US Preliminary Extended Forecast thru Jun 1

...Overview And Preferences...

Guidance Shows Reasonable Agreement In The Large Scale... With A
Broad Mean Trough Covering The Wrn States And A Strengthening
Ridge Moving Into The East. However There Is Continued Uncertainty For Some Details Within The Mean Trough As Well As For The Amplitude/Orientation Of Ern Canada/Nern Conus Flow Aloft By The Latter Half Of The Fcst.

Operational Model Runs Still Display Enough Scatter With Various Features To Recommend Emphasizing The Ensemble Means Through The Medium Range Period. Prefer A 70/30 Blend Of The 12z Ecmwf/12z Gefs Means Days 3-5 Tue-Thu Based On Reasonable Agreement Of Their Solns And Long Term Verification.

The 12z Ecmwf Mean Is Used Exclusively After Early Thu For Its
Intermediate Soln With New England Frontal Posn Although The 12z
Gefs Mean Remains An Acceptable Blend Component Over The Wrn 2/3 Of The Conus.

...Guidance Evaluation...

The Majority Of Models/Ensembles Expect Leading Shrtwv Energy
Reaching The West As Of Early Tue To Continue Into The Plains
While Upstream Energy Flowing Into The Northwest Catches Up To The Leading Energy.

The Best Clustering Of Solns Has These Two Bundles Of Energy Consolidating Into A Closed System Aloft Over/Near The Nrn Plains By Day 6 Fri... Supporting A Fairly Vigorous Sfc Low.

This System Should Begin To Progress Ewd By Next Sat.

Operational Ecmwf Runs Continue To Lean On The Slower/More Amplified Side Of Guidance With The Leading Shrtwv Reaching The High Plains By Thu.

Ecmwf Trends Have Been Gradually Faster Over The Past Couple Days. The 18z Gfs/Gefs Mean Are On The Faster Side Of The Spread With Upstream Energy And Flatter With Leading Energy... With The 12z Gfs/Gefs Mean Closer To The Overall Guidance Mean.

Sufficient Continuity Exists To Have Above Average Confidence In The Idea Of Sfc Low Development Over/Near The Nrn Plains Around Thu-Fri.

The Uncertainty In How Multiple Pieces Of Shrtwv Energy Will Interact Leads To A Deterministic Fcst Not Much Stronger Than The Ensemble Means For The Sfc Low...And Not As Wrapped Up As The 12z Ecmwf/Cmc.

Meanwhile Strength Of The Downstream Ridge And Occasionally Fast Gfs/Gefs Biases Would Favor Leaning A Little Slower Than Recent Gfs Runs And 18z Gefs Mean During Fri-Sat. Ultimately Cannot Fully Discount Any Soln At This Time In Light Of Typical Days 6-7 Fcst Errors.

By Next Sat The Latest Gefs/Ecmwf/Cmc Means Indicate That Fast/Low Amplitude Pac Flow Should Begin To Amplify In Response To Troughing S Of The Aleutians... Leading To A Sharper Trough Near
The West Coast. The 12z Gfs Offers The Closest Match To The Means For This Part Of The Fcst. The 12z Ecmwf Brings Its Ern Pac Ridge Ewd Of Consensus While The 18z Gfs Soln Of Stalling A Closed Low Off The Pac Nw Coast Wed Onward Does Not Compare Well To Most Other Solns Either.

Farther Ewd The Most Significant Issue Involves Amplitude Of Ern
Canada/Nern Conus Flow Aloft During The Latter Half Of The Period
And Resulting Sfc Front Posn. The Past Three Ecmwf Runs Have Been Fairly Aggressive With Trough Amplitude Thus Bringing A Sfc Front Rather Far Swd. On The Other Hand Gfs/Gefs Runs Keep Hgts A Lot Higher With A Much Farther Nwd Frontal Zone. Teleconnections
Relative To The Wrn Trough And An Atlc Ridge In The D+5 Means
Suggest Lower Nern Conus Hgts Than Fcst By Gfs/Gefs Solns But Not Conclusively To The Extent Of The Ecmwf. This Leaves The 12z
Ecmwf Mean As The Best Option For Frontal Placement At This Time.

...Sensible Weather Highlights...

The Mean Trough Aloft Over The West Will Support Unsettled Weather
Over The Wrn-Cntrl States... And Below Normal Temps Over The West
Eventually Reaching The Nrn Plains.

Potential Still Exists For Some Wrn Pcpn To Extend Unseasonably Far Swd.

The Srn Half Or 2/3 Of The West Should See A Drying Trend By Fri-Sat.

Hgt Falls Aloft Reaching The Cntrl/Srn Plains Mid-Period And Mid Lvl/Sfc Development Farther Nwd Late In The Week May Support Multiple Areas Of Mdt-Hvy Rnfl Over/Near The Plains. The Warm Front Fcst To Lift Across The Nern Quadrant Of The Lower 48 Tue Onward Is Also Expected To Be Convectively Active.

After Passage Of The Warm Front Expect Persistently Above To Well Above Normal Temps Over Much Of The East Albeit With Some Uncertainty Over The Northeast.

Finally Expect A Wet Pattern Over Srn/Ern Parts Of The Fl Peninsula Due To Ely Flow On The Srn Side Of Atlc/Ern Conus Sfc High Pressure.

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