Gale Watch 1, NWS New Orleans, LA

AREA FORECAST DISCUSSION
National Weather Service New Orleans LA
331 AM CST Fri Jan 20 2017

.SHORT TERM...
The next couple days still looking to be quite impactful with bouts
of rain and possibly a couple rounds of strong to even severe
thunderstorms. Today would be considered "the calm before the
storm." An upper low located near the upper Mississippi Valley will
rotate northeast towards the Great Lakes today. The surface trough
associated with convection yesterday has stalled across the northern
Gulf of Mexico due to the upper trough moving away from the local
area. Post-trough dry air in place will keep most of the area stable
except along coastal areas, closer to the boundary. Temperatures
will rebound today, moderating back into the upper 70s.

Models show another shortwave trough moving across the southern
Mississippi Valley tonight. The NAM soundings show a stable
atmosphere today quickly destabilizing from 00z-06z as mid level
cooling begins from the lower heights and moisture surges in. This
will also cause lapse rates to steepen. At the same time, mid-
upper level jet will be brings winds into the 50 to 80 knot range
with 120kt 250mb jet overhead. The main potential limiting factor
will be a low level inversion which the GFS shows may be in place.
This will disrupt updrafts as they develop. However, stronger
speed shear throughout the column increases the chances for severe
weather to Slight Risk with the best chances around the Baton
Rouge Metro and especially northward in southwest Mississippi. May
be a scenario which commonly happens in which storms are
intensifying as they move northeast into central Mississippi.

Moving into Saturday, model soundings begin to depict what could be
an even better chance for severe weather, and one maybe with
somewhat significant impacts to a few locations. The previously
mentioned steep lapse rates (Li of -8 or less) and cape values (over
2000 j/kg) will still be in place as well as strong mid and upper
level winds. As the day progresses, the lower level inversion will
begin to erode while convection is ongoing. Storms could begin to
become severe, mainly in the afternoon hours. The nose of a 130kt
jet will be coming in from the west early afternoon. Such steep
lapse rates are conducive for large hail, potentially golfball to
maybe even baseball size if what the model soundings show now,
does occur tonight and Saturday. Tornadoes and damaging winds are
possible as well but to a somewhat lesser degree. These storms
will progress east into coastal Mississippi Saturday evening with
a lull in convection during the middle of the night Saturday
night.

Models show a deepening upper low moving across northern Louisiana
and central Mississippi Sunday morning through the afternoon.
Showers and possibly a few thunderstorms will develop along the
associated frontal boundary as it swings through during the
morning hours. Very strong boundary layer winds will develop
behind the cold front in the southern half of the forecast area
(New Orleans and southward). Will likely need a wind advisory as
some locations along the Louisiana coast will see sustained winds
over 30 knots.

.LONG TERM...
Finally will have a dry period in the forecast going into Monday as
post-frontal high pressure moves in. Temperatures will fall quite a
bit, to near normal. This will be short lived as upper ridge quickly
builds in over the area from the south on Tuesday. Temperatures will
moderate back up into the lower 70s. The next chance of rainfall
comes on Wednesday as a weak cold sags into the area. Could have a
few thunderstorms but mainly looking at showers with this boundary.
Models show an upper trough to the north, slowly progressing
southward thru the end of the week. This will lead to cooler temps
and CAA persists but possibly increased rain changes with
overrunning moisture.

MEFFER
&&

.AVIATION...

Variability in ceilings and vis remains with us again this morning.
But only MCB experiencing vis restrictions to less than 1/2sm at
this moment. There may be one or two sites that go to 1sm or less
this morning but for the most part, terminals should not be impacted
to a great extent. Conditions will eventually improve to VFR this
morning as ceilings will rise from OVC003 to OVC025 then OVC045.
TSRA conditions will begin to affect all terminals late tonight and
Saturday morning.

&&

.MARINE...

Southerly winds will be around 10kt today and up to 15kt well
offshore. Winds will begin to increase throughout all marine areas
to around 15 knots by Saturday afternoon, and further increase to
around 20 knots and advisory levels Saturday night. A strong front
will move through the northern gulf Sunday morning causing westerly
winds to rapidly rise to around 35kt not long after daylight Sunday.
Northwest winds will remain at gale force into Monday morning before
easing back into the 25-30kt range by noon Monday and around 20kt by
that evening. Will post a gale watch starting Sunday morning for
most coastal waters with this marine pack. Lake Pontchartrain, Lake
Borgne, and Mississippi Sound areas will not be included at this
time. But winds could be as high as 30kt sustained with gusts to
gale force during the same time frame. Conditions will rapidly
improve Monnight into Tuesday as winds abate.

&&

.DECISION SUPPORT...
DSS code:   Green.
Deployed:   None.
Activation: None.
Activities: Severe weather potential. Gale watch.

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  76  61  76  56 /  10  90  60  60
BTR  78  63  78  57 /  10  80  60  60
ASD  78  65  78  60 /  10  90  80  60
MSY  77  66  79  60 /  20  90  80  50
GPT  73  65  75  61 /  20  90  90  70
PQL  78  65  75  60 /  20  90  90  70

&&

.LIX WATCHES/WARNINGS/ADVISORIES...
LA...None.
GM...Gale Watch from Sunday morning through late Sunday night for
     GMZ536-538-550-552-555-557-570-572-575-577.

MS...None.
GM...Gale Watch from Sunday morning through late Sunday night for
     GMZ538-550-552-555-557-570-572-575-577.

&&

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