Denver, Colorado

Winter Outlook 2014-2015, Part 1: Analogs

Posted by @BrianBledsoe

If you didn’t attend the Weather5280 Meetup last week, you missed a great hang, but fear not: a) we’re likely to have another one in the coming months; b) I’m going to share a lot of the same material that I talked about that evening, and how it relates to what will happen for our winter/spring 2014-15. So, here we go... 

Sea Surface Temperature Anomalies:

SST September 2014Source: UNISYS

The above image represents how the sea surface temperature anomalies looked on September 21st, just one month ago.

Here is how they look now:

SST October 2014Source: UNISYS

Notice how much the northern Pacific Ocean has cooled! It is completely different than it was a month ago. This has allowed a blocking ridge of high pressure to break down, which is allowing more storms to come into the West Coast. This is
potentially quite good news for California, as it could well allow for more storms to impact the state. Part of this is due to seasonal change, but the overall shift that is occurring in the Pacific is mostly responsible due to the current PDO phase and some sort of El Niño episode that is trying desperately to get underway. You hear me mention the PDO a lot, because it plays such an important part in our weather. While we are predominantly in the cool/negative phase of the PDO, we have taken a short detour to the warm/positive phase in the PDO since January. We still have a +PDO, and I believe it has been instrumental in helping erase drought conditions for the whole state. In fact, check out these moisture totals since April across Colorado:

Total Precipitation Colorado April-October 2014Source: WeatherBell Analytics

Some areas along and north of I-70 have received between 20 and 30 inches of moisture! Conversely, areas south of I-70 haven’t received as much. However, the moisture that they have received has gone a long way in helping cure the awful drought. The most recent drought monitor suggests that too.

Here’s how things looked just five months ago on May 20, 2014.

Drought Monitor Colorado May 2014Source: Drought Monitor

Much of the drought that you see above was the result of two years of below normal moisture. In fact, that two year period was one of the driest on record for many areas in far Southeast Colorado. I firmly believe that it was a result of the PDO being in a long term cool/negative phase. That phase is more prone to La Nina episodes which are notoriously windy and dry for many areas east of the mountains.

Here’s the most recent drought monitor:

Drought Monitor Colorado October 2014Source: Drought Monitor

Bottom-line, the short detour in the PDO to a warm/positive phase has been very instrumental in helping us in the moisture department.

Here is a look at sea surface temperature (SST) anomalies associated with the two phases of the PDO:

PDO phases
If you look at the SST anomaly maps above, you will see that we are dealing with a warm/positive PDO. However, I believe that this phase of the PDO will be pretty short lived. Thus, we had better continue to capitalize on it in terms of moisture, before we go back to a pattern that will be more conducive to drought conditions once again. Let’s see if that is possible…

Analog Years
You have heard me mention analog years before. These are simply other years in the past that have similar global weather patterns to those that are occurring currently. Contrary to the belief of the Climate Prediction Center, they are a very important part of long range and seasonal weather prediction. In fact, through about mid-to-late summer this year, 2009-10 was acting like it would be the perfect analog year to project the rest of 2014 and into 2015. While it is still in the running, there are other years that look even better. We have to break them down in terms of what the SSts looked like during each particular year, then we can see how the temperature and moisture panned out.


Sea Surface Temperature Anomalies October - May


This has a similar look to what’s happening now. We see colder than normal water extending eastward from Japan, warm water in the ENSO (El Niño Southern Oscillation) region extending westward from South America, and some residual warm water along the western coast of North America.

Temperature Anomaly October - May

NOAA NCDC Temps 1957

Yellow to red means warmer than normal, while the greens and blues mean colder than normal. In general Colorado was normal to slightly colder than normal, with the coldest weather being just east and south of us.

Precipitation Anomaly October - May

1957 Precipitation Anomalies

Yellows to reds mean drier than normal, while greens and blues mean wetter than normal. For this period, Colorado was slightly wetter than normal, as was most of the southern tier of the country.


Sea Surface Temperature Anomalies October - May

1976-77 SST

Same story here, with a very cold pool of water in the northwest Pacific Ocean and relatively warmer than normal water near the West Coast and in the ENSO region.

Temperature Anomaly October - May

1076-77 Temperature Anomalies

We see colder than normal for the southern and eastern tier of the country, with warmer than normal temperatures in the far Northern Rockies/Plains. This winter was legendary in the eastern part of the country due to how cold it was.

Precipitation Anomaly October - May

1976-77 Precipitation Anomalies

Above normal moisture was hard to find here. The west was dry, as was the Mississippi and Ohio Valleys. At least the eastern part of Colorado had normal moisture during this time, with above normal moisture in parts of the Nebraska and Texas.


Sea Surface Temperature Anomalies

1986 SST

This is another year that looks very similar to what we are currently experiencing. However, the ENSO region was pretty warm in late 86 and 87, and I’m not sure we will see that strong of an El Niño. More on that later…

Temperature Anomaly October - May

1986-87 Temperature Anomalies

We see this analog year was quite warm in the northern tier of the country, with mostly normal temperatures for the rest of the country. The one exception was areas of west Texas and New Mexico.

Precipitation Anomaly October - May

1986-87 Precipitation Anomalies

This is where the signal really shows up...Dry California, Great Lakes and Ohio Valley. Wet Colorado and most of the Plains states, eastward into the Southeast.


Sea Surface Temperature Anomalies:

SST 2002 2003


While a lot of the Pacific looks very similar to where we are and likely where we are heading, that warm pool just off the coast of Western Canada may be too warm. Otherwise, I really like this particular SST analog year.

Temperature Anomaly October - May

2002-03 Temperature Anomalies
Precipitation Anomaly October - May

Precipitation Anomalies 2002 - 2003
This year has a less clear cut signal unless you live in the far south and southeast. That slightly wetter than normal signal in the northern part of Colorado was largely due to the major blizzard in mid March 2003. Otherwise, the winter and early spring was quite dry. The lack of moisture for the whole state was largely made up in the spring.


Sea Surface Temperature Anomalies:

2009-10 SST


This analog used to be our favorite, but is now running behind a bit. The overall SST structure isn’t as good as the other analogs, but there are some signals that keep it intriguing. The less than warm North Pacific and a weak El Niño make it one that we have to give some weight…

Temperature Anomaly October - May

2009-10 temperature anomalies

Almost the entire country was generally cooler than normal during this time. The obvious exception was the Great Lakes Region and The Northeast. Otherwise, this was one of the colder fall/winter periods in recent memory for folks in the Southern Plains and Southeast.

Precipitation Anomaly October - May

2009-10 precipitation anomalies

The wettest areas were the Western High Plains just east and southeast of Colorado, parts of the Mississippi Valley, and of course the Southeast. Colorado had decent moisture, but nothing excessive after a wet and cold fall.

Here is the composite analogs factoring in the years from above:


Composite temperature anomalies


Composite precipitation anomalies
Overall, I think it is safe to say that our analogs produce cooler than normal weather in the south, warmer than normal weather in the north, and generally “normal” temperatures for Colorado. They also produce slightly wetter than normal weather in the South/Southeast, drier than normal weather in the Pacific Northwest and Great Lakes Region. Again, Colorado shows up as having “normal” precipitation. Do I think it will be like this? Not exactly. Whatever type of El Niño episode that develops will likely be weak. That means that some of the traditional signals will be a bit weaker, and possibly displaced. Coming up in a few days, I will post part two of this outlook, which focuses on model data and why I think that ONE particular model has a good handle on the overall forecast.

The State of the Atmosphere: Monday, October 20th, 2014

Posted by @coloradowx

Recap of month so far
If it feels like we have had a lot of warm days so far in October, you’re not mistaken: Denver is now a not-insignificant +2.2℉ above normal for temperatures month-to-date. In fact, the last 7 consecutive days (including today) have featured well above-normal temperatures, and over this one-week period, we’re actually averaging a sizable 7.7℉ above normal.

What has caused this prolonged stretch of above normal temperatures? Quite simply, we’re in an amplified -- or “blocky” -- atmospheric pattern aloft, which has generally featured a trough to our west and a trough to our east, with a ridge overtop of us, in between. The downstream trough has prevented much movement in the jet stream, so we’ve been stuck with a plethora of ridging dominating our weather. These blocky patterns can be notoriously difficult to decay, and it looks like we’re in for at least another week of continued above normal temperatures and drier-than-normal conditions until then. (We’re running somewhat behind on precipitation for the month, as Denver International Airport (DIA) has reported 0.50” of rain so far this month, or ~49% of our normal total monthly amount, with approximately 65% of the month having already passed.)

The week ahead
There are few forcing mechanisms to push our current blocky jet stream configuration out of its current orientation. That said, we will have a very short-lived respite from above normal temperatures during the middle of this week as a weak trough of low pressure and associated cold front pushes through the area Tuesday night. That likely means our well-above normal high temperatures today and Tuesday (in the mid-to-upper 70s, which is >10℉ above normal) will be pushed to closer near 60℉ on Wednesday. Also, scattered showers may accompany this system late Tuesday into early Wednesday, but most models are quite bearish regarding precipitation potential in #Denver --  probably <0.10” of rain can be expected.

Behind this weak, and short-lived cold front, a ridge of high pressure will build into the area anew by Thursday into Friday, bringing temperatures right back up to well above-normal levels by late week into the weekend. In fact, I wouldn’t be shocked if we flirt with the 80 degree mark again by this coming weekend -- which would imply close to record-high temperatures once again.

Note forecast temperature anomalies over the next 10 days from the CFSv2 shows above-normal temperatures continuing.

CFSv2 Forecast Temperatures USASource: WeatherBell Analytics

What changes going forward?
We all know above-normal temperatures can’t last forever, and we are now beginning to see some indications that this warm, dry pattern over the western US may begin to break down towards the end of the month. This is a bit more technical, but we’re currently under a strong +PNA pattern, which favors a ridge over the western US; you can see, however, that teleconnection forecasts weaken the +PNA considerably over the next few days, and even suggest it may go negative by next week, which could support a turn to colder temperatures.

Forecast teleconnections October 2014Source: NOAA

As our +PNA begins to collapse, we can expect an upper-level trough developing off the coast of the western US. Indeed, all medium-range models do show an offshore trough by next weekend. Most models believe this trough will come ashore by around Monday of next week, but there are some fairly large differences in regards to timing, strength, and location of this trough. Those details will need to be sorted out before we can get a clearer image of exactly what effects this trough may have on weather around our neck of the woods. Here is a look at what the Canadian GEM control run is showing valid 6pm Sunday, October 26.

GEM forecast 500 hpa USASource: WeatherBell Analytics

As such, the period next Monday through Wednesday may offer unsettled weather, with the
possibility of cooler temperatures, more clouds, and the chance for some precipitation, particularly in the high country. It is too soon to know with any more confidence exactly how this trough will impact our weather, but we’ll probably have a much better handle by mid-week.

The end game?
I don’t think, however, that it is this trough the puts a decisive end to our warmer-than-normal pattern. Indeed, most models start to warm us up again by the middle of next week, as high pressure once again builds right back into the region. Our eyes will then be on the next upstream trough which is likely to pay us a visit during the first few days of November. I believe that it is this system which offers better chances for finally squelching our warmer-than-normal pattern, as well as bringing notably cooler temperatures and the chance for snow -- perhaps even on the Plains. In short, while it’s a ways out, I believe that the period November 1-3 needs to be monitored for possible impacts from a (deep?) trough aloft, which could finally bring central Colorado a taste of wintry weather!

Here is the latest Canadian ensemble control run valid 6pm on Saturday, November 1.

GEM 312 hour forecast CONUSSource: WeatherBell Analytics

...we will surely be talking about this, probably higher-impact, trough in next week’s State of the Atmosphere! Until then, enjoy our continued warmer-than-normal temperatures, and the probability of a brief respite in the warmth early next week, before one last (perhaps brief, only a few days) stretch of mild temperatures before we head into November. Note that the CFSv2 shows cooler-than-normal temperatures attempting to establish themselves over the western US during days 10-15 (which would be the first week of November.)

cfsv2 forecast temperature anomalies

NOAA, AccuWeather Issue 2014-2015 Winter Outlooks

Posted by @brendansweather

It is always an exciting time of year when meteorological organizations start issuing their winter outlooks, often conflicting with one another and even themselves.

This week both AccuWeather and NOAA released their Winter Outlooks. As is typically the case, NOAA’s outlook is far more conservative with any bold predictions (much of the country, according to them, will see equal chances for near-normal, colder than normal, and warmer than normal temperatures), while the AccuWeather’s outlook is a bit more descriptive for most regions.

NOAA’s Winter Outlook
NOAA has put out an outlook that features a warm west western US and a cool South. The outlook from NOAA's Climate Prediction Center will not come as welcome news for those in the west hoping for a real winter. For Dec-Feb NOAA has greater than 50% chances for warmer than normal temperatures across the west, with equal chance for much of the middle of the country (including Colorado), and greatest odds for below normal temperatures across the South.

NOAA Winter Outlook 2014 - 2015 TemperaturesSource: NOAA

As for precipitation, Colorado is again under the equal chances category -- with the exception of extreme southern Colorado which is included in the >33% chance for above normal precipitation (looks very Nino).

NOAA Winter Outlook Precipitation 2014-2015Source: NOAA
AccuWeather Winter Outlook
The outlook from AccuWeather is in many ways very similar, and looks highly based on climatology. They too are predicting a mild and dry Northwest and wet South. Their outlook, however, includes “snowy periods” for much of Colorado (that’s the case every winter I think), and a good area of “cold” across the middle of the country (anyone remember last winter?). In fact, their outlook specifically calls for a return of the Polar Vortex by January and February.

AccuWeather Winter Outlook 2014-2015Source: AccuWeather

Brian will be discussing our latest thoughts on the long-range outlook at tonight’s meetup; we look forward to seeing you there!

The Impact of Pacific Typhoons on the United States

Posted by @MattMakens247wx

The 2014 tropical storm season has favored the Pacific, while it’s been much quieter in the Atlantic
The Pacific tropical season has been an active one. We’ve seen 19 storms so far this year, with 16 being average total seasonal number. The 19th is Vongfong, currently hammering Japan.

Meanwhile, the Atlantic season has been very quiet. Gonzalo is just the 7th named storm in a season that averages 12. Gonzalo is not likely to impact the US as the current projection takes it over the eastern Caribbean islands north to northeastward over the open Atlantic, curling away from mainland US.

Hurricane Gonzalo Forecast MapWhile we typically defer our attention to the Atlantic for tropical system impact on the US,the Pacific can have a bigger impact on the weather the country experiences as a whole -- albeit indirectly.

Remember Typhoon Haiyan of last year? That’s the one that decimated sections of the Philippines. A quick summary on this, one of the most powerful typhoons ever recorded:

  • Formed          November 3, 2013

  • Dissipated        November 11, 2013

  • Highest winds    10-minute sustained: 230 km/h (145 mph)

  • 1-minute sustained: 315 km/h (195 mph)

  • Lowest pressure         895 mbar (hPa); 26.43 inHg (Estimated)

  • Fatalities         6,340 confirmed, 1,061 missing

  • Damage          $2.86 billion (2013 USD)

Well, about ten days after Haiyan slammed the Philippines, it’s energy contributed to the mid-November tornado outbreak in Indiana -- some 8,000 miles apart!

The 17th of November, 2013 had 73 tornadoes across the midwest, most in Indiana and Illinois. Two of those 73 were rated EF-4. (yes this report page says there were 136 tornadoes, but remember those reports may include multiple reports  for the same tornado).

SPC storm reports 11/17/13Source: SPC

That outbreak was the second worst in Indiana history, and, yes, it happened out of the traditional severe weather season, but during what’s often referred to as “
second season”.

Compare Haiyan to Vongfong
Vongfong, meaning ‘the wasp’, first made landfall near Okinawa, Japan on Sunday with wind more than 100 mph. Just Friday the storm had wind of 155mph.

Vongfong from the International Space StationVongfong taken from the International Space Station on October 8, 2014

At least 61 people were injured, and more than 44,000 were left without power; one person remains missing from the storm’s impact Sunday, according to
the Japan Times.

Imagine the chaos involved with the 506,000 people ordered to evacuate. Especially with much of public transportation shut down with nearly 16 inches of rainfall expected.

This is the second typhoon to hit japan in a week, last week we were tracking Typhoon Phanfone which is the one that killed three us airman stationed at Okinawa.

Although Vongfong is one of the strongest this season, the typhoon did not reach the intensity of Haiyan. Haiyan had a minimum central pressure of 895mb and peak wind of 195mph versus Vongfong’s 900mb minimum pressure and 155mph peak wind.

Like Haiyan, Vongfong (and Phanfone for that matter) has utilized a lot of potential energy to create itself.


Energy headed to US
Typhoons contain a great deal of energy -- we are talking energy on the order of tens of  thousands of nuclear weapons. In the meteorology community, this energy is known as vorticity, or spin of the storm. This energy doesn’t simply disappear as a storm weakens and dies; it is utilized by the atmosphere somewhere else.

In the case of the past two typhoons that hit Japan -- Phanfone and Vongfong -- their energy is grabbed by the jetstream and taken toward Alaska and the lower 48. So, Japan may have been hit directly by the typhoons, but we too may have that energy impact us down the line.

Toward Halloween, we will be tracking several pushes of colder air that will try to hit our area. The Great Lakes and Eastern US will certainly feel the cold, but Colorado may be on the edge of these systems. The energy pushing this cold at us is partially that from the typhoons.  Weather is a “crazy cycle”.

The CFSv2 and ECM are hinting at some cold conditions with associated 500mb troughing near late October and early November. Part of the energy creating these troughs is that of the current typhoon(s).