575
FXUS02 KWBC 050701
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 AM EDT WED JUL 05 2023
VALID 12Z SAT JUL 08 2023 - 12Z WED JUL 12 2023
...SOUTHERN TIER HEAT EXPECTED TO REBUILD OVER THE SOUTHERN
ROCKIES/PLAINS DURING THE WEEKEND AND PERSIST INTO NEXT WEEK...
...HEAVY RAIN/RUNOFF CONCERNS LIKELY TO FOCUS OVER PORTIONS OF THE
SOUTH-CENTRAL PLAINS INTO TENNESSEE/LOWER OHIO VALLEYS AND THEN
POSSIBLY INTO PARTS OF THE EAST SATURDAY THROUGH AT LEAST SUNDAY
NIGHT...
..OVERVIEW
THE UPPER LEVEL PATTERN SHOULD GRADUALLY AMPLIFY FROM THE WEEKEND
INTO THE MIDDLE OF NEXT WEEK, AS MEAN TROUGHING BECOMES MORE
ESTABLISHED OVER THE EASTERN HALF OF THE COUNTRY DOWNSTREAM FROM A
STRENGTHENING SOUTHERN ROCKIES UPPER HIGH AND RIDGE EXTENDING TO
ITS NORTH/NORTHWEST. WITHIN THE MEAN TROUGH THAT EXTENDS INTO
CENTRAL CANADA, A RATHER DEEP UPPER LOW MAY DESCEND AT LEAST AS
FAR SOUTH AS NORTHERN ONTARIO. MEANWHILE EXPECT WEAK TROUGHING TO
PERSIST ALONG OR OFFSHORE THE NORTHWEST COAST BUT WITH A LOT OF
UNCERTAINTY FOR THE EMBEDDED DETAILS. THE FORECAST PATTERN
EVOLUTION WILL LIKELY LEAD TO AN ACTIVE PERIOD OF SHOWER AND
THUNDERSTORM ACTIVITY ACROSS MULTIPLE AREAS EAST OF THE ROCKIES
ALONG WITH HOTTER THAN AVERAGE TEMPERATURES PERSISTING OVER THE
SOUTHERN ROCKIES/PLAINS THROUGH THE PERIOD AND POSSIBLY EXPANDING
INTO THE SOUTHWEST BY EARLY NEXT WEEK.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
THE MODELS AND ENSEMBLES CONTINUE TO SHOW GOOD AGREEMENT FOR THE
OVERALL PATTERN EVOLUTION BUT THERE HAVE BEEN ONGOING SHORTWAVE
DETAIL UNCERTAINTIES (HAVING LOW PREDICTABILITY DUE TO THEIR
SMALLER SCALE) THAT HAVE BEEN CAUSING DIFFICULTY IN RESOLVING
SPECIFICS OF INDIVIDUAL SURFACE WAVES/FRONTAL SYSTEMS (AND
CONVECTIVE EPISODES) TO THE EAST OF THE ROCKIES. SOMEWHAT LARGER
SCALE DIFFERENCES BECOME MORE APPARENT OVER THE EAST BY AROUND
DAYS 4-5 SUNDAY-MONDAY AS LATEST CMC RUNS SHOW GREATER UPPER
TROUGH AMPLITUDE THAN OTHER GUIDANCE WHILE THE UKMET HAS BEEN ON
THE OTHER SIDE OF THE SPECTRUM WITH A SLOWER EASTWARD ADVANCE OF
HEIGHT FALLS. SENSITIVITY OF SURFACE DETAILS TO SHORTWAVE
SPECIFICS HAS LED TO SOME UNAVOIDABLE CONTINUITY ADJUSTMENTS FOR
SOME SURFACE DETAILS IN RECENT RUNS. MEANWHILE, MODEL TRENDS AND
CONTINUITY ARE STEADILY INCREASING CONFIDENCE IN THE IDEA OF A
RATHER DEEP UPPER LOW OVER CANADA DROPPING DOWN AT LEAST AS FAR AS
NORTHERN ONTARIO BY EARLY NEXT WEEK. IN LATEST RUNS, THE NEW 00Z
CMC IS A SOUTHERN EXTREME AS IT TRACKS THE UPPER LOW OVER LAKE
SUPERIOR BY DAY 7 WEDNESDAY WHILE THE 00Z GFS SHOWS A TRACK JUST A
LITTLE FARTHER NORTH A DAY OR TWO LATER. IN RECENT DAYS THE
OPERATIONAL GFS/ECMWF RUNS HAVE GENERALLY BEEN LEADING THE
ENSEMBLE MEANS A BIT OVERALL, THOUGH WITH TYPICAL VARIABILITY IN
EXACT UPPER LOW TRACK AND SHAPE OF THE OVERALL CIRCULATION. THE
UPPER TROUGH NEAR THE PACIFIC NORTHWEST COAST SHOULD BE COMPRISED
OF MULTIPLE SMALLER SCALE FEATURES, INCLUDING AN INITIAL VANCOUVER
ISLAND LOW, A SEPARATE COMPACT FEATURE THAT TRACKS IN FROM THE
SOUTHWEST, AND THEN ADDITIONAL ENERGY ARRIVING FROM FARTHER
UPSTREAM.
BASED ON THE ARRAY OF 12Z/18Z GUIDANCE AVAILABLE FOR THE UPDATED
FORECAST, THE STARTING BLEND USED AN OPERATIONAL MODEL COMPOSITE
FOR DAYS 4-5 SATURDAY-SUNDAY WITH GREATER EMPHASIS ON THE
GFS/ECMWF RELATIVE TO THE CMC/UKMET. THE CMC DIVERGED ENOUGH FROM
OTHER GUIDANCE OVER THE EAST BY DAY 5 MONDAY TO FAVOR EXCLUDING IT
FROM THE FORECAST MID-LATE PERIOD. THE FORECAST INCORPORATED
30-40 PERCENT TOTAL WEIGHT OF THE 18Z GEFS/12Z ECENS MEANS BY DAYS
6-7 TUESDAY-WEDNESDAY TO MITIGATE SOME OF THE DETAIL DIFFERENCES
THAT DEVELOP FARTHER OUT IN TIME.
..WEATHER/HAZARDS HIGHLIGHTS
THE BROAD CYCLONIC FLOW OVER THE EASTERN HALF TO TWO-THIRDS OF THE
COUNTRY WITH EMBEDDED SHORTWAVES WILL PROMOTE AN ACTIVE PERIOD FOR
SHOWERS AND THUNDERSTORMS. DURING THE DAYS 4-5 PERIOD COVERING
SATURDAY THROUGH SUNDAY NIGHT, THE MOST PROMINENT FOCUS FOR
EPISODES OF STRONG AND HEAVY CONVECTION SHOULD EXTEND OVER PARTS
OF THE SOUTH-CENTRAL PLAINS INTO THE TENNESSEE/OHIO VALLEYS WITH A
COMBINATION OF ONE OR MORE SURFACE WAVES/FRONTS, UPPER SHORTWAVES,
ALONG WITH FAVORABLE MOISTURE/INSTABILITY. BOTH DAYS OF EXCESSIVE
RAINFALL OUTLOOKS DEPICT A SLIGHT RISK AREA OVER PARTS OF THIS
OVERALL REGION. MODEL/ENSEMBLE PROBABILITY GUIDANCE CLUSTERS
FAIRLY WELL FOR THE CENTRAL/EASTERN PART OF THE DAY 4 SLIGHT RISK
AND MOST OF THE DAY 5 SLIGHT RISK, WHILE ON DAY 4 THE 00Z
GFS/UKMET/CMC OFFER A DEVELOPING CLUSTER HINTING AT A BAND OF
HEAVY RAINFALL POTENTIAL ALONG A MOISTURE/INSTABILITY AXIS
EXTENDING BACK THROUGH THE SOUTH-CENTRAL PLAINS. MEANWHILE ON DAY
5, THE LATEST GFS/ECMWF RUNS AND THEIR CORRESPONDING ENSEMBLES
OFFER THE BEST CLUSTERING FOR HEAVY RAINFALL POTENTIAL FROM THE
NORTHERN MID-ATLANTIC INTO PARTS OF THE NORTHEAST WITH A
SHORTWAVE/SURFACE SYSTEM THAT MAY PROVIDE A FAIRLY PRONOUNCED
MOISTURE FOCUS. THE CMC/UKMET DIFFER WITH THEIR SHORTWAVE/QPF
DETAILS SO CONFIDENCE IN THE SPECIFICS IS A BIT LOWER THAN OVER
SOME AREAS FARTHER WEST. ONE AREA THAT MAY BE WORTH MONITORING
FOR A MARGINAL RISK ON DAY 5 MAY BE OVER NORTHERN MINNESOTA INTO
THE UPPER GREAT LAKES, AS GUIDANCE SUGGESTS DEVELOPMENT OF
CONVECTION FROM A COMBINATION OF A WEAKENING STALLED FRONT NEAR
THE AREA AND THEN A STRONGER FRONT DROPPING SOUTH FROM CANADA.
POTENTIAL EAST-WEST ORIENTATION OF ENHANCED RAINFALL COULD BE AN
ISSUE, BUT GUIDANCE DIFFERS ON THE SPECIFICS AND MOST OF THIS AREA
HAS HAD BELOW AVERAGE RAINFALL OVER THE PAST COUPLE WEEKS WITH
MINIMAL TOTALS EXPECTED IN THE SHORT RANGE. THUS WILL WAIT FOR
IMPROVED CLUSTERING IN LOCATION/AMOUNTS BEFORE DEPICTING AN AREA.
AFTER EARLY MONDAY, EXPECT THE POTENTIALLY HEAVY RAINFALL OVER THE
NORTHEAST TO CONTINUE PROGRESSING THROUGH THE REGION WHILE
SOUTH-CENTRAL U.S. CONVECTION MAY DROP TOWARD THE EASTERN HALF OF
THE GULF COAST. THE FRONT DROPPING INTO THE NORTHERN TIER BY
MONDAY SHOULD PUSH SOUTHWARD WITH TIME AND MAY SERVE AS A FOCUS
FOR SHOWERS/STORMS THROUGH MIDWEEK. MOST OF THE WEST SHOULD
REMAIN DRY THROUGH THE PERIOD.
THE STRENGTHENING SOUTHERN ROCKIES/HIGH PLAINS RIDGE, WHICH MAY
DRIFT A BIT WEST WITH TIME, WILL LIKELY EXPAND COVERAGE OF
HAZARDOUS HEAT ACROSS THE SOUTHERN TIER DURING THE FORECAST
PERIOD. EXPECT THE GREATEST TEMPERATURE ANOMALIES OF PLUS 10-13F
FOR HIGHS TO BE NEAR THE UPPER HIGH CENTER (WESTERN TEXAS AND
SOUTHEASTERN NEW MEXICO) WITH BROADENING COVERAGE OF HIGHS AT
LEAST A FEW DEGREES ABOVE NORMAL ELSEWHERE, INCLUDING INTO THE
SOUTHWEST BY THE START OF NEXT WEEK. LIKEWISE, EXPECT GRADUALLY
INCREASING COVERAGE OF MAXIMUM HEAT INDEX VALUES REACHING 110F OR
GREATER OVER SOUTHERN/EASTERN TEXAS INTO THE LOWER MISSISSIPPI
VALLEY, WHILE LOWER HUMIDITY WILL LEAD TO MAXIMUM HEAT INDEX
VALUES OVER THE SOUTHWEST NEAR OR SLIGHTLY BELOW THE EXPECTED AIR
TEMPERATURES REACHING UP TO 110-115F FROM LATE WEEKEND ONWARD.
LOW TEMPERATURES IN THE UPPER 70S TO LOW 80S WILL NOT PROVIDE MUCH
RELIEF OVERNIGHT AND COULD EXACERBATE HEAT STRESS AS WELL AS YIELD
SOME DAILY RECORDS FOR WARM MINIMUM TEMPERATURES. MEANWHILE PARTS
OF THE NORTHERN-CENTRAL PLAINS SHOULD SEE HIGHS UP TO 10-15F BELOW
NORMAL ON SATURDAY FOLLOWED BY A TREND TOWARD NORMAL READINGS FOR
THE FIRST HALF OF NEXT WEEK. THE INTERIOR NORTHWEST/FAR NORTHERN
ROCKIES SHOULD SEE HIGHS 5-15F ABOVE NORMAL SATURDAY-MONDAY AND
THEN A MODERATING TREND. MUCH OF THE EASTERN HALF OF THE LOWER 48
SHOULD SEE NEAR TO SLIGHTLY BELOW NORMAL READINGS.
RAUSCH
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, EXCESSIVE RAINFALL OUTLOOK,
WINTER WEATHER OUTLOOK PROBABILITIES, HEAT INDICES AND KEY
MESSAGES ARE AT:
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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