June 10, 2024
Dr. Judah Cohen from Atmospheric and Environmental Research (AER) embarked on an experimental process of regular research, review, and analysis of the Arctic Oscillation (AO) and Polar Vortex (PV). This analysis is intended to provide researchers and practitioners real-time insights on one of North America’s and Europe’s leading drivers for extreme and persistent temperature patterns.
During the winter schedule the blog is updated once every week. Snow accumulation forecasts replace precipitation forecasts. Also, there is renewed emphasis on ice and snow boundary conditions and their influence on hemispheric weather. In late Spring, we transition to a spring/summer schedule, which is once every two weeks. Snow accumulation forecasts will be replaced by precipitation forecasts. Also, there will be less emphasis on ice and snow boundary conditions and their influence on hemispheric weather
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The AO/PV blog is partially supported by NSF grant AGS: 1657748.
Summary
- The Arctic Oscillation (AO) is currently neutral and is predicted to first turn positive this week and then flip negative next week as pressure/geopotential height anomalies across the Arctic are currently mostly mixed but then pressure/geopotential height anomalies across the Arctic turn more negative this week and more positive next week. The North Atlantic Oscillation (NAO) is currently mixed with weak pressure/geopotential height anomalies across Greenland and the NAO is predicted to trend mostly negative the next two weeks as pressure/geopotential height anomalies turn more positive across Greenland.
- Over the next two weeks general ridging/positive geopotential height anomalies across Greenland will support troughing/negative geopotential height anomalies across Western Europe with ridging/positive geopotential height anomalies across Eastern Europe. This pattern will support the next two weeks normal to below normal temperatures across Western Europe including the United Kingdom (UK) with normal to above normal temperatures across Eastern Europe.
- This week ridging/positive geopotential height anomalies across Eastern Europe will extend into Western Asia forcing troughing/negative geopotential height anomalies across Northeast Asia. However next week the pattern is predicted to flip with troughing/negative geopotential height anomalies across Western Asia with ridging/positive geopotential height anomalies across Eastern Asia. This pattern favors normal to above normal temperatures across Western and Southern Asia and much of Siberia with normal to below normal temperatures in Northeastern Asia this week. But next week, warm temperatures will become widespread across all of East Asia with normal to below normal temperatures across Western Russia and Kazakhstan.
- This week predicted ridging/positive geopotential height anomalies in the Beaufort Sea will support troughing/negative geopotential height anomalies Western Canada extending into the Eastern United States (US) with ridging/positive geopotential height anomalies across Northeastern Canada and the Western US. Then next week the Arctic ridging/positive geopotential height anomalies will retrograde towards Alaska and Eastern Siberia supporting troughing/negative geopotential height anomalies in Western Canada and the Western US with more ridging/positive geopotential height anomalies across Eastern Canada and the Eastern US. This pattern favors normal to above normal temperatures across Alaska, Eastern Canada and the Western US with normal to below normal temperatures across Western Canada and the Eastern US this week. Then next week below normal temperatures will become more widespread across Western Canada and the Western US with normal to above normal temperatures becoming more focused in Alaska, Eastern Canada and the Eastern US.
- In the Impacts section I discuss where we might expect heat domes across the Northern Hemisphere (NH).
Plain Language Summary
Heat is currently focused in western North America, Western Asia and parts of Central Asia with cooler temperatures in the Eastern US and much of Europe (see Figure i). However, next week heat is predicted to overspread the Eastern US and much of Europe (e.g., Figures 6 and 9). Right now, the heat domes/core of above normal temperatures seems to be shifting around and I am trying to figure out where the heat will settle for the longest period this summer.
Impacts
With global temperatures, but especially ocean temperatures still running at record high levels, hard to imagine that most places across the Northern Hemisphere will not be warmer than normal this summer. The challenge then becomes where will the heat domes setup, i.e., where above normal temperatures are amplified, and where are the few exceptions that might even average below normal for the summer mean temperature.
Currently we have heat domes centered across western North America, Western Asia and at least relative to normal some impressive above normal departures in Siberia (see Figure i). But those heat domes are predicted to be on the move setting up in the Eastern US and Eastern Europe (see Figure 5) next week and some exceptional heat is predicted in Central Asia as well (see Figure 6).
Figure i. Observed surface temperature anomalies (°C; shading) from 10 June 2024. The forecast is from the 00Z 10 June 2024 2024 GFS ensemble.
One important question is where will the heat domes settle for the longest period this summer? In recent summer the heat domes have been favored over western North America, Eastern Europe into Western Asia and parts of Eastern Asia including parts of Siberia and possibly one more along the US East Coast. But the pattern did differ last summer
One wild card are the positive polar cap geopotential height anomalies (PCHs) throughout the troposphere and stratosphere (see Figure 11), though the shading makes the anomalies looking more ominous than they really are. When the positive PCHs robustly reach the surface, high latitude blocking increases and the Eastern US and/or Europe are less vulnerable to heat domes. When the positive PCHs retreat away from the surface and low pressure dominates the high latitudes the Eastern US and/or Europe are more vulnerable to heat domes.
Seems that the models are arguing with each other or providing conflicting forecasts with the GFS favoring the heat dome drifting westward onca again across North America and remaining more confined to Eastern Europe/Western Asia consistent with the trend of recent summers. The Canadian model seems to disagree with the heat dome remaining more firmly entrenched in the Eastern US and Western Europe looking more susceptible to a heat dome of its own. And from what I can tell the ECMWF is more of a mixed bag.
Right now I am favoring the heat dome centered in the Western and Central US more so than the Eastern US and Eastern Europe more so than Western Europe but this isn’t much more than an educated guess. And I am certainly open to modfying my expectations based on the most recent data.
Near-Term
This week
The AO is predicted to be positive this week (Figure 1) with mostly negative geopotential height anomalies across the Arctic and with mixed geopotential height anomalies across the mid-latitudes of the NH (Figure 2). With predicted mixed mostly positive geopotential height anomalies across Greenland (Figure 2), the NAO is predicted to be neutral to negative this week.
Figure 1. The predicted daily-mean AO at 1000 hPa from the 00Z 10 June 2024 2024 GFS ensemble. Gray lines indicate the AO index from each individual ensemble member, with the ensemble-mean AO index given by the red line with squares.
This week, weak ridging/positive geopotential height anomalies across Greenland will support troughing/negative geopotential height anomalies across Northern and Western Europe with ridging/positive geopotential height anomalies across Western Asia (Figures 2). This pattern favors normal to below normal temperatures across Northern and Western Europe including the UK while southwesterly flow will support normal to above normal temperatures mostly confined to far Eastern Europe (Figure 3). This week ridging/positive geopotential height anomalies predicted in Asia will anchor troughing/negative geopotential height anomalies across Eastern Asia with more ridging/positive geopotential height anomalies across Southern Asia (Figure 2). This pattern favors normal to above normal temperatures across much of Asia with normal to below normal temperatures across parts of Northeastern Asia (Figure 3). 
Figure 2. Forecasted average 500 mb geopotential heights (dam; contours) and geopotential height anomalies (m; shading) across the Northern Hemisphere from 11 – 15 June 2024. The forecasts are from the 00z 10 June 2024 2024 GFS ensemble.
This week predicted ridging/positive geopotential height anomalies in the Beaufort Sea will support troughing/negative geopotential height anomalies in Western Canada and extending into the Eastern US with ridging/positive geopotential height anomalies across Northeastern Canada and the Western US (Figure 2). This pattern will favor normal to above normal temperatures across Alaska, Northern and Eastern Canada, New England and the Western US with normal to below normal temperatures across Western Canada and the Eastern US (Figure 3).
Figure 3. Forecasted surface temperature anomalies (°C; shading) from 11 – 15 June 2024. The forecast is from the 00Z 10 June 2024 2024 GFS ensemble.
Troughing will support above normal rainfall across the parts of Northern and Southeastern Europe, Spain, parts of Northeast Asia, the Tibetan Plateau and Southeast Asia with normal to below normal rainfall elsewhere across Eurasia this week (Figure 4). Troughing will support above normal rainfall across the Western Canada, the Canadian Plains, an area centered in the Texas Panhandle and Florida with normal to below normal rainfall across the remainder of North America this week (Figure 4).
Figure 4. Forecasted precipitation anomalies (mm/day; shading) from 11 – 15 June 2024. The forecast is from the 00Z 10 June 2024 2024 GFS ensemble.
Near-Mid Term
Next week
With geopotential height anomalies turning more postive across the Arctic and with mixed geopotential height anomalies across the mid-latitudes this period (Figure 5), the AO will likely be neutral to negative this period (Figure 1). With positive pressure/geopotential height anomalies across Greenland (Figure 5), the NAO will likely be negative this period.
Figure 5. Forecasted average 500 mb geopotential heights (dam; contours) and geopotential height anomalies (m; shading) across the Northern Hemisphere from 16 – 20 June 2024. The forecasts are from the 00z 10 June 2024 2024 GFS ensemble.
Increasing ridging/positive geopotential height anomalies across Greenland will support persistent troughing/negative geopotential height anomalies across Western Europe with ridging/positive geopotential height anomalies across Eastern Europe this period (Figure 5). This pattern will favor normal to below normal temperatures across Western Europe including the UK with normal to above temperatures across Central and Eastern Europe (Figures 6). Predicted ridging/positive across Eastern Europe and Western Asia will support troughing/negative geopotential height anomalies across Eastern Asia with more ridging/positive geopotential height anomalies across Southern Asia this period (Figure 5). This pattern favors normal to above normal temperatures widespread across Asia with normal to below normal temperatures mostly limited to Southeastern Siberia and parts of Northeastern Asia this period (Figure 6).
Figure 6. Forecasted surface temperature anomalies (°C; shading) from 16 – 20 June 2024. The forecasts are from the 00z 10 June 2024 2024 GFS ensemble.
Retrograding ridging/positive geopotential height anomalies across Alaska to Eastern Siberia will support troughing/negative geopotential height anomalies across Western Canada and the Western US with ridging/positive geopotential height anomalies across Eastern Canada and the Eastern US this period (Figure 5). This pattern favors normal to above normal temperatures across Alaska, Northern and Eastern Canada, the Southern Rockies and the Eastern US with normal to below normal temperatures across Western Canada and the Western US (Figure 6).
Figure 7. Forecasted precipitation anomalies (mm/day; shading) from 16 – 20 June 2024. The forecast is from the 00Z 10 June 2024 2024 GFS ensemble.
Troughing will support above normal rainfall across Western Europe, the Tibetan Plateau and widespread in East Asia with normal to below normal rainfall elsewhere across Eurasia this period (Figure 7). Troughing will support above normal rainfall across Central Canada, the US Northern Plains, the western Great Lakes and possibly along the Gulf of Mexico with normal to below normal rainfall across the rest of North America this period (Figure 7).
Mid Term
Week Two
With predicted mostly mixed geopotential height anomalies across the Arctic and mixed geopotential height anomalies across the mid-latitudes this period (Figure 8), the AO will likely be near neutral this period (Figure 1). With weak positive pressure/geopotential height anomalies across Greenland (Figure 8), the NAO will likely be neutral to negative this period.
Figure 8. Forecasted average 500 mb geopotential heights (dam; contours) and geopotential height anomalies (m; shading) across the Northern Hemisphere from 21 – 25 June 2024. The forecasts are from the 00z 10 June 2024 2024 GFS ensemble.
Ridging/positive geopotential height anomalies, albeit weak, across Greenland will continue to support weak troughing/negative geopotential height anomalies across Western Europe with ridging/positive geopotential height anomalies across Eastern Europe this period (Figure 8). This pattern should favor widespread normal to above normal temperatures across Europe including the UK this period with normal to below normal temperatures limited to France and the Iberian Peninsula (Figures 9). Ridging/positive geopotential height anomalies are predicted to continue retrograding into Eastern Europe and will support troughing/negative geopotential height anomalies near the Urals with more ridging/positive geopotential height anomalies across Southern and Eastern Asia this period (Figure 8). The predicted pattern favors widespread normal to above normal temperatures across much of Asia with normal to below normal temperatures mostly confined to Western Russia this period (Figure 9).
Figure 9. Forecasted surface temperature anomalies (°C; shading) from 21 – 25 June 2024. The forecasts are from the 00z 10 June 2024 2024 GFS ensemble.
Troughing/negative geopotential height anomalies now in the Gulf of Alaska will support ridging/positive geopotential height anomalies across Alaska, Western Canada and much of the US with downstream troughing/negative geopotential height anomalies across Eastern Canada this period (Figure 8). This pattern favors widespread normal to above normal temperatures across Alaska, Western and Northern Canada and the US with normal to below normal temperatures limited to pockets across Eastern Canada this period (Figure 9).
Figure 10. Forecasted precipitation anomalies (mm/day; shading) from 21 – 25 June 2024. The forecast is from the 00Z 10 June 2024 2024 GFS ensemble.
Troughing will support above normal rainfall across Central Europe, the Tibetan Plateau and widespread across East Asia with normal to below normal rainfall elsewhere across Eurasia this period (Figure 10). Troughing will support above normal rainfall for Western Canada the US Upper Midwest and possibly along the Gulf of Mexico with normal to below normal rainfall across the remainder of North America this period (Figure 10).
Longer Term
30–day
The latest plot of the polar cap geopotential height anomalies (PCHs) currently shows warm/positive PCHs through much of the stratosphere and troposphere with the exception of cold/negative PCHs in the upper stratosphere (Figure 11). Then for the next two weeks warm/positive PCHs will persist throughout most of the stratosphere and troposphere with the exception of cold/negative PCHs in the upper stratosphere and at times in the lower troposphere (Figure 11).
Figure 11. Observed and predicted daily polar cap height (i.e., area-averaged geopotential heights poleward of 60°N) standardized anomalies. The forecast is from the 00Z 10 June 2024 2024 GFS ensemble.
The predicted vacillating but always near normal PCHs near the surface this week (Figure 11) are consistent with the predicted near neutral surface AO the next two weeks (Figure 1). However, for a period next week, the warm/positive PCHs in the middle troposphere are predicted to descend to the surface forcing a brief period of a negative AO.
Figure 12. Forecasted average 500 mb geopotential heights (dam; contours) and geopotential height anomalies (m; shading) across the Northern Hemisphere for July 2024. The forecasts are from the 00Z 10 June 2024 2024 CFS.
I include in this week’s blog the monthly 500 hPa geopotential heights (Figure 12) and surface temperatures for July (Figure 13) from the Climate Forecast System (CFS; the plots represent yesterday’s four ensemble members). The forecast for the troposphere is ridging south of Iceland, Western and Southern Asia, the Aleutians, Western and Central Canada and the Central US with troughing in Western Europe, Central Asia, Eastern Siberia, the US West Coast, Eastern Canada and the Northeastern US (Figure 12). This pattern favors seasonable to relatively warm temperatures across Northern and Eastern Europe, much of Asia, Alaska, much of Canada, the Western US and New England with seasonable to relatively cool temperatures for Western Europe, Kazakhstan, Eastern Siberia and the Southeastern US (Figure 13).
Figure 13. Forecasted average surface temperature anomalies (°C; shading) across the Northern Hemisphere for July 2024. The forecasts are from the 00Z 10 June 2024 CFS.
SSTs/El Niño/Southern Oscillation
Equatorial Pacific sea surface temperatures (SSTs) anomalies are above normal, especially along the Equator, indicating El Niño conditions but it is weakening (Figure 14) and neutral conditions are expected through the summer. Observed SSTs across the NH remain well above normal especially in the central North Pacific (west of recent years), the western North Pacific, the eastern North Atlantic and offshore of eastern North America though below normal SSTs exist regionally especially in the South and North Pacific and the North Atlantic.
Figure 14. The latest daily-mean global SST anomalies (ending 9 June 2024). Plot taken from https://psl.noaa.gov/map/clim/sst.shtml
Madden Julian Oscillation
Currently the Madden Julian Oscillation (MJO) is iweak where no phase is favored (Figure 15). The forecasts are for the MJO to remain weak for teh next two weeks and therefore the MJO seems to be having little influence on the weather across North America weather next week. But admittedly this is outside of my expertise.
Figure 15. Past and forecast values of the MJO index. Forecast values from the 00Z 10 June 2024 ECMWF model. Yellow lines indicate individual ensemble-member forecasts, with the green line showing the ensemble-mean. A measure of the model “spread” is denoted by the gray shading. Sector numbers indicate the phase of the MJO, with geographical labels indicating where anomalous convection occurs during that phase. Image source: https://www.cpc.ncep.noaa.gov/products/precip/CWlink/MJO/CLIVAR/clivar_wh.shtml
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