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US Final Extended Forecast thru May 23

...Heavy Rainfall Possible For The Upper Missouri And Mississippi
River Basins...

...Overview...

The Transition From Winter To Summer Continues As Evidenced By The Resurgent Amplified/Blocky Pattern. Several Closed Lows Are
Forecast To Evolve Through The Medium Range... North Of Hawaii...
Along The Pac Nw Coast... Over The Upper Midwest... And In The
Central Atlantic. Suny Albany Cstar* Research Has Shown That The
Climatological Maximum In Closed Low Frequency In The Northern
Hemisphere Occurs In June... So This Pattern Is Fairly Typical.

...Model Preferences...

The Gfs/Ecmwf/Ukmet All Clustered Fairly Well Together Through
About Mon/D4... When The 00z-06z Gfs Runs Became To Quick To Lower Heights In The Pac Nw Compared To The Consensus And Perhaps Too Quick To Push The Upper Low Over The Upper Midwest Northward.

Ongoing Wpc Continuity Favored A Bit Slower Progression Via The
Ensemble Means And This Was Best Represented By A 00z Ecmwf/Ukmet Blend Early In The Forecast Before Incorporating About Half Weighting Of The Ensemble Means Days 6-7... Which Remained In Good Agreement Through Thu/D7. Felt Little Reason To Stray Far From Their Idea But Capitalized On The Nearby Deterministic Models For Added Detail.

...Sensible Weather Highlights...

The Slowly-Moving Surface Boundary Has Been Advertised As A Potent Weather Maker For The Plains... And The Model Guidance Has Not Backed Down... Focusing Convective Precipitation For The Upper
Midwest. Gfs/Ecmwf/Ukmet Focus Significant Rainfall... 2-4
Inches... For A Large Portion Of The Upper/Mid Missouri And Upper
Mississippi River Basins Days 3-5... With A Secondary Rainfall
Maxima... 1-3 Inches... Centered On The Central Appalachians And
Southern Mid Atlantic States By The End Of The Period.

Ecens Probability Of At Least 1 Inch Of Qpf Days 3-7 Exceed 50 Percent Over A Very Large Area From The High Plains Southward To The Mid-Ms Valley And Eastward Toward The East Coast... Where Gefs Pw Anomalies Exceed +1 Std Deviation.

Spc Continues To Advertise The Threat For Severe Weather Along The Boundary And Ahead Of The Upper Height Falls From The Central Plains Into The Mid-Ms Valley Sun-Mon/D3-4 In The Warm Airmass.

In The Pac Nw... The Guidance Also Generate Considerable Precipitation For Northern/Coastal Washington Into Coastal Oregon With An Extended Onshore Flow But Also Into The Idaho Panhandle And Western Montana As The Cutoff Low Eases Into Wa/Or. Upper Ridging And Sfc High Pressure Over South Central Canada Should Help In Gradually Increasing Pw Values Along The Divide Before The Best Forcing And Sfc Boundary Approaches From The West.


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