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

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FXUS64 KLIX 251027

Area Forecast Discussion
National Weather Service New Orleans LA
427 AM CST Sun Feb 25 2018

.SYNOPSIS...Intense s/w that led to todays severe weather and
significant flash flooding across the OH/TN Valleys and Mid MS
Valleys is now lifting north into south-central Canada. Southwest
flow remains in place over much of the eastern CONUS. Broad L/W
trough is sitting over the western CONUS with the main trough axis
along the Rockies. At 6z the cold front was still off to our
northwest stretching south from northern IL down to northeastern MS
and then southwest lying just north of the TX coast. /CAB/


.SHORT TERM...Overall it has been another quiet night although we
are getting showers beginning to enter the northwestern portions of
the CWA associated with the front. Ahead of this front it has been
another warm and muggy night with temps in the lower 70s and
dewpoints near 70.

As for today, it may not turn out so bad at first. We will have to
deal with lingering showers associated with the cold front which is
being reinforced with outflow from previous storms. This is why it
is still pushing south but it should hang up over the area later
this morning possibly laying up along the 10/12 corridor. Along this
boundary and to the north light to even moderate showers are
expected. There may even be a few thunderstorms. By late this
morning and through the afternoon the front will lose its mid level
support with mostly light scattered showers mainly along and to the
north of the front.

Late this afternoon and more so tonight things will get far more
active. First we continue to keep the atmosphere primed with
substantial moisture. LL flow continue to send GOM moisture north
into the region with dewpoints mentioned earlier near 70. LL winds
will begin to veer around to the southwest pumping higher 330-334
h85 theta E values into the region and the H85 theta e ridge will be
draped across the CWA through much of the overnight hours. Southwest
flow aloft continues to send PAC moisture in and with all of this
forecast pws still look to be in the 1.6-1.75 range all night. K
index values are also forecast to be around 32-36C. Moisture will
not be a problem and it never has been but we will have any forcing
and instability and both of these appear to be yes tonight. There
appears to be a weak impulse or enhancement seen in the wv and this
feature is just now coming onshore over Mexico off the PAC. It is a
little subtle but can be seen in all 3 channels. Models also show a
weak impulse moving through the southwest flow aloft so this agrees
with what is being seen. This times out for early this evening
possibly even late this afternoon and should actually lead to
activity developing west of us initially. This feature will help
to provide a little punch but will also cool the mid levels about
2C and just this little bit of cooling will provide a steeper
lapse rate and far greater elevated instability than we have seen
the last few days. The mid level winds respond too with 50-60kts
moving in. Aloft a strong jet will remain north of the area but we
will be close to the RRQ with broad diffluence aloft.

So with the front basically stalled over the area through at least
the early morning hours and parallel to the mid level flow we could
see storms training over the region for a little while. Combine that
with diffluence aloft, very rich moisture to work with, the theta e
ridge over the area, and some instability and it looks like showers
and especially any thunderstorms could be quite efficient rain
producers. The main concern is how fast can these storms move to the
east or at least get east of the theta e ridge and that will depend
on the cold front. The front initially will not move much tonight
but as the stronger s/w comes across the Plains states and through
the Mid MS valley it will finally get another surge southward and
around sunrise should be nearing the coast. Of course if there is
some decent convection we could see some cold pooling which may
augment the front(much like has opened last night) and pushes it
south earlier than expected but this would still likely be well
after midnight.

Even though we have not seen a bunch of rain yet we could still see
1-3 inches of rain with locally higher amounts through tomorrow
morning if things line up. WPC does have much of the northern half
of the CWA in a Slight risk for excessive rainfall. Overall the area
can handle a decent bit of rain and FFG is suggesting most locations
can handle near 3 inches or more in 3 hours and with that feel we
can hold off on any Flash Flood Watch at this time. That said there
is still a threat of localized flash flooding and the bigger
concern is that it could occur overnight.

Monday the front will finally be pushing south of the coast
before stalling once again. We will likely be dealing with
lingering light showers along the coast through the morning but we
should see rain come to an end or at least be confined to the
coastal waters by afternoon. Temperatures will cool nicely when
compared to what we saw the last few weeks however, would like to
point out that it will still be abv normal which just emphasizes
how hot it has been.

.LONG TERM...The stalled front will quickly retreat to the north
Tuesday and return flow will be back in place. Temperatures will
begin to warm again and moisture will start to return. We should see
some light showers and a storm or two Tuesday afternoon and into the
evening hours but on Wednesday we could be mostly dry as much of
the showers could remain north of the region. Still looks like we
will be watching a strong s/w come out of the four corners region
Wednesday and into the Lower Ms Valley Thursday. This will drive
another and likely much stronger cold front through Thursday night
and that should cooler the area off Fri and into the weekend. we
will also see another good shot of showers and thunderstorms with
this system. /CAB/


.AVIATION...Expect mostly MVFR conditions to prevail through the
TAF period as a front makes is way towards the forecast area. Low
stratus has been the rule overnight into this morning. There will
be periods of VFR conditions but cloud decks should mainly be at
or below 3K feet. Showers and storms will be in the forecast for
today at all terminals. This would create periods of IFR
conditions if caught in a storm. 13/MH


.MARINE...Onshore flow will continue ahead of a front that will
push into the coastal waters today. Expect showers and
thunderstorms to develop as the front moves into the region. High
pressure will build back in Monday night into Tuesday and that
will once again keep up in onshore flow through a good portion of
the week. Winds will likely become weaker and shift to northwest,
northeast then east during the Monday and Monday night periods
with speeds around 10 knots or less and seas of 2 to 3 feet. The
high is expected to shift east again heading into mid week which
will bring a return to southerly winds of 10 to 15 knots and
higher wave heights again Wednesday into Thursday.


DSS code: Yellow.
Deployed: None.
Activation: None.
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.


MCB  64  57  71  55 /  80 100  20  10
BTR  72  59  73  59 /  80 100  20  10
ASD  74  64  73  60 /  40  90  50  10
MSY  74  65  73  64 /  30  90  60  10
GPT  74  65  73  61 /  30  90  60  10
PQL  77  66  73  60 /  30  80  70  10



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