Stuart

Cold snap ahead

Sep 082010

Fall is upon us. After a very nice weekend and a nice passing rain, we are lined up for a cold weekend. Thursday Night’s low temperatures are project to drop near freezing. Just a quick refresher, Here is what the growing season and fall freeze probabilities look like for Flagstaff. Seems a little early to be this cold, but definitely in the realm of possibility.

Freezing-Growing-Season1

Fall Freeze Probability for Flagstaff Airport

A more complete Fall Freeze post is here. Remember that some areas may be cooler and could see a freeze on Thursday night through the weekend. Here are the project overnight lows for Thursday.

NOAA Graphical Forecast for Pacific Southwest - Low Temperatures Thursday Night

Rainy Tuesday?

Monsoon, Northern Arizona Weather 1 Response »

Sep 062010

There is a chance of rain on Tuesday. But, I think the winds will make it tough for anything to form and deliver much precipitation. Although, this is the biggest chance we have had for a while. The NWS is showing 12-15 mph winds for Tuesday afternoon. Slighterly higher in altitude, and the winds will be whipping by at 40+ miles an hours. Just not great for thunderstorm dynamics. We could see scattered fast moving storms that leave very little water in their wake. If the winds are calm and the clouds slow moving, it could be wetter. We will see.

For those of you that missed it, the next post down is my first winter outlook for 2010-2011. August review sometime this week.

Winter Outlook

Climate, Hurricane, Northern Arizona Weather Comments Off

Sep 042010

Well, La Nina isn’t looking like it will back-off in time for winter. The typical La Nina effects for Northern Arizona are slightly warmer than normal (near normal) temperatures with substantially below average precipitation.

La Nina Precipitation Effects - Winter

La Nina Temperature Effects - Winter

1998 continues to look like a reasonable analog year. Both ENSO (El Nino Southern Oscillation) and the PDO (Pacific Decadal Oscillation) moved strongly to the cool side. They are forecast to stay cool for the winter. However, I think the move this year happened a little earlier than 1998. This gives some concern about the onset of the changes as a result.

The tropical storm season in the Atlantic got off to an earlier start this year than in 1998. Still, the number of storms could be very similar. In both years we have strong clusters of storms forming in early September. The early start makes me wonder about the precipitation in the fall in Arizona. Hurricanes and tropical storms can limit the flow of moisture to the region. At this point it looks like the Monsoon Season is over and the typical fall and winter weather pattern has begun. This pattern has storm fronts sweeping through and past Arizona.

1998 Hurricane Season - Wikipedia

2010 Hurricane Season - Wikipedia

September and October had above average and near average precipitation amounts in 1998. Right now, it doesn’t look like we will see anything for a couple weeks. I still think there is a good chance for near normal precipitation in September and October. However, the earlier transition from El Nino to La Nina could mean we will see an earlier chance to dry conditions. Temperatures in these months should be pretty close to normal, I think.

So, where does that leave us for the winter? Sorry folks. As of the start of September, it appears this winter will be near climitological normals for temperature. Now, the global outlook is for a colder than normal winter. This may cause Northern Arizona to be colder than normal. I’m just not sure. I doubt it will be warmer. This cooling trend is being driven by a very weak solar cycle among other things.

On the precipitation side, we will be dry. Probably very dry. December – February may see precipitation totals of less than 1.5 inches. I won’t be buying a season pass at Snowbowl. Then again, I never buy one. I just don’t get up there enough.

Is there a chance for change? Can I be out to lunch? Sure. Rapid changes in the sea states linked to ENSO and PDO are possible. Last year at this time, most thought El Nino would fade before winter. It didn’t, and we had a wet winter.

postscript: I installed a heated sidewalk this summer. This almost guarantees a dry winter, right?

What is typical precipitation?

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Sep 032010

With the end of August, one of the climatic annual time frames has come to an end. Here is how precipitation record ending with the month of August:

000 CDUS45 KFGZ 010737 CLIFLG CLIMATE REPORT NATIONAL WEATHER SERVICE FLAGSTAFF, AZ 1235 AM MST WED SEP 1 2010 WEATHER ITEM OBSERVED TIME RECORD YEAR NORMAL DEPARTURE LAST

                VALUE   (LST)  VALUE       VALUE  FROM      YEAR
                                                 NORMAL
..................................................................
PRECIPITATION (IN)

YESTERDAY 0.00 1.79 1963 0.08 -0.08 0.00

  MONTH TO DATE    3.56                      2.89   0.67     0.74
  SINCE SEP 1     23.69                     22.91   0.78    13.30
  SINCE JAN 1     18.98                     15.17   3.81     6.94

SNOWFALL (IN)
  YESTERDAY        0.0           0.0    MM   0.0    0.0      0.0
  MONTH TO DATE    0.0                       0.0    0.0      0.0
  SINCE SEP 1    144.2                     109.8   34.4     86.0
  SINCE JUL 1      0.0                       0.0    0.0      0.0
  SNOW DEPTH       0

Wow! 144.2 inches of snow. 23.69 inches of total water. But wait! While the 144.2 inches of snow, excuse me, 12 feet of snow is well above normal, the total precipitation is only about 3/4 of an inch above average. But, hasn’t it been wet? Or, has it been dry?

Joth J. took the data from 1950 to 2008 and plotted this histogram.

Annual Flagstaff Precipitation, 1950 - 2008

We see that 50% of all years fall in the range of 17 to 24 inches. While this September to September annual precipitation of 23.69 inches is in the upper end of the middle section, it’s not outrageously high. This was due to last fall and spring being very dry by comparison. On the other hand, for September 2008- September 2009, the precipitation total was only 13.30 inches. Clearly, 2008-2009 was a dry year that was easily outside of the 17-24 inch band. Here is how the last few years have come in for the same time frame.

Year          Precipitation

2000-2001          19.9
2001-2002          11.6
2002-2003          18.3
2003-2004          15.9
2004-2005          33.5
2005-2006          12.4
2006-2007          14.6
2007-2008          19.3
2008-2009          13.3
2009-2010          23.7
Average            18.2

The average is right where is should be during this 10 year time frame. But, look at the swing over that time.33.5 inches in 2004-2005 and 11.6 inches in 2001-2002. Seems like it matches the longer-term picture. Still, there were more dry years (5 years with less than 17 inches) in the last 10 years than wet years (1 year with greater than 24 inches).

I will try to finish up a winter forecast this weekend to publish next week. How will this recent trend effect it?

Jet stream dips far to the south

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Aug 292010

This picture tells the tale of our weekend. But, does it foretell our future? Is the monsoon season coming to an early, wintry end?

North American Mesoscale Model - Jet Stream Forecast Overnight 8/29-8/30

As you can see, the jet stream has dipped far to the south in an almost winter pattern. This dried out our air and dropped our temperatures. Yesterday’s high in Flagstaff was 72F, six degrees below normal. The air is substantially drier as seen in the water vapor image below.

Satellite Water Vapor Image - August 29, 2010

The jet stream is drawing the dry air from over the cool waters of the Pacific Ocean. This has completely shutdown the monsoonal flow. What does this mean for the long-term? I still think 1998 is the model year. The Altantic Hurricane Season is in full swing right now. Danielle and Earl are named. In the chart below, note that the names Danielle and Earl were also used in 1998. Also, note that they occurred in late August and early September. There is another area that has a high likelihood for development in the Eastern Atlantic. Behind all thosee, there is a line of disturbances across Africa that are marching to the west. Each has a good chance at developing into a hurricane. This doesn’t even count the potential for development in the Gulf of Mexico. So, 1998 still seems like a good match.

1998 Hurricane Season

But, it looks like the strong southwest winds, associated with the jetstream, didn’t start until later in September. We are already there. Also, the bulk of the September precipitation came with monsoonal flow early in the month. The end of the September and early October were dry. But, but the end of October, the winter storm pattern had started. Has the 2010 timeline shifted? Are we one month ahead of 1998? We have had almost 10 inches of rain since June at the airport.

I’m still not ready to forecast for the winter, but, the winter of 1998-1999 ended up fairly dry.

How wet?

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Aug 272010

Below are two models for precipitation during the next 60 hours. They tell slightly different stories. The North American Mesoscale model is a shorter term, higher resolution model. It shows lighter precipitation for the much of the northland, with Flagstaff being in the 0.25-0.50 inch range. The GFS model shows the northland in the 0.10-0.25 inch range for precipitation. Also, it shows the Valley of the Sun to be up for a major rainfall event. I don’t think this weekend will be like some others we have seen this summer. There are some drier bands in the moisture plume that is coming our way.

Should be a good monsoon weekend

60 hour NAM Precipitation Model August 27, 2010 - NOAA

60 hour GFS Precipitation Model August 27, 2010 - NOAA

Another Wet Weekend

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Aug 262010

Tonight or tomorrow, we will get back in the wet zone. This weekend shouldn’t be as bad as some, but we should see more rain in many or most areas around Flagstaff on Saturday and Sunday. Then we should dry out for a few days. Long range models continue to show a monsoon flow stretching into early to middle September. Today should be like yesterday.

Interesting point to watch is how we finish the month wiht respect to temperature. While there is a lot of hype about a record warm summer, we have been pretty close to historic normals.

Yes, it was(is) a wet summer

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Aug 252010

This summer’s monsoon season has been one of the wettest on record. Yesterday’s public information statement from the National Weather Service in Flagstaff give the details below. We aren’t quite done, yet. The rest of this week is looking similar to the first part of the week. Then, yet another wet weekend is in store for us. However, next weekend is looking fairly dry. The longer range GFS computer model is showing additional chances for precipitation in the distant future.

PUBLIC INFORMATION STATEMENT NATIONAL WEATHER SERVICE FLAGSTAFF AZ 940 AM TUE AUG 24 2010

…NORTHERN ARIZONA`S WET MONSOON SEASON CONTNIUES…

YESTERDAY`S RAINFALL OF 1.15 INCHES MEASURED AT FLAGSTAFF`S PULLIAM AIRPORT MARKS THE FIFTH OCCURANCE OF AN INCH OR GREATER DAILY RAINFALL THIS SUMMER. ONLY ONE OTHER SUMMER HAS EXCEEDED THIS YEARS FREQUENCY OF 1 INCH OR GREATER DAILY RAINFALL DAYS, WHICH WAS 1986, WHEN SIX DAILY OCCURANCES OF AN INCH OR GREATER WERE OBSERVED.

ADDITIONALLY, THE ACCUMULATED RAINFALL SO FAR THIS MONSOON SEASON (WHICH OFFICIALLY BEGAN JUNE 15TH) HAS MEASURED 9.54 INCHES AS OF AUGUST 24TH, MAKING THE 2010 MONSOON SEASON THE 4TH WETTEST TO DATE SINCE RECORD KEEPING BEGAN.

WETTEST MONSOONS

(JUNE 15TH – AUGUST 24TH)

1. 14.25 – 1986

2. 10.33 – 1919

3. 9.97 - 1904

4. 9.54 - 2010

5. 9.24 - 1908

THE NORMAL PRECIPITATION TOTAL FOR JUNE-AUGUST IN FLAGSTAFF IS 5.09, AND WITH THE 9.54 INCHES COLLECTED SO FAR, WE`RE RUNNING AT 187% OF NORMAL. THUNDERSTORM CHANCES CONTINUE THIS WEEK SO STAY TUNED TO SEE IF FLAGSTAFF REACHES ANY HIGHER INTO THE TOP 5 WETTEST MONSOONS.

Where is the dry southwest flow

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Aug 232010

As you can see below in the water vapor satellite image, the dry southwesterly flow(orange band) is passing us just to the north. As a result, the big puff of moisture that soaked Tucson and Phoenix over the weekend didn’t quite make it to Flagstaff. We are still very humid and have typically chances for rain for most of the week ahead.

There are a couple tropical entities playing into this pattern. To the west of Baja California, there is a slowly spinning low pressure area. To the south of the Baja Peninsula, there is a Tropical Storm Frank, soon to be Hurricane Frank. The way I look at this is that the low to the west has squeezed the dry air to the north for now. If it persists, we should have typical 30-40% chances of rain for the next couple days.

Western United States Satellite Water Vapor - 23 August 2010

As Frank moves north, it should bring more moisture. It doesn’t look like it will dry create a dry layer ahead of it. However, as with all tropical entities, it could go either way. I expect we will get a nice moisture boost from Frank.

Also, the 4th tropical storm of the season was named Danielle over the weekend.

Is the Hurricane season a GO or a BUST?

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Aug 212010

Forecasts for this year have been for a fairly aggressive hurricane season, but so far it has been an average season. But, we are right at the point where the season gets going with fervor. By August 22, 2005, we were up to Tropical Storm Jose, the 10th named storm of that year. 2005 was the year of Katrina. This year we have made it up to Tropical Storm Colin.

2005 Hurricane Season

And area of disturbed weather, tagged as Invest 95, is developing off the coast of West Africa. It is expected to continue to develop. Will it become Danielle, the next named storm of the year? Here is a very cool chart from WeatherStreet.com. It will have to be a very aggressive fall to hit the forecasts.

2010 Named Storms - WeatherStreet.com

Just a brief update…Saturday and Sunday will see a return to rainy, thundery conditions. Enjoy. There will probably be a break in a few days. But, remember, tropical development can change things quickly.

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Cold snap ahead

Rainy Tuesday?

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Jet stream dips far to the south

How wet?

Another Wet Weekend

Yes, it was(is) a wet summer

Where is the dry southwest flow

Is the Hurricane season a GO or a BUST?

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