294
FXUS02 KWBC 090710
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
310 AM 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, ALL WILL 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 WEST 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
MODERATION OF TEMPERATURES AND SOME MONSOONAL MOISTURE TO SPREAD
INTO THE WEST. TO THE NORTH OF THE UPPER RIDGE, PROGRESSIVE
SHORTWAVES WILL MOVE ACROSS CANADA AND THE U.S. NORTHERN TIER FOR
SOME ROUNDS OF RAIN IN THE NORTH-CENTRAL U.S. TO NORTHEAST.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODEL GUIDANCE IS REASONABLY AGREEABLE IN DEPICTING THE OVERALL
PATTERN, BUT WITH MORE SPREAD IN THE DETAILS ESPECIALLY AS QUASI-
ZONAL FLOW BEGINS TO PREVAIL WITH ROUNDS OF SMALLER-SCALE
SHORTWAVES MOVING THROUGH THE NORTHERN TIER. AS THE PERIOD BEGINS,
THE GREAT LAKES TO OHIO VALLEY TROUGH SEEMS WELL HANDLED BY A
DETERMINISTIC MODEL BLEND. GUIDANCE CONTINUES TO SHOW STEADY
WEAKENING OF THE GREAT LAKES/MIDWEST UPPER TROUGH INTO EARLY
SATURDAY AS STRONG ATLANTIC RIDGING (ANCHORED BY A 600+ DM HIGH
NEAR 60W LONGITUDE BY FRIDAY-SATURDAY) BUILDS INTO PARTS OF THE
EAST. MEANWHILE THE UPPER HIGH IN THE WEST SHOWS GOOD AGREEMENT IN
DRIFTING EASTWARD AND AT TIMES PERHAPS JOINING WITH THE WESTERN
PART OF THE ATLANTIC RIDGE. THERE IS SOME MODEL DISAGREEMENT IN HOW
MUCH/WHEN THE UPPER HIGH WEAKENS EARLY NEXT WEEK, WITH THE EC
SLOWER TO WEAKEN THAN OTHER GUIDANCE. WEAK TROUGHING COULD SET UP
IN THE EASTERN PACIFIC TO THE WEST OF THE RIDGE. BUT THE PRIMARY
MODEL DIFFERENCES ARE WITH SHORTWAVES ALONG THE NORTHERN SIDE OF
THE RIDGE. THESE ARE LOWER PREDICTABILITY AND ALSO AFFECT SURFACE
LOW/FRONTAL SYSTEMS. THE NEWER 00Z GUIDANCE CONTINUES TO SHOW
SPREAD WITH BROAD BUT SHALLOW TROUGHING IN THE GREAT LAKES TO
NORTHEAST EARLY NEXT WEEK, NOT REACHING AS FAR SOUTH AS THE 12/18Z
CYCLE, AND SHOWING A WEAKER SURFACE LOW IN SOUTHERN CANADA.
THE WPC FORECAST WAS BASED ON A BLEND OF THE DETERMINISTIC
GUIDANCE EARLY IN THE PERIOD, FAVORING THE 18Z GFS AND 12Z ECMWF.
INCLUDED THE GEFS AND EC ENSEMBLE MEANS FROM DAY 5 ONWARD, BUT WAS
ABLE TO MAINTAIN MAJORITY DETERMINISTIC GUIDANCE, WITH SOME
INCLUSION OF THE MEANS AND THE BLENDING PROCESS SERVING TO LESSEN
TOO MUCH INFLUENCE ON THE SMALLER MODEL DIFFERENCES.
..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. HEAVY RAIN IS FORECAST FROM THE
CAROLINAS INTO THE MID-ATLANTIC AND PARTS OF THE NORTHEAST. A
SLIGHT RISK IS IN PLACE WHERE THE HEAVIEST RAIN IS EXPECTED, ACROSS
THE EASTERN HALF OF NORTH CAROLINA INTO THE COASTAL MID-ATLANTIC,
WITH A MARGINAL SURROUNDING 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; LINGERING MODERATE TO HEAVY RAIN LOOKS TO
FOCUS PERHAPS IN EASTERN NORTH CAROLINA WHERE SANDY SOILS DO NOT
MAKE THE REGION TOO SUSCEPTIBLE TO FLOODING. HOWEVER, EXPECT
SCATTERED SHOWER AND THUNDERSTORM CHANCES TO CONTINUE AND EXPAND
THROUGH THE SOUTHEAST OVER THE WEEKEND INTO EARLY NEXT WEEK.
ADDITIONALLY, FRONTAL SYSTEMS AND SHORTWAVES WILL PROVIDE SUPPORT
FOR ROUNDS OF RAIN ACROSS THE UPPER MIDWEST TO GREAT LAKES AND
NORTHEAST, WITH SOME MODEL SPREAD FOR AMOUNTS AND TIMING DETAILS.
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 HAS PROMPTED A MARGINAL RISK FOR DAY 5 FOR 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. SOME MODERATION
OF THE TEMPERATURES CLOSER TO NORMAL (BUT STILL A BIT ABOVE) IS
FINALLY FORECAST IN THE DESERT SOUTHWEST OVER THE WEEKEND INTO
EARLY NEXT WEEK. 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.
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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