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000 
FXUS64 KLIX 300225
AFDLIX

Area Forecast Discussion
National Weather Service New Orleans LA
925 PM CDT Wed Mar 29 2017

...SEVERE THUNDERSTORMS POSSIBLE LATER TONIGHT INTO THURSDAY...

.UPDATE...

Updated forecast earlier this evening for Tornado Watch #101 and 
to increase the PoP tonight, mainly for areas in the I-55 corridor
and a bit east to account for a slightly faster eastward
progression of the current leading edge of thunderstorms.
Thunderstorms that have been producing hail up to around 1 inch at
times (with larger sizes indicated by radar hail algorithms) have
been moving across south central Louisiana and some of these 
storms may prompt severe thunderstorm warnings after 9:30 pm 
starting in Iberville Parish if current intensity is maintained.

Special note about web page problems...due to a national server
issue, some of the graphical information on the top of the
National Weather Service New Orleans/Baton Rouge page /
weather.gov/lix may not be current. Recent postings will still be
available on our Facebook and Twitter pages. 22/TD 

&&

.PREV DISCUSSION... /issued 402 PM CDT Wed Mar 29 2017/ 

DISCUSSION...Difficult forecast shaping up. The risk for severe 
storms is impressive and tonight could even be more of a concern 
than tomorrow.  That said a few things could actually help keep the 
risk mostly out of the area tomorrow. As for today it was a warm and 
generally quiet day for our region but a few severe storms have 
developed over southeastern TX and southwestern LA and south into 
the northwestern Gulf. This activity could move into our area during 
the overnight hours. 

Tonight and tomorrow should be active. As has been mentioned the 
last few days this activity will be driven by a strong upper low 
over the southern Plains and moving into the Mid MS Valley by 
tomorrow evening. We are currently outlooked with an Enhanced Risk 
in the extreme northwest with a Slight Risk almost all the way to I 
55 across SELA for tonight. Tomorrow the entire area is under a 
Slight Risk.

The first piece of concern will be overnight tonight and as 
mentioned earlier may actually be the greatest risk for severe 
weather. There will actually be quite a bit of ingredients in place 
tonight across the northwestern portions of the outlook area and the 
models have struggled to catch up with the environment and speed of 
convection. First as the main trough axis slowly swings through 
TX forcing will increase but in addition a lead vort max will 
swing through overnight. Mid lvl winds will increase with h5 winds
increasing to 50 kts. The best LL convergence will set up late 
this evening and through the overnight hours across the northwest.
In addition the LL wind field will respond to the increasing 
forcing and h85 winds could approach 40 kts. An unstable 
environment will be in place with impressive mid level lapse rates
still anticipated and showalters still expected around -4 to -5 
and MLCAPE around 1000j/kg. The difluent feature aloft that we 
have been advertising will likely be more over the region tonight 
now and displaced to the south over the Gulf tomorrow. The 
combination of shear, instability, and forcing looks like it could
be in place during the overnight hours and this would suggest a 
decent risk of severe storms. Ongoing activity could continue
through the night and possibly expand as we feel the impact of the
increasing lift. All modes of severe weather are possible but of
somewhat greater concern is the model soundings have been showing
a rather curved hodograph overnight. This is favorable for 
tornadoes especially if the storms are more cellular in nature and
not necessarily a line. 

Tomorrow we are under a Slight Risk but there are numerous 
questions. First it seems like models have trended towards the 
difluent area aloft lining up in the Gulf and this would favor 
convection, possibly an MCS, developing over the Gulf quickly 
tomorrow morning and this would effectively shut us down. If the MCS 
doesn't develop then we could see strong to severe storms tomorrow 
with large hail being the greatest concern. The other possibility is 
if the MCS develops and pushes east really quick. If this occurs 
it would allow the region to recover and destabilize. Then as the 
cold front and the main trough push in we could see thunderstorms 
begin to fire right along the front. These storms would mainly 
pose a hail risk. Storms should quickly come to an end early 
tomorrow evening with much drier air moving in. 

One other thing to mention, there will be a lot of moisture 
available. With the rather impressive upper level jet in place, an
increasing LL jet and h85 theta E ridge nosing into the region, 
storms will be very efficient and could quickly drop 1-2 inches of
rain in less than half an hour. This could lead to isolated areas
of flash flooding if storms hit the wrong areas. /CAB/

Fri through Sat will be quiet as ridging takes place. Conditions 
begin to go downhill once again Sun. Still some uncertainty 
regarding timing  but another very potent system will makes its way 
through the Southern Plains Sun and into the Lower MS Valley 
sometime Mon/early Tue. This will bring more showers and 
thunderstorms with severe weather possible but also very heavy rain 
and could drop over 5 inches across portions of the region. 

AVIATION... Main concern will be timing out convective arrival at 
the terminals with approaching frontal QLCS feature moving out of SE 
Texas. GFS model timing has it at KBTR around 09Z, then progressing 
through KMCB/KHDC around 10Z, KHUM/KMSY 11Z, KNEW/KASD around 12Z, 
KGPT 1330Z. Otherwise, mostly VFR or high end MVFR ceilings through 
00Z with a lowering to MVFR ceilings prior to QLCS arrival, then 
maintaining MVFR conditions through end of the valid TAF period as 
rain tapers from west to east through 18Z Thu. 24/RR

MARINE...Small craft exercise caution headlines have been extended. 
Mariners will also have to concern themselves with the threat of a 
line of thunderstorms moving through the coastal waters late tonight 
and Thursday. Another round of strengthening winds as well as 
thunderstorms may require headlines late in the weekend. 35

DECISION SUPPORT...
DSS CODE...Blue.
DEPLOYED...None. 
ACTIVATION...None. 
ACTIVITIES...Monitoring Severe Weather Potential on Thursday

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  66  78  54  80 /  60  60  20   0 
BTR  67  79  54  83 /  60  60  10   0 
ASD  68  76  58  80 /  30  70  30   0 
MSY  69  78  60  81 /  30  70  30   0 
GPT  70  75  60  78 /  10  70  50   0 
PQL  67  77  58  78 /  10  70  60   0 

&&

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

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