• We've made some major changes to the website. You can view a short list : Here
  • Hello guests. Please take a minute to sign up and join in the conversation. It's free, quick, and easy!

DEEP SOUTH Severe Weather threat 18-20th (1 Viewer)

Status
Not open for further replies.
Joined
Jan 5, 2017
Messages
830
Likes
753
Location
Mountain in East AL
#1
Looking over the models appears severe weather threat including hail and tornadoes going to be possible for the Mississippi and Alabama area Sunday night into Monday. Front progged to come through the area tomorrow and Saturday will stall and lift northward Sunday/Sunday night resulting in dew points surging into to the low to mid 60's for much of Mississippi and Alabama along with cape around 1500-2000j's. Area of low pressure will form to our W and race off to the E/NE cutting through central TN. SPC had no defined risk at this time for the area but believe this will change over the next 24-36 hrs. if models remain consistent in regards to the last couple runs.

Edit to say along the warm front could be the focal point for tornados (if system produces)
F69C7489-EF01-46B9-B7B5-4A8F47B40F6F.jpeg D8FF9B59-987A-4326-9003-8BCBA8DA47FA.jpeg BEE781C9-9355-4254-AF5A-D5B0371B58D6.jpeg

Carry on...
 
Last edited:
Joined
Jan 5, 2017
Messages
830
Likes
753
Location
Mountain in East AL
#3
I think this could be our first real good threat around here.
Looking more likely disco from Owen at BMX laying out the probs.

Later Monday morning into the early afternoon, the upper low
intensifies and the surface low deepens. This will bring a dryline
boundary across the MS River Valley and through MS by Monday
afternoon. Ahead of this dryline, models are in decent agreement
right now with the moisture rebound and afternoon destabilization
across Central AL. MUCAPE values in both the GFS and ECMWF are 1500-
2000 J/kg with surface based CAPE exceeding 1500. Surface winds are
backed to the south for most of the area, with some spots forecast
to see more southeasterly winds according to the GFS. These backed
surface winds, coupled with the flow around the deepening upper low
will result in a fairly deep shear. 0-6km Bulk shear is around 55-
65kts with 0-3km being 40-50kts. Essentially, the forecast
hodographs have good curvature and SRH values are greater than 300,
which would support rotating updrafts. I`m not overly impressed with
the strength of the LLJ that both the GFS and EC are showing, but
that wouldn`t prevent a severe threat. The biggest uncertainty right
now is the Sunday night/Monday morning MCS. Timing and location of
that MCS will almost fully determine where and what kind of severe
threat we`ll see on Monday afternoon/evening. The MCS could very
well cut us off and limit any destabilization, but for now the
models show moisture and instability building back in. Because of
that, and with the models now showing more backed surface winds and
better low level shear, I will change the severe thunderstorm threat
in the HWO to a tornado threat and increase the confidence slightly
(to a 2). At this time, all modes of severe weather look possible
(damaging hail, wind, and tornadoes) for Monday afternoon/evening.
We`ll need to monitor model trends in the next couple of days to
determine specifics on timing and location.
 
Joined
Jan 5, 2017
Messages
830
Likes
753
Location
Mountain in East AL
#4
"
Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0400 AM CDT Fri Mar 16 2018

Valid 191200Z - 241200Z

...DISCUSSION...
Numerical models are in relatively good agreement with the movement
of a shortwave trough from the southern Plains across the lower MS
Valley on Monday, with a surface low moving from AR into TN during
the day or evening. The ECMWF is faster/farther east with the low
than the GFS, which lends uncertainty. However, the risk area can be
adjusted in later outlooks.

On Monday Day 4, a cold front is forecast to stretch roughly from
middle TN southward across MS by 00Z Tuesday, continuing eastward
across AL and into GA by Tuesday morning. A warm front will also
lift north across the region, stretching from northern AL into
central GA at 00Z. Dewpoints in the 60s F and cool midlevel
temperatures will result in around 1500 J/kg MUCAPE, with strong
deep-layer shear profiles supporting organized convection. Low-level
shear will be maximized near the warm front, and forecast wind
profiles do support supercells. Conditional on storm mode, a tornado
threat may exist. The northern threat into TN will depend on
instability, but otherwise the synoptic setup appears most favorable
there. To the south, instability will be much greater and one or
more clusters of storms are expected to spread across AL and GA with
damaging winds likely given strong mean wind profiles."
 

Arcc

Supporter
Member
Joined
Jan 5, 2017
Messages
1,885
Likes
2,415
Location
Extreme North Coosa County
#7
Matt Grantham's discussion had me looking at this yesterday. I haven't checked today but yesterday's 18z GFS looks very favorable for Supercells with large hail. Anytime I see 500mb vectors out of the west it sounds alarm bells in my mind.

The biggest argument against tornadoes is as was low level helicity as was in his discussion. The other thing is shallow boundary layer moisture. Definitely may be our first really legit threat if the GFS is correct.
 

Arcc

Supporter
Member
Joined
Jan 5, 2017
Messages
1,885
Likes
2,415
Location
Extreme North Coosa County
#10
Yeah the NAM is pretty ridiculous, but even the GFS is getting into very concerning numbers. Here we go into the spring severe season

Edit: After looking over the soundings on both NAM and GFS, I'd still like to see deeper moisture. I've seen numerous times over the years where shallow moisture in the boundary layer prevented an big event due to the dry air mixing down.
 
Last edited:

Arcc

Supporter
Member
Joined
Jan 5, 2017
Messages
1,885
Likes
2,415
Location
Extreme North Coosa County
#15
Yeah, hail will be a problem with a sounding like this. Helicity increases later as the LLJ strengthens, but based on a blend of the NAM and GFS, monster hail will be the largest threat.

 

StoneMtnWx

Supporter
Member
Joined
Jan 5, 2017
Messages
326
Likes
365
Location
Stone Mountain, Ga
#16
Latest from SPC has 15% svr probs with a hatched area in parts of N Al into parts of N/NW GA and S TN
...Discussion...
The timing of a shortwave trough will play a critical role in severe
potential on Monday across TN, MS, AL and GA. At this time, the NAM
appears to be too slow and more amplified with this wave over MO
compared to the ECMWF and GFS which show it over central KY or
Middle TN at 00Z Tuesday. As a result, severe potential looks quite
different amongst the models. For example, the latest NAM shows an
extremely volatile setup over middle TN and northern AL clearly
favoring strong tornadoes. However, the most likely solution appears
to be a blend of the ECMWF and GFS, both showing a faster and
lower-amplitude shortwave, as well as less low-level shear with
relatively veered 850 mb flow.

The most probable scenario appears to be for isolated, potentially
significant severe storms from Middle TN into northern AL and GA,
dependent on how much destabilization occurs especially in TN.
Models also indicate substantial storm coverage across much of
southern GA into northern FL, possibly in the form of an MCS, with
mainly wind damage potential given unidirectional flow.

Given the potential for significant severe storms, a categorical
upgrade is possible in later outlooks once predictability increases
and the centroid of severe coverage is better established.
 

Arcc

Supporter
Member
Joined
Jan 5, 2017
Messages
1,885
Likes
2,415
Location
Extreme North Coosa County
#18
Looks like the 6z NAM pretty much caved to the GFS regarding more veered and weaker low level wind fields. That said I noticed some of the soundings had the WBZ level around 750mb, yikes. Add in those high lapse rates and the result is lots of insurance claims.
 
Joined
Jan 5, 2017
Messages
830
Likes
753
Location
Mountain in East AL
#22
GFS says what SVR threat LoL to the North confines greatest risk over Southern portions

3K NAM was scary as well line fires up along I-65 corridor yikes STP parameters of the charts if correct
 
Last edited:

PEA_RIDGE

FIREFIGHTER
Member
Joined
Jan 20, 2017
Messages
260
Likes
136
Location
MONTEVALLO, AL
#23
Looking a little deeper at the 12z NAM, by far the highest threat for tornadoes will be north of I20 and west of I65 in AL. I would say probably in the Fort Payne to Rome area.
Fort Wayne is East of I65 is it not??


Sent from my Pixel 2 using Tapatalk
 

Arcc

Supporter
Member
Joined
Jan 5, 2017
Messages
1,885
Likes
2,415
Location
Extreme North Coosa County
#25
GFS says what SVR threat LoL to the North confines greatest risk over Southern portions

3K NAM was scary as well line fires up along I-65 corridor yikes STP parameters of the charts if correct
The WRFs should be a good indication to which way we should be leaning.

The 3km NAM would definitely be concerning. I'd like to see a deeper moisture profile, but if we get to what it's showing it may not matter. It has temp of 69 with a dewpoint of 67 across east AL. That would put LCLs on the ground.
 
Last edited:
Status
Not open for further replies.

Users Who Are Viewing This Thread (Users: 0, Guests: 1)

Top