Monday, September 30, 2013
Saturday, September 28, 2013
We are heading into the time of year when sub zero temperatures occur somewhere in Alaska every day. In 2013 the first occurrence of a subzero day in the databases that NCDC maintains was on October 10th. A couple of stations nearly reached zero the other day as Richard noted but it doesn't appear to have happened yet in Alaska. The following chart shows the statewide average high and low temperature (red colums) and the daily extremes (gray shaded area) between January 1, 2012, and September 24, 2013. It appears that June 18th was the warmest day in Alaska in 2013.
Note: You can zoom into the chart to see much shorter time periods. Click the Reset Zoom button to go back to the original view.
Friday, September 27, 2013
Yes, Deadhorse was the warmest day in Alaska on 7/23/12 with a high of 78F. Nuiqsut was #2 at 77F.
Wednesday, September 25, 2013
The low of 6 °F is the coldest so early in the season for Barrow since 1985, when 3 °F was observed on the same date. The earliest that 0 °F has been observed is October 3.
The chart below show that temperatures have been close to normal in Barrow since mid-August, but were frequently much above normal throughout the early and middle summer. The June-August average temperature was the sixth warmest on record, and 2013 was the fifth consecutive summer that was warmer than the 1981-2010 average.
Tuesday, September 24, 2013
Monday, September 23, 2013
Sunday, September 22, 2013
|Courtesy of Environment Canada|
The anomalies show up dramaticly in the this plot from the Penn State e-wall:
There are three centers with more than 240 meter anomalies: the near-pole high, the high centered over the United Kingdom and the broad low heights stretching from the Chukchi Se southeastward across Alaska and into the Northwest CONUS and a very deep center in the Gulf of Alaska.
Saturday, September 21, 2013
The coldest location in the State of Alaska today was Anaktuvuk Pass (low temperature of 9°F). Looking at an entire year, I thought it would be interesting to see which station recorded the daily low temperature the most times. The first map below shows each station that recorded a statewide daily low temperature in 2012 and the count of days that the station was the state's low. In total, 72 stations recorded the daily, statewide low temperature for a calendar day. If more that one station recorded the statewide low, each station earned a tally. Therefore, even though 2012 had 366 days, adding up all the numbers on the map yields a grand total of 468. Rick communicated to me via e-mail that FAA data are not archived at NCDC (i.e., Anaktuvuk Pass, Arctic Village, etc.), so this map should be taken with a grain of salt. Also, cooperative stations usually take their temperature measurements at 7 a.m. so there is often a time of day confound. As you can see from the map, there is a concentration in the central and southeastern Interior. Remember that this map is for the entire year. The second map below shows the September 2012 daily low stations. Who can guess the station that was both the September and the annual winner for 2012?
Friday, September 20, 2013
To take a first look at the data, I pulled out the years in which measurable (0.1" or greater) snow was observed in Fairbanks on or before September 20. Since 1930, there have been 10 of these years prior to this year: 1930, 1933, 1948, 1962, 1972, 1978, 1980, 1989, 1992, and 1993. Looking at the temperature and snowfall data from the subsequent winters, it seems there is a tendency for warmer than normal and snowier than normal conditions in each of November, December, and January. For the three-month average, 2 of the 10 years had below-normal temperature, 2 had near-normal temperature, and 6 had above-normal temperature (based on the 1930-2012 tercile categories). The distribution was the same for snowfall: 2 below-normal, 2 near-normal, and 6 above-normal.
Below are histograms of the November-December snowfall and temperature, with the columns split between the early-snow and no-early-snow years. Although a subset of 10 years is rather small to draw a robust conclusion, the distribution does seem to be shifted towards relatively warm and snowy conditions in the years when early snow occurred.
In conclusion, the early Fairbanks snowfall seems to give us a very tentative hint that November through January might be warmer and snowier than average in Fairbanks this winter. It's not clear why this might be the case, although the early snowfall might be signaling something about the oceanic or atmospheric pattern that is likely to persist or influence the winter conditions. There is a lot more that could be said about the outlook for the winter, based on other factors, and I hope to put up some more posts in the weeks ahead.
Thursday, September 19, 2013
The 2013 value is the second most on record for the snow-free period. Only 2004 had more GDDs. What is remarkable is that the accumulated GDDs occurred during one of the shortest snow-free periods on record. Looking at it on a per snow-free day, 2013 was far and away the largest value for any year on record.
Wednesday, September 18, 2013
Last year the first trace of snow at the Fairbanks Airport was on September 30th. So, today's trivia question is: what's the earliest and latest "first snow" (not hail) in the autumn at Fairbanks?
7pm update: Snowfall picked up after 5am and it snowed smartly for several hours this morning. Fairbanks Airport wound up with 0.6" of snow and UAF West Ridge 0.9". This is 12 days earlier than the average date of the first measurable snow (at the Airport). These are the earliest measurable snows in the autumn at these low elevation locations since 1993.
Here at Keystone Ridge the 0.1" of snow before midnight Tuesday made this the earliest accumulating snow in the autumn since way back in 2004, and another 0.8" fell this morning.
Monday, September 16, 2013
From a philosophical point of view, both Fall and Spring are seasons without meaning. They represent the transition period from the warm season (Summer) to the cold season (Winter) - and vice versa. As humans we give them attributes (fall foliage, greenup, breakup, etc.) but they lack the definitive markers that summer and winter have. I have done some preliminary research of alternate definitions of season boundaries but given other time constraints have not made much progress. Do they necessarily need to be equal lengths (90 days)?
Using the definition of Fall as the time period between Summer and Winter, and defining Summer and Winter by their respective peaks and troughs, a midpoint for Fall can be defined. In essence, it represents the date falling exactly between the warmest day of the year and the coldest day of the year.
The following three maps show the climatological date for the climatological midpoints of 1) Fall, 2) Summer, and 3) Winter, based on the 1981-2010 climate normals published by NCDC.
I find the Summer and Winter midpoint maps fairly intriguing but the Fall map is rather uninspiring. Anecdotally, I would define Summer in Interior Alaska as May 25th to August 10th and would define Winter as October 20th to April 20th; but I digress. Perhaps seasons can be grouped according to the climate divisions laid out in Climate Divisions for Alaska Based on Objective Methods by Bienief et al.
Sunday, September 15, 2013
The rapid evolution of the upper level pattern can be seen in the 12 hourly 500mb height and anomaly plots from the NCEP/NCAR reanalysis (4pm AKDT Sep 14, 1992 right, 4am Sep 15 center, 4pm Sep 15 right):
|NCEP/NCAR Reanalysis 500mb Heights & Anomalies 00Z Sep 15 (left), 12Z Sep 15 (center) and 00Z Sep 16, 19 (right)|
The deep cold low that had been north of Barrow two days below sent one piece of energy southeast across the northern and eastern Interior, with a second center remaining in the Beaufort Sea.This resulted in rapid end to the precipitation over the central Interior during the day on the 15th.
The snowfall amounts from the 12th through the 15th were truly remarkable in the central Alaska Range and also in the Fairbanks area:
- Denali National Park Headquarters: 38.1"
- Healy coop: 24"
- Two Rivers coop: 17.8"
- Fairbanks IA: 16.8"
- College 5NW coop: 16.4
Here are a couple of plots of most of the snowfall amounts and liquid equivalents I could find, done shortly after the event. The locational plots are primitive but it's what we had to work with in 1992:
Here's a similar clunky-looking plot from the time for the Delta Junction area:
Here the main item of interest is the dramatic drop-off in precipitation south of Fort Greely. The accuracy was of these observations were confirmed at the time with the met team at Fort Greely, who reported at the snow on the ground south of Bolio Lake went to very little in just a couple miles.
The plot below shows the raw date (not adjusted for leap years) of the date of first freeze at the Fairbanks Airport. As you can see, September15th is in keeping with first freeze dates over the past 15 years.
Saturday, September 14, 2013
Thursday, September 12, 2013
|500mb Heights and Anomalies, 18Z Sep 12 (left) and 00Z Sep 14 (right), courtesy NCEP/NCAR Reanalysis|
The corresponding reanalysis for 850mb temperatures and anomalies are below. Note the temperature anomalies under the massive high aloft are not so dramatic except over the central Aleutians:
For August, it's remarkable that every location experienced above-normal temperatures, although none of the anomalies was extreme: the highest standardized anomaly was at Cold Bay, where August mean temperature was 1.4 standard deviations above normal. Both Cold Bay and Kodiak received more rainfall than in any August between 1981 and 2010, although neither location broke a record relative to the long-term history.
Tuesday, September 10, 2013
I'll be doing several posts on this historic event, starting with retrospective of September 10, 1992. Here is the mean 500mb pattern and height anomalies. The remarkably deep low north of Barrow was well forecast by the numerical models at the time, though we did not believe it in the days leading up to this event, referring to it jokingly as the "death star". Such a deep low so early in the autumn was beyond reasonableness.
The 850mb temperatures show a deep cold airmass over nearly all of the state. Temperatures in this NCEP/NCAR reanalysis are in degrees Kelvin, so freezing is 273K. The low temperature on the 10th at Fairbanks was 18F, easily a new record low for the date and the first of what would be eight daily record lows set during the month. And there was no snow on the ground yet.
Here is the list that was used to make the maps above. It is sorted by max number of days with measurable precipitation.
|KETCHIKAN INTL AP||88||101|
|LITTLE PORT WALTER||69||71|
|YAKUTAT STATE AP||53||90|
|JUNEAU INTL AP||49||68|
|ANNETTE ISLAND AP||47||81|
|CORDOVA M K SMITH AP||45||57|
|MAC LEOD HARBOR||38||38|
|ST PAUL ISLAND AP||38||164|
|ST GEORGE ISLAND AP||29||115|
|JUNEAU FORECAST OFFICE||29||55|
|MIDDLETON ISLAND AUTO||27||49|
|BARROW POST ROGERS AP||21||80|
|NOME MUNI AP||19||36|
|ANCHORAGE MERRILL FLD||19||28|
|KENAI MUNI AP||18||22|
|NENANA MUNI AP||17||50|
|ST MARYS AP||17||49|
|ANCHORAGE INTL AP||17||31|
|MATANUSKA EXPERIMENT FARM||16||19|
|KOTZEBUE RALPH WEIN AP||15||32|
|ANCHORAGE FRCST OFC||15||31|
|ANCHORAGE LAKE HOOD AP||15||17|
|BIG DELTA AP||15||24|
|FAIRBANKS INTL AP||15||23|
|UNIVERSITY EXP STN||13||26|
|EIELSON VISITOR CTR||12||14|
|FAIRBANKS AP #2||12||23|
Sunday, September 8, 2013
To address this, I've calculated the frequency of days with measurable precipitation (≥0.01") by week (starting Jan 01, not smoothed) for the past 84 years:
By this definition, the climatologically wettest time of year is from mid-July through August, with a sharp drop-off in the frequency of measurable precipitation the first week in September. This is followed by a weak secondary maximum in late October. I'm speculating here, but I suspect that the sharp decline of damp days in early September is due to a decline in the climatological frequency of a big North Pacific ridge centered south of south of Alaska (which results in southwest flow aloft that brings moisture around the Alaska Range).
Saturday, September 7, 2013
The winner for greatest average temperature during Summer 2013 was the Fairbanks International Airport. Their average temperature was 63.5°F. The lowest temperature was Barrow 4ENE. Their temperature was 38.7°F. To qualify for the ranking, a station had to record at least 89 (of a possible 92) days with complete (and unflagged) temperature data. A grand total of 142 of the 249 stations in Alaska qualified. The first map below shows the locations of the 142 stations and colors represent the temperature categories. An inverse distance weighted surfacing technique was used.
Friday, September 6, 2013
As anyone who has read the blog can plainly see, I never get into second order attribution of events. I have done a few posts on climate variability, mostly in regard to PDO, which, being nothing more than a way to characterize North Pacific sea surface temperature anomaly patterns, is an important factor in Alaska (south of the Brooks Range) decadal-scale climate.
Readership has always been tiny. The blog received enough comments to know that a few folks had found the blog useful. Typical page views were in the 15 to 45 range. This is so tiny that I wound up using the blog as a place to "store" graphics, typically plots of some data or another, so that I could get to them regardless of where I was at or what computer I was on, suspecting that they would be of minimal interest to anyone else.
As my personal circumstances changed, I had less time for posting, and after some thought, I invited a couple of folks to contribute to Deep Cold who are very knowledge about high latitude weather and climate and have insights and analytical skills complimentary to my own. As a result, the blog now has more frequent posts and more the content is "beefier". And the small readership seemed to agree.
So it was with great dismay that a well known political website picked up a short post on record low temperatures over the weekend. In three days this blog had nearly a quarter million page views, more than five times the total in the previous three years combined.
More importantly, the record cold post was swamped with comments that had nothing to do with Alaska weather and climate. Personal attacks on politicians have nothing to do with Alaska weather and climate and are not welcome here, nor is this a blog about climate change. A as a result I turned off comments. There are a myriad of websites that cater to those. This is not one of them.
I'm interested in Alaska weather and climate and I'm interested in having a blog that addresses that. It would be nice if a few of the quarter million visitors stick around because they are interested in the same things, but this is not the place for political arguments. If you're interested in Alaska weather and climate for its own sake, then thanks for visiting Deep Cold.
Thursday, September 5, 2013
Tuesday, September 3, 2013
A truly remarkable rain event has unfolded in Southwest Alaska over the last several days. Both McGrath and Aniak have received 2-day rainfalls with recurrence intervals of greater than 10-years. Aniak's total of 2.41" is their 8th largest 2-day precipitation value and McGrath's 2.12" is their 4th largest 2-day value. At Togiak, 3.35" was recorded during the same 2-day period – including an amazing 1.50" in three hours. Unfortunately there is no GHCN database for Togiak to determine where this falls in the historical record.
Below is the storm total precipitation radar image for 8/31/13 through 9/2/2013.
Monday, September 2, 2013
Finally, here is a picture from the top of South Suicide Peak (5,005') near Anchorage on one of the very warm 850mb temperature days. The pressure level was 851mb and the temp was 18C (64.4F). It is not exactly a free-air temperature but it was very, very warm.