# Presentation: 206666

## Drought Task Force and Climate Division Evaluations

- Klaus Wolter
- NOAA-CIRES Climate Diagnostics Center
- klaus.wolter@noaa.gov

**•****  *****Getting to know you***** - my interaction with the task force from 1999-2004 (attend and listen; ENSO; regional climate; experimental forecasts)**
**• **** *****Climate divisions***** play key role in climate monitoring and prediction, and they “suck” in the West**
**• **** *****New climate divisions***** - progress report and outlook**

**With Kudos to Russell Bigley and Jon Eischeid**

**Notes:**
Revise for title page - basically, this is about what I have been up to - outreach, task force, experimental forecasts and new climate divisions 
Include: drought monitor(based on divisions), risk maps (ENSO impacts in the West - coarse scales), also with divisions; problems that arise -
No SNOTEL in there, divisions are not representative in CO and other western states, and the users want “downscaled” info. Easy in 1997, but
More subtle in other events; show and explain the dot plot for 2002-3; show a few experimental forecasts (and verifications); show new divisions
- should I shoot for NER T&P? - step back: also show something on wettest/driest seasons? - total of 25 figures

## Western U.S. Drought from 1999-2002

**Notes:**
One of the original motivations for the drought monitor was the severe drought that developed in much of the western U.S. after the 97-98 El Nino. The severe fire seasons of 2000 and 2002 were preceded/accompanied by particularly dry and hot conditions.

## The ‘Big Picture’ should be plenty, right?

- Based on previous work (Wolter et al., JCL, 1999), we thought we just need to get
- ‘the word’ out. Turns out that most recipients of this type of information like to get
- it in higher spatial resolution than U.S. Climate Divisions, especially in the West,
- where spatial and orographic features are often finer than seen through this filter.
- Furthermore, they would like to get seasonal forecasts up to a year in advance, and
- higher skill than your average daily weather forecast (at 1km x 1km, if you please).

## ‘But what does it mean for us’?  The case of the ‘October Blizzard’ 1997 three weeks after our briefings

- Top 10 Snowstorms in Fort Collins, Boulder, and Denver (since 1950)
- Units are 1/10”; MEI >0.5/<-.5 for El Niño/La Niña conditions (+/- for smaller ∆)
- 	FCL			BOU			DEN
- 1.  278(_5-7my78_-)    *299(*_*24-26oc97*_*)*   238(24-25de82)
- 2.  221(_**20-22no79**_)   259(_29-31mr70_+)  *219(*_*24-25oc97*_*)*
- 3.  214(_29-31mr70_+)  241(8-10ap59+)   215(26-27no83-)
- 4.  214(3-5ap83)     240(_**20-21no79**_)   187(5-6mr83)
- 5.  208(_**2-3ap57**_+)    230(_5-6my78_-)    177(_**19-21no79**_)
- 6.  195(30mr-1ap88)  229(_**2-3ap57**_+)    173(_**2ap57**_+)
- 7.  187(1-3ja71)     215(23-25no92)   169(20-21mr52+)
- 8.  187(2-4no73)     210(17-19se71)   162(16-18no91)
- 9.  185(9-11ap53)    208(18-19mr98)   160(29se-1oc59-)
- 10. 180(9-11de85-)   201(30oc-1no72)  160(3-5oc69)
- Balance:     4 E, 2 L;                           5 E, 1 L ;                         **6 E**, **0 L** .
- #spring storms: 6 (APR: 4)       Spring: 5 (NOV: 3)          Spring: 3 (NOV: 3)
_**17-19mr03**_: >30”(>5”)*  “only” 22.5” (4.69”*)   31.8”* (DIA: 19”)

## Meanwhile, a reality check...

- A lot of the water supply in the South Platte basin was assumed to be ‘safe’, since there were trans-mountain diversions, and we never get a drought to hit on both sides of the continental divide, right?  Our initial work showed that the moisture totals were actually higher correlated than water managers thought, providing for less of a safety cushion than hoped for. By 2002, this insight was brought home through Mother Nature.

## What is the problem with CDs?

- How representative are climate divisions for the local/ regional climate (here: precip) they are supposed to portray? Turns out that they are particularly lousy in CO (WY, etc.). And that is just with reference to COOP data.  Incidentally, climate forecasts issued by CPC are trained on so-called ‘Mega-divisions’, which in turn are based on Climate Divisions.

**Notes:**
Get revised figures from Russ - maybe, WY as well as CO?

## What is the problem with CDs?

- For much of the West, the important climate variability resides over the mountains where seasonal snowpack provides for the bulk of the water supply of the region. SNOTEL sites are carefully placed adjacent to long-term snow courses, and are designed to monitor the snowpack. Yet, traditional climate divisions do NOT make use of this information! Therefore, it is not surprising that CD’s do a poor job in monitoring the precipitation falling on the mountains.

**Notes:**
Get revised figures from Russ - maybe, WY as well as CO?

## Seasonal Outlook for July-December ‘04

- Klaus Wolter
- NOAA-CIRES Climate Diagnostics Center
- klaus.wolter@noaa.gov
*http://www.cdc.noaa.gov/~kew/SWcasts/*

**•****  ****Recent climate anomalies & forecast verifications**
**•****  ****ENSO: Status and Prospects**
**• **** ****CPC forecasts for August-December 2004**
**• **** ****Experimental forecasts (JUL-DEC 2004)**
**• **** ****Executive Summary**

- Last presentation to Colorado Water Availability Task Force (July 27)
- + latest SWcasts update from last night

## Comparing forecasts against observations

- Late spring 2003 precipitation was predicted to be above normal for eastern CO, while continued drought was anticipated for the San Juans and southern AZ/NM. Again, it verified for us, as well as for the drought regions (worst mismatch again for northeastern NM).

## Comparing forecasts against observations

- Late fall 2003 precipitation was predicted to be below normal for most of the interior southwest, in particular for NM. The verification shifted the center of gravity of the dry signal into eastern CO, but the general dryness was confirmed for much of the domain.

## Current stateof ENSO compared to two months ago- El Niño is making a comeback?!

## ECMWF vs. NCEP coupled models: much more in sync than

- before, and both advertizing at least mild El Niño conditions

- Updated last night:

**Percentage of Significant Departures  During Moderate to Strong**
**El Ni****ñ****o: 18.0%**
**10 cases:**
**1957, 63, 65, 72, 82,  86, 87, 91, 94, 97**
**If the MEI were used, 1977 would replace 1963.**

## Soil Moisture Analog Forecasts

- For September, this tool predicts a **wet** month for most of CO.  For OCT-DEC, **wet** and **cool** conditions are forecast over much of the Southwest - consistent with El Niño?!

## Precipitation Forecasts (CPC)

- The official CPC forecast for September shows CO in between continued cool weather to the east and warmth to the west. Consistent with the ‘constructed analog’ forecast, above normal precipitation odds cover all of Colorado.
- Source (for CPC forecasts): *http://www.cpc.ncep.noaa.gov/products/forecasts/*

## Precipitation Forecasts (CPC)

- The official CPC forecast for October-December shows CO with climatological odds (“EC”) for temperatures and precipitation. The budding El Niño is not expected to be strong enough to give us any tilt of the odds away from normal.
- Source (for CPC forecasts): *http://www.cpc.ncep.noaa.gov/products/forecasts/*

## Experimental CDC Forecasts

- For OCT-DEC ‘04, one can find a slight nod towards a dry fall for UT and CO, compared to better chances for a wet fall in AZ.  For comparison, I also include last month’s “JAS” forecast which was ‘up in the air’ for CO, but decent for NM.
- Source: *http://www.cdc.noaa.gov/people/klaus.wolter/SWcasts/*

## Executive Summary (24 August 2004)

- The most recent El Niño event - declared over more than a year ago - tried to make a comeback in late '03, but lapsed back into near-neutral conditions by early '04. Over the last three months, the tropical Pacific has warmed yet again, and another El Niño event appears possible later this year. The odds for this to happen are better than last year.
- After a mixed spring (dry March, wet April, dry May), June continued our roller-coaster ride by dropping prodigious amounts of moisture from southeastern Colorado into parts of the Front Range, while leaving the western third of the state drier than normal. Interestingly, both July and August so far appear to have repeated June's rainfall pattern over Colorado, with above-normal rainfall along and east of the divide, and below-normal rainfall over far western Colorado in particular.  Compared to the last six summers,  this one has been much cooler,  especially over eastern Colorado.
- In my experimental forecasts for October through December 2004, Arizona appears to be the only state with a good shot at a wet fall season, while both southern Utah and northeastern Colorado run a slight risk of yet another dry fall season. I hope to augment these forecasts with targeted ENSO composites by next month's update. If a moderate El Niño event develops, it should improve the precipitation odds over Colorado and Utah.
- 4.	Bottomline: Recent warming in the central equatorial Pacific may allow for the return of El Niño later this year, even though its eventual strength is still uncertain. Meanwhile, tilts in the precipitation odds remain weak over much of Colorado for the foreseeable future. If El Niño were to gain in strength over the next few months,  Colorado may be able to extend its recent wet spell into the fall season.

## Gratuitous snow picture

- Speaking of records, the mid-March 2003 storm was easily one of the biggest three snowstorms of the last century in Colorado, rivaling or exceeding totals last seen in April 1921 (24h U.S. record at Silver Lake, Boulder County), and December 1913 (the ‘analog’ case in terms of the synoptic set-up?). Liquid totals reached 7-9” H2O at numerous COOP and SNOTEL sites along the Front Range, or 20-30% of the average annual precipitation at these locales.

## Creating new Climate Divisions based on statistical techniques

**Multivariate statistical approach:** cluster and RPC analyses
- Dividing the U.S. into **10 subdomains** - RPCA would not yield sufficient number of regions, if applied nationally
- In order to optimize usage of SNOTEL data, the analyses are first conducted for **WY 1979-2002**
- For comparison, we also analyze data for WY 1948-1978, so far for **precipitation** only.

## Base Map with 545 SNOTEL & 7037 COOP stations with usable precipitation records

- 	In order to be included, a station has to have at least 50% data in the 1978-2002 record, and be either ‘active’ into at least 2001, or ‘long-lasting’ (at least 50% of 1948-78). We are trying to merge duplicate stations (there may be up to 1000 stations that qualify). There are more precip than temp station records available (7582 vs. 5275). The period 1948-78 has 8125 valid precip stations.

## Two rotated principal component solutions for the PNW. The left one (RPC8.6) has fewer viable “cores” than the right one (RPC13.10).

## Average linkage clustering (left) often yields fewer clusters (here: 14) than Ward linkage clustering (right; here: 19). 

## Initial core “seeds” for PNW in 1978-2002 (left); final core map after a few iterations (right).

## Final core map for 1948-78 (left); “Hard core” map between 48-78 and 78-02 (right).

## What is gained/lost in giving up 45 climate divisions for 14 new ones?  Explained variance map for traditional (left) and new climate divisions (right) during 78-02.

## Difference map of expl.

- variances at the station
- level based on new vs. old
- Climate Divisions during
- 1978-2002 Water Years.
- Sizable improvements over
- interior mountains have to
- be balanced against worse
- results for certain interior
- basins. It can be shown that
- the “blue” regions are all
- particularly well resolved
- by traditional CD’s. We
- hope that the addition of
- temperature information, as
- well as subdividing the new
- divisions (<>) will help.

## Ditto for “Interior South-

- West” (ISW).
- Interesting improvements
- focus on statelines (in
- addition to SNOTEL),
- since our new divisions can
- straddle these, while the
- ones  cannot.

## Next steps

- Create true national map by optimizing transition zones between regions (similar to “hard cores”)
- Add temperature stations to the mix (how to deal with precip only?)
- Sensitivity to changing temporal resolution (pentads)
- In regions of high station density, as well as clear gradients in the station means, easy to add subdivisions for further differentiation
- Workshop in 2005?