Severe Weather Threat thru Jul 19

Sat Jul 12 Convective Outlook
Storm Prediction Center Norman Ok
Slgt Risk Svr Tstms for Mid-Mo Valley to Srn Lk Mi Region...

Isolated To Scattered Severe Storms Are Anticipated From Parts Of The Mid-Missouri Valley To The Southern Lake Michigan Region During The Late Afternoon Into Tonight. Damaging Winds Should Be The Primary Hazard...But Severe Hail And A Tornado Or Two Will Be Possible.

An Upper-Level Trough Will Amplify Over S-Cntrl Canada As A Vigorous Shortwave Impulse Digs Se Towards The International Border Along N Mn/Lk Superior.

Upstream...A Mid-Level Ridge Will Build N From A Strengthening Anticyclone Over The Great Basin.

A Weak Convectively Induced Mid-Level Impulse Over The Cntrl High Plains Should Track Towards The Cntrl Great Lakes. This Feature In Conjunction With Convective Outflow Should Aid In The Consolidation Of Two Frontal Boundaries Over The Cntrl Plains By Evening.

Farther N...A Cold Front Will Sweep Into Nd/N Mn This Evening.

Mid-Mo Valley To The Lk Mi Region...

Decaying Convection Should Be Ongoing From Parts Of The Dakotas To Il At 12z This Morning In Association With Low-Level Waa And Ascent Aided By The Weak Mid-Level Impulse Tracking E Across The Upper Midwest. In The Wake Of This Activity...Intense Insolation Should Occur From Ks To The Mid-Mo Valley Along/S Of The Srn Front. Differential Heating Should Be Pronounced And Amidst A Reservoir Of 1.5-2.0 Inch Pw Values...Aid In The Development Of Scattered Late Afternoon To Evening Storms Across Parts Of Neb/Ia.

Mid-Level Lapse Rates Will Be Marginal And May Hinder Development Of Strong Buoyancy. Nevertheless...Guidance Is Consistent In Depicting A Belt Of Enhanced Mid-Level Wlys /Around 35-45 Kt To 700 Mb/ Downstream Of The Amplifying S-Cntrl Canadian Trough. This Enhancement Should Help Foster Upscale Growth Into An Mcs On Sat Evening With Scattered Swaths Of Wind Damage And A Couple Tornadoes Possible.

E Nd/Nw Mn...

Fast-Moving Scattered Convection Should Develop S/Se Across Parts Of Sk/Mb/Ont During The Late Afternoon Along The Sharp Cold Front. Buoyancy Should Remain Meager With Convection Likely Diminishing Rapidly After Sunset Over Nd/Mn. But...Nearly Unidirectional Wind Profiles With Moderate-Strong Deep-Layer Speed Shear Could Support A Short-Duration Strong To Isolated Severe Wind/Marginal Hail Risk In The Early Evening.

Black Hills/Cntrl High Plains...

Isolated To Scattered Storms Should Develop Over The Higher Terrain During The Mid-Afternoon To Early Evening. Parts Of The Region Will Remain On The Fringe Of Sufficient Mid-Level Nwlys For Multicell Clusters. Modest Buoyancy And Moderately Steep Lapse Rates May Yield A Few Strong To Locally Severe Wind/Hail Events.

Se Az...

Modest Enhancement To Mid-Level E/Nelys Should Occur As The Anticyclone Builds Over The Great Basin. With Effective Shear Values Approaching 20-25 Kt...Loosely Organized Multicell Clusters May
Develop Off The Higher Terrain With An Attendant Risk Of Strong To Locally Severe Wind Gusts Given Deep Inverted-V Thermodynamic Profiles.

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Sun Jul 13 Convective Outlook
Storm Prediction Center Norman Ok
Slgt Risk Svr Tstms for Ohio Valley and Northeast...

Severe Thunderstorms Will Be Possible Over Parts Of The Ohio Valley And Northeast On Sunday.

More Isolated Strong To Severe Storms Will Also Be Possible Across Front Range And Central Plains...The Southwest...As Well As Oregon.

A Strong Positive-Tilt Mid/Upper Trough And Associated Deep-Layer Cyclone Will Undergo Amplification/Deepening From James Bay Southwest To The Northern Plains/Upper Ms Valley Regions Through Sunday. A Leading Shortwave Trough On The Eastern Flank Of The Amplifying Upper Low Will Track From The Great Lakes Across The Northeast And Southern Quebec As A Stronger Shortwave Impulse Pivots Around The Western Flank Of The Upper Low And Digs South Across The Northern Plains And Upper Ms Valley Through Monday Morning.

Between These Two Shortwaves...A Belt Of Modest Cyclonic And Difluent Flow Aloft Will Extend From The Dakotas Across The Great Lakes To Northern New England...Coincident With A Leading Surface Cold Frontal Surge. A Warm/Moist Conveyor Belt Will Exist Ahead Of This Leading Front... From The Midwest/Oh Valley Northeast To Ny/New England.

A Secondary Cold Front Associated With Aforementioned Stronger Shortwave Trough And Deepening Upper Low Will Spread South And East From The Upper Ms Valley And Ia To The Upper Midwest Through Early Monday.

Elsewhere...A Mid-Level Anticyclone Will Remain Centered Across The Great Basin While A Compact Shortwave Trough Acts To Break Down The Upper Ridge Across The Pacific Northwest.

Northeast...

The Warm/Moist Conveyor Belt Will Be Characterized By A 30-40kt Southwesterly Low-Level Jet Ahead Of A Strong Mid/Upper Jet Exit Region Arcing From Lake Huron To The Ontario/Quebec Border. Modest Mass Transport And Isentropic Ascent Will Result In A Number Of Showers/Storms And Debris Clouds That May Limit Stronger Destabilization From Pa Northeast Across Ern Ny And Into Vt Through The Afternoon. However...Forecast Soundings From Nam And Parallel Nam Indicate Weak To Modest Surface-Based Instability Will Evolve In The Slgt Risk Area With Surface Temperatures Around 80f And Dewpoints 65-70f Contributing To Sbcape Of 1000-1500 J/Kg. Effective Deep-Layer Vertical Shear Of 35-40kt Will Be Adequate For Updraft Persistence While Low-Level Jet Acts To Enhance 0-3km Storm-Relative Helicity.

Both Line Segments And Supercells May Evolve Through The Afternoon As Leading Cold Frontal Surge Spreads East Into The Warm Sector. Expect The Possibility Of Strong To Severe Storms With
Marginal Hail...Strong To Damaging Winds...And Perhaps A Couple Of Tornadoes.

Higher Severe Probabilities May Be Warranted In Later Outlooks Depending On Timing And Greater Confidence In Degree Of Destabilization.

Oh Valley...

An Axis Of Stronger Instability /Mlcape 1500-2500 J Per Kg/ But Weaker Flow/Shear Will Exist Farther Southwest Ahead Of The Frontal Surge...From Western Pa Westward Across The Midwest And Oh Valley. Nonetheless...Height Falls Will Contribute To Ascent Across These Areas As Mid-Level Flow Strengthens Coincident With Diurnal Destabilization And Storm Initiation. Expect One Or More West-East Bands Of Convection To Evolve Through The Late Afternoon With Damaging Winds Likely Becoming The Primary Hazard.

Front Range...

Isolated Stronger Storms Will Likely Develop Across The Higher Terrain In The Presence Of Modest Instability/Lapse Rates And 15-20kt Northwest Flow Aloft. A Cluster Or Two Of Storms May Be
Capable Of Marginally Severe Wind/Hail Into The Early Evening.

Central Plains...

Secondary Frontal Surge Will Spread Southeast Across Ern Neb/Ia And Nrn Il Coincident With Max Heating. Lift Along The Advancing Boundary And Antecedent Low Level Moisture Could Spur A Couple Of Stronger Cells Through Early Evening With Some Chance Of Strong Winds And/Or Marginal Hail.

Oregon...

A Compact Shortwave Trough And Associated 40-50kt Mid-Level Wind Max Will Spread Northeast Across Oregon During The Day. Lift And Shear With This Impulse May Be Sufficient For A Few High-Based Storms And Perhaps A Supercell With Hail And Strong To Isolated Damaging Winds Possible.

Southwest...

Rich Boundary Layer Moisture And Intense Heating Will Contribute To Strong Storm Initiation In A Regime Characterized By 10-20 Easterly Flow Above 700mb. This Should Be Sufficient For Storms To Spread West Where Drier Sub-Cloud Layer Will Support Strong Evaporational Cooling And Downburst Potential.

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Mon Jul 14 Convective Outlook
Storm Prediction Center Norman Ok
Slgt Risk Svr Tstms for Mid Ms Valley to Nj/Pa/Ny and Nrn Delmarva Areas...

Severe Thunderstorms With High Winds Will Be Possible Over Areas Of The Mid-Atlantic West To The Ohio River Valley And South To The Tennessee River Valley.

More Widely Dispersed Storms With Hail And Strong Gusty Winds Will Be Possible In An Arc From The Middle Mississippi River Valley West And Northwest To The Northern Rockies.

A Trough Of Substantial Amplitude Will Evolve Across The Upper Ms Valley And Great Lakes Regions Through Monday With The Greatest Mid-Level Height Falls Of 60-90m Per 12h Forecast To Spread From Mn/Wi To Mi/Oh/Indiana During The Period.

A Strong Cold Front Associated With The Amplifying Trough Is Forecast To Spread East-Southeast From The Upper Midwest To The Middle Ms Valley Through The Period With Cyclogenesis Possible Along The Front Over The Eastern Great Lakes...Per Latest Ecmwf. The Forecast Is Made More Complex Given A More Diffuse Front From New England To The Mid-Atlantic Will Precede The Stronger Cold Front...And There Are Model Differences As To The Strength And Timing Of Cyclogenesis Along The Trailing Front...And The Degree Of Airmass Destabilization That Will Take Place Along/Near Both Boundaries And The Developing Frontal Low.

Elsewhere...An Extensive Zone Of Storm Development Will Be Possible Ahead Of The Front...And Across The Higher Terrain Of The West And Southwest.

Mid Ms Valley To Nj/Pa/Ny And Nrn Delmarva Areas...

Given The Aforementioned Forecast Complexities Only A Broad Zone Of Relatively Low Severe Probabilities Can Be Depicted In This Outlook. The Leading Front Will Be Interspersed With Convective Outflow...And Likely Ongoing Storms...That Should Spread East / Northeast Into A Corridor Of Increasing Instability. Shear And Forcing As Depicted In Both Nam And Parallel Nam...As Well As Gfs And Ecmwf...Would Support A Few To Several Organized Storms With Strong To Damaging Winds And Also Some Tornado Potential.

Midwest/Oh Valley...

Another Corridor Of Convective Potential Will Evolve Ahead Of The Stronger Cold Front...From Oh West-Southwest To Mo Bootheel. These Storms May Take On More Linear Structure Given The Potential For Strong And Focused Ascent Along The Advancing Cold Front. Sufficient Instability Should Exist For Some Hail/Wind Events.

Tornado Risk May Also Exist If Stronger Cyclogenesis As Indicated Ecmwf Were To Occur Across The Northern Portion Of The Slgt Risk Area.

Plains West And Northwest Into The Northern Rockies...

Isolated To Scattered Strong Storms Driven Primarily By Diurnal Heating And/Or Orographic Ascent Will Be Possible. Shortwave Trough Cresting Upper Ridge In The Nrn Rockies Will Lend A Bit More Forcing Here For Organized Storms With Wind/Hail Potential.

Southwest...

Easterly Flow Will Persist Along The Southern Flank Of The Great Basin Anticyclone And Act To Steer Mountain Convection West To Where Dry Sub-Cloud Layers Will Support Isolated Downbursts.

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Jul 15-19 Convective Outlook
Storm Prediction Center Norman Ok

Generally Weak Flow And High Heights Will Persist Across The Western U.S. While A Trough Dominates The East...At Least For The First Part Of The Medium-Range Period.

Day 4...

Unusually Large Differences Appear At The Start Of This Forecast Period Between Deterministic Versions Of The Gfs And Euro With The Gfs Indicating
1) Faster Eastward Progression Of The Strong Cold Front Off The Eastern Seaboard...And
2) Faster De-Amplification Of The Large-Scale Trough In The East.

The Euro Ensemble Mean Appears Similar To The Deterministic Gfs With Respect To Surface Low Location In Central Quebec But The Trailing Cold Front Remains Near/Along The East Coast Through Middle Of Day 4.

Meanwhile...Deterministic Ukmet Is A Compromise And Suggests A Surface Low In Southern Quebec With A Trailing Cold Front Along The Eastern Seaboard At 00 Utc 16 July/Tuesday Evening.

A Majority Of Guidance Does Suggest At Least Some Severe Weather Potential Continuing As The Front Moves To The East Coast On Day 4/Tuesday. However...Given The Spread In Solutions At Such A Relatively Short Forecast Range...The Prudent Approach Is To Forecast Predictability Too Low At This Time.

Days 4 Through 6....

Somewhat Better Model Consistency Is Evident From The Front Range / High Plains Into The Southern Plains Where Most Guidance Indicates A Regime Supportive Of Upscale Mcs Evolution.

Given The Potential For Low-Level Upslope Flow Beneath Northwest Flow Aloft...Diurnally And Orographically Forced Convection May Grow Upscale And Spread East And Southeast Amidst Northwest Steering Flow And Sustained Ascent Along Frontal Zone Forecast To Stall Over The Region.

Since Widespread/Significant Severe Weather In This Type Of Regime Is So Dependent On Mesoscale Factors Such As Frontal / Outflow Boundary Location/Placement And Low-Level Jet Intensity... Predictability At This Stage Remains Too Low To Highlight A Greater Probability Risk Area.


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