Pattern shift will bring potential record heat to the West, cool and wet conditions in the East

A Scorching Hot Week in the West

By Linda Lam, The Weather Channel

A shift in the weather pattern is ongoing for much of the country as June begins.

This shift is bringing temperature changes for many, as well as an increase of showers and thunderstorms across portions of the South and East.

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An upper-level trough, or southward dip in the jet stream, that has been in place over the West is slowly sliding eastward and being replaced by an upper-level ridge of high pressure.

Very warm temperatures will continue to build across the West as the week progresses, just in time for the start of meteorological summer (June 1 - August 31).

Meanwhile, cooler conditions will be found across parts of the East, although for most locations highs will be close to average for this time of year.

In fact, this temperature setup is very similar to what is expected for this June. The June forecast by The Weather Company, an IBM Business, calls for above-average temperatures in the West, colder-than-average conditions for portions of the Central U.S. and near to slightly above-average temperatures in the East.

In addition to the temperature changes, there will be an increase of showers and thunderstorms, especially for the Southern Plains where more rain is not needed, especially after the flooding that took place in Texas last week.

Western Heat

Temperatures across much of the West were near to below-average last week. However, a warming trend already underway as the strong ridge of high pressure continues to build into the region.

The above-average temperatures will continue expanding across the West through the week and into the weekend. It will also be dry across the region through the week, with the exception of northwestern Washington which may see a few showers return Wednesday night into Thursday.

This Week's Forecast

High temperatures Wednesday and Thursday will be up to 20 degrees above average for the Pacific Northwest and into central California.

(MAPS: 10-Day Forecast)

By Friday and Saturday, there will be a widespread area of above-average high temperatures, with highs up to 30 degrees warmer than average in the Pacific Northwest.

Saturday's Forecast Highs Compared To Average

This translates into many locations seeing highs top out in the 80s and 90s. Triple-digit heat will also become more common by Friday and into the weekend.

Portions of southeastern California and southwestern Arizona are under excessive heat watches for Friday morning through Sunday evening, as highs near 110 degrees are likely. Phoenix usually sees their first 110 degree day in mid-June. In fact, some places, including Phoenix, are already under excessive heat warnings for Friday morning through Sunday evening.

Las Vegas has not reached the 100 degree mark yet this year, but is expected to this week. Their first 100 degree day usually occurs around May 24, so this year they are running a little behind.

Record highs are also a possibility late this week including (current record is in parenthesis):

  • On Friday: Phoenix (110 degrees); Tucson (108 degrees); Las Vegas (107 degrees); Fresno, California (106 degrees); Salt Lake City (94 degrees).
  • On Saturday: Phoenix (112 degrees); Las Vegas (107 degrees); Medford, Oregon (100 degrees); Boise, Idaho (98 degrees); Reno, Nevada (95 degrees); Eugene, Oregon (93 degrees); Portland, Oregon (91 degrees).

​Low temperatures will be warmer than average for early June, as well. Widespread lows in the 50s and 60s are expected, with 70s and 80s in portions of California and the Desert Southwest.

If you are looking to escape the heat, areas along the immediate West coast will be cooler, with highs generally in the 60s and 70s.

Cooler and Wet East

While the West will experience hot and dry days ahead, the East will see cooler temperatures and wet conditions.

Record heat was experienced in the Northeast on Saturday and warmer than average temperatures will persist for much of the Midwest and Northeast into midweek. Most locations east of the Mississippi River will see highs near to above-average through at least Wednesday.

Then, late this week a cold front will push eastward through the Midwest and into the mid-Atlantic and Northeast. Cooler temperatures are expected behind this system, although many areas will see temperatures return to near average for early June.

Areas from the Midwest into the Ohio Valley and Northeast will see temperatures drop 10 to 15 degrees by the end of the week. Boston will get stuck in the low 60s by Thursday while Chicago sees highs only in the mid 70s.

Late Week Forecast

The cold front will also be accompanied by showers and thunderstorms, although severe thunderstorms are not expected to be widespread.

(MORE: Heavy Rain Threat in Southern Plains)

Heavy rain, however, is a concern mid to late week in Texas and southern Oklahoma, where flooding is a threat. Much of central and eastern Texas will see rainfall totals through Saturday of 3 to 5 inches and this is an area that does not need additional rainfall after recent flood events.

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