WunderBlog Archive » Category 6™

Category 6 has moved! See the latest from Dr. Jeff Masters and Bob Henson here.

Pineapple Express Bringing Significant Rains to Drought-Stricken California

By: Dr. Jeff Masters, 10:10 PM GMT on February 06, 2014

A very moist “Pineapple Express” flow of air from the Hawaiian Islands will impact California through Sunday, likely bringing enough precipitation to make a noticeable dent in the state’s dire drought conditions (though the exceptionally dry and hard soils caused by California’s driest year in its history are forcing the heavy rains to run off faster than usual, reducing the amount of moisture that can soak into the soil.) Some locations may see more rain in a four-day period than they have had during the previous eight months. NOAA’s Weather Prediction Center is calling for most of Northern California to receive more than 2” of precipitation through Sunday, with many higher elevation areas expected to get 4 - 6”. Up to three feet of snow is predicted to fall in the Sierra Mountains, though it appears much of the precipitation will fall as rain, reducing the benefit of the moisture during the coming summer months (when Sierra snow melt provides an important source of water.) As of Thursday at 1 pm PST, Big Sur had received 2.14” of rain, which triggered a rock slide onto Highway 1.


Figure 1. Total precipitable water (TPW) for Thursday, February 6, 2014. TPW is how much rain (in inches) would fall at a given location if one condensed out all of the water vapor in a column above the location into rain. For reference, 1 inch = 25.4 mm. A narrow “Atmospheric River” of moisture is seen extending from the subtropics near Hawaii into California. Image credit: University of Wisconsin SSEC.

Drought far from busted
This weekend’s Pineapple Express is a marvelous break from the extraordinary dry conditions that have gripped California for the past thirteen months. If one could put a monetary value on the moisture from this storm, I speculate that it would easily be worth a billion dollars. But the state is in such a deep precipitation hole that it needs at least six more events like this over the next two months to pull them out of drought. Between January 1, 2013 and February 5, 2014, the San Francisco Airport received just 4.24” of rain, which is 21.19” below normal for the period—by far the driest such period in their history. The last time San Francisco had more than 1” of rain was Christmas Day, 2012. Thursday’s new Drought Monitor product showed that drought conditions in the state had remained almost the same as the previous week, with 94% of the state in drought, and a slight expansion of the area in the worst category of drought—exceptional—from 9% to 10%.


Figure 2. Comparison of how much rain is needed to relieve drought conditions in Central California, via Twitter from NWS Sacramento.


Figure 3. Amount of precipitation needed in one month to end drought conditions. In San Francisco, more than 18” of rain is needed in one month, and the average annual rainfall in the city is about 20”. Image credit: NOAA.

Atmospheric rivers: California’s big drought busters
Narrow bands of copious moisture originating in the subtropics like this weekend’s “Pineapple Express” are called “atmospheric rivers”, and are responsible for about 30 - 50% of California’s yearly precipitation. A strong “atmospheric river” transports an amount of water vapor roughly equivalent to 7.5 - 15 times the average flow of liquid water at the mouth of the Mississippi River. As discussed in a blog post today by Climate Central’s Andrew Freedman, research by Michael Dettinger of the U.S. Geological Survey and the Scripps Institution of Oceanography, published in December 2013 in the Journal of Hydrometeorology, found that atmospheric river events can effectively end major droughts in California within just one month, pulling the state from a significant precipitation deficit to a surplus. Wunderground weather historian Christopher C. Burt has a post on the last drought-busting atmospheric river event, in March 2012. I don’t see that happening this month, though. The latest 2-week run of the GFS model shows the state returning to relatively dry conditions beginning on Monday, with a ridge of high pressure dominating the weather for the remainder of the week. The most recent 1-month and 3-month forecasts from NOAA’s Climate Prediction Center call for higher than average possibilities of dry conditions into the spring of 2014. California’s best hope of busting the drought lies in the formation of an El Niño event next winter. The warm waters that El Niño events bring to the Eastern Pacific typically shift the jet stream to a position over California, bringing numerous low pressure systems and the occasional atmospheric river during the winter rainy season. The latest February 6, 2014 El Niño outlook from NOAA gives some hope that this will happen:

”An increasing number of models suggest the possible onset of El Niño. Strong surface westerly winds in the western Pacific and the slight eastward shift of above-average temperatures in the subsurface western Pacific potentially portend warming in the coming months.”

Have a great weekend, everyone, and I’ll be back Monday with a new post.

Jeff Masters

Drought

The views of the author are his/her own and do not necessarily represent the position of The Weather Company or its parent, IBM.

Reader Comments

1501. LargoFl

THIS HAZARDOUS WEATHER OUTLOOK IS FOR EAST CENTRAL FLORIDA.

.DAY ONE...TODAY AND TONIGHT.

.RIP CURRENT IMPACT...
A LONG PERIOD EAST SWELL WILL PRODUCE A MODERATE THREAT FOR RIP
CURRENTS AT THE BEACHES OF EAST CENTRAL FLORIDA. IF YOU ENTER THE
CHILLY SURF MAKE SURE TO SWIM NEAR A LIFEGUARD AND NEVER SWIM
ALONE.

.DAYS TWO THROUGH SEVEN...TUESDAY THROUGH SUNDAY.
AN ABOVE NORMAL THREAT FOR RIP CURRENTS WILL EXIST AT THE ATLANTIC
BEACHES THROUGH MIDWEEK.

A LOW PRESSURE SYSTEM WILL PUSH ACROSS NORTH FLORIDA LATE IN THE
DAY ON WEDNESDAY. THIS WILL BRING A SLIGHT CHANCE FOR
THUNDERSTORMS TO EAST CENTRAL FLORIDA LATE WEDNESDAY AFTERNOON
AND EVENING.

MARINE CONDITIONS WILL DETERIORATE WEDNESDAY NIGHT INTO THURSDAY
IN ASSOCIATION WITH THE LOW PRESSURE SYSTEM.

.SPOTTER INFORMATION STATEMENT...
SPOTTER ACTIVATION WILL NOT BE NEEDED TODAY.

$$

SEDLOCK
About the current forecasts.
Here's the PAX for Texas, below.
However, consider the current temps across Texas as already shown on Wundermap. It doesn't look right.
Temps already are freezing further SW and will likely only get colder, sooner this evening -- not waiting for the wee hours of the morning, this time, IMO.
That, plus the higher rain chances make me think more icy weather will get further south this time.

Monday Night Forecast
1503. barbamz
Hello, but whith bad pictures esp. from England ...

David Cameron backs Environment Agency as Berkshire hit by floods - video
The Guardian, Monday 10 February 2014 16.11 GMT
Aerial footage follows the course of the Thames through Surrey and part of east Berkshire where hundreds of properties have been flooded on Monday. Residents take their pet dogs to safety in in Wraysbury after the Environment Agency issued 14 warnings of danger to life along the Thames. The prime minister, David Cameron, gives his response

Flooding crisis hits the Thames as political row worsens - live updates
Nem models coming in a little more snowy... local models trending drier..
1505. LargoFl
1506. hydrus
GFS upped snow totals with the initial swath again...sub 0c 850mb temps




still in flux
Quoting 1474. Patrap:
How do we get off Oil ?



does Hawaii not use oil? :)
1509. nash36
Looks like the 12z GFS is wanting to push the ice further S and E to include folks E of 1-95
JeffMasters has created a new entry.
Models are also tryna give me sleet instead of freezing rain.... boooo
1512. N3EG
Things happen here too in Western Washington state. 10 inches of snow this weekend.

Statement as of 3:35 AM PST on February 10, 2014

... Freezing Rain Advisory in effect until 10 am PST this morning for the lower Columbia and I-5 corridor in Cowlitz County...

The National Weather Service in Portland has issued a Freezing Rain Advisory... which is in effect until 10 am PST this morning.

* Timing... through 10 am this morning.

* Ice accumulations... less than a tenth of an inch.

* Impacts... freezing rain will create slick roads and hazardous travel conditions.

Precautionary/preparedness actions...

A Freezing Rain Advisory means that periods of freezing rain or freezing drizzle will cause travel difficulties. Be prepared for slippery roads. Slow down and use caution while driving.

1513. hydrus
Quoting 1426. hydrus:


That top map seems to be the likeliest projection I've seen for SE TX so far on this storm, but I think the frozen precip may come on into the Houston area.
Quoting 1399. StormTrackerScott:
NWS is saying -14C 500 millibar temps for Orlando Wednesday evening. That is very impressive!! Anytime you get that amount of cold air aloft over C FL this time of year then you better watch out. I think this will be more of a severe wind and hail event for C & S FL with maybe a tornado or two. We had one of these event last March and it brought 80 mph winds to Orlando. The key is getting sufficient daytime heating before the storms move in to fully take advantage of all the dynamics that will be in place.



Yes 500 mb temps do look supportive of severe weather, something we haven't seen much of since the end of the rainy season.

We'll see if this model depiction holds the next couple days.
Jeff,

Tell them the whole truth. This California and western drought is permanent because it is driven by the new, high level of CO2 in our atmosphere - 400 part per million.

We can handle the truth - I hope. Emission levels were ignored by the US and governments worldwide. Now the bill is due.

Jeff, your climate guys told us - DO NOT EXCEED 350 PARTS PER MILLION. We didn't listen. Now we need to react to the facts, not do wishing and hoping and rain dances.

Mr. Masters - tell the public the stark facts fully.