Special Marine Warning 61, NWS New Orleans, LA

Area Forecast Discussion
National Weather Service New Orleans LA
1227 AM CDT Fri Apr 9 2021

.AVIATION...06 TAF Package...Low cigs have begun to impact
numerous terminals and will likely continue until few hours after
sunrise. Expect most if not all terminal to deal with cigs
between 600 and 1500 feet this morning. BTR may be the one hold
out. As for fog, still not overly impressed with the threat but
will hold onto 3sm at MCB between 09-14z. SHRA coverage should
slowly increase through the night and there may even be a few TSRA
but confidence is not high enough to have prevailing SHRA this
morning but convection will likely impact some terminals today and
this afternoon. /CAB/

&&

.PREV DISCUSSION... /issued 940 PM CDT Thu Apr 8 2021/

UPDATE...Already seeing showers developing south of the SELA
coast. This is in response to increasing isentropic lift already,
likely in the 295-300 K level. This should expand inland after
midnight and then continue to the north through the morning hours.
The isentropic lift doesn't appear to be that strong but should
be enough to get a few thunderstorms to develop. Also looks like
the nose of the h85 theta e ridge and slightly increasing LL jet
will slide right into SELA and southwest MS during the early
morning hours. This all suggest that activity should generally
increase in coverage some but most of the more recent CAMS are
rather dry for tonight and tomorrow with the exception of coastal
MS. Given the trend in radar and the thought that the models are
slightly under doing the activity we did increase PoPs a little
for overnight.

The other concern is fog. There is a boundary that has been
slowly working north across the northern half of the CWA and
appears to be slowing considerably now over southern MS. This
boundary could provide a good setup for fog as locations north of
the 10/12 corridor are still able to cool into 60s, locations
along and south of the 10/12 corridor have seen dewpoints jump
significantly and low likely will be in the upper 60s to lower
70s in those areas. SREF and even some of the MOS guidance are
favorable with respect to fog and we did add fog to the forecast
however, not really confident we will see anything more than areas
of light fog with maybe some patchy fog. Part of that is cloud
cover. Already a lot of cirrus sliding over the area from storms
in east TX. This along with likely increasing low clouds should
keep dense fog out of reach. /CAB/

PREV DISCUSSION... /issued 642 PM CDT Thu Apr 8 2021/

AVIATION...00z TAF Package...All terminals are currently in VFR
status and this will likely persist through the evening but around
8/9z low level moisture will quickly surge back to the north. This
along with increasing LL winds should lead to stratus building in
across the region with most of the terminals dropping into MVFR
status after 9z. A few locations may even drop into IFR status.
Convection if there is any during the day tomorrow will likely
hold off till the afternoon hours. /CAB/

PREV DISCUSSION... /issued 311 PM CDT Thu Apr 8 2021/

SYNOPSIS...

High pressure ridge to the east of Florida extends westward into
the eastern Gulf of Mexico this afternoon. Stacked low pressure
under a negatively tilted upper low over Iowa has an occluded
front across western Indiana southwestward to about Interstate
20, then westward to another low pressure in Texas. This morning's
convection pulled drier air into the area, dropping dew points
into the 50s (and even upper 40s in a few places) and lower 60s
early this afternoon. Don't have to go too far offshore to find
dew points in the upper 60s to mid 70s. Most mid-afternoon
temperatures ranged from the mid 70s to lower 80s under partly to
mostly sunny skies.

SHORT TERM (through Saturday night)...

As winds return to an onshore component in most areas by later
this evening, moisture levels will again increase with dew points
in the mid and upper 60s by sunrise Friday. A weak impulse riding
through the southern stream has the potential to produce scattered
convection over eastern portions of the area prior to sunrise. A
stronger impulse will approach the area Friday afternoon into
Friday night. Scattered convection could again break out late
Friday afternoon, mainly across the northern half of the area.
While areal coverage may be somewhat lacking during the afternoon
hours, steep mid-level lapse rates (near 8C/km) and wet bulb zero
levels near 10k feet, would indicate the potential for large hail
with any storms that do develop. The more widespread threat is
expected to occur Friday night into early Saturday as the main
impulse passes just to the north of the area. This is likely to
develop into a more organized cluster of storms that should move
east-southeastward late Friday night. All modes of severe weather
will be possible with this cluster, especially if we get isolated
supercells in advance of the cluster. Heavy rain will also be a
concern with the potential for another 2-3 inches of rain on top
of what occurred early this morning.

Some question as to where the effective boundary ends up on
Saturday, with some solutions keeping the boundary along the
Interstate 10/12 corridors. Will hold at least some threat of
severe weather through the morning hours on Saturday, with still
mention of convection during the afternoon, mainly across the
south and east.

Will trend toward the warmer end of guidance for temperatures, as
the warm, moist airmass returns tonight and we do expect at least
some sunshine on Friday. Will trend closer to the MAV/ECM guidance
as we get into Saturday and Saturday night. Would note, however,
that the eventual location of the boundary provides at least some
potential for a shift in the temperature forecast toward the end
of the forecast period. 35

LONG TERM (Sunday and beyond)...

Sunday and Monday should be comparatively quiet under surface high
pressure, before the southern branch of the westerlies becomes
more active again. Timing differences between solutions limits
forecast confidence in specific timing, but potential for
convection exists from Monday night onward. Blended solution is
the path of least regret for now. We'll have to keep an eye on any
potential heavy rain threat for the middle of next week, depending
on rain amounts in the short term portion of the forecast. 35

MARINE...

Expect onshore flow to return tonight as high pressure shifts
eastward. Will probably need Small Craft Exercise Caution
headlines for a good portion of the waters on Friday into Friday
night. May need Small Craft Advisories for at least the open
waters Friday night into Saturday morning, but it's a close call
at this point. Conditions should subside Saturday night as
pressure gradient relaxes with front becoming stationary. Onshore
flow may restrengthen enough for headlines by Monday night, but
that's at the back end of the forecast package. 35

&&

.PRELIMINARY POINT TEMPS/POPS...
MCB  83  66  79  55 /  50  90  60  10
BTR  84  67  82  57 /  30  80  50  10
ASD  82  68  82  60 /  50  80  80  20
MSY  84  70  82  64 /  30  70  80  20
GPT  79  68  79  61 /  50  80  90  30
PQL  79  65  78  60 /  60  80  90  30

&&

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