Severe Weather Threat thru May 11

Sun May 4 Convective Outlook
Storm Prediction Center Norman Ok
No Svr Tstm Areas Forecast...

Isolated Thunder May Occur Over Parts Of Maine/New Hampshire... And From Eastern Kentucky Into The Western Virginias Today.

Widely Scattered Thunderstorms Are Possible Late Tonight Into Early Monday Morning Over Parts Of Indiana And Ohio.

Elsewhere...A Few Thunderstorms May Develop From Western Oregon/Washington Into Southern Montana And Southwestern South Dakota.

Only Minor Changes Have Been Made To The Ongoing Forecast.

The Thunder Forecast Has Been Adjusted Slightly In New England To
Account For Short-Term Trends.

Prev Discussion...

Western Oregon/Washington...

Onshore Flow And Expansive Cloudiness Currently Dominate The Pacific Nw.

However...Modified 12z Soundings Suggest Buoyancy Sufficient For Deep Convection May Evolve If Sfc Temperatures Can Warm To Near
60f.

Afternoon Sbcape May Reach 300 J/Kg Which Could Allow Cloud Heights To Reach Levels Near 6km...Levels Supportive Of Lightning
Discharge Given 500mb Temperatures Around -24c.

For This Reason Have Expanded 10 Percent Thunder Line West To Include Portions Of The Nrn Cascades.

Earlier Thoughts Regarding Convective Potential Across The Nrn
Rockies/High Plains Remain.

Strong Heating Should Remove Early-Day Inhibition And Sct Weak Convection May Evolve After 21z.

Oh Valley/Cntrl Appalachians...

Warm Advection Will Be The Primary Forcing Mechanism For Convection Along A Corridor From Ecntrl Il To Wrn Va Through Tonight.

Models Continue To Erroneously Over Moisten 850mb Across Pars Of The Oh Valley.

Latest Nam Guidance Suggests 850mb Dew Points Will Approach 12c Across Ecntrl Il/Wrn Indiana By 06z Tonight.

Upstream Soundings Do Not Support This And Lightning Should Be More Sparse Than Forecast Soundings Would Otherwise Suggest... Though Shallow Elevated Convection Will Be Common.

Nrn New England...

Daytime Heating Beneath Upper Low Should Be Adequate In Generating Scattered-Numerous Convection Across Nrn New England Today.

A Few Showers May Attain Heights Supportive Of Lighting Discharge... Though This Activity Should Remain Sparse.

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Mon May 5 Convective Outlook
Storm Prediction Center Norman Ok
No Svr Tstm Areas Forecast...

Showers And Thunderstorms Are Expected Across Parts Of The Pacific Northwest...Northern Inter-Mountain West...And The Western Dakotas During The Afternoon And Evening.

Showers And Embedded Thunderstorms Are Also Expected From Portions Of The Mid- And Upper-Ohio Valley To The Mid-Atlantic Region.

An Initially Quasi-Zonal Large-Scale Pattern Will Become More Amplified Throughout The Period...In Response To A Digging Upper
Trough Along The Pacific Coast And Into The Wrn Great Basin.

Isolated To Scattered Diurnally-Enhanced Tstms Are Likely To Develop
From Nrn Ca Into The Pac Nw...And Ewd Into The Nrn High Plains.

Farther Downstream...A Series Of Weak Upper Speed Maxima Will
Traverse Ewd From The Mid-Ms Valley Into The Mid-Atlantic Region.

A Seasonably Dry Air Mass Will Encompass Most Of The Conus... Which Will Limit Svr Potential.

Cntrl Appalachians Into Wrn Va...

A Warm Front Is Forecast To Slowly Lift Nwd From The Wrn Carolinas
Into Swrn Va...Ahead Of A Weak Speed-Max Moving Through The Region During The Late Morning And Early Afternoon.

Latest Suite Of Model Guidance Is Likely Over-Estimating The Quality Of Boundary Layer Moisture Over The Region...As Supported By Both Sfc Observations And Satellite-Derived Pw Data.

It Also Is Uncertain Whether Sfc-Based Convection Will Develop To Support A Threat For Gusty Winds...With Showers/Tstms More Likely To Develop N Of The Boundary.

Given These Limiting Factors And Uncertainties...Low-End Svr Probabilities Will Not Be Introduced.

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Tue May 6 Convective Outlook
Storm Prediction Center Norman Ok
No Svr Tstm Areas Forecast...

Afternoon And Evening Showers And Thunderstorms Are Forecast Across Portions Of The Rockies And Intermountain Region Tuesday... As Far East As The Northern High Plains.

Elevated Evening Thunderstorms Are Also Forecast To Develop Across Parts Of The Mid Missouri And Upper Mississippi Valleys...A Few Of Which May Be Capable Of Producing Hail Up To Severe Levels.

Finally...Showers And A Few Thunderstorms May Occur Over Parts Of Southern Virginia And North Carolina...And Across Portions Of Texas Including The Big Bend Region And The Permian Basin Vicinity.

Continued Amplification Of The Upper Pattern Will Occur Tue/Day 3 ... As The Wrn U.S. Trough Continues Digging/Advancing Sewd Across
The Great Basin.

As This Occurs...A More Organized/Deepening Area Of Surface Low Pressure Should Gradually Evolve Across The Ern Co/Wrn Ks Vicinity -- Emerging From The More Broad Zone Of Lee-Side Low Pressure Over The High Plains.

Though The Warm Sector Of This Developing Low Pressure System Should Remain Capped By A Warm Eml Atop A Marginally Moistening Boundary Layer...Elevated Storms Are Forecast N Of A W-E Warm Front Across The Central Plains/Mid Mo Valley Vicinity.

Farther E...The Ern Extension Of The Developing Plains Warm Front Will Linger Across The Oh Valley/Carolinas Vicinity...Though Large-Scale Subsidence Associated With A Strengthening Upper Ridge Should Suppress Convective Potential To A Large Degree.

Ia/Srn Mn Vicinity...

A Diurnally Strengthening Sly Low-Level Jet -- And Associated
Increase In Warm Advection -- Should Result In Scattered To
Widespread Thunderstorm Development Across Portions Of Ern Sd/Ern Neb And Ewd Across The Upper Ms Valley During The Evening Hours.

Across Wrn Portions Of This Area -- I.E. Invof The Mid Mo Valley... Steeper Lapse Rates Aloft Will Combine With Increasing Moisture In Roughly The 850 To 800 Mb Layer To Support Moderate Elevated Cape Development...And Thus The Possibility Of A Few Stronger / Robust Updrafts.

While Mid-Level Flow Should Remain Marginal Across This Area Thus Limiting Cloud-Layer Shear And Any Associated Potential For Rotating Updrafts...A Few Marginally Severe Hail Events May Occur During The Evening Hours.

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May 7-11 Convective Outlook
Storm Prediction Center Norman Ok

Medium-Range Models Have Continued Over The Past Several Runs To Come Into Better Agreement With Depiction Of The Upper Trough
Advancing Into The Central U.S. Days 4-5 /I.E. Wed.-Thu./...With The
Gfs And Ecmwf Now Showing Strong Similarity Through Day 5 But
Diverging Gradually Thereafter.

Both Models Advance A Longitudinally Extensive Wrn Trough To Roughly The Front Range Of The Rockies By The End Of Day 4.

With The Evolving Plains Warm Sector Likely To Remain Generally Capped Through The Afternoon/Evening Of Day 4...Most Deep Convective Activity Should Remain To The Cool Side Of The Warm Front...And Thus Severe Risk Should Remain Limited.

Day 5....
Both Models Depict A Shunting Of The Most Energetic Portion Of The Upper Trough Quickly Newd Across The Central Plains And Eventually The Upper Ms Valley...As It Impinges On A Fairly Stout Ern U.S. Ridge.

As Such...A Similar Newd Acceleration Of A Deepening Surface Low... From Its Initial Position Over The Central Plains To The Lk Superior Vicinity Late In The Period...Is Expected.

As This Occurs...Ewd Advance Of A Cold Front Across A Thermodynamically Unstable Warm Sector Will Yield Widespread Warm-Sector Thunderstorm Development.

A Complicating Factor With Respect To Evolution Of Severe Risk Day 5
Is That Both Models Activate Convection Across Tx Late Day 4 And
Into The Day 5 Period.

While Some Severe Risk Would Exist With This Convection Late Day 4 Across Parts Of Wrn And Central Tx...Greater Risk Is Evident Day 5 Across Parts Of N Central Tx And Into The Ern Half Of Ok And The Arklatex Region...As The Moistening Boundary Layer Diurnally Destabilizes.

Here...Severe Risk -- Including Some Tornado Potential -- Is Expected.

This Srn Batch Of Convection May Have Effects On Areas Farther N --
I.E. Into Parts Of Nern Ok/Sern Ks And The Ozarks...But A Second
Area Of Likely Severe Risk Is Expected Across Parts Of Ern Ks/Nrn Mo
And Into Ia/Srn Mn -- Nearer The Surface Low Where The Strongest
Flow Aloft/Most Favorable Shear Is Expected.

Risk For Hail/Damaging Winds Along With Isolated Tornadoes Is Expected In This Region Through The Afternoon And Evening.

While Two Distinct Areas Of Severe Risk May Result -- A Nrn And Srn
Area -- A Larger Risk Area Will Be Included Attm Pending Later
Forecast Details.

With The Upper Trough Progged To Continue Quickly Newd Into Canada Day 6...Lesser Severe Risk Is Progged And Thus No Risk Areas Will Be Included Attm.


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