Scientific Forecaster Discussion
fxus64 klix 160922
Area forecast discussion
National Weather Service New Orleans la
422 am CDT Mon Sep 16 2019
our area is stuck between two strongly different air masses this
morning. One is Continental dry air north and a tropical air mass
south. Pws range from 1.4" north near mcb to 2.4" near msy. That
is a strong contrast and it will play out in not only number of
sh/ts that are produced but also rainfall amounts. Wpc has set the
deeper moist area under a marginal risk of excessive rainfall and
this should be the case today as a few thunderstorms could train
over a few locations mainly south of Lake Pontchartrain. The
amount of rainfall will be much needed at this point but rainfall
rates and possible training could cause a few low lying and poor
drainage locations to flood. Areas north of Lake Pontchartrain are
not expected to see flooding conditions and numbers will be lower
with respect to sh/ts.
The poorly organized mass of thunderstorms over the northwest Gulf is
trying to evolve but is finding lots of difficulty in doing so.
First the main sfc circulation, if one can call it that, is found
well to the SW of the mass of strongest convection. The
circulation is basically a reflection of the warming upper low
above it. Eventually this circulation will stretch northward as
the large area of sh/ts to its north also wraps to the north then
northwest of it. The area is also surrounded by a deep dry air layer
which is seen on WV imagery this morning. Should continue to see
pulsing of thunderstorm activity through the day with this
feature. This whole mess is expected to move inland later and will
provide some needed but possible too much rain for locations
along the Texas coastal Bend. As some of the moisture spreads out
from this system and a back door front moves this way as Humberto
exits stage right, we may see a little more rainfall area wide
finally by Thursday night and/or Friday. This front will not have
much in the way of cooling though. The cold front that is supposed
to move near the area is still being advertised by models but
only makes it to about northern la/MS before stalling. But this
could change and we are getting to that time of the year when we
should start seeing a few frontal passages.
VFR conditions can be expected early this morning. However,
increasing coverage of tropical rain showers will begin across far
southeast la coastline areas, and press north through late morning and into
the afternoon hours. Main impacts expected will be for terminals
along and south of I-10/12 where periods of heavy rainfall will
cause temporary reductions in flight categories to IFR/LIFR.
Additionally, some storms may produce gusty, erratic surface winds
in excess of 25 to 30 knots. Look for most of this activity to
diminish late this afternoon and evening with VFR conditions
prevailing through the overnight hours tonight. Klg
winds remain elevated this morning but will begin to ease later
today. Strong to severe thunderstorms are occurring just outside
our coastal waters but a few strong thunderstorms will continue to
develop from time to time along a coastal trough axis today. Some
of these could cause wind speeds in the 35-40kt range. These
sh/ts will move west today. Otherwise, a flat pressure field will
cause synoptic winds to be weak mainly near and east of the miss
dss code: blue.
Activities: marginal risk for excessive rainfall southeast la.
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; marginal risk severe or excessive rain.
Yellow = heightened impacts with short-fused watch, warning or
advisory issuances; radar support for slight risk severe
or excessive rain.
Orange = high impacts; enhanced risk severe; nearby tropical events;
hazmat or other large episodes.
Red = full engagement for moderate to high risk of severe and/or
excessive rainfall, or direct tropical threats; events of
Preliminary point temps/pops...
mcb 93 71 95 72 / 20 0 10 0
btr 92 73 93 74 / 40 0 20 0
asd 92 72 95 72 / 30 0 0 0
msy 90 77 93 77 / 60 0 20 0
gpt 91 74 93 74 / 20 0 0 0
pql 93 73 97 73 / 20 0 0 0