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

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FXUS64 KLIX 212136

Area Forecast Discussion
National Weather Service New Orleans LA
336 PM CST Tue Nov 21 2017

.SHORT TERM...A vigorous shortwave trough currently diving
through the Southern Plains will push further south into the
western Gulf of Mexico tonight. The trough axis should then sweep
through the forecast area during the day tomorrow. In advance of
this fast moving feature, a broad region of increased positive
vorticity advection and omega will overspread Louisiana. As this
upper level forcing increases, scattered showers and increased
cloud cover can be expected to take hold of the western half of
the forecast area tonight. Rain chances will tend to be highest
from Baton Rouge down through Houma and westward across the
Atchafalaya Basin. A much drier airmass further to the east will
keep rain chances at 20 percent or less through the night
generally along and east of a Hammond to New Orleans line.

By tomorrow morning, the cold front associated with the upper
level trough should be just offshore of Louisiana, and a surge of
drier air should begin to feed into the region. Still expect to
see some showers lingering along the Louisiana coast tomorrow
morning. By the afternoon, increased dry air advection and
subsidence throughout the atmospheric column will result in
clearing skies and the end to any rain chances. Temperatures will
near average tonight in the upper 40s and lower 50s, but northerly
winds in the wake of the front will usher in some colder air
tomorrow. As a result, daytime highs should be a few degrees below
average in the middle 60s.

Deep layer northerly flow will dominate the Gulf South both
Thanksgiving Day and Black Friday. Strong subsidence and dry air
advection will keep skies clear, and temperatures will remain
cooler than average through the remainder of the week. The clear
and dry air will allow for strong radiational cooling each night,
and expect to see lows dip into the middle to upper 30s at most
locations. Only areas along the immediate Louisiana coast and
south of Lake Pontchartrain will see warmer lows in the lower 40s
during this time frame.


A very quiet weather pattern will continue across the Gulf South
this weekend and early next week as deep layer northerly flow
remains in place. With little to no available moisture in place, a
second reinforcing cold front will sweep through the area Saturday
night. At most, some passing mid and high level clouds could
accompany this frontal passage. Otherwise, clear skies can be
expected from Saturday through next Tuesday. Temperatures will
gradually modify over the weekend. Highs should climb back to near
70 degrees, and lows should range from near 40 over northern
zones to the lower 50s over southern zones along the Louisiana
coastline for the entire period.


.AVIATION...Generally VFR conditions despite frontal passage late
this evening and overnight from N to S. Expect a wind shift to NE
between 09Z- 12Z. 24/RR


.MARINE...Another surge of cold high pressure was advancing through the Plains
States towards the gulf today. Front should begin to push off the
coast in the overnight hours with high pressure building steadily
into the north gulf much of Wednesday before moderating Thursday.


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.


MCB  45  61  33  59 /  20   0   0   0
BTR  47  63  34  60 /  40   0   0   0
ASD  48  65  36  62 /  10   0   0   0
MSY  54  65  44  61 /  30  10   0   0
GPT  50  64  40  62 /  10   0   0   0
PQL  47  65  39  64 /  10   0   0   0


GM...Small Craft Advisory from 4 AM Wednesday to 4 AM CST Thursday
     for GMZ536-538-550-552-555-557-570-572-575-577.

GM...Small Craft Advisory from 4 AM Wednesday to 4 AM CST Thursday
     for GMZ538-550-552-555-557-570-572-575-577.



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