The dominant and anomalous upper-level ridge parked over the central Great Basin responsible for the ongoing western U.S. heat wave is anticipated to finally begin dissolving on Thursday and offer a cooling trend for areas experiencing record shattering September heat.
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Preceding the long awaited relief, well above average temperatures are forecast once again today from California to the northern/central High Plains, including much of the Intermountain West and northern/central Rockies.
Widespread high temperatures are expected to reach into the upper 90s and triple digits throughout these regions, with 110s possible in the interior valleys of California.
These dangerously hot temperatures will likely break dozens of additional daily and possibly monthly records.
A strong cold front entering from southwest Canada will usher in a much cooler airmass to the northern Plains and northern Great Basin, before reaching the central Plains on Friday.
In fact, high temperatures are actually forecast to only reach the low 60s throughout the northern High Plains on Friday, which equates to around 20 degrees below average.
This cold front will also aid in producing gusty winds throughout the northern Great Basin and northern High Plains today.
Combined with low relative humidity, conditions are likely to support the potential for new wildfires to start and existing fires to spread uncontrollably.
SPC has issued an Extremely Critical (level 3/3) fire weather area over north-central Montana, where winds could gust up to 60 mph.
The Critical Fire Weather conditions are forecast to sweep ahead of the cold front and enter the central Plains on Thursday, while remaining over parts of the Intermountain West.
For California, heat will be much slower to dissipate as highs will continue to reach into the 100s on Thursday and Friday.
More drastic cooling is possible throughout southern California on Friday as cloud cover and rainfall associated with Hurricane Kay enters the region.
Residents and visitors within regions impacted by the ongoing heat wave are urged to continue following proper heat safety and check in on individuals who may be more susceptible to heat related illnesses.
Hurricane Kay is forecast to begin producing impacts in the form of heavy rain and gusty winds throughout southern California and the Desert Southwest on Friday as the center of the storm slides northward just to the west of Baja California.
Currently, the main impacts from Kay are anticipated to be from heavy rainfall as tropical moisture surges into southern California and southwest Arizona.
Rainfall amounts of 2 to 4 inches, with maximum amounts of 6 inches possible through Saturday morning.
This amount of rainfall is likely to produce scattered instances of flash flooding, particularly near recent burn scars and within susceptible terrain across the peninsular ranges of southern California.
Refer to the National Hurricane Center for additional information.
An elongated upper-level trough extending from the Northeast to the Gulf of Mexico will continue producing scattered showers and thunderstorms throughout the eastern U.S.
today, with activity confining to the Gulf Coast and Southeast by Thursday and Friday.
The main threats associated with these storms will be the potential for downpours and isolated flash floods.
Eventually, a strengthening upper-level low over the northern Gulf of Mexico will help funnel deep tropical moisture to the eastern Gulf Coast by late week, creating the threat for additional instances heavy rain and flash flooding.
A Slight Risk (level 2/4) of Excessive Rainfall has been issued for much of the Southeast and eastern Gulf Coast on Friday as more widespread thunderstorm activity develops capable of containing intense rainfall rates. ■