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Severe Weather Threat Day 1 Sun May 26

Cntrl Plains Area...

Visible Imagery Show Cumulus Increasing Along N-S Convergence Axis Extending Through Wcntrl Neb From A Sfc Low Over Swrn Neb...As Well As Along The E-W Quasi-Stationary Front Across Cntrl Neb.

The Atmosphere Is Becoming Strongly Unstable With Mlcape Approaching 3000 J/Kg...But Still Appears To Be Capped To Sfc Based Storms. As The Sfc Layer Continues To Warm...Hrrr Guidance Indicate Storms Will Develop Over Wcntrl Neb By Late Afternoon.

Effective Shear Is Sufficient For Supercells...And 0-2 Km Hodographs Will Increase In Size As The Llj Strengthens During Early Evening. Very Large Hail And Isolated Tornadoes Will Be The Main Initial Threats...Before Activity Evolves Into One More Clusters Later This Evening.

Nrn Plains...

Primary Change To This Region Was To Introduce A Gap In The Sig And 30% Hail Coverage Lines. A Relative Minimum In Storm Coverage Might Occur Where Convectively Modified Air Has Been Advected Swwd And Is Serving To Maintain Stratus Into Parts Of Wrn Sd. More Robust Development Appears More Likely Farther Nw Where Storms Will Spread Ewd Off The Higher Terrain Of Mt And Nern Wy.

Srn Plains...

Will Maintain A Conditional Threat For Isolated Large Hail And
Damaging Wind With Any Storms That Can Develop Within Zone Of Deeper Mixing On Dryline Circulation. Any Storms That Develop Should Remain Isolated.

Prev Discussion...

Little Change To The Synoptic Pattern Is Forecast Through The D1
Period With Upper Lows Over Bc/Ab And Over New England Into The
Canadian Maritimes. Between These Features...A Ridge From Mb/On
Into The Mid-Mo Valley Will Gradually Lose Amplitude In Response To
The Ewd Progression Of A Series Of Vorticity Maxima Originating
Within The Cyclonic Flow Regime Over The Wrn States. One Impulse Of Potential Importance Is Apparent In Water Vapor Imagery Over The
Great Basin As Of Mid Morning. This Feature Is Forecast To Translate Newd Into The Nrn High Plains By This Evening.

In The Low Levels...Considerable Convective Outflow Has Masked The Synoptic Boundaries Across The Nrn Plains This Morning. However...It Appears That A Pair Of Lee Cyclones Will Deepen Today
Over Cntrl Or Ern Wy And Over Ern Co...Along A Lee Trough/Dry Line
Which Will Extend Along The High Plains. A Quasi-Stationary
Boundary Will Intersect The Lee Trough Over Ern Wy Before Extending
Sewd Through The Mid-Mo Into Mid-Ms Valleys.

Nrn/Cntrl Plains This Afternoon And Tonight...

Steep Midlevel Lapse Rates And Modest Boundary Layer Moisture Content Will Combine With Daytime Heating To Yield A Moderately Unstable Air Mass By Afternoon Along And East Of The Lee Trough Where Mlcape Values Will Approach 1000-1500 J/Kg Over Ern Mt... To As High As 2000-3000 J/Kg Across Parts Of Wrn Neb Into Wrn And Cntrl Ks.

In The Wake Of The Initial Elevated Storms Currently Moving Through The Mid-Mo Valley...Latest Model Guidance Suggests That Surface-Based Storm Development Will Be Most Probable By Mid To
Late Afternoon Invof The Lee Trough And Favored Terrain Over Ern
Parts Of Mt And Wy...As Well As To The Northeast Of The Ern Co Lee
Cyclone.

Another Area Of Potential Storm Initiation Will Be Along Or Just North Of The Outflow Boundary/Synoptic Front Over Cntrl Or N-Cntrl/Nern Neb Late This Afternoon Into Evening Where Convergence/Uplift Is Augmented At The Terminus Of A Developing Llj.

Ely/Sely Low-Level Winds Veering To Swly At 25-35 Kt In The Midlevels Will Result In Sufficient Vertical Shear For Supercells As
The Initial Storm Mode.

Large Hail /Some Significant/ Will Be The Primary Hazard With These Storms...Though A Few Tornadoes Will Be Possible. This Is Especially The Case This Evening Over Wrn Neb Where The Strongest Buoyancy And Deep-Layer Shear Will Align With A Corridor Of Enhanced Low-Level Shear.

By Tonight...Storms May Grow Upscale Into One Or Multiple Mcs/S With A Continued Risk For Hail And Damaging Winds Spreading Ewd Into The Lower Elevations Of The Plains.

Srn High Plains This Afternoon And Evening...

Strong Daytime Heating Will Combine With Steep Midlevel Lapse Rates And Boundary Layer Dewpoints In The Upper 50s To Low To Mid 60s To Yield Afternoon Mlcape Values Of 1500-3000 J/Kg Ahead Of The Dryline. Morning Water Vapor Imagery Shows A Low-Amplitude Short-Wave Trough Moving Through The Lower-Co Valley Which Will Likely Remain To The West Of The Region Through Today. Thus...While The Upper-Level Pattern Will Become Slightly Diffluent By 27/00z...Large-Scale Forcing For Ascent Will Remain Negligible. As Such...Storm Initiation Will Be Strongly Tied To The Developing Dryline Circulations With Only Isolated Coverage Anticipated.

The Combination Of The Moderate To Strong Instability And Deep-Layer Shear Increasing To 30-35 Kt Will Promote Intense Storms...Including The Possibility Of Supercells...With The Primary Hazards Being Large Hail And Locally Damaging Winds. Storms Should Tend To Weaken By Late Evening Into Tonight As The Boundary Layer Cools And Stabilizes.


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