Area Forecast Discussion
Issued by NWS New Orleans/Baton Rouge, LA

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628
FXUS64 KLIX 182221
AFDLIX

Area Forecast Discussion
National Weather Service New Orleans LA
421 PM CST Wed Jan 18 2017

.SHORT TERM...
Forecast for the last few days remains on track. Marine fog will
be an issue tonight and we will have to watch if that fog will
sneak onshore tonight. We have already issued a Dense Fog Advisory
for the Mississippi Gulf Coast counties for this reason. We
expect a chance of some strong to severe thunderstorms to be
possible tomorrow across the forecast area. The threat is a
marginal as it remain very conditional. Based on some of the
guidance and indicies that we use to measure severe potential this
particular system lacks the instability needed for significant
severe threat. There is some instability expected to be around
but it remains to be seen if we will be able to utilize it as
showers and storms should be ongoing most of the day, and the
daytime heating aspect may not be a factor due to the cloud cover
that will be around. Looking at the forecast soundings heavy rain
will be the main threat on Thursday as most soundings are mostly
moist adiabatic meaning the entire column of the atmosphere
should be completely saturated and they follow the moist adiabats
on a sounding. For severe weather you would like for there to be
some cooler drier air aloft...and it seems like we will not a lot
of have that tomorrow. However, saturated soundings do yield
efficient rainfall, and this is the reason why heavy rain will be
the biggest threat to us Thursday. The precipitable water values
tomorrow will be 1.5 to 1.7 range across the region and for this
time of the year that is more than sufficient as the highest PW
ever recorded on tomorrow is 1.71. The good thing is that this
system will be progressive and should be out of the forecast area
for the most part by Thursday evening. Rain amounts of 1-3 inches
likely with Thursday convection. The main takeaway is that there
will be some rain tomorrow with the chance of a few strong to
severe thunderstorms.

We catch a small break during the day on Friday as we are in
between systems. Another much more impressive system starts the
effect the forecast area as early as Friday night. Another period
of active weather is expected to last through the weekend for most
of the southeast United States. Temperatures well above normal
through Friday. Thursday will be the coolest of the 3 days due to
better precipitation chances. 13/MH

.LONG TERM...
As stated above the next threat for severe weather may impact the
forecast area late Friday night into Saturday morning as strong
impulse moves out of the southern Plains this weekend. Guidance
still shows a couple rounds of strong to severe thunderstorms
effecting the southeastern United States this weekend. Guidance
suggests that an area of strong to severe storms could develop on
a lead shortwave Friday night and move across the region. Some of
the parameters when that occurs does cause some concern as the
best tornadic type indices occur over our area during that time as
well...that is if you take the guidance at face value. One thing
to point out as far as the tornadic threat is concerned for this
time period is that the storms could very well be elevated as
there is plenty of elevated CAPE and a little warm nose depicted
on the soundings. This would favor more of a hail threat for
Friday night into Saturday morning...to me this looks like the
greatest threat during this timeframe eventhough the tornadic
parameters are there. The Storm Prediction Center has introduced a
marginal risk for this time period. We will have to watch this
develop as we still have a few more runs of guidance before we
really have to crank up the heat.

Again as in previous forecasts this system will be a possible
multiple round event for the southeast United States. CAPE values
around 2000 j/kg and lifted indices near -10 on both GFS and NAM
forecast soundings. SPC has 15 percent threat for entire area for
24 hour period ending at 12Z Sunday. There is still a lot of if`s
in this setup for our area. The parameters look good over the area
but if any one thing does not line up we could not have much and
the bulk of the severe weather misses us to the east. A little bit
slower solution the more strong storm initiation could be
directly over our area. Needless to say, strong to severe
thunderstorms will be possible at anytime this weekend just due to
the atmosphere that should be in place, and any impulse that
could cause any sort of decent lift could trigger strong to severe
storms. We will again have to continue to nail down the details as
more information becomes available. Behind the Saturday/Sunday
systems, a couple of relatively quiet days before the next front
approaches Wednesday. Temperatures should remain above normal
through the period. 13/MH

&&

.AVIATION...
Issues come up tonight once again. Low cigs should impact all
terminals this evening and overnight with many of them dropping to
at least IFR status. As for fg/br, think most terminals will see
a drop in vsbys however the best chance for fog looks like coastal
MS terminals.

in addition to fg/br there is a good chance that shra and maybe
even some embedded tsra will move in across western sections
overnight, likely impacting BTR and MCB. /CAB/

&&

.MARINE...
No changes made to marine forecast except we issued a Dense Fog
Advisory for the tidal lakes and sounds. A low pressure system
will pass through the region Thursday and Thursday night. The
increased pressure gradient near this low will push southerly flow
up to around 15 to 20 knots. These conditions will also push seas
up to around 4 to 6 feet by Thursday night. High pressure should
then quickly fill back in behind this low and a sharp decrease in
the pressure gradient over the Gulf is expected for Friday. Winds
should fall back to 10 knots or less and seas should also drop off
quickly.

This period of calmer weather will be short-lived as another strong
low pressure system moves in from the west over the weekend. Onshore
winds should increase to around 15 knots by Saturday afternoon, and
then further increase to around 20 knots and advisory levels
Saturday night and early Sunday.  Seas should also turn rough due to
these winds with seas of 5 to 8 feet expected by Sunday morning.  In
the wake of this low, model guidance is indicating that gale force
winds could impact the coastal waters beginning Sunday afternoon and
persisting through Monday.  These conditions will be highly
dependent on the strength of the longwave trough axis projected to
slide through the region Sunday.

&&

.DECISION SUPPORT...
SS code: Blue.
Deployed: None.
Activation: None.
Activities: Dense Fog Advisories. Monitoring convective trends for
            Thursday through Sunday.

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  66  72  58  77 /  50 100  40  10
BTR  66  72  58  78 /  60 100  20  10
ASD  65  74  60  77 /  30 100  80  10
MSY  66  75  61  76 /  30 100  50  10
GPT  65  72  60  72 /  20 100  80  10
PQL  63  74  60  75 /  10 100  80  10

&&

.LIX WATCHES/WARNINGS/ADVISORIES...
LA...None.
GM...Dense Fog Advisory until 6 AM CST Thursday for GMZ530-532-534-
     536-538-550-552-555.

MS...Dense Fog Advisory from 9 PM this evening to 6 AM CST Thursday
     for MSZ080>082.

GM...Dense Fog Advisory until 6 AM CST Thursday for GMZ532-534-536-
     538-550-552-555.

&&

$$



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