Denver, Colorado

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).

The State of the Atmosphere: Sunday, October 12, 2014

Posted by @brendansweather

The weather pattern really quiets down over the next week to 10 days after today’s system works through the region and exists Monday. If you’re not quite ready for snow, this forecast is for you; if you’re jumping at the bit for our first measurable snow… we’re going to keep you waiting a while longer.

Sunday and Sunday night
Afternoon highs will be chilly across the region Sunday, as a strong upper level trough passes through. We may see our high temperatures for the day early, with temperatures dropping into the 40s and low 50s through early evening. Morning lows Monday will be in the low to mid 30s for lower elevations, with widespread 20s forecast at higher elevations.

There will be some moisture to work with associated with this system, but most should come in the form of rain for lower elevations. The coolest temperatures of the coming week will work into the region Monday morning, but likely
after the best chance for precipitation at lower elevations.

At higher elevations there will definitely be some snow. The latest ECMWF produces upwards of 7 inches for the higher peaks of north central Colorado through Monday morning.

GFS 3 hour QPF 00z tonight. Snow at higher elevations, rain showers at lower elevations.
GFS precipt type map ColoradoWeather5280

The week ahead
By Monday we really start to clear things out. The week ahead looks to be very quiet and warm overall. Our Sunday/Sunday night system will push into the middle of the country sparking several days of severe weather across the south central U.S. and eventually up into the mid-Atlantic. Behind it, high pressure builds in and we enter a period of sustained quiet weather.

Really all ensemble suites are in pretty good agreement with this. A large trough off the west coast, upper ridging across the mid-section of the U.S., and troughing to the east for the next week -- if not longer. Typhoon Vongfong is forecast to recurve and eventually help to super-change that trough off the west coast which offers additional confidence to this pattern.

Vongfong GEFS Ensemble Guidance
Vongfong guidance trackSource: WeatherBell Analytics

Deep trough in the northern Pacific Ocean, ridging overhead…

GEFS 500 hpaSource: WeatherBell Analytics

The pattern can’t last forever. Our attention will start to shift toward the latter part of October and beginning of November for possibly the best chance at seeing winter finally arrive.

Meetup Thursday!
Thursday is weather meetup day, and we hope to see you there (weather won’t be an excuse!). There are still a few tickets left, and while free (you don’t need to bring your ticket to get in), we do ask that you let us know if you’re coming so we have some idea of how many to expect.


We’ll try to get started as close to 6:30pm as possible. There will be three presentations and some time to hang around and chat afterwards. If you’ve got a favorite snow dance, maybe you’ll consider sharing it with the group, as it seems we need it!