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Severe Weather Threat thru May 15

Thu May 8 Convective Outlook
Storm Prediction Center Norman Ok
Mdt Risk Of Svr Tstms for parts of S Mn...Central/Nrn Ia...
Slgt Risk Of Svr Tstms from S-Central Tx to Mo Valley...

The Greatest Threat Today Will Be This Afternoon With An Arc Of Thunderstorms Forecast To Develop Into Supercells Over Parts Of Minnesota And Iowa...Then Move Northeastward.

Tornadoes--Some Potentially Strong--As Well As Large...Damaging Hail And Sporadic Severe Gusts Are Expected.

Damaging Hail Will Be The Main Severe-Storm Threat Over Parts Of Oklahoma...Kansas And Southward Toward Central Texas.

Cyclonic Mean Flow Characterizes Upper-Air Pattern Over Wrn 1/2-2/3
Of Conus...While Synoptic-Scale Ridge Extends From Yucatan Peninsula Across Upper Great Lakes To Hudson Bay And Beyond.

Ridge Will Shift Ewd To Lower Great Lakes...Carolinas And Fl thru Period.

Meanwhile Series Of Shortwaves Will Contribute To Advancement Of
Troughing Across Rockies And Plains States...S And Se Of
Quasistationary Mid-Upper-Level Cyclone Over Nrn Sk.

Leading Shortwave Trough -- Now Evident In Moisture-Channel Imagery Over Extreme Ern Co And Swrn Neb -- Is Fcst To Eject Newd To E-Central Sd And Central Neb By 00z...Then Mn/Ia 12 Hours Later. Trailing/Basal Perturbation Now Over Az Is Fcst To Move Enewd To Ern Nm Around 00z...Then To Central Ks And Swrn Ok By End Of Period.

At Sfc...11z Analysis Showed Frontal-Wave Low Near W-Central Part Of
Ks/Neb Border. This Low Should Shift/Redevelop Newd Across Sern Sd To Srn Mn By 00z...While Warm Front Now Over Nern Ia Moves Nwd
Across Sern Mn And Swrn Wi.

By 00z...Trailing Cold Front Should Reach Wrn Ia...Extreme Nwrn Mo And S-Central Ks..Intersecting /Overtaking Dryline There. Dryline Will Extend Swd Across W-Central Ok And Edwards Plateau Of Tx. Sfc Cyclone Center Should Reach Dlh Area By End Of Period...Cold Front Ern Ia..Swrn Mo...And Swrn Ok.

Mn/Ia Region...In And Near Mdt Risk...

Once Warm-Sector Air Mass Favorably Destabilizes...Supercells Should Develop This Aftn Near Sfc Low And Along Adjoining Cold-Frontal Arc.

Some Of These Cells Should Be Discrete And May Mature Long Enough For Cyclic Tornado Production And Large/Damaging Hail... Before Passing Too Far Over Warm Front And/Or Merging With Other
Convection.

As Tstms Move Newd Into Lower-Lcl Thermodynamic Setting... Enhanced Low-Level Vorticity Along Warm Front...As Well As Backed Sfc Flow On Warm Front And In That Wedge Of Warm-Sector Air Adjacent To Sfc Low...Will Maximize Hodograph Size And Srh.

Steep Low-Midlevel Lapse Rates And Sfc Dew Points In Upper 50s To Mid 60s F Should Contribute To 2000-3000 J/Kg Mlcape...Amidst 50-60 Kt Effective-Shear Magnitudes...And 200-400 J/Kg Of Effective Srh That Will Be Locally Greater.

Warm-Sector Development Also Is Possible Over Swrn Wi And Ia Se Of Mdt-Risk Area And E Of Cold Front...Also Offering Risk Of Svr Hail/Gusts And A Tornado Or Two.

Central Plains To Mid Ms Valley...Aftn/Evening...

Widely Scattered To Scattered Tstms Are Possible Along Front And
Possibly Across Foregoing Warm Sector This Aftn...Especially
Wherever Narrow Corridor Of Sustained Insolation Opens To Boost
Prefrontal Buoyancy.

With Mean-Wind And Deep-Shear Vectors Aligned Nearly Parallel To Front...Fairly Quick Modal Transition To Linear Is Likely.

However...Intervening/Transient Supercell And Bow Structures Are Possible With Attendant Risks Of Large Hail And Damaging Gusts. Cold-Frontal Convection Should Increase In Coverage Into Evening And Backbuild Swd To Triple Point.

Srn Plains...Aftn/Evening...

Widely Scattered To Scattered Tstms Should Develop In Swath Of
Diabatically Destabilized Moist-Sector Air Bracketed By Cold Front... Dryline And Precip-Affected Area.

Deep-Layer Lapse Rates Should Steepen Favorably Due To Both Boundary-Layer Heating And Late-Aftn/Evening Onset Of Substantial Midlevel Dcva Preceding Basal Shortwave Trough.

Capping Is Not Expected To Be Stg.

As Such...Warm-Sector Storms Are Possible Along Subtle/Mesoscale Boundaries...In Addition To Potential For Episodic Dryline Initiation In More Intensely Heated Air Mass.

Spatial Extent Of This Regime Is Uncertain And Conditional... Especially With Swd And Ewd Extent Away From Dryline Into N Tx And Central/Ern Ok...Dependent On Persistence/Intensity Of Antecedent Clouds/Precip.

Deep Shear Will Be Favorable Throughout Aftn/Evening...Though Substantial Weaknesses Should Characterize Hodograph 1-3 Km Agl Until Llj Strengthens Around 00z.

Early Left-Moving Tstms May Be More Prominent/Dominant Than Right-Moving Convection...However Cyclonic Supercells Will Be More Probable With Time Into Early Evening. Damaging Hail...Svr Gusts And A Tornado Or Two Are Possible.

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Fri May 9 Convective Outlook
Storm Prediction Center Norman Ok
Slgt Risk Of Svr Tstms for Arklatex & Low Ms Valley Ne to Oh Valley...

Isolated To Scattered Severe Thunderstorms Will Be Possible For
Friday Afternoon And Evening From Portions Of The Arklatex And Lower Mississippi Valley Northeastward Into The Ohio Valley Region.

Weakly Phased Mid-Level Shortwave Impulses Lying Along An Axis From The Upper Ms Valley To The Srn Plains Will Lift Newd Into The Great Lakes Region And Adjacent Canada.

An Associated Sfc Front Will Extend Swd From The Upper Great Lakes To The Srn Plains.

As A Relatively Compact Sfc Cyclone Attached To This Boundary Tracks Newd Across Ontario...The Conus Segment Of The Front Will Weaken.

Farther S Across The Srn Plains...Maritime Tropical Air -- Earlier Shunted To Sern Parts Of The Srn Plains -- Will Begin To Retreat Nwd As Cyclogenesis Is Favored In The Lee Of The Rockies. This Will Be In Response To Strengthening Zonal Flow Aloft Downstream Of A Cyclone Moving Into The Pacific Nw.

Parts of Arklatex & Low Ms Valley Ne to Oh Valley...

A Pre-Frontal Llj Will Shift Newd In Association With The Track Of The Aforementioned Cyclone.

Accompanying Showers And Storms Will Be Ongoing At The Beginning Of The Period From The Lower Great Lakes To The Cntrl Gulf Coast.

This Activity Will Shift Newd In Tandem With The Trajectory Of Isentropic Ascent Attendant To The Llj.

In Their Wake And E Of The Weakening Front...Diabatic Heating Of A Moist Boundary Layer -- E.G. Middle 60s Dewpoints -- Will Support A
Corridor Of Moderate Buoyancy.

A Band Of 45-55-Kt H5 Swlys Glancing This Buoyancy Will Offer Sufficient Deep Shear For Convection Developing Invof The Front During The Afternoon To Organize Into Quasi-Linear Segments.

Dmgg Wind Gusts And Svr Hail Will Be Possible. More Isolated Storms...And Perhaps One Or Two Supercell Structures...May Evolve From Parts Of Ar To The Mid-South Where Deep Forcing For Ascent Will Be Weaker And Buoyancy Will Be Stronger.

All Of This Activity Will Spread Ewd Across The Slight-Risk Area Into
The Evening Hours Before Weakening...As It Encounters Weaker
Buoyancy Related To Earlier Precipitation And Nocturnal Stabilization.

Parts of Edwards Plateau / Tx Hill Country / South Texas...

Low-Level Ascent Associated With Moist Upslope Flow Into The
Serranias Del Burro And Diurnally Deepening Solenoids Along An
E/W-Oriented Moisture Gradient May Foster The Development Of
Isolated To Widely Scattered Thunderstorms Around Peak Heating.

Strong Buoyancy Could Support Vigorous Updrafts/Downdrafts And
Isolated Severe Wind/Hail.

However...With Stronger Mid-Level Flow Relegated To Higher Latitudes ...Deep Shear Juxtaposing This Buoyancy Will Only Be Modest Potentially Limiting Convective Organization.

Furthermore...Weak Deep-Layer Ascent May Limit The Svr Coverage.

Accordingly...Slight-Risk Designation Has Not Been Included At This
Time.

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Sat May 10 Convective Outlook
Storm Prediction Center Norman Ok
No Svr Tstm Areas Forecast...

Isolated Severe Thunderstorms Will Be Possible From Portions Of
Central Oklahoma Northeastward To The Mid Mississippi Valley For
Saturday Afternoon And Evening.

A Low-Amplitude...Quasi-Zonal Mid-Level Flow Pattern Will Exist
Between A Shortwave Trough Lifting Newd From The Ern Great Lakes
Region And An Upstream Shortwave Trough Amplifying/Progressing Ewd Over The Wrn States.

Poleward Low-Level Moisture Transport Will Continue To Be Encouraged Over The Srn Plains To The Mid Ms Valley.

This Will Occur As A Hybrid Lee Trough/Front Tracks Ewd Across The
N-Cntrl States To The S Of Sfc Low Pressure Advancing Ewd Across The Srn Canadian Prairie Provinces.

Cntrl Ok Newd To Mid Ms Valley...

A Neutral To Slightly Positive Mid-Level Isallohypsic Pattern Will
Overlie The Area During Peak Heating -- A Reflection Of The Dearth
Of Mid-Level Forcing For Ascent Related To The Quasi-Zonal Flow
Aloft.

However...Returning Low-Level Moisture -- E.G. Sfc Dewpoints In The Lower/Middle 60s -- Beneath Steep Mid-Level Lapse Rates Will Establish Moderate-Strong Potential Instability During Peak Heating.

Modest Low-Level Ascent /1/ Along A Dryline Extending From Sw Ok To
S-Cntrl Ks.../2/ Amidst Broad Warm-Sector Confluence Extending Well
S Of The Aforementioned Sfc Low...And /3/ Invof The Front May
Encourage Diurnal Convective Development.

Given 35-45-Kt H5 Wlys Offering Moderate Deep Shear For Convective Organization...A Conditional Svr Wind/Hail Threat Will Exist.

However...Unconditional Svr Probabilities Will Remain Low Owing To The Lack Of Stronger Deep-Layer Forcing For Ascent Limiting Convective/Svr-Tstm Coverage.

Upper Oh Valley To Mid Atlantic Swd To Cntrl Gulf Coast...

Sfc Diabatic Heating Amidst A Broad Area Of Lower/Middle 60s
Dewpoints Will Bolster Diurnal Destabilization.

However...Antecedent Clouds And Precipitation Will Stunt The Destabilization To Some Extent.

Nevertheless...Isolated To Scattered Storms Will Be Possible In The Low-Mlcinh Environment...But Will Largely Remain Unfocused As Low-Level Convergence Will Be Weak.

A Few Strong Storms Cannot Be Ruled Out Beneath A Band Of 35-Kt Wly/S From Parts Of The Upper Oh Valley To Middle Tn And Ewd To The Atlantic Coast...Though Organized Svr Storms Will Be Unlikely.

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May 11-15 Convective Outlook
Storm Prediction Center Norman Ok

D4/Sun...

The Latest Medium-Range Model Guidance Is Exhibiting Stronger
Consensus Regarding The Potential For Severe Thunderstorms Over
Portions Of The Cntrl And Srn Plains.

This Potential Will Be Related To A Deep Cyclone Currently Progressing Sewd To The S Of The Gulf Of Alaska.

For The Remainder Of This Week Into The Weekend...This Feature Is Forecast To Advance Sewd Into The Wrn United States.

By Early D4/Sun...Model Solutions Vary Slightly Regarding The
Amplitude/Depth Of The Cyclone As It Loosely Phases With An Impulse Evolving From A Fujiwhara Interaction Over The Canadian Prairies.

Regardless...Numerical Guidance Offers Strong Agreement That A
Prominent Mid-Level Vort Max Will Be Progressing Across The Cntrl
Great Basin/Four Corners Region...With Downstream Height Falls
Commencing Over The Cntrl/Srn High Plains During The Day.

Meanwhile...Lee Sfc Cyclogenesis Will Be Encouraged Roughly From The Tx/Ok Panhandles Into Swrn Ks By Strengthening Mid-Level Swlys
Downstream Of The Trough.

This Will Further Reinforce Poleward Fluxes Of Relatively Rich Low-Level Moisture -- E.G. Sfc Dewpoints In The Middle 60s -- To The E Of Dryline

That Will Link With A Front Extending Wwd/Swwd To The Lee Cyclone.

Provided The Influx Of An Overlying Eml Plume...Strong Buoyancy Is Expected To Materialize E Of The Dryline And S Of The Front During The Afternoon.

As Mid-Level Ascent Increases Through The Diurnal Heating Cycle And Antecedent Capping Is Breached...The Preponderance Of Deterministic And Ensemble Model Guidance Suggests Convective Initiation Within A Confined Corridor Invof The Dryline From The Ern Tx Panhandle/Far Wrn Ok To A Triple Point Near Srn Ks And Newd Along The Front.

This Activity Should Spread Ewd/Newd Into The Overnight Hours... With Some Possible Swd Development Related To The Advance Of The Front.

Moderate-Strong Mid-Level Swlys Downstream Of The Wrn Trough Will Support Sufficient Deep Shear For Organized Convection...With
Scattered Severe Thunderstorms Forecast.

Severe Hail -- Potentially Significantly Severe -- And Damaging Winds Will Be The Primary Concerns With This Activity.

Some Tornado Potential May Conditionally Exist With Any Discrete Supercells Developing Along The Dryline And Shifting Ewd Into Richer Low-Level Moisture Over Wrn Ok During The Evening.

Despite Some Uncertainty Regarding The Magnitude Of Dryline Convergence And Associated Storm Coverage...And Despite Relatively Minor Differences In Frontal Progression Amongst Model Solutions...Confidence Is Sufficient For The Inclusion Of An Aoa-30-Percent Svr Tstm Area.

Isolated Svr Storms Will Be Possible Farther S Along The Dryline Across W Tx...With Isolated Svr Storms Also Possible Farther Ne Along The Front...Though Confidence In Higher-Coverage Svr Activity In Both Of These Areas Is Too Limited For A Larger Areal Delineation.

D5/Mon Through D8/Thu...

Growing Model Dispersion After D4/Sun...Combined With A General
Consensus For The Perturbation Accompanying The Aforementioned Vort Max To Devolve Into An Open-Wave/Positively Tilted Trough... Reduces Confidence In The Svr Potential For Next Week.

Regardless...Some Svr Risk May Evolve Ahead Of The Trough And Attendant Sfc Front As They Progress Across Ern Portions Of The Cntrl/Srn Plains Ewd/Newd To The Atlantic Coast Early/Middle Next Week.

However...Antecedent Episodes Of Convection Depleting Pre-Frontal Buoyancy Coupled With Front-Parallel Mid-Level Flow...Along With A Tendency For The Sfc Low To Develop/Occlude Well N Of The Warm Sector...All Suggest That The Overall Svr Risk Will Be Limited.


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