122
FXUS01 KWBC 130803
PMDSPD
SHORT RANGE FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
402 AM EDT SUN AUG 13 2023
VALID 12Z SUN AUG 13 2023 - 12Z TUE AUG 15 2023
...FLASH FLOODING AND SEVERE THUNDERSTORMS POSSIBLE FOR PORTIONS
OF THE PLAINS/MISSISSIPPI VALLEY SUNDAY, SHIFTING TO THE GREAT
LAKES/OHIO VALLEY/MID-ATLANTIC MONDAY...
...DANGEROUS HEAT PERSISTS ACROSS MUCH OF THE SOUTH WHILE ANOTHER
HEAT WAVE BEGINS ACROSS THE PACIFIC NORTHWEST SUNDAY...
...MONSOONAL SHOWERS CONTINUE ACROSS THE FOUR CORNERS REGION WITH
SOME LOCALLY HEAVY DOWNPOURS POSSIBLE...
AN UPPER-LEVEL SHORTWAVE MOVING SOUTHEASTWARD FROM CANADA OVER A
PAIR OF FRONTAL BOUNDARIES OVER THE PLAINS/MISSISSIPPI VALLEY WILL
HELP TO TRIGGER NUMEROUS SHOWERS AND THUNDERSTORMS THROUGHOUT THE
DAY SUNDAY. ONGOING STORMS CONTINUING THROUGH EARLY SUNDAY MORNING
ARE EXPECTED TO BE FOLLOWED BY ANOTHER ROUND OF STORMS SUNDAY
AFTERNOON INTO SUNDAY NIGHT ALONG THE BOUNDARIES AS WELL AS ANY
OUTFLOWS. MOISTURE POOLING BETWEEN THE BOUNDARIES FROM PORTIONS OF
THE CENTRAL/SOUTHERN PLAINS INTO THE MIDDLE MISSISSIPPI VALLEY
WILL HELP PROMOTE EFFICIENT RAINFALL RATES WITH THE PROSPECT OF
STORMS MOVING PARALLEL TO THE FRONTS REPEATEDLY OVER THE SAME
REGION HEIGHTENING THE RISK FOR SEVERAL INCHES OF RAINFALL. A
MODERATE RISK OF EXCESSIVE RAINFALL (LEVEL 3/4) HAS BEEN
INTRODUCED OVER SOUTHWESTERN MISSOURI WHERE THE HIGHEST
PROBABILITIES OF HEAVIER RAINFALL TOTALS AND SCATTERED TO NUMEROUS
INSTANCES OF FLASH FLOODING ARE CURRENTLY FORECAST, WITH A BROADER
SLIGHT RISK (LEVEL 2/4) ACROSS THE REGION. IN ADDITION TO HEAVY
RAINFALL, THE STORM PREDICTION CENTER HAS OUTLINED SIMILAR AREAS
OF SOUTHWESTERN MISSOURI WITH AN ENHANCED RISK OF SEVERE WEATHER
(LEVEL 3/5), WITH A BROADER SLIGHT RISK (LEVEL 2/5) IN PLACE AS
WELL, AS SUFFICIENT DEEP LAYER SHEAR WILL BE IN PLACE FOR SOME
ORGANIZED SEVERE STORMS CAPABLE OF DAMAGING WINDS, A FEW
TORNADOES, AND LARGE HAIL.
THE FRONTAL BOUNDARIES ARE EXPECTED TO CONSOLIDATE INTO A POTENT
SUMMER COLD FRONT AS THEY PUSH EASTWARD OVERNIGHT SUNDAY INTO THE
DAY MONDAY, WITH STORM CHANCES SHIFTING INTO THE GREAT LAKES, OHIO
VALLEY, AND MID-ATLANTIC. VERY MOIST, SOUTHERLY FLOW WILL CONTINUE
TO HELP PROMOTE STORMS WITH HEAVY RAIN RATES, AND A SLIGHT RISK OF
EXCESSIVE RAINFALL IN EFFECT FOR THE RISK OF SOME SCATTERED
INSTANCES OF FLASH FLOODING. ADDITIONAL SEVERE STORMS ARE POSSIBLE
AS WELL, WITH A SLIGHT RISK OF SEVERE WEATHER FOCUSED ON THE UPPER
OHIO VALLEY INTO THE MID-ATLANTIC, MAINLY FOR THE RISK OF SOME
DAMAGING WINDS. THE COLD FRONT PUSHING EASTWARD WILL BRING QUITE
THE CONTRAST IN HIGH TEMPERATURES BROADLY FROM THE PLAINS TO THE
EAST COAST. MUCH BELOW AVERAGE HIGHS IN THE UPPER 60S TO LOW 70S
ARE FORECAST FOR THE NORTHERN PLAINS INTO THE UPPER MIDWEST
SUNDAY. THE COOLER TEMPERATURE WILL SPREAD INTO THE MIDWEST AND
PORTIONS OF THE CENTRAL/SOUTHERN PLAINS MONDAY, WITH HIGHS IN THE
MID 70S TO LOW 80S. HIGHS WILL BE CLOSER TO AND ABOVE SUMMERTIME
AVERAGES AHEAD OF THE FRONT, WITH UPPER 70S AND LOW 80S FOR NEW
ENGLAND AND MID-80S TO LOW 90S FOR THE MID-ATLANTIC.
A BROAD UPPER-LEVEL RIDGE ANCHORED OVER THE SOUTH WILL KEEP
DANGEROUS HEAT IN PLACE THIS WEEKEND AND INTO EARLY NEXT WEEK.
WIDESPREAD HEAT-RELATED ADVISORIES AND WARNINGS ARE IN EFFECT FROM
FLORIDA NORTH TO THE CAROLINAS AND WEST TO TEXAS/OKLAHOMA. THE
MOST EXCESSIVE HEAT IS EXPECTED TO FOCUS ACROSS A LARGE PORTION OF
TEXAS INTO THE LOWER MISSISSIPPI VALLEY. DAILY HIGH TEMPERATURES
ARE FORECAST TO RANGE FROM THE MID-90S IN FLORIDA AND THE
CAROLINAS, THE UPPER 90S INTO PORTIONS OF THE SOUTHEAST, THE LOW
100S IN OKLAHOMA AND THE LOWER MISSISSIPPI VALLEY, AND THE MID
100S INTO PORTIONS OF TEXAS. THESE TEMPERATURES WHEN COMBINED WITH
HIGH HUMIDITY WILL ALLOW FOR HEAT INDICES AS HIGH AS 110 TO 120F
FOR MANY LOCATIONS. NUMEROUS RECORD-TYING/BREAKING HIGHS ARE
FORECAST BOTH DAYS, WITH SIMILARLY RECORD-LEVEL WARM LOW
TEMPERATURES IN THE UPPER 70S TO LOW 80S PROVIDING LITTLE RELIEF
FROM THE HEAT OVERNIGHT. SOME MODERATION OF THE HEAT IS EXPECTED
FOR NORTHERN PORTIONS OF THE REGION BY THE MIDDLE OF THIS UPCOMING
WEEK AS COOLER AIR FOLLOWS THE SOUTHWARD MOVING COLD FRONT CUTTING
ACROSS THE COUNTRY, STARTING WITH THE NOTED PORTIONS OF THE
SOUTHERN PLAINS MONDAY.
UNFORTUNATELY, ANOTHER HEATWAVE IS FORECAST TO BEGIN SUNDAY ACROSS
THE PACIFIC NORTHWEST THANKS TO A STRONG RIDGE OF HIGH PRESSURE
THAT WILL SETTLE IN OVERHEAD. THE MORE EXCESSIVE TEMPERATURES WILL
INITIALLY BE FOCUSED ALONG THE INTERIOR VALLEYS WEST OF THE
CASCADES IN OREGON, WITH HIGHS SOARING INTO THE 100S SUNDAY. THIS
HEAT WILL CONTINUE TO INTENSIFY AND EXPAND ACROSS THE REGION
MONDAY, WITH HIGHS RANGING FROM UPPER 80S TO LOW 90S AROUND PUGET
SOUND, THE UPPER 90S TO LOW 100S EAST OF THE CASCADES, AND THE
MID-100S TO POTENTIALLY OVER 110 DEGREES FOR THE INTERIOR WEST OF
THE CASCADES. NUMEROUS NEAR RECORD-TYING/BREAKING HIGHS ARE
POSSIBLE HERE AS WELL. THESE TEMPERATURES COMBINED WITH THE
DURATION OF HEAT, EXPECTED TO CONTINUE THROUGH THIS WEEK, WILL
INCREASINGLY POSE A HEIGHTENED HEALTH RISK, ESPECIALLY FOR THOSE
WITHOUT ADEQUATE AIR CONDITIONING.
A LINGERING FRONTAL BOUNDARY IN ADDITION TO MONSOONAL MOISTURE
WILL LEAD TO CONTINUED DAILY ROUNDS OF AFTERNOON THUNDERSTORMS IN
THE FOUR CORNERS REGION WITH A FEW LOCALLY HEAVY DOWNPOURS
POSSIBLE, AND SOME ISOLATED CONCERNS FOR FLASH FLOODING. HIGHS
WILL GENERALLY BE NEAR SUMMERTIME AVERAGES ACROSS THE SOUTHERN
TIER OF THE WEST, WITH 70S ALONG THE CALIFORNIA COAST, LOW TO
MID-90S FOR THE GREAT BASIN, UPPER 90S TO LOW 100S FOR THE
INTERIOR CALIFORNIA VALLEYS, AND 100S FOR THE DESERT SOUTHWEST.
PORTIONS OF THE CENTRAL/SOUTHERN ROCKIES AND ADJACENT HIGH PLAINS
WILL BE MORE INFLUENCED BY THE COLD FRONT PASSAGE, WITH MUCH
COOLER HIGHS IN THE UPPER 70S TO LOW 80S FORECAST.
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