Indications are the seemingly endless cool weather pattern from the Upper Midwest to the East will change toward the end of June, thanks in part to warm air coming from an unusual source: Alaska.
Temperatures have challenged record highs over portions of Alaska in recent days. The pattern producing that warmth over The Last Frontier will shift toward the southeast.
A river of strong winds high in the atmosphere, known as the jet stream, will push the warm air farther south and east over the Canada Prairies as the month progresses. As this happens, Alaska will trend cooler.
Toward the end of June, a zone of high pressure at most levels of the atmosphere will expand over the Central states, allowing temperatures to trend upward over much of the nation.
According to Paul Pastelok, head of the AccuWeather.com long range team of meteorologists, "Even though the jet stream will continue to dip into the Northeast U.S. during much of the time from late June to mid-July, the source region of the air coming in will no longer be chilly."
Toned-down warmth from Alaska will have moved over central Canada, then that will be filtered across the Great Lakes and into the Northeast.
Temperatures during the first part of June have averaged near-normal (+/- 2 degrees Fahrenheit) over much of the Central and Eastern states.
"We should see more areas have temperatures swing to the above side of normal during the period from late June into July, but some areas from the Ohio Valley to the South may continue to lag a bit due to rounds of showers and thunderstorms persisting."
Pastelok stated that this long-range team of meteorologists still did not expect a large number of locations east of the Mississippi River to have positive temperature departures of 3 degrees or more for the entire summer and the July pattern now on the horizon was figured in when the forecast was made in May.
When the ground is wet, some of the sun's energy goes to evaporating the moisture rather than heating the air and is expected to be a factor in a large part of the South, reaching into parts of the Ohio Valley and mid-Atlantic.
At least folks hoping for a greater number of warm days or warmer, sunnier days in general from the Mississippi Valley eastward to the Atlantic coast should be pleased.
Pastelok did caution that the pattern will still favor some complexes of thunderstorms running from the Upper Midwest into part of the Northeast and South, but with less of a temperature contrast, there should be lower numbers of the storms.
The air will heat up from near the Mississippi River, westward to the central and northern High Plains.
Problems with heat, drought and wildfires will continue over part of the West and will expand to new territory, as discussed in the Summer 2013 Forecast.
The Southwest Monsoon will come into Play during July in part of the region. While the moisture is needed, there is also the risk of new fires being started by dry thunderstorms initially.