Scientific Forecaster Discussion
fxus64 klix 191710
Area forecast discussion
National Weather Service New Orleans la
1110 am CST Tue Nov 19 2019
updated for the 18z aviation discussion.
VFR conditions prevail at all area airports and will persist
through the evening hours. Fog is expected at most area airports
during the early morning hours that will cause lower visibilities
and ceilings. Some wind shifts are possible overnight as well.
Previous discussion... /issued 358 am CST Tue Nov 19 2019/
Discussion...it was another quiet day as anticipated however,
highs were again a little warmer than anticipated and that was even
going at the high end or above guidance. Biggest issue in the next
few hours will be fog. Not anticipating widespread or even areas of
dense fog however patchy dense fog has already developed and this
will likely continue through sunrise. It appears the main areas of
concern are the marshy regions of south-central and southeast la
along with a few of the river channels. This is likely due to these
very shallow bodies of water, marshy areas warming up nicely during
the day and then with very favorable radiational cooling conditions
in place shallow patches of fog have been able to develop. This is
radiational fog and not airmass replacement so this will likely not
be a major issue however going from unlimited visibility to near a
quarter of a mile multiple times in rapid succession could be
hazardous so we have issued a dense fog advisory for most areas
along and south of I-10. This does not include the city of New
Orleans as conditions in the city appear fine and should remain
so. Both current GOES night image and sref are in great agreement
with the placement of this advisory.
The moderation of our airmass will continue today and through
Thursday as ridging aloft dominates the region. H925 temps will
climb to between 14-16c today and tomorrow and this should lead
to mid and possibly isolated upper 70s. Guidance and especially
the nbm continue to struggle coming in too low. This has been the
case for the last 3-4 days and with that will continue to go with
the high end MOS values or even a degree or two above that
through Thursday. That is with respect to highs, however lows we
will actually go on the low end of the MOS values(nbm is not too
bad in most areas however the river drainage areas it appears too
warm). Main reason for this is due to the dry conditions and the
slow increase of moisture and with that diurnal fluctuations
should be fairly large. Avg change from morning low to afternoon
high is around around 18-23 degrees but we will likely continue
to see 25 to as much as 35 degree change from low to high for at
least the next 2 days.
Fog may continue to be a small concern each morning as low level
moisture starts to finally increase tomorrow morning and Thursday
morning. Not expecting widespread fog but can not rule out patchy
dense fog. Models didn't really catch onto this morning's fog
well but they do show some indications of it tomorrow morning and
they may be trying to play catch up.
Main forecast dilemma is the system Friday and into Saturday. Deep
cutoff low currently sitting in the Pacific just off the baja is
expected to lift north-northeast into the Desert Southwest as a S/W
dives down the pac coast. This S/W and pac low will merge together
and into the main northern stream. The system will then begin to
slowly move across the 4 corners Thursday night and through the
Central Plains Friday. We will see a sfc low begin to take shape
over the lower MS valley late Friday and it will lift to the
northeast overnight Friday and early Saturday. This will drag a cold
front through the region. The combination of a cold front, falling
hghts aloft, and increasing lift and forcing should lead to decent
rain chance beginning as early as Friday afternoon with the best
chance for showers and a few thunderstorms overnight Friday. The
front should quickly push through Saturday morning with the trough
axis through all or most of the County Warning Area Saturday afternoon which could
lead to most if not all of the rain being out of the area by noon.
As for the potential of severe weather, there is still a small
chance of seeing a few strong to severe storms. Overall this isn't
the most favorable setup. The trough will be positively tilted
however forcing will still be sufficient. Speed shear will be in
place however directional shear will be lacking. What will be the
biggest issue for strong storms will be the lack of instability
however, with that said though the combination of the lift from
the cold front and the forcing aloft may be able to compensate to
get a few potent storms. If any severe storms do develop, and
this is a big if the main concern would be straight line winds.
However, as always the case down here we can never rule out the
potential for tornadoes.
Heading into Saturday night and through Sunday things look quiet and
cool. Cold front moves through and we move back under northwest
flow with dry weather expected into the beginning of next week.
Now just peaking out a little ahead in the extended there are some
indications that a potent system could move across the central Continental U.S.
During the mid portions of next week. Next week is Thanksgiving and
the Wednesday before Thanksgiving is the highest traveled day of the
year so we will keep an eye on this. If this does play out but the
system doesn't impact sela directly it could have some impacts on a
few major airports. /Cab/
Marine...high pressure sliding directly over the region today
will lead to winds transitioning from offshore to light and variable.
Overnight tonight the sfc high will move to our northeast and with
it onshore flow will slowly develop. By Thursday onshore flow should
be well in place and continue until a cold front moves through early
Saturday. Moderate northwest winds will develop in the wake of the
cold front passage. /Cab/
Aviation...seeing some vlifr conditions at khum and kmsy in
radiation fog early this morning. Can't rule it out at other
terminals, but will handle with amendments as needed. Expect
improvement to VFR by 15z and perhaps earlier. Beyond 15z, VFR
conditions will be the rule until at least 06z. Could see a repeat
of fog issues on Wednesday morning. /35/
Dss code: green.
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; marginal risk severe or excessive rain.
Yellow = heightened impacts with short-fused watch, warning or
advisory issuances; radar support for slight risk severe
or excessive rain.
Orange = high impacts; enhanced risk severe; nearby tropical
events; hazmat or other large episodes.
Red = full engagement for moderate to high risk of severe and/or
excessive rainfall, or direct tropical threats; events of
Preliminary point temps/pops...
mcb 44 74 50 76 / 0 0 0 0
btr 46 76 54 77 / 0 0 0 0
asd 44 74 48 76 / 0 0 0 0
msy 51 74 56 76 / 0 0 0 0
gpt 47 71 51 73 / 0 0 0 0
pql 43 73 46 76 / 0 0 0 0