Severe Weather Threat 4/13-4/14

Will be stalking this thread. I’m part of an outdoor wedding Saturday evening in Lockport. 😬

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0348 AM CDT Tue Apr 10 2018

Valid 131200Z - 181200Z

...DISCUSSION...
Medium-range models continue to highlight continued deepening of the
upper low/trough as it moves eastward across the Plains Day 4
(Friday), though differences between the GFS and ECMWF are evident
-- particularly with respect to the surface frontal advance across
Kansas/Texas/Oklahoma.

At this time, the much faster GFS appears to be the outlier (in
accordance with its typical bias), as the Canadian and UKMET runs
also suggest slower frontal progression more similar to that
depicted by the ECMWF. Given the uncertainties, it remains
difficult to confidently narrow down the envelope of highest severe
potential, but will make minor adjustments to the prior outlook
northward (into central Missouri) and westward (toward the DFW
Metroplex).

Otherwise, an area centered over the Arklatex appears to be at risk
for severe storms, as boundary-layer moistening/strengthening
southerly flow spread beneath increasing mid-level winds yield an
amply sheared/unstable warm sector. Along with risk for hail,
locally damaging winds and potential for a couple of tornadoes will
be possible during the afternoon and evening.

By Day 5/Saturday, uncertainties highlighted for Day 4 become
increasingly apparent. This -- combined with the likelihood for
widespread/ongoing convection Saturday morning -- precludes
confident assessment of severe potential into the
Mississippi/Ohio/Tennessee Valleys and central Gulf Coast area.

Predictability concerns linger through the remainder of the medium
range, as this system shifts into the eastern U.S. and the next
upper trough shifts into/across the western half of the country.

^^^not to mention with CAPE values around 1500 j/kg and LI's -7 to -8.

Valid 141200Z - 191200Z

...DISCUSSION...
Variability is evident amongst the latest medium-range model runs,
particularly with the progression of the front across the Tennessee
Valley/central Gulf Coast region Day 4/Saturday. Still, with a
strong upper system progged to be shifting into the region and
taking on neutral to slight negative tilt with time, pronounced
ascent along the front and at least modest CAPE expected from
roughly the Tennessee Valley southward suggests a band of vigorous
convection will evolve. Again, timing remains uncertain, but expect
at least local severe risk -- primarily in the form of damaging
winds -- to accompany a frontal band of convection as it shifts
eastward across the area.

Day 5/Sunday, differences in frontal location/progression persist
amongst the various models, and with widespread/ongoing clouds and
precipitation to accompany the front, uncertainty prevails with
respect to amount of pre-frontal CAPE which may evolve. Though at
least low-end severe potential will be possible over the
Georgia/Florida vicinity with passage of the convective band, will
refrain from introduction of a 15% area at this time.

All models suggest that the front will have moved off the entire
Atlantic Coast by the start of the Day 6/Monday period. Meanwhile
in the West, the next upper trough is progged to be moving onshore,
along with an attendant surface front. The system is expected to
weaken with time through latter stages of the period, as it
encounters persistent central U.S. ridging. As such, any severe
risk with the system as it eventually emerges into the Plains late
in the period remains far too uncertain to forecast at this time.

The order of concerns for this round looks to be:

1. Damaging Winds
2. Tornadoes
3. Heavy Rainfall
4. Hail

However this can change as we move closer.


LONG TERM...
The next system to bring impacts to the CWA will take place the
first half of this weekend. An upper level trough will enter the
Pacific northwest Thursday...amplifying as it tracks across the mid
section of the country Friday night through Saturday. A wide swath
of showers and thunderstorms will accompany the cold front
associated with this trough. We will again be looking at another
severe weather potential with this one but with the additional
threat of heavy rainfall. The average qpf totals of the GFS and
ECMWF are in the 2 to 4 inch range. Moderately paced cold fronts
aren't typically known to be big flash flood producing systems.
Don't think this one will be much different but with model
soundings indicating precip water values around the average max
for this time of year (~1.8"), very heavy rain will likely fall at
times throughout the CWA.

Models show the upper trough will be transitioning from positive to
neutrally tilted as it approaches the Mississippi River. In
addition, model soundings show the pre-storm environment to have
steep lapse rates throughout the column. This will lead to quite
high CAPE values (nearing 2000 j/kg). Shear won't be particularly
high but high cape/low shear environments commonly produce
tornadoes in SELA and southern MS. Wet bulb temps of around 12kft
are a little to high for hail to be of much concern. Damaging
winds though will still be a threat. One note about the model
soundings, there looks to be a warm nose at ~850mb Friday night.
Cooler air moving in will erode this, leading to virtually no CIN.
It will however, keep pre-system activity limited to very
light showers if anything at all. In terms of timing, thinking
really hasn't changed much. A blend of the GFS and ECMWF is a good
estimate at this time. Those models will likely come back in line
with each other on Thursday as the trough enters the PAC-NW and
is sampled by radiosondes.

332 PM CDT Wed Apr 11 2018

This Hazardous Weather Outlook is for portions of central
Louisiana, south central Louisiana, southwest Louisiana, west
central Louisiana, and southeast Texas.

.DAY ONE...This Afternoon and Tonight

No hazardous weather is expected at this time.

.DAYS TWO THROUGH SEVEN...Thursday through Tuesday

A cold front expected to push through the region late Friday
night/early Saturday morning will have the potential to produce
severe weather in the forecast region. The Storm Prediction Center
has put the whole region at a marginal-slight risk of severe
weather. All modes of severe weather (hail, tornadoes, damaging
winds) will be possible.There is a also a slight risk of excessive
rain fall per the Weather Prediction Center. At the very least,
expect periods of heavy rain with thunder and lightning. This
front and the associated weather should be completely out of the
forecast area by early Saturday afternoon.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will not be needed this afternoon/tonight. May
be required for Friday night/Saturday morning.

00z NAM wasn't any help...stormy Saturday