629
FXUS01 KWBC 132004
PMDSPD
SHORT RANGE FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
400 PM EDT THU JUL 13 2023
VALID 00Z FRI JUL 14 2023 - 00Z SUN JUL 16 2023
...A COUPLE ROUNDS OF HEAVY RAIN COULD TRIGGER ADDITIONAL FLASH
FLOODING OVER INTERIOR NEW ENGLAND THROUGH TONIGHT...
...ADDITIONAL ROUNDS OF SEVERE WEATHER AND FLASH FLOODING PERSIST
ACROSS THE CENTRAL PLAINS, MID-MISSISSIPPI VALLEY AND INTO THE
EASTERN GULF COAST OVER THE NEXT COUPLE DAYS...
...SIGNIFICANT HEAT WAVE CONTINUES TO EXPAND ACROSS MUCH OF THE
WESTERN AND SOUTHERN TIER OF THE U.S....
A LOW PRESSURE WAVE THAT HAD DEVELOPED ALONG A COLD FRONT
CONTINUES TO TRACK INTO QUEBEC IN CANADA THIS THURSDAY AFTERNOON.
MOIST SOUTHERLY FLOW AHEAD OF THE FRONT COMBINED WITH INSTABILITY
FROM AN APPROACHING UPPER TROUGH HAS TRIGGERED A COUPLE OF LINES
OF HEAVY SHOWERS AND EMBEDDED THUNDERSTORMS ACROSS UPSTATE NEW
YORK. THE HEAVY RAIN AND THUNDERSTORMS ARE FORECAST TO MOVE
THROUGH INTERIOR NEW ENGLAND THIS EVENING/TONIGHT OVER WHERE THE
WET GROUND IS ESPECIALLY SENSITIVE TO ADDITIONAL HEAVY RAINFALL.
A MODERATE RISK OF EXCESSIVE RAINFALL (LEVEL 3/4) IS MAINTAINED
FOR SOUTHERN VERMONT AND ADJACENT UPSTATE NEW YORK. A SEPARATE
SLIGHT RISK (LEVEL 2/4) REMAINS IN EFFECT FOR THE UPPER OHIO
VALLEY WHERE ANOTHER FOCUSED AREA OF HEAVY RAINFALL IS EXPECTED.
STRONG FLOW ALOFT AS WELL AS MODERATE INSTABILITY WILL ALSO LEAD
TO A FEW ROBUST, ORGANIZED THUNDERSTORMS CAPABLE OF LARGE HAIL,
DAMAGING WINDS, AND A COUPLE OF TORNADOES FOR THE INTERIOR
NORTHEAST/UPPER OHIO VALLEY. A SLIGHT RISK OF SEVERE WEATHER
(LEVEL 2/5) HAS BEEN ISSUED BY THE STORM PREDICTION CENTER FOR THE
REGION. THE HEAVY RAIN THREAT WILL SHIFT SLIGHTLY SOUTHEASTWARD
FRIDAY AHEAD OF THE THE SLOW-MOVING COLD FRONT WITH A SLIGHT RISK
OF EXCESSIVE RAINFALL FOR SOUTHERN NEW ENGLAND AND THE COASTAL
MID-ATLANTIC.
THE PREVAILING UPPER-LEVEL PATTERN ACROSS MAINLAND U.S. WILL
CONTINUE TO FEATURE PERIODIC INTRUSIONS OF COOL AIR FROM CENTRAL
CANADA INTO THE NORTHERN TIER STATES. THIS PATTERN WILL TEND TO
MAINTAIN BROAD TROUGHING ACROSS THE EASTERN TWO-THIRDS OF THE
COUNTRY WITH THE MAIN TROUGH AXIS EDGES TOWARD THE EAST COAST WITH
TIME AS AN ANOMALOUSLY STRONG UPPER RIDGE BUILDS OVER THE
SOUTHWEST. ROUNDS OF SHOWERS AND STORMS BETWEEN THESE SYNOPTIC
SYSTEMS WILL LIKELY CONTINUE ACROSS THE MIDSECTION OF THE COUNTRY.
HIGH MOISTURE TO THE SOUTH AND POOLING ALONG THE BOUNDARY WILL
HELP PROMOTE VERY HEAVY DOWNPOURS WITH INTENSE RAINFALL RATES AND
THE RISK OF FLASH FLOODING. THE TENDENCY FOR STORMS TO GROW
UPSCALE INTO ORGANIZED CONVECTIVE SYSTEMS WILL INCREASE THE AREAL
COVERAGE OF RAINFALL AND HEAVY RAIN TOTALS. MEANWHILE, AN ONGOING
CONVECTIVE SYSTEM WILL LIKELY PROMOTE ADDITIONAL HEAVY RAIN AND
STORMS INLAND FROM THE CENTRAL TO EASTERN GULF COAST REGION WHERE
A MODERATE RISK OF EXCESSIVE RAINFALL REMAINS IN EFFECT OVER
CENTRAL MISSISSIPPI INTO TONIGHT. A SLIGHT RISK IS IN PLACE MORE
BROADLY ACROSS THE LOWER MISSISSIPPI VALLEY TO THE CENTRAL GULF
COAST THROUGH FRIDAY WITH THE POTENTIAL MORE ORGANIZED CONVECTIVE
SYSTEMS. FURTHER WEST, MORE ISOLATED, SCATTERED STORMS ARE
EXPECTED, BUT POOLING MOISTURE AND UPSLOPE FLOW ALONG THE
FOOTHILLS OF THE SOUTHERN ROCKIES WILL PROVIDE INSTABILITY FOR
ROBUST THUNDERSTORM DEVELOPMENT LATER FRIDAY INTO EARLY SATURDAY
WITH A SLIGHT RISK OF EXCESSIVE RAINFALL INTO THE SOUTHERN HIGH
PLAINS.
MEANWHILE, A STAGNANT UPPER-LEVEL HIGH IN PLACE OVER THE
SOUTHWEST/NORTHERN MEXICO THAT HAS LED TO HOT TEMPERATURES OVER
PORTIONS OF THE SOUTHWEST AND SOUTH-CENTRAL U.S. THIS WEEK WILL
CONTINUE TO BUILD IN COVERAGE, PARTICULARLY TO THE NORTHWEST OVER
THE GREAT BASIN/CALIFORNIA/PACIFIC NORTHWEST. WIDESPREAD
HEAT-RELATED ADVISORIES AND WARNINGS ARE IN PLACE ACROSS THE
CENTRAL/SOUTHERN PLAINS AND LOWER MISSISSIPPI VALLEY AS WELL AS
PORTIONS OF THE DESERT SOUTHWEST AS A SIGNIFICANT HEATWAVE
INTENSIFIES ACROSS THE SOUTHERN TIER OF THE COUNTRY. FORECAST
HIGHS WILL BE IN THE UPPER 90S AND LOW 100S FOR LOCATIONS IN THE
EASTERN HALF OF THE PLAINS AND THE LOWER MISSISSIPPI VALLEY WHICH,
WHEN COMBINED WITH VERY HIGH HUMIDITY, WILL LEAD TO OPPRESSIVE
HEAT INDICES IN THE 110-115 DEGREE RANGE. A FRONTAL BOUNDARY AND
CONVECTIVE OUTFLOWS SLIDING INTO NORTHERN PORTIONS OF THE SOUTHERN
PLAINS/LOWER MISSISSIPPI VALLEY WILL LIKELY BRING A BIT OF RELIEF
FRIDAY. TO THE WEST, WHILE THERE WILL BE LESS HUMIDITY, AIR
TEMPERATURES WILL SOAR MUCH HIGHER INTO THE MID 100S FOR WEST
TEXAS AND NEW MEXICO AND INTO THE 110S FOR THE DESERT SOUTHWEST. A
FEW RECORD-TYING/BREAKING TEMPERATURES ARE POSSIBLE. THE HEAT WILL
BEGIN TO BUILD NORTHWARD INTO CALIFORNIA, THE GREAT BASIN, AND THE
PACIFIC NORTHWEST ON FRIDAY, WITH HIGHS INTO THE 90S AND LOW 100S.
HEAT ADVISORIES ALSO REMAIN IN EFFECT FOR SOUTH FLORIDA WHERE
RELATIVELY WARM TEMPERATURES IN THE MID-90S AND HEAT INDICES UP TO
110 CONTINUE. IN ADDITION TO THE OPPRESSIVE HEAT DURING THE DAY,
OVERNIGHT LOWS WILL REMAIN ABNORMALLY WARM, BRINGING LITTLE RELIEF
FROM THE HEAT OVERNIGHT. NUMEROUS NEAR RECORD-TYING/BREAKING WARM
LOWS ARE EXPECTED. UNFORTUNATELY, THE LONG TERM OUTLOOK THROUGH
THE WEEKEND AND INTO NEXT WEEK IS FOR AN INCREASINGLY SIGNIFICANT
AND OPPRESSIVE HEAT WAVE. IN CONTRAST, MUCH COOLER AIR FROM
CENTRAL CANADA WILL DIP FURTHER INTO THE NORTHERN PLAINS BY EARLY
SATURDAY.
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