200
FXUS02 KWBC 091858
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
258 PM EDT TUE JUL 9 2024
VALID 12Z FRI JUL 12 2024 - 12Z TUE JUL 16 2024
...HEAVY RAIN AND FLOODING CONCERNS FOR THE EASTERN SEABOARD LINGER
INTO LATE WEEK...
..DANGEROUS HEAT WAVE IN THE WEST PERSISTS THROUGH LATE WEEK
..OVERVIEW
TROUGHING OVER THE GREAT LAKES AND A SHORTWAVE ON THE WESTERN SIDE
OF AN ATLANTIC UPPER RIDGE, AS WELL AS MOISTURE FROM WHAT WAS
BERYL AND A STALLING FRONTAL BOUNDARY, WILL ALL CONTRIBUTE TO THE
POSSIBILITY OF HEAVY RAINFALL OVER MUCH OF THE EASTERN SEABOARD ON
FRIDAY. MEANWHILE, A PERSISTENT UPPER HIGH OVER THE WEST WILL
CONTINUE TO SUPPORT A DANGEROUS HEAT WAVE THAT COULD CONTINUE TO
SET RECORDS, ESPECIALLY THROUGH LATE WEEK. THE WESTERN U.S. RIDGE
WILL DRIFT EAST AND COULD COMBINE AT TIMES WITH THE ATLANTIC RIDGE
ACROSS THE SOUTHEAST, CAUSING HEAT TO SPREAD ACROSS THE CENTRAL AND
EASTERN U.S. THIS WEEKEND AND EARLY NEXT WEEK, BUT ALLOW FOR SOME
MONSOONAL MOISTURE TO SPREAD INTO THE WEST ALONG WITH MODERATING
TEMPERATURES. TO THE NORTH OF THE UPPER RIDGE, PROGRESSIVE
SHORTWAVES MOVING ACROSS CANADA AND THE U.S. NORTHERN TIER WILL
PUSH A MEAN FRONTAL BOUNDARY INTO THE NORTHERN STATES. ACCOMPANYING
ROUNDS OF SHOWERS AND THUNDERSTORMS WILL BE POSSIBLE FROM THE
NORTH-CENTRAL U.S. TO NORTHEAST.
..GUIDANCE/PREDICTABILITY ASSESSMENT
DYNAMICAL AND MACHINE LEARNING (ML) GUIDANCE AGREES FAIRLY WELL
WITH THE LARGE SCALE PATTERN EVOLUTION DURING THE PERIOD, WITH
PRIMARY DIFFERENCES INVOLVING LOW-PREDICTABILITY SHORTWAVES WITHIN
SOUTHERN CANADA/NORTHERN TIER U.S. FLOW AND LATE-PERIOD SPECIFICS
OF ROCKIES/PLAINS UPPER RIDGING.
WITHIN THE EARLY PERIOD MEAN TROUGH OVER THE GREAT LAKES/MIDWEST,
GUIDANCE IS COMING INTO FOCUS FOR INDIVIDUAL SHORTWAVES, NAMELY A
LEADING ONE THAT PROGRESSES FROM THE GREAT LAKES THROUGH NORTHEAST
FRIDAY-SATURDAY AND FOLLOWED BY THE NEXT SHORTWAVE REACHING THE
GREAT LAKES BY EARLY SUNDAY. TO THE SOUTH OF THESE SHORTWAVES,
MODELS CONTINUE TO SHOW A STRONG ATLANTIC RIDGE (ANCHORED BY A
600+ DM HIGH NEAR 60W LONGITUDE BY FRIDAY- SATURDAY) BUILDING
ACROSS THE SOUTHERN HALF OF THE EAST.
FROM THE WEEKEND INTO EARLY NEXT WEEK, THE SOUTHEAST RIDGE MAY
WEAKEN A BIT WHILE BROADER MEAN TROUGHING DEVELOPS OVER SOUTHERN
CANADA INTO THE UPPER MIDWEST THROUGH NORTHEAST AS RIDGING DEVELOPS
OVER WESTERN CANADA. NOT SURPRISINGLY, GUIDANCE HAS VARIED SOMEWHAT
FOR SHORTWAVE DETAILS BY EARLY NEXT WEEK BUT GENERALLY SUPPORT
CANADIAN LOW PRESSURE IN SOME FORM HELPING TO PUSH A SURFACE FRONT
GRADUALLY SOUTHWARD OVER THE NORTHERN TIER U.S. AT THE MOMENT THERE
ARE NO PROMINENT CLUSTERS AMONG THE VARIOUS DYNAMICAL/ML SOLUTIONS
FOR SPECIFICS. MEANWHILE THE UPPER RIDGE OVER THE WEST SHOULD
EVENTUALLY DRIFT INTO THE CENTRAL ROCKIES AND THEN WEAKEN A BIT AS
IT EXTENDS INTO THE PLAINS. ECMWF RUNS HAVE BEEN MAINTAINING RIDGE
STRENGTH A LITTLE LONGER THAN OTHER SOLUTIONS WHILE THE MAJORITY
SUGGESTS THE GFS MAY BE A LITTLE QUICK TO SHIFT THE STRONGEST PART
OF THE RIDGE INTO THE PLAINS.
THE RELATIVE LACK OF LARGE-SCALE/HIGHER-PREDICTABILITY
DISCREPANCIES ALLOWED FOR AN OPERATIONAL MODEL COMPOSITE AMONG
00Z/06Z MODELS TO COMPRISE THE UPDATED FORECAST DURING THE FIRST
HALF OF THE PERIOD AND THEN A TRANSITION TO A MODEL/ENSEMBLE MEAN
MIX THEREAFTER. THIS APPROACH MAINTAINED THE THEME FOR THE
AGREEABLE LARGE SCALE PATTERN WHILE TEMPERING DETAILS THAT HAVE
LOWER CONFIDENCE.
..WEATHER/HAZARDS HIGHLIGHTS
SEVERAL INGREDIENTS WILL COME TOGETHER FOR HEAVY RAIN AND FLASH
FLOODING POTENTIAL ALONG THE EASTERN SEABOARD CONTINUING INTO
FRIDAY. A POSITIVELY TILTED TROUGH WITH ITS AXIS OVER THE GREAT
LAKES WILL PROVIDE LIFT IN THE RIGHT ENTRANCE REGION OF THE JET.
AMPLE MOISTURE WITH PRECIPITABLE WATER VALUES OVER 2 INCHES SHOULD
POOL NEAR A STALLING FRONT. THESE SHOULD LEAD TO THE BEST POTENTIAL
FOR HEAVY RAIN FROM THE CAROLINAS INTO THE MID-ATLANTIC AND PARTS
OF THE NORTHEAST. A SLIGHT RISK AREA IN THE DAY 4 EXCESSIVE
RAINFALL OUTLOOK REPRESENTS WHERE THE HEAVIEST RAIN IS EXPECTED,
ACROSS THE EASTERN HALF OF NORTH CAROLINA INTO THE COASTAL MID-
ATLANTIC, WITH A SURROUNDING MARGINAL RISK EXTENDING FARTHER WEST
TOWARD THE APPALACHIANS AND NORTH INTO NEW ENGLAND. SOME SHOWERS
COULD CONTINUE INTO SATURDAY ALONG THE EASTERN SEABOARD BUT THE
HEAVIEST RAINFALL SHOULD BE OVER BY THEN. POCKETS OF LINGERING
MODERATE TO HEAVY RAIN MAY FOCUS OVER EASTERN NORTH CAROLINA BUT
THE SANDY SOILS DO NOT MAKE THE REGION TOO SUSCEPTIBLE TO FLOODING,
THUS NO MARGINAL RISK AREA HAS BEEN DEPICTED. HOWEVER, EXPECT
SCATTERED SHOWER AND THUNDERSTORM CHANCES TO CONTINUE AND EXPAND
THROUGH THE SOUTHEAST OVER THE WEEKEND INTO EARLY NEXT WEEK. AN
AREA OF ANOMALOUS MOISTURE MOVING INTO FLORIDA FROM THE EAST MAY
ALSO SUPPORT SOME LOCALLY HEAVY CONVECTION BUT WITH LOW-
PREDICTABILITY SMALL SCALE UPPER LEVEL FEATURES LIKELY PLAYING A
ROLE AS WELL, TEMPERING CONFIDENCE IN SPECIFICS.
BY FRIDAY NIGHT THROUGH THE WEEKEND, THE COMBINATION OF NORTHERN
TIER U.S./SOUTHERN CANADA SHORTWAVES AND A COUPLE SURFACE FRONTS
MAY PROMOTE ONE OR MORE CLUSTERS OF SHOWERS/STORMS FROM THE UPPER
MIDWEST INTO THE GREAT LAKES. GUIDANCE SIGNALS FOR THIS ACTIVITY
ARE NOT COHERENT ENOUGH IN TERMS OF MAGNITUDE AND LOCATION FOR A
MARGINAL RISK AREA IN THE EROS YET, BUT MUCH OF THIS REGION WILL BE
SENSITIVE TO ANY HEAVY RAINFALL SO FUTURE MODEL TRENDS/CLUSTERING
WILL REQUIRE MONITORING. EXPECT THIS ACTIVITY TO PROGRESS INTO THE
APPALACHIANS/NORTHEAST BY EARLY NEXT WEEK.
FARTHER WEST, SOME MOISTURE WILL FEED INTO THE FOUR CORNERS STATES
IN A MONSOONAL PATTERN, ESPECIALLY OVER THE WEEKEND AND BEYOND AS
THE UPPER RIDGE FINALLY WEAKENS SOME AND DRIFTS EAST. A NONZERO
CHANCE FOR HEAVY RAIN TO CAUSE FLASH FLOODING IS POSSIBLE ACROSS
ARIZONA IN PARTICULAR ON FRIDAY, BUT THE BETTER MOISTURE ARRIVING
SATURDAY SUPPORTS MAINTAINING A MARGINAL RISK FOR DAY 5 OVER
PORTIONS OF THE FOUR CORNERS STATES. THIS MOISTURE PLUME LOOKS TO
EXPAND FARTHER NORTH INTO EARLY NEXT WEEK FOR INCREASING
RAIN/THUNDERSTORM CHANCES FOR THE ROCKIES TO HIGH PLAINS.
THE WEST WILL CONTINUE TO SEE A MAJOR TO EXTREME AND LONG-LIVED
HEAT WAVE THROUGH LATE THIS WEEK. HIGHS EXCEEDING 110F SHOULD BE
WIDESPREAD IN THE DESERT SOUTHWEST. FARTHER NORTH, HIGHS INTO THE
100S ARE FORECAST INTO THE INTERMOUNTAIN WEST AS TEMPERATURES SOAR
10-20F ABOVE NORMAL. NUMEROUS DAILY RECORDS ARE LIKELY TO BE BROKEN
DURING THIS HEAT WAVE, WITH MONTHLY/ALL-TIME RECORDS NOT OUT OF
THE QUESTION. THE PROLONGED NATURE OF THE HEAT WAVE AND RECORD WARM
OVERNIGHT TEMPERATURES WILL INCREASE HEAT STRESS. EXPECT THE WEST
TO SEE SOME MODERATION OF TEMPERATURES CLOSER TO (BUT STILL ABOVE)
NORMAL BY THE WEEKEND AND EARLY NEXT WEEK. HIGHS OVER THE NORTHERN
HALF OF THE REGION MAY STILL BE 5-12F ABOVE NORMAL THROUGH TUE
WHILE THE MONSOONAL MOISTURE MAY HELP DESERT SOUTHWEST HIGHS TO
DECLINE TO WITHIN A FEW DEGREES OF NORMAL. MEANWHILE THE WARMER
THAN AVERAGE TEMPERATURES WILL BE SPREADING FARTHER EAST INTO THE
NORTHERN AND CENTRAL PLAINS LATE THIS WEEK/WEEKEND, AND INTO THE
MIDWEST AND EAST THIS WEEKEND INTO EARLY NEXT WEEK. BEST POTENTIAL
FOR SOME AREAS OF PLUS 10-15F ANOMALIES WILL BE OVER THE PLAINS.
RAUSCH/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
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