Stories from the Sonoran Stories from the Sonoran DesertDesert

Severe Weather Technology Severe Weather Technology WorkshopWorkshop

10 July 200710 July 2007

Doug GreenDoug Green

Warning decisionmaking Warning decisionmaking shortcomingsshortcomings

Tools…or lack thereof…to help forecasters discriminate Tools…or lack thereof…to help forecasters discriminate between microburst and non-microburst storms. Three between microburst and non-microburst storms. Three and four dimensional radar data displays (such as GR2 and four dimensional radar data displays (such as GR2 Analyst) are very useful to forecasters.Analyst) are very useful to forecasters.

Basin flash flood guidance does NOT take important Basin flash flood guidance does NOT take important basin characteristics into account (e.g., Greg Smith’s basin characteristics into account (e.g., Greg Smith’s FFPI information is not integrated into FFMP.) Office FFPI information is not integrated into FFMP.) Office typically uses “forced FFG” in order to increase typically uses “forced FFG” in order to increase usefulness of FFMP.usefulness of FFMP.

The question “Where’s the line between urban/small The question “Where’s the line between urban/small stream flooding and flash flooding?” is tricky. Rainfall stream flooding and flash flooding?” is tricky. Rainfall rate and amount guidelines are used to help delineate rate and amount guidelines are used to help delineate between the two…is this “good enough”?between the two…is this “good enough”?

Warning decisionmaking Warning decisionmaking shortcomingsshortcomings

Precipitation estimates often leave much to be Precipitation estimates often leave much to be desired, and are not adjusted for environmental desired, and are not adjusted for environmental conditions (ex: 24 Aug 2006 flash flood over and near conditions (ex: 24 Aug 2006 flash flood over and near Indian Bend Wash in Phoenix metro).Indian Bend Wash in Phoenix metro).

Max hail size predictions from SCAN never seem to be Max hail size predictions from SCAN never seem to be observedobserved

Lightning data, including # of c-g strikes, is not Lightning data, including # of c-g strikes, is not incorporated into the SCAN Cell Table. incorporated into the SCAN Cell Table.

TDWR data: available, but not heavily used. It’d be TDWR data: available, but not heavily used. It’d be great if TDWR and nearby WSR-88D data could be great if TDWR and nearby WSR-88D data could be combined to generate dual-Doppler radar displays.combined to generate dual-Doppler radar displays.

Warning decisionmaking Warning decisionmaking shortcomingsshortcomings

Current verification scheme discourages Current verification scheme discourages issuance of warnings in low-population areas, issuance of warnings in low-population areas, since it’s unlikely a severe event will be since it’s unlikely a severe event will be reportedreported– When WFOs warn for what they deem to be severe When WFOs warn for what they deem to be severe

events, they should not be penalized; however, that’s events, they should not be penalized; however, that’s not the case todaynot the case today

High impact vs significant eventsHigh impact vs significant events– Don’t want to miss any high impact events, so Don’t want to miss any high impact events, so

tendency is to warn for borderline severe events over tendency is to warn for borderline severe events over high population areas and nowcast same over low high population areas and nowcast same over low population areas…is this what we should be doing?population areas…is this what we should be doing?

More shortcomings…More shortcomings…

WES is a great training tool, and data WES is a great training tool, and data upload/download has been streamlined…but it’s upload/download has been streamlined…but it’s still cumbersome. We need the ability to store still cumbersome. We need the ability to store several months’ worth of data on the system at several months’ worth of data on the system at one time…and that doesn’t exist attm.one time…and that doesn’t exist attm.– Examine numerous cases…to improve capability to Examine numerous cases…to improve capability to

provide useful warning guidelines for various provide useful warning guidelines for various synoptic/mesoscale regimessynoptic/mesoscale regimes

– Have ability to examine a case from time to time Have ability to examine a case from time to time without worrying about unloading/reloading the datawithout worrying about unloading/reloading the data

Anything that makes working with WES easier for our Anything that makes working with WES easier for our forecasters “greases the skids” and encourages its use!!forecasters “greases the skids” and encourages its use!!

How should we address the shortcomings?How should we address the shortcomings?

AWIPS needs to have GR2Analyst-type capabilities!AWIPS needs to have GR2Analyst-type capabilities! Reliable flash flood guidance needs to be created and Reliable flash flood guidance needs to be created and

provided over the entire CWA provided over the entire CWA Rain gauge data definitely needs to be incorporated into Rain gauge data definitely needs to be incorporated into

any rainfall estimation scheme.any rainfall estimation scheme. Microburst potential algorithm needs to be provided to, Microburst potential algorithm needs to be provided to,

and evaluated by, field forecasters.and evaluated by, field forecasters. Vertical numerical profiles of cell-based reflectivity and Vertical numerical profiles of cell-based reflectivity and

radial velocity convergence/divergence need to be radial velocity convergence/divergence need to be provided to forecasters.provided to forecasters.

Increase data storage capacity for case review purposesIncrease data storage capacity for case review purposes TDWR help! Dual Doppler output? Cell table? TDWR help! Dual Doppler output? Cell table?

Microburst prediction output for forecasters?Microburst prediction output for forecasters?

And now…for something completely And now…for something completely different…here’s a brief overview of different…here’s a brief overview of a couple of radar issues at WFO a couple of radar issues at WFO Phoenix Phoenix Unusually large reflectivity Unusually large reflectivity

discrepancy observed between KIWA discrepancy observed between KIWA and KYUX radarsand KYUX radars

Apparent KIWA velocity data quality Apparent KIWA velocity data quality problemsproblems

Reflectivity Discrepancy Reflectivity Discrepancy between KIWA and KYUX between KIWA and KYUX

During September 2006, forecasters began During September 2006, forecasters began to notice an unusual discrepancy regarding to notice an unusual discrepancy regarding storm intensity and precipitation estimates storm intensity and precipitation estimates for storms nearly equidistant from KIWA and for storms nearly equidistant from KIWA and KIWA RDAsKIWA RDAs– KIWA returns much strongerKIWA returns much stronger– KIWA precipitation estimates much greaterKIWA precipitation estimates much greater– Storms were tall, and beam blockage was not “the Storms were tall, and beam blockage was not “the

issue”issue” Sent a few examples of what we observed to Sent a few examples of what we observed to

Tony Ray at the ROCTony Ray at the ROC

ROC determined that…ROC determined that…

KYUX was running “cold”KYUX was running “cold” KESX was running “hot”KESX was running “hot” KIWA was running a tad “hot”KIWA was running a tad “hot” KEMX (Tucson) was running a little “hot”KEMX (Tucson) was running a little “hot”

Bottom line: enough discrepancy in Bottom line: enough discrepancy in transmitted power existed amongst transmitted power existed amongst neighboring radars to lead to noticeable neighboring radars to lead to noticeable differences in dBZ displays, irrespective of differences in dBZ displays, irrespective of sampling issues!sampling issues!

What happened?What happened?

ROC determined that, when ORDA build 8 ROC determined that, when ORDA build 8 was installed, radar calibration changed (the was installed, radar calibration changed (the old calibration information was not retained). old calibration information was not retained). – Some radars began to run “hot” or “cold” Some radars began to run “hot” or “cold”

compared to their pre-ORDA build 8 performance.compared to their pre-ORDA build 8 performance.

ROC decided each WSR-88D radar needed to ROC decided each WSR-88D radar needed to be checked out by local ETs…and directed be checked out by local ETs…and directed field personnel to complete this task. field personnel to complete this task.

KIWA Velocity Data Quality KIWA Velocity Data Quality Problems Problems

For the past couple of years, forecasters and the SOO For the past couple of years, forecasters and the SOO noted several problems with data quality regarding noted several problems with data quality regarding low-level radial velocity images from KIWAlow-level radial velocity images from KIWA– Spikes or localized areas of moderate to strong outbound/ Spikes or localized areas of moderate to strong outbound/

inbound velocities were often observed, especially over inbound velocities were often observed, especially over the eastern half of the Greater Phoenix metropolitan the eastern half of the Greater Phoenix metropolitan area. area.

Very problematic, especially when mesoscale and microscale Very problematic, especially when mesoscale and microscale outflows existed outflows existed

– Areas of unrepresentative velocity data observed in the Areas of unrepresentative velocity data observed in the vicinity of hills/small mountainsvicinity of hills/small mountains

Not totally unexpected, but forecasters thought bypass map Not totally unexpected, but forecasters thought bypass map would filter out unrepresentative radar returnwould filter out unrepresentative radar return

WFO contacted ROC…WFO contacted ROC…

ROC analysis of the data revealed…ROC analysis of the data revealed…

Commanded elevation angle for every Commanded elevation angle for every lowest cut is 0.48 deg. lowest cut is 0.48 deg.

Most data collected at cuts much lower Most data collected at cuts much lower than 0.48 degthan 0.48 deg– Consequently, automobiles and terrain Consequently, automobiles and terrain

features have a greater influence on the features have a greater influence on the returned power than what was expected or returned power than what was expected or desireddesired

Lowest level velocity data collection Lowest level velocity data collection cut cut via VCP 11 for KIWA on 4/16/07 via VCP 11 for KIWA on 4/16/07

Doppler Data Collection: 4/17/2007Doppler Data Collection: 4/17/2007

Initially, Doppler cut data collection begins at Initially, Doppler cut data collection begins at an elevation of 0.35 deg (255-305 degree an elevation of 0.35 deg (255-305 degree azimuth).azimuth).

Data collected at approximately 0.4 deg in Data collected at approximately 0.4 deg in the 300-360 degree rangethe 300-360 degree range

After that, data were once again collected at After that, data were once again collected at a slightly lower elevation.a slightly lower elevation.– 88D “hunts” for the assigned elevation slice of 0.48 88D “hunts” for the assigned elevation slice of 0.48

deg, which explains the upward and downward deg, which explains the upward and downward movements of the antenna movements of the antenna

What happened?What happened?

Lowest elevation slice has been raised about Lowest elevation slice has been raised about 0.1 degree. Still see occasional problems 0.1 degree. Still see occasional problems with velocity data, but the problems are not with velocity data, but the problems are not as widespread nor as frequent.as widespread nor as frequent.