US Extended Forecast thru Sep 7

...Pattern Overview...

The Models Maintain A Nearly Steady-State To Slightly Retrograding
Pattern In The Lower Half Of The Conus Below 40 Degrees Latitude
Through The Medium Range Period...Sat/Sep 07...With An Upper High
Over The Central/Southern Plains The Most Prevalent And Dominant
Feature.

Its Persistence And Strength Support Above Average Confidence That Hot And Dry Conditions Will Continue Beneath And Along The Perimeter Of The High.

Across The Northern Half Of The Conus...Above 40 Degrees Latitude ...The Pattern Is Expected To Consist Of An Initially Stalled Upper Cyclone Offshore The Pacific Northwest...That Should Eventually Move Inland With Cooler Temperatures And Precipitation...But With Very Uncertain Timing...While From The Northern Plains Across The Great Lakes/Northeast...Progressive Flow Influenced By Multiple Streams Likely Leads To Multiple Frontal System Passages And Generally Cooler Temperatures...The Details Of Which Are Also Unclear Due To The Pattern's Short Wavelength And Possibility Of Phasing.

...Guidance Preferences And Uncertainty...

The Nearly Stationary Upper High Over The Plains And Eventually
Stalling Upper Cyclone Near The Pacific Northwest Alone Suggest
That Persistence Should Be Part Of The Final Model Preference.

However...12/18/00z Guidance Have Broken Continuity With The
Timing Of The Upper Cyclone By Becoming About A Day Faster Moving Inland Beginning Day 6/Fri Compared To Yesterday.

Given The Tremendous Spread That Forms Upstream During This
Period...Confidence In Any Particular Solution...Even A Consensus... Remains Low. Therefore...The Overall Preference Is To Nudge The Previous Forecast Toward The Newer Model Consensus...That Accounts For The Faster Trend Across The Pacific Northwest...But Not So Fast To Exclude Previous Solutions And Forecasts. Specifically...The Final Model Blend Is The Same Through Day 5/Thu ...Then 1/2 Each Continuity And 00z Model Consensus.

...Regional Highlights...

Across The Pacific Northwest...The 00z Gfs/Ukmet Are Close To
Their Recent Runs In Depicting Faster Timing With The Cyclone
Moving Inland By The End Of Next Week...But Again Have Chosen
Slower Timing That Is About Halfway Between The Gfs/Ukmet And The Previous Forecast.

The Cyclone Should Be Accompanied By Falling Temperatures And A Surge In Precipitation...Some Which Could Be Quite Heavy... Particularly For The Cascades.

Elsewhere...Precipitation Will Likely Be Most Pronounced Within
Proximity To Weakening Or Decaying Cold Fronts Across The
Southeast As Well As Within The Continued But Generally Weak
Monsoonal Pattern Across The Southwest...While Hot And Dry
Conditions With Temperatures Possibly Remaining Near 100 Continue Across Portions Of The Central/Southern Plains.


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