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Tn Valley Severe Weather


jaxjagman
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Good call. Locking the previous thread also saves the December 10-11 outbreak as the most recent material.

12Z Monday Euro and GFS (globals) have more of a surface low than the NAM for Wednesday. At 60 hours the globals are more trusted than the NAM. Regardless of what the NAM does overnight to 48 hours, SPC should go Enhanced for Wednesday as Day 2. Additional strengthening of the low level wind forecast could open the door to higher probabilities, but we're not there at this time. 

Wednesday soundings have eerie similarities to those of Dec. 10-11 in that they have more low level CAPE than recent April setups. Any strengthening and backing of low level winds could be trouble. Also we have the instability to promote another around of activity along the east-west boundary (as opposed to needing a prefrontal trough) IFF the low level wind forecast strengthens. 

Saturday could be big, or trash out with an Arctic front surge. This reminds me of a big week in the Plains. Saturday oh Saturday! Prior Wednesday ends up the big day.

 

 

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Large SLGT risk from TN into the mid South for Day 2.  Interesting re the bolded below 

Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1257 AM CST Tue Dec 28 2021

   Valid 291200Z - 301200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR PORTIONS OF
   THE MID-SOUTH AND TENNESSEE VALLEY...

   ...SUMMARY...
   Severe thunderstorms are possible for portions of the Deep South
   into the Tennessee Valley. Large hail, damaging winds, and a few
   tornadoes will be possible.

   ...Synopsis...
   A mid-level shortwave trough can be seen off the Oregon coast early
   Tuesday morning. This shortwave will round the base of the
   large-scale trough to near the Southern High Plains by 12Z Wednesday
   and into the northern Great Lakes by Thursday night. This will
   overspread weak height falls across the warm sector during the day
   Wednesday. Meanwhile, a lee cyclone is expected to develop near the
   Oklahoma Panhandle Wednesday morning and move quickly eastward along
   the surface front through the day. Guidance has come into better
   agreement showing a closed surface low developing along the front,
   but there still remains some uncertainty in the exact location and
   strength of this surface low.

   ...Portions of the Mid-South and Tennessee Valley...
   A long-fetch Caribbean moisture feed will be in place across the
   Southeast on Wednesday morning with mid-60s dewpoints into southern
   Tennessee at 12Z. Low-level flow will strengthen in response to the
   developing surface low along the front Wednesday afternoon. This
   will advect higher theta-e air northward with mid 60s dewpoints into
   north central Tennessee and upper 60s dewpoints into portions of
   northern Mississippi and Alabama. Some breaks in the clouds are
   anticipated in this region as low-level cloud streaks advect
   northward across the warm sector, which may allow temperatures to
   warm into the mid to upper 70s. As a result, ample instability is
   anticipated across the warm sector, with MLCAPE in excess of 1500
   J/kg possible as far north as Columbus, Mississippi.

   Thunderstorms will likely be ongoing at the beginning of the period
   near the Red River in southeast Oklahoma/northeast Texas in response
   to increasing isentropic ascent as the low-level jet strengthens.
   This activity is expected to continue northeastward through the day
   and may eventually overspread the warm sector, and become surface
   based. The marginal and slight risk have been expanded northward to
   account for this possibility given the favorable severe parameter
   space across much of the warm sector Wednesday afternoon.

   The primary severe weather threat will be focused on thunderstorms
   east of this activity in a region of broad, weak isentropic ascent
   where a confluence band could set up off the Gulf of Mexico. Expect
   storms to develop out of cloud streaks which will be streaming north
   through the morning. 00Z CAM guidance appears to be subdued in
   reflectivity and updraft helicity depiction. Forecast soundings in
   proximity of this convection would suggest more intense storm
   development than is currently shown. CAM guidance has had similar
   issues in past cool-season Southeast severe events, and therefore it
   could be a false depiction of storm intensity based on the
   environment. However, there are times when lackluster CAM reflection
   of storm intensity is hinting at a greater problem with forcing.
   This is at least somewhat of a concern given the mostly neutral
   height tendency across the region for much of the event.

   Any storms which develop in this region will encounter favorable
   vertical shear for supercells with effective shear in excess of 50
   knots. In addition, the weakly forced nature of the convection will
   likely favor a mostly discrete storm mode. These storms should have
   a tornado threat, given the strengthening low-level jet, with a
   broad region of 40 knots of southwesterly flow at 850mb depicted by
   most guidance. This will yield effective SRH around 250 m2/s2 which
   will be more than sufficient for a few tornadoes.

   An upgrade to enhanced (10%/sig) was considered across northern
   Mississippi and northwest Alabama, but ultimately settled on an
   expansion of the slight risk for this outlook. If guidance continues
   to trend toward a stronger surface low, and if CAM guidance starts
   to show more intense storm development, an upgrade to enhanced may
   be necessary.

   ..Bentley.. 12/28/2021
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Also Friday and Saturday 

   Day 4-8 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0404 AM CST Tue Dec 28 2021

   Valid 311200Z - 051200Z

   ...DISCUSSION...
   ...Day4/Friday - Arklatex to the Mid-Mississippi Valley...
   A mid-level shortwave trough will move from near the Baja Peninsula
   Friday morning to the southern Plains by late Friday night. This
   approaching shortwave and deepening lee cyclone across the southern
   High Plains will elicit a strong mass response across the Arklatex
   late Friday and into Friday night. As the low-level jet strengthens,
   storm coverage is expected to increase in a broad zone of isentropic
   ascent north of a warm front from southeast Oklahoma to the
   Tennessee Valley. In addition to this elevated storm activity, most
   guidance also shows surface-based storm development on the warm side
   of the boundary Friday evening into the early morning hours
   Saturday. A very moist boundary layer will be in place ahead of this
   storm activity with mid-60s dewpoints as far north as southern
   Kentucky at 06Z Saturday. Therefore, convection will form and
   propagate into an unstable environment which will allow
   thunderstorms to continue through the overnight hours and into the
   Day5 period with a severe threat throughout. Strong deep-layer and
   low-level shear will support all severe hazards.  

   ...Day5/Saturday - Mid South and the Tennessee Valley to the
   Southern Appalachians...
   Severe weather will likely be ongoing at the beginning of the period
   from the early morning thunderstorms across Arkansas and vicinity.
   There may be a slight lull in storm coverage/intensity during the
   diurnal minimum Saturday morning, as the lead wave continues
   northeastward and the primary trough approaches from the west.
   However, by midday, significant height falls will start to
   overspread the warm sector and widespread storm development is
   anticipated. The location of overnight convection will have a
   significant impact on the zones within the broader risk area where a
   higher severe weather threat will exist. However, all guidance shows
   a broad warm sector with a broad 50 knot low-level jet, which would
   foster an environment favorable for all severe weather types. The
   greatest uncertainties are related to the northward extent of the
   risk and the surface low track. Given the widespread convection
   expected north of the warm front, a convectively reinforced warm
   front could set up farther south than the surface low track may
   suggest. Also, global guidance still varies with the intensity and
   location of the surface-low as it tracks northeast. The track and
   intensity of this surface-low will have some impact on the storm
   evolution and intensity within the warm sector, especially as it
   relates to storm mode and the tornado threat. Maintained 15 percent
   probabilities from the previous Day 6 forecast with an expansion on
   the southern and eastern extent to account for the threat continuing
   late Saturday night. 
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My take of the 12Z Tuesday guidance is after dark, but not super late. 

12 hours ago, Albedoman said:

Memphis tv stations will be on board Wednesday again  tracking the supercells.  Its coming like a thief in the night.  This freakish warm severe weather has to end soon

Short wave looks a little clumsy. I guess that's non-technical talk for odd ejection with poor low level wind fields. CAPE is high for this time of year, so any uptrend in low level wind fields would have to be watched closely.

Look for heavy rain and some severe, but I don't think Wednesday evening will be too bad (if low level wind field forecast holds meh).

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Thanks MRX I'll look forward to that sh!t after dark. At least it'll still be evening, not late night. Remember even storm chasers don't like that crap after dark.

Virtual chase target is northeast Mississippi to northwest Alabama, into southern Middle Tenn. That's hideous chase terrain so no real chasing. Lunch in Corinth, Miss. would offer options south into Miss. or back east into Bama. However the immediate tri-state (with TN) is completely unchasable terrain. Punt!

Oh yeah, lots of college football on today too. Cheers!

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Boundary, clearing skies, and increasing surface winds has reached the Tennessee border with Mississippi and Alabama. Watch is valid. Another Southern event looks poised to over-achieve relative to 36 hours out.

Still think Enhanced 10% hatched covers it. Not quite Moderate material, but it's getting close. I'd keep Enhanced. Word watches bluntly, but not strongly.

In addition to the lifting boundary, appears a pre-frontal trough runs north to south in Mississippi. Could be a focus for robust new development.

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48 minutes ago, PowellVolz said:


Are you talking about in that area out west where the clouds are moving NW in that clearing area?


.

I was meaning the line I've drawn in blue.

XHWfRid.png

It was really interesting up here in MoCo this AM. Left my house for a run at Frozen Head and it was ~ 61 Got to Frozen Head (~5 miles N of my house) and it was a cool 57. It wasn't a huge temp drop, but distincvtive. 

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First tor warning of today's episode back in Arkansas

BULLETIN - EAS ACTIVATION REQUESTED  
TORNADO WARNING  
NATIONAL WEATHER SERVICE LITTLE ROCK AR  
246 PM CST WED DEC 29 2021  
  
THE NATIONAL WEATHER SERVICE IN LITTLE ROCK HAS ISSUED A  
  
* TORNADO WARNING FOR...  
  NORTHERN DESHA COUNTY IN SOUTHEASTERN ARKANSAS...  
  NORTHEASTERN DREW COUNTY IN SOUTHEASTERN ARKANSAS...  
  SOUTHEASTERN LINCOLN COUNTY IN SOUTHEASTERN ARKANSAS...  
  SOUTHEASTERN ARKANSAS COUNTY IN SOUTHEASTERN ARKANSAS...  
  
* UNTIL 330 PM CST.  
      
* AT 245 PM CST, A SEVERE THUNDERSTORM CAPABLE OF PRODUCING A TORNADO  
  WAS LOCATED 7 MILES SOUTHWEST OF MILLS, OR 10 MILES WEST OF DUMAS,  
  MOVING EAST AT 50 MPH.  
  
  HAZARD...TORNADO AND QUARTER SIZE HAIL.  
  
  SOURCE...RADAR INDICATED ROTATION.  
  
  IMPACT...FLYING DEBRIS WILL BE DANGEROUS TO THOSE CAUGHT WITHOUT   
           SHELTER. MOBILE HOMES WILL BE DAMAGED OR DESTROYED.   
           DAMAGE TO ROOFS, WINDOWS, AND VEHICLES WILL OCCUR.  TREE   
           DAMAGE IS LIKELY.  
  
* LOCATIONS IMPACTED INCLUDE...  
  DUMAS...                          MITCHELLVILLE...  
  WATSON...                         WINCHESTER...  
  YANCOPIN...                       OMEGA...  
  MILLS...                          MERRISACH LAKE...  
  TRUSTEN HOLDER WMA...             ARKANSAS POST...  
  GARRETT BRIDGE...                 PENDLETON...  
  GOURD...                          FLORENCE...  
  TYRO...                           ROSE HILL...  
  REEDVILLE...                      MORGAN POINT RECREATION AREA...  
  YUKON...                          PICKENS IN DESHA COUNTY...  
  

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I was meaning the line I've drawn in blue.
XHWfRid.png
It was really interesting up here in MoCo this AM. Left my house for a run at Frozen Head and it was ~ 61 Got to Frozen Head (~5 miles N of my house) and it was a cool 57. It wasn't a huge temp drop, but distincvtive. 

Well I could see that boundary you drew in blue but I thought maybe that was some kind of inverted trough on top of the mountains.


.
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  • 2 weeks later...
  • 2 weeks later...

CFS and GFS weeklies are both trending toward the ECMWF weeklies, in that the second week of February may return to warmer than normal. Depending on the amount of toughing in the West and Plains -PNA? it will be time to think about early season severe weather and storm chasing. Waiting for the Plains has not been rewarding recent years. Chase everything in Dixie!

Barring a sharply colder forecast change over the weekend, I'm about done in the winter threads. Chatty doesn't have a snowball in hell prayer early next week. Look for me in this thread. La Nina! Tee up early and often Southern severe!!

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