US Extended Forecast thru Sep 2

The Longwave Pattern Is Expected To Remain Nearly Steady Through
The Medium Range Period... Days 3-7...With An Upper High Over The Central/Southern Plains...And Mean Troughs Positioned Across The Pacific Northwest And Western Atlantic.

Regarding The Short Wavelength Pattern... The Solution Spread Has Decreased For Days 3-4/Thu-Fri Compared To This Time Yesterday ...Thus More Strongly Supporting Modest Use Of Deterministic Solutions Mixed With The Ensembles To Determine The Sensible Weather. As A Starting Point...Preferred About 30 Percent Each 06z Gfs/00z Ecmwf With 20 Percent Each 06z Gefs Mean/00z Ecmwf Ensemble Through Day 4. The Uncertainty And Accompanying Solution Spread Increase Noticeably By Day 5/Sat...Suggesting A Fairly Rapid Transition Toward The Ensemble Means.

The 00z Ecmwf Is The First Solution To Be Discarded For Depicting The Pressures/Fronts...With Its Unusually Strong And Nearly Outlying Solution With A Shortwave Trough Crossing Central Canada On Saturday. The 06z Gfs Is Not Much Better...Particularly Across Alaska/Northern Pacific...Where Its Solution Differs From The Consensus More Than Most Other Solutions. The Largest Shift In Model Solutions Compared To The Last Couple Days Is A Trend Toward A Slower/Deeper Low Reaching The Pacific Northwest Coast By Day 7/Mon...Which Is Well Depicted In The Spaghetti Diagrams.

The Evolution Of The Low Is Rather Complicated...Involving The
Interaction Of At Least 2 Separate Streams Over The Northwest
Pacific Along With Abundant Moisture Left In The Wake Of 2 Tropical Systems In The Southwest Pacific. Therefore...Confidence In Its Details Are Very Low...With Again A Preference Toward The Ensemble Means To Address The Uncertainty. If This Trough Were In Fact To Develop...The Slower 00z Ecmwf Ensemble Mean Appears More
Likely To Occur Compared To The 00-06z Gefs Means.

The Trough's Position May Also Have Implications For The Trough Continuing Across The Western Atlantic...With The Slower Ecmwf Ensemble Mean Favoring More Amplitude In The East Than Shown By The Recent Gefs Means. The Slowly Retrograding Upper High Over The Plains Also Favors Leaning Toward The Amplified Side Of The Guidance In The East. Therefore... Beginning With Day 5/Sat... The Preference Is For A 70 Percent 00z Ecmwf Ensemble Mean To 30 Percent 06z Gefs Mean...With Below Average Confidence Beginning With Day 6.

The Slowly Evolving Pattern Favors Using Persistence As A Guide
For Determining The Sensible Weather...With Mainly Hot And Dry
Conditions Continuing Across The Central/Southern Plains...While
Mostly Unsettled And Cool Conditions Continue Across The Pacific
Northwest As Well As The Upper Midwest/Great Lakes/Northeast ...With No Imminent High-Impact Hazards Expected At This Time.

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