Tn Valley Severe Weather

[nwohweather]

19 hours ago, burrel2 said:

Tornados that do this type of damage aren't common in any environment. What the f*** are you talking about?

Easy rusty. I've seen quite a few tornadoes in chillier than usual temperatures, helicity can do some incredible things with limited instability

[nrgjeff]

Low CAPE high shear events happen. Wait! This was not exactly that...

I'm watching KPAH get the hail treatment about 5pm Monday. Back of my mind I know it's westerly flow aloft over a boundary - but a little early in the season for that set-up. Text my buddy a boundary rider is going off on PAH, but don't think too much about it. Cell weakens, and I start gearing up for Big Monday college basketball on ESPN. Wake up Super Tuesday to Middle Tennessee super tragedy on the news. WTF?

Going back to Monday afternoon shear was never in question. I've written here many times, look for westerly flow aloft instead of that SSW flow junk. Nearly 90 degrees of turning was noted. 850 was a little veered, but upstream was deep moisture - count it as backed in Dixie. 925 mb was straight south and both increased going overnight - all forecast ahead of time! Surface of course had the notorious boundary related SRH.

CAPE and instability was more complicated. Steep mid-level lapse rates were in place, but low-level CAPE was close to zero. Forecast soundings had the latter improving; but, I'm such a skeptic of those. Normally early season other rain is falling, and it remains stable. Well no rain was falling south of the boundary. Surface chart in retrospect shows an unstable airmass advecting in unfettered. Sure enough it arrived at the boundary in Middle Tennessee. LLJ strengthened. Alas the 2% TOR area was under the gun.

CAMs actually had robust storms, but not necessarily a boundary rider beast. Old fashioned meteorology could have provided a more obvious heads up before the evening news. However, credit some local TV Mets for sounding the alarm on the evening news. Still, it's tough to overcome a 1am long-track cyclical damaging tornado.

Dixie Alley is just so awful. It's either busted chases, or much much worse. The human suffering down here is cruel. At least the Vols cheered up Tennessee.

https://davieswx.blogspot.com/2020/03/march-3-2020-double-digit-death-toll.html excellent article from Davies.

[Witness Protection Program]

Good:  The Weather Channel is doing follow up coverage of the TN tornadoes.

Bad:  Can anyone watch for very long?  That shameless drama queen Justin Whatever is horrible.  LOL,  a lady picking up bricks kinda turned and looked at him like she wanted to hit him with one as he stood there endlessly babbling cornball cliches while she's trying to clean up.  Was like a Geico commercial.

[CheeselandSkies]

33 minutes ago, nrgjeff said:

...CAMs actually had robust storms, but not necessarily a boundary rider beast. Old fashioned meteorology could have provided a more obvious heads up before the evening news. However, credit some local TV Mets for sounding the alarm on the evening news. Still, it's tough to overcome a 1am long-track cyclical damaging tornado...
 

Good to hear this. Any YouTube uploads of this "pregame" coverage? It seems to me far too often most local TV mets (**coughcough the ones in my local market**) just parrot what the models are spitting out/what the NWS says, are reluctant to do their own mesoscale forecasting; go out on a limb and either downplay an event that everybody else is hyping (would have served them well in most of the snow events this past winter) or sound the alarm about what had seemed like a low-key situation (like overnight Monday-Tuesday). It's high reward, get it right and you look like a genius and earn major credibility for your station over the competition, but also high risk if you get it wrong.

[METALSTORM]

Here is Bree Smith's forecast from WTVF. Not an over alarming forecast but she did emphasize that severe weather was possible and to have a way to get warnings overnight. I consider her one of the better TV mets out there. 

 

[Chinook]

Low-level rotation track for the tornadic supercell at Nashville

[Bob's Burgers]

2 hours ago, METALSTORM said:

Here is Bree Smith's forecast from WTVF. Not an over alarming forecast but she did emphasize that severe weather was possible and to have a way to get warnings overnight. I consider her one of the better TV mets out there. 

 

That model (probably the RPM?) had trouble with storm mode. 

[geddyweather]

"Public Information Statement
National Weather Service Nashville TN
420 PM CST Wed Mar 4 2020

...Update on Davidson/Wilson/Smith County Tornado...

NWS survey teams have concluded that one long-track tornado
occurred in Davidson, Wilson, and Smith Counties on Tuesday
morning. The path of this tornado stretched roughly 50.25 miles
from beginning to end, starting in the John C Tune area and ending
3.50 miles west of Gordonsville.

Survey teams are continuing to work on where this tornado began
near the John C Tune area. The final tornado path remains subject
to revision as teams complete their survey."

No word on Putnam County/Cookeville area. Believe there are still 17-20 MIA so that may be why surveys have not progressed there.

[crossbowftw3]

No longer waiting for Cookeville. EF4 with winds of 175.

 

 

[Indystorm]

I think this may be the first EF-4 tornado of the year.

[crossbowftw3]

3 minutes ago, Indystorm said:

I think this may be the first EF-4 tornado of the year.

It is. coincidentally on the same date as Lee County from last year.

[Windspeed]

[Windspeed]

[Windspeed]

Some crazy survival stories coming out of this long-lived tornado. I do wish news agencies would stop referring to the event as an "outbreak" however.

https://www.cbsnews.com/news/nashville-tornado-putnam-county-death-toll-rises-today-2020-04-03/

[Windspeed]

Plenty of incredible damage videos and images, but this particular photo of the damage path looking east towards Cookeville is disturbing. Any number of deaths is awful and I am certainly not downplaying this tragedy for those suffering, only just to say that considering the time of night and the track/damage path, it is perhaps a miracle the numbers aren't much higher. Please consider finding a legitimate donation fund setup to help those in need.

 

[nrgjeff]

European weekly charts are ugly for severe wx the next few weeks. Great Lakes Ridge with Gulf Coast underbelly is replaced with more traditional East Coast ridge. +AO and -PNA spell more Dixie Alley trouble. I'm not rooting for this. Rather postpone to May Plains.

[CheeselandSkies]

Ugly in the sense of favorable for svr wx?

[Matthew70]

He means more severe wx.  Trouble for Dixie alley and Jeff not rooting for it says a lot.  I will pass please.  I am definitely looking into getting a storm shelter.  
 

[PowellVolz]

European weekly charts are ugly for severe wx the next few weeks. Great Lakes Ridge with Gulf Coast underbelly is replaced with more traditional East Coast ridge. +AO and -PNA spell more Dixie Alley trouble. I'm not rooting for this. Rather postpone to May Plains.

Take a look at this screenshot from the Cookeville tornado and tell me what I’m missing. Obviously the CC on the left shows the debris field in blue. Why isn’t there a strong TVS sig showing up on the right in Velocity? Also the rotation below Cookeville, could it have hindered the radar from picking up rotation on the Cookeville storm that far from the radar?






.

[Calderon]

That top frame, the tornado had already dissipated. This tornado spun up rapidly and dissipated rather abruptly, according to OHX survey. It managed to die off before hitting both Cookeville Regional Medical Center and the Tennessee Tech University campus. 

[nrgjeff]

Yes @Calderon is absolutely correct! @PowellVolz that's not a TDS. That is lofted debris carried into the forward flank. Also a sign of a violent tornado. Sure enough OHX finds EF-4 damage.

Though the lofted debris signature didn't last as long, it has similarities to the Kansas City tornado last May. Middle Tennessee tornado itself might have lasted longer than the KC one. Have to look back at all that. At any rate, this Tennessee tornado was historical.

[jaxjagman]

Chance of some strong storms. upcoming next week with a trough just passing East Asia recently.Have to see how teleconnections play out past the middle of the month.Euro and GFS tho seem to be hinting at building blocking into the GOA and even as strong as a Rex block,this would/could promote a -AO.Regardless, east Asia is fixing to get active upcoming

[John1122]

A friend of mine found a photo in her backyard here in Campbell County. It's one of people whose home was hit in Cookeville. It's probably 90 or more miles away.  Wild. 

[jaxjagman]

We shall see.Today, there looks to be a ERW moving along the IDL  with Kelvin so this is what the RMM'S show the MJO INTO 5 today and should be the next couple days.There seems to be all kinds of mixed signals afterwards.There still looks as there will be some better blocking into the GOA in the Mid to long range,this should choke off the theta into the Valley during this time unless something changes so more than likely as the theta returns it should be more into the plains as the Mid level heights should rise into the Valley

 

 Day 4-8 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0345 AM CDT Sun Mar 08 2020

   Valid 111200Z - 161200Z

   ...DISCUSSION...
   Medium-range model output continues to indicate that mid/upper flow
   over the eastern Pacific may continue to evolve toward a more
   prominent blocking regime late this coming work week through next
   weekend. This may include the development of large-scale troughing
   and an embedded close low, which could eventually encompass much of
   the West.  As this commences, the remnants of a preceding mid-level
   closed low may finally emerge from the Southwest.  

   After accelerating east-northeast of the southern Rockies on Friday,
   guidance suggests that the lead perturbation will undergo
   considerable weakening and deformation within a confluent regime to
   the north of prominent subtropical ridging centered over the
   southern Gulf basin.  Furthermore, it appears that this may be
   preceded by a substantive reinforcing cold intrusion across much of
   the nation to the east of the Rockies.  And any subsequent wave
   development along the front across the southern tier of the U.S. is
   currently forecast to remain weak.  

   While destabilization along and particularly above/to the cool side
   of the surface front may contribute to considerable thunderstorm
   development during the latter half of the period, severe weather
   potential currently appears best characterized as "low", with 
   probabilities less than 15 percent.  However, it is still possible
   that this could change in later outlooks much closer to this time
   period.

   ..Kerr.. 03/08/2020

[jaxjagman]

Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1258 AM CDT Wed Mar 11 2020

   Valid 111200Z - 121200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE LOWER MS VALLEY INTO THE CENTRAL GULF COAST STATES...

   ...SUMMARY...
   Strong to severe thunderstorms may impact parts of the Ozarks into
   the Mid-South, lower Mississippi Valley, and central Gulf Coast
   states today. Isolated damaging winds and large hail may occur,
   along with a couple tornadoes.

   ...Ozarks into the Mid-South and Lower Mississippi Valley...
   A small cluster of thunderstorms will likely be ongoing at the start
   of the period later this morning across northwestern AR and adjacent
   southern MO. This convection is expected to continue southeastward
   across AR and into parts of the Mid-South through the early
   afternoon in tandem with a 30-40 kt southwesterly low-level jet.
   These storms will eventually encounter greater low-level moisture
   across central/southern AR and northern MS as they cross a surface
   warm front. The potential for strong/gusty winds to reach the
   surface and produce isolated damage should also gradually increase
   as diurnal heating occurs ahead of the storms.

   The southwesterly low-level jet is forecast to gradually weaken
   through the afternoon as stronger forcing for ascent associated with
   a large-scale upper trough shifts eastward across the OH/TN Valleys
   and away from the lower MS Valley. Still, strong northwesterly
   mid-level flow (50+ kt at 500 mb) will remain over this region,
   which should support similar values of effective bulk shear. There
   may be some chance for the bowing cluster to evolve into a broken
   line of supercells by late morning/early afternoon before the
   low-level jet weakens substantially. If this occurs, then isolated
   large hail and perhaps a couple tornadoes would be possible, mainly
   across parts of eastern AR into northern MS where somewhat greater
   low-level moisture should be present. Otherwise, mainly an isolated
   severe hail/wind threat may continue into parts of northern/central
   AL through the early evening before instability wanes with eastward
   extent.

[jaxjagman]

 Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1200 AM CDT Wed Mar 11 2020

   Valid 121200Z - 131200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THURSDAY AFTERNOON
   AND EVENING ACROSS PARTS OF SOUTHEAST MISSOURI AND NORTHEAST
   ARKANSAS  INTO SOUTHERN ILLINOIS...SOUTHERN INDIANA...WESTERN AND
   CENTRAL KENTUCKY...WESTERN AND MIDDLE TENNESSEE AND PARTS OF
   ADJACENT NORTHERN MISSISSIPPI...

   ...SUMMARY...
   Severe thunderstorms are possible across parts of the lower Ohio
   Valley and Mid South into parts of the southeastern Plains Thursday
   afternoon and evening.

   ...Synopsis...
   Amplifying mid/upper flow characterized by increasingly prominent
   blocking appears likely to continue to evolve across the eastern
   Pacific during this period.  To the southeast of a building high,
   becoming centered near the western Gulf of Alaska, a significant
   short wave trough is forecast to evolve and dig to the west of the
   British Columbia coast.  As this proceeds, models indicate that a
   downstream mid-level low, initially to the southwest of the southern
   California coast, will finally begin to slowly accelerate
   east-northeastward into parts of the Southwest.

   In advance of the low, downstream mid-level ridging will attempt to
   build across the southern Rockies through the southern and central
   Plains and lower/middle Mississippi Valley.  However, this may
   initially be suppressed by a vigorous short wave trough advancing
   through a more progressive branch of westerlies, from parts of the
   northern Plains through the Great Lakes by late Thursday night. 
   This interaction may be one source of considerable spread that has
   been evident among the various models and their respective
   ensembles, but this spread appears to be decreasing.

   While guidance indicates that strongest mid-level jet streak
   (intensifying in excess of 100 kt at 500 mb) will dig through the
   mid Missouri Valley before nosing eastward across southern portions
   of the Great Lakes region, another speed maximum (around 50-70 kt at
   500 mb) may develop across the central Plains before propagating
   eastward into the lower Ohio Valley.  

   Models suggest that the southern jet streak may be accompanied by a
   developing surface low, near the intersection of a cold front
   trailing the primary cyclone migrating across Ontario, and an
   initially stalled remnant frontal zone extending across the southern
   Mid Atlantic coast through the Ozark Plateau and south central
   Plains at 12Z Thursday.  The latter boundary may advance
   northeastward into the lower Ohio Valley ahead of the secondary low,
   accompanied by low-level moistening and destabilization in the
   presence of strengthening vertical shear and large-scale ascent.

   ...Lower Ohio Valley into Southeastern Plains...
   In association with the mid-level perturbation, models indicate that
   a west-southwesterly 850 mb jet will nose from the Ozark Plateau
   through Kentucky and Tennessee, while strengthening from 30-50+ kt,
   Thursday afternoon through Thursday night.  This is expected to
   support the northeastward advection of a fairly moist boundary
   layer, characterized by surface dew points in the lower 60s, which
   may become supportive of CAPE in excess of  500 J/kg, despite fairly
   modest mid-level lapse rates and the possibility of limited surface
   heating.

   Discrete storms may initiate near the Missouri/Arkansas border
   Thursday afternoon before spreading eastward and intensifying in the
   presence of strong deep-layer and low-level shear.  This may include
   a few supercells which could pose a risk for tornadoes in addition
   to severe hail and locally damaging wind gusts.

   Eventually large-scale forcing for ascent may support an upscale
   growing and organizing convective system across western into central
   Kentucky, and adjacent portions of southern Illinois and Indiana, as
   well as western and middle Tennessee by Thursday evening.  This
   probably will be accompanied by increasing potential for damaging
   wind gusts, and continuing risk for a couple of tornadoes, before
   activity weakens during the late evening or overnight.

   While the main cluster of storms spreads through the lower Ohio
   Valley Thursday evening, at least scattered additional strong to
   severe thunderstorms may develop southwestward toward the
   southeastern Great Plains, where boundary-layer CAPE may be larger,
   but forcing for ascent weaker ahead of the cold front.

   ..Kerr.. 03/11/2020

[jaxjagman]

Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1230 PM CDT Wed Mar 11 2020

   Valid 121200Z - 131200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE OZARKS 
   TO THE LOWER OHIO VALLEY/MID-SOUTH VICINITY...

   ...SUMMARY...
   Severe thunderstorms are possible across parts of the lower Ohio
   Valley and Mid South into parts of the southeastern Plains Thursday
   afternoon and evening.

   ...ArkLaTex Vicinity to the Ohio/Tennessee Valley Region...

   A shortwave impulse embedded in larger-scale upper trough over the
   central U.S. will deepen and eject eastward from the central Plains
   to the Great Lakes on Thursday. The main surface low associated with
   this system will track eastward across Ontario with a surface cold
   front extending south/southwest from the Upper Midwest to western
   portions of the southern Plains during the morning. A warm front
   will extend eastward from a weak surface low over northern OK into
   northern AR/western TN early Thursday, lifting northward toward the
   Ohio River during the day. Strong warm advection ahead of the
   east/southeastward progressing cold front will allow low-to-mid 60s
   F dewpoints to overspread the south-central U.S. from eastern OK/TX
   into parts of KY/TN. 

   Surface heating likely will be limited by cloud cover and areas of
   ongoing showers, and strong warm advection between 850-700 mb will
   result in pockets of stronger capping. However, a 40-50 kt
   southwesterly low level jet will develop by late afternoon/early
   evening and pockets of MLCAPE up to 1000 J/kg are forecast
   along/just ahead of the cold front/triple point near the MO/AR
   border southwestward into southeast OK, as well as eastward near the
   warm front across KY/TN. Semi-discrete cells in the warm sector are
   possible initially, but clusters are expected to grow upscale into
   during the evening as vertical shear become aligned with the frontal
   boundary. All severe hazards appear possible, with hail more likely
   earlier in storm evolution where midlevel lapse rates are expected
   to range from 7-7.5 C/km across western portions of the Slight risk
   area. SRH values greater than 250 m2/s2, and enlarged low level
   hodographs will support tornado potential in both discrete cells and
   within any bowing line segments. Furthermore, intense low level wind
   field will support damaging winds through the evening hours as
   convection spreads eastward into the OH/TN Valley vicinity. 

   ...Central/Southern Appalachians Vicinity...

   Several forecast models indicate isolated storms may develop across
   parts of northern GA into Upstate SC/western NC. Dewpoints in the
   lower 60s will increase across the region, and backed southeasterly
   surface winds are forecast as a surface trough develops near higher
   terrain. There is indication that subtle impulses will eject across
   the region ahead of the main upper trough, leading to weak upper
   forcing and low level convergence along the surface trough. Stronger
   heating is likely this far east, and MLCAPE could climb to near 1000
   J/kg with marginal low-to-mid level lapse rates forecast withing an
   adequately sheared environment. While conditional, any cells that
   develop could pose a risk for marginal hail/gusty winds.

   ...Lower Colorado Valley Vicinity...

   An upper low off the coast of southern CA will pivot eastward toward
   the Lower CO Valley on Thursday. Surface dewpoints near 60F will
   spread northward along the CA/AZ border beneath steep midlevel lapse
   rates. Low level shear will be weak, but effective shear will
   support some organized cells with strong flow expected in mid and
   upper levels. Instability will be limited, but a couple of strong
   cells are possible. If trends continue, probability may become
   warranted in later outlooks, mainly for a marginal hail risk.

   ..Leitman.. 03/11/2020

[Bob's Burgers]

Looks active. 

[Matthew70]

Surprised no one is talking about possible threat of severe wx

[jaxjagman]

Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0754 AM CDT Thu Mar 12 2020

   Valid 121300Z - 131200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM
   SOUTHEASTERN MISSOURI AND NORTHEASTERN ARKANSAS TO PARTS OF THE
   LOWER OHIO VALLEY...NORTHERN TENNESSEE AND CENTRAL KENTUCKY...

   ...SUMMARY...
   The greatest severe-weather threat will be during the day from the
   eastern Ozarks region to the lower Ohio Valley and central Kentucky,
   featuring tornadoes, damaging wind and isolated large hail.

   ...Synopsis...
   In mid/upper levels, a strong shortwave trough now over the Gulf of
   Alaska will move southeastward and amplify, approaching the coastal
   Pacific Northwest by 12Z tomorrow.  As this occurs, a persistent/
   cut-off cyclone now offshore from southern CA and northern Baja will
   pivot northeastward across southern CA and the lower Colorado River
   Valley tonight.  In the northern stream, a series of closely
   associated vorticity maxima and shortwaves will cause an eastward
   shift of a synoptic trough now extending from north-central Canada
   to the central Rockies.  By 12Z, this should evolve into a
   strong/closed cyclone over northern ON north or northeast of Lake
   Superior, with cyclonic flow southward to the Ohio Valley.

   Surface analysis at 11Z depicted a low near FSD with cold front
   arching southwestward over northeastern CO, then into southern WY. 
   Another low was located over central KS near GBD, with warm front
   east-southeastward over the Ozarks western/mid TN, and the
   Carolinas.  The northern low should move northeastward to near Lake
   Superior and deepen considerably by 00Z in response to mid/upper-
   level cyclogenesis.  Meanwhile, the southern low should become a
   triple-point feature as the cold front catches up, and is expected
   to shift east-northeastward across central/southern MO to
   southeastern IL by 00Z.  The warm front then should extend across
   parts of IN/OH and northern WV.  Convective boundaries may exist
   south of the warm front, with more baroclinicity.  The cold front
   should extend across southeastern MO, southeastern OK and northwest
   TX.  By 12Z, the cold front should reach southern PA, middle TN the
   Arklatex region, and the southern TX Panhandle, with little or no
   movement over the southern High Plains. 

   ...Ozarks to central KY/northern TN and north TX...
   Multiple episodes of severe thunderstorms are possible today, most
   concentrated in and near the "enhanced risk" area, from mid/late
   morning through afternoon.  Supercells and organized multicells are
   expected, with the potential for a few supercells to mature/persist
   long enough for a tornado threat.  Significant/EF2+ rated tornadoes
   may occur.  Large hail is possible, especially from supercells, and
   with modes potentially becoming clustered or messy with time, the
   wind-damage potential will extend farther eastward.  The severe
   threat will extend down the front across AR to parts of north TX,
   but in briefer, less-organized fashion with southwestward extent.

   Activity is expected to develop initially in a zone of strong
   low-level theta-e advection, south of the warm front and southeast
   of the cold front, with MUCINH weakening as the warm sector
   destabilizes from both that effect and weak diabatic surface
   heating.  Sustained surface-based parcels are uncertain with this
   activity, especially in middle/northern parts, given its position on
   the northern rim of the warm sector in a low-CAPE, moderate to
   strong-shear setting.  A second round of storms will form along the
   surface cold front with access to greater CAPE and perhaps stronger
   shear as well.  Buoyancy generally will decrease northward through
   the warm sector.  By contrast, hodograph sizes increase, in
   concordance with: 
   1.  More-backed surface winds nearer to the warm front, and
   2.  A LLJ strengthening to 50-60 kt through the day, as part of the
   mass response to the strong trough passing north of the area.
   That trough also will tighten height gradients and boost deep shear,
   rendering 45-50-kt effective-shear magnitudes in forecast soundings
   in the "enhanced" area, weakening southward as pre-cold-frontal flow
   becomes weaker and more-veered in the boundary layer.

   A narrow corridor of theta-e advection ahead of the cold front,
   combined with diurnal heating and relatively steep midlevel lapse
   rates, will support a ribbon of 1000-2000 J/kg MLCAPE, transitioning
   to pockets of 500-1000 J/kg MLCAPE south of the warm front as far
   east as the southern Appalachians, away from areas of persistent
   convection.  

   ...West-central/southwest TX late tonight...
   Isolated, perhaps widely scattered thunderstorms may develop
   overnight -- especially after 06Z.  The main concerns would be large
   hail and damaging gusts.  Large-scale ascent will increase across
   this area the last several hours of the period in two ways:
   1.  Early-stage mass response to the approaching Pacific
   perturbation -- a corridor of elevated low-level warm/moist
   advection from the Rio Grande Valley.
   2.  Shots of DCVA related to small-scale perturbations (some
   convectively induced/enhanced back across northwestern MX) ejecting
   out of the cyclone within southwest flow.

   Air-mass recovery above a relatively shallow/stable surface layer
   may support MUCAPE in the 300-700 J/kg range, amidst 40-55-kt
   effective-shear magnitudes.  Enough residual subcloud drying may
   persist to support gusts intense enough to penetrate to the surface.
   Hail is possible, though buoyancy and lapse rates do not appear to
   support more than marginally severe hail.  Concentration of
   convection in this regime is uncertain, with the potential very
   conditional.  Still, a consistency of synoptic and convection-
   allowing guidance indicates non-negligible potential for a sustained
   thunderstorm or two developing in a favorable environment,
   compelling extension of marginal unconditional probabilities into
   the region at this cycle.  Activity may get as far as north-central
   TX by the end of the period.

   ...Portions of AZ/southeastern CA...
   Widely scattered to scattered thunderstorms should develop from
   midday through this afternoon and evening, in an arc of strong
   large-scale lift across northern Baja, southeastern CA and
   northwestern Sonora.  Isolated severe hail/gusts are possible.  This
   activity should move northwestward over parts of southern CA,
   northward to northeastward over parts of AZ, beneath
   correspondingly, strongly difluent mid/upper-level flow east of the
   cyclone.  Antecedent moist advection from subtropical latitudes has
   resulted in anomalously rich low-level moisture, manifest as 50s to
   60s F surface dew points across this region.  In concert with
   continued warm advection and muted diabatic heating beneath the
   cloud cover, this should yield surface-based effective-inflow
   parcels across much of the region.  Peak MLCAPE will be highly
   variable (300-1000 J/kg, locally higher) amidst favorably strong
   mid/upper winds and cloud-layer shear.  Mostly multicellular mode is
   expected, though an isolated supercell or two may occur given the
   presence of marginal effective shear and low-level SRH in a few
   forecast soundings.