Posted at 9:51 AM on June 1, 2009
by Ken Paulman
(the following was written by Paul Huttner, who's having technical difficulties today)
Forecasting weather is risky business some days. Sometimes it's tough to get tomorrow right, let alone next weekend. Imagine trying to forecast several months ahead.
That's what the folks at NOAA's Climate Prediction Center (CPC) do. They've shown considerable success over the past few years with seasonal forecasts. They often do best with winter forecasts during El Niño years. The climatic "signals" are strongest during El Niño for regional weather patterns.
Going into last winter, the CPC three-month outlook called for milder than average temperatures in the Upper Midwest. What we got was an old fashioned winter with January temperatures more than 4 degrees below average.
So you'll forgive me if I grab the salt shaker when CPC is forecasting a cool summer for Minnesota. My skepticism is no reflection on the forecast skills at CPC, they are the best. My grain-of-salt approach lies in the fact that the tropical Pacific Ocean is in a state of flux. Tropical Pacific sea surface temperatures (SST's) are on the rise. The cool La Nina pattern of the past year is history. Temperatures have warmed to near average, and nobody knows how warm they will get.
Will El Niño return next winter?
Changes in the Pacific throw climate and weather systems into chaos around the globe, and right here in Minnesota. Seasonal outlook skill is best with certainty in the Pacific. Now CPC is faced with trying to forecast months in advance based on a changing Pacific Ocean. Hurricane forecasters are dealing with the same chaos. How much will changes in the Pacific affect the Atlantic hurricane season that starts today?
One thing is for sure. We're in a drought and it's going to take a significant pattern change to get us out. We're over 10 inches below our precipitation average since last May.
In times like this I'm glad I forecast weather and not climate. I feel a lot better saying we're going to be a bit cool this week, with plenty of sun and a slight chance of showers Tuesday. Even our rain chances this weekend seem far, far away.
Why is the rain not falling?. On Friday I was warning neighbors who were in the middle of a move of the rain that was imminent over the Twin Cities in the late afternoon. Green radar returns were NW of the city and heading rather quickly towards the SE with Mpls right in its sights, but nothing fell! How can we have green returns and no rain? Perhaps it fell somewhere else in the TC?
Welcome to the Scandinavian Desert. Dew points have been so low near the ground that much of the rain that falls from clouds 5,000 feet or so up is evaporating before it reaches the ground. Radars see the raindrops at that height, but they are gone by the time they get to us at ground level.
This is called "virga." It's very common in the Sonoran Desert southwest. I'm with you, we need rain!