Unseasonably cool weather will continue through the end of the work week across the Northeast and Mid-Atlantic as an upper-low slowly meanders eastward into the Atlantic Ocean.
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Thursday will feature widespread temperature departures of 10-20 degrees below average throughout the region, with daytime high temperatures remaining in the 50s and low 60s, albeit a tad warmer than the last few days.
The cool weather will continue into Saturday, however, temperatures should gradually return closer to normal as the upper-low shifts eastward, with high temperatures on Friday approaching the upper 60s to low 70s regionwide..
Moreover, with high-pressure building in from the northwest, the damp conditions will come to an end, leading to some possible peeks of sunshine to usher in the first weekend of May.
On the opposite side of the lower 48, an upper-low churning off the California coastline has led to a cool and unsettled weather pattern spreading eastward across the West Coast.
While the unseasonably cool temperatures will remain confined to California, the southern Great Basin region, and the Southwest on Thursday, with daytime temperature departures approaching 15 to 25 degrees below normal, they will spread inland, encompassing all areas west of the Continental Divide through Saturday.
In the meantime, much of the northern Intermountain West will experience very warm temperatures on Thursday, with widespread daytime highs approaching the 70s and 80s, leading to significant snowmelt, which could lead to localized flooding concerns.
Furthermore, unsettled weather will increase across the Pacific Northwest on Thursday as an upper-level shortwave trough and surface frontal system approaches from the northwest.
Widespread showers and thunderstorms, including high-elevation mixed precipitation and snow, are forecast through the end of the week.
A broad swath of 0.5 to 1"+ 48-hour rainfall totals throughout Washington, Oregon, and Idaho, in addition to snowmelt across the Great Basin and Pacific Northwest due to recent above-average temperatures, may cause isolated flooding issues in nearby streams and rivers.
Shifting eastward, a stationary boundary draped across the southern Plains and mid-South will produce heightened chances of showers and thunderstorms through the end of the week.
As a surface low forms across southeastern Colorado during the early Thursday hours, warm, moist air will surge northward behind a warm front lifting north through eastern Texas and Oklahoma while a dryline develops across central Texas, allowing for the initiation of strong to severe thunderstorms.
As a result, the Storm Prediction Center has placed much of the region in a Slight Risk of Severe Thunderstorms, with the primary threats being large hail, damaging wind gusts, and isolated tornadoes.
Heavy rainfall rates of 2-3" per hour embedded in these thunderstorms may also lead to flooding concerns as localized areas, including the ArkLaTex region, continue to have anomalously moist soils due to recent rainfall.
As the eastern flank of the frontal boundary pushes northward on Friday, the threat of heavy rainfall will shift into the Tennessee Valley, with a Slight Risk of Excessive Rainfall hoisted for much of the region. ■