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Severe Weather Threat thru Jul 11

Fri Jul 4 Convective Outlook
Storm Prediction Center Norman Ok
Slgt Risk Svr Tstms for E Nd to NW Mn...

Severe Thunderstorms Are Possible This Afternoon And Evening Across Parts Of Northeast North Dakota Into Northwest Minnesota. Strong Winds And Hail Will Be The Main Threat...But A Tornado Or Two Also Is Possible.

Isolated To Widely Scattered Thunderstorms Are Expected Southward Across The Central Plains...Where A Few Strong Wind Gusts And Hail Will Be Possible During The Afternoon And Evening.

Additional Strong Wind Gusts Will Be Possible Across Parts Of Southern Arizona With Afternoon Storms.

The Upper Trough Over The Great Lakes And Appalachians Will Shift
E/Ne Today. Hurricane Arthur Should Start To Become Absorbed Within The Trough By The End Of The Period...With Impacts Mostly Remaining Offshore The Eastern Seaboard. Sfc High Pressure Building In The Wake Of The Eastern Trough Will Lead To Widespread Stable Conditions East Of The Mississippi River.

Across The Western And Central U.S...A Broad Upper Ridge With Quasi-Zonal Flow Will Overspread The Nrn/Cntrl Rockies Into The Nrn/Cntrl Plains. Weak Shortwave Impulses Will Track Ewd Through The Ridge Into The Plains...Aiding In Thunderstorm Development In A
Moist And Unstable Airmass During The Afternoon And Evening From The Cntrl/Nrn High Plains Eastward Into The Nrn/Cntrl Plains.

Additional Thunderstorms Are Expected Across Parts Of The Arizona Deserts In Increasing Boundary Layer Moisture On Ely Low Level Flow.

Nrn/Cntrl Plains...

Southerly Low Level Flow Will Transport Low To Mid 60s Dewpoints
Northward Across The Plains To The East Of A Sfc Trough Situated N-S From The Wrn Dakotas Into Wrn Ks By Late Afternoon. Strong Sfc
Heating Of This Moist Airmass Beneath Steep Lapse Rates Will Lead To Moderate Instability This Afternoon. Deep Layer Shear Will Be
Enhanced Over Ern Nd Into Nw Mn Where A Shortwave Impulse Will
Rotate Through Upper Ridge...And Closer Proximity To The Sfc Low
Over The S-Cntrl Canadian Prairie Will Result In Better Low Level
Convergence/Backed Sfc Winds. 25-35 Kt Deep Layer Shear Should Allow For Organized Storm Clusters Capable Of Large Hail And Strong Wind Gusts.

Given Backed Low Level Flow And Mean Mixing Ratios Approaching 13 G/Kg...A Brief Tornado Or Two May Be Possible As Well.

Farther South And West...Thunderstorms Are Expected To Develop Over The Higher Terrain Of The Nrn/Cntrl High Plains And Track Ewd In Conjunction With A Shortwave Impulse Moving Out Of The Rockies And Into The Central Plains. Deep Layer Shear Will Be Weaker... Generally Less Than 25 Kt...Than That To The North...And Warming 850-700 Mb Temps May Pose Capping Issues. For This Reason... Storm Longevity/Organization And Coverage Are All In Question.

However...Steep Lapse Rates And Strong Instability Will Be Present... So At Least An Isolated/Conditional Severe Threat Will Be Present Into The Evening Hours. Should Storms Develop And Be Maintained Into The Nighttime Hours Over Parts Of Neb/Ks...Some Upscale Growth Could Occur As The Llj Increases. Any Overnight Storms Should Be Elevated But Would Pose A Hail Threat.

Se Az...

Boundary Layer Moisture Will Increase Over The Southwest Deserts On Ely Low To Midlevel Flow Around Low/Midlevel Anticyclone. Strong Sfc Heating Beneath Modest Midlevel Lapse Rates /6.5-7.0 Deg C Per Km/ Will Result In Weak Instability /Generally Less Than 1000-1500 J Per Kg/ By Afternoon And Widely Scattered Thunderstorms Are Expected. Weak Deep Layer Shear Will Limit Overall Organization / Longevity Of Storms...But Marginally Severe Hail And A Few Strong Wind Gusts Will Be Possible.

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Sat Jul 5 Convective Outlook
Storm Prediction Center Norman Ok
Slgt Risk Svr Tstms for Northern Plains...

A Severe Weather Risk Including The Potential For Large Hail And
Damaging Winds Will Exist Across The Northern Plains Mainly Saturday Late Afternoon And Night.

The Main Belt Of Westerlies Will Be Relegated To The Northern Tier Of The Conus And Canada On Saturday...With Tstms /Some Strong To
Severe/ Possible Across The Northern Plains...Upper Midwest...And
Lower/Middle Mo River Valley.

Tstms Will Also Remain Common Across The Southwest States/Four Corners Area On The Periphery Of An Upper Ridge Centered Over The Eastern Great Basin/Central Rockies.

Northern Plains/Upper Midwest...

While Some Of The Details Vary Among Numerical Guidance...The Generally Expected Scenario Is For Storms To Develop/Increase Through Late Afternoon/Early Evening...Initially Across Northeast Mt And Nd. This Will Be Influenced By A Modestly Amplifying Shortwave Trough And East-Southeastward Moving Mid/High-Level Speed Max
Near/Just North Of The International Border...With Aforementioned
Convective Development Likely Focused To The North Of A Surface Low And Near/North Of An Advancing Surface Front.

Moderate To Strong Buoyancy And 40+ Kt Of Effective Shear Will Support Initial Supercells Capable Of Large Hail And Possibly A Tornado. By Late Evening...It Seems Likely That Storms Will Increase / Grow Upscale Into An East-Southeastward Moving Convective Cluster Capable Of Damaging Wind Gusts Across Nd/Northern Mn Through
The Late Night Hours Of Saturday Into Early Sunday.

Lower/Middle Mo Valley...

It Appears That Lingering Convection Friday Night Could Influence
Tstm Redevelopment East-Southeastward Across The Region Into
Saturday Afternoon And/Or Night. Well South Of The Stronger
Westerlies Aloft...Mid-Level Temperatures Will Be Relatively Warm
And Forcing/Vertical Shear Will Be Relatively Weak Aside From Any
Possible Mcv Influences. That Said...A Pulse-Type Or Localized
Severe Wind/Hail Risk May Be Possible Across The Region.

Az...

A Moist Air Mass May Allow For Some Stronger Storms On Saturday... However An Uncertain Degree Of Cloud Cover/Destabilization And Weaker Mid-Level/Steering Winds Precludes Severe Probabilities At This Time.

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Sun Jul 6 Convective Outlook
Storm Prediction Center Norman Ok
Slgt Risk Svr Tstms for Upper Ms River Valley/Lake Mi Vicinity...

Severe Thunderstorms Capable Of Damaging Thunderstorm Wind Gusts And Severe Hail Will Be Possible Across Parts Of The Upper Mississippi River Valley And Lake Michigan Vicinity On Sunday.

Large-Scale Pattern Amplification Is Expected To Occur On Sunday ... With An Amplifying Upper Trough Over The Great Lakes Region While An Upper Ridge Shifts A Bit Westward Over The Great Basin. A Southeastward-Moving Cold Front Will Be A General Focus For Thunderstorm Development Across The Upper Ms River Valley/Great
Lakes Region And Possibly The Central Plains On Sunday.

Upper Ms River Valley/Upper Great Lakes...

Current Expectations Are For The Remnants Of At Least A Small Mcs
Will Be Across Northern/Eastern Mn Into Wi/Upper Mi Sunday Morning.

As A Cold Front Continues To Otherwise Spread Southeastward Across The Region...Renewed Surface-Based Thunderstorm Development Should Occur By Afternoon/Early Evening Near The Front With Aid Of Weak Height Falls And Possibly An Embedded Shortwave Trough/Convectively-Induced Vort Max.

On The Southern Periphery Of Residual Early Day Thicker Cloud Cover And Any Possible Outflow...The Boundary Layer Should Aggressively Destabilize By Afternoon /3000-5000 J Per Kg Mlcape/ Within A Moist Pre-Frontal Environment Across Ia Into Wi/Southern Mn And Far Northern Il. Where Storms Develop/Mature...Around 40 Kt Of Effective Shear May Allow For Both Supercells And Well-Sustained Line Segments Capable Of Severe Hail And Damaging Winds Into The Evening Hours.

Central Plains/Middle Mo River Valley...

A Cold Front Is Expected To Advance Generally Southeastward Across
The Region On Sunday...But Overall Forcing For Ascent Will Remain
Modest Coincident With Relatively Strong Capping /Increasing With
Southwestward Extent/. While The Spatial Extent/Likelihood Of Deep
Convective Development Is Not Certain...Any Sustained Tstm
Development That Occurs Near/Just Behind The Front Could Pose A
Severe Hail/Locally Damaging Wind Risk Across The Middle Mo Valley.
This Would Be In The Presence Of Moderate To Strong Buoyancy
/2500-4000 J Per Kg Mlcape/ And Modest Vertical Shear /Generally
Below 30 Kt Effective/.

Farther West-Northwest...A Couple Of Strong/Possibly Severe Tstms Could Occur Across The North-Central High Plains Saturday Late Afternoon/Evening Within A Post-Frontal Low-Level Upslope Regime.

Az...

00z-Based Numerical Guidance Details Vary...But It Appears Possible
That Mid-Level Easterly Winds Could Modestly Increase Across The
Region On The Southern Periphery Of The Great Basin/Central
Rockies-Centered Upper Ridge. In The Presence Of A Moist
Environment...Downbursts/Strong Wind Gusts Will Be Possible Over The High Terrain And Possibly Parts Of The Desert Floor.

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Jul 7-11 Convective Outlook
Storm Prediction Center Norman Ok

Large-Scale Trough Amplification Will Occur Over Ontario/Great Lakes
Region Early Next Week...With Increasingly Prevalent Cyclonic
Westerlies Coincident With A Southward-Sagging Frontal Zone.

Given That A Moist/Unstable Environment Will Exist Along/South Of The Front...It Does Seem Probable That A Severe Risk Will Exist Early
Next Week...Including The Potential For East-Southeastward Moving
Mcs Development And Severe Hail/Damaging Winds.

This Could Include A Corridor From The Central Plains And Lower / Middle Mo Valley To The Oh Valley On Days 4/5 Monday/Tuesday.

The Front Should Continue To Gradually Settle Southward Into Day 6/Wednesday...With At Least Some Severe Potential In Areas Potentially Including The Ozarks/Tn Valley.

However…Inherent Variability Regarding Relevant Mesoscale Details Precludes 30 Percent Severe Probabilities In Spite Of A Discernible Severe Risk Early Next Week.


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