A Spatial View of a Wet Winter

This has been an amazingly wet winter-- but where has it been most unusual?   To gain insights into this important question, here is an analysis from the Western Regional Climate Center (WRCC) showing the percent of normal for October 2016-March 2017 precipitation over the western U.S.  The darkest greens indicate the wettest on record.  A huge region region stretching from northern CA through northern Nevada, into Idaho,  Wyoming, Montana and eastern WA.  Nearly the entire Northwest U.S. was in top 10% wet season.  The April version will add parts of western WA.

The late winter (Feb-March) maps shows how wet conditions were particularly unusual in the northern Rockies.  Eastern Washington, Idaho, and western Montana had unprecedented large amounts of precipitation.

Mean temperatures from October through March?  Cooler than normal over Washington and Oregon....no big surprise.

This week, a colleague at the US Army Corps of Engineers told me that the soils of our region are extraordinarily saturated....and that he was worried about spring flooding.   Well, here is the latest soil moisture observations based on the GRACE satellite (measures moisture using its effects of gravity). The entire Northwest is WAY wetter than normal (darker blue colors).

A front is now approaching our region and there will be rain later this afternoon, tonight and early Sunday morning (see forecast precipitation for the 3 hr ending 8 PM tonight).  So get out now.

Fortunately, the latest forecasts suggest drying from mid-Sunday through the middle of next week, and the latest NOAA Climate Prediction Center forecast indicates drier than normal conditions for much of the West Coast for the 6-10 day forecasts (see below).  Time for me to try planting grass seeds again...

from Cliff Mass Weather Blog http://ift.tt/2psAAgW

A Spatial View of a Wet Winter

This has been an amazingly wet winter-- but where has it been most unusual?   To gain insights into this important question, here is an analysis from the Western Regional Climate Center (WRCC) showing the percent of normal for October 2016-March 2017 precipitation over the western U.S.  The darkest greens indicate the wettest on record.  A huge region region stretching from northern CA through northern Nevada, into Idaho,  Wyoming, Montana and eastern WA.  Nearly the entire Northwest U.S. was in top 10% wet season.  The April version will add parts of western WA.

The late winter (Feb-March) maps shows how wet conditions were particularly unusual in the northern Rockies.  Eastern Washington, Idaho, and western Montana had unprecedented large amounts of precipitation.

Mean temperatures from October through March?  Cooler than normal over Washington and Oregon....no big surprise.

This week, a colleague at the US Army Corps of Engineers told me that the soils of our region are extraordinarily saturated....and that he was worried about spring flooding.   Well, here is the latest soil moisture observations based on the GRACE satellite (measures moisture using its effects of gravity). The entire Northwest is WAY wetter than normal (darker blue colors).

A front is now approaching our region and there will be rain later this afternoon, tonight and early Sunday morning (see forecast precipitation for the 3 hr ending 8 PM tonight).  So get out now.

Fortunately, the latest forecasts suggest drying from mid-Sunday through the middle of next week, and the latest NOAA Climate Prediction Center forecast indicates drier than normal conditions for much of the West Coast for the 6-10 day forecasts (see below).  Time for me to try planting grass seeds again...

from Cliff Mass Weather Blog http://ift.tt/2psAAgW

Strong Spring Convergence Zone Demonstrates Improvements in Numerical Weather Predicton

The most important western Washington weather feature is probably the Puget Sound convergence zone, a band of clouds and precipitation that stretches roughly east-west across northern Puget Sound and into the Cascades (see schematic)

Puget Sound Convergence Zones typically occur when the low-level  winds on the coast are from the west to northwest, peel around the Olympics, and then converge over Puget Sound.  The converging air streams cause upward motion, and thus clouds and precipitation.  Spring is the big season for convergence zones:  westerly winds are more frequent than any other time of the year and the air is often unstable, which gives lots of clouds/rain when the air is given an upward nudge.

Such conditions were evident yesterday (Wednesday).  A satellite image around noon showed the telltale signs of a convergence zone with a band of clouds across the north sound and clear zones to the north and south.  Why clear?  Due to sinking on the Olympics mountains and the mountains of Vancouver Island.

The convergence zone held into the early evening, as suggested by the Camano Island radar image at 7:30 PM.   Wow...that is a nice band of precipitation north of Seattle!

Convergence zones typically drop modest to heavy precipitation from north Seattle to Everett, and this one was no different.   To illustrate, here is the 24-h precipitation ending 5 AM Friday morning.  A few hundredths of an inch over south Seattle, a half inch north of the ship canal, and roughly an inch over Snohomish county.  Even more around Monroe and the Cascade foothills.

A radar-derived 24-h precipitation total from Seattle RAINWATCH suggests a similar picture.

When the convergence zone moves southward, the weather changes  as it crosses a location are dramatic.  Around noon, the convergence line passed the UW, resulting in an abrupt wind shift (southerly to northerly), a few tenths of an inch of rain, a jump in relative humidity from 60 to over 90%, the loss of most of the sun's radiation, and a roughly five degree temperature drop (see below).

Now let me show you how good high resolution numerical weather prediction of the convergence zone has become.

For example, here is the 27-h forecast of the 3 hr precipitation ending at 8 PM Wednesday from the high-resolution (1.3 km grid spacing) UW WRF model forecast started on 5 PM Tuesday....very nice convergence zone.

Or the 24 hr total ending 5 AM Friday from the same run.   Looks good, with heavier precipitation north of Seattle and dry zones to the north and south.  An expanded view over Puget Sound is also shown.

A decade ago we couldn't make such skillful forecasts, but today it is not an outlier.   It represents the impacts of better data and use of data over the Pacific Ocean, higher resolution models, better model physics, and much more.

The Puget Sound Convergence Zone got me interested in NW weather and I still find it fascinating.

from Cliff Mass Weather Blog http://ift.tt/2p9AZGg

Strong Spring Convergence Zone Demonstrates Improvements in Numerical Weather Predicton

The most important western Washington weather feature is probably the Puget Sound convergence zone, a band of clouds and precipitation that stretches roughly east-west across northern Puget Sound and into the Cascades (see schematic)

Puget Sound Convergence Zones typically occur when the low-level  winds on the coast are from the west to northwest, peel around the Olympics, and then converge over Puget Sound.  The converging air streams cause upward motion, and thus clouds and precipitation.  Spring is the big season for convergence zones:  westerly winds are more frequent than any other time of the year and the air is often unstable, which gives lots of clouds/rain when the air is given an upward nudge.

Such conditions were evident yesterday (Wednesday).  A satellite image around noon showed the telltale signs of a convergence zone with a band of clouds across the north sound and clear zones to the north and south.  Why clear?  Due to sinking on the Olympics mountains and the mountains of Vancouver Island.

The convergence zone held into the early evening, as suggested by the Camano Island radar image at 7:30 PM.   Wow...that is a nice band of precipitation north of Seattle!

Convergence zones typically drop modest to heavy precipitation from north Seattle to Everett, and this one was no different.   To illustrate, here is the 24-h precipitation ending 5 AM Friday morning.  A few hundredths of an inch over south Seattle, a half inch north of the ship canal, and roughly an inch over Snohomish county.  Even more around Monroe and the Cascade foothills.

A radar-derived 24-h precipitation total from Seattle RAINWATCH suggests a similar picture.

When the convergence zone moves southward, the weather changes  as it crosses a location are dramatic.  Around noon, the convergence line passed the UW, resulting in an abrupt wind shift (southerly to northerly), a few tenths of an inch of rain, a jump in relative humidity from 60 to over 90%, the loss of most of the sun's radiation, and a roughly five degree temperature drop (see below).

Now let me show you how good high resolution numerical weather prediction of the convergence zone has become.

For example, here is the 27-h forecast of the 3 hr precipitation ending at 8 PM Wednesday from the high-resolution (1.3 km grid spacing) UW WRF model forecast started on 5 PM Tuesday....very nice convergence zone.

Or the 24 hr total ending 5 AM Friday from the same run.   Looks good, with heavier precipitation north of Seattle and dry zones to the north and south.  An expanded view over Puget Sound is also shown.

A decade ago we couldn't make such skillful forecasts, but today it is not an outlier.   It represents the impacts of better data and use of data over the Pacific Ocean, higher resolution models, better model physics, and much more.

The Puget Sound Convergence Zone got me interested in NW weather and I still find it fascinating.

from Cliff Mass Weather Blog http://ift.tt/2p9AZGg

Darth Vapor Strikes Again (And Again)

The ominous music rises...in a galaxy far, far away... a band of unnatural moisture strikes incessantly on a sodden land .... the dark side shows its power.....

The satellite-observed water vapor imagery tonight highlights the huge menace, unimaginably wide and extending across the largest ocean basin of the planet. Its tentacles spread so wide that is covers the entire west coast of the U.S. Extraordinary for April.

An infrared satellite imagery at the same time shows a disturbing form, not unlike deadly structures in horror/sci-fi films.

And a strange ship has just docked in Elliot Bay.

But this is a scientific blog, so let's consider the facts. During the past week, as much as five inches has fallen on the windward side of the coastal mountains from northern CA to the Olympics, with similar amounts over the Oregon/southern WA Cascades.

And it is not over.  The forecast for the 72hr total precipitation ending Friday AM shows as much as 2-5 inches in the Cascades.

The dark side of the atmosphere has produced, well, dark skies, as illustrated by the Space Needle cam later this afternoon.  No sun glasses needed.

And as noted in my previous blog, we are experiencing the wettest October 1- April 30th in the history of Seattle, as depressingly shown in this figure of cumulative precipitation at Sea-Tac for the water year (starting October 1).  The dark green show the amount above normal (44.69 inches total so far).  At this point in time, we should have 30 inches.

Did you know that the West Coast has been so wet, that San Francisco had more than Seattle's normal precipitation this water year?  Unbelievable but true. 

Here is the proof with a cumulative precipitation chart for San Fran--more than 30 inches so far. Beware the dark side of the force.

No wonder the SF imports in our high-tech industries haven't run back to the Bay area...it has been savage even there.

Darth Vapor is certainly something to be feared.

from Cliff Mass Weather Blog http://ift.tt/2q5kDQo

Darth Vapor Strikes Again (And Again)

The ominous music rises...in a galaxy far, far away... a band of unnatural moisture strikes incessantly on a sodden land .... the dark side shows its power.....

The satellite-observed water vapor imagery tonight highlights the huge menace, unimaginably wide and extending across the largest ocean basin of the planet. Its tentacles spread so wide that is covers the entire west coast of the U.S. Extraordinary for April.

An infrared satellite imagery at the same time shows a disturbing form, not unlike deadly structures in horror/sci-fi films.

And a strange ship has just docked in Elliot Bay.

But this is a scientific blog, so let's consider the facts. During the past week, as much as five inches has fallen on the windward side of the coastal mountains from northern CA to the Olympics, with similar amounts over the Oregon/southern WA Cascades.

And it is not over.  The forecast for the 72hr total precipitation ending Friday AM shows as much as 2-5 inches in the Cascades.

The dark side of the atmosphere has produced, well, dark skies, as illustrated by the Space Needle cam later this afternoon.  No sun glasses needed.

And as noted in my previous blog, we are experiencing the wettest October 1- April 30th in the history of Seattle, as depressingly shown in this figure of cumulative precipitation at Sea-Tac for the water year (starting October 1).  The dark green show the amount above normal (44.69 inches total so far).  At this point in time, we should have 30 inches.

Did you know that the West Coast has been so wet, that San Francisco had more than Seattle's normal precipitation this water year?  Unbelievable but true. 

Here is the proof with a cumulative precipitation chart for San Fran--more than 30 inches so far. Beware the dark side of the force.

No wonder the SF imports in our high-tech industries haven't run back to the Bay area...it has been savage even there.

Darth Vapor is certainly something to be feared.

from Cliff Mass Weather Blog http://ift.tt/2q5kDQo