824
FXUS01 KWBC 181944
PMDSPD
SHORT RANGE FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
344 PM EDT TUE JUL 18 2023
VALID 00Z WED JUL 19 2023 - 00Z FRI JUL 21 2023
...LENGTHY & DANGEROUS HEAT WAVE TO CONTINUE ACROSS THE SOUTHERN
TIER THIS WEEK...
...FLASH FLOODING & SEVERE WEATHER IN PORTIONS OF THE NATION'S
HEARTLAND AND NORTHEAST, HEADLINED BY A MODERATE RISK FOR
EXCESSIVE RAINFALL IN THE PARTS OF THE LOWER OHIO & TENNESSEE
VALLEYS...
...TROPICAL STORM CALVIN WEAKENING ON APPROACH TO HAWAII TONIGHT,
BUT HEAVY RAINS AND TROPICAL STORM FORCE WIND GUSTS STILL
EXPECTED...
...CANADIAN WILDFIRES/SMOKE RESPONSIBLE FOR AIR QUALITY ALERTS
OVER PARTS OF THE NORTHERN HIGH PLAINS, MIDWEST, GREAT LAKES, AND
NORTHEAST...
A PROLONGED AND EXTREMELY DANGEROUS HEAT WAVE CONTINUES FOR MUCH
OF THE SOUTHERN TIER OF THE LOWER 48 THANKS TO AN EXPANSIVE DOME
OF HIGH PRESSURE ALOFT, WHERE APPROXIMATELY 80 MILLION PEOPLE
COULD EXPERIENCE AN AIR TEMPERATURE OR HEAT INDEX ABOVE 105
DEGREES THROUGH THIS WEEKEND. IN LIGHT OF WIDESPREAD RECORD
BREAKING HEAT ACROSS THE THE SOUTHERN TIER THIS PAST WEEKEND,
PLENTY MORE RECORD BREAKING HOT WEATHER IS EXPECTED ACROSS THE
FOUR CORNERS STATES, TEXAS TO THE LOWER MISSISSIPPI VALLEY, AND
SOUTH FLORIDA THROUGH THE END OF THE WORK WEEK. DAYTIME HIGHS WILL
RESIDE IN THE TRIPLE DIGITS IN THE DESERT SOUTHWEST AND TEXAS,
WHILE THE GULF COAST AND MID-SOUTH CAN EXPECT DAYTIME HIGHS IN THE
UPPER 90S THAT COINCIDE WITH OPPRESSIVELY HIGH DEW POINTS,
RESULTING IN SWELTERING HEAT INDICES UPWARDS OF 120 DEGREES IN
PLACES. MEANWHILE, DAILY LOW TEMPERATURES WILL REMAIN QUITE WARM,
BREAKING RECORD WARM DAILY MINIMUMS IN SOME AREAS WHICH LIMITS
RELIEF FROM THE HEAT OVERNIGHT. ACCORDINGLY, AN EXPANSIVE AREA OF
EXCESSIVE HEAT WARNINGS AND HEAT ADVISORIES REMAINS IN THE
SOUTHWEST, SOUTHERN PLAINS, WESTERN AND CENTRAL GULF COAST, AND
EVEN PARTS OF SOUTH FLORIDA WHERE WELL ABOVE NORMAL SEA SURFACE
TEMPERATURES AND LIGHTER THAN NORMAL WINDS ARE CONTRIBUTING TO
STIFLING HEAT. PLEASE VISIT HEAT.GOV FOR MORE INFORMATION ON
IMPACTS FROM THE HEAT WAVE. THE NORTHEAST AND MID-ATLANTIC WILL
CONTINUE TO SEE HOT AND HUMID CONDITIONS THROUGH TUESDAY (ALBEIT
MORE SEASONAL), WHILE A COLD FRONTAL PASSAGE HELPS TO MAKE
CONDITIONS A LITTLE LESS MUGGY BY WEDNESDAY. TO THE WEST, A PAIR
OF COLD FRONTS WILL PROVIDE THE MIDWEST AND GREAT LAKES WITH
COOLER THAN NORMAL TEMPERATURES. SOME LOCATIONS IN THE UPPER
MIDWEST WILL STRUGGLE TO GET OUT OF THE 70S FOR THROUGH MIDWEEK.
A STORMY COUPLE OF DAYS REMAIN ON TAP FROM THE MIDWEST TO THE OHIO
AND TENNESSEE VALLEYS. TODAY AND INTO TUESDAY NIGHT, A
QUASI-STATIONARY FRONTAL BOUNDARY OVER THE MIDDLE MISSISSIPPI
VALLEY WILL BE THE FOCUS FOR STRONG-TO-SEVERE STORMS. SINCE
OVERNIGHT, THE STORM PREDICTION CENTER (SPC) HAS UPGRADED TO AN
ENHANCED RISK (THREAT LEVEL 3/5) EXTENDING ACROSS SOUTHEAST
MISSOURI, SOUTHERN ILLINOIS, WESTERN KENTUCKY, AND TENNESSEE
(INCLUDING NASHVILLE) FOR DAMAGING WIND GUSTS, LARGE HAIL, AND
TORNADOES. MEANWHILE, DEVELOPING THUNDERSTORMS WILL CONTAIN
COPIOUS AMOUNTS OF MOISTURE AND COULD TRAIN OVER PARTS OF THE
REGION, RESULTING POSSIBLY IN DANGEROUS FLASH FLOODING. A MODERATE
RISK (THREAT LEVEL 3/4) OF EXCESSIVE RAINFALL REMAINS ACROSS THE
MISSISSIPPI-OHIO RIVER CONFLUENCE TO NORTHWEST TENNESSEE, WHERE
5-8" OF RAINFALL IS POSSIBLE WHERE THE MAIN AXIS OF TRAINING SETS
UP. THERE IS ALSO A SLIGHT RISK (THREAT LEVEL 2/4) OF EXCESSIVE
RAINFALL IN THE NORTHEAST DUE TO MORE ROUNDS OF THUNDERSTORMS IN
AREAS THAT FEATURE HIGHLY SATURATED SOILS, WITH SOME SEVERE WIND
GUSTS ALSO POSSIBLE WITH THIS ACTIVITY. ELSEWHERE, SPC MAINTAINS A
SLIGHT RISK AREA THIS AFTERNOON IN NORTH DAKOTA WHERE STORMS COULD
PRODUCE VERY LARGE HAIL. ON WEDNESDAY, MORE SHOWERS AND STORMS
WILL FORM FROM THE CENTRAL ROCKIES AND MIDWEST TO THE
MID-ATLANTIC. SPC AND WPC BOTH HAVE LARGE MARGINAL RISK AREAS IN
PLACE, WHILE WPC DOES HAVE A SLIGHT RISK IN THE TENNESSEE VALLEY
AND SOUTHERN APPALACHIANS WHERE THE THREAT FOR FLASH FLOODING IS
GREATER FROM SATURATED SOILS OWING TO EARLIER HEAVIER RAINFALL.
THE THREAT OF HEAVY RAINFALL LOOKS TO CONTINUE INTO THURSDAY WHERE
SCATTERED FLASH FLOODING REMAINS POSSIBLE ACROSS THE APPALACHIANS
AND NORTHERN MID-ATLANTIC, WITH A SEPARATE EXCESSIVE RAINFALL AREA
ALSO HIGHLIGHTED ACROSS THE CENTRAL HIGH PLAINS. WEST OF THE
ROCKIES, THE SOUTHWEST MONSOON IS SHOWING SIGNS OF LIFE WITH
ROUNDS OF SHOWERS AND STORMS POSSIBLE EACH DAY, WHERE THE
STRONGEST STORMS COULD PRODUCE BOUTS OF ISOLATED FLASH FLOODING
AND DAMAGING WIND GUSTS.
IN THE NORTH CENTRAL PACIFIC OCEAN, TROPICAL STORM CALVIN IS
WEAKENING AS IT APPROACHES HAWAII'S BIG ISLAND WHERE TROPICAL
STORM WARNINGS HAVE BEEN ISSUED. THE LATEST FORECAST FROM THE
CENTRAL PACIFIC HURRICANE CENTER SHOWS THE STORM MAINTAINING
TROPICAL STORM STATUS AS IT TRACKS SOUTH OF THE BIG ISLAND
TONIGHT. THE FORECAST REMAINS ON TRACK FOR CALVIN TO LIKELY
PRODUCE LOCALLY HEAVY RAINFALL WITH AS MUCH AS 4-8 INCHES AND
LOCALIZED AMOUNTS UP TO 10 INCHES ALONG THE WINDWARD SLOPES OF THE
BIG ISLAND. A LITTLE FARTHER NORTH, 3-6 INCHES OF RAINFALL ARE
POSSIBLE ALONG THE WINDWARD SLOPES OF MAUI. CALVIN IS ALSO LIKELY
TO CAUSE ROUGH SEAS AND LOCALLY STRONG WINDS AROUND "THE ALOHA
STATE." SEE CENTRAL PACIFIC HURRICANE CENTER ADVISORIES ON CALVIN
FOR MORE INFORMATION ON THE STORM.
SMOKE FROM THE CANADIAN WILDFIRES WILL REMAIN IN THE PICTURE
THROUGH MID-WEEK AS NORTHWESTERLY WINDS ALOFT THAT ORIGINATE OVER
CANADA CONTINUE TO DIRECT SMOKE INTO THE LOWER 48. THERE ARE AIR
QUALITY ALERTS ISSUED FOR AREAS THE INCLUDE THE NORTHERN HIGH
PLAINS, THE MIDWEST, GREAT LAKES, SOUTHERN MID-ATLANTIC, AND INTO
THE NORTHEAST WHERE HIGHER CONCENTRATIONS OF SMOKE WILL RESULT IN
UNHEALTHY AIR QUALITY FOR SENSITIVE GROUPS.
ASHERMAN/MULLINAX
GRAPHICS AVAILABLE AT
HTTPS://WWW.WPC.NCEP.NOAA.GOV/BASICWX/BASICWX_NDFD.PHP
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