13.02.2013 Views

Download the entire proceedings as an Adobe PDF - Eastern Snow ...

Download the entire proceedings as an Adobe PDF - Eastern Snow ...

Download the entire proceedings as an Adobe PDF - Eastern Snow ...

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

Figure 2. Linear correlations between winter (DJF) (green line) <strong>an</strong>d April–May (blue line) snowfall<br />

<strong>an</strong>omalies <strong>an</strong>d summer moisture <strong>an</strong>omalies (Z-index) calculated for all 15 yr time periods between 1929 <strong>an</strong>d<br />

1999. D<strong>as</strong>hed lines indicate <strong>the</strong> 95% signific<strong>an</strong>ce level.<br />

The relationship between April–May snowfall <strong>an</strong>d summer moisture <strong>an</strong>omalies is fur<strong>the</strong>r<br />

streng<strong>the</strong>ned if <strong>the</strong> c<strong>an</strong>didate years are restricted to those occurring during <strong>the</strong> two periods (1929–<br />

1954 <strong>an</strong>d 1970–1987) when l<strong>an</strong>d surface conditions appear to be <strong>the</strong> domin<strong>an</strong>t source of se<strong>as</strong>onal<br />

climate predictability. During <strong>the</strong>se two periods <strong>the</strong>re were 8 yrs with April–May snowfall<br />

<strong>an</strong>omalies that were more th<strong>an</strong> one st<strong>an</strong>dard deviation below <strong>the</strong> me<strong>an</strong>. Seven of <strong>the</strong>se 8 yrs were<br />

<strong>as</strong>sociated with drier th<strong>an</strong> normal moisture conditions during <strong>the</strong> summer (me<strong>an</strong> Z-index = –0.73).<br />

There were also 8 yrs with April–May snowfall <strong>an</strong>omalies that were more th<strong>an</strong> one st<strong>an</strong>dard<br />

deviation above <strong>the</strong> me<strong>an</strong>. Seven of <strong>the</strong> 8 yrs with large positive April–May snowfall <strong>an</strong>omalies<br />

were followed by wetter th<strong>an</strong> normal moisture conditions during <strong>the</strong> summer (me<strong>an</strong> Z-index =<br />

0.63). B<strong>as</strong>ed on <strong>the</strong>se 16 yrs <strong>the</strong> linear correlation between April–May snowfall <strong>an</strong>d summer<br />

moisture is 0.70 (statistically signific<strong>an</strong>t at <strong>the</strong> 95% confidence level).<br />

Signific<strong>an</strong>t spatial variability is also evident in <strong>the</strong> relationship between April–May snowfall<br />

<strong>an</strong>d summer moisture <strong>an</strong>omalies (Figure 3). Linear correlations across <strong>the</strong> study region are<br />

generally positive with <strong>the</strong> highest correlations (up to 0.63) in sou<strong>the</strong>rn M<strong>an</strong>itoba <strong>an</strong>d South<br />

Dakota. There is only one grid cell in Wyoming where <strong>the</strong>re is a statistically signific<strong>an</strong>t negative<br />

correlation (–0.23). Statistically signific<strong>an</strong>t correlations between April–May snowfall <strong>an</strong>d summer<br />

moisture <strong>an</strong>omalies are found in approximately 56% of <strong>the</strong> study area. These grid cells tend to be<br />

concentrated on <strong>the</strong> e<strong>as</strong>tern side of <strong>the</strong> study region <strong>an</strong>d are notably absent from most of<br />

Wyoming, <strong>the</strong> e<strong>as</strong>tern part of Mont<strong>an</strong>a, <strong>an</strong>d sou<strong>the</strong>rn S<strong>as</strong>katchew<strong>an</strong>.<br />

68

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!