Another week of a similar jet stream pattern as this past week is in store for the contiguous US as a large ridge of high pressure remains dominate across the West while an unusually deep trough of low pressure builds back into the eastern US by midweek. The pattern will then change by next week as the ridge drifts toward the east, bringing heat to most of the country for the first weekend of August.
A persistent 594-plus decameter ridge will remain situated over the southwestern US through at least the duration of this week, keeping the heat around to much of the western US. High temperatures will generally be 5 to 10 degrees above average across the region, although as much as 25 degrees higher than normal in the Northwest through Tuesday ahead of an incoming trough by midweek.
The hottest day overall out West will be on Monday when high temperatures will top off into the 90s and 100s across many locales. Many of the valleys will likely surpass the century mark through at least the next seven days.
According to the National Weather Service office at Hanford, CA, “[Saturday] was the 37th day this year of 100-degree heat in [Fresno]. That’s one day more than a normal year and more than any other [year] during the past 22 [years] of record keeping through July 28th. 2017 ended up with 53 days of triple digit heat in [Fresno].” Fresno is forecast to hold above 100 degrees through at least the next 7 days thanks to the persistent heat dome.
In Seattle, the city broke their record streak of 85 degree-plus days. Reaching 7 days on Saturday, that breaks the previous record of 6 days from the year of 2015. Seattle is forecast to remain above this threshold until Tuesday or Wednesday when temperatures will return closer to normal and eventually below average into the 70s.
For 4 straight days (Tuesday through Friday), Death Valley in California has recorded a remarkable high temperature of at least 127 degrees. That is the 3rd longest streak of temperatures at that magnitude on record. The longest was 8 days in the year of 1913. High temperatures will hover between 110 and 115 degrees in the foreseeable future in the hottest place of the US.
127 degrees F again in Furnace Creek today! This is the thermometer the park rangers use to record the weather each day, in addition to the digital system by @NWSVegas #hottest pic.twitter.com/7jBRDTEAMm
— Death Valley NP (@DeathValleyNPS) July 28, 2018
This heat is dangerous, and with the dry and windy weather fueling the dozens of large wildfires in the West, that is making conditions even more hazardous for the firefighters to battle. Almost all of the West Coast and Southwest is currently experiencing at least abnormally dry conditions.
Cool Eastern Two-Thirds:
The nation’s midsection is in for a cool week overall, but that may not be so bad given the fact it’s the middle of the summer — often the hottest time of the year. With temperatures forecast to be below average, it will definitely feel cool out there but it sure won’t be chilly compared to the below normal conditions in the wintertime.
An incoming trough from the northern Plains will tilt from a negative phase (oriented from southwest to northeast) to the neutral phase (oriented from south to north) by midweek, aiding in this cool down. It will also make for a favorable setup mid- to late- week for additional rounds of heavy, flooding rains to much of the East Coast. Oftentimes it’s the jet stream that delineates the below and above average temperatures. South of the strong winds at about 30-thousand feet is the warmth while north of it is the cooler air.
On Sunday, the coolest of air relative to average will be found in the central Plains behind a cold front. Temperatures in this part of the country will be as much as 20 degrees below average, translating to highs mainly into the 70s. That cooler air will extend all the way to most of the East Coast with the exception of eastern New England. Temperatures will generally be just a few degrees off from average, however, making for actual highs into the 70s and 80s. South of the front is where the warm air will be locked in with high temperatures in the 90s across the Southeast and 100s in the southern Plains.
By Monday, that cooler air will reach northern Texas and into most of the Southeast, dropping temperatures to as much as 20 degrees in the Texas and Oklahoma Panhandles. The cool spots will remain the central Plains with highs mainly 10 to 15 degrees below average. Much of the eastern US will also be below average but more around the 5 degree negative anomaly. The only areas east of the Continental Divide where it will be warmer than average is southern Texas, the central Gulf Coast, and New England.
During the midweek time period, the large area of below average temperatures will reach the Gulf Coast. By this point in time, temperatures will be below normal across all of the central and eastern US. The only region that will on the warmer side relative to average will be in New England as a large dome of high pressure offshore funnels warm and humid air inland. High temperatures across the eastern two-thirds of the nation will generally be in the 70s and 80s. It’s not until you reach the southern Plains and Florida where it will be in the 90s.
As a pattern change takes place by next weekend, we’ll begin to see warmer air stream in from the west as that heat dome finally moves. The Southeast, however, can expect the cooler temperatures to persist into mid-August.