Pattern Change Will Bring Drier Conditions to West, Cooler Temperatures to East to Begin May

Linda Lam
Published: April 30,2017
For those who have been waiting for a modification in the weather, your wait may finally be over.
A pattern change will take shape as May begins, with a much-needed break in the stormy weather for the West and assurances for the East that spring has not been skipped.
(MORE: May Temperature Outlook)
Wet weather has dominated much of the West since fall, but a drier stretch is on the way. Meanwhile, much of the East will see an end to the summer-like warmth.
The overall pattern in April has featured a southward dip in the jet stream in the West and an upper-level ridge, or northward bulge of the jet stream, over the East. This upper-level pattern is expected to last through the end of April.

Upper-level setup will bring summer-like warmth to parts of the East and will keep parts of the West wet through the end of April.

This week, the upper-level pattern will shift. An upper-level ridge of high pressure is expected to build into the West Coast, which will allow the jet stream to dip southward over portions of the East.

Pattern shift in early May will bring cooler temperatures to the East and drier conditions to the West.

This means drier and slightly warmer conditions for much of the West and temperatures more like spring instead of summer in parts of the East and South.
Here's a breakdown of the changes expected.

Drier Conditions Will Start May in the West

The jet stream has brought a parade of storms to the West Coast since October, dumping abundant precipitation on the region. The silver lining has been the elimination of drought for much of the region.
Numerous records have been set this water year, which began Oct. 1. Seattle set a record for most precipitation from October through April on Monday with 44.69 inches and broke the record for most days with measurable precipitation during these 144 days.
(MORE: Seattle Smashes Rainy-Season Precipitation Records)
Other locations have also set records, including Portland, Oregon, which has also had the most days with measurable precipitation since Oct. 1 with 145 days. Earlier this month, California's northern Sierra Nevada surpassed its all-time wettest water year.

Early May Forecast

All this precipitation has left many in the region wishing for sunshine to return. It appears that May will finally bring the long-awaited stretch of dry conditions.
As the upper-level ridge of high pressure begins to push into the West, high pressure will also build at the surface. Dry weather will prevail as May begins, even in the rain-weary Pacific Northwest – though a few showers could still clip Washington and northwestern Oregon at times.
(FORECAST: Seattle | Portland | Sacramento | Salt Lake City)
Temperatures will also begin to warm and most of the West Coast will see highs near to above average, especially midweek.
Portland, Oregon, has yet to reach 70 degrees this year, but this elusive mark could be reached this week. The latest 70-degree day on record for Portland is May 5.

East Temperature Changes Are Ahead

On the other side of the country, this pattern shift will also bring noticeable changes. Much of the East and South have seen above-average temperatures since the fall, although the Northeast saw cool conditions in March.
Washington D.C. saw its first 90-degree day of the year Saturday, tying the daily record high of 91 degrees. Nashville, Tennessee (91 degrees), also set a new record high while New York's LaGuardia airport tied its record of 88 degrees.
(MORE: 10-Day Forecast)
This warmth will be replaced by temperatures closer to average to start May.

Forecast Highs

By Monday, temperatures will be above average along the East Coast and in parts of the Northeast, but below-average temperatures are likely in the Midwest and in the lower Mississippi Valley.
By midweek, areas from the Plains to the East Coast will generally be near or below average. Instead of highs in the 80s, temperatures will top out in the 60s, with 50s from the upper Midwest into northern New England.
Areas of the South will likely see slightly-below average temperatures by late week, with highs only reaching the 60s, with 70s toward the Gulf Coast.
(MAPS: Weekly Planner)
Mornings will be cooler, as well, for the first week of May, with lows in the 50s in much of the South and 40s farther north, and 30s from the northern Plains into the Upper Peninsula of Michigan. A late-season freeze may stunt growth or even damage crops in the upper Midwest.

MORE: Florida Wildfires, April 2017 (PHOTOS)

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