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

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FXUS64 KLIX 101639 CCA
AFDLIX

Area Forecast Discussion...Correction
National Weather Service New Orleans LA
1036 AM CST Sat Dec 10 2016

.UPDATE (with reminder/clarification of our freeze warning
policy)...

Updated temperatures in near/short term to indicate faster warming
this morning, minor adjustments of a degree or so for highs today,
and a slight lowering of the lows tonight at a few locations.

Looking at the history of freezing temperatures thus far this
season in our forecast area, there has been at least one or more
light to moderate freezes (locally defined as temperatures in the 26
to 32 degree range) northward of the area along and just south of a
Baton Rouge/I-12 to I-10 in coastal MS line. This should have ended
the growing season for the more seasonal, sensitive, open field
crops, and like the standard practice for similar to colder
climates, freeze warnings for light to moderate freezes are usually
not reissued again until after the historic start of the next
growing season in late winter/early spring. A light to moderate
freeze anytime of year is considered significant/rare enough for
freeze warning issuance for areas south of Lake Pontchartrain
including metro New Orleans and the southeast Louisiana coastal
parishes, and these areas have not experienced a killing freeze thus
far this season.

A hard freeze is locally defined as low temperatures of 25 degrees
or lower, even in our most inland southwest Mississippi tier of
counties even though occurrences there are more common in an
average winter. These conditions normally puts exposed/unwrapped
water pipes at risk of freezing, and a hard freeze warning is
usually issued when conditions are forecast in the near term.
22/TD

&&

.PREV DISCUSSION... /issued 708 AM CST Sat Dec 10 2016/

..SOUNDING DISCUSSION...

A stable, unusually dry, and cold atmosphere is over the region as
high pressure moves towards the Appalachians. An inversion extends
from the surface to 9000 feet and the precipitable water value is
0.33 inches, which is well below normal. The wind profile is
backing, which is indicative of the cold air advection that has been
occurring. Winds near the surface are from the northeast at the
surface and then turn counter-clockwise and blow from the west-
southwest by the upper levels. A peak wind speed of 115 knots was at
39000 feet.

12z balloon info: A routine flight ascending for 100 minutes
reaching a height of 20.1 miles above the ground bursting near
Pascagoula 81 miles downrange from the office.

Ansorge

PREV DISCUSSION... /issued 345 AM CST Sat Dec 10 2016/

SHORT TERM...
Model solutions are at least in short term agreement with timing
and placement of the first two of three fronts. The first front
will move into northern Miss/La and eastern Texas before slowing
to a crawl Monday. This front will ever-so-slowly move near the
gulf coast by Tuesday evening before the second stronger front
reinforces the first and moves brings the unified front offshore.
This is where the global models end their agreement. A blend of
sensible weather will be used from the GFS and the Euro.

They both develop at least two disturbances that move along the
frontal interface Monday through Tuesday. But only the GFS wants
to produce a widespread fog scenario possibly starting as early as
Monday morning. As the first front slowly sinks south, mesoscale
advective and inversion properties look to be strong enough to
produce a widespread fog event Monday morning and Mon night but
conditions look favorable for fog to stay most if not all day
Tuesday. This will depend heavily on how strong the disturbance is
that moves through Tuesday. If the GFS is right, there will be
widespread fog with some light showers now and again Tuesday. If
the Euro is right, there will be widespread fog lifting for short
times as convective pulses moves through.

The second cold front reinforces the first Wednesday and moves out
into the gulf by Thursday. But the cloud cover and light drizzle
does not leave as the next(third) even stronger cold front is
quickly moving eastward causing return flow to develop by as
early as Thursday evening. This will cause low clouds, light rain
and fog to once again develop for Friday morning and Saturday
morning. This third front`s timing, and hence placement, is where
the models stop agreeing. The GFS is a full 24hrs later with fropa
than the Euro. Since this front actually sits outside the current
forecast`s domain, it will allow for a few more model runs before
trying to find a credible solution.

AVIATION...

VFR conditions will prevail through the TAF period. 13/MH

MARINE...

Winds will continue to decrease throughout the day. Small Craft
should exercise caution through this evening as winds will still be
in the 15 to 20 knot range for a portion of the day. Winds will
finally die down later on this afternoon and evening. As high
pressure moves east, winds should remain below headline criteria
into the middle of next week, until the next cold frontal passage
Wednesday night or Thursday. 13/35

DECISION SUPPORT...

DSS code: Blue.
Deployed: None.
Activation: None.
Activities: None.

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  52  35  67  56 /   0   0   0  30
BTR  54  39  69  58 /   0   0  10  30
ASD  54  35  68  55 /   0   0  10  20
MSY  54  45  70  59 /   0   0  10  20
GPT  55  38  67  58 /   0   0  10  20
PQL  55  34  67  54 /   0   0  10  20

&&

.LIX WATCHES/WARNINGS/ADVISORIES...
LA...None.
GM...None.
MS...None.
GM...None.
&&

$$


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