004
FXUS02 KWBC 051848
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
247 PM EDT SAT AUG 05 2023
VALID 12Z TUE AUG 08 2023 - 12Z SAT AUG 12 2023
..HEAT WAVE TO PERSIST OVER THE SOUTH INTO THE SOUTHWEST
...EXCESSIVE RAIN/FLASH FLOOD THREAT FOR THE EASTERN GREAT LAKES
INTO THE NORTHEAST TUESDAY, AND PART OF THE MIDDLE MISSISSIPPI AND
TENNESSEE VALLEYS WEDNESDAY...
..OVERVIEW
A STRONG UPPER RIDGE WILL PERSIST OVER THE U.S.-MEXICO BORDER,
WEAKENING SLIGHTLY MID-WEEK THEN REBUILDING BY FRIDAY-SATURDAY.
THIS RIDGE WILL CONTINUE TO FUEL THE ONGOING SOUTHERN TIER HEAT
WAVE WITH DAILY RECORD HIGH TEMPERATURES POSSIBLE EVERY DAY NEXT
WEEK. THE MOST ANOMALOUS TEMPERATURES WILL OCCUR UNDER THE CENTER
OF THE RIDGE WHICH WILL LIKELY BE POSITIONED RIGHT OVER TEXAS.
UPPER LEVEL TROUGHING WILL BE IN PLACE OVER THE NORTH-CENTRAL AND
EASTERN U.S., AND MULTIPLE SHORTWAVES TRANSITING AROUND THE BASE
OF THE TROUGH WILL SUPPORT AT LEAST A COUPLE FRONTAL SYSTEMS WITH
THE POTENTIAL TO CREATE LOCALLY HEAVY RAINFALL. IN THE WEST, UPPER
LEVEL TROUGHING AND WEAKENING FRONTAL SYSTEM WILL BRING RAINFALL
TO THE PACIFIC NORTHWEST MID-WEEK, THEN WEAK RIDGING AND DRY
CONDITIONS WILL RETURN LATE NEXT WEEK. THE NATIONAL HURRICANE
CENTER IS ISSUING ADVISORIES FOR A TROPICAL SYSTEM IN THE PACIFIC,
WHICH WILL REMAIN OFFSHORE BUT COULD HAVE MODEST EFFECTS ON
SENSIBLE WEATHER.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
LATEST GUIDANCE CONTINUES TO SHOW REASONABLE AGREEMENT ON THE
OVERALL MEAN PATTERN, BUT LOW PREDICTABILITY OF EMBEDDED SMALLER
SCALE DETAILS. UNCERTAINTY IN THE TIMING, POSITION, AND STRENGTH
OF UPPER LEVEL SHORTWAVES WILL LIKELY HAVE THE MOST INFLUENCE ON
THE FORECAST, IMPACTING FRONTAL PROGRESSIONS AND STRENGTH OF LOW
PRESSURE SYSTEMS. MODELS GENERALLY AGREE ON TIMING AND LOCATION OF
THE SHORTWAVE OVER THE NORTHEAST EARLY IN THE PERIOD, BUT
AGREEMENT SIGNIFICANTLY DECLINES FOR THE FOLLOWING SHORTWAVES OVER
THE REST OF THE PERIOD. THE SECOND WAVE WILL LIKELY MOVE OFF THE
ROCKIES AND ACROSS THE CENTRAL U.S. WITH HEAVY RAINFALL POTENTIAL
ON WEDNESDAY. THE GFS AND CMC BRING THIS FEATURE ACROSS EARLIER
WHILE THE ECMWF LAGS BEHIND A BIT. THIS HAS CREATED SIGNIFICANT
UNCERTAINTY IN THE LOCATION OF HEAVY PRECIPITATION AND FLASH FLOOD
THREAT. A FRONTAL SYSTEM WILL CLOSELY FOLLOW THE WAVE OF ENERGY
AND PUSH PRECIPITATION INTO THE EASTERN U.S. ON THURSDAY. LATE
NEXT WEEK, ANOTHER SHORTWAVE WILL LIKELY MOVE ACROSS THE NORTHERN
TIER OF THE NATION WITH YET ANOTHER FRONTAL SYSTEM PUSHING SOUTH
FROM CANADA.
SHORTWAVE DETAILS ARE ALSO RELATIVELY UNCERTAIN CONCERNING THE
UPPER LEVEL ENERGY ASSOCIATED WITH THE SURFACE TROPICAL SYSTEM IN
THE PACIFIC. THE UPPER LEVEL LOW WILL BECOME NEARLY STATIONARY
OFFSHORE OF CALIFORNIA, AND MAY DRIFT NEAR ENOUGH TO THE COAST TO
HAVE SOME EFFECT ON SENSIBLE WEATHER.
FOR THIS FORECAST, A BLEND OF OPERATIONAL MODELS WAS USED FOR THE
FIRST HALF OF THE PERIOD, AND ENSEMBLE MEANS WERE INTRODUCED TO
THE BLEND FOR THE SECOND HALF.
..WEATHER/HAZARDS HIGHLIGHTS
THE RATHER VIGOROUS SYSTEM FORECAST TO TRACK FROM THE EASTERN
GREAT LAKES THROUGH OR NEAR NEW ENGLAND DURING TUESDAY-WEDNESDAY
WILL SPREAD POTENTIALLY STRONG THUNDERSTORMS/HEAVY RAINFALL ACROSS
PORTIONS OF THE NORTHEAST. THE DAY 4 EXCESSIVE RAINFALL OUTLOOK
FOR TUESDAY-TUESDAY NIGHT MAINTAINS A SLIGHT RISK AREA FROM
UPSTATE NEW YORK TO MAINE, WITH THE RECENT SHIFT IN GUIDANCE FOR
THE SYSTEM'S STRUCTURE AND SLOWER TIMING LEADING TO SOMEWHAT
HIGHER RAINFALL POTENTIAL OVER THE REGION. SOME AREAS WILL BE
PARTICULARLY SENSITIVE GIVEN RECENT SIGNIFICANT RAINFALL. AS FOR
OTHER DAY 4 AREAS, PARTS OF THE LOWER MISSISSIPPI VALLEY AND
SOUTHEAST REMAIN IN A MARGINAL RISK WITH THE NORTHEAST SYSTEM'S
TRAILING FRONT SETTLING OVER THE REGION WHILE THE COMBINATION OF A
COUPLE FRONTS MAY PRODUCE LOCALLY HEAVY RAINFALL WITHIN A MARGINAL
RISK AREA OVER THE NORTH-CENTRAL PLAINS. DURING THE DAY 5 OUTLOOK
PERIOD OF WEDNESDAY-WEDNESDAY NIGHT, EXPECT A FAIRLY BROAD AREA OF
LOCALLY HEAVY RAINFALL POTENTIAL DUE TO A NORTHERN TIER FRONT
PROGRESSING SOUTHEASTWARD INTO THE MIDWEST AND PERSISTENCE OF THE
FRONT OVER THE SOUTH. GUIDANCE SPREAD IS STILL RELATIVELY LARGE,
MAKING IT DIFFICULT TO TARGET AREAS WITH THE HIGHEST FLASH FLOOD
RISK, BUT THERE WAS SOME OVERLAP IN SOLUTIONS IN THE MID
MISSISSIPPI AND TENNESSEE VALLEYS WHERE A SLIGHT RISK AREA WAS
INTRODUCED. ADDITIONAL SLIGHT RISK AREAS AND/OR ADJUSTMENTS TO THE
CURRENT SLIGHT RISK AREA WILL LIKELY BE NEEDED IN FUTURE FORECASTS
AS DETAILS BECOME MORE CLEAR.
CONTINUED PROGRESSION OF THE MIDWEST FRONT SHOULD BRING SHOWERS
AND THUNDERSTORMS INTO THE EAST BY LATER IN THE WEEK, WITH SOME
HEAVY ACTIVITY STILL POSSIBLE THROUGH THURSDAY AND MAYBE BECOMING
SOMEWHAT LESS ORGANIZED BY FRIDAY-SATURDAY. CONFIDENCE IS LOWER
FOR ANOTHER POSSIBLE SYSTEM/FRONT THAT COULD PRODUCE SOME
SHOWERS/STORMS OVER PARTS OF THE PLAINS/MIDWEST TOWARD
FRIDAY-SATURDAY. MEANWHILE THE PACIFIC NORTHWEST SHOULD SEE SOME
RAINFALL TUESDAY-WEDNESDAY AS A WEAKENING FRONT APPROACHES.
AMOUNTS SHOULD BE LIGHT TO MODERATE IN ABSOLUTE TERMS, BUT STILL
SOMEWHAT UNUSUAL FOR EARLY AUGUST. CONVECTION OVER THE FOUR
CORNERS STATES/SOUTHWEST SHOULD BE LIGHTER AND MORE SCATTERED THAN
AVERAGE GIVEN BELOW-CLIMATOLOGY PRECIPITABLE WATER VALUES THROUGH
MIDWEEK OR SO. ACTIVITY MAY INCREASE SLIGHTLY TOWARD
FRIDAY-SATURDAY AS MOISTURE GRADUALLY INCREASES TOWARD MORE NORMAL
LEVELS.
THE ONGOING HEAT WAVE OVER THE SOUTHERN TIER SHOULD CONTINUE
THROUGH NEXT WEEK, WITH GREATEST EMPHASIS OVER THE SOUTHERN HIGH
PLAINS WHERE HIGHS COULD REACH 10-15F ABOVE NORMAL. TEMPERATURES
MAY REACH OR EXCEED DAILY RECORD HIGHS MOST DAYS NEXT WEEK FROM
THE WESTERN GULF COAST INTO THE SOUTHERN ROCKIES. THE DESERT
SOUTHWEST SHOULD BE QUITE HOT AS WELL WITH HIGHS REACHING AROUND
110F, BUT MAY STAY A BIT SHORT OF RECORD HIGHS. THE FLORIDA
PENINSULA COULD ALSO SEE A FEW RECORD HIGHS. RECORD WARM LOWS WILL
BE POSSIBLE ACROSS A BROADER PORTION OF THE SOUTHERN TIER EACH
NIGHT. HIGH HUMIDITY SHOULD LEAD TO MAXIMUM HEAT INDICES AT LEAST
IN THE 110-115F RANGE ALONG AND NEAR THE WESTERN HALF OF THE GULF
COAST. IN CONTRAST, THE COOLEST TEMPERATURES VERSUS NORMAL WILL BE
OVER THE NORTHERN ROCKIES/HIGH PLAINS NEXT TUESDAY-WEDNESDAY WITH
SOME HIGHS UP TO 10-15F OR SO BELOW AVERAGE. TEMPERATURES SHOULD
TREND CLOSER TO NORMAL THEREAFTER, WHILE OTHER LOCATIONS ACROSS
THE NORTHERN HALF OF THE PLAINS/MISSISSIPPI VALLEY MAY SEE ONE OR
MORE DAYS WITH HIGHS MODESTLY BELOW NORMAL. THE UPPER TROUGH/LOW
DEVELOPING NEAR CALIFORNIA SHOULD KEEP HIGHS OVER MOST OF THE
STATE NEAR OR SLIGHTLY BELOW NORMAL.
RAUSCH/DOLAN
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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