Severe Weather Threat Jul 16-20

Medium Range Model Guidance From The Ecmwf And Gfs
Deterministic/Ensemble Systems Is In Reasonably Good Agreement
Indicating Gradual Amplification Of The Flow Pattern With A Broad
Long Wave Trough Developing Across The Great Lakes And Nern States During The Second Half Of The Period.

An Associated Surface Low Is Forecast To Move Ewd From The Great Lakes Into The St Lawrence Valley With A Trailing Cold Front Moving Sewd Across The Great Lakes And Nern States...Especially During Days 7-8 /Fri Jul 19-Sat Jul 20/.

A Warm/Moist Low Level Air Mass Is Expected To Be In Place Ahead Of The Front In The Wake Of The Weakening Upper Ridge... Suggesting Increasing Potential For Organized Convective Storms To Develop.

There Are Differences In The Handling Of The Short Wave Troughs And Surface Low Development Between The Different Models. However...In A General Sense The Latest Guidance Suggests The Convective Threat Will Increase Over Upper Ms Valley And Wrn Great Lakes On Day 6 /Thu Jul 18/ Then Spread Ewd Across The Entire Great Lakes Region On D7 /Fri Jul 19/ Before Continuing Across Much Of The Nern States/Mid Atlantic Region On D8/.

Since The Primary Severe Storm Threat Appears To Be In The Second Half Of The D4-8 Period...Prefer To See Additional Model Agreement In Thermodynamic And Kinematic Forecasts Over Multiple Model Cycles Before Delineating Any 30% Severe Probability
Areas With This Much Lead Time.

However...If Subsequent Model Runs Maintain The Previously Described Scenario With Relatively Small Variance In Their Solutions ... The Possibility Of A Multi-Day Severe Event From The Upper Ms Valley Into The Nern States Will Become More Likely.

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