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Enhanced Severe risk and storms Dec 31,Jan1


jaxjagman
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 Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1254 AM CST Fri Dec 31 2021

   Valid 011200Z - 021200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS
   OF THE DEEP SOUTH AND TENNESSEE VALLEY....

   ...SUMMARY...
   Widespread thunderstorms are expected from the ArkLaTex to the
   Western Appalachians on New Year's Day. All severe-weather hazards
   are possible including large hail, damaging winds, and tornadoes, a
   couple of which may be strong.

   ...Synopsis...
   A positively tilted upper-level trough will be centered near the
   Great Basin to start the period. This trough will maintain its
   positive tilt as it shifts eastward across the Plains and into the
   Midwest by 12Z Sunday. An embedded mid-level shortwave trough will
   move quickly from the southern High Plains across the Midwest and
   Ohio Valley Saturday to the Northeast by Sunday morning. A surface
   reflection of this mid-level shortwave trough is expected to travel
   along the front from the Ozarks to the Ohio Valley and into the
   Mid-Atlantic.

   ...Ohio Valley into the central Appalachians...
   There is still considerable uncertainty regarding the northward
   extent of the destabilization and severe-weather threat based on the
   position of the position of the surface front and the strength of
   the surface low. The NAM is stronger with the surface low with a
   much farther north warm front bringing low 60s dewpoints north of
   the Ohio River into southern Illinois, southern Indiana, and
   Southwest Ohio. However, the operational GFS is much weaker and
   southeast with the surface low and only brings low 60s dewpoints
   into south-central Kentucky. The ECMWF solution is between these two
   locations with the frontal position, which also closely resembles
   the GEFS mean. Therefore, the northern extent of the marginal and
   slight risk threat areas match the ECMWF and GEFS mean. 

   A line of storms is expected to move through this region during the
   afternoon and early evening hours. Forecast soundings show more than
   50 knots of flow only a few hundred meters above the surface.
   Therefore, mixing this strong flow to the surface should not be that
   difficult, even in a weak buoyancy environment. Low 60s dewpoints
   should yield MLCAPE around 250 to 500 J/kg across southern Kentucky,
   which increases the confidence for severe winds as the squall line
   moves through. In addition, a QLCS tornado threat will exist given
   the strong low-level speed shear present ahead of this line of
   storms. However, the limited instability and veered surface flow
   will be limiting factors to a greater tornado threat along this
   portion of the line. 

   ...Portions of the Deep South into the Tennessee Valley...
   A large area of thunderstorms, some of which may be severe, is
   expected to be ongoing from western Kentucky to northern Texas
   Saturday morning. As the surface low moves from the Plains into the
   Ozarks Saturday morning, this convection is expected to become
   better organized, likely into a squall line, and start to advance
   eastward. Dewpoints are forecast in the mid to upper 60s ahead of
   these storms, which should yield MLCAPE around 500 to 1500 J/kg from
   north to south. This should be more than sufficient to maintain a
   strong squall line through the afternoon and into the overnight
   hours across eastern Arkansas, most of Tennessee, and northern
   Mississippi and Alabama. A 50 to 60 knot low-level jet will result
   in strong low-level speed shear across the entire warm sector.
   Forecast soundings show mostly unidirectional flow in the lowest 1
   km due to the veered surface flow across most of the warm sector as
   a result of the elongated nature of the surface pressure pattern.
   This should temper the tornado threat somewhat, but with the strong
   speed shear and the expectation of a well balanced squall line, the
   environment will still be supportive for QLCS tornadoes. 

   Most guidance hints at the potential for some warm sector supercell
   development across portions of Mississippi, Alabama, and Tennessee
   Saturday afternoon/evening. The ECMWF has been especially bullish
   with pre-frontal convection for the last several days, which
   continues through the latest 00Z run. Any strong supercells which
   can develop in the open warm sector will likely have the greatest
   threat for significant to potentially intense tornadoes. The most
   likely region for pre-frontal supercell development will be from
   eastern Arkansas to northern Alabama and possibly southern Tennessee
   where greater instability is forecast. Veered low-level flow will
   keep low-level directional shear limited during the first half of
   the day. However, at least slightly greater low-level turning is
   shown by forecast soundings during the late afternoon into the
   evening hours as surface flow remains south-southwest, while the
   low-level jet starts to veer more westerly as the main wave shifts
   east. This may result in a slightly higher tornado threat into the
   overnight hours from far eastern Mississippi into northern/central
   Alabama and northwest Georgia.

   ..Bentley.. 12/31/2021
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Saturday will depend on the prefrontal trough. Main front is veered off with parallel upper level flow, not really a tornado machine.

Mississippi and Alabama will start Saturday capped. However the cap will gradually erode. Prefrontal trough is forecast and will be there. Question is the cap.

If the cap breaks down there, discrete supercells will bring their usual threats. They would probably go from rooted to tornado in an hour. That kind of shear, this time with low level flow, would spin up tornadoes rapidly. Would be MDT but too early to make the call now. That's only if the cap breaks.

If the cap holds then it'll look a lot like Wednesday - which still had Sand Mountain tornado(es). However that's not a huge day across the region. SPC should hold with ENH on this afternoon's Day 2.

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Saturday will depend on the prefrontal trough. Main front is veered off with parallel upper level flow, not really a tornado machine.
Mississippi and Alabama will start Saturday capped. However the cap will gradually erode. Prefrontal trough is forecast and will be there. Question is the cap.
If the cap breaks down there, discrete supercells will bring their usual threats. They would probably go from rooted to tornado in an hour. That kind of shear, this time with low level flow, would spin up tornadoes rapidly. Would be MDT but too early to make the call now. That's only if the cap breaks.
If the cap holds then it'll look a lot like Wednesday - which still had Sand Mountain tornado(es). However that's not a huge day across the region. SPC should hold with ENH on this afternoon's Day 2.
This just came out but obviously with the caveats if/will supercells fire in the warm sector. If so it could be a bad evening.e646d647319eb7c6bd5a8c52a27bd278.jpg
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 Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0636 AM CST Sat Jan 01 2022

   Valid 011300Z - 021200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON
   THROUGH EARLY TONIGHT ACROSS THE TN VALLEY...

   ...SUMMARY...
   Damaging winds and tornadoes, a couple of which could be strong,
   will be possible through early tonight, especially across the
   Tennessee Valley.

   ...TN Valley and vicinity through tonight...
   Convection has persisted through the early morning hours along a
   baroclinic zone demarcating the northwest edge of the richer
   low-level moisture from AR into TN/KY.  The convection has
   reinforced this boundary and it is unlikely to return northward
   today, given the lack of strong cyclogenesis as a result of an
   expansive cold air mass across the central U.S. that will undercut
   the stronger forcing for ascent in advance of the primary shortwave
   trough over AZ/UT this morning.  Even though the main surface
   cyclone will not be particularly intense and will develop farther
   northeast away from the warm sector (in tandem with an ejecting
   shortwave trough now over TX/OK), strong deep-layer wind fields and
   vertical shear will persist through the day and into tonight in the
   warm sector across the TN Valley.

   Given the persistence of the subtropical ridge over FL and only
   glancing/small height falls through the day, much of the convection
   may remain confined to the convection-reinforced frontal zone. 
   Still, there will be the potential for embedded supercells within a
   broken band of storms along the front, and a lower chance for a
   couple of supercells in the open warm sector along diffuse
   confluence zones a little south of the front this afternoon/evening.
   Effective bulk shear of 60-70 kt, effective SRH near 300 m2/s2, and
   MLCAPE of 500-1500 J/kg will conditionally support supercells
   capable of producing tornadoes, damaging winds, and marginally
   severe hail.  The prospects for a strong tornado or two will likely
   hinge on pre-frontal supercell development (which is uncertain) from
   northern MS into northern AL and TN late this afternoon/evening.

   The frontal convection will spread southeastward through the
   overnight hours, with a gradually lessening severe threat and
   shrinking warm sector centered on AL toward the end of the period.

   ..Thompson/Kerr.. 01/01/2022
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 URGENT - IMMEDIATE BROADCAST REQUESTED
   Tornado Watch Number 3
   NWS Storm Prediction Center Norman OK
   1050 AM CST Sat Jan 1 2022

   The NWS Storm Prediction Center has issued a

   * Tornado Watch for portions of 
     South-central Kentucky
     Western to middle Tennessee

   * Effective this Saturday morning and evening from 1050 AM until
     600 PM CST.

   * Primary threats include...
     A few tornadoes likely with a couple intense tornadoes possible
     Scattered damaging winds likely with isolated significant gusts
       to 75 mph possible

   SUMMARY...An intensifying squall line should spread east-northeast
   with a threat for damaging winds and embedded tornadoes. A couple
   pre-frontal supercells may develop as well with the possibility of a
   strong tornado.

   The tornado watch area is approximately along and 60 statute miles
   east and west of a line from 90 miles east northeast of Bowling
   Green KY to 35 miles south southeast of Jackson TN. For a complete
   depiction of the watch see the associated watch outline update
   (WOUS64 KWNS WOU3).
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Mesoscale Discussion 0008
   NWS Storm Prediction Center Norman OK
   1238 PM CST Sat Jan 01 2022

Areas affected...Central KY...Middle TN...Northern AL
Concerning...Tornado Watch 3...
Valid 011838Z - 012015Z
The severe weather threat for Tornado Watch 3 continues.
SUMMARY...Threat for damaging wind gust and tornadoes continues
   across central KY and middle TN within Tornado Watch 3. This threat
   will persist downstream into more of central KY, middle TN, and
   northern AL, where a watch will likely be needed.

   DISCUSSION...Recent observations place the outflow boundary from
   about 20 miles south of LEX southwestward to just southeast of BWG,
   continuing southeastward through western TN to about 20 miles
   southeast of MEM. Numerous shallow but strong/organized cells have
   developed along this outflow boundary and lightning has become
   slightly more frequent over the last hour. General trend with the
   stronger storms developing within the line is for an initially
   cell-in-line structure with a strong, more organized updraft. This
   more cellular structure then relatively quickly trends towards
   bowing line segments as the outflow boundary continues pushing
   southeastward. As such, a relatively brief period for tornadogenesis
   exists before the storms then transition to more of a damaging wind
   threat. Initial, more discrete development has also occurred
   sporadically ahead of the line, with a longer duration of more
   cellular structure contributing to a slightly greater tornado risk.
   These storms also trend towards bowing line segments as the outflow
   overtakes them.

   This overall pattern is expected to continue for at least the next
   few hours as the outflow pushes quickly eastward/southeastward.
   Current motion places the outflow near the edge of Tornado Watch 3
   by 1930Z-2000Z. Winds are currently a bit more veered downstream,
   but vertical shear remains very strong. As such, supercells capable
   of damaging wind gusts and tornadoes remain possible and a
   downstream watch will likely be needed.
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