  71 /  30  20  30  20
MSY  92  75  90  75 /  20  20  30  20
GPT  91  75  90  72 /  30  20  30  20
PQL  91  73  89  72 /  30  10  30  20

&&

.LIX Watches/Warnings/Advisories...
LA...None.
GM...None.
MS...None.
GM...None.
&&

$$


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