US Extended Forecast thru Apr 5

Extended Forecast Discussion
Nws Weather Prediction Center College Park Md
252 Am Edt Sat Mar 29 2014
Valid 12z Tue Apr 01 2014 - 12z Sat Apr 05 2014

Overview...

Medium Range Package Finally Covering The First 5 Days Of April.
Definitely A Spring Weather Pattern Is Anticipated Across The Lower 48.

A Series Of Surface Cyclones And Well-Defined Frontal Boundaries Will Make Their Mark--Delivering Their Typical 'April Showers' And Some Volatility To The Sensible Weather Pattern From The Continental Divide To The Southern Plains And Into The Great Lakes.

Model Preferences/Uncertainty Assessment...

Been Utilizing A Heavily-Weighted Ecmwf And Ecens Means For Its
Rather Good 4-Cycle Run-To-Run Continuity Versus The Gefs/Gfs. And This Package Is No Exception.

If The Gfs/Gefs Was Preferred Over The Ecmwf...Then Recommend
Using The 28/18z Gfs/Gefs Cycle Rather Than The 28/12z Gfs/Gefs
For Its Somewhat Slower Solution...That Matches Up A Little Better
With The Broad Ensemble Clustering For The West Coast And Southern Plains.

But Overall...Only Saw Utility In The 28/18z Gefs Mean To Day
5...And Incorporated About 1/3rd Of It Into The 500mb And Surface
Graphics...With The 28/12z Ecens Mean And 28/12z Deterministic
Ecmwf Comprising The Other 2/3rds.

After Day 5...Went Strictly Ecens Mean And 20 Pct Of The Deterministic Ecmwf For Added Detail In The Surface Graphic For Frontal Progression Along The West Coast And Into The East Coast.

The Over-Arching Theme Of This Medium Range Forecast And Flow
Pattern Is The Storm Track.

The Progressive Pacific Troughs Migrating Through The Intermountain West Take On What Appears To Be A Very Seasonal Or Typical April Cyclone Track Through Eastern Colorado...The Mid-Missouri Valley And Into The Upper Midwest. And Through Day 4...The 28/12z Gefs/Ecens Ensembles And Their Mean Do Not Waver From This Approach...Sending A Cyclone Across The Platte River Valley And East-Northeastward Into The U.P. Of Michigan.

Ahead Of The System...A Deep South To Southwest Flow...Warm
Advection And Low-Level Moisture Transport. A Dry Slot And Strong
Afternoon Surface Heating Should Be Enough To Generate
Convection...And Behind The Intensifying Surface Low And Cold
Front...A Rush Of Cold Canadian Air Spreading Rapidly Southward
Through The Plains And Midwest.

Where The Differences Begin And End--Concern The Second System
(And Generally Around Thursday Afternoon_End Of Day 5).

The Next Trough Exiting The Rockies May End Up Ejecting Out In Several Pieces Rather Than As One Well-Defined Entity.

Granted...The 28/12z Deterministic Ukmet...Canadian...Gfs And Ecmwf Agree That The Bulk Of The 500mb Circulation And Its Associated Vorticity Migrates Through The Four-Corner Area And Will Emerge From The High Plains Thursday Afternoon.

But They Also To Some Degree...Provide A Secondary Wave That Glides Along The Warm Front And Fans Out Across The Mid-Ms And Ohio Valleys On Wednesday Night And Early Thursday Morning.

Not Surprisingly...The Surface Pattern Reflects This As An Inverted Trough With The Ukmet...Canadian And Gfs Not That Unrealistic With Their Weak Surface Trough Solutions Developing Across Sern Missouri Northeastward To West Central Ohio.

All Of Which Precedes The Vigorous Upper System That The Ecmwf Wraps Into A Deep Sub-996mb Low Across West Central Iowa At
4/00z.

The Gfs And Canadian Like This Low Invof Oklahoma And A
Secondary Surface Wave Along The Warm Front Near Cincinnati.

So There Is Room For Improvement And Better Consensus.

Yesterday...I Liked The Idea Of Less Positive Tilt And More Negative Tilt Downstream For This System As It Consolidates Over The East-Central Us By Day 6-7. And Will Hold On To This Notion... Continuing This Theme...With The Ecens Mean Leading The Way Into Day 7 Off The Mid-Atlantic Coast.

Furthermore...Using The Ecens Mean As A Baseline In The West... Makes For A Smooth Run-To-Run Transition Between Onshore Flow Episodes This Medium Range Period.

Again...If There Was A Preference To The Gfs...Then The 27/18z Deterministic Gfs/Gefs Might Better Serve Those Interests Along The Pacific Northwest Coast...But Overall...The Past 4-Cycle Trend Of The Gfs Is Riddled With Flip-Flop Forecasts.

Previous Shift Synopsis Of The West Probably Says It Better And
Follows...

In The West... Larger Disagreement Between The Quicker Gefs
Ensemble Members And The Slower Ecmwf Members Becomes Evident By Tue/D4.

Trend Has Been Toward A Slower And More Amplified Trough... Despite The Opposite Trend Downstream In The East... So Preference Lied With The Ecmwf/Ecens Mean Cluster Of Solutions
Along With Ongoing Wpc Continuity.

System Should Dive Through The Southern Plains Wed/D5 And Turn The Corner Toward The Midwest/Great Lakes By The End Of The Week.

Models Diverge In Somewhat Typical Fashion With The 28/00z Gfs Quickest... 28/00z Ecmwf Slowest... And The 28/00z Canadian And 28/06z Gfs Somewhat In The Middle.

28/00z Ecmwf Ensemble Mean Offered A Most Reasonable Solution And Has Support From Several Individual Ensemble Clusters. Incorporated Wpc Continuity Which Fit Well With Preference.

Sensible Weather Highlights...

The System Moving Through The Central Plains Mon-Tue/D3-4 Will
Produce Some Wintry Weather Along Its Northern Periphery As The
Deformation And Comma Head Cloud Shield Wraps Up From The
Mid-Missouri Valley Northeastward Into The Upper Midwest.

For The Northern Plains... Cold Air Plunges Southward With Temps 10-20f Below Climo.

Ahead Of The Cold Front... Warm Advection Surges Into The Central Lakes Region And Mid-Mississippi Valley With High Temperatures About 10f Above Climo.

This Cold Pool Will Move Eastward For Tue/D4.

By Wed/D6... Height Falls Entering Southern Plains Along With Sfc
Low Pressure Exiting Se Co And Increased Gulf Moisture Will Set
The Stage For Convection In The Southern Plains.

Spc Has Highlighted A Risk Of Severe Weather Centered Over Eastern Ok Into Western Ar. System And Associated Convection Should Push Into The Southeast Fri/D6.

Ensembles And Deterministic Models Indicate Potential For Widespread Moderate Rain Between I-20 And I-70 At Week's End As The Upper Trough And Sfc Boundary Slides Eastward.

Any Wintry Precip Should Be Confined To The Upper Midwest Into The
Western Great Lakes.


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