Scientific Forecaster Discussion
fxus64 klix 241041
Area forecast discussion
National Weather Service New Orleans la
441 am CST Sat Feb 24 2018
Synopsis...deep southwest flow in the mid levels can easily be
seen on all WV channels. This is due the the deep trough located
over The Rockies with the base of the trough axis running through
The Four Corners region and the large ridge that still resides
over the western Atlantic and into the extreme southeast Continental U.S. And
gom. Over the sfc at 6z the Bermuda ridge remains in place
centered between Bermuda and the East Coast. A cold front was
draped back to the southwest from WV to the arklamiss while a weak
sfc low is beginning to take shape over the arklatex. /Cab/
Short term...quiet night as most of the shra activity came to an
end. There were still a few light shra streaming north across
coastal MS and la. Areas of light fog and low clouds have been
impacting much of the region.
Forecast hasn't changed much. The ridge and Bermuda high that have
dominated the region for the last week or so is finally beginning to
lose some of its grip on the area today, well at least the ridge is.
As mentioned earlier deep southwest flow in the mid levels is in
place across much of the Continental U.S. East of the MS and as the S/W makes
its way east out of The Rockies and into the central and northern
plains today it will further suppress the ridge. This S/W is expected
to be the catalyst in bringing active weather across the mid MS
valley and into the Tennessee/Ohio valleys both in the form of severe weather
and heavy rain. It will also aid in lowering heights across our
region today and tonight. This may lead to a few shra and possibly a
tsra or two today however the best chance for storms across the
region will be tonight and again tomorrow into tomorrow night as
this system finally helps to drive a cold front into the region.
There is really not much support over the region outside of just
having a very moisture loaded airmass and mesoscale features that
could get shra and maybe a few tsra going today, but most likely
shra. Broad lift and no real ll convergence again suggest mostly
shra today but that could change tonight as the front tries to
The moderate onshore flow around the Bermuda high will continue to
pump moisture in across the region through tonight while the
southwest flow continues to stream Pacific moisture in at the mid and
upper levels. Pws could climb into the 1.6-1.9 range and this would
easily be abv the top 10% and could even be a new record. Combine
that with the rrq of the upper jet leading to broad diffluence aloft
and the recipe is being set for a bout of moderate to heavy rain
tonight and or maybe more so late tomorrow and into Sunday night.
The front will approach northwestern portions of the County Warning Area overnight
and this could provide the ll convergence and forcing needed to get
some decent storms which will be efficient rain producers. Lift
increases in the mid levels due to a few weak impulses making its
way across the area along with h5 winds increasing to around 55-
60kts as well.
All that said there are a few issues though with respect to rain
locations and amounts. First the front will begin to slow down if
not stall as the sfc low it's associated with pulls way off to the
north into the Great Lakes. In addition we remain in southwest flow
so this will also aid in the front losing its support and it isn't
until the next S/W comes across the mid MS valley late Sunday and
Sunday night when the front will finally get another push southward.
As for tonight where the front is, along it and just to the north,
will be where the heaviest rain will occur and this may be north
and northwest of our area. As the support pulls out and the front
stalls there will likely be a lull in activity early Sunday.
There is still a good chance of light shra across much of the
region but moderate to heavy rain may be a little hard to come by
as ll convergence will be gone and we may actually be dealing with
divergence through the first half of the day. Once the front
begins to move back to the south, the front and the increase in
mid level support will get shra and tsra again. This looks to be
possibly as early as Sunday afternoon and through the night.
As for severe weather, we still look to be lacking instability both
today and tomorrow. Mid level lapse rates are not impressive around
6 c/km. Ll winds are not responding and ll convergence wont be great
either, even with the front. However, moderate to heavy rain will
be a concern. If the front gets far enough south tonight then we
could see one bout of moderate to heavy rain tonight and another
late tomorrow and overnight Sunday. Right now feel the best
chance for the heavy rain will be with Sunday and Sunday nights
activity as we will finally have the front to work with and more
mid level support.
Long term...heading into next week the cold front will push all the
way into the Gulf Monday and we will dry out behind the front. This
looks to be short lived though as the front will quickly retreat
back to the north Monday night. This will lead to onshore flow
returning. In addition the mid level ridge which did get suppressed
will still be around and start to build back Tuesday and into
Wednesday which will again lead to above avg temps. There are
indications that a strong front will finally move through late this
week which could cool the area back down to normals but ahead of is
we would see another round of shra and tsra and this could even
bring a round of severe weather with it. It will be one we keep a
close eye on over the next few days. /Cab/
Aviation... expect MVFR to IFR conditions this morning as patchy
fog and low ceilings are being reported at most sites this morning.
Expect conditions to improve later on this morning to MVFR to VFR
conditions. Some showers and thunderstorms are possible throughout
the entire day but mainly in the afternoon and evening hours. Storms
could be in greater coverage late tonight. This will have to be
monitored through future taf updates. 13/mh
no major changes to the forecast this morning as onshore flow
continues ahead of a cold front slowly making its way south. Have
added exercise caution headlines for portions of the coastal waters
for today. As stated in previous forecast the air mass is quite
conducive for waterspout development. This will have to be watched
again today. Expect this onshore flow to continue through at least
Sunday before the front makes it into the coastal waters. The front
returns north as a warm front with a return to deep onshore fetch
later Tuesday and particularly Wednesday ahead of the next front.
dss code: yellow.
Activities: radar support and monitoring marginal risk conditions.
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 81 62 67 55 / 40 90 90 80
btr 82 64 71 58 / 30 70 80 80
asd 81 68 76 63 / 40 50 70 80
msy 82 69 78 65 / 30 40 60 80
gpt 79 69 74 64 / 40 40 60 80
pql 80 69 77 63 / 40 30 60 80