US Extended Forecast thru Apr 18

Extended Forecast Discussion
Weather Prediction Center College Park Md
251 Am Edt Fri Apr 11 2014
Valid 12z Mon Apr 14 2014 - 12z Fri Apr 18 2014

...Overview And Preferences...

Upstream A Split Flow Configuration Is Fcst To Move Into The Wrn Half Of Noam With A Trough Over The Conus And A Ridge Over Canada.

An Amplifying Trough Then Comes Into The Picture Offshore The West Coast By Next Fri.

From Early In The Period Operational Models Display Shrtwv Diffs With The Ern Trough And Corresponding Spread For Frontal Wave/S And Timing... While Upstream Spread For Some Details From The Ern Pac Into The Wrn Conus Quickly Becomes Quite Large.

Current Operational Model Spread Favors Emphasis Of The Ensemble Means With Minor Adjustments To Enhance Detail Where Enough Support Exists.

The Preferred Fcst Blend Starts With 2/3 Weighting Of The 12z Ecmwf
Mean With The Remainder Consisting Of The 18z Gefs/12z Naefs Means Due Primarily To Relative Clustering Of Guidance Toward Slower Frontal Progression Over/Near The Southeast Around Tue-Wed.

...Guidance Evaluation...

Within The Ern Trough Aloft There Is A Majority Cluster Whose
Handling Of Srn Rockies Shrtwv Energy Crossing The Srn Tier Is
Slower/Sharper Than Recent Gfs/Gefs Mean Runs... Leading To A
Slower Frontal Wave Eventually Tracking Into The Wrn Atlc.

However Non-Gfs Solns Are Still Diverse Enough In Their Specifics
To Recommend Leaning More To The 12z Ecmwf Mean Until Details
Aloft Become Better Resolved.

Among New 00z Solns The Gfs Is Still Fastest/Weakest With The Srn Tier Shrtwv While The Ukmet Becomes An Extremely Fast Soln With The Nrn Part Of The Trough By Tue.

Significant Spread Exists Off The West Coast Already At The Start Of The Period Early Mon With Ern Pac Energy Heading Into The Ridge
Initially Over Wrn Noam.

At Varying Latitudes The 12z/18z/00z Gfs Runs Bring A Rather Deep Closed Low Into The Wrn States While Other Models Generally Favor Tracking The Core Of Mid Lvl Energy Into Swrn Canada.

Wide Spread Among 12z Ensemble Members Precludes Fully Discounting A Particular Operational Soln But The Ensemble Means Through The 12z/18z Cycles Are Not All That Supportive Of A Closed Low Tracking As Far Swd As Recent Gfs Runs.

By The Latter Half Of The Period It Is The 12z Ecmwf That Strays
From The Ensemble Consensus In Depicting Faster Ern Pac/Conus Flow Than The Majority Scenario.

By Day 7 Fri Latest Gefs/Ecmwf/Cmc Means Are Quite Similar In Showing A Mid Lvl Trough Axis Reaching 100w Longitude.

...Sensible Weather Highlights...

Strong Cold Front Crossing The East Will Likely Be Accompanied By
Bands Of Locally Hvy Rnfl Aided By Low Lvl Gulf Inflow.

Temps Reaching 10-25f Below Normal Behind The Front May Be Cold Enough For Some Pcpn To Fall In The Form Of Snow In The Wrn Periphery Of The Pcpn Shield Across Parts Of The Upr Grtlks And Then From The Cntrl Aplchns Into The Northeast.

Before The Cold Air Arrives... Expect Some Anomalies Of Similar Magnitude In The Warm Sector With Highest Departures From Normal Over The Northeast.

In The Wake Of This Front High Pressure Should Settle Over/Near New England With Enough Gradient Surrounding It To Support Breezy Conds Away From The High Center. Temps Should Moderate To Within 10f Of Normal By Late Next Week.

Details Remain Uncertain But There Is Reasonable Agreement That
Ern Pac To Plains Troughing Will Spread Mstr Into The Nwrn States
Tue And Then The Nrn-Cntrl Rockies Through The Plains.

Gulf Inflow Could Begin To Enhance Amts Over The Plains By Late Next Week But At This Time There Is Not Full Agreement On That Idea.

Some Snow Is Psbl In Higher Elevs Of The West... As Well As The
Nrn Plains Depending On Evolution Aloft And Time Of Day Pcpn
Occurs.

Wrn Conus Temps Should Be Above Normal Early In The Week
And Then Within A Few Degs Either Side Of Normal Thereafter.


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