The more I looked at the NSSL WRF forecast from yesterday the more interesting it was.
While the model initiated storms off the warm advection cloud band in Iowa after 0100 UTC, which did turn out to be correct, it was not severe nor was it the major player. Observations indicate this was part of an alto-cumulus castellanus area.
The area in NE where storms initiated in the real world along the warm front sharpened until 23-00 UTC where in model land it weakened considerably. There was an indication in the model that reflectivity was small but non-zero when the convergence was strong. This is a good albeit weak signal.
Another area under consideration for convection initiation was along the dryline in KS and northern Oklahoma where one storm formed around 23 UTC. The model had little in the way in convection here until 2 hours later, along the dryline.
Another area was in SW OK, where observations indicated a small, weak storm developed around 01 UTC and quickly died off. The closest model storm was at 05 UTC. Of course, the whole forecast goes awry in these latter two isolated storms as the model initiates convection all along the dryline from KS through Southern Oklahoma. The last 6 hours of the forecast looks little like what happened in terms of storms. I would caution that the model is not entirely wrong, just very aggressive. The cloud fields in the model develop into convection but closely resemble the cloud fields observed.
We are just beginning to harvest the wealth of information contained within such forecasts. I believe we will learn a lot more about these types of forecasts when we get down to looking at cloud fields (not at the grid scale but over substantive areas) and use these to compare the model with observations. This perspective should give forecasters more confidence in the overall appearance, and solidify what to look for when examining fine resolution forecasts. I think information extraction will be much more successful than reflectivity alone.
http://www.nssl.noaa.gov/wrf/110409/
Showing posts with label Uncertainty. Show all posts
Showing posts with label Uncertainty. Show all posts
Sunday, April 10, 2011
Friday, March 4, 2011
Uncertainty and skill
I was reading about what the National Hurricane Center will be doing this year. It was quite interesting:
1. Watch lead time to 48 hours; warning lead time to 36 hours
2. The size of the cones will be based on 5 year running mean of 2/3 of track error. The cone size radius varies in the Atlantic basin from 36 to 59 miles from 12 to 24 hours and grows about 35-40 miles per 24 hours thereafter.*
This means they have skill out to 48 hours in advance. They will be communicating actively their uncertainty via the graphical product (cones).
My foolish expectation would be to shy away from any sort of climatological cone of uncertainty and use ensemble guidance. This may not be the best option since it could provoke the so-called meteorological cancer i.e. over-dependence on models which have little value, not necessarily little skill. On the plus side it allows forecasts to be naturally consistent ... fairly certain in their ability to track where storms are, where they are going in the immediate future. To be fair the cone widens for a reason: tropical storms and hurricanes can encounter harsh or favorable environments quickly and these types of environments are hard to recognize over the ocean at longer lead times. Of course these environments can bring about changes to the inner workings of tropical storms in which case certain status quo forecasting rules may not work so well, and of course models also tend to not be spot on with hurricane intensity changes.
If nothing else, just seeing the products and how they are discussed should be interesting. It will be worth paying attention to see how the "public" reacts to be under "threat" for longer periods of time.
* I have not seen what this will look like but it will certainly be interesting!
1. Watch lead time to 48 hours; warning lead time to 36 hours
2. The size of the cones will be based on 5 year running mean of 2/3 of track error. The cone size radius varies in the Atlantic basin from 36 to 59 miles from 12 to 24 hours and grows about 35-40 miles per 24 hours thereafter.*
This means they have skill out to 48 hours in advance. They will be communicating actively their uncertainty via the graphical product (cones).
My foolish expectation would be to shy away from any sort of climatological cone of uncertainty and use ensemble guidance. This may not be the best option since it could provoke the so-called meteorological cancer i.e. over-dependence on models which have little value, not necessarily little skill. On the plus side it allows forecasts to be naturally consistent ... fairly certain in their ability to track where storms are, where they are going in the immediate future. To be fair the cone widens for a reason: tropical storms and hurricanes can encounter harsh or favorable environments quickly and these types of environments are hard to recognize over the ocean at longer lead times. Of course these environments can bring about changes to the inner workings of tropical storms in which case certain status quo forecasting rules may not work so well, and of course models also tend to not be spot on with hurricane intensity changes.
If nothing else, just seeing the products and how they are discussed should be interesting. It will be worth paying attention to see how the "public" reacts to be under "threat" for longer periods of time.
* I have not seen what this will look like but it will certainly be interesting!
Sunday, February 27, 2011
Uncertainty cont.
I have been able to examine the NSSL-WRF, 00 UTC and 12 UTC NAM this morning.
With regard to the trough that is forecast to be the major player, it is likely that significant severe will break out colocated with the strong forcing along the triple point, in the dry punch into MO, and then another round even later in AR.
The main uncertainty lies in OK, where my hopecast suggests storms could try to break out along the dryline. The problem is that it occurs just around 22-23 UTC when the wind profile might be considered terrible for tornadoes. The wind profiles in general become more favorable further east and later on putting the tornado threat into AR but the window for discrete supercells appears to be small. Rather a squall line of some type will form with probably the chance for embedded supercell structures.
Further south however, there are better wind profiles, but the cap is somewhat stronger. The 00 UTC NSSL-WRF forms a squall line there as indicated by the synthetic satellite imagery.
I don't have a good intuitive feel for what may occur given some of the wind profiles I have seen. I do think the overnight models will struggle as they are typically too far east with any convection. They also struggle to produce individual storms ... will only produce storms in stronger forcing. The resolution of the models, the tendency to produce weaker lapse rates, etc all contribute to the storm bias. That said, the main threat appears to Normans east (Tulsa area and north), northwest (along the triple point), and southeast (secondary dry punch). There is still a chance for central OK. It all depends on if any storms attempt to go up along the dryline, which ultimately depends on the relative balance between the depth of moisture in the warm sector and the cap strength.
I am hoping that LMN and OUN will launch 21 UTC soundings, and maybe 18 UTC soundings so we can really examine the wind profile evolution as well as the cap. This will be a good case for analysis either way as it is a strong forcing case that is highly dependent on mesoscale details that our models may not get correct.
With regard to the trough that is forecast to be the major player, it is likely that significant severe will break out colocated with the strong forcing along the triple point, in the dry punch into MO, and then another round even later in AR.
The main uncertainty lies in OK, where my hopecast suggests storms could try to break out along the dryline. The problem is that it occurs just around 22-23 UTC when the wind profile might be considered terrible for tornadoes. The wind profiles in general become more favorable further east and later on putting the tornado threat into AR but the window for discrete supercells appears to be small. Rather a squall line of some type will form with probably the chance for embedded supercell structures.
Further south however, there are better wind profiles, but the cap is somewhat stronger. The 00 UTC NSSL-WRF forms a squall line there as indicated by the synthetic satellite imagery.
I don't have a good intuitive feel for what may occur given some of the wind profiles I have seen. I do think the overnight models will struggle as they are typically too far east with any convection. They also struggle to produce individual storms ... will only produce storms in stronger forcing. The resolution of the models, the tendency to produce weaker lapse rates, etc all contribute to the storm bias. That said, the main threat appears to Normans east (Tulsa area and north), northwest (along the triple point), and southeast (secondary dry punch). There is still a chance for central OK. It all depends on if any storms attempt to go up along the dryline, which ultimately depends on the relative balance between the depth of moisture in the warm sector and the cap strength.
I am hoping that LMN and OUN will launch 21 UTC soundings, and maybe 18 UTC soundings so we can really examine the wind profile evolution as well as the cap. This will be a good case for analysis either way as it is a strong forcing case that is highly dependent on mesoscale details that our models may not get correct.
Saturday, February 26, 2011
Uncertainty foci
1. The trough in question is still only half over the upper air network, thus there is uncertainty in its exact structure. It appears to be currently moving more south than east but that trend may be shifting to more east.
2. I found a website to scrutinize the 3 hourly soundings from the NAM. It turns out the cold air advection over OK around 00 UTC may actually be a reflection of a boundary layer deepening up to 550 hPa at KGAG! Thus while it is getting cooler aloft, it does not necessarily imply a forcing mechanism for ascent. Note that 3 hours later, descent is implied from the inversion yielding net warming in the same layer while the boundary layer significantly cools. The exact role this feature plays remains uncertain.
3. Soundings from central OK show a very shallow moist layer and cap aloft which although weakens some remains strong until after 03 UTC. This is saying a lot since the previously mentioned odd double low level jet is clearly playing a big role in the development of deep moisture. Its even difficult to get moisture into KLZK under this scenario.
2. I found a website to scrutinize the 3 hourly soundings from the NAM. It turns out the cold air advection over OK around 00 UTC may actually be a reflection of a boundary layer deepening up to 550 hPa at KGAG! Thus while it is getting cooler aloft, it does not necessarily imply a forcing mechanism for ascent. Note that 3 hours later, descent is implied from the inversion yielding net warming in the same layer while the boundary layer significantly cools. The exact role this feature plays remains uncertain.
3. Soundings from central OK show a very shallow moist layer and cap aloft which although weakens some remains strong until after 03 UTC. This is saying a lot since the previously mentioned odd double low level jet is clearly playing a big role in the development of deep moisture. Its even difficult to get moisture into KLZK under this scenario.
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