838
FXUS02 KWBC 052012
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
411 PM EDT WED JUL 05 2023
VALID 12Z SAT JUL 08 2023 - 12Z WED JUL 12 2023
...HEAT EXPECTED TO REBUILD FROM THE SOUTHWEST TO THE NORTHERN
GULF COAST THIS WEEKEND 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 WEATHER PATTERN OVER THE MEDIUM RANGE PERIOD WILL FEATURE MEAN
TROUGHING OVER THE EASTERN HALF OF THE COUNTRY AND A STRENGTHENING
RIDGE OVER THE SOUTHWESTERN STATES. SEVERAL FRONTAL SYSTEMS ARE
FORECAST TO PUSH ACROSS THE CENTRAL AND EASTERN U.S. AS A DEEP
UPPER LEVEL LOW DESCENDS INTO NORTHERN ONTARIO. THIS PATTERN WILL
LIKELY LEAD TO AN ACTIVE PERIOD OF SHOWER AND THUNDERSTORM
ACTIVITY FOR MULTIPLE AREAS EAST OF THE ROCKIES AND ABOVE AVERAGE
TEMPERATURES FROM THE SOUTHWEST TO THE NORTHERN GULF COAST.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
THE MODELS AND ENSEMBLES CONTINUE TO SHOW GOOD AGREEMENT FOR THE
OVERALL PATTERN EVOLUTION, BUT UNCERTAINTY REMAINS IN THE SMALLER
SCALE DETAILS. A GENERAL BLEND OF DETERMINISTIC MODELS WAS USED
FOR THE WEEKEND FORECAST, THEN ENSEMBLES WERE INTRODUCED TO THE
BLEND FOR EARLY NEXT WEEK'S FORECAST TO SMOOTH OUT SMALLER SCALE
DIFFERENCES. THE CMC STARTS TO DIVERGE FROM THE OTHER MODEL
SOLUTIONS EARLY NEXT WEEK WITH THE POSITION OF THE DEEP UPPER
LEVEL LOW, PULLING IT CONSIDERABLY FURTHER SOUTH OVER THE GREAT
LAKES WHILE THE OTHER MODELS KEEP IT NEAR THE SOUTHERN HUDSON BAY.
WITH THE CMC BEING A CLEAR OUTLIER, IT WAS NOT INCLUDED IN THE
MODEL BLEND FOR THE LATER PART OF THE PERIOD. MODELS ARE IN GOOD
AGREEMENT THAT AN UPPER LEVEL SHORTWAVE WILL ROUND THE BASE OF THE
TROUGH AND SWING OVER THE OHIO VALLEY TOWARDS THE NORTHEAST MONDAY
THROUGH WEDNESDAY NEXT WEEK. THE GFS AND THE ECMWF ALIGN FAIRLY
WELL WITH THE STRENGTH AND POSITION OF THE SHORTWAVE, SO A BLEND
OF THE GFS/ECMWF/GEFS/ECENS WAS USED TO CAPTURE IT IN THE
FORECAST. WEAK TROUGHING WILL ALSO PERSIST OVER THE COASTAL
PACIFIC NORTHWEST, WITH SOME UNCERTAINTY IN THE STRENGTH AND
POSITION. FOR THIS FORECAST, THE GENERAL MODEL BLEND RESULTED IN A
MIDDLE GROUND SOLUTION.
..WEATHER/HAZARDS HIGHLIGHTS
18Z UPDATE: MODELS REMAIN IN GOOD AGREEMENT IN HEAVY RAIN
POTENTIAL FROM THE CENTRAL/SOUTHERN PLAINS TO THE MID/LOWER
MISSISSIPPI AND TENNESSEE VALLEYS OVER THE WEEKEND. ONLY MINOR
CHANGES WERE MADE TO THE DAY 4 AND 5 EROS TO ACCOUNT FOR LATEST
MODEL GUIDANCE. THERE IS A SIGNAL FOR HEAVY RAIN FOCUSING OVER
PARTS OF THE NORTHERN MID-ATLANTIC REGION ON DAY 4, BUT THERE WAS
NOT ENOUGH CONFIDENCE TO INTRODUCE A NEW SLIGHT RISK AREA AT THIS
TIME. THIS AREA SHOULD BE MONITORED FOR A POSSIBLE UPGRADE IN
FUTURE FORECASTS AS A WAVE OF LOW PRESSURE MOVES NORTH AHEAD OF AN
APPROACHING FRONTAL BOUNDARY.
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 AND 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.
DOLAN/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
- HEAVY RAIN ACROSS PORTIONS OF THE MIDDLE MISSISSIPPI VALLEY, THE
LOWER MISSISSIPPI VALLEY, THE
SOUTHERN PLAINS, THE OHIO VALLEY, AND THE TENNESSEE VALLEY,
SAT-SUN, JUL 8-JUL 9.
- HEAVY RAIN ACROSS PORTIONS OF THE CENTRAL PLAINS, THE LOWER
MISSISSIPPI VALLEY, THE TENNESSEE
VALLEY, THE MIDDLE MISSISSIPPI VALLEY, THE SOUTHERN PLAINS, AND
THE OHIO VALLEY, SAT, JUL 8.
- HEAVY RAIN ACROSS PORTIONS OF THE SOUTHEAST, THE LOWER
MISSISSIPPI VALLEY, AND THE TENNESSEE
VALLEY, MON, JUL 10.
- HEAVY RAIN ACROSS PORTIONS OF THE MID-ATLANTIC AND THE
NORTHEAST, SUN-MON, JUL 9-JUL 10.
- FLOODING POSSIBLE ACROSS PORTIONS OF THE NORTHERN PLAINS.
- FLOODING OCCURRING OR IMMINENT ACROSS PORTIONS OF THE NORTHERN
PLAINS.
- FLOODING LIKELY ACROSS PORTIONS OF THE NORTHERN PLAINS.
- HAZARDOUS HEAT ACROSS PORTIONS OF THE LOWER MISSISSIPPI VALLEY,
CALIFORNIA, THE SOUTHERN PLAINS,
AND THE SOUTHWEST, SAT-WED, JUL 8-JUL 12.
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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