Sunday, 29 July 2018

A forecast of further heatwaves

Many "Stuck" Pattern Regimes Coming The Next Month
Nicholas Humphrey

25 July, 2018
It appears many places suffering major extremes will not catch a break in the month of August...although a couple places may swing the pendulum. 
I looked at long range models which consider longer averaged anomalies compared to climatology. They use an ensemble of different model conditions. From this, we can use these models to forecast the most likely areas which will have highest chances for above or below average precipitation and temperatures. It's not the same type of forecasting as for short range (within days) because it's impossible to reliably forecast specific temperatures and precipitation amounts weeks in advance (atmospheric fluid chaos and rapid growth in model errors prevent this). But the models used in the way described above can be instead used to estimate areas where anomalies may develop based on their tendencies and previous performance in forecasts.
Note, there is no way for me to say how extreme the anomalies I'm forecasting may be in the end. That is still a short-term weather prediction situation. However, given what we've seen thus far, any strong signals produced by the forecast pattern regimes can certainly lead to more opportunities for extreme events (short-lived or prolonged) as our climate continues to more abruptly shift to more extreme conditions. So stay tuned on that front!
So with that out of the way, let's look at some areas which are currently under the gun for these major summertime extremes we are witnessing, exacerbated by our planet's rapidly shifting climate.
Northern Europe appears likely to continue to deal with below average precipitation through the end of August. Especially Scandinavia and Northwest Russia. Areas to the south, particularly Greece and Southeast Europe will likely see above average precipitation. Because of the strong signal and given recent problems with fires, any heavy precipitation from thunderstorm activity in Greece would be capable of producing flooding in those areas. As for Northern Europe, these are not favorable conditions given the widespread drought, wildfires and crop failures ongoing.
(Ensemble total precipitation anomalies in Europe through August 23th). 
Temperatures will likely remain above to well above normal over much of Europe through the first third of August with below normal temps in southeast Europe. Toward the middle of the month, the heat anomalies should become more focused on western and central Europe with continued near or below average conditions near Greece. 
(5-Day ensemble mean temperature anomalies in the lower atmosphere through August 9th above and August 19th below. Note the pattern signal decreases with increasing lead time, but abnormal temperatures appeared favored in central and western Europe going into the middle of the month). 
North America
There is a strong signal for above or well-above average precipitation across portions of the US South, Mid-Atlantic, into southern New England. These areas have already received and continue to receive copious amounts of rain with flooding problems and that appears likely to continue into August. There is a possibility of above average precipitation over the High Plains into Arizona and New Mexico as monsoon season continues. The Climate Prediction Center does indicate some improvement in drought conditions is possible over that region. However, near normal rainfall on the Southern Plains and the Pacific Northwest is not enough given previous weeks to months of dryness and drought conditions may actually worsen in those areas over the next month into Autumn. 
Although not a particularly strong signal, there is some risk of above normal precipitation in Quebec with below normal precipitation in parts of western and northwestern Canada. Given the abnormal dryness in the West, this would mean increasing drought conditions possible.
(Ensemble total precipitation anomalies in North America through August 23th). 
(Seasonal Drought Outlook by the US Climate Prediction Center. Widespread drought likely over the Southern Plains and Midwest into parts of the South. Will continue over the Southwest US even with the improvement possible, with expansion over the Pacific Northwest). 
(North American Drought Monitor showing abnormally dry conditions over much of British Columbia extending into the Prairies as of June 30th). 
Overall Western North America and New England appear to be the most favorable areas for above normal temperatures going into much of August. Alaska will also likely see above to well-above average temperatures. Meanwhile, much of the center of North America (Canada and US) will likely see below average temperatures. As the month progresses, the focus of heat anomalies is expected to be more over the US Pacific Northwest/Southern BC, with continued favored heat over the Northeast US and eastern Canada. A signal for below normal temperatures is possible over the Desert Southwest as monsoon activity intensifies. 
(5-Day ensemble mean temperature anomalies in the lower atmosphere through July 31st above and August 19th below. Note the pattern signal decreases with increasing lead time, but abnormal temperatures appeared favored in the US Pacific Northwest and the Northeast as well as Quebec going into the middle of the month). 
It looks like the heat anomalies over much of Japan will decrease going into August, although there will be more persistent heat over Eastern China and the Korean Peninsula through the earlier days of August. Temperatures look to be much below normal over much of Siberia in response to the persistent extreme heat in Europe. Through the middle of month, some abnormal warmth may continue over northeast China. Also note, throughout the month Iran has a persistent signal for above normal temperatures. Drought and heat waves are ongoing there right now.
 (5-Day ensemble mean temperature anomalies in the lower atmosphere through August 4th above and August 19th below. Note the pattern signal decreases with increasing lead time, but abnormal temperatures appeared favored in the Iran and Northeast China going through the middle of the month). 
As for precipitation, a much below normal precipitation regime is likely over northeast China, much of mainland Japan and particularly over the Korean Peninsula where it has been hot and dry recently. The dryness appears to intensify through much of August. Significant negative anomalies are present over parts of India as well. Meanwhile, above average precipitation is likely over Southeast Asia and the Philippines, some of which is likely to be related to tropical cyclone activity. A growing El Nino regime developing in the Tropical Pacific favors a more active monsoon trough (where converging winds caused localized lift and widespread thunderstorm activity can develop low pressure areas and cyclones, if favorable). Vietnam has been dealing with extensive heavy rain and flooding. The pattern favorable for this looks to continue into next month.
 (Ensemble total precipitation anomalies in Asia through August 23th). 
4:50 pm CDT Tuesday: Edited to add the total precipitation anomaly map for Asia.
---Meteorologist Nick Humphrey 

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