Monday, November 2, 2009

Somewhat of a forecast bust

Today, both I and the NWS was expecting a dry day over Puget Sound, with perhaps a sprinkle overnight when no one would notice...then improving conditions tomorrow.  The basis of these forecasts were the output from computer forecast models--such as the ones shown below (three hour rainfall ending 1 pm and 4pm, probabilistic forecasts from the UW ensemble system--red indicates 90% probability of rain):




The approaching front was somewhat stronger than forecast and moved in more quickly, so that there were some light showers during the midafternoon (see radar images at 1 and 2:42 PM).  Not the forecast bust of the century, but it shows how things can go wrong, even for a short-term forecast.

11 comments:

smokejumper said...

Well usually if the weather deviates the day of the event, they issue short term forecasts but todays case in Seattle, it was too late, the showers came and went. Why? Well, maybe if the entire SW quadrant of the radar wasn't missing, forecasters could have seen that the speed and rain was off a little and planned accordingly.

It is absurd that there isn't a coastal radar with such a large population downwind. No, lets make sure the small town of Eureka knows what going on, but leave the aviation, military, shipping, energy, and outdoor recreation capital of the west coast in the dark. Sorry for the rant, I feel better.

Cliff Mass Weather Blog said...

I agree...a coastal radar would reveal such timing/strength errors as systems approach our coast. Fortunately, Senator Cantwell has solved this problem..in two years we should have a radar.

natchrl8r said...

Bellingham had hard steady rain for hours. Did I miss the short-term forecast for the North? If not, the radar should have caught it entering the straights.

mainstreeter said...

some viewpoints on the upcoming winter for eastern Washington.

WEATHER: Mild winter on horizon
By The Spokesman-Review

Spokane If you’ve been dreading another winter of heavy snow, something is happening thousands of miles away that might ease your mind.

El Nino is brewing in the tropical Pacific Ocean, and it’s expected to keep temperatures above normal and snowfall below normal this winter in the Inland Northwest.

The federal government reported Monday that the moderate El Nino should have wide-ranging effects on weather in the U.S., said Ron Miller, of the National Weather Service in Spokane.

The most recent moderate El Nino was in the winter of 2002-’03, when 20.5 inches of snow fell at Spokane International Airport. The average winter snowfall is 47.6 inches.

A strong El Nino in 1997-’98 brought only 15.5 inches of snow at the airport.

El Nino typically causes Pacific storms to move south and strike across California and the Great Basin states, leaving the Pacific Northwest under a fair weather pattern. Air stagnation can be a problem in this region without frequent storms to clear out low-lying temperature inversions.

Eastern Washington University geography professor Bob Quinn, an El Nino expert, said he expects the mild winter to bring more rain than snow. Wet weather in October -- with 2.31 inches of precipitation in Spokane -- may be a sign of things to come this winter.

“It’s more of the warm, wet variety” of El Nino, Quinn said.

In the past 60 years, there have been 17 documented El Nino events. In all but three, snowfall in Spokane was below normal.

The term El Nino is derived from folklore in South America, where El Nino can disrupt fisheries and cause storms around Christmastime. El Nino means boy, or the Christ child, in Spanish.

The Farmers’ Almanac isn’t buying into the idea that El Nino will cause a mild winter here. The almanac forecasts cool weather and average precipitation across the Inland Northwest. Bitter cold will remain east of the Continental Divide, the almanac says.

Spokane set a record of 97.7 inches of snow in 2008-’09 and saw a near-record season the year before, with 92.6 inches.

The average date for the first measurable snow at Spokane International Airport is Nov. 12. Last year, the first measurable snow came Nov. 28.

Cliff Mass Weather Blog said...

It isn't raining in Bellingham!...just fog!

Josh said...

Its all good Cliff
Mother Nature just reminding us who is in charge. Keeps the digital age somewhat humble.

smokejumper said...

hey mainstreeter, just wanted to comment on your post about E. Washington and El Nino because that is where I grew up and currently live.

If you check the website, http://www.cpc.ncep.noaa.gov/products/predictions/threats2/enso/elnino/wa_bar.html, click on the normal vs. el nino average and distribution of totals during ENSO events.

There is no dispute that El Nino brings overall warming over the entire state. But precipitation is interesting because western washington and especially the cascades are below average but E. washington above average. In fact, a few events amoung the 1/3rd wettest.

Reason, just an opinion, not scientific fact, the weather pattern is more amplified during El Nino, blocking highs, cutoff lows, southern tropical jetstreams, etc. and E. Washington is more acceptable to rainy events because orographics don't play as much as a role.

Last month perfect example. For that one week when the jet stream was pointed into northern california, in 5 days it rained 1.20 inches, 1/8th our annual average. Hasn't rained a single drop since while it countinued to dump on the westside.

And last winter, la nina (persistant cool and moist NW jetstream), it was actually a pretty temperate and dry season for the majority of the area until you got to the eastern fringes of the state where the air starts to rise and cool again.

Temperature wise, we do often get persistant upper level blocking ridges during El Nino, but that spells stagnant and foggy weather weeks at a time in the valleys, so daytime temps are actually colder but nighttime temps stay way up, so I think that's a partial reason why the daily average mean is pushed so far above average.

I have a economics degree, not meteorology, but being your neighbor wanted to put in my two cents.

natchrl8r said...

I was referring to yesterday, Cliff. The downpour was unanticipated here. This a.m. it was foggy as forecast.

mainstreeter said...

smokejumper, I grew up in Kennewick, I remember the cold spells in the winter followed by a "chinook" or 2 over there. I still visit frequently. E wa seems to get it's secondary max precip in the early spring. I did see more wooly worms this year which is also folklore. Don't know if that will play into anything.

It snowed on Oct 31, 1973 there. The Pasco depot used to keep a 'snow board' with all the early snowfalls back to the 1910 period.

RobbyRob said...

The winds have really picked up in the North Bend/Snoqualmie area, is this a gap event or a mountain wave event? How strong of gusts should we expect tonight?

mjgrota said...

So I guess the moral of this story is that it is good to have a team of human forecasters who can identify a bad model solution and add value with timely amendments. If you depended only on computer outputs like Probcast you would need to wait for the next run to add that value and hope the guidance was better.