The upper-level pattern over the contiguous U.S. remains blocked going into the next few days, indicating that there will not be many large-scale changes in the short-term forecast period.
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There is a broad trough over the western half of the country, a positively-tilted trough over the southeast U.S. and into the western Atlantic Ocean, and a closed upper-level high over the central and Northeastern U.S.
Widespread scattered showers and thunderstorms will continue to impact much of the West, particularly over areas extending from northern California into the Yellowstone region, as well as into portions of the central Plains.
Showers and thunderstorms will be more numerous during the daytime, where daytime heating and terrain-induced lift may initiate showers and thunderstorms.
Heavy rainfall rates of 0.5-1"/hr are possible across a broad portion of the West, which may result in localized flash flooding, especially in urban/poor drainage areas.
Therefore, a Marginal Risk (level 1/4) of Excessive Rainfall is in effect for portions of the Intermountain West/northern High Plains.
By Wednesday into Thursday, a mid-upper low over the Four Corners region will eject toward the northern High Plains and increase chances for heavy precipitation over northern Wyoming and Montana.
Therefore, a Slight Risk (level 2/4) for Excessive Rainfall is in effect for portions of Montana on Thursday.
Temperatures will generally cool across the region through the middle of this week, with mostly seasonal high temperatures expected across the region by midweek.
Over the High Plains, shortwaves embedded in the broad trough over the West may initiate showers and thunderstorms, with locally heavy and severe impacts possible.
In addition, sustained moist, southerly flow from the Gulf of Mexico may act to enhance rainfall rates/totals and induce severe weather.
This setup has the potential to produce isolated heavy rainfall accumulations of 1-2" (locally higher) across portions of the central/southern Plains.
A Marginal Risk of Excessive Rainfall is in effect for this region for the aforementioned reasons.
Additionally, the Storm Prediction Center has issued an Enhanced Risk (level 3/5) of severe weather for much of far-eastern Colorado, far western Kansas, as well as the adjacent surrounding areas.
The primary severe hazard will be high wind gusts.
Given the blocked upper-level pattern, isolated regions of heavy rainfall and severe weather are possible over the western High Plains through the rest of the forecast period.
Across the Mid-Atlantic, a weakening upper low will slowly drift into the Atlantic as a back-door cold front pushes colder air from New England down the East Coast and Appalachians.
Light scattered showers and thunderstorms will slowly dissipate throughout Tuesday evening, with conditions becoming cooler and drier over in the short-term forecast.
To the south, an upper-level trough will settle over the central Gulf of Mexico, which may spawn a new low-pressure system at the surface.
This system is being currently being monitored by the National Hurricane Center, with a 10% chance of formation through the next 48 hours.
The exact track of this system remains uncertain, but current forecasts keep it relatively stationary over the central Gulf in the near-term.
Scattered showers and thunderstorms, with locally heavy amounts possible, are expected to initiate over the Florida Peninsula starting on Wednesday with high moisture content draped across the region.
A closed upper high will remain relatively stationary across the northeastern portion of the nation from the Great Lakes into New England.
Dry conditions and well above average temperatures will accompany this upper high with high temperatures 15 to 20 degrees above average across much of the northern tier from the northern Plains, through the upper Great Lakes, northern New York State into northern New England.
Some high temperature records may be broken this week over portions of the Great Lakes and Northeast, particularly on Thursday afternoon.
In contrast, cooler than average temperatures over the next few days will be associated with the showery pattern across the southeastern U.S. and along the West coast into the Desert Southwest. ■