HSD Attachment 97-2 5-1-97

DEVELOPING LOCAL GUIDELINES FOR INITIAL PUBLIC FLOOD PRODUCTS
AT WFO TULSA--AND SIMPLIFYING THE DECISION-MAKING PROCESS

Alvin L. Hong
Service Hydrologist, WFO Tulsa OK

1. Introduction

On February 3, 1997, the Arkansas Red Basin River Forecast Center began a new program in which river forecasts (RVF) to the WFOs would be sent in a dual format. This format would indicate not only river stage forecasts with QPF, but also stage forecasts without QPF. This was done to give the WFOs a better idea of when one should issue a Flood Watch and when one should issue a Flood Warning (or when it may be best to just delay taking any immediate action).

ROML S-40-96 gave Southern Region offices guidelines for issuing products based on QPF. They are stated as guidelines and not as rules due to the variety of basin characteristics and the diversity of events possible. It was left to each office to develop guidelines appropriate to their local areas.

In order to prepare the Tulsa WFO to adapt to the Southern Region guidelines, I wrote several products to both users and the staff. Attached are the following products with hopes that they may be helpful to other WFOs in the Southern Region within the umbrella of the ABRFC:

  1. Written suggested guidelines for the issuance of initial public flood products.
  2. A flow chart/decision tree that can be helpful as a quick-reference.
  3. A Public Information Statement directed to users of flood products.
2. Caveats

Our local guidelines do not cover every public flood product. For instance, Flood Statements (FLS) are not included in the guidelines or flow chart. They will be used at WFO Tulsa only as a follow-up to Flood Warnings (FLW). In ROML S-40-96, there is an option given to the WFOs for the issuance of Flood Statements when only "nuisance" flooding is expected. However, we decided not to use this option at Tulsa when a river is forecast to rise above flood stage, because it might confuse the public.

Flood Potential Outlooks (ESF) were also not included in the local guidelines or flow chart. The ESF has been traditionally used as an area-wide long-lead time flood forecast product initiated by the WFO's assessment of rainfall potential. We believe it might confuse the public if the ESF were also used to make a site-specific flood forecast. For the Tulsa WFO area of responsibility, we decided to issue only Flood Warnings when the river is forecast to rise above flood stage due to downstream routing of water. When a river is forecast to exceed flood stage based on QPF, either Flood Watches or Flood Warnings will be issued.

3. Suggested Procedures in Initial Flood Situations

The following procedures for WFO Tulsa have been summarized from WSOM Chapter E-42 and Southern Region ROML S-40-96 with local adaptations. When the forecast flooding is due to Quantitative Precipitation Forecasts (QPF), the length of lead time becomes the critical element in deciding between a Flood Watch or a Flood Warning. This lead time can be easily determined graphically from the AWIPS HFS display software. (The AWIPS HFS procedure is indicated in Appendix A). It can also be determined by reading the coding within the RFC's River Forecast Product (RVF). The decision process is shown by the attached flow chart and explained below.

If flooding is forecast regardless of any additional rainfall, issue a Flood Warning (FLW). If flooding is forecast due to additional forecast rainfall, one needs to determine when that flooding would begin.

If forecast rainfall would cause flooding within 12 hours, then a Flood Warning should still be issued. If flooding would occur between 12 and 36 hours, then a Flood Watch (FFA) should be issued. If it is beyond 36 hours, then no issuance is required. However, it might be advisable to alert certain Civil Defense officials who may be concerned about even the remote chance of flooding in their area.

Decide if a Watch or a Warning should be generated for each individual forecast point. Since several forecasts may be contained in one RVF, it may be necessary to isolate the forecast points before RiverPro generates the products.

At an AWIPS site, the first choice for the automatic generation of initial flood products will be RiverPro (see Appendix B). River Pro, part of the AWIPS Hydrologic Forecast System (HFS), comes with templates that will automatically generate Flood Warnings, Flood Statements, and River Statements (RVS). The templates for the FLW, FLS, and RVS can be edited and modified to meet national and regional mass media header criteria as well as for local use. A template was created in RiverPro which will generate Flood Watches (FFA).

After RiverPro generates the product, it should be carefully checked. RiverPro includes recommended actions which may be irrelevant to certain situations, and those action statements should be deleted. Also, one should especially be careful when editing numerical values to be consistent through the entire product. For example, changing a current stage in one sentence will require changing its height above flood stage in a subsequent sentence.

With the emphasis on anticipated rainfall in the text of the Flood Watch product, it would be helpful to the users to add a sentence specifically stating how much additional rainfall is anticipated. If time doesn't allow one to do this, a generic statement has been added into the text of the Flood Watch product defining what a Flood Watch means.

4. Acknowledgment

I would like to thank Steve Amburn (SOO) for his suggestions and review of this paper.

Appendix A

AWIPS HFS HydroView Instructions:

  1. From the Workbench window, click Hydrology.
  2. From the Hydrology window, click Hydrologic Data Viewer.
  3. From the mp window, double-click Hydrologic Data Viewer.
  4. If a Possible Hang Condition window opens, click Ignore for now.
  5. Double-click the triangle at the desired forecast point. This will open the Time Series Display.
  6. Examine the two line graphs in the top window. Ignore the labels on the left-side legend. The graph with the highest peak will be the QPF forecast; the other will be the non-QPF forecast.


Appendix B

AWIPS HFS RiverPro Instructions:

  1. From the Workbench window, click Hydrology.
  2. From the Hydrology window, click River Product Formatter.
  3. Ensure that the latest stage is correct.
  4. From the RiverPro window, click on the product you wish to generate in the Product
  5. Description list. Until we receive an upgraded version which will generate usable tables with proper headings, select the products which generate "no table".
  6. Look at the forecast points on the right side of the RiverPro window. Clear the points not needed and highlight the forecast points desired.
  7. From the RiverPro window, click File, then Create.
  8. Examine the product in the RiverPro Editor. Edit as needed. Click Save, then Exit.
  9. From the RiverPro window, click File, then Issue.


FLOW CHART GUIDELINES FOR WHEN A RIVER IS
INITIALLY FORECAST TO RISE ABOVE FLOOD STAGE

Notes:
  1. This flow chart is only a guideline based on suggested local office procedures followed at WFO Tulsa OK. (ROML S-40-96 allows individual offices to modify procedures for their local area). The forecaster has discretion to override guidelines based upon his confidence of QPF and RFC guidance.

  2. This is intended to help the forecaster decide primarily between a Flood Warning or a Flood Watch. After the issuance of a Flood Warning--follow-up Flood Statements are issued. After the issuance of a Flood Watch--a Flood Warning or a River Statement is usually issued as new RFC guidance is received. However, a Flood Watch may be extended if much uncertainty remains.


ZCZC OKCPNSTUL ALL
TTAA00 KTUL 181345
OKZ054>076-AR001-002-010-011-019-029-181500-

PUBLIC INFORMATION STATEMENT
NATIONAL WEATHER SERVICE TULSA OK
745 AM CST MON FEB 18 1997

...NEW PUBLIC FLOOD PRODUCT...

A NEW PUBLIC FLOOD PRODUCT WILL NOW BE AVAILABLE FROM THE NATIONAL WEATHER SERVICE IN TULSA. THE PRODUCT IS CALLED A FLOOD WATCH. IT WILL BE ISSUED AS CONDITIONS WARRANT...AND WILL BE STORED UNDER AFOS HEADER (OKCFFATUL). THE AFOS HEADER (OKCFFATUL) IS IDENTICAL TO THAT OF A FLASH FLOOD WATCH... SO NO CHANGES WILL NEED TO BE MADE BY USERS WHO ARE ALREADY PROGRAMMED TO RECEIVE (OKCFFATUL) ON THEIR NWWS RECEIVER UNITS.

A FLOOD WATCH WILL BE ISSUED WHEN RIVER FORECASTS...BASED ON QUANTITATIVE PRECIPITATION FORECASTS...ARE EXPECTED TO EXCEED FLOOD STAGE...BUT FLOODING IS NOT EXPECTED TO OCCUR UNTIL THE NEXT 12 TO 36 HOURS.

THE KEY PHRASE IS "BASED ON QUANTITATIVE PRECIPITATION FORECASTS". RIVER FORECASTS CURRENTLY INCORPORATE Forecast RAINFALL AMOUNTS INTO THE MODELS. THIS USUALLY RESULTS IN A MORE ACCURATE RIVER FORECAST. HOWEVER...THERE ARE TIMES WHEN A RIVER IS EXPECTED TO RISE ABOVE FLOOD STAGE PRIMARILY BECAUSE OF Forecast RAINFALL... AND NOT PRIMARILY BECAUSE OF RUNOFF AND ROUTING FROM UPSTREAM WATER.

THE FLOOD WATCH PRODUCT SHOULD HELP TO CLARIFY THOSE SITUATIONS. IT WILL BE SIMILAR TO OTHER WATCH PRODUCTS ISSUED BY THE NATIONAL WEATHER SERVICE IN THAT IT IS ISSUED WHEN THERE IS A SIGNIFICANT RISK... BUT THAT ITS OCCURRENCE IS UNCERTAIN. A WATCH IS INTENDED TO PROVIDE ENOUGH LEAD TIME SO THAT THOSE WHO NEED TO SET THEIR PLANS IN MOTION CAN DO SO.

WHEN A FLOOD WATCH IS ISSUED...USERS SHOULD BEGIN TO PREPARE FOR POSSIBLE FLOODING IN THE NEXT 12 TO 36 HOURS. A FLOOD WATCH WILL BE UPDATED TO A FLOOD WARNING (OKCFLWTUL) IF THE RIVER IS EXPECTED TO RISE ABOVE FLOOD STAGE WITHIN THE NEXT 12 HOURS. IF IT APPEARS THAT THE RIVER WILL NOT REACH FLOOD STAGE...THE FLOOD WATCH WILL BE UPDATED BY A RIVER STATEMENT (OKCRVSTUL).

IN SUMMARY...WHEN A RIVER IS FORECAST TO RISE ABOVE FLOOD STAGE IN

THE NEXT 12 HOURS... A FLOOD WARNING WILL BE ISSUED. WHEN A RIVER IS FORECAST TO RISE ABOVE FLOOD STAGE BETWEEN 12 AND 36 HOURS REGARDLESS OF ANTICIPATED RAINFALL... A FLOOD WARNING WILL BE ISSUED. WHEN A RIVER IS FORECAST TO RISE ABOVE FLOOD STAGE BETWEEN 12 AND 36 HOURS DUE PRIMARILY TO Forecast RAINFALL AMOUNTS...A FLOOD WATCH WILL BE ISSUED.

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