Sunday, October 13th 2013
CFS 7 day 2 meter temps to norm
Despite a cool breeze, temperatures today warmed into the mid to upper 60s across the metro area to close out the weekend. No day over the next week is likely to be as warm as today's weather.
The coming week is shaping up to be much cooler than last, with highs mostly in the 40s and 50s for the metro area. The NCEP CFS surface temperature departure for the next seven days (right), shows a broad swath of the middle of the country of well below normal temperatures.
There is a rather potent disturbance that will bring rain and snow to the state Monday and Tuesday. For the north-central mountains, winter storm warnings and advisories are already in effect as another round of heavy snow
could bring upwards of 10" of snow for some locations by Tuesday morning.
In Denver, we may see some shower activity Monday into Tuesday, and at times this may mix with wet snow. Not a whole lot of precipitation is expected with this disturbance for Denver, so only keeping a slight chance for rain and snow in the forecast through Tuesday evening. No accumulation of any type is expected at this point.0z ECM Total Accumulated Snowfall
Where the forecast starts to get complicated is Thursday into Friday. The Euro and GFS models have been remarkably consistent, but each with a different solution. The Euro digs another strong trough across the region and with it our coldest temperatures of the season and first widespread accumulating snow. The GFS on the other hand, has the trough well east of Colorado, with a big goose egg for any precipitation across the Front Range, and moderating temperatures. Case in point: the 0z runs last night featured a nearly 25 degree; temperature difference between the Euro and GFS for next Saturday morning.
To complicate the matter, there is no real agreement one way or the other from the Canadian GEM and or Japanese JMA models either. The GEM which was closer to the Euro model yesterday has wobbled a bit more in the direction of the GFS solution, while the JMA produces a pretty good trough, but is slower than the Euro.
With little confidence in either solution, will stick to a middle of the road forecast for now. I have knocked temperatures back a bit for Friday, and introduced a slight chance for precip (rain or snow), and will wait for the models to begin to come to an agreement before making additional changes one way or the other.
Next Saturday marks date of the average first snowfall in Denver. As we are still awaiting our first measurable snow here in the metro area, and with the opening of Arapahoe Basin
this morning, here is a list of the first measurable snow over the last ten years to get you in a snowy mood:
- October 5, 2012
- October 25, 2011
- November 15, 2010
- October 21, 2009
- November 14, 2008
- October 22, 2007
- October 18, 2006
- October 10, 2005
- November 1, 2004
- November 5, 2003
We will track all the latest developments (or lack there of) as the week progresses, stay tuned
Friday, October 11th 2013
With another round of severe weather yesterday, just one week after several tornadoes
were confirmed across Iowa and Nebraska, many people are asking us: is this unusual?
The answer, not surprisingly, is yes and no. Fall, particularly in October, is often referred to as the "second season" for severe weather. Many of the same ingredients in place during the spring severe weather season come back into play as cold air masses from the north begin to dive south and collide with the warm moist air masses left from summer.Tornado Probabilities - SPC
Typically, the so-called second season is not nearly as active as the spring and early summer months, but sometimes large and devastating
outbreaks do occur. Climatologically, the highest potential for severe weather during the fall months occurs much further south than what we saw a week ago. On the right is the probabilistic map for tornadoes for October 11, from 1982 - 2011. The majority of all the major outbreaks (> 10 tornadoes) this time of year have occurred across Texas, Louisiana, and Mississippi.
What is slightly less common is to see that severe weather threat spill so far north, especially with such a great tornado threat as we saw last week. Typically, the moisture return is just not there (as was the case yesterday), so the primary threat with these setups becomes damaging wind
and some hail, but with less tornadic activity.
Here in Colorado the threat for severe weather drops dramatically this time of year. While it is possible to get thunderstorms with some of the more dynamic systems we see in October, most of the severe weather will usually stay well east of Denver where dewpoints can warm enough to support such weather. In Denver, we will usually be on the cooler side of these episodes - meaning a good early season snow, or even a chilly rain.
Today we see the severe weather threat from yesterday move well north and east of Colorado, with a large area of 5% risk for tornadoes
across portions of North Dakota, South Dakota, and Minnesota. Denver has a slight chance for showers this afternoon, but no severe weather is in the forecast.
Wednesday, October 9th 2013
NAM Snowfall Totals Through Sat
As mentioned earlier in the week, the warm temperatures would not last forever. Our next storm system is in California now, but will spread clouds across the state overnight and bring rain and snow to the mountains.
As the system moves across the state Thursday, heavier snow will fall in the mountains (6-12" above 10,000ft
less below 8,000ft), rain and thunder will be possible in the Denver area and along the Front Range, with severe storms
will be possible east of I-25 through Thursday evening. Winter Storm Warnings
and advisories have already been posted for much of the high country. They will go into effect this evening and extend through 6pm Thursday.
By Friday, cooler air moves in (low 60s for the Denver area) and the rain and snow begin to weaken throughout the day statewide.
Just a left over shower early Saturday before sunshine returns for much of the weekend. Temperatures around the region are expected to be in the low 60s, before possibly dropping a degree or two to start next week.
Unlike last week's system, this one does not appear to bring much of a chance of snow to the metro areas. Snow this time will definitely favor the mountains.
Sunday, October 6th 2013
After our first flakes of the season on Friday and our first widespread hard freeze across the region Saturday morning, temperatures rebounded nicely today. According to the National Weather Service, Denver officially received only a trace of snow Friday, which means the snowfall prediction contest still has no winner, and that the 18 contestants that guessed last Friday were no doubt robbed. The contest requires that at least 0.1" of an inch of snow be recorded at Denver International Airport to bring the competition to a close. Please visit our Facebook page for more details
More warm weather is in the forecast to start the week along the Front Range, before another trough could bring more cool and unsettled weather to end the week.
Highs Monday will be near 80 degrees, with mid 80s possible by Tuesday. There will be very little cloud cover to speak of through Wednesday. While the average high in Denver this time of year is a near-perfect 70 degrees, it is not at all uncommon for afternoon highs to make it into the lower 80s with the intense sun still quite high in the sky.
Our focus then turns to Thursday, as models continue to suggest that another trough may dig into the region from the Pacific Northwest. Suffice it to say, there is very little agreement at this time with regard to timing and strength of this system. Last week nearly all mid-range models showed a good burst of cold air, before nearly all backing away from this solution. Today the ECM reintroduced a better chance for precip Friday, but clearly the consistency just is not there yet.
We will mostly just have to wait and see how things progress as we get closer to Thursday's events. It is a long shot, but it will be interesting to watch model trends over the next day or two to see if any of them try to bring snow out over the plains, which would be in similar fashion to last week's system. The upper level trough appears quite strong with this system, although to date we have very little support for snow from the positioning of the surface low and cold air. In any scenario, it is looking more and more promising that we see a good round of base-building snow for high country by Friday.
For now, we have introduced cooler temperatures to end the week with a slight chance for showers. We will continue to modify as necessary over the coming days.