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Next 12 Hours

Forecast data from the National Digital Forecast Database.

5 Day Forecast

• Wednesday
• 
• High: 88 °
• Low: 68 °
• T-Storms

• Thursday
• 
• High: 91 °
• Low: 68 °
• Chance of a Thunderstorm

• Friday
• 
• High: 91 °
• Low: 64 °
• Partly Cloudy

• Saturday
• 
• High: 88 °
• Low: 66 °
• Partly Cloudy

• Sunday
• 
• High: 90 °
• Low: 64 °
• Partly Cloudy

Area forecast discussion 
National Weather Service New Orleans la 
1216 PM CDT Wednesday may 22 2013 


Aviation... 
18z taf discussion...scattered showers and isolated thunderstorms 
continue to impact southeast la and S MS. Outside of any convection... 
expect VFR conditions to prevail through the afternoon hours. With 
increased moisture and light winds forecast overnight...low ceilings 
and patchy fog will once again be possible. Have included tempo 
groups at nearly all taf sites for MVFR or IFR ceilings and/or visibilities. 
Expect conditions to improve after sunrise. 


&& 


Previous discussion... /issued 806 am CDT Wednesday may 22 2013/ 


Sounding discussion... 
no issues with the flight this morning. Precipitable water measured at 1.66 
inches with moisture measured from the surface through 35k feet. Moist 
southerly flow from the surface through 10k feet then SW to west upward. 
Not a severe sounding but there is support for heavy rain 
associated with the current area of showers and storms on the 
radar. Freezing level measured at 12753 kft. Overall sounding is 
warmer then 24 hours ago. 


Short term... 
models having a tough time with amount and timing of this mornings 
convection. Updated probability of precipitation and quantitative precipitation forecast as the area of showers and 
thunderstorms pushes east. Rainfall rates being represented very 
well on the wsr88d dual pol with over 2 inches in many areas 
overnight. Rainfall rates are high with an inch reported at kbtr 
in 7 minutes. 


Decision support... 


Previous discussion... /issued 519 am CDT Wednesday may 22 2013/ 


Short term... 
showers and thunderstorms have already moved into about the 
northwest third of the forecast area. The only model that had a 
decent handle on this was a hi-res WRF run from yesterday...as 
most of the other models are not fast enough. This convection is 
in advance of the wake surface low near the Texas/Louisiana border 
and the middle/upper level shortwave trough moving from the Southern 
Plains into the lower Mississippi Valley. The acceleration of 
convective activity is typical in this very divergent upper level 
pattern which should persist strongly over the forecast area today 
along with deep moisture profiles. The big question and forecast 
problem today is whether the showers and thunderstorms will be 
able to build back north against the momentum of the southward 
moving outflow boundary...and if a surface boundary will stall and 
produce heavy rainfall. It appears it is more likely a boundary 
will stall rather than move back north at this point. 


Heavy rain and flash flooding concerns have already started in 
some areas north of Baton Rouge early this morning...and locally 
heavy rainfall amounts of 2 to 3 inches in a short period of time 
with a few isolated areas possibly seeing 4 inches are expected 
given the current radar trends. These heavier rainfall amounts are 
most likely during the early to middle morning hours...then the 
heavier rain areas should become more isolated as convection 
becomes more scattered by late morning and afternoon. Given the 
high flash flood guidance...will hold off on issuing a Flash Flood 
Watch at this time. The threat of organized severe thunderstorms 
is low today...however...some of the stronger clusters of storms 
that develop mini-Bow structures could approach severe levels and 
produce wind gusts in the 40 to 50 miles per hour range and possibly some 
small hail. 


Shower and thunderstorm activity will gradually diminish from the 
west late in the afternoon and tonight as the main upper level 
support pushes east of the forecast area. On Thursday...a 
middle/upper trough will amplify over the eastern Seaboard region as 
a middle/upper low/trough persists over the Pacific coast. In 
between...an upper level ridge will build over the central U.S. On 
Thursday with northwest flow across the central Gulf Coast. There 
will be a west to east frontal boundary sagging slowly south or 
temporarily stalling across the northern portion of the forecast 
area on Thursday as weak upper level disturbances move across the 
boundary. The atmosphere will have much less moisture content to 
work with which means a lack of clouds and fairly hot temperatures 
will be expected. Middle level temperatures will be rather cool with 
steep lapse rates...so instability will be high. Since the 
dynamics will be weak...will only carry a slight chance of 
afternoon thunderstorms at this time. 


Thursday night and Friday...the digging upper trough over the 
eastern states will cause surface high pressure to strengthen and 
build south and southeast from the Midwest into the southeast 
states. This will push a weak cold front with much drier air south 
through the forecast area. The boundary may be hung up just enough 
for a few afternoon showers near the Atchafalaya River...but most 
areas should be dry and less humid. Temperatures will fall to more 
comfortable and below average levels Friday night as the surface 
high continues to build in from the north. 


Long term... 
little change in the overall weather pattern is expected from 
Friday through the Holiday weekend as the upper systems over both 
the west and east coasts will only slowly progress east while a 
ridge persists over the central states. Surface high pressure will 
gradually weaken and shift east...but will maintain its grip on 
the Gulf Coast region. This means there should be no threat of 
rain with abundant sunshine. Temperatures will be noticeably 
cooler during the nights and mornings over the weekend due to the 
lower humidity...and have lowered the forecast lows more in line 
with the GFS trends from the last few runs. The high temperatures 
are expected to be near the seasonal averages in the middle to upper 
80s. 


The next slight chance of rain is expected to return about next 
Wednesday as some moisture return from the Gulf of Mexico may 
allow for some isolated diurnal showers or thunderstorms. 22/dew point 


Marine... 
while high pressure remains over the Gulf...a weak frontal 
boundary will approach the coast and become stationary. High 
pressure will bridge across the front Friday into Saturday...with 
flow becoming offshore. There is some potential...especially in 
the eastern waters...of a period of exercise caution conditions 
Friday night into Saturday morning as drier air works in. Onshore 
flow returns Sunday night and will continue through much of next 
week. 35 


Decision support... 
dss code...blue. 
Deployed...none. 
Activation...none. 
Activities...slurry support. 
Monitoring river flooding. 
Monitoring convection and heavy rainfall trends. 


Decision support services (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 severe; nearby 
tropical events; hazmat or other large episodes 
red = full engagement for moderate to high risk severe 
and/or direct tropical threats; events of National 
significance 


&& 


Preliminary point temps/pops... 
mcb 86 65 91 63 / 70 10 20 20 
btr 86 68 92 68 / 80 10 20 10 
asd 85 68 89 66 / 100 10 20 10 
msy 85 71 89 70 / 100 10 20 10 
gpt 83 69 87 67 / 100 20 20 10 
pql 85 67 89 65 / 90 20 20 10 


&& 


Lix watches/warnings/advisories... 
la...none. 
GM...none. 
MS...none. 
GM...none. 
&& 


$$ 


Aviation...95/dm 
sounding...keg 
previous discussion...22/35