NSSL WRF performance over OK

I grabbed some 2 meter temperature forecasts from NSSL's WRF 4 km model simulation from 00 UTC 5 February 24 hour forecast to compare with what happened on Saturday.

The model did not do terribly well but it highlighted the issue with snowpack. Lets go to the pictures:

The images depict the 2m temperature in 2 hour increments from 18 to 22 UTC; with the 22 UTC image being the warmest time of this day. What stands out is the warm air over the TX panhandle which does not expand rapidly into OK. Just east of the OK panhandle it warms rapidly, but it does not expand and penetrate eastward. Over OK, the cold patch, which aligns perfectly with the storm total snowfall and thus snow pack, does not appreciably change shape but it does warm a bit. Clearly the model had a poor representation of the snow cover, both in areal extent and depth.

From the previous post, the high temperatures even over the deep snow pack near Tulsa in the core of the model cold patch, got to near 40F ... a difference of 20 F!

The situation eases later as night arrives by 00 UTC. Below are the 24 hour forecast from the model and the initialization from the next cycle.

The differences between these 2 images is difficult to discern but they are still large, because of the eastward shift of the OK cold patch and the eastward extent of warmer air. This is an interesting case where I would expect this type of model to perform better. Diagnosing the evolution of the snow pack and the low level temperature tendencies both aloft and from within the model physics (boundary layer scheme) should shed some light on why the model performed poorly.

Temperature forecasting over the snow cover

How high will the temperature get across OK over the snow pack?

The sounding above at OUN was taken at the morning low according to the Norman mesonet site. Now it snowed another inch or two yesterday  to make the compacted snow depth anywhere from 3 to 5 inches. The snow we had was an icy consistency. I walked on it and only in the drifts was it actually loose snow.

The forecast high for today was 36 (as of this writing was upped to 38) from the NWS, and I thought that was pretty good. But it is always difficult to predict the high temperature when the ground is snow covered. The high for the day in these situations depends how far from the bare ground you are relative to the low level air mass that is moving in. The 1845 UTC visible satellite image shows where the snow is. The whiter the ground the deeper the snow:

I can't mark where Norman is but trust that we are not very far from the edge of the snowpack and points to the west of us didn't get that much snow in the first storm and barely received any in yesterdays.

However, a forecasting technique I learned at UAlbany was the 850 hPa method. This method assumes that air from above the surface will serve as the upper limit as the boundary layer grows upward.  Of course the atmosphere aloft is not usually stagnant so you need to account for that. This mornings OUN sounding had an 850 T of 1.6 C with even warmer temperatures of 6.4C at 911 hPa.  This suggests a temperature of 14.3 C from 850, or a temperature of 13.6 C from 911 hPa ... again assuming these temperatures change very little during the day. So the mid to upper 50's!

So the forecast problem is the battle between surface effects: how the incoming radiation can heat the ground and help that mixing process along versus how the mixing occurring elsewhere (in this case to the northwest and west) brings in warmer air over the snowpack. The latter is usually referred to as an internal boundary layer.

Now, the temperature is obviously controlled by the snow depth and snow cover and there should be an obvious temperature contrastor gradient across the plains:

Note, the yellow shading which tells us the potential temperature gradient pretty much aligned along the edge of the snow pack from this morning.
I will add the 18UTC and 21UTC maps when available below:

The potential temperature gradient shifted somewhat east as the snow below has melted and temperatures have warmed.

So far at 4pm local time the temperatures in western OK have risen to 62+F and Norman is currently around 45F! This is pretty much going to be the high for the day.
 I will add the mesonets max T plot when it is available:

Now where did this warm air layer aloft come from? Downslope off the mountains as the large scale trough passed through our region. Temperatures at 850 hPa warmed from -15C to 2C in 24 hours at Dodge City, and from -18C to 2C at Amarillo.

A comparison of soundings from Lamont indicated a slow warmup primarily in the boundary layer with just a minor change in the height of warm layer. However by 00 UTC it was clear that the entire column was warming significantly downstream from the mountains. LMN and OUN  were clearly situated in a warm advection regime at 00 UTC. Given the sounding structures, you could have used the 850 method with forecast soundings, not upstream soundings given how much the entire temperature profile changed.

Of course, it is very interesting that the sounding at AMA can not be used to show the large surface warming over western OK. AMA only reached 12 C which is around 50F, while western OK reached 62F. The implication is that the warm pocket over Oklahoma this morning was bigger (or may have even developed aloft) than could be revealed by the sounding network.  Either way these mesoscale details (snow cover or lack thereof, warm pockets of air aloft from downsloping) made it difficult for forecasters to utilize observations for short term forecasts of temperature. This is a much more complex scenario for what seems like a straightforward case of temperature forecasting over snowpack.


As a side note, the temperature warmed above freezing and so all the snow in the rain gauge is melting. Now a ton of it was blown around but what was secured to the gauge from the last two snowfalls should tell us something about the sleet that fell, then the snow, and then yesterdays heavier snow. The liquid total from the melt is: as of 9:40pm is 0.32".

I take exception

A recent article appeared on Foxnews.com that I found noteworthy.

I wish to challenge the notion that anyone, with any certainty, can use any recent weather event no matter how large as a sign of or lack of global climate change. Climate as we all should know is about statistics. It will take a decade or longer to know how epic this latest blizzard was.

What Al Gore got correct was the scientific evidence. He correctly stated that under global warming scenarios it has been shown that variability increases. And even during a warming trend, globally, there can be dips, significant dips (even negative anomalies) regionally. This evidence suggests that this CAN be part of global warming scenarios. Of course we don't know the reverse because I am not sure that anyone has done a global cooling experiment. Please enlighten me if such a study has been done.

The second issue I wish to be picky about is the notion of predictions associated with climate. We are assuming a CO2 increase in what can only be described as complex models, but models that do not represent the full coupled climate system. This is necessary because building complex models requires a solid foundation upon which to add complexity. And unfortunately by building complex models we can not say that a model error at this point is actually wrong because all the processes we observe in the real world are not present in the model. It is an interesting problem to say the least. One that is being tackled on the weather side as well.

What we do know is that as model resolution improves we get better, but not perfect solutions. That is good news for weather and climate. But long term climate prediction is still not an initial value problem. Though some argue this point feverishly. It is a true scientific issue and debate will continue in the scientific arena, not in the media.

Speaking of media:

            "If it all seems confusing and contradictory, other experts say, the real blame lies not with the     climate, or with science, or even scientists or former politicians, but with the incompetent media for failing to provide critical context for readers. "

Indeed. In this very article! Examine it closely. The first half of the article presents one side and then trails off into the other side and only by the late middle does context begin to appear. And then just as context settles in, they bring in the 1970's cooling argument. This argument was created and propagated by press reports which misrepresented the science. Which makes it irrelevant in the current discussion.

And then they close by stating that science changes! Of course science changes. It does so because we update our theories based on new evidence, new data, new analysis. And yes even scientists can be wrong. They go where the science leads them and not every avenue leads somewhere or even leads to the correct somewhere. Thats why we attempt to make results reproducible.

We call it climate change because we know way more about the weather and climate and can state with confidence that change is the best way to describe it. Some regions will warm, others may cool. Some will get more precipitation, others less. It is an important scientific distinction. It is not changing the message, however. 

Climate change is not contentious because the science is weak. It is contentious because the science is young. It is further complicated because of the economic impact any action on carbon emissions might have. Scientists still have the duty to warn about impending climate fluctuations or even climate change. And the climate scientists have spoken, in consensus, to warn us about the effects of increasing CO2. They do so with uncertainty; the range of possible warming scenarios. They do so with caution. What our policymakers should be doing is deciding how to act responsibly not deciding which science is correct. The science updates all on its own. 

What is not easily updated is how well scientific communication occurs between scientists and policymakers, scientists and the public, and policymakers and the public.

Read more: http://www.foxnews.com/scitech/2011/02/03/worsening-winters-come-global-warming/#ixzz1Cx8RXypD

Education on Snow

It is late. I am on a snow day. And I feel like teaching.

Real snow days are not for play dates, driving around, or going to the movies. No offense Freakonmics blogger. But snow days in my mind are dedicated to physics, science, engineering, and daredevil stunts. That is, when you have finished getting paid for shoveling driveways and sidewalks around the neighborhood. Lets not forget some good family time where you build a snowman family.*

Designing, building, and organizing an awesome sledding hill complete with jumps is an effort in fun, design, creativity, and organization. Furthermore constructing snow walls or barriers in order to have epic snowball fights is also a must. And lets not forget finding a wall so that you can pile up 3-6 feet and jump into it from above. Going super fast down a hill (engineering, physics, design), jumping off a wall (testing gravity and snow compression), and snowball fights (principles of compression, strengths of materials, chemistry) are all awesome feats of awesomeness (copyright jimmyc, because its late and I said so)!

Kids don't go outside nearly as often as when I was a kid, but they should, and snow is the perfect excuse. "Its cold" is not a reason to stay inside. Your kids have abercrombie and fitch Eddie Bauer  (I am old) gloves, hats, scarves, underarmour, goretex coats, etc. Use them dammit! I might be strange, but I would walk miles in the snow just to do it. And I know I am not alone. I saw it in a movie once, "O Captain, My Captain". 

The blog post had the air of "old" people having a snow day. Snow days are about kids (movie: Snow Day). And if kids have snow days they should be out being kids learning about the awesomeness of snow. And, yes sometimes that means doing hard work to achieve your goals. Maybe it is shoveling the sidewalk or digging out the family car, or snow removal from the roof. And then its sledding but not before gathering all the snow on your block to make the awesome luge run you saw on the Olympics ... getting water to make it nice and icy (Chemistry, engineering, physics, science!). Just to go faster.**

So stop being "old". You will have plenty of time to make your kids old. Give them the tools to be young, creative, and inventive ... away from the computer (unless autocad can do design work on snow).  I guess I am saying we should always be thinking about investments not immediate, gratifying incentives.

* Not to be confused with collegiate activities which involve constructing *other things* with snow.

**Someone in OK was killed when she tied her sled to a truck and stood in it as they crossed a bridge. Not the kind of activity I endorse.