801
FXUS01 KWBC 192049
PMDSPD
SHORT RANGE FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
449 PM EDT SAT AUG 19 2023
VALID 00Z SUN AUG 20 2023 - 00Z TUE AUG 22 2023
...THERE IS A SLIGHT TO HIGH RISK OF EXCESSIVE RAINFALL OVER PARTS
OF SOUTHERN CALIFORNIA AND THE GREAT BASIN...
...THERE ARE AIR QUALITY WARNINGS OVER THE PARTS OF THE PACIFIC
NORTHWEST AND NORTHERN ROCKIES...
...EXCESSIVE HEAT WARNINGS AND ADVISORIES FROM PARTS OF THE
PLAINS, THE MISSISSIPPI VALLEY, AND CENTRAL/WESTERN GULF COAST...
HURRICANE HILARY IS FORECAST TO MOVE NORTHWARD OVER THE EASTERN
PACIFIC ON SATURDAY AND MAKE LANDFALL OVER BAJA CALIFORNIA
PENINSULA ON SUNDAY. HILARY IS THEN FORECAST TO CONTINUE TO MOVE
NORTHWARD INTO SOUTHERN CALIFORNIA BY SUNDAY EVENING AND THEN INTO
CENTRAL NEVADA BEFORE DISSIPATING ON MONDAY. HILARY WILL ALSO
PRODUCE POTENTIALLY HISTORIC RAINFALL AMOUNTS EXPECTED TO CAUSE
FLASH, URBAN, AND STEEP-SIDED GULLY FLOODING, INCLUDING
LANDSLIDES, MUDSLIDES, AND DEBRIS FLOWS. DANGEROUS TO LOCALLY
CATASTROPHIC FLOODING IMPACTS ARE EXPECTED LATE TONIGHT THROUGH
EARLY MONDAY. THEREFORE, THE WPC HAS ISSUED A HIGH RISK OF
EXCESSIVE RAINFALL OVER SOUTHERN/CENTRAL CALIFORNIA FROM SUNDAY
INTO MONDAY. SEVERE, WIDESPREAD FLASH FLOODING IS EXPECTED. AREAS
THAT NORMALLY DO NOT EXPERIENCE FLASH FLOODING WILL FLOOD. LIVES
AND PROPERTY ARE IN GREAT DANGER FROM SUNDAY INTO MONDAY.
AS THE MOISTURE FROM HILARY FLOWS NORTHWARD, HEAVY RAIN WILL
DEVELOP OVER PARTS OF NEVADA, EASTERN OREGON, IDAHO, AND
NORTHWESTERN MONTANA. THEREFORE, THE WPC HAS ISSUED A SLIGHT RISK
OF EXCESSIVE RAINFALL FROM MONDAY INTO TUESDAY MORNING. THE
ASSOCIATED HEAVY RAIN WILL CREATE MAINLY LOCALIZED AREAS OF FLASH
FLOODING, WITH URBAN AREAS, ROADS, AND SMALL STREAMS THE MOST
VULNERABLE. IN ADDITION, SHOWERS AND THUNDERSTORMS WILL DEVELOP
OVER MOST OF THE WEST COAST INLAND TO THE GREAT BASIN, SOUTHWEST,
NORTHERN INTERMOUNTAIN REGION, AND NORTHERN ROCKIES THROUGH MONDAY
EVENING.
FURTHERMORE, WILDFIRE SMOKE OVER NORTHERN CALIFORNIA AND THE
PACIFIC NORTHWEST HAS PROMPTED AIR QUALITY ALERTS OVER PARTS OF
THE PACIFIC NORTHWEST, NORTHERN INTERMOUNTAIN REGION, AND NORTHERN
ROCKIES.
MEANWHILE, A FRONT CROSSING THE GREAT LAKES WILL PRODUCE SCATTERED
SHOWERS AND THUNDERSTORMS OVER PARTS OF THE UPPER GREAT LAKES/OHIO
VALLEY FROM SATURDAY EVENING INTO SUNDAY MORNING. MOREOVER, THE
SAME FRONT WILL PRODUCE SHOWERS AND THUNDERSTORMS OVER PARTS OF
THE NORTHEAST MONDAY INTO TUESDAY.
IN ADDITION, UPPER-LEVEL ENERGY AND TROPICAL MOISTURE WILL PRODUCE
SHOWERS AND THUNDERSTORMS OVER PARTS OF FLORIDA THROUGH SUNDAY
NIGHT. FURTHER, ONSHORE FLOW OFF THE ATLANTIC WILL CONTINUE TO
PRODUCE SHOWERS AND THUNDERSTORMS OVER THE SOUTHERN TIP OF FLORIDA
THROUGH MONDAY.
FURTHERMORE, AN UPPER-LEVEL HIGH OVER THE CENTRAL PLAINS/MIDDLE
MISSISSIPPI VALLEY WILL CREATE OPPRESSIVE DAYTIME HEAT, LIMITED
OVERNIGHT COOLING, WHICH WILL ALSO CONTRIBUTE TO THE EFFECTS OF
HEAT, PROMPTING EXCESSIVE HEAT WARNINGS AND HEAT ADVISORIES OVER
PORTIONS OF THE CENTRAL/SOUTHERN PLAINS AND A SMALL SLIVER OF THE
NORTHERN PLAINS, THE UPPER/MIDDLE/LOWER MISSISSIPPI VALLEY,
CENTRAL/WESTERN GULF COAST.
IN ADDITION, DANGEROUS HEAT WILL CONTINUE TO INTENSIFY AND EXPAND
INTO THE PLAINS STATES, WITH NUMEROUS DAILY HIGH-TEMPERATURE
RECORDS EXPECTED, ESPECIALLY IN THE CENTRAL PLAINS AND TEXAS. THE
HEAT WAVE WILL THEN EXPAND ON SUNDAY AND EARLY NEXT WEEK TO
INCLUDE MUCH OF THE CENTRAL AND SOUTHEAST U.S. SOME LOCATIONS IN
THE MIDWEST MAY SEE THEIR HOTTEST DAY OF THE YEAR SO FAR THIS
WEEKEND. PORTIONS OF THE SOUTH CENTRAL U.S. AND GULF COAST MAY
FURTHER EXTEND THEIR RECORD NUMBER OF HOURS WITH A HEAT INDEX
READING OF AT LEAST 110ĀF.
MOREOVER, THE PROLONGED NATURE OF THE HEAT WAVE, COMBINED WITH
VERY WARM OVERNIGHT TEMPERATURES, WILL LIMIT THE RELIEF FROM THE
OPPRESSIVE DAYTIME HEAT AND COMPOUND OVERALL HEAT IMPACTS.
FURTHER, EXCESSIVE HEAT IS ANTICIPATED TO FOCUS OVER THE
SOUTHEASTERN QUADRANT OF THE COUNTRY NEXT WEEK. THE GREATEST RISK
OF EXCESSIVE HEAT IS FOR EASTERN TEXAS AND PARTS OF THE GULF COAST
STATES.
ZIEGENFELDER
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