Record Highs Possible in Parts of the Northeast Through Tuesday; Western Heat Expands

Expansive high pressure in the upper atmosphere will focus on parts of the East and West this week, sending heat indices well into the triple digits from the Mid-Atlantic states into the South.

(MORE: Check the Forecast for the Next 10 Days)

Here's a look at what to expect through early this week.

Sweltering Days 

Eastern States

Washington D.C. and Philadelphia may see highs in the upper 90s to near 100 degrees through Tuesday. Highs in the middle 90s are expected in New York City Monday and Tuesday.

If Washington D.C. hits 100 degrees, it would be the first time that's happened there since July 2012.

(MORE: Heat is the Deadliest Kind of Weather)

Some daily record highs are likely to be either tied or broken Monday and Tuesday from the NYC Tri-State metro to Washington D.C.

Heat indices could be as high as 110 degrees early this week.

(MORE: What is the Heat Index?)

Central States

Relief from the extreme heat will arrive in parts of the Midwest and Great Lakes early this week, first as dewpoints tumble, then as temperatures finally slide near or below late-July averages by late this week. 

(MORE: Forecast Temperature Maps)

Western Heat Builds

West of the Rockies, a hot week is ahead as high pressure aloft over the Desert Southwest bulges northward into the northern Great Basin and Northwest.

Triple-digit heat is expected as far north as interior parts of eastern Washington and northern Idaho this week, including Boise and Salt Lake City, among other locations.

Parts of California's Central Valley, as well as southern Nevada and the low deserts of southern Arizona will likely top 110 degrees. 

Reports: 

Sunday's daily record highs included El Paso, Texas (106 degrees; tied), Zanesville, Ohio (97 degrees), Scranton/Wilkes-Barre, Pennsylvania (95 degrees, tied), and Binghamton, New York (90 degrees).

Except for the Pacific Northwest, all other states in the Lower 48 had at least one location reporting a temperature of 90 degrees or above on Friday afternoon.

The heat index at Memphis, Tennessee, reached 114 degrees on Friday afternoon while up in Sioux Falls, South Dakota it felt like 110 degrees.

Dallas reached 100 degrees on Friday for the first time this year, and then reached 100 degrees again on Saturday.

On Thursday, the heat index at Cedar Rapids, Iowa, topped out at an extremely dangerous 116 degrees.

Waco, Texas, recorded its first 100-degree day of the year on Wednesday. The average date for Waco's first 100-degree day is July 4, so this came over two weeks later than average. Dallas reached 100 degrees on Friday for the first time this year.

Incidentally, Salt Lake City's daily low temperature of 81 degrees on July 18 was the city's all-time hottest record low in records dating to 1874. It was also the hottest string of nights on record in the Utah capital city.

Heat Safety Tips

The hot conditions this week will be particularly dangerous for vulnerable groups such as the sick and the elderly. The National Weather Service offered useful heat safety tips that can be incorporated into a daily routine when extreme heat sets in.

• Job sites: Stay hydrated and take breaks in the shade as often as possible.
• Indoors: Check up on the elderly, sick and those without air conditioning.
• In vehicles: Never leave children or pets unattended – look before you lock.
• Outdoors: Limit strenuous activities and find shade. Drink plenty of water and avoid alcohol.

Atmospheric Heat Dome

So far this summer, there have been a couple of high-pressure ridges aloft (bulges in the jet stream) that have prevailed across the U.S. One ridge was positioned around the Western U.S., and the other was in the Southeast. The Western ridge has occasionally expanded a bit to the north and east, while the Southeast ridge has expanded north and west, but only for short periods of time.

A bridging of these ridges occurred late last week, resulting in one massive dome of high pressure. Beneath this dome, air sinks and warms, resulting in hot temperatures.

Under these conditions, thunderstorm activity has become sporadic, so many areas have been dry.

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