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Area forecast discussion 
National Weather Service New Orleans la
347 PM CST Sat Nov 28 2015

Short term...

A broad middle and upper level ridge axis parked over the Gulf of
Mexico and the eastern portion of the Gulf Coast will gradually
weaken over the next couple of days. As this ridge weakens...a
stationary front currently extending across the arklatex and middle-
Mississippi Valley will slowly slide to the south and east toward
the forecast area. Have kept some low probability of precipitation in the 20 to 30 percent
range in place for the northwest portions of the forecast area
beginning late tonight and persisting through Monday. The rain
chances will be highest across southwest Mississippi and the Baton
Rouge region.

Temperatures will remain very mild through Monday...with highs in
the lower to middle 70s...and overnight lows in the lower to
middle 60s. The warm temperatures will be due to continue onshore
flow that will be also keep pumping ample moisture into the
region. This moisture combined with light winds should allow some fog
to form tonight and tomorrow night. The fog may turn locally
dense at times...but have decided to hold off on issuing a dense
fog advisory for now. Fog looks to be most likely across the
Northshore...Mississippi Gulf Coast...and the Houma region.

Long term...

The stationary front will continue to linger over the area heading
into Tuesday...and another round of fog may develop Monday night
as conditions continue to look favorable for some fog formation.
However...the front will finally begin to sweep through the
forecast area Tuesday into Tuesday night in response to a surge of
upper level vorticity and an associated trough axis swinging
through the Mississippi Valley. This upper level feature will
drive the front to the south...and have high end chance probability of precipitation
developing by late Tuesday night. Although temperatures will
remain well above average on Tuesday...only scattered showers are
expected out of this system. No thunderstorm activity is
anticipated due to very weak lapse rates aloft and the resultant
lack of instability.

By Wednesday...the frontal boundary should be offshore...and a
northerly wind should be in place across the forecast area. This
northerly flow will be rather shallow...with southwest flow
continuing in the middle and upper levels. As a result...clouds and
showers will continue to overrun the cooler air at the
surface...and keep chance probability of precipitation in for the entire day. The cloud
cover combined with weak cold air advection in the low
levels...will also push temperatures down into the upper 50s and
lower 60s Wednesday afternoon.

Model differences between the Euro and GFS begin to arise
Wednesday night and amplify heading into Thursday and Friday. The
GFS shows a rather potent upper level trough pushing out of Texas
and sweeping across the forecast area on Thursday and Friday. The
Euro on the other hand shows a much weaker and more open wave of
vorticity sweep through on Thursday and Friday. The stronger GFS
solution has a low forming over the western Gulf of Mexico and
then sweeping eastward with the parent trough. This solution has
moisture lingering over the southern half of the forecast area
Thursday into Thursday night as the low passes to the south.
The Euro does not have a low forming in the Gulf...which allows
for continued dry air advection into the region on Thursday and
Friday. This leads to clearing skies and lower humidities across
the area for Thursday and Friday. Both solutions agree that
temperatures will remain below average on Thursday...with lows in
the lower to middle 40s and highs in the middle to upper 50s. By
Friday...there should be some moderation in temperatures back into
the 60s. This is reflected by both model solutions.

Given these model differences and below average confidence in the
extended forecast...have went with a blend of the models for the
latter part of the forecast. This solution keeps some scattered
showers in place across the southern half of the forecast area on
Thursday...but then has the drier air winning out by Friday with
clearing skies and drier air advecting in. Basically...the
solution depicts a weaker low developing the Gulf and passing
through the coastal waters on Thursday. As this low pulls to the
east...drier air should wrap around the low and advect into the
region for Thursday night and Friday.



Marine layer flow will likely result in a low cloud and eventual fog
bank generally after 06z as low level winds decouple. Expecting IFR
and LIFR conditions in near-water locations to be impacted initially
and spread into more interior locations through the night.
Conditions are then expected to improve to MVFR ceilings middle to late
morning...then low end VFR conditions after 18z. 24/rr



Light onshore flow is expected to prevail through Monday
ahead of stalled cold front currently draped from upper Mississippi
Valley into central Texas. Surge of high pressure builds into the
plains states to eventually nudge the cold front into and through
the coastal waters late Tuesday into Wednesday. The affects of the
high pressure and cold air advection will eventually bring an
increase in winds and seas for much of the day Wednesday into early
Thursday before abating as high pressure moderates. There may be a
need for small craft advisories Wednesday and early Thursday for
winds around 20kts and seas building to 7 feet in the outer coastal
waters. 24/rr


Decision support...


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 risk severe and/or direct
tropical threats; events of National significance


Preliminary point temps/pops...
mcb 63 73 60 73 / 20 30 30 20
btr 64 76 62 76 / 20 20 20 20
asd 62 76 59 76 / 10 20 20 20
msy 64 76 61 76 / 10 20 20 20
gpt 62 73 60 75 / 10 20 20 20
pql 60 75 58 75 / 10 20 20 20


Lix watches/warnings/advisories...



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