Area Forecast Discussion
Issued by NWS New Orleans/Baton Rouge, LA
FXUS64 KLIX 280941
Area Forecast Discussion
National Weather Service New Orleans LA
341 AM CST Tue Feb 28 2017
Conditions that are present point to marine fog production.
Looking to see if that type of fog is possible, a few issues
emerge. The first is saturated or nearly saturated dew pt temps
moving toward shore are around 70 while the water temps are in the
upper 60s. Wind speeds are within tolerance but just barely. These
conditions will keep the possibility of patchy fog moving in and
out rather quickly this morning mainly over water and immediate
coastal sections. Fog that moves onshore will be within a short
distance of the coast. As the frictional effects of land causes
the wind speed to slow, the incoming air moves in and compacts
causing the air to lift. This causes the fog at the coast to lift
into a low level deck just inland. This scenario is quite
different inside the Mississippi River channel. Water temps are in
the low 50s. This is causing the saturated air at 70 to become
supersaturated with a large amount of deposition occurring.
Basically, dense fog is expected in the river and will be packed
into the bends by the wind. Almost a carbon copy of this occurs
A stong cold front stalled over central Oklahoma/central Texas
will begin to move east late tonight and enter our area just after
noon Wedensday. The short wave responsible for this is currently
moving through California. The main thrust of potential severe
weather looks to be well north of the area as the short wave
ejects out of Texas.
SPC has placed the northern half of the area in a marginal risk
of severe ts for Wednesday. The main concern with anything capable
of becoming severe would be hail and winds. But the issue with
this front producing severe wx is two fold. First, winds begin to
parallel the boundary in the vertical above 7k` causing weaker
vertical forcing while the sfc front remains with robust forcing
as it moves through the area. This will simply cause the front to
be relatively shallow(~7k`depth). Second, the sfc high that moves
in behind the front will bridge the southern end above this 7k`
level producing stability and drying. This all said, the sensible
weather associated with the front begins to weaken and decay as
the boundary moves through the area. The strongest sensible
weather potential looks to be when it first enters the area in the
High pressure will move east over the weekend bringing return flow
back to the area by the start of the week. The next system to
affect the area should move in from the north by Tuesday or
Wednesday of next week. At the moment, there is some weak evidence
showing this boundary making it through the area. But confidence
is not high enough to make a strong judgement call for now.
Wide range of conditions early this morning from MVFR to LIFR.
Except for KBTR, all terminals reporting ceilings below FL010. Only
locations where visibilities are being reduced significantly are on
the Mississippi coast where visibilities are 3sm at KBIX and 3/4sm
at KGPT. May be a bit of sea fog blowing in from Mississippi Sound,
as winds at KGPT are 10 knots. Wind is aiding in preventing low
visibilities at most terminals. If winds should decouple around
sunrise, which isn`t currently expected, fog could form fairly
quickly. Where conditions fall to IFR or lower, expect improvement
to MVFR by about 15z and VFR by midday. VFR should continue through
at least early evening, but low stratus cloud deck likely to return
beyond 06z Wednesday. 35
Winds over marine areas likely to remain near or below 15 knots
until the passage of a strong cold front Wednesday night. Likely to
need Small Craft Advisories from Wednesday evening into Saturday for
some or most of the coastal waters. 35
DSS code: Blue.
Activities: Support for City of New Orleans today.
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 84 66 79 47 / 10 20 60 20
BTR 83 68 81 51 / 10 10 50 20
ASD 83 66 82 53 / 10 10 40 30
MSY 81 68 82 56 / 10 10 30 30
GPT 77 66 78 54 / 10 20 30 40
PQL 79 65 79 52 / 10 10 30 40