Severe Weather event East Texas / LA / Miss / Ala / GA - April 2 -3

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Severe Weather event East Texas / LA / Miss / Ala / GA - April 2 -3

#1 Postby cycloneye » Sat Apr 01, 2017 6:16 am

Valid 021200Z - 031200Z

...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS SUNDAY ACROSS
MUCH OF SOUTHEAST TEXAS AND SOUTHWEST LOUISIANA...

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS
SURROUNDING AREAS OF EASTERN TEXAS INTO WESTERN AND CENTRAL
LOUISIANA...

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS SURROUNDING
AREAS OF CENTRAL AND EASTERN TEXAS INTO THE LOWER MISSISSIPPI
VALLEY...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS
SURROUNDING AREAS OF THE LOWER RIO GRANDE VALLEY...SOUTHEASTERN
PLAINS AND LOWER MISSISSIPPI VALLEY...

...SUMMARY...
Organized severe thunderstorm development is expected across parts
of eastern Texas into western and central Louisiana Sunday through
Sunday night. This includes a risk for tornadic supercells, a few
of which could be strong, along with considerable potential for
damaging wind gusts with an evolving squall line.

...Synopsis...
There remains little change to the general large-scale pattern with
a series of significant short wave perturbations emanating from a
strong mid/upper jet over the mid-latitude Pacific, before migrating
inland, and digging into/through the Southwest. One now is in the
process of advancing toward the British Columbia/Pacific Northwest
coast, and is forecast to progress inland, before digging through
parts of the northern intermountain region and California Sunday
through Sunday night. As this occurs, one or two vigorous
perturbations (digging into the base of elongating troughing near
the southern Rockies today) appear likely to accelerate east
northeast of the Rio Grande Valley.

Various model output, including the latest ECENS,NCEP MREF and SREF
mean fields appear to be coming into at least somewhat better
consensus concerning the evolution and progression of this latter
system. Confidence is increasing that the negatively tilted axis of
larger-scale troughing will reach the southeastern Plains/Sabine
Valley by 12Z Monday, supporting the development and northeastward
migration of a deepening surface low from portions of
central/northeast Texas into the Ozark Plateau.

All indications continue to suggest that this will be favorably
timed with an increasingly substantive return flow of moisture off
the Gulf of Mexico, including surface dew point increases through
the 60s to around 70f across the mid/upper Texas and southwest
Louisiana coastal plain. In the presence of steep mid-level lapse
rates, sizable mixed layer CAPE may exceed 2000 J/kg across this
region by Sunday morning. Destabilization is expected to coincide
with strengthening of lower/mid tropospheric wind fields, including
30-50 kt (southerly) at 850 mb and 50-70 kt (west southwesterly) at
500 mb, across central and eastern Texas into the lower Mississippi
Valley.

...Southeastern Plains into northwestern Gulf coast region...
Aforementioned warm sector environment conditions appear more than
favorable for organized severe storm development, in the presence of
increasing large-scale forcing for ascent. Timing of initiation of
intense boundary layer based storm development remains somewhat
unclear, but it appears possible as early as Sunday morning in the
presence of low-level warm advection across southeast Texas. This
activity may be mostly discrete in nature, in the presence of
moderately large CAPE, strong deep layer shear and sizable
clockwise-curved low-level hodographs. Evolving supercells are
expected to be accompanied by the risk for tornadoes, a few of which
may be strong.

Discrete supercell development may persist through the afternoon
hours, and perhaps the remainder of the period, spreading toward the
lower Mississippi Valley, ahead of an evolving convective system
which may be accompanied by a considerable risk for potentially
damaging wind gusts. Portions of central and eastern Texas into
Louisiana still appear the mostly likely areas that could be
impacted by an evolving convective system, but northeastward
development into portions of the Ozark Plateau and adjacent
Mississippi Valley may not be out of the question by late Sunday
night.

..Kerr.. 04/01/2017

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Re: Severe Weather event East Texas / Louisiana - April 2

#2 Postby Tireman4 » Sat Apr 01, 2017 6:35 am

The parameters are there for a rough day in the Houston area.
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Re: Severe Weather event East Texas / Louisiana - April 2 - Moderate Risk includes Houston

#3 Postby cycloneye » Sat Apr 01, 2017 6:55 am

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Re: Severe Weather event East Texas / Louisiana - April 2 - Moderate Risk includes Houston

#4 Postby cycloneye » Sat Apr 01, 2017 7:21 am

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Re: Severe Weather event East Texas / Louisiana - April 2 - Moderate Risk includes Houston

#5 Postby cycloneye » Sat Apr 01, 2017 7:30 am

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Re: Severe Weather event East Texas / Louisiana - April 2 - Moderate Risk includes Houston

#6 Postby cycloneye » Sat Apr 01, 2017 7:33 am

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Re: Severe Weather event East Texas / Louisiana - April 2 - Moderate Risk includes Houston

#7 Postby TheProfessor » Sat Apr 01, 2017 8:31 am

I haven't had the chance to take a look at this set up, but I'll definitely will be taking a look at it when I've finished my assignments today.
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Re: Severe Weather event East Texas / Louisiana - April 2 - Moderate Risk includes Houston

#8 Postby cycloneye » Sat Apr 01, 2017 9:03 am

Good graphic with the cities covered by the Moderate Risk zone and the other ones in the general zone.Of course the big city is Houston with the most population but there are other ones that have a lot of people like Waco,Austin,and in Louisiana, Shreveport and Alexandria that have to be very vigilant to the sky.

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Re: Severe Weather event East Texas / Louisiana - April 2 - Moderate Risk includes Houston

#9 Postby srainhoutx » Sat Apr 01, 2017 9:04 am

Saturday morning briefing from Jeff:

[i]***Significant outbreak of severe weather expected over SE TX Sunday***

Large damaging hail, straight line winds, and a few violent long tracked tornadoes possible.

SPC has upgraded the area into a rare moderate risk threat (4 out of 5)…the last time the threat level was this high was Feb. 2008

Discussion:
Powerful upper level storm system over the SW US will eject into TX late tonight and on Sunday spreading strong height falls across strong Gulf moisture return. Surface warm front/trough near the coast this morning will begin to return northward late tonight/early Sunday spreading a very moist and unstable warm sector across SE TX early Sunday (before sunrise). There seems to be two developing camps within the model guidance on how storms may evolve early Sunday into the evening hours.

1. Discrete supercells develop across the large warm sector between 600am-noon on Sunday ahead of a line of storms that will arrive in the early afternoon.

2. Discrete supercells do not develop over the warm sector and instead a line of storms approaches from the west late morning into the early afternoon hours.

Forecast models show a weak cap eroding rapidly after 600am Sunday with an air mass over SE TX highly sheared (30-40kts 0-3km and 50-70kts 0-6km) with CAPE values of 2000 J/kg or greater. Significant tornado parameters will be in place on Sunday morning and any cells that develop are going to rotate. Very low cloud bases with low LCL’s over the area combined with strong near surface helicity values supporting low level rotation. If supercells can develop in the warm sector air mass the threat for damaging long tracked tornadoes is very possible in the moderate risk outline. Maximum tornado parameters will begin to shift east of SE TX by late morning, so if supercells fail to develop in the morning warm sector the threat for tornadoes, while still there, will be lowering in the afternoon hours. Threat will transition more towards a damaging wind and large hail potential.

Secondary factor appears to be heavy to excessive rainfall, but this is now secondary to the severe weather threat, which should be taken seriously for this event. While little has changed with respect to the heavy rainfall potential, the severe parameters overnight have increased. Moisture profiles will be high by early Sunday morning with PWS surging to over 1.8 inches. Surface dewpoints have already increased into the 60’s which is higher than forecasted model guidance for this time period giving confidence that significant moisture values will be in place Sunday. Expect storms to produce maximum rainfall productions given a nearly saturated air mass and any supercells that develop could easily produce 2-3 inches in a hour. Main mitigating factor at this time appears to be 20-25kts of cell motion which will negate heavy rainfall for a longer period of time. The exception would be within any areas of cell training where totals could quickly add up. Widespread rainfall amounts of 1-3 inches is likely over the region with isolated totals upwards of 4 inches or greater under training cells. High resolution guidance continues to suggest the warm front will be located from about Lake Livingston to near Brenham tomorrow and will be the focus for potentially training of cells. Will need to watch this boundary very closely as the greatest excessive rainfall and flash flood threat will likely be tied to its presence over the region. Models can be fast in lifting such features northward especially when showers and thunderstorms develop that help to slow the boundary and even at time push it back southward through convective outflows.

Summary:

· Sunday is likely to be a significant weather day across SE TX with all modes of severe weather possible (large hail, damaging winds, and tornadoes) along with heavy rainfall and flooding.

· Residents should be aware of the magnitude of this storm system and keep updated on forecasts on Sunday.

· Everyone should have a way to receive warning information on Sunday…if a warning is issued for your area take it seriously and react…it may save your life.

Tornado Safety Actions:

· The best place to be during a tornado is in an interior room on the lowest floor of a structure (an interior powder bathroom or closet). Do not seek shelter against outside facing walls

· In large buildings such as churches, office buildings, and schools: interior hallways or stairwells offer the most protection…never stay in a room with large vaulted ceilings.

· Abandon vehicles for sturdy structures…if no structure is available as a last resort lie flat in a nearby ditch…never stay in a vehicle and never try to outrun a tornado in a vehicle. Do NOT shelter under overpasses.

SPC Day 2 (Sunday) Severe Weather Outlook:
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Re: Severe Weather event East Texas / Louisiana - April 2 - Moderate Risk includes Houston

#10 Postby cycloneye » Sat Apr 01, 2017 9:37 am

Significant Tornado Parameter (STP) is over 8 and that is not good to see.

 https://twitter.com/spann/status/848181287231909888


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Re: Severe Weather event East Texas / Louisiana - April 2 - Moderate Risk includes Houston

#11 Postby TheProfessor » Sat Apr 01, 2017 10:28 am

3K NAM has some potent atmospheres for Southeast Texas. Very high CAPE, wind shear looks like it will be sufficient, very low LCL and LFC on the model and a high Equilibrium level. If it were to verify there would be some very tall thunderstorms occurring.
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Re: Severe Weather event East Texas / Louisiana - April 2 - Moderate Risk includes Houston

#12 Postby Ntxw » Sat Apr 01, 2017 10:50 am

Piney woods is no easy place to chase, Often news out of here when a tornado comes through is after it happens, ground truth is hard to get during the event. Folks there should heed warnings and not wait fro eyes on the ground to verify.
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Re: Severe Weather event East Texas / Louisiana - April 2 - Moderate Risk includes Houston

#13 Postby bubba hotep » Sat Apr 01, 2017 10:52 am

The 00z NCAR ensembles highlighting risk for the DFW area and points south tomorrow:

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Re: Severe Weather event East Texas / Louisiana - April 2 - Moderate Risk includes Houston

#14 Postby Ntxw » Sat Apr 01, 2017 10:57 am

bubba hotep wrote:The 00z NCAR ensembles highlighting risk for the DFW area and points south tomorrow:


There's definitely a risk with severe weather for DFW but it's more likely to be contaminated by the several rounds of MCS/thunderstorm activity early and throughout the day. Best parameters for supercells will be S-central and Se Texas
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Re: Severe Weather event East Texas / Louisiana - April 2 - Moderate Risk includes Houston

#15 Postby cycloneye » Sat Apr 01, 2017 12:40 pm

Update from SPC at 17:30z expands a little bit more the Moderate Risk area.

Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1234 PM CDT Sat Apr 01 2017

Valid 021200Z - 031200Z

...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS ACROSS EASTERN
TEXAS INTO WESTERN LOUISIANA...

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVER MOST OF
EASTERN TEXAS INTO LOUISIANA...

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM CENTRAL TEXAS
ACROSS THE ARKLATEX AND INTO THE LOWER MISSISSIPPI VALLEY...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM TEXAS INTO
MISSISSIPPI...

...SUMMARY...
Dangerous severe thunderstorms capable of strong tornadoes,
extensive wind damage and hail are possible beginning Sunday morning
east of I-35 in Texas and developing eastward across Louisiana
throughout the day and into the night. Severe storms are also
possible across the Arklatex during the day and into western
Mississippi by Monday morning.

...Synopsis...
Low pressure will gradually translate northeastward through the
period with a cold front to the west, from the lower Rio Grande
Valley Sunday morning into Arkansas by Monday morning. Ahead of the
low, a warm front will rapidly lift northward across east Texas
toward the Arklatex and extend into southern Mississippi by 00Z.
Across the warm sector, a very moist and unstable air mass will
exist, characterized by upper 60s to near 70 dewpoints, beneath
cooling profiles aloft and steep midlevel lapse rates. This volatile
air mass will exist over a large area, suggesting potential for
widespread severe weather.

Both mid and high-level southwesterly flow aloft will increase
throughout the period as the upper trough moves northeastward across
TX. The northward transport of moisture and instability will be
aided by a broad, southerly low-level jet which will increase to 50
kt by late afternoon and will shift eastward across the lower MS
valley overnight. This will create strong, veering winds with height
which will clearly favor significant severe thunderstorms including
tornadic supercells, damaging bows, and quasi-linear convective
systems. The severe threat is expected to begin by mid morning
across central and northern Texas, and evolve/expand eastward
through the rest of the period to near the Mississippi river by 12Z
Monday.

...Central into northeast Texas and across the Arklatex -- Sunday
morning through afternoon...
Model consensus is that supercells may begin forming in the 12-15Z
time frame from near Austin TX to just east of Dallas, aided by
convergence within the low pressure trough and where rapid moisture
advection will be underway. Any capping inversion is expected to be
minor, and relatively low for this part of Texas. This suggests that
early development is indeed feasible, and increases the chances of
strong low-level accelerations in the storms as opposed to
situations where the LFC is much higher. The cells may take some
time to become better organized as the low level jet will be on the
increase during the day. However, by 18-21Z, these storms should
pose a tornado and wind threat across northeast TX approaching the
Arklatex, with strong tornadoes possible. CAMs suggest that
supercells may eventually merge into an MCS, in which case damaging
straight-line winds would be likely. In addition, re-generation of
supercells is possible along the southern fringe or along any
outflow boundary laid out by this earlier activity, possibly
affecting areas along the northern edge of the Moderate Risk area
such as Shreveport LA.

...East Texas into Louisiana -- Midday through evening...
The fast erosion of any capping inversion Sunday morning and
widespread destabilization of the air mass lends uncertainty to
exact placement and timing of tornadic supercell development, with a
potential extending from east TX to New Orleans, and timing anywhere
from midday through evening across the warm sector. Some models such
as the ECMWF produce storms over southeastern LA during day, and the
environment would already be favorable for tornadoes. However, the
most likely scenario is for supercells to begin developing by
midday, near the warm front and intensifying low-level jet core
which will be across east TX into western LA, then eventually
spreading eastward as the cold front approaches from the west. At
least a few strong tornadoes are expected given large looping
hodographs with effective SRH in excess of 300 m2/s2 along with
impressive instability profiles. Overnight, cells may merge into a
QLCS, with both tornado and damaging wind threat persisting into
Monday morning.

..Jewell.. 04/01/2017


 https://twitter.com/NWSSPC/status/848228115629432832




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Re: Severe Weather event East Texas / Louisiana - April 2 - Moderate Risk includes Houston

#16 Postby Hypercane_Kyle » Sat Apr 01, 2017 12:45 pm

It's been quite a long time since there's been a moderate risk including the Houston area.
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Re: Severe Weather event East Texas / Louisiana - April 2 - Moderate Risk includes Houston

#17 Postby 1900hurricane » Sat Apr 01, 2017 1:39 pm

Hypercane_Kyle wrote:It's been quite a long time since there's been a moderate risk including the Houston area.

Yep, since February 16, 2008, or over nine years ago.
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Re: Severe Weather event East Texas / Louisiana - April 2 - Moderate Risk includes Houston

#18 Postby cycloneye » Sat Apr 01, 2017 1:40 pm

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Re: Severe Weather event East Texas / Louisiana - April 2 - Moderate Risk includes Houston

#19 Postby KatDaddy » Sat Apr 01, 2017 1:49 pm

Its has been awhile since SE TX saw a Moderate Risk area and still remember Feb 2008. If memory serves me correct; it was a bust thanks to just enough cap in place. That was a very concerning day with all the parameters in place for a significant event. There was one severe cell that went up near College Station. The amazing part is how fast it went from a developing cell to severe which was less than 20 minutes. The atmosphere will primed again tomorrow for another significant event.
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Re: Severe Weather event East Texas / Louisiana - April 2 - Moderate Risk includes Houston / Galveston

#20 Postby EF-5bigj » Sat Apr 01, 2017 2:13 pm

The probabilities are pretty high 45% :eek:
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