So what is a "Polar Vortex" and how can it happen in July?
Briefly, the "Polar Vortex" is nothing more than the cooler Canadian air mass (in the Northern hemisphere) that generally resides around the top (North) of our planet. It generally sits up there nicely and is responsible for the much colder temperatures that our neighbors to the North usually experience. Here is a bit more detail on the trendy Polar Vortex we all have come to dread this past winter (See below for the current Polar Vortex forecast):
"‘Polar vortex’ is the new buzzword of 2014 for the millions of Americans learning about its role in producing record cold temperatures across the country. Meteorologists have known for years that the pattern of the polar vortex determines how much cold air escapes from the Arctic and makes its way to the U.S. during the winter. Now climate scientists want to know if a warmer Arctic is influencing its behavior.
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| Maps show the 500-millibar geopotential height (the altitude where the air pressure is 500 millibars) on January 5, 2014 (left), and in mid-November 2013 (right). The cold air of the polar vortex is purple. Maps by NOAA Climate.gov, based on NCEP Reanalysis data from NOAA ESRL Physical Sciences Division. |
The polar vortex is a high altitude low-pressure system that hovers over the Arctic in winter. When the polar vortex is strong, it acts like a spinning bowl balanced on the top of the North Pole. The image on the right shows a strong phase of the polar vortex in mid-November 2013. Dark purple depicts the most frigid air tightly contained in an oval-shaped formation inside the invisible bowl. The light purple line forming the outermost boundary of the cold Arctic air is the jet stream in its normal west-to-east pattern.
In early January, the polar vortex weakened and broke down, allowing fragments of cold air to slosh out of the bowl into mid-latitudes. The image on the left shows the weakened vortex formation on January 5, 2014. The high pressure building up in the Arctic slowed down the jet stream, which caused it to buckle into deep folds and flow farther south than usual, introducing cold Arctic air into the central and eastern U.S.
In recent years, climate scientists have noticed that the jet stream has taken on a more wavy shape instead of the more typical oval around the North Pole, leading to outbreaks of colder weather down in the mid-latitudes and milder temperatures in the Arctic, a so-called “warm Arctic-cold continents” pattern. Whether this is normal randomness or related to the significant climate changes occurring in the Arctic is not entirely clear, especially when considering individual events. But less sea ice and snow cover in the Arctic and relatively warmer Arctic air temperatures at the end of autumn suggest a more wavy jet stream pattern and more variability between the straight and wavy pattern.
Understanding the connections between the Arctic warming trend and more severe weather in the mid-latitudes remains an active area of research. But even as Earth’s average temperature rises, natural patterns of climate variability are expected to still operate in a warmer world. There have been many other cases of natural climate oscillations influencing our winter weather in recent years. The unusually cold winter of 2009-2010 proved that record-breaking snowstorms can still coexist with global warming, as did the frigid start to 2011, which resulted in another wintry winterfor the eastern United States."
JULY 2014 "POLAR VORTEX" FORECAST:
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| MUCH COLDER THAN NORMAL TEMPERATURES EXPECTED OVER THE CENTRAL US DUE TO SAGGING COLD AIR FROM CANADA ... JULY 11th - JULY 20th 2014 |
Synopsis: A strong cold front is expected to move from the Great Lakes to the East Coast at the beginning of this period. Behind the front, cool high pressure is forecast to bring below normal temperatures to most of the eastern half of the Lower 48. In the Intermountain West, high pressure is forecast to prevail, favoring warmer temperatures.
Hazards
Hazards
- Much above-normal temperatures for parts of the Great Basin and Northern Intermountain West, Mon-Fri, Jul 14-18.
- High winds for northwest Alaska, Tue-Wed, Jul 15-16.
- Heavy rain for northwest Alaska, Wed, Jul 16.
- High winds for the Aleutians and southwestern coast of Alaska, Wed-Thu, Jul 16-17.
- Severe weather for parts of the Mississippi and Ohio Valleys and the Mid-Atlantic, Mon, Jul 14.
- Heavy rain for parts of the southern Rockies, Ohio and Tennessee Valleys and the Northeast, Mon-Tue, Jul 14-15.
- Heavy rain for coastal portions of the Carolinas and southern Plains, Wed-Thu, Jul 16-17.
- Flooding occurring or imminent for parts of North Dakota and the Middle Mississippi Valley.
- Severe drought for parts of the Great Plains, Southwest, Pacific Northwest, Great Basin, and California.
Detailed Summary
For Monday July 14 - Friday July 18: The first part of this forecast period is expected to feature an amplified upper-level trough across the Great Lakes region. As this trough amplifies, a surface cold front is predicted to move from the Upper Midwest to the Southeast. As it makes its way towards the East Coast, warm, moist air in advance of the front coupled with an upper-level jet streak is expected to set the stage for a severe weather outbreak from eastern Pennsylvania to northeast Arkansas. However, based upon where the greatest amounts of atmospheric moisture are expected to be, the greatest chances for heavy rain include the Tennessee Valley and New England on Monday and Tuesday, the 14th and 15th. Because the cold front is forecast to linger along the coastal Carolina region, this part of the country is expected to receive heavy rain from Monday the 14th through Thursday the 17th.
The cold front is forecast to stretch from the East Coast back to the Rockies as high pressure is expected to be situated over the northern and central Plains. The combination of upslope flow and the focus of precipitation associated with the front, heavy rain is anticipated for parts of the southern Rockies. With rainfall totals of more than 2 inches predicted over high terrain, localized flash flooding is possible as well.
In addition, an upper-level ridge is forecast to amplify in the western states, favoring much above normal temperatures in parts of the Pacific and Intermountain West, with daily maximum temperatures 12 to 20 degrees above normal possible throughout this entire forecast period.
An upper-level shortwave currently in the eastern Pacific is forecast to rotate around the western ridge axis and move into the southern Plains. The divergence associated with this shortwave, combined with northwest flow, makes conditions favorable for the formation of a mesoscale convective system. Thus, a heavy rain hazard is indicated on the map for parts of Oklahoma and Texas on the 16th and 17th, with severe weather also possible.
In Alaska, a large closed upper-level low slowly rotating near the Aleutians is expected to be the impetus for unsettled weather. Towards the end of this period, the low is forecast to open up and move into the state. The associated surface low is predicted to move parallel to the Aleutians and bring high winds of 30-40 knots to the islands as well as the southwestern coast. In addition, a separate upper-level shortwave is forecast to move east from northern Russia. It is expected to bring high winds of at least 30 knots to the North Slope from the 15th to the 16th. Heavy rain is also possible with totals of 1 inch or more on the 16th. Because this part of the state is very dry this time of year, significant impacts from this storm could occur. Some models are forecasting that the shortwave impacting the North Slope will phase with the large low south of the Aleutians. If this were to happen, it would increase the chances of high winds and heavy rain for the entire western coast, Aleutians and southern coast.
Flooding in the mid-Mississippi Valley and North Dakota is predicted to continue during this forecast period, as water from recent rainfalls of 3-8 inches (and up to 19 inches during the month of June) continues to flow into the large rivers.
For Monday July 14 - Friday July 18: The first part of this forecast period is expected to feature an amplified upper-level trough across the Great Lakes region. As this trough amplifies, a surface cold front is predicted to move from the Upper Midwest to the Southeast. As it makes its way towards the East Coast, warm, moist air in advance of the front coupled with an upper-level jet streak is expected to set the stage for a severe weather outbreak from eastern Pennsylvania to northeast Arkansas. However, based upon where the greatest amounts of atmospheric moisture are expected to be, the greatest chances for heavy rain include the Tennessee Valley and New England on Monday and Tuesday, the 14th and 15th. Because the cold front is forecast to linger along the coastal Carolina region, this part of the country is expected to receive heavy rain from Monday the 14th through Thursday the 17th.
The cold front is forecast to stretch from the East Coast back to the Rockies as high pressure is expected to be situated over the northern and central Plains. The combination of upslope flow and the focus of precipitation associated with the front, heavy rain is anticipated for parts of the southern Rockies. With rainfall totals of more than 2 inches predicted over high terrain, localized flash flooding is possible as well.
In addition, an upper-level ridge is forecast to amplify in the western states, favoring much above normal temperatures in parts of the Pacific and Intermountain West, with daily maximum temperatures 12 to 20 degrees above normal possible throughout this entire forecast period.
An upper-level shortwave currently in the eastern Pacific is forecast to rotate around the western ridge axis and move into the southern Plains. The divergence associated with this shortwave, combined with northwest flow, makes conditions favorable for the formation of a mesoscale convective system. Thus, a heavy rain hazard is indicated on the map for parts of Oklahoma and Texas on the 16th and 17th, with severe weather also possible.
In Alaska, a large closed upper-level low slowly rotating near the Aleutians is expected to be the impetus for unsettled weather. Towards the end of this period, the low is forecast to open up and move into the state. The associated surface low is predicted to move parallel to the Aleutians and bring high winds of 30-40 knots to the islands as well as the southwestern coast. In addition, a separate upper-level shortwave is forecast to move east from northern Russia. It is expected to bring high winds of at least 30 knots to the North Slope from the 15th to the 16th. Heavy rain is also possible with totals of 1 inch or more on the 16th. Because this part of the state is very dry this time of year, significant impacts from this storm could occur. Some models are forecasting that the shortwave impacting the North Slope will phase with the large low south of the Aleutians. If this were to happen, it would increase the chances of high winds and heavy rain for the entire western coast, Aleutians and southern coast.
Flooding in the mid-Mississippi Valley and North Dakota is predicted to continue during this forecast period, as water from recent rainfalls of 3-8 inches (and up to 19 inches during the month of June) continues to flow into the large rivers.
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