369
FXUS02 KWBC 242012
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
411 PM EDT MON JUL 24 2023
VALID 12Z THU JUL 27 2023 - 12Z MON JUL 31 2023
...HEAT CONTINUES ACROSS THE SOUTHWEST WHILE ABOVE NORMAL
TEMPERATURES ARE ALSO LIKELY FROM THE MIDWEST TO THE EAST COAST
INTO LATE WEEK...
..OVERVIEW
THE PERSISTENT UPPER HIGH ATOP THE SOUTHERN ROCKIES MAY DRIFT
SLIGHTLY EAST TOWARD THE SOUTHERN PLAINS BY EARLY NEXT WEEK,
BRINGING DANGEROUS HEAT IN THE DESERT SOUTHWEST CLOSER TO NORMAL
TEMPERATURES (THOUGH STILL HOT) AS THE PERIOD PROGRESSES. SOME
RIDGING WILL LIKELY STRETCH INTO THE MIDWEST AND PROMOTE MUCH
ABOVE NORMAL TEMPERATURES THERE AND EAST INTO THE OHIO
VALLEY/GREAT LAKES AND THE MID-ATLANTIC/NORTHEAST THROUGH LATE IN
THE WORKWEEK BEFORE MODERATING. LOW AMPLITUDE UPPER FLOW TO THE
NORTH OF THE UPPER HIGH PRESENTS SOME FORECAST CHALLENGES
ESPECIALLY ON THE SMALLER SCALES, BUT THE OVERALL TENDENCY SHOULD
BE FOR NORTHERN TIER FLOW TO REFLECT A RIDGE AXIS OVER THE HIGH
PLAINS AND BROAD TROUGHING OVER THE GREAT LAKES/NORTHEAST BY THE
WEEKEND. THIS MEAN TROUGH SHOULD GRADUALLY AMPLIFY INTO THE START
OF NEXT WEEK. THIS PATTERN/EVOLUTION, WHICH WILL BRING ONE OR MORE
FRONTS INTO THE NORTHERN PLAINS THROUGH NORTHEAST, WILL FAVOR
EPISODES OF POTENTIALLY HEAVY CONVECTION BUT CONFIDENCE REMAINS
LOW IN THE DETAILS. DIURNALLY DRIVEN SHOWERS AND THUNDERSTORMS
WILL BE POSSIBLE OVER AND NEAR THE FOUR CORNERS STATES THROUGH
LATE WEEK AND THE WEEKEND WITH MONSOONAL MOISTURE INCOMING UNDER
THE RIDGE.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
GUIDANCE CONTINUES TO SHOW DIFFICULTIES WITH IMPORTANT BUT VERY
LOW-PREDICTABILITY SHORTWAVE DETAILS ACROSS THE NORTHERN TIER U.S.
AND SOUTHERN CANADA, WITHIN AND SOUTH OF INITIALLY ELONGATED
TROUGHING THAT EXTENDS FROM EASTERN CANADA/HUDSON BAY THROUGH
SOUTHWESTERN CANADA INTO THE PACIFIC NORTHWEST COAST MEAN TROUGH.
WHILE SHORTWAVE DETAILS CONTINUE TO PLAGUE THE DAY-TO-DAY FORECAST
OF FRONTS/WAVES/QPF AS FLOW ALOFT TRANSITIONS FROM A NEARLY ZONAL
CONFIGURATION TOWARD EASTERN U.S. TROUGH AMPLIFICATION THAT DRIVES
THE LEADING COLD FRONT FARTHER SOUTHWARD, LATEST GUIDANCE AT LEAST
SEEMS TO BE GETTING A LITTLE CLOSER IN A BROAD SENSE. THIS IS BY
WAY OF 00Z ECMWF-BASED GUIDANCE TRENDING A LITTLE MORE AMPLIFIED
WITH THE EASTERN TROUGH AND THE 06Z/12Z GFS BACKTRACKING FROM ITS
POTENTIALLY EXCESSIVE TROUGH AMPLITUDE IN THE 00Z RUN. IN THE NEW
12Z CYCLE, THE CMC APPEARS TO STRAY A BIT TO THE AMPLIFIED SIDE OF
THE SPREAD FOR THE TROUGH. ALSO WORTH NOTING, THE 12Z GFS/ECMWF
HAVE ADJUSTED TOWARD THE FAST SIDE WITH EJECTING PACIFIC NORTHWEST
TROUGH ENERGY DURING THE WEEKEND. THESE ISSUES OUT WEST MAINTAIN
SOME UNCERTAINTY FOR THE FORECAST FARTHER EASTWARD. MEANWHILE
THERE ARE SOME ONGOING DETAIL DIFFERENCES REGARDING EXACTLY HOW
STRONGLY ATLANTIC UPPER RIDGING BUILDS INTO THE SOUTHEAST/GULF AND
POSSIBLY CONNECTS WITH THE ROCKIES/PLAINS RIDGE. THE GFS/GEFS
STILL ARE GENERALLY ON THE WEAKER SIDE OF THE SPREAD. MASS FIELD
PREFERENCES REFLECTING AN OPERATIONAL MODEL BLEND EARLY
TRANSITIONING TO A MODEL/ENSEMBLE MEAN MIX BY THE LATTER HALF OF
THE FORECAST LED TO MERELY TYPICAL DETAIL ADJUSTMENTS EARLY-MID
PERIOD, THOUGH BY DAY 7 SUNDAY REFLECTED THE AVERAGE OF GUIDANCE
THAT HAD ADJUSTED A LITTLE FARTHER SOUTH WITH THE EASTERN COLD
FRONT IN ASSOCIATION WITH A MORE AMPLIFIED UPPER TROUGH. QPF AGAIN
BROADENED AMOUNTS ACROSS THE NORTH-CENTRAL U.S. AND EASTERN U.S.
COMPARED TO THE NBM USING A MULTI-MODEL AND ENSEMBLE BLEND TO
PROVIDE SOME DEPICTION OF THE RAINFALL POTENTIAL, THOUGH MORE
CHANGES ARE LIKELY YET TO COME WITH TIME.
..WEATHER/HAZARDS HIGHLIGHTS
SHOWERS AND THUNDERSTORMS LOOK LIKELY ACROSS PARTS OF THE CENTRAL
AND EASTERN U.S. THROUGH THE LATTER PART OF THE WORKWEEK, WITH ONE
OR MORE WAVY FRONTAL SYSTEMS REACHING THE NORTHERN TIER PROVIDING
THE BEST FOCUS BUT WITH LESS DEFINED FORCING ELSEWHERE. EVEN WITH
THE NORTHERN TIER FRONTAL SYSTEMS, THERE HAS BEEN CONSIDERABLE
UNCERTAINTY OVER THE PRECISE EAST-WEST TIMING AND SOUTHWARD
EXTENT--KEEPING CONFIDENCE LOWER THAN DESIRED. FOR THE
THURSDAY-THURSDAY NIGHT PERIOD COVERED BY THE DAY 4 EXCESSIVE
RAINFALL OUTLOOK, THERE ARE STILL TWO AREAS OF INTEREST FOR
RELATIVELY BETTER RAINFALL FOCUS. ONE EXISTS OVER THE UPPER
MIDWEST WHERE THE WAVY FRONTS WILL BE APPROACHING, WITH ANOTHER
EXTENDING FROM THE EASTERN GREAT LAKES INTO THE FAR NORTHERN
MID-ATLANTIC INTO SOUTHERN-CENTRAL NEW ENGLAND WHERE A COMPACT
UPPER LEVEL SHORTWAVE MAY GENERATE LOCALLY HEAVY CONVECTION. AT
THIS TIME GUIDANCE APPEARS TO BE PROVIDING ENOUGH SIGNAL TO
INTRODUCE MARGINAL RISK AREAS IN BOTH CASES TO REFLECT THE
POTENTIAL EVENTS, WITH THE UNDERSTANDING THAT SOME ADJUSTMENTS MAY
OCCUR IN COMING MODEL CYCLES. BY THE DAY 5 ERO TIMEFRAME
FRIDAY-FRIDAY NIGHT, CONVECTION SHOULD BE MORE STRONGLY FORCED
WITH SHORTWAVES ALOFT AND MORE FOCUSED NEAR THE COLD FRONT,
INCREASING CONFIDENCE FOR HEAVY RAIN AND HIGHER RAIN RATES ALONG
WITH TRAINING/REPEAT ACTIVITY THAT COULD LEAD TO FLOODING ISSUES.
WHILE MODEL QPF SOLUTIONS ARE STILL EXHIBITING THE SPREAD THAT HAS
BEEN SEEN OVER RECENT DAYS, THE OVERALL COMBINATION OF THE PATTERN
(WAVY FRONT TAKING ON A FAIRLY EAST-WEST ORIENTATION) ALONG WITH
FAVORABLE MOISTURE ANOMALIES/INSTABILITY PLUS LOCATIONS OF
RELATIVE EMPHASIS IN ENSEMBLE PROBABILITIES SEEM TO FAVOR
INTRODUCING A MARGINAL RISK AREA FROM LOCATIONS NEAR THE
SOUTHWESTERN GREAT LAKES INTO THE CENTRAL APPALACHIANS AND A
MAJORITY OF NEW ENGLAND AS A STARTING POINT. EXPECT RAIN AND
THUNDERSTORMS TO CONTINUE INTO THE WEEKEND, WITH BEST CHANCES
LIKELY DRIFTING SOUTHWARD WITH THE COLD FRONT. SCATTERED STORMS
ARE ALSO POSSIBLE IN THE NORTHERN HALF OF THE PLAINS AND
MISSISSIPPI VALLEY EACH DAY, AGAIN WITH LOW CONFIDENCE IN THE
EXACT PLACEMENT AND AMOUNTS OF RAINFALL. CONVECTION COULD BECOME A
LITTLE MORE ORGANIZED AT TIMES OVER THE NORTHERN HIGH PLAINS DUE
TO LOW LEVEL UPSLOPE FLOW.
ELSEWHERE, THE FOUR CORNERS STATES ARE LIKELY TO SEE DIURNALLY
DRIVEN CONVECTION EACH DAY THIS WEEK AS MONSOONAL MOISTURE COMES
IN UNDERNEATH THE SOUTHERN ROCKIES UPPER RIDGE. THE EROS DEPICT A
MARGINAL RISK AREA ON BOTH DAYS. FLOW TO THE SOUTH OF
ROCKIES/PLAINS UPPER RIDGING COULD BRING AN INCREASE OF MOISTURE
AND SHORTWAVE ENERGY INTO PARTS OF THE REGION TOWARD THE END OF
THE PERIOD, SO RAINFALL AMOUNTS MAY BECOME LOCALLY HEAVIER BY
SUNDAY-MONDAY. FLORIDA AND PARTS OF THE GULF COAST SHOULD SEE SOME
SCATTERED SHOWERS AND THUNDERSTORMS AS WELL, AND MARGINAL RISKS OF
FLASH FLOODING ARE IN PLACE FOR SOUTH FLORIDA FOR THURSDAY AND
FRIDAY AS PRECIPITABLE WATER VALUES WILL BE WELL ABOVE AN ALREADY
HIGH AVERAGE AND CONVECTION COULD PRODUCE HEAVY RAINFALL RATES,
WITH URBAN AREAS PARTICULARLY SENSITIVE.
THE PERSISTENT UPPER HIGH CENTERED OVER THE SOUTHERN ROCKIES WILL
KEEP TEMPERATURES IN THE DESERT SOUTHWEST AROUND 5-10F ABOVE
AVERAGE FOR HIGHS IN THE 110S THROUGH LATE WEEK. BY THE WEEKEND
INTO EARLY NEXT WEEK, HIGHS MAY FINALLY EASE TO NEAR NORMAL THERE
WITH SOME CHANCE FOR THE UPPER HIGH TO DRIFT EAST. FARTHER
NORTHEAST, TEMPERATURES APPROACHING 100F ARE LIKELY ACROSS THE
PLAINS TO THE MIDDLE/UPPER MISSISSIPPI VALLEY WITH ANOMALIES FOR
HIGHS OF 10-20F ABOVE NORMAL, WHILE PLUS 10-15F ANOMALIES ARE
LIKELY ACROSS THE OHIO VALLEY AND MID-ATLANTIC/NORTHEAST PEAKING
THURSDAY-FRIDAY. SOME RECORD TEMPERATURES FOR HIGHS AND WARM LOWS
ARE POSSIBLE ACROSS THE EAST. TEMPERATURES IN MOST OF THESE AREAS
SHOULD MODERATE BY THE WEEKEND AS COLD FRONTS PUSH THROUGH THE
NORTHERN TIER, THOUGH WARMER THAN NORMAL TEMPERATURES MAY CONTINUE
FROM THE CENTRAL/SOUTH-CENTRAL PLAINS INTO MISSISSIPPI VALLEY
DEPENDING ON EXACTLY WHERE THE NORTHERN TIER COLD FRONT ULTIMATELY
STALLS. THE SOUTHEAST/GULF COAST COULD SEE SLIGHTLY INCREASING
TEMPERATURES INTO THE WEEKEND AND EARLY NEXT WEEK UNDER RIDGING
ALOFT THAT BUILDS WEST FROM THE ATLANTIC AND SOUTHEAST FROM THE
PLAINS. DETAILS OF CONVECTION AND RESIDUAL CLOUD COVER WILL ADD AN
EXTRA ELEMENT OF UNCERTAINTY TO THE FORECAST OF DAYTIME HIGHS OVER
MANY AREAS. MEAN TROUGHING NEAR THE PACIFIC NORTHWEST WILL GIVE
THAT REGION THE MOST PERSISTENT AREA OF POTENTIALLY BELOW NORMAL
TEMPERATURES, THOUGH STILL WITH HIGHS NO COOLER THAN A FEW DEGREES
BELOW AVERAGE. COOLER TRENDS OVER THE NORTHEAST UNDER UPPER
TROUGHING COULD NUDGE HIGHS A LITTLE BELOW NORMAL BY EARLY NEXT
WEEK.
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
HAZARDS:
- HAZARDOUS HEAT ACROSS PORTIONS OF THE CENTRAL PLAINS, THE LOWER
MISSISSIPPI VALLEY, THE NORTHERN
PLAINS, THE MIDDLE MISSISSIPPI VALLEY, THE UPPER MISSISSIPPI
VALLEY, THE SOUTHERN PLAINS, AND THE
OHIO VALLEY, THU-FRI, JUL 27-JUL 28.
- HAZARDOUS HEAT ACROSS PORTIONS OF THE LOWER MISSISSIPPI VALLEY,
THE TENNESSEE VALLEY, THE MIDDLE
MISSISSIPPI VALLEY, THE SOUTHERN MID-ATLANTIC, THE SOUTHERN
APPALACHIANS, THE SOUTHEAST, THE
SOUTHERN PLAINS, AND THE OHIO VALLEY, SAT-MON, JUL 29-JUL 31.
- HAZARDOUS HEAT ACROSS PORTIONS OF THE MID-ATLANTIC AND THE
CENTRAL APPALACHIANS, FRI-SAT, JUL
28-JUL 29.
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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