116
FXUS02 KWBC 061904
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
304 PM EDT SAT JUL 6 2024
VALID 12Z TUE JUL 09 2024 - 12Z SAT JUL 13 2024
...BERYL WILL SPREAD HEAVY RAINFALL ACROSS THE SOUTH-CENTRAL U.S.
AS IT TRANSITIONS TO POST-TROPICAL...
..DANGEROUS HEAT WAVE IN THE WEST PERSISTS INTO NEXT WEEK
..OVERVIEW
THE MOST PROMINENT LARGE SCALE FEATURES DURING THE PERIOD WILL BE
A PERSISTENT UPPER RIDGE OVER THE WEST SUPPORTING A DANGEROUS AND
LIKELY RECORD-SETTING HEAT WAVE ACROSS MUCH OF THE REGION INTO NEXT
WEEK, AND A POSITIVELY TILTED PLAINS/MISSISSIPPI VALLEY/GREAT
LAKES MEAN TROUGH WHOSE SOUTHERN PERIPHERY WILL INTERACT WITH BERYL
AS IT TRANSITIONS TO POST-TROPICAL. HEAVY RAIN IS LIKELY TO SPREAD
FROM EASTERN TEXAS NORTHEASTWARD INTO MIDWEEK AND BEYOND AS
BERYL'S LOW PRESSURE AND MOISTURE INTERACT WITH A FRONTAL BOUNDARY.
MEANWHILE, SEASONABLY HOT AND HUMID CONDITIONS ALONG WITH
SCATTERED THUNDERSTORMS AT TIMES SHOULD PERSIST ACROSS THE
SOUTHEAST TO EAST COAST.
..GUIDANCE/PREDICTABILITY ASSESSMENT
GUIDANCE CONTINUES TO HAVE DIFFICULTY WITH THE FORECAST OF BERYL,
AS THERE IS CONSIDERABLE SENSITIVITY TO EXACTLY HOW THE
MIDWEST/GREAT LAKES INTO PLAINS UPPER TROUGH INTERACTS WITH THE
SYSTEM. AMONG THE DYNAMICAL MODELS, THE ICON HAS CONSISTENTLY BEEN
A FAST/NORTHEAST EXTREME WHILE RECENT GFS RUNS HAVE BEEN ON THE
SLOW SIDE AND TENDING TO WEAKEN THE SURFACE REFLECTION MORE THAN
OTHER GUIDANCE. RESPECTIVELY, THESE EXTREMES CORRESPOND TO RAPID
PHASING OF TROUGH ENERGY WITH BERYL VERSUS WEAKENING THE SHORTWAVE
ENERGY AND/OR RELUCTANCE TO SHOW MUCH PHASING. THE NEW 12Z GFS HAS
AT LEAST TRENDED FASTER INTO MIDWEEK BUT THEN STILL BECOMES
SUPPRESSED/DIFFUSE THEREAFTER (THOUGH THE NEW 12Z CMC ALSO TRENDS
MORE SUPPRESSED). MEANWHILE THE 00Z ECMWF-INITIALIZED MACHINE
LEARNING (ML) MODELS FAVOR A FAIRLY PROGRESSIVE EVOLUTION, WITH
FOUR OUT OF FIVE MLS CLUSTERED BETWEEN THE ICON AND SLOWER
REMAINDER OF DYNAMICAL MODELS. BY EARLY THURSDAY THE NEW 12Z UKMET
HAS ADJUSTED CONSIDERABLY FASTER THAN ITS 00Z RUN TO BE CLOSER TO
THE ML CLUSTER, THOUGH IT MAY STRAY A LITTLE TOO FAR EAST WITH ITS
UPPER TROUGH AXIS.
MEANWHILE THERE ARE STILL LOWER-PREDICTABILITY DIFFERENCES FOR
EASTERN CANADA UPPER TROUGHING THAT BRUSHES THE GREAT LAKES/NEW
ENGLAND TUESDAY-THURSDAY, WITH RESULTING EFFECTS ON ONE OR MORE
SURFACE FRONTS. IN VARYING WAYS, MOST GUIDANCE SUGGESTS THAT GREAT
LAKES INTO PLAINS/MISSISSIPPI VALLEY UPPER TROUGHING SHOULD PERSIST
INTO SATURDAY BUT WITH A GRADUAL WEAKENING TREND. THIS WILL OCCUR
AS STRONG ATLANTIC RIDGING (ANCHORED BY A 600+ DM HIGH OVER 50-65W
LONGITUDE BY FRIDAY-SATURDAY) BUILDS INTO PARTS OF THE EAST. A
MODEST UPPER WEAKNESS (WITH PREDICTABILITY LOW ENOUGH NOT TO
REFLECT YET IN A DETERMINISTIC FORECAST BY SATURDAY) COULD
APPROACH THE EAST COAST FROM THE ATLANTIC ON THE WESTERN PERIPHERY
OF THE RIDGE. A COMPOSITE OF MODEL/ENSEMBLE GUIDANCE APPEARS
REASONABLE FOR AFOREMENTIONED TROUGHING AND THE RETROGRADING
ATLANTIC RIDGE.
ASIDE FROM TYPICAL DETAIL DIFFERENCES, DYNAMICAL/ML GUIDANCE SHOWS
GOOD AGREEMENT WITH EASTWARD DRIFT OF THE WESTERN U.S. RIDGE FROM
CALIFORNIA/NEVADA INTO THE FOUR CORNERS REGION OVER THE COURSE OF
THE PERIOD. HOWEVER AROUND THE TOP OF THE RIDGE THERE HAS BEEN A
FAIR AMOUNT OF SPREAD AND RUN-TO-RUN VARIABILITY FOR NORTHEAST
PACIFIC INTO WESTERN CANADA DYNAMICS WEDNESDAY ONWARD. THE MOST
COMMON THEME IS FOR THIS ENERGY TO BE SLOWER TO CROSS SOUTHERN
CANADA VERSUS THE 06Z GFS BY LATE WEEK, AND THE 12Z GFS HAS INDEED
TRENDED FAVORABLY TOWARD OTHER GUIDANCE.
WITH THE GFS LEAST PREFERRED FOR THE DEPICTION OF BERYL, THE
EARLY-PERIOD MODEL BLEND BASED ON 00Z/06Z GUIDANCE STARTED WITH A
MORE EVEN WEIGHT OF THE ECMWF/UKMET/CMC/GFS THAN WOULD TYPICALLY BE
THE CASE. THE LATTER PART OF THE FORECAST GRADUALLY INCORPORATED
SOME OF THE 06Z GEFS/00Z ECENS MEANS. THE QPF ASSOCIATED WITH BERYL
CONSISTED OF MORE 00Z ECMWF/UKMET/CMC INPUT (BUT TEMPERING MAX
AMOUNTS DUE TO ONGOING UNCERTAINTY) TO REFLECT AN EVOLUTION CLOSE
TO THE OFFICIAL NATIONAL HURRICANE CENTER TRACK.
..WEATHER/HAZARDS HIGHLIGHTS
BY THE START OF THE MEDIUM RANGE PERIOD EARLY TUESDAY, THE 15 UTC
NHC ADVISORY SHOWS BERYL WEAKENING TO A TROPICAL DEPRESSION OVER
EASTERN TEXAS. THEN BERYL SHOULD QUICKLY PHASE WITH AN UPPER
TROUGH AND SURFACE FRONT TO THE NORTH. THESE FEATURES SHOULD LEAD
TO THE POTENTIAL FOR HEAVY RAIN CAUSING FLASH FLOODING CONCERNS
OVER SOME AREAS FROM EASTERN TEXAS NORTHEASTWARD THROUGH TUESDAY-
WEDNESDAY. GENERALLY FASTER MODEL TRENDS FOR BERYL CONTINUE TO
FAVOR SOMEWHAT OF AN EASTWARD SHIFT IN THE SLIGHT RISK AREA
DEPICTED IN THE DAY 4 EXCESSIVE RAINFALL OUTLOOK. WITHIN THE SLIGHT
RISK AREA, THERE IS AN IMPROVING SIGNAL TOWARD THE BEST HEAVY RAIN
POTENTIAL BEING CENTERED OVER A MAJORITY OF ARKANSAS. POOR MODEL
BEHAVIOR FOR THIS SYSTEM SO FAR, AND STILL A LOT OF SPREAD,
PRECLUDE INTRODUCTION OF A MODERATE RISK AREA AT THIS POINT. THEN
THE DAY 5 ERO INTRODUCES A LOWER-CONFIDENCE SLIGHT RISK AREA OVER
AND NEAR THE LOWER OHIO VALLEY TO REFLECT THE HEAVY RAINFALL
POTENTIAL ASSOCIATED WITH THE OFFICIAL TRACK OF BERYL. A MUCH
BROADER MARGINAL RISK AREA SURROUNDS THE SLIGHT RISK, WITH
INGREDIENTS FOR ISOLATED FLASH FLOODING LIKE ABOVE NORMAL MOISTURE
FORECAST TO BE IN PLACE ACROSS THE SOUTH-CENTRAL U.S. AND
NORTHEASTWARD INTO THE MID-ATLANTIC AND PARTS OF NEW ENGLAND.
INTERACTION OF MOISTURE AHEAD OF BERYL AND A FRONT SETTLING OVER
THE MID-ATLANTIC/SOUTHERN NEW ENGLAND MAY FAVOR ANOTHER AREA OF
HEAVY RAINFALL POTENTIAL (AND POSSIBLE RISK UPGRADE) OVER THIS
REGION.
LEADING INTO THIS MIDWEEK SETUP, UPPER TROUGHING PUSHING ONE OR
MORE COLD FRONTS ACROSS THE NORTHEASTERN U.S. WILL ALSO LEAD TO
SOME THUNDERSTORM CHANCES. SOME FOCUS OF THE CONVECTIVE RAIN AHEAD
OF THE FRONT(S) AND SUFFICIENT INSTABILITY FOR HEAVY RAIN RATES IN
THE NORTHERN MID-ATLANTIC TO NORTHEAST FAVOR MAINTENANCE OF A
MARGINAL RISK IN THE ERO FOR DAY 4/TUESDAY. PERSISTENT MOIST
CONDITIONS WILL PROMOTE SCATTERED STORMS CONTINUING THROUGH
LATE WEEK ACROSS THE SOUTHEAST/CAROLINAS AND INTO THE MID-
ATLANTIC. THE DAY 4 ERO INTRODUCES A MARGINAL RISK AREA OVER PARTS
OF THE FAR SOUTHEAST/FLORIDA PENINSULA GIVEN ABUNDANT MOISTURE AND
SOME MODEL SIGNALS FOR LOCALLY HEAVY RAINFALL. FARTHER WEST, SOME
MOISTURE MAY FEED INTO THE FOUR CORNERS STATES IN A MONSOONAL
PATTERN. MARGINAL RISKS ARE IN PLACE FOR TUESDAY AND WEDNESDAY
MAINLY FOR NEW MEXICO--ESPECIALLY CONSIDERING SENSITIVITIES DUE TO
BURN SCARS AND AREAS THAT HAVE SEEN AMPLE RAINFALL RECENTLY.
THE WEST WILL CONTINUE TO SEE A MAJOR TO EXTREME AND LONG-LIVED
HEAT WAVE INTO NEXT WEEK. HIGHS EXCEEDING 110F SHOULD BE WIDESPREAD
IN THE DESERT SOUTHWEST, WITH TYPICALLY HOTTER LOCATIONS EXCEEDING
120F. FARTHER NORTH, HIGHS INTO THE 100S ARE FORECAST INTO OREGON
AND WASHINGTON AND EAST INTO THE INTERMOUNTAIN WEST, AS
TEMPERATURES SOAR 10-20F ABOVE NORMAL WITH LOCALLY HIGHER
ANOMALIES. 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. THE PACIFIC
NORTHWEST LOOKS TO MODERATE CLOSER TO NORMAL LATER WEEK WITH
POSSIBLE TROUGHING ALOFT, BUT INTERIOR AREAS AND EXPANDING INTO THE
NORTH-CENTRAL U.S. WILL BE ABOVE NORMAL. MEANWHILE, WARMER THAN
AVERAGE HIGH TEMPERATURES IN THE NORTHEAST TUESDAY SHOULD MODERATE
BY MIDWEEK BUT THE FORECAST PATTERN MAY KEEP MORNING LOWS 5-10F
ABOVE NORMAL INTO NEXT WEEKEND. THE SOUTHEAST CAN EXPECT NEAR
NORMAL HEAT FOR THIS TIME OF YEAR--WHICH IS STILL HOT AND HUMID.
THE SOUTH-CENTRAL U.S. SHOULD SEE SOME MINOR HEAT RELIEF THROUGH
THURSDAY OR SO WITH BELOW AVERAGE TEMPERATURES GIVEN THE CLOUDS AND
RAIN CHANCES.
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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