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US Extended Forecast thru May 10

Overview...

Sensible Weather Changes For The Lower 48 Will Be Associated With An Upper-Level Trough Migrating From The West Coast To The Central Us And Its Associated Downstream Upper-Level Ridge.

Model Preferences...

The 2/12z Gefs/Ecens Means And Their Deterministic Runs Generally
Handled The Migration And Structure Of The Pacific Cutoff Into The
Plains States And The Upper-Level Trough Over West Central Canada Without Issues Into Day 7.

However After Day 5...The Spread Increases In The Southeast Gulf
Of Alaska...East Central Pacific And Downstream Into The Pacific
Northwest And British Columbia. The 2/12z Gefs/Naefs Were
Supportive Of A Flatter/Faster Mid-Latitude Flow Pattern Between
40n-45n North...With The 2/12z Ecens A Slightly Slower And
Higher-Amplitude Pattern Developing Across The East Central
Pacific And Downstream Into The Western States.

Of Note... With The 2/12z Deterministic Gfs Offering Better
Run-To-Run Continuity For Days 6-7 In The Gulf Of Alaska Versus
The 3/00z Deterministic Ecmwf With The Overall Position Of A
Second Cutoff Upper-Level Invof 43n 174w (As Of 3/06z).

With This In Mind...The Wpc 500mb And Surface Graphics Ran With A
Blend Of The Ecens/Gefs Means After Day 5 To Handle The Spread... But Saw Little Advantage To Be Gained By Using Either The
Gfs/Ecmwf Deterministic In The Eastern Pacific After Day 5.

Guidance Evaluation...

The Key Feature Of This Medium Range Pattern Is The Cold... Upper-Level Trough Over North Alberta And Northern Saskatchewan. Its Positioning--Along The Downwind Side Of A Closed Upper-Level High Lodged In Central Alaska--Will Be The Anchor Point For The Near-Term Pacific Cutoff To Steer Eastward...Then East-Northeast Into North Central Manitoba By Period's End.

The Result Will Be A Broad Region Of Diffluent Southwest Flow Lee
Of The Continental Divide With A Series Of Mid-Level Waves Ejecting Out Of The Northern High Plains...That Will Migrate Downwind Across The Northern Plains...Upper Ms Valley...Great Lakes And Eventually Over The Top Of The Broad Upper-Level Ridge And Into The Northeast.

The Models Are Coming Around To The Idea That The Better Forcing
Will Be Focused Across The Northern Third Of The Rocky Mountains ...And When The Bulk Of The Pacific Cutoff And Height Falls Eject Into The Northern High Plains Between Wednesday And Thursday... A Surface Cyclone Emerges Over North Central Kansas And Begins To Track Through The Upper Great Lakes Region And Eventually Into Western Quebec By Day 7.

This Surface Cyclone Will Draw Upon A Dry And Very Warm Airmass And Strong Southwest Winds Aloft...To Spread A Broad Warm Front Across The Central Midwest...The Entire Ohio Valley And Eventually Lift Into New England By Next Weekend.

What Uncertainty That Remains In The Medium Range Forecast...Is
The Volatility Of The Atmosphere...And Outcome Of Convective
Rainfall Potential Over The Southern Plains.

And What--If Any Well-Defined Dry Line Assistance And Lift Can Be Generated Into What Appears To Be A Heavily-Capped Mid-Level Environment And Negligible Low-Level Gulf Moisture Feed.

The Uncertainty Starts Out On Wednesday Evening...Well Ahead Of The Height Falls In The Northern Rockies.

The 2/12z Deterministic Gfs/Ecmwf 250mb Wind Progs Illustrate This Nicely.

By Friday Morning...When The Trough Ejects Into The Northern Plains...The Deterministic Gfs And Ecmwf Have Some Subtle Differences...Though Both Support An Axis Of Intense Winds Aloft From North Central Texas Northeastward Into The Central Great Lakes.

Sensible Weather Highlights...

Wet And Cool For The Northwest...And Northern Rockies.

Temperature Anomalies Of 15f-20f Over The Southern Plains Look
Likely During This Forecast Period...And Will Have An Alleyway To
Spread Northeastward Into The Midwest And Great Lakes...Ohio
Valley In The Warm Sector Of The Developing Cyclone.

Warm Sector Lift And Cloud Cover Could Dampen Out The Widespread Heat However.


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