Thank you for the guidance, especially Chris.  The solution was to include the Index_ID in the first SELECT as shown below.  The run time is now 3 seconds on the...

USE [DMHDB]
SET ANSI_NULLS ON
SET QUOTED_IDENTIFIER ON

IF EXISTS (SELECT TABLE_NAME FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_NAME = 'CalcEvap')
DROP TABLE CalcEvap;

CREATE TABLE [dbo].[CalcEvap](
[ID] [decimal](38, 0) IDENTITY(1,1) NOT NULL,
[LEVEL_ID] [int] NOT NULL,
[MONITORING_DATETIME]...

Uploading as txt

Thanks for the guidance in cleaning up the SQL.  It is attached but I haven't been able to run it because the connection to the remote system is down right...

The run took just as long when using the CE alias in the update.

The order of the columns in the index can not be changed.  The PK is clustered and there are indexes for Level_id, Monitoring_datetime, and for variable_ID.