# Presentation: 281831

## QPF Methodologies in GFE/NDFD	

- Kevin Lynott and Shannon White
- Office of Climate, Water and Weather Services
- 03/11/04

## Objectives

**To provide guidelines for forecasting QPF and discuss issues with producing a QPF grid for NDFD which is well-**
**collaborated**

## Outline

**QPF Decision and its Impact**
**10-506 and QPF**
**QPF across the NWS**
**HPC QPF**
**WFO Collaboration and Smart Tools **
**Open Discussion****	**

## Corporate Board and QPF

**On June 12, 2003 the NWS Corporate Board decided that the NDFD QPF would be populated by a mosaic of WFO QPF grids**
**HPC QPF should be used by WFOs and RFCs as a starting point**
**QPF forecasts should be made in collaboration with other offices**
**RFCs continue to have responsibility for QPF input to river models (NWSRFS)**

## QPF in NWSI 10-506

**QPF - the total amount of expected liquid precipitation (in hundredths of inches).  A QPF will be specified when a measurable (0.01") precipitation type is forecast for any hour during a QPF valid period.  **
**Valid periods for the NDFD begin and end at 0600, 1200, 1800, and 0000 UTC**

## What This Means for You

**As NWSHQ policy stands right now, a**
**QPF (at least .01”) must correspond with**
**a floating PoP value of 15 percent or**
**higher.**
**Based on previous IFPS Workshops and**
**discussions with the HPC, this condition**
**will be re-evaluated.   **

## QPF in the NWS 

**HPC – ****Forecasters use Areal Average method for QPF ****on a national scale (32 km resolution).  Dissemination of 5 km QPF grids (on test basis) to match resolution of NDFD coming in May (every 6 hours out to 72 hours).**
**RFCs – Use isohyets of Mean Areal Precipitation for their basins for ingest to NWSRFS (4 km resolution out to 72 hours).**

## HPC QPF

**Observational data is used to identify favorable locations of moisture, instability, and lift**
**Model bias and trends are assessed (operational and ensemble) **
**HPC Forecaster adds value to model QPF by:**
**Adjusting model QPF according to pattern regime**
**Accounting for model tendencies**
**Primary QPF Challenges at HPC**
**Keeping current on model tendencies as models are upgraded**
**Learning local effects over national scale**
**Convective QPF in patterns of weak synoptic and mesoscale scale forcing**
**Why use HPC QPF ?**
**Good starting point**
***Consistently out performs models ***
***40 years + experience***
***Seamless grid***

## HPC QPF

**Forecaster starts with model QPF**
**Adjusts as needed based on meteorological information**
**Areal average is forecast with the area being where precip is expected**
**Trying to forecast a QPF field which will match the analysis **
**No specific tie to PoP**
**Only exception is during convective season when they try to indicate scattered storms**
**Amounts under 0.25 are not verified**

## Things to Avoid in a QPF Grid

**Assigning one value arbitrarily to the entire grid **
- - **Try to point out areas that may be more or less favored**
**Gaps**
- - **Smooth where necessary**
**Late grids – waiting until the end**

## Recommended QPF Smart Tools

**QPF_SmartTool**** **
**Baseline tool which has a forecaster-input upslope/downslope factor**
** **
**SnowAmt_from QPF**** **
**Assigns SnowAmt based on forecaster-input ratio and will not add SnowAmt where no snow is forecast**
** **
**QPF_from_WxPoP**
**Will produce QPF grids based upon the Wx and PoP grids**
**User can accept the default settings or choose the minimum and maximum QPF values that appear on the QPF grid**
**Others can be found on the Smart Tool Repository**** **
- _[http://140.90.90.253/~applications/STR/index.php3](http://140.90.90.253/~applications/STR/index.php3)_** **

## Things to Remember 

**QPF approach not much different from way things done in the past, except that you inherit grids **
**Focus on meteorological situation**
**Use QPF Smart Tools and HPC guidance to your advantage**
**Collaborate!**
**Talk to your local customers (including RFCs)**

## QPF Methodologies in GFE/NDFD 

**Questions?**
_**[Kevin.Lynott@noaa.gov](mailto:Kevin.Lynott@noaa.gov)**_
_**Shannon.White@noaa.gov**_

## Collaboration		

- Integral part of the grid preparation process
- QPF collaboration threshold (*.25 in/6 hr.)*
- 12Planet
- Intersite Coordination of Grids (ISC)
- Telephone
- Collaboration Presentations – IFPS Professional Development Series  _[http://www.nwstc.noaa.gov/nwstrn/d.ntp/meteor/ifpspcu4.html](http://www.nwstc.noaa.gov/nwstrn/d.ntp/meteor/ifpspcu4.html)_