583
FXUS02 KWBC 031814
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
214 PM EDT MON JUN 3 2024
VALID 12Z THU JUN 06 2024 - 12Z MON JUN 10 2024
...MAJOR HEATRISK EXPECTED FOR MANY AREAS IN THE WEST LATER THIS
WEEK WITH RECORD HIGH TEMPERATURES...
..OVERVIEW
BROADLY, A WESTERN UPPER RIDGE AND EASTERN UPPER TROUGH PATTERN
WILL SET UP LATER THIS WEEK THROUGH THE WEEKEND, THOUGH WEAK
TROUGHING MAY APPROACH THE WEST COAST EARLY NEXT WEEK. THE RIDGE
WILL PRODUCE POTENTIALLY HAZARDOUS HEAT ACROSS MUCH OF THE WEST
THROUGH THE END OF THE WEEK. MEANWHILE LIGHT TO MODEST RAIN IS
QUITE LIKELY IN THE EAST THURSDAY INTO THE WEEKEND IN THE
NORTHEASTERN U.S. UNDERNEATH THE TROUGH AND A SLOWLY-MOVING UPPER
LOW, WHERE TEMPERATURE WILL BE NEAR TO SLIGHTLY BELOW AVERAGE.
ADDITIONALLY, THE FORECAST PATTERN SHOULD SUPPORT INCREASING
COVERAGE AND INTENSITY OF SHOWERS/STORMS OVER THE CENTRAL OR SOUTH-
CENTRAL ROCKIES AND PLAINS AS SYSTEMS RIDE THE RIDGE THROUGH MUCH
OF THE FORECAST PERIOD.
..GUIDANCE/PREDICTABILITY ASSESSMENT
WHILE MODEL GUIDANCE IS GENERALLY AGREEABLE IN SHOWING THE WESTERN
RIDGE/EASTERN TROUGH PATTERN IN SOME FASHION, DIFFERENCES IN THE
DETAILS WILL IMPACT SENSIBLE WEATHER ACROSS THE LOWER 48. THE FIRST
CONCERN IS THE DEPTH OF THE TROUGH/UPPER LOW EXTENDING SOUTH AND
EAST FROM THE ANCHORING UPPER LOW NEAR THE GREAT LAKES. DYNAMICAL
AND AI/MACHINE LEARNING (ML) MODELS HAVE DIFFERED IN THE LOW/TROUGH
POSITION AND DEPTH; NAMELY, MANY ML MODELS INDICATED A FARTHER
SOUTH OR SOUTHWEST CENTROID OF THE UPPER LOW AND THUS THE RESULTANT
TROUGH'S SOUTHERN EXTENT COMPARED TO THE DYNAMICAL MODELS. ASPECTS
OF THE PATTERN AFFECTING THE UPPER LOW INCLUDE RIDGING TO THE
NORTH AND EAST OVER HUDSON BAY/NORTHERN ONTARIO (A STRONGER RIDGE
PUSHING THE UPPER LOW FARTHER SOUTH) AND THE ULTIMATE EVOLUTION OF
A DEVELOPING WEST-CENTRAL CANADA UPPER LOW THAT STILL SHOWS
CONSIDERABLE SPREAD IN THE GUIDANCE (DETERMINISTIC MODELS WERE MUCH
SLOWER TO RAISE HEIGHTS COMPARED TO THE ENSEMBLE MEANS). CONTINUED
TO FAVOR A SLIGHTLY DEEPER LOW OVER THE NORTHEAST THAN THE
ENSEMBLE MEANS, WHICH WAS GENERALLY A BLEND OF THE
GFS/ECMWF/UKMET/CANADIAN DETERMINISTIC MODELS. SPREAD AND THUS
UNCERTAINTY CONTINUED TO GROW WITH WHAT BECOMES OF THE TROUGH INTO
EARLY NEXT WEEK -- I.E., HOW QUICKLY WILL THE TROUGHING DEPART AND
WILL IT BE REINFORCED FROM THE NORTHWEST. TRENDS SEEMED TO FAVOR
THE SLOWER AND LESS PROGRESSIVE SOLUTIONS.
RIDGING IN THE WEST THROUGH LATE WEEK IS AGREEABLE IN THE MODEL
GUIDANCE, THOUGH OF COURSE THE EASTERN SIDE WILL BE DEPENDENT ON
THE TROUGH'S SHAPE. MODELS SHOW A SOUTHERN STREAM UPPER LOW
NEAR/WEST OF BAJA CALIFORNIA OPENING UP AS IT APPROACHES THE
SOUTHWEST THIS WEEKEND, WITH SOME EXPECTED DETAIL DIFFERENCES BUT
WILL AT LEAST HELP DECREASE THE HEAT. MUCH FARTHER NORTH, UPPER LOW
DEVELOPMENT IN THE NORTHEAST PACIFIC FRIDAY-SATURDAY WILL EXTEND
TROUGHING SOUTH THAT APPROACHES THE WEST COAST EARLY NEXT WEEK.
DIFFERENCES WITH THIS HAVE PLAGUED THE FORECAST (ESPECIALLY
TIMING), AT LEAST PARTIALLY RELATED TO THE COMPLICATED EVOLUTION OF
THE UPPER PATTERN OVER THE GULF OF ALASKA AS TWO UPPER LOWS
EXHIBIT A FUJIWARA EVOLUTION.
OVERALL, THE WPC FORECAST FAVORED A BLEND OF THE DETERMINISTIC
MODELS EARLY IN THE FORECAST, AND ONLY GRADUALLY INCREASED THE
PROPORTION OF ENSEMBLE MEANS TO ~40% BY THE END OF THE PERIOD AS
THE SIGNAL FOR THE UPPER LOW IN THE NORTHEAST WAS FAIRLY WEEK.
..WEATHER/HAZARDS HIGHLIGHTS
ON THURSDAY, THE UPPER TROUGH AND THE SURFACE COLD FRONT WILL
SHIFT INTO THE EASTERN SEABOARD AND LEAD TO RAIN AND THUNDERSTORMS
THERE. MODEST MOISTURE INFLUX COUPLED WITH POTENTIAL FOR TRAINING
IN THE SLOWLY-EVOLVING PATTERN YIELDS A LOWER-END (MARGINAL) THREAT
OF EXCESSIVE RAINFALL OVER PARTS OF THE NORTHEAST (ESPECIALLY IN
THE TERRAIN OF NY INTO WESTERN NEW ENGLAND NEAR THE BEST
FORCING/MOISTURE PLUME AND LOWER FLASH FLOOD GUIDANCE).
UNCERTAINTIES PERSIST REGARDING THE PRECISE EVOLUTION AND TRACK OF
THE APPROACHING UPPER LOW/TROUGH WHICH WILL AFFECT THE SPEED OF THE
SURFACE FRONT AND IN TURN INTENSITY/DURATION OF HEAVIEST RAINFALL.
EVEN BEHIND THE FIRST COLD FRONT, THERE MAY BE DIURNALLY-ENHANCED
EPISODES OF RAINFALL IN THE NORTHEASTERN U.S. INTO LATE WEEK AND
NEXT WEEKEND GIVEN THE PERSISTENCE OF UPPER TROUGHING. HELD OFF
FROM ISSUING ANY MARGINAL RISK THERE FOR DAY 5/FRIDAY AS RAIN
AMOUNTS LOOK TO DECREASE COMPARED TO THURSDAY, BUT THERE IS A NON-
ZERO RISK OF FLOODING CONCERNS ESPECIALLY IF HEAVY RAIN FALLS IN
SIMILAR AREAS AS THE PREVIOUS DAY.
FARTHER WEST, SOME RETURN FLOW OF MOISTURE (INCLUDING PERHAPS
PACIFIC MOISTURE ADVECTING AROUND THE UPPER RIDGE) IS POSSIBLE
ACROSS THE SOUTHERN/CENTRAL ROCKIES AND PLAINS, WITH ONE OR MORE
SURFACE BOUNDARIES HELPING TO FOCUS SHOWERS AND THUNDERSTORMS.
PLACEMENT AND TRACK OF THIS CONVECTION EACH DAY IS RATHER UNCERTAIN
BASED ON THE SHAPE OF THE RIDGE, AS REFLECTED BY THE RELATIVELY
LOW QPF. HOWEVER, POTENTIAL EXISTS FOR MUCH HIGHER AMOUNTS AS
EVIDENCED BY THE 90TH-95TH PERCENTILE QPF. SCATTERED SHOWERS AND
STORMS MAY BEGIN THURSDAY BUT THE SIGNAL FOR THEIR EXISTENCE AND
INTENSITY IS TOO LOW TO DELINEATE ANY ERO RISK. BY DAY 5/FRIDAY,
STORMS SHOULD INCREASE IN COVERAGE AND MAGNITUDE IN THE CENTRAL
U.S., POTENTIALLY PRODUCING HEAVY RAIN. MAINTAINED A MARGINAL RISK
CENTERED OVER KANSAS/OKLAHOMA AND CLIPPING SURROUNDING STATES. THIS
IS SOMEWHAT BROAD DUE TO THE UNCERTAINTY IN PLACEMENT--NOT ALL
AREAS WITHIN MAY SEE HEAVY RAINFALL--BUT IT MAY BE ABLE TO LESSEN
IN SIZE IN FUTURE FORECASTS IF MODELS CONVERGE. ADDITIONAL ROUNDS
OF RAIN ARE LIKELY IN SOUTH- CENTRAL PARTS OF THE PLAINS AND
MISSISSIPPI VALLEY INTO THE WEEKEND, WITH RAIN CHANCES ALSO
INCREASING FOR THE SOUTHERN/CENTRAL ROCKIES AND FRONT RANGE. SOME
SCATTERED RAINFALL IS POSSIBLE LATE IN THE WEEK OVER PARTS OF THE
INTERIOR WEST/NORTHERN ROCKIES, LIKELY INCREASING IN COVERAGE EARLY
NEXT WEEK AS TROUGHING APPROACHES.
THE WESTERN RIDGE WILL PROMOTE NOTABLY/RECORD HOT TEMPERATURES
ACROSS THE WEST ESPECIALLY FOR THE LATTER PART OF THIS WEEK. HIGHS
BROADLY WILL RUN 10-20 DEGREES ABOVE AVERAGE AND LOCALLY 20+
DEGREES ABOVE AVERAGE IN THE GREAT BASIN. HIGH TEMPERATURES ABOVE
110F ARE FORECAST FOR THE DESERT SOUTHWEST (INCLUDING LAS VEGAS),
WITH 90S AND 100S STRETCHING INTO THE CENTRAL CALIFORNIA VALLEYS TO
THE GREAT BASIN TO MUCH OF TEXAS. DAILY RECORD HIGH MINIMUM AND
MAXIMUM TEMPERATURES ARE POSSIBLE, WITH THE EXPERIMENTAL HEATRISK
PRODUCT SHOWING A LARGE AREA OF MAJOR (LEVEL 3 OF 4) AND SOME
EXTREME (LEVEL 4 OF 4) OUTLINE. THE HIGHER TEMPERATURE ANOMALIES
LOOK TO SHIFT INTO THE NORTHWEST FOR THE WEEKEND WITH SOME MINOR
MODERATION OF THE TEMPERATURES IN THE SOUTHWEST AS THE WEAKENING
UPPER LOW APPROACHES FOR NORTHWESTERN MEXICO. MEANWHILE, MOST AREAS
EAST OF THE ROCKIES SHOULD TREND TO SLIGHTLY BELOW NORMAL BEHIND
THE COLD FRONT. EXCEPTIONS TO THIS TREND WILL BE TEXAS (ESPECIALLY
SOUTHERN AREAS) AND FLORIDA WHERE HIGHS SEVERAL DEGREES ABOVE
NORMAL MAY LEAD TO SOME DAILY RECORDS.
FRACASSO/TATE
ADDITIONAL 3-7 DAY HAZARD INFORMATION CAN BE FOUND ON THE WPC MEDIUM
RANGE HAZARDS OUTLOOK CHART AT:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
WPC MEDIUM RANGE 500MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,
QUANTITATIVE PRECIPITATION FORECAST (QPF), EXCESSIVE RAINFALL
OUTLOOK (ERO), WINTER WEATHER OUTLOOK (WWO) PROBABILITIES, HEAT
INDICES, AND KEY MESSAGES CAN BE ACCESSED FROM:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST500_WBG.GIF
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST_WBG_CONUS.GIF
HTTPS://WWW.WPC.NCEP.NOAA.GOV/5KM_GRIDS/5KM_GRIDSBODY.HTML
HTTPS://WWW.WPC.NCEP.NOAA.GOV/QPF/DAY4-7.SHTML
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=ERO
HTTPS://WWW.WPC.NCEP.NOAA.GOV/WWD/PWPF_D47/PWPF_MEDR.PHP?DAY=4
HTTPS://WWW.WPC.NCEP.NOAA.GOV/HEAT_INDEX.SHTML
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=OVW
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page