SSTA's Cast Dominant Influence on Pattern Through Mid-July

[donsutherland1]

July 2004 has seen sea surface temperature anomalies cast a large shadow over regional temperature anomalies.

Coming into July, one saw an expansive pool of colder than normal water off eastern New England/Atlantic Canada, a warm pool off the Mid-Atlantic and Southeast coasts, a large warm pool off the Pacific Northwest, and a pool of warm water in the eastern Gulf of Mexico. Somewhat of a cool pool was embedded in an area of warmer than normal waters off the lower California/Baja California coast:

<img src="http://www5.wright-weather.com/bb/attachment.php?s=&postid=291125">

Through July 17, temperature anomalies as depicted by the NCEP/NCAR reanalysis have largely mirrored the SSTAs:

<img src="http://www5.wright-weather.com/bb/attachment.php?s=&postid=291114">

However, as noted in this morning's S2K forecast discussion, the pool of cool water off New England has been showing signs of diminishing. Consequently, this is a factor that could argue for Boston seeing a warmer August than July. However, as based on the discussion, odds are still against Boston's witnessing an exceptionally warm August (a mean temperature above 73°).

Statistics for that are as follows, in an August that precedes a July with a mean temperature of below 72°:

• August with a mean temperature of 74° or above: 1/46 or 2%
• August with a mean temperature of 73° or above: 4/46 or 9%
• August with a mean temperature of 72° or above: 6/46 or 13%

The overall mean temperature for such Augusts is 70.1°. With the pool of cool water shrinking off the New England coast, I believe one will likely see August finish in the upper half of such situations (probably with a mean temperature at or above 71.5°).

The same situation likely lies ahead for the provinces of Atlantic Canada: a warmer August but nothing extreme in terms of warmth.

Meanwhile, anomalously warm water remains expansive along the Pacific Northwest. Hence, it does appear that at least the first half of August should experience above normal readings there.

[ATS]

Don, very well written and informative post.

I can't argue with the methodology behind what you’re saying, however I believe through much of June and into the early part of this month, the Pacific signal has been slightly more dominant over the Atlantic Signal.

If we consider the 500 hPa height verifications from June of this year, there are three things which pop out at me.

1. The strong Blocking over Northwest Canada forced by the SSTA configuration over the North Pacific at a time when a Positive PNA pattern and the PNA signal as a whole is normally weakest. This is due to the seasonal changes in the Position and intensity of the Aleutian low.

2. Frequently negative NAO, and pronounced blocking over Greenland. You can see the Dipole of dissimilarly signed anomalies over the North Atlantic with the positive anomaly over Greenland and the negative Anomaly near Newfoundland (which extended back westward into South central Canada)--again a result of the SSTA configuration in the Atlantic and climatologically normal for the strong ATC cycle.

3. The Abnormal heat (for any time of the year) and Severe weather In Alaska.

Then, if we examine the Surface temperature verifications from the first 17 days of the month, we’re noticing the only area which has really above normal temperatures is western Canada, and portions of the Pacific Northwest (underneath the unusually strong ridge). The eastern United States was cooler than normal, which is again, an effect of the mean trough position.

If the cooler water off of New England begins to warm of shifts into the central Atlantic, you would be correct in assuming that a warmer month may be in the cards for the northeast in august, however the North pacific signal has not changed, and if anything is intensifying, which of course would argue for a continuation of the current pattern (western ridge eastern trough configuration in the means) however may not be as prevalent as it was when the Atlantic signal was in agreement with it.

[USAwx1]

Don, very well written and informative post.

I can't argue with the methodology behind what you’re saying, however I believe through much of June and into the early part of this month, the Pacific signal has been slightly more dominant over the Atlantic Signal.

If we consider the 500 hPa height verifications from June of this year, there are three things which pop out at me.

1. The strong Blocking over Northwest Canada forced by the SSTA configuration over the North Pacific at a time when a Positive PNA pattern and the PNA signal as a whole is normally weakest. This is due to the seasonal changes in the Position and intensity of the Aleutian low.

2. Frequently negative NAO, and pronounced blocking over Greenland. You can see the Dipole of dissimilarly signed anomalies over the North Atlantic with the positive anomaly over Greenland and the negative Anomaly near Newfoundland (which extended back westward into South central Canada)--again a result of the SSTA configuration in the Atlantic and climatologically normal for the strong ATC cycle.

3. The Abnormal heat (for any time of the year) and Severe weather In Alaska.

Then, if we examine the Surface temperature verifications from the first 17 days of the month, we’re noticing the only area which has really above normal temperatures is western Canada, and portions of the Pacific Northwest (underneath the unusually strong ridge). The eastern United States was cooler than normal, which is again, an effect of the mean trough position.

If the cooler water off of New England begins to warm of shifts into the central Atlantic, you would be correct in assuming that a warmer month may be in the cards for the northeast in august, however the North pacific signal has not changed, and if anything is intensifying, which of course would argue for a continuation of the current pattern (western ridge eastern trough configuration in the means) however may not be as prevalent as it was when the Atlantic signal was in agreement with it.

basically agree w/ you. only thing I dont think you noted is that the NINO 3.4 SSTA continue to increase. It's back up to +.4 again on the week and the 4.0 region is approaching +1.0 (around .8 to be more exact) and the SOI is becoming increasingly negative. A few good Kelvin waves could put us over the top. but even still you need 3 months w/ nino 3.4 anomalies >.5 for statistical El NINO conditions. BTW, WELCOME aboard, it's great see you here.

[donsutherland1]

ATS,

No major disagreements with you.

You're absolutely right about the height verifications.

I was also taking into consideration the occasions where the east wind crushed temperatures in eastern New England. BTW, as perhaps a reinforcing hint that the pool of anomalously cool water is shrinking (both in terms of anomalies and size) off eastern New England, yesterday saw the wind switch to east in Boston. The temperature merely rose a little further to 80° then gradually eased into the lower and middle 70s.

Earlier this month, the east wind consistently sent temperatures there diving into the middle and upper 60s.

August should prove to be an interesting month especially if there are conflicting Pacific and Atlantic signals. Certainly, through at least mid-August and perhaps beyond, I believe the Pacific Northwest (and also British Columbia) will feature generally warmer than normal temperatures given the continuing Pacific pattern.