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

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FXUS64 KLIX 251308
AFDLIX

Area Forecast Discussion
National Weather Service New Orleans LA
808 AM CDT Sat Mar 25 2017

...SOUNDING DISCUSSION...
The sounding is from ahead of the storms this morning and
indicates instability is present with mixed layer CAPE at
970 J/KG and most unstable at 1260 J/KG. Winds are SSE right at
the surface and veer to SW at 50 kts by 500 mb. Surface to 6 km
shear is at 49 kts suggesting strong to severe storms are at least
possible, though the winds are likely a bit more unidirectional
with the actual line. The storms have been weakening this morning.
Winds at about 30 kts are the highest observed in the line so
far, though daytime heating will add some more instability for
additional development later today. Hail might be possible with a
couple of the stronger storms with higher updrafts this
afternoon. Wet bulb zero height is relatively low at 8400 ft.

Krautmann

&&


.PREV DISCUSSION... /issued 339 AM CDT Sat Mar 25 2017/

SHORT TERM...
A line of convection extending from northeast Louisiana to the
southwest corner of the state was continuing to push eastward
early this morning. This line has shown signs of weakening over
the last couple of hours and the latest HRRR model data as well as
the 06Z run of the NAM forecast this trend to continue as it
pushes into the western and northern sections of the P/CWA during
the early morning hours. Models then forecast redevelopment of
this line later today farther to the east with additional
convection moving in from the west as well. Despite the current
trends and near term forecast for weakening of convection this
morning, the threat of strong to severe thunderstorms will exist
today across the forecast area and SPC has included the entire
area in a slight risk for severe thunderstorms. The main severe
weather threats will be damaging thunderstorms winds and large
hail; however, an isolated tornado or two is not out of the
question, primarily during the morning hours.

The convection today is the result of a vigorous upper low/trough
progressing slowly east-northeastward across the mid and lower
Mississippi Valley. This system will act on a moist and unstable
atmosphere to produce numerous to widespread thunderstorms today
which will diminish late in the day and during the evening as the
upper low/trough pulls off to the east-northeast. Decent upper
level divergence should aid development and help maintain the
convection today. Forecast soundings show veering of the winds
with height in the lowest levels yielding SRH values in the 200
to 300 m2/s2 this morning which signals a threat for tornadoes.
This veering in the lowest levels becomes less prominent as the
day progresses, thus a decreasing threat for tornadoes as the day
goes by. The forecast soundings also indicate a threat for hail
with relatively low WBZ heights. This makes sense as a the cold
pool aloft associated with the upper low/trough spreads eastward.
The cold front associated with this system will not push through
the P/CWA.

A much more tranquil and dry day is expected on Sunday as this
weather system continues to move away from the area. 11

LONG TERM...
A warm and active pattern will prevail through the work week and
into next weekend. A short wave trough moving across the
Mississippi Valley at the beginning of the work week will be the
next system to impact the local area. Convection is expected
across the area Monday into Monday night. An isolated strong
storm is not out of the question; however, the best chance for
this will be to the north of the forecast area. Some residual
moisture may also yield a shower or thunderstorm on Tuesday with a
frontal boundary nearby or just to the north. Again, the front
will not push through the area.

A more impressive system will affect the area for the last half of
the work week. At this time, it looks as if an upper low/trough
will move out of the southern Plains and into the lower/mid
Mississippi Valley on Thursday with a threat of convection across
the P/CWA from Wednesday night through Thursday night. It would
appear that some strong to severe thunderstorms will again be
possible with this system. There are now some differences with how the
the GFS and ECMWF handle this system with regards to the strength
and timing.

Yet another system may impact the lower Mississippi Valley next
weekend or just beyond the current forecast period into the
following week. The GFS and ECMWF are again offering solutions
with some differences on the strength and timing of this system.
11

AVIATION...
Main concern will be timing of thunderstorms associated with a
squall line. The squall line currently stretches from near Monroe,
to just east of Alexandria, to Lake Charles. Northern end continues
to move a bit faster than the southern end as the front elongates.
Model guidance appears too fast with the arrival of thunderstorms,
and will likely need to adjust TAFs in the next hour or so to
account for further slowing of the convective line. Outside of
convection, general MVFR conditions due to cloud deck between 15kft
and 25kft. Conditions will drop to IFR during peak of convection,
then should improve to VFR behind the line. 95

MARINE...
Small craft advisory conditions with winds over 20 knots and rough
seas will persist through 7am for open waters west of the
Mississippi River, and through 7pm for open waters east of the
Mississippi River. Elsewhere, exercise caution headlines are in
effect. The pressure gradient will weaken tonight and Sunday as high
pressure overspreads the coastal waters.  Expect to see southerly
flow of 10 to 15 knots and seas of 3 to 5 feet by Sunday, and then
to see these conditions persist through Tuesday. A second low
pressure system could bring another round of small craft conditions
to the waters for Wednesday and Thursday. 95

DECISION SUPPORT...
DSS CODE...Orange.
DEPLOYED...None.
ACTIVATION...None.
ACTIVITIES...Monitoring Severe Weather Potential.

Decision Support Service (DSS) Code Legend:
GREEN  = No weather impacts that require action
BLUE   = Long fused Watch/Warning/Advisory in effect or high
         visibility event
YELLOW = Heightened impacts with short fused
         Watch/Warning/Advisory issuances; Radar support
ORANGE = High Impacts - Slight to Moderate risk of severe weather;
         Nearby tropical events, HAZMAT or other large episodes
RED    = Full engagement for moderate risk of severe weather; Direct
         tropical threats; events of national significance.

&&

.PRELIMINARY POINT TEMPS/POPS...
MCB  78  61  83  63 /  80  30  10  10
BTR  81  62  83  64 /  80  20  10  10
ASD  79  62  81  63 /  80  30  10  10
MSY  80  66  82  66 /  80  20  10  10
GPT  77  64  79  65 /  70  30  10  10
PQL  78  64  80  63 /  70  30  10  10

&&

.LIX WATCHES/WARNINGS/ADVISORIES...
LA...None.
GM...Small Craft Advisory until 7 PM CDT this evening for GMZ555-557-
     575-577.

MS...None.
GM...Small Craft Advisory until 7 PM CDT this evening for GMZ557-575-
     577.

&&

$$



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