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US Extended Forecast thru Apr 19

...Overview And Preferences...

An Amplified Trough Aloft Pushing A Wavy Cold Front Off The East
Coast Early In The Period Will Rapidly Flatten/Lift Newd...
Leaving The Front Over The Wrn Atlc For The Rest Of The Fcst.

Meanwhile Pacific Energy Initially Near The West Coast Will Amplify As It Moves Into The West/Plains With Psbl Incorporation Of Srn Canada Energy Leading To Uncertainty In Sfc Evolution/Timing From The Plains Into Wrn Grtlks.

Guidance Is Continuing To Indicate Establishment Of Broad Cyclonic Flow Over The Ern Pac By Late In The Period.

With Primary Features Of Interest The Operational Model Runs Continue To Differ Enough From Each Other And The More Stable Ensemble Means To Favor Continued Emphasis Of The Gefs/Ecmwf Means As The Starting Point For The Medium Range Fcst.

Days 3-4 Tue-Wed Are Weighted 70 Pct Toward The 12z Ecmwf Mean Versus The 18z Gefs Mean Based On Prefs For Slower Timing Of The Ern Front... Followed By An Even Blend Due To More Similar Solns For Days 5-7 Thu-Sat.

...Guidance Evaluation...

With The Initial Amplified Trough Aloft Crossing Ern Noam Early In
The Period There Is Still A Fairly Pronounced Consensus Indicating
That The Shrtwv Crossing The Southeast Will Be Slower And/Or
Stronger Than Multiple Gfs Runs.

However This Majority Cluster Suggests The Feature Should Become More Sheared Than Operational Ecmwf Runs During Tue-Wed So Would Currently Expect Waviness Along The Front To Be Less Concentrated And Farther Ewd Than In Recent Ecmwf Runs.

The Ecmwf Mean Has Trended A Little Slower With The Nrn Part Of The Front Over The Past Day While But A Number Of Operational Solns Show A Broader Nrn Stream Trough That Would Push That Part Of The Front Farther Ewd. Adding In 30 Pct Weighting Of The 18z Gefs Mean Helps To Account For This Possibility.

Rather Quickly The Flow Aloft Becomes Parallel To The Front So Expect The Front To Linger Off The East Coast For A While.

The Preferred Ensemble Means Hold Back Upstream Energy Enough To Keep Waviness Along The Front To A Minimum Through Day 7 Sat... With Fewer Than 20 Pct Of 12z Ecmwf/Gefs/Cmc Members As A Whole Showing Any Defined Sfc Low Off The East Coast Fri-Sat.

In Contrast Some Operational Solns Are Faster With Upstream Energy And Are More Eager To Develop A Frontal Wave.

As West Coast Energy Amplifies Into The West And Then The Plains
There Are Two Primary Uncertainties That Arise... Timing Of The
Overall Trough And Extent To Which Shrtwv Energy Over Srn Canada
Is Incorporated Into The Nrn Part Of The Trough.

The Past Couple Ecmwf Runs Have Been Noticeably Fast Relative To Ensemble Guidance While The 12z/18z Gfs Runs Also Become Rather Progressive In The Latter Half Of The Period.

Meanwhile The Complex Nature Of Cntrl-Srn Canada Flow Early In The Period Leads To Low Predictability For Energy Near The Us-Canadian Border.

Evolution Of This Nrn Energy Will Play A Significant Part In Sfc Evolution From The Plains Into The Grtlks.

Over The Past Couple Days A Number Of Operational Model Runs Have Been Stronger Than The Means Aloft... Leading To A Stronger/Farther Nwd Sfc System.

Trends In The Means Over The Past Day At Least Support A Stronger Inverted Sfc Trough But Confidence Is Not Sufficiently High To Depict More Definition Than That.

Fast Nature Of Upstream Pac Flow Leads To Reduced Confidence In
Shrtwv Details By Late In The Fcst But There Is Reasonable Agreement With The Idea Of Broad Troughing Of Moderate Amplitude
Becoming Established Over The Ern Pac.

...Sensible Weather Highlights...

The Wavy Cold Front Crossing The East Early In The Period Will Be
Accompanied By One Or More Bands Of Locally Hvy Rnfl With Some
Snow Psbl In The Colder Air Over Parts Of The Grtlks/Nrn Half Of
The Aplchns/Northeast.

Temps Behind The Front Will Offer Quite The Contrast To The Warmth Before Frontal Passage... With Daytime Highs 10-25f Below Normal Tue-Wed.

Readings Should Trend Closer To Normal Later In The Week.

From Mid To Late Week Ely Low Lvl Flow Should Keep Periods Of Rnfl Over The Fl Peninsula.

Also The Stnry Front Over The Atlc Will Have To Be Watched For Any Waves...Currently Of Low Confidence... That Could Bring Mstr Back To Parts Of The East Coast.

Nrn Parts Of The West Should See Multiple Periods Of Pcpn With The
Combination Of A Leading Trough Aloft Moving Into The West And
Trailing Pacific Energy Streaming Into The Pac Nw/Swrn Canada.

The Leading Trough Will Bring A Brief Cooling Toward Normal Over
The West Before Temps Return To Above Normal Lvls By Fri-Sat.

Farther Ewd Expect Mstr To Spread Across The Nrn-Cntrl Rockies
Into The Plains And Psbly As Far As The Upr Grtlks... With Some
Pcpn Potentially In The Form Of Snow Over The Rockies And Nrn Tier
States Where Below Normal Temps Will Prevail For One Or More Days.

Timing/Amplitude Of The Trough Aloft Once It Reaches The Plains
Will Determine How Much Gulf Mstr Is Drawn Into The Plains/Ms Vly
By The Latter Half Of The Week.

Current Prefs For The Ensemble Means Would Lead To More Plains/Ms Vly Mstr Than Some Recent Operational Runs... Though 00z Solns Thus Far Seem To Be Trending Closer To The Means Aloft Through Thu.


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