Midwinter Moisture in June

Tomorrow is going to be an unusual June day over the Northwest.  An extraordinary plume of moisture that stretches across the the Pacific is now approaching our shores, and mid-winter amounts of rain will spread over the region.  A satellite image of the amount of water vapor in the upper atmosphere shows a "river "of moisture stretching from the southwest north Pacific to our coast.

Another satellite product of the amount of water vapor in a column of the atmosphere (for 3 AM this morning), shows large amounts of water vapor in the tropics as well as the extension of moisture heading northeastward towards the Northwest.

A forecast for this water vapor at 8 AM Thursday morning shows a very strong plume of moisture headed for the West Coast.  

This moisture plume and associated strong westerly flow will cause substantial precipitation over our region tomorrow as the moisture is forced up by our terrain.  Here are the 24h totals ending 5 AM Friday.   Really amazing amounts for mid-June, with 1-2 inches (pink colors) in many mountain areas and roughly a half-inch in Seattle.   Even eastern WA gets moistened.

To get an  idea of how unusual this moisture plume is for this time of the year, here is the standardized or normalized anomaly for the plume at 11 AM on Thursday from the European Center model (courtesy of Weatherbell, Inc.)   In this approach, the difference of the total water vapor in the column and the normal value for that date are found (the anomaly) and this is divided by a measure of the climatological variability (the standard deviation).  The plume approaching our coast has a normalized anomaly of about 4.5, which would have a return time of several years.

The implications of this event are substantial.  A major wet system in June, moistens the ground and pushes off the wildfire season.  It will also suppress water usage, which started to surge after our recent dry spell (see graphic).  Enjoy the rain....

from Cliff Mass Weather and Climate Blog http://ift.tt/2torouD