Severe WX Severe Weather Threat Jan 12th, 2023

[Clancy]

Yep 3/18/13

Tornadoes of 2013 - Wikipedia

en.wikipedia.org

Yep, was just about to post the SPC archive page here. FFC issued a TOR the size of a SVR on that day for the whole line as it approached us.

SPC Severe Weather Event Review for Monday March 18, 2013

www.spc.noaa.gov

Edit: the TOR of reference (one of a few large ones on that day), including a small typo on the initial warning

BULLETIN - EAS ACTIVATION REQUESTED
TORNADO WARNING
NATIONAL WEATHER SERVICE PEACHTREE CITY GA
600 PM EDT MON MAR 18 2013

THE NATIONAL WEATHER SERVICE IN PEACHTREE CITY HAS ISSUED A

* TORNADO WARNING FOR...
SOUTHERN CHEROKEE COUNTY IN NORTH CENTRAL GEORGIA
NORTHERN COBB COUNTY IN NORTH CENTRAL GEORGIA
NORTHWESTERN DEKALB COUNTY IN NORTH CENTRAL GEORGIA
FORSYTH COUNTY IN NORTH CENTRAL GEORGIA
NORTHEASTERN FULTON COUNTY IN NORTH CENTRAL GEORGIA
NORTHWESTERN GWINNETT COUNTY IN NORTH CENTRAL GEORGIA
SOUTHERN BARTOW COUNTY IN NORTHWEST GEORGIA
NORTHERN PAULDING COUNTY IN NORTHWEST GEORGIA
NORTHEASTERN POLK COUNTY IN NORTHWEST GEORGIA

* UNTIL 645 PM EDT

* AT 557 PM EDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A
LINE OF SEVERE THUNDERSTORMA CAPABLE OF PRODUCING A TORNADO NEAR TAYLORSVILLE...
MOVING EAST AT 60 MPH. THERE IS ANOTHER AREA OF ROTATION CAPABLE OF PRODUCING
A TORNADO SOUTHEAST OF BRASWELL.

* OTHER LOCATIONS IN THE WARNING INCLUDE BUT ARE NOT LIMITED TO
EMERSON...ACWORTH...KENNESAW...MARIETTA...WOODSTOCK...HOLLY
SPRINGS...CANTON...MOUNTAIN PARK...SANDY SPRINGS...BUFFINGTON...
ROSWELL...DUNWOODY...ALPHARETTA...MILTON...FREE HOME...NORCROSS...
BERKELEY LAKE...JOHNS CREEK...DULUTH...CUMMING AND SUWANEE.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

HEAVY RAINFALL MAY OBSCURE THIS TORNADO. TAKE COVER NOW! IF YOU WAIT
TO SEE OR HEAR IT COMING...IT WILL BE TOO LATE TO GET TO A SAFE
PLACE.

IF YOU SEE WIND DAMAGE...HAIL OR FLOODING...WAIT UNTIL THE STORM HAS
PASSED...AND THEN CALL THE NATIONAL WEATHER SERVICE TOLL FREE AT 1 8
6 6 7 6 3 4 4 6 6. YOU CAN ALSO TWEET YOUR REPORT USING HASHTAG GAWX.

A TORNADO WATCH REMAINS IN EFFECT UNTIL 1000 PM EDT MONDAY EVENING
FOR NORTHWESTERN GEORGIA. A SEVERE THUNDERSTORM WATCH ALSO REMAINS IN
EFFECT UNTIL 1000 PM EDT MONDAY EVENING FOR NORTHWEST GEORGIA.

 

[ashtonlemleywx]

Latest NAM CWASP. SW Miss and South Alabama look to have the best potential for Thursday.

 

[KevinH]

View attachment 16629
Latest NAM CWASP. SW Miss and South Alabama look to have the best potential for Thursday.

Will be interesting to see how this changes in the coming days.

 

[ashtonlemleywx]

Yea a slower progression could change things in a big way. Setups like this can be tricky and we really won't have confidence until HRRR is in range.

But if you're a betting man.....go to South Alabama.

 

[UncleJuJu98]

Initiation of convection will be a big factor, looks as if it has a bit more lift it'll be lifting earlier, not sure but seems as if when the flow around 200mb becomes different it starts to initiate. This whole event is still a crapshoot too be honest one what will be where and how bad. Makes my head dizzy

Yea a slower progression could change things in a big way. Setups like this can be tricky and we really won't have confidence until HRRR is in range.

But if you're a betting man.....go to South Alabama.

 

[UncleJuJu98]

View attachment 16629
Latest NAM CWASP. SW Miss and South Alabama look to have the best potential for Thursday.

Seems like a mixed mode event based on this map, with your more isolated robust development further South with the semi different directional shear.

 

[UncleJuJu98]

Honestly I can't wait for the dang WRF models suites to come out I trust those more than anything the nam will spit out, usually goes in the order of the euro / wrf/ short range HRRR in terms of reliability to convection. I'll take. A short look at the new ram run in a bit.

 

[UncleJuJu98]

By looking at the 3km nam barely on the cusp of range into the event, I think convection has a good possibility of initiating sooner, from a forecast confluence band

 

[Clancy]

18Z NAM shows pretty broad area of destabilization Thursday afternoon. New AFD from FFC below.

Thursday will be the main event of the longterm outlook. A
developing Colorado Low will makes its way over the Ohio River
Valley and Great Lakes. One thing that will be slightly unusual for
this system is the time in which the cyclone will begin occluding.
Usually, systems like this are fully occluded by the time they begin
to affect our area. This system looks to be a little different, with
the occlusion occurring further eastward. What does this mean for us?
Well, this means that storm development will have greater large
scale dynamic support as they push through our area. Along with
this, models have continue to agree on a storm arrival time
coinciding with peak heating 18-00Z, further amplifying storm
development.

Just like baking a cake, storms need the correct ingredients to form
correctly. In our case, models have been particularly aggressive with
near surface shear ahead of the coldfront. The actual timing and
position of the shear axis will need further examining, however
synoptic scale models are in agreement that we could see a corridor
of nearly 70kt sfc-500mb shear with 35-50 kts of this being in the 0-
1km. Other ingredients we are seeing for this set up are MUCAPE
values on the order of 250-500 J/Kg, driven by dewpoints of 60+
possible for much of Central and North GA. Model guidance is fairly
high confidence in this with GEFS probs of >250 J/Kg of CAPE being
40-80% for a large portion of North and Central GA. While in other
times of the year this may seem low, this is ample energy for any
January system. Furthermore, a mid level dry intrusion is leading to
enhanced DCAPE values. If this is realized and storms are able to
tap into this, downward momentum transfer of the 40-50kt LLJ will
mean increased risk for damaging winds. With these ingredients, the
main storm threats may include damaging wind gusts, flash flooding
due to heavy rainfall, and tornados. Overall, we will continue to
monitor this system closely, with consideration that this is still
in the day 4 outlook and forecasts could be subject to change.

 

[UncleJuJu98]

When the frontal boundary catches up with the confluence later in the day your initiation will possibly start there , this is one of the few mesoscale features that'll determine storm mode and threat area

 

[UncleJuJu98]

The moisture difference between the 3km nam and nam is pretty big. a lot larger warm sector for when the sun comes out to destabilize. Confluence is already lowering temps in the atmosphere and causing instability, really think somewhere in east Mississippi will be your initiation point instead of east Alabama.

 

[CheeselandSkies]

That's a pretty wide warm sector, similar to the last one although not quite as robust. Remains to be seen if other factors will compensate.

 

[UncleJuJu98]

That's a pretty wide warm sector, similar to the last one although not quite as robust. Remains to be seen if other factors will compensate.

Honestly upper 100s and low 1000s is pretty good for a winter event, it's really sneaking up on us. Most all of the deep souths decent tornado events have come from those type of instability events your low topped wispy tornadic events, the cips large 15% area goes very well with the Nam 3kms warm sector.

In fact the two tornadoes that hit near me in the past 10 years where from low topped supercells with low 1000s upper 900s instability in a semi broken line segment if my memory is correct. BOTH in January lol so it's right around that time of the year

 

[UncleJuJu98]

Black line is your frontal boundary at 9 am Thursday, purple shade is the vertical velocity of possible storm motion, indicating the probability of storms firing ahead in the semi unstable environment. Red circle is the area were you have a better area for lift due to the lesser winds up high, your initiation for discreet stuff will be around middle east missippi, your highest chance for significant tornadic stuff will definitely be south of the i20 corridor. As NWS of Birmingham states a line form Alexander city to demopolis

 

[KevinH]

Black line is your frontal boundary at 9 am Thursday, purple shade is the vertical velocity of possible storm motion, indicating the probability of storms firing ahead in the semi unstable environment. Red circle is the area were you have a better area for lift due to the lesser winds up high, your initiation for discreet stuff will be around middle east missippi, your highest chance for significant tornadic stuff will definitely be south of the i20 corridor. As NWS of Birmingham states a line form Alexander city to demopolis View attachment 16654View attachment 16655

Shocker SMH

 

[UncleJuJu98]

Shocker SMH

Probably will have a lot of rouge possible tornadic supercells if prefrontal trough/ front or confluence band initiates convection before the cold fronts gets there, better veering of winds as well. Question is when will this happen if it does? Midday morning afternoon and what's the quality of the warm sector. Not sure but I think with prefrontal troughs winds will shift more to it which aids in the veering but I'm not 100% sure. Overall better directional sheer if initiation is before the cold front

 

[UncleJuJu98]

Comparison between 3km nam and nam for 6am. Check the differences.

 

[KevinH]

Comparison between 3km nam and nam for 6am. Check the differences. View attachment 16658View attachment 16659View attachment 16660View attachment 16661View attachment 16662

Pardon my ignorance, but what is the diff betw 6km and 3km? What do these images tell us (you lol)

 

[JPWX]

00z NAM has the moisture, wind shear, and CAPE values around just above 900 around noon Thursday across parts of North/Eastern MS. The composite reflectivity around this time though on the 00z NAM shows nothing.

 

[UncleJuJu98]

Just taking a glance at the FV3 for convection at the end of the model run hour 60, don't really use this to make any forecasting descions but nice to check other convective allowing models. Shows the general idea of what i was thinking with convection begging in missippi albeit it's elevated.