642
FXUS01 KWBC 170755
PMDSPD
SHORT RANGE FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
354 AM EDT THU AUG 17 2023
VALID 12Z THU AUG 17 2023 - 12Z SAT AUG 19 2023
...HOT/RECORD TEMPERATURES TO SHIFT FOCUS OUT OF THE NORTHWEST AND
INTO THE CENTRAL U.S.; CRITICAL RISK OF FIRE WEATHER IN THE
NORTHWEST...
...SHOWERS, THUNDERSTORMS, AND AN INCREASING RISK OF FLASH
FLOODING FOR THE SOUTHWEST...
...SCATTERED SHOWER AND THUNDERSTORM CHANCES CONTINUE ALONG THE
EAST COAST...
AN UPPER-LEVEL RIDGE SHIFTING FROM THE NORTHWEST EASTWARD OVER THE
CENTRAL U.S. WILL CONTINUE TO BE THE DRIVER OF AN EXPANSIVE
HEATWAVE. ONE MORE DAY OF OPPRESSIVELY HOT TEMPERATURES ARE
FORECAST FOR THE INTERIOR NORTHWEST AND PORTIONS OF THE NORTHERN
ROCKIES/ADJACENT HIGH PLAINS THURSDAY. HIGHS WILL GENERALLY BE IN
THE UPPER 90S TO LOW 100S, NEAR RECORD-TYING/BREAKING LEVELS FOR
PORTIONS OF THE NORTHERN ROCKIES. IN ADDITION, LOW RELATIVE
HUMIDITY AND SOME GUSTY WINDS ON TOP OF THE HOT TEMPERATURES HAS
RESULTED IN A CRITICAL RISK OF FIRE WEATHER FROM THE STORM
PREDICTION CENTER FOR PORTIONS OF EASTERN WASHINGTON AND NORTHWEST
MONTANA THURSDAY AND FRIDAY. A PACIFIC SYSTEM/COLD FRONT PUSHING
SOUTHEAST ACROSS THE REGION LATE THURSDAY AND INTO THE DAY FRIDAY
WILL BRING AN END TO THE MORE DANGEROUS HEAT FOR THIS REGION, WITH
HIGHS REMAINING HOT BUT RETURNING TO MORE REASONABLE, SUMMER-TIME
TEMPERATURES GENERALLY IN THE LOW 90S. AS THE RIDGE SHIFTS EAST,
TEMPERATURES WILL BEGIN TO SOAR INTO THE UPPER 90S TO LOW 100S
OVER WESTERN PORTIONS OF THE NORTHERN/CENTRAL PLAINS ON FRIDAY.
THIS EASTWARD SHIFT IN THE RIDGE WILL ALSO BRING TEMPERATURES BACK
UP INTO THE MID- TO UPPER 100S IN TEXAS AND LOW 100S FOR THE LOWER
MISSISSIPPI VALLEY, NEAR RECORD-TYING/BREAKING LEVELS, AFTER A
BRIEF REPRIEVE FOR MANY THE PAST COUPLE OF DAYS. THE RIDGE
UNFORTUNATELY LOOKS TO SETTLE IN AND LEAD TO A LONG-DURATION
HEATWAVE OVER THE CENTRAL U.S. INTO NEXT WEEK. PLEASE SEE WPC'S
HEAT KEY MESSAGES FOR MORE INFORMATION ON THIS EXPANSIVE HEAT
WAVE.
AN UPPER-LEVEL CLOSED LOW LINGERING OVER THE CALIFORNIA COAST WILL
CONTINUE TO PROVIDE SUPPORT ALOFT FOR DAILY SHOWER AND
THUNDERSTORM CHANCES OVER PORTIONS OF THE SOUTHWEST/GREAT BASIN.
ANOMALOUSLY HIGH MOISTURE IN THE REGION WILL LEAD TO LOCALLY HEAVY
DOWNPOURS WITH THE RISK FOR SOME ISOLATED FLASH FLOODING,
PARTICULARLY FOR MORE SENSITIVE LOCATIONS SUCH AS URBAN AREAS,
BURN SCARS, DRY WASHES, AND SLOT CANYONS. ENHANCED LIFT ALOFT AND
HIGHER INSTABILITY WILL RESULT IN A LOCALLY HIGHER RISK OF A FEW
SCATTERED INSTANCES OF FLASH FLOODING OVER PORTIONS OF SOUTHWEST
UTAH AND NORTHWEST ARIZONA ON FRIDAY, WITH A SLIGHT RISK OF
EXCESSIVE RAINFALL (LEVEL 2/4) IN PLACE. CONFIDENCE HAS INCREASED
IN SIGNIFICANT HEAVY RAINFALL/FLOODING IMPACTS FROM INCREASING
MOISTURE STREAMING INTO SOUTHERN CALIFORNIA AND THE SOUTHWEST FROM
HILARY IN THE EASTERN PACIFIC, BUT THIS WILL LIKELY BEGIN JUST
BEYOND THE CURRENT FORECAST PERIOD DURING THE DAY SATURDAY. HIGH
TEMPERATURES BROADLY ACROSS THE SOUTHERN TIER OF THE WEST WILL
RANGE FROM THE 70S ALONG COASTAL CALIFORNIA, 80S IN THE FOUR
CORNERS REGION, AND LOW TO MID-90S FOR THE CENTRAL/SOUTHERN
ROCKIES AND GREAT BASIN. HEAT-RELATED ADVISORIES/WARNINGS ARE IN
EFFECT THURSDAY FOR THE CENTRAL CALIFORNIA VALLEYS FOR HIGHS IN
THE MID 100S AND THE DESERT SOUTHWEST FOR HIGHS INTO THE 110S
BEFORE A RETURN TO MORE TYPICAL SUMMERTIME TEMPERATURES FRIDAY.
ELSEWHERE, A FRONTAL SYSTEM PASSING THROUGH THE GREAT LAKES WILL
CONTINUE TO BRING A CHANCE FOR SHOWERS AND THUNDERSTORMS THROUGH
EARLY THURSDAY BEFORE SHIFTING INTO THE INTERIOR NORTHEAST BY
THURSDAY AFTERNOON AND NEW ENGLAND BY FRIDAY. SOME LOCALLY HEAVY
DOWNPOURS/ISOLATED FLASH FLOODING AND AN INSTANCE OR TWO OF GUSTY
WINDS WILL BE POSSIBLE. COOLER TEMPERATURES WILL FOLLOW BEHIND THE
FRONT, WITH HIGHS IN THE 70S TO LOW 80S FOR MUCH OF THE
MIDWEST/NORTHEAST. OVER THE SOUTHEAST, A LINGERING FRONTAL
BOUNDARY WILL PROVIDE THE FOCUS FOR MAINLY AFTERNOON SHOWERS AND
STORMS. HIGHS WILL BE NEAR AVERAGE FROM THE SOUTHERN MID-ATLANTIC
THROUGH THE SOUTHEAST AND INTO FLORIDA, WITH UPPER 80S TO LOW 90S
EXPECTED.
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