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

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FXUS64 KLIX 260919

Area Forecast Discussion
National Weather Service New Orleans LA
319 AM CST Sun Feb 26 2017


Today will be a rather benign weather day as a zonal flow regime
in the upper levels combined with a departing surface high bring
near normal temperatures and mostly sunny skies to the area.

This benign weather pattern will abruptly come to an end later
tonight as a fast moving vorticity max and associated speed max
aloft move through the Lower Mississippi Valley. The greatest
amount of lift associated with this upper level feature will
remain well north of the area, but there should be enough omega
and instability in place tomorrow to spark off some shower and
thunderstorm activity. Fortunately, the threat of any severe
thunderstorm activity looks very low for tomorrow due to a lack of
wind shear with 0-3km wind shear of only 19 knots noted when
thermodynamic support is greatest. Thermodynamic support for
deeper convection and overall stronger thunderstorm activity will
be over the northern third of the forecast area in Southwest
Mississippi and the adjacent Louisiana Parishes with MLCAPE values
of around 800 to 1000 J/KG and lifted indices of -4 to -5.
Farther to the south, only weaker convection is expected due to
less overall instability and even less wind shear. Temperatures
will remain quite warm across the area with highs expected to
climb into the upper 70s.

The parent vorticity max driving the convective risk for Monday
will quickly pull out of the area Monday night. An increase in
negative vorticity advection and some weak subsidence aloft should
overspread most of the forecast area resulting in much lower POP
of only around 20 percent for very isolated showers and
thunderstorms. Even this may be generous if the amount of
subsidence and resultant capping in the mid-levels is greater than
expected. This period of increased subsidence and capping will
persist into Tuesday, and have a dry forecast in place for the
vast majority of the forecast area. The sinking airmass over the
area should also allow temperatures to warm into the lower 80s for
much of the area. Overall, Mardi Gras looks to be a warm and muggy
day beneath a partly cloudy sky. At most, there is a 10 percent
chance of a stray shower trying to develop during peak heating in
the afternoon hours.  32


A stronger short wave trough will swing through the Lower
Mississippi Valley on Wednesday. This feature will tap into some
colder air in place over the Northern Plains, and a strong cold
front should accompany the passage of the trough axis on
Wednesday. With ample moisture in place as noted by PW values of
1.5 inches and mixing ratios of around 13 g/kg along with strong
forcing throughout the atmospheric column there should be very
little to limit convective development on Wednesday. MLCAPE values
will be decent at around 800 J/KG Wednesday over the northern half
of the CWA, and 0-3km wind shear will be in the range of 25 knots.
These values are not supportive of a significant severe weather
event, but a few strong to possibly severe thunderstorms could
develop ahead of the front Wednesday afternoon and evening. At
this time, it appears the most likely area for any deeper
convection will be over the northern third of the forecast area.
Temperatures will remain very warm ahead of the front with highs
easily climbing back into the lower 80s Wednesday afternoon.

The front will clear the offshore waters by Thursday morning, and
expect to see a surge of cooler and drier air feed into the area.
Temperatures will be significantly cooler as 925mb temperatures
fall nearly 12C from Wednesday to Thursday afternoon. Daytime
highs should only climb into the middle 60s on Thursday, and
overnight lows will cool into the 30s and 40s beneath a clear sky
Thursday night. The thermal trough should linger over the area on
Friday with another day of clear skies and seasonably cool
temperatures in the upper 60s expected.

Heading into the upcoming weekend, both the ECMWF and the GFS
indicate that an unsettled weather regime will develop along the
Gulf Coast. The driving force behind this will be a surface low
forming over the western Gulf of Mexico along a remnant frontal
boundary. This low will develop in response to a speed max and
area of enhanced upper level lift moving from the Four Corners
into Texas and the West Gulf. As the low deepens in the western
Gulf, isentropically induced cloud cover and showers will
gradually overspread the forecast area. Saturday will be a day of
transition as cloud cover thickens and spreads further inland and
some isolated showers begin to develop. Temperatures will remain
near seasonal norms in the upper 60s as the area remains north of
the warm frontal boundary developing in the Gulf. Rainfall will
become more widespread Saturday night and Sunday as the low
approaches from the west and isentropic forcing over the area
further increases. 32



VFR across all terminals early this morning, and this should
continue through the daytime hours. Only issue today is expected to
be wind at KNEW, which is in the 15-20 knot range this morning.
These winds should ease into the 10 to 15 knot range by evening. As
moisture returns tonight, cloud cover will increase from the west.
Could see MVFR ceilings as early as 03z-06z for KBTR, but will take
the remainder of the night to spread eastward to all the other
terminals. Any significant precipitation likely to hold off until
beyond 12z Monday.  35



Will continue Exercise Caution headlines through the daytime hours.
Should be able to drop it this evening across most or all the lakes
and sounds, but will need it through the overnight hours into Monday
morning over the open waters. Conditions should be a little quieter
for Monday through Tuesday night. Winds will again increase ahead of
the next front, which will move through Wednesday night. Small Craft
Advisories look to be necessary at that point through Thursday. 35



DSS code: Green.
Deployed: None.
Activation: None.
Activities: Support for City of New Orleans through Tuesday.

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.


MCB  68  53  76  63 /   0  20  70  30
BTR  71  59  77  66 /   0  20  70  30
ASD  69  57  77  64 /   0   0  60  30
MSY  71  62  78  66 /   0  10  60  20
GPT  67  59  74  65 /   0   0  50  20
PQL  68  55  77  64 /   0   0  50  20




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