US Extended Forecast thru May 9


A Pacific Cutoff Low Currently Invof 45n 140w Will Migrate Along The Us/Canadian Border This Forecast Period...And Focus Rain And Rain Showers Across The Pacific Northwest And Northern Rockies.

The System Will Gradually Amplify Downstream Along The Continental Divide...With The Base Of This Upper-Level Trough Eventually Exiting The South Central Rockies Day 6-7.

Ahead Of The System...A Broad Ridge...Milder Conditions And 'Warm Frontal' Precipitation Will Spread From The South Central Plains To The Ohio Valley-Northeast And Northern Mid-Atlantic Region.

Model Preferences/Uncertainty Assessment...

Had No Issue With The 1/12z Gefs/Ecens Mean...Depicting The
Breakdown Of A Blocky Ridge And Closed High Across The West Coast Of North America And Interior Alaska Respectively.

The Pattern Break Down Allows A Cutoff Low In The Eastern Pacific To Release Inland...Beneath The Ridge Axis...And Slowly Migrate A 'Pacific' Front Inland And Into The Northern Rockies.

The Previous Wpc Graphics And Preferred Blend Utilized Both Of These Means Beyond Day 5. And This Morning's Package...Was Able To Use The Means As A Baseline And Their Deterministic Runs (1/12z Ecmwf/Gfs) Through Day 6 Were Good Pieces Of Guidance To Pin Down Some Of The Smaller-Scale Details Related To Rainfall Potential Over The Northern Rockies And Downstream Through The Upper Midwest.

Of Note...A Quick Look At The Deterministic 2/00z Gfs Appeared To Be A Little Faster Than The 1/12z Deterministic Ecmwf With The West To East Progression Of The Precipitation From West Coast To The Great Lakes.

Sensible Weather Highlights...

Above Normal Temperatures Will Come To An End In The West...With
The Expansive Cutoff And Associated Long Wave Trough Generating An Onshore Flow Through The Entire West Coast And Great Basin.

Downstream And East Of The Divide...The Leading Edge Of The
Pacific Front (Wpc Day 5 Graphic) Shows A Dying Cold Front Pushing
Into The Central And Southern Plains...But The Northern Rockies... Adjacent Foothills Of The High Plains--South To The I-80 Corridor Should Observe A Cooler...Relatively Wet Pattern That Generally Persists Through The End Of This Forecast Period.

The True Cold Front...Will Be A Secondary Surge (When Height Falls
Exit The Divide In Earnest) And This Cold Front Will Not Reach The
Southern Plains Until Day 6--And Slowly Push Into The Lower
Missouri Valley And Mid-Mississippi Valley Til Day 7.

A Sub-1004 Mb Surface Cyclone Emerges Invof East Central Kansas Wednesday Night...And Is Expected To Migrate Northeastward Into The Midwest Day 6.

The Cyclone's Broad Warm Front And Expanding Cold Front Should Be The Focus For Organized Showers And Embedded Deep
Convection Across The Nation's Midsection.

Along The Warm Front...More Of The Same Downstream Into The Ohio Valley...Central Appalachians With Scattered Convection Leaping Across The Appalachians To The Atlantic Coast Line.

The Day 6-7 Time Frame Will Likely Be The More Convectively-Active
Period Along The Cold Front As The Western Fringes Of The Gulf Of
Mexico Attempt To Open Up--And A Broad Warm Front And
Southwesterly Flow Aloft Along The Upwind Side Of The Ridge Axis
Migrates East Of The Mississippi River.

Best Prospects For Significant But Localized Heavy Rainfall Appears To Be Across Portions Of Texas...Oklahoma...Kansas And The Ozarks.

Prior To Day 6...Warm And Dry Air Underneath The Ridge Will Keep The Southern Plains 'Capped' With Dryline Activity At A Minimum.

The Building Ridge In The East Appears To Keep The Southeast Under Stable And Relatively Dry Conditions This Forecast Period.

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