US Extended Forecast thru Aug 23

Upper-Level Jet Intensification Across The Northern Pacific Leads To The Transition From High-Amplitude Trough Over Eastern Canada And The Northeast Us--To A More Zonal And Flatter Low Amplitude / Progressive Pattern For The This Medium Range Period.

In The West And North Central Us...The Pattern Will Be Dominated By A Progressive Longwave Trough Taking Shape As The Upper-Level Jet Begins To Amplify And Carve A Longwave Trough Across Much Of Western Canada And The Northwest Quarter Of The Lower 48 Beyond Day 5.

A Blocky Pattern Downstream Over Atlantic Canada And Greenland Will Create A Temporary Split-Flow Pattern Across The Lower 48 This Forecast Period.

Best Way To Describe The Changes--The Persistent Cool Pattern In The Northeastern Us Becomes Cloudier With Higher Temperatures And Humidity. And The Relatively Dry Northwest States Become Cooler And Wetter.

A Locally-Active Monsoon Flow For Parts Of The Southwest (Az Nm Co) And In The Mid-Section Of The Country...A Pacific Cold Front And Appreciably Moist And Cooler Weather Pattern Migrates From The Northern Divide Eastward Into The Upper Half Of The Missouri River
Valley For Days 6-7.

Downstream Of The Rockies...What Significant Differences Emerging From This Pattern Transition During The Medium Range Period... Appeared To Follow The Intensity And Latitude Of The Developing Split-Flow Pattern And 'Weaker' Southern Branch Of The Jet. This Leads To A Variety Of Perplexing Ridge/Trough Solutions (Low-Amplitude Waves Mind You)...Originating Anywhere From North Central Wyoming To South Central Colorado. Consequently This Leads To A Rather Broad Range Of Day 4-5 And Day 5-6 Qpf Possibilities Along And East Of 98w Longitude Between Southeast Dakota And Northeast Kansas Starting Around The Day 5 Mid-Point (21/12z).

In The West...A Mid-Level Cyclonic Circulation Drifts Off The Central California Coast Between Cape Mendocino...Pt Reyes And The Bay Area. Then Takes A Southwestward Track And Heading Well Out To Sea--West Of Point Concepcion. After Day 4 And Into Day 5...That Looks Reasonable.

Wet And Stormy Weather Will Accompany The Surface Wave Tracking Through The Ohio Valley/Mid-Atlantic States Early Next Week...With Periods Of Heavy Rains And Strong Thunderstorms Possible.

Showers And Thunderstorms Are Expected With The Shortwave Dropping Into The Upper Midwest / Great Lakes And At The Leading Edge Of Height Falls Digging Into The Northwest...Which Should Impact The Northern Plains By Late Next Week.

The Relatively Flat And Progressive Flow Over The Conus Should Limit Any Large Temperature Extremes.

In General...Temperatures Will Be Above Normal Surrounding The Central Rockies/High Plains...Beneath Modest Ridging Aloft. Also...With Mean Troughing Setting Up Over The Western U.S. Late Next Week...Highs And Lows Should Be Below Normal.


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