# Presentation: 725852

##    A Study of North American Stormtracks:

**     ****Climatology, Interannual Variability &  **
**       ****Trends**

**Tim Eichler, Wayne Higgins, and Gerry Bell**
**Climate Prediction Center/NCEP**
**22nd Oct 2003**

## Question:  Why Study Storms?

**Answer:  It’s all about the:**

## Impacts!

**Impacts!**

**Ocean Damage**

**Blizzards**

- Severe Weather

- Wind

**Floods**

## 1)  Where do we start?

-     **Storm track program run at CDC**
**    ****Tracks storms on a 6-hour timescale**
**    ****Data includes lat/lon, SLP, and a unique tag**
**      **

**1)  Where do we start?**

##          2)  How Does it work?

-      **Interpolate SLP data onto a (lat,lon)=(250 KM,250 KM) grid.  **
**     ****Find SLP minima (> 1 mb below surrounding gridpoints).**
**     ****Assume a maximum distance threshold of 800 km to track storms.   **

## Storm Tracks for Jan.-Mar. 1983

## Storm Track Frequency Climatology

- C

- D

- A

- B

** ****Bin  stormtrack frequencies  into (lat,lon)=(5°x 5°) gridboxes **
** ****Average over 1950-2001 for each season**

**Notes:**
To filter out “false positives” from artificial storms generated by topography or thermal lows, only those storms that were able to move at least 5 degrees longitude in an eastward direction were counted.  Special care was also taken to insure that if a storm appeared more than one time in a gridbox, that it was only counted once.

## Climatology of Extreme Storms 

- D

- B

- A

- B

**Average lowest 2 standard deviations of SLP for storms  from (A)     Winter through (D) Summer**

- A

- C

## El Nino Ranking Used in Composite Analysis

-    1     2.1   1983   2     2.1   1998   3     1.7   1992   4     1.5   1958

-    5     1.2   1966   6     1.2   1973   7     1.1   1987   8     1.0   1969   9     0.9   1995

-   10     0.6   1977  11     0.5   1952  12     0.5   1993  13     0.5   1964  14     0.5   1988

-   15     0.4   1959  16     0.4   1991  17     0.4   1980  18     0.4   1970  19     0.4   1978  20     0.3   1953  21     0.2   1990  22     0.2   1994  23     0.2   1954  24     0.1   1982  25     0.1   1979  26    -0.1   2002  27    -0.2   1960  28    -0.2   1961  29    -0.3   1997  30    -0.3   1984  31    -0.3   1957  32    -0.3   1965  33    -0.4   1981  34    -0.4   1972  35    -0.4   1963  36    -0.4   1962

-   37    -0.5   1986  38    -0.5   1967  39    -0.6   2001  40    -0.6   1975

-   41    -0.7   1996  42    -0.7   1951  43    -0.8   1955  44    -0.8   1968  45    -0.8   1956  46    -0.8   1985

-   47    -1.2   1999  48    -1.3   1976  49    -1.4   2000  50    -1.4   1971  51    -1.5   1989  52    -1.6   1974  53    -1.7   1950

- RANK   NINO3.4   YEAR

- RANK    NINO3.4  YEAR

- RANK     NINO3.4   YEAR

***Strong El Nino***

***Moderate El Nino***

***Weak El Nino***

***Neutral ***

***Weak La Nina***

***Moderate La Nina***

***Strong La Nina***

##          Composites by ENSO Phase 

- Neutral

- El Nino

- La Nina

## Composite Stormtrack Frequency Anomaly for Strong El Nino and La Nina 

- Composite Stormtrack Frequency Anomaly for Strong El Nino and La Nina

## Storm Track Trends

-   **Generate regression lines from frequency and SLP timeseries for each gridbox (1950-2001)    **
**   ****Examine differences at each end of regression line.  **

## A

- B

- Stormtrack Frequency Trend for JFM (A)  and t-test for trend significance (B)   (Values >2 denote 95% Significance)

## Stormtracks and Precipitation

-           **Apply a 9x9 mesh centered on storm location **
**       ****Composite precipitation (1x1) for all boxes within 4° of storm **
**       ****Composite for ENSO phase**
**       ****Compare with composite of precipitation without regards to storms**

- QUESTION:  What percentage of precipitation is associated with storms?

## El Nino

- La Nina

- Neutral

- Precipitation Anomaly Due to Storms as a Function of ENSO for JFM

## El Nino

- La Nina

- Neutral

- Cumulative Precipitation Due to Storms as a Function of ENSO for JFM

## El Nino

- La Nina

- Neutral

- Cumulative Precipitation as a Function of ENSO for JFM

## Percent Precipitation Due to Storms by ENSO Phase

- El Nino

- La Nina

- Neutral

## CURRENT APPLICATION

- Assessment of U.S. Climate During April-June 2003
-     One of coldest wettest April-June periods on record
-      Featured North Atlantic blocking
-      Outstanding for its persistence

## Slide 20

## Mean 700 mb Heights and Anomalies for April-June 2003

## Slide 22

##  Composite 700-hPa heights for 

** ****(a) days with rainfall >6 mm day****-1**** in gridbox (****77.5W-80W, 35N-40N)**** **
** ****(b) days with rainfall < 1mm day ****–1 ****in gridbox (****77.5W-80W, 35N-40N)**** **

- QUESTION:    What does the circulation look like during significant rain events
- 	         (> 6 mm/day)?

## 700 mb heights (contour) and anomalies (shaded) composited (A) for days in which rainfall exceeded 6 mm/day (meters) and (B) for days in which rainfall was less than 1 mm/day

- A

- B

## SST Anomalies for April-June 2003

## April-June 1000 hPa Temperature Anomalies (shaded) and 1000 hPa wind (vector) for (A) days in which precip exceeded 6 mm/day and (B) days in which precip was less than 1 mm/day

- A

- B

- B

##     Split Flow over midwest

-     Confluence over Northern New England
-     Blocking from Canada to Europe
-     Cool easterly flow in the Mid-Atlantic

- BUT:  Storm tracks only IMPLIED from 700 mb circulation

- Wet Days Characterized by:

## Storm tracks for April-June 2003 (the real deal)

## Storm Track Frequency Anomaly April-June 2003 (relative to April-June 2003 climatology)

## Conclusions

** ****A reasonable climatology of stormtracks/intensity with appropriate seasonal shifts was presented**
** ****Storm trends suggest El Niño/NAO trends**
** ****Storms contribute to the water budget the most in the eastern U.S. during El Niño**
** ****Storms contribute least to the water budget on the West Coast especially noticeable in El Nino (possibly due to subtropical jet disturbances and/or fronts being the major contributors...  More analysis needed here)**
-  **Real-Time Applications show that a coastal stormtrack contributed to cool, wet Spring 2003 along the U.S. East Coast**

## Future Work

** ****Create web site for stormtracks**
** ****Use to monitor and assess storminess**
-  **Use storm tracks program to create prognostic stormtracks...  Potential new forecast tool...**

## Slide 32