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Area forecast discussion 
National Weather Service New Orleans la
833 am CDT Tuesday Jul 26 2016

..sounding discussion...
The tropical airmass is still in place over the central Gulf Coast
today. Precipitable water is above average at 2.3 inches. Near saturated low level
environment... light easterly winds... and plenty of cape are all
favorable conditions for waterspouts. Several have been spotted
over Lake Pontchartrain this morning so similar storms over
coastal areas may have them as well. Easterly winds are present
through the profile. Gusty winds up to around 30 kts are possible
in some of the passing showers and storms given the tropical



Previous discussion... /issued 355 am CDT Tuesday Jul 26 2016/

Short term...

Very little change in thinking concerning the forecast through
Thursday. A broad inverted trough axis will continue to linger
over the Gulf of Mexico and the central Gulf Coast through
Wednesday. This inverted trough will merge with some northern
stream energy moving through the Midwest by Thursday resulting in
an elongated region of lower pressure stretching along the
Mississippi River valley. Given the persistent troughing over the
area, rain chances will be higher than average through the period.

The main driver of how high rain chances will be is the amount of
moisture content in the atmosphere. A pool of deep tropical
moisture as indicated by higher Theta east values and precipitable
water values in excess of 2.5 inches will overspread the forecast
area today and linger into tomorrow. With ample moisture, lift,
and instability in place, numerous showers and thunderstorms are
expected to form both today and tomorrow. Have kept in the 70
percent chance of rain for the region both days. Precipitation
efficiency will be very high, so any thunderstorms could produce
locally heavy rainfall of 2 to 4 inches in a short period of time.
As a result, some localized street flooding issues may occur today
and tomorrow. The increase in convection and resultant cloud cover
will also keep temperatures slightly cooler than average in the
upper 80s and lower 90s both today and tomorrow. Overnight lows
will cool into the middle to upper 70s.

Heading into Thursday, the deep pool of moisture is expected to
pull to the north of the forecast area allowing atmospheric
moisture content to return to more seasonal levels. As a result,
convective coverage is expected to become more scattered. Pop
falls back into the 40 to 50 percent chance range, and
temperatures should be slightly warmer due to less cloud cover and
increased solar insolation. There should be a gradient in
convective coverage as well with areas closer to the coast showing
lower convective chances. This is mostly due to the growing
influence of a ridge over Florida and the eastern Gulf on
Thursday. Rain chances in the coastal waters should be 30 percent
or less on Thursday.

Long term...

The elongated southwest to northeast oriented upper level trough
should continue to linger over the lower Mississippi Valley
through the weekend. This should keep a risk of scattered daytime
convection in the forecast from Friday through Sunday. Rain
chances should range from 30 to 50 percent each day with higher
chances further inland where forcing is expected to be strongest.
Temperatures are forecast be near seasonal norms in the lower to
middle 90s each day. Overall, the weather pattern during this
period is forecast to be fairly close to what is expected for
late July.

Both the Euro and GFS indicate that a weak upper level ridge
should develop in the Southern Plains early next week. At the same
time, both models also show another inverted upper level trough
moving through the Gulf of Mexico and the forecast area. This
inverted trough should bring another surge of deeper tropical
moisture to the area, and have pop remaining around 50 percent
both days. This may be on the low side, but given the extended
nature of the forecast confidence is not high enough to place
likely pops in the forecast. Temperatures should generally be near
seasonal norms early next week.


Scattered to numerous showers and thunderstorms are expected again
today, primarily from late morning through the afternoon with
respect to terminal locations. Otherwise, VFR category conditions
will generally prevail at the terminals through the taf forecast
period outside of the showers and thunderstorms.


The weak surface low near the miss river mouth and attendant
inverted trough will begin its slow move northward late today.
It's a good thing too since it is these type of weaknesses that
can become a problem if they remain over very warm water in a
conducive environment. The low will deepen enough to keep winds
around 15 knots over mainly open Gulf waters before moving north
today. These winds will move east of the miss river Wednesday as
the low moves north into northern Louisiana. Winds may even get
as high as 20 knots in some locations before easing back to around
10 knots Wednesday night into Thursday. Gusty winds will
accompany thunderstorms as well.

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 90 73 89 73 / 60 50 70 50
btr 91 74 91 74 / 70 60 70 50
asd 89 76 92 77 / 70 60 70 50
msy 90 77 91 78 / 70 60 60 50
gpt 88 77 91 78 / 70 60 70 40
pql 89 77 91 77 / 70 60 60 40


Lix watches/warnings/advisories...


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