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

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FXUS64 KLIX 200335 AAA

Area Forecast Discussion...UPDATED
National Weather Service New Orleans LA
935 PM CST Thu Jan 19 2017

The forecast girds and products have been updated to include a
marine Dense Fog Advisory for tonight and Friday morning for the
near shore waters...sounds and tidal lakes. The thinking at this
point is that any dense fog over land areas will be more patchy in
nature given that lower and mid level cloud decks are moving into
the area from the west. The exception to this may be across the
land areas adjacent to the coastal waters which may have a better
chance of seeing dense fog overnight. 11


.PREV DISCUSSION... /issued 703 PM CST Thu Jan 19 2017/

The sounding this evening has low level westerly flow in the wake
of the storms earlier. Winds become southwest aloft as the upper
level trough axis is almost overhead. Peak wind is 120 kts at 250
mb. The profile is moist throughout and still has an overall PW
above average at 1.4 inches. With really just a sfc trough passing
through there is no real change in airmass overnight. Therefore
the warm and moist conditions... aided by damp ground from the
rain... will be favorable for fog development by morning.


PREV DISCUSSION... /issued 405 PM CST Thu Jan 19 2017/

Showers and a few thunderstorms continue to push across the
forecast area. The heaviest of them are currently moving across
the Mississippi Gulf Coast counties as I type this. These will be
efficient rain producers and we will continue to have the Flash
Flood Watch out for the area until 6 PM even though the threat
has diminished significantly for portions of our area west of the
I-55 corridor. The showers and storms should end later on this
evening as this system pulls to the northeast. Patchy fog could
develop later on tonight. We will be in a lull on Friday as a much
more impressive system approaches the forecast area Friday night
into Saturday.

Things still point to a chance of a pretty stout severe
weather episode for the southeast United States starting across
our area Friday night and lasting through Sunday. Right now it
looks as if the best chances for our area to see severe weather is
Friday night into mid morning on Saturday. This is when the best
dynamics and possibly a boundary moving northward across the area
enhances spin in the atmosphere. If you take a look at some of the
SREF probabilities and other severe indices the best ingredients
correspond to this time frame as well. The atmosphere will have
the instability needed to sustain severe thunderstorms. The main
threats will be large hail and the possibility of tornadoes. This
atmosphere that could be in place this weekend could be volatile
for this time of the year. Some guidance shows CAPE values over
2000 J/KG over a large area of the SE US and LIs up to -10.
Multiple rounds of severe weather could impact the area over the
next 72 hours. Some guidance suggest that most of the convection
could be east of our area on Saturday and Sunday as the upper low
is digging so far south that the best jet structures and
diffluence will be to the east of us. So...going with that we
still have our prime window as of now is Friday night into
Saturday morning.

The Storm Prediction Center maintains a large Slight Risk area
for Friday night, Saturday, and Sunday. I would not be surprised
if they upgrade portions of the risk area to Enhanced or greater
depending on how the event unfolds. The main takeaway is that
severe weather will be possible Friday night through Sunday.
Please stay weather aware this weekend as the atmosphere will be
primed for severe weather. 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

Main concerns will be dealing with ongoing and approaching
convection during the next 6 hours, and the likelihood of sea fog
returning to the area overnight, maintaining MVFR to IFR
conditions for much of the valid TAF period with perhaps improving
to VFR CAVOK conditions closer to 18Z. 24/RR

A low pressure system will pass through the region tonight. 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 5 feet tonight. High pressure should then quickly
fill behind this front 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.

DSS code: Blue.
Deployed: None.
Activation: None.
Activities: Flash Flood Watch. Monitoring convective trends for
            Friday 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.


MCB  58  76  62  75 /  10  10  90  40
BTR  58  77  63  76 /  10  10  80  50
ASD  61  77  65  77 /  20  20  90  70
MSY  61  76  65  78 /  20  20  90  70
GPT  61  72  65  73 /  30  20  90  80
PQL  61  75  65  74 /  30  20  90  80


GM...Dense Fog Advisory until 9 AM CST Friday for GMZ530-532-534-536-

GM...Dense Fog Advisory until 9 AM CST Friday for GMZ532-534-536-538-


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