Area Forecast Discussion
Issued by NWS New Orleans/Baton Rouge, LA
FXUS64 KLIX 280824
Area Forecast Discussion
National Weather Service New Orleans LA
324 AM CDT Tue Mar 28 2017
The trough over the Louisiana Arkansas line will continue to back
off today with only a hint of sh/ts developing mainly due to
heating and some boundary interaction well to the north. Will
keep only a slight chance of rain for the northern most zones
today. Stability increases as the boundary moves north late today
and tonight. This will last through at least the Wednesday
Wed night into Thursday morning we will begin to observe some
rapid changes with a cold front moving out of Texas. The feature
that will cause this is located over the SW conus at the moment as
a sharp upper trough. Two key elements will occur over the next
36 hours to bring severe thunderstorms to the area. First the
upper trough will begin to kick out as it moves east but at the
same time, stronger energy will dump into the back side of the
upper trough causing it to slow and dig a little more Wed morning
over west Texas. This will then allow the second element to occur
as the subtropical jet couples with the stronger polar jet and
associated upper trough.
Eventhough the main sfc low will be displaced farther north of our
area, it will be this stronger energy moving through the base of
the polar trough along with the enhanced split flow by the subtropical
jet that will cause most of the issues. As the stronger jet winds
move through the base of the upper trough and begin exiting the
east side, the trough will begin to finally kick out. This occurs
at the same time that the subtropical jet helps to cause an even
stronger divergent flow aloft as it rips away from the polar jet
downstream. This very strong divergent flow aloft will have
dynamic variables very high, although the GFS may be overdoing
things just a bit with its possible feedback. An MCS type feature
should begin to initialize where this split flow exists over SE
Texas and move east during the day Wednesday. This feature should
start to move into the area late Wednesday night into Thursday
morning and take much of, if not all day, to move through. All
modes of severe weather will accompany this feature including the
potential for heavy rainfall. SPC currently has the area under a
slight risk for this scenario as well.
The uncertainty lies with the subtropical jet strength and
placement. There is a pretty good consensus on the polar jet but
the subtropical jet has not been well sampled just yet. This may
occur today though. Basically, the scenario mentioned above will
occur, just where it occurs will be somewhat in question. If the
jet moves into and folds northward along with the polar jet, this
MCS like feature will move through our area and NE. If the coupled
jets are slightly farther south, this severe weather feature would
stay mainly along and offshore. At the moment, we will keep this
feature moving along with the GFS solution until there is ample
sampling of the subtropical jet.
The next system will move in rather quickly on the heels of the
last and by Sunday we may begin to see some affects from it. This
time the main sfc low looks to be closer to the area providing
strong dynamic and kinematic support for severe weather once
again. But since this feature is on the back side of the weekend,
we will concentrate more on Thursday`s system for now.
Most terminals reporting ceilings in the IFR or MVFR ranges early
this morning. Most will see at least a brief period of IFR
conditions. Improvement to VFR conditions is expected by mid to late
morning, around 15-16z. Those conditions should continue for the
remainder of the daytime hours. Another round of MVFR to IFR
conditions is expected to redevelop near or shortly after 06z
Winds will remain in the 10 to 15 knot range for today and tonight.
As next system moves out of the Rockies, pressure gradient will
tighten somewhat and winds over the western waters should increase
to 15-18 knots by late Wednesday. This will eventually require Small
Craft Exercise Caution headlines. Conditions to spread eastward
across the remaining waters and continue into Friday morning.
Another round of strengthening winds may require headlines late in
the weekend. 35
DSS code: Green.
Activities: Assessing convective threats for this week.
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 82 65 85 66 / 20 10 10 20
BTR 84 65 87 67 / 10 10 10 20
ASD 82 66 84 66 / 10 10 0 10
MSY 82 69 85 69 / 10 10 10 10
GPT 77 68 81 66 / 10 10 10 10
PQL 79 64 82 65 / 10 10 0 10