A rough day all around for CI forecasting

To bring us up to date, yesterdays forecast domain for the afternoon warning program forecasters centered on the area covered by the Grand Forks and Duluth CWAs. These areas were decided upon using the inputs from all of the participants of both the EFP and EWP, based on model input, observations, and the vast experience present in the room. My last entry ended with a dinner break to pass the time waiting for CI to initiate somewhere... anywhere.

Unfortunately, Mother Nature did not cooperate and the area stayed pretty well capped into the forecast period. In the short time I was away, the decision was made to shift the focus area to Bismarck, ND, where we had a better chance of seeing some storms. Shortly after my return, some storms popped, giving the forecasters something to look at, analyze, and even issue some statements and a warning on.

So how did SATCAST do? Well, we got the convection in North Dakota as the system moved east, approaching out original focus area. It did catch the 3 cells that caused the increased activity, with lead-times of about 30 minutes as well as some other areas of convection as the afternoon progressed.

SATCAST image at 1845 UTC
The area of clouds (marked by the green arrow) consistently flagged CI in subsequent satellite images. These storms started to show up on radar at 1958 UTC and went on to be warned on as early as 2330 UTC.

NMAP2 radar reflectivity at 1958 UTC.
NMAP2 radar reflectivity at 2337 UTC.
Unfortunately, SATCAST also indicated CI sporadically across the northern part of Minnesota that never had a chance of getting to verify. The capped environment just couldn't be pushed through by the rapidly growing systems that tended to pop up along the boundary. End result, some False Alarms.

A known problem area of the techniques includes high CAPE areas that are capped. The algorithm exploits the satellite signals to flag rapidly growing clouds. Although there are post-processing techniques in place to help eliminate false alarms (such as masking out areas that have no CAPE) it doesn't pick up as well in areas where significant CIN is also present. We as a research group are still hunting for the "best" way to reduce the false alarms without masking out the good data. Also compounding the problem in this area, was the presence of high level cirrus associated with the low-pressure system. The cloud-typing algorithm does a good job identifying ares that need to be masked out, yet high level cirrus seems to be the bane of both CI algorithms tested during this experiment, as evidenced by the CI flags along the boundaries of the system as the afternoon progressed.

In contrast, the UWCI algorithm did not have as many CI flags in the Grand Forks/Duluth focus areas. The one or two flags they did have, verified shortly thereafter. And yes, the UAH SATCAST algorithm did pick up on those cases as well. To be fair, I did not get a chance to see if UWCI flagged the storms in the Bismarck area later, so I am only commenting on the 2-3 hours over the first focus area. But it does bring up an interesting question, is it better to have a few indicators that verify at the cost of missing many of the other cases, or is it better to have more indicators in/of the environment, that although will catch the definite cases of CI, but will also result in higher false alarms?

I asked each of the forecasters and got a few different answers. For one, watching where SATCAST flagged rapidly growing clouds caused him to focus in on the associated environment to ensure a good understand of what is occurring at that time and check for agreement with previous thinking. If he wasn't looking at it, he was checking to see if the environment had changed since he looked last. In short, a situational awareness tool. For another, watching where the algorithm was flagging CI ahead of the warning area he was responsible for queued him in to watch for radar echoes. There were also some statements indicating that the jury was still out. Overall, a broad spectrum of answers yet not overall negative, especially after playing with both tools for only one day. I imagine that in the next day or two, more definite opinions will be formed and shared...

Then again, isn't that the point?

Nearcast training for severe

UW-CIMSS scientist Ralph Petersen explaining the Nearcast product to EFP participants
This morning UW-CIMSS scientists Ralph Petersen and Bob Aune sat down with the EFP's severe desk to help train the participants on how to use the Nearcast product during morning forecast operations. UW-CIMSS provides us with 10 fields from the Nearcast product, which includes individual layers of theta-e and preciptable water (PW), which are then differenced to provide the differential theta-e and PW water fields that we typically use for forecasts. The most effective way to help forecasters understand what they are looking at in these differential fields is to start with the individual layer PW and theta-e fields and then the forecaster can mentally calculate the differences and compare to what the product is showing them. Ralph and Bob helped the participants understand how the Nearcast can assist them in making their forecasts by pointing out that the Nearcast fields will show you where relatively convectively stable and unstable areas are. Because no forcing mechanisms are included within the Nearcast's output, it doesn't guarantee where convection will occur, but it can help narrow down where you should be focusing your attention. If there is an area of strongly stable air, you're not likely to have any deep convection, even if there is some sort of light forcing present. This may be especially useful within SPC operations for forecasters issuing mesoscale discussions (MD) to determine where a severe thunderstorm or tornado watch will or will not be needed. It may also be useful during the early afternoon convective outlook updates to help trim areas that will not be expected to have thunderstorms later during that day. Following the group training, Steve Weiss (SPC SOO) asked if I would be willing to work with the forecasters in operations this summer in exposing this product to them. In addition, we expect to provide a training session within the SPC's bi-annual forecaster training this fall to help expose all of the SPC personnel to the product.

Impressions of a first day...

Sitting through the various discussions on the likelihood of the development of CI, it quickly became apparent that the low pressure system moving eastward along the Canadian border was garnering plenty of interest from the 3 main desks located in the HWT. Watching it through the morning with the morning shift of EWP forecasters, the area remained on the "it's going to be an interesting day" and "it didn't really produce much" line, due to the favorable conditions in moisture and afternoon heating being held back by a pretty definite cap that may or may not break sometime before 00Z. Moving in the afternoon, warning portion of the EWP program, conditions remain decent, yet the cap is still firmly in place. Interest in the CI products is in the forefront of the forecaster's minds and the handy, four panel, product is up on the main screens of the AWIPS displays of all four forecasters present.

In all, so far, SATCAST has been indicating CI sporadically in and around the North Plains for most of the afternoon. Taking into account the capped environment, the algorithm has been picking up the signal of rapidly growing clouds, as it is trained to do, yet convection has been slow to develop in CWA's of Grand Forks and Duluth. This has resulted in some red objects (in the area of interest) that will likely not verify, due to the capped environment and some interfering cirrus atop the low pressure system as it moves east.

So far, the forecasters have still indicated an interest in the product as the afternoon has progressed. Being able to look at the data in a loop has allowed for an awareness of the environment, allowing for the forecaster to be "queued in" to an area of interest. As an example, the UAH CI algorithm has indicated a consistent CI signal moving across western North Dakota that verified about 35 minutes later on radar (according to the notes of forecasters assigned to the Grand Forks CWA).

It is still early, we will see how things evolve after a quick dinner break..

Nearcast in short-term warning operations

EWP forecaster issuing an experimental severe weather outlook using the Nearcast output.
EWP forecasters have come up with some novel ways to utilize the Nearcast differential precipitable water/theta-e forecasts within their warning operations. Generally we think of the Nearcast as a forecast tool, but the EWP forecasters have been using it to issue warnings and severe weather statements (see image above). Forecasters have been analyzing increased near-storm convective instability as depicted in the 0-2 hour forecasts from the Nearcast product to help increase their confidence that the storm will intensify. Conversely, the Nearcast is very useful to show when storms will die if the storm is expected to move into an area with very low convective instability or dryer atmospheric columns. This is another example of how forecasters will find some additional utility of these experimental products that the developers may not have originally intended.

Final week of the experiment...

Today marks the first day of the 5th and final week of this year's Spring Experiment. This week the EWP rejoins the EFP from its week off and resumes normal activities. Today the EWP will be providing forecasters with a load of training material as they prepare to use the experimental products during real-time forecast/warning operations. Following the 4-hour PowerPoint session we will have the forecasters work through a WES case to get familiar with where the products are, what they look like and how to use them within their AWIPS workstations.

UW Overshooting Top Algorithm Hits Storm Prior to Springfield, MA Tornado

Yesterday, 1 June 2011, climatologically rare tornadoes hit New England. The University of Wisconsin Overshooting Top algorithm identified an overshooting top with a severe thunderstorm at 2002 UTC 1 June 2011, just west of Springfield, MA (right). The overshooting top magnitude is filled atop the GOES visible imagery. The overshooting top identification occurred 28 minutes ahead of the first tornado report in Westfield, MA at 2030 UTC (a western suburb of Springfield).

UW Nearcast Product and Developing Convection

The GOES Sounder Nearcasting product is being used today on the EFP CI-desk to identify possible forcing mechanisms for the deep convection. In the image below the nearcasting theta-e difference is shown, valid 1700 UTC 01 June 2011. Strong convection has been ongoing and continually developing in eastern to north-central Kansas along the minimum (maximum instability) and northeastward toward the strong gradient in the nearcasting theta-e difference. It was noted this gradient is also coincident with a strong dewpoint gradient at 850 hPa. It is believed southerly flow across this gradient is helping force the convection. Further east across the Mid Atlantic region, convection was developing largely in the minimum of the theta-e difference, with a strong gradient to the west as low-level moisture decreases behind the front. It has also been noted there are many other areas of strong potential instability indicated by the nearcasting product, however there is not deep convection associated with many of these areas. One hypothesis is there needs to be not only instability present, but also a forcing mechanism. Possible forcing mechanisms maybe inferred by a strong gradient in the instability indicated by the nearcasting product, suggestion strong temperature and/or moisture advection.

NSSL-WRF Simulated ABI Imagery and CI forecast

This morning on the EFP CI-desk, the simulated ABI imagery from the NSSL-WRF provided guidance on location and timing of initial CI location for many of the forecasters. As can be seen in the image below, there was a tight cluster of forecasted first CI location points over the higher terrain of northern New Mexico. The simulated ABI band 13 image valid at 1900 UTC shows newly developing convention over northern New Mexico. A few other forecasters favored convective initiation along the moisture gradient in the lower troposphere in eastern Kansas. (Ongoing storms northwest of Salina, Kansas were excluded from the forecast area.)

UW CTC Highlights Most Rapid Development of Convective Line

The UW Cloud-Top Cooling (CTC) rate cannot only be used to nowcast convection initiation, but also highlight the most rapid vertical growth along a line of developing convective clouds. Below is the GOES visible imagery/UW CTC valid at 1732 UTC 31 May 2011 and base radar reflectivity at the same time. The entire line of towering cumulus over central Michigan looks similar on visible imagery, but the UW CTC highlights (green circle) the most rapidly growing and hence precipitating portion of the line (also green circle).

Simulated ABI Radiances Compared to GOES Observations

This week there is no EWP running so all support is geared towards the EFP. Early Tuesday on the CI desk of EFP, the NSSL-WRF simulated ABI radiances were compared to the current GOES observations for judging the timing/placement of the upper level vorticity maxima/upper level dry intrusion over the Central US, as well as impact of cloud cover on convective intiation forecasts over the western Great Lakes.

Below are the 15 UTC simulated ABI brightness temperatures (top) and observed GOES brightness temperatures (bottom). The consensus of the forecasters on the CI desk was the NSSL-WRF had excellent placement of the upper level vorticity as depicted by the water vapor channels. On the other hand, the NSSL-WRF struggled to capture the intensity and magnitude of a band of clouds and decaying convection over the Upper Mississippi Valley/western Great Lakes. The images below show the GOES observed clouds are much more expansive and have colder brightness temperatures than the simulated ABI clouds from the NSSL-WRF. Discussion is ongoing on how these clouds will impact convective initiation timing and location later today.







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