Area Forecast Discussion

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