558
FXUS02 KWBC 252026
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
425 PM EDT TUE JUL 25 2023
VALID 12Z FRI JUL 28 2023 - 12Z TUE AUG 01 2023
...HEAT CONTINUES ACROSS THE SOUTHWEST WHILE ABOVE NORMAL
TEMPERATURES ARE ALSO LIKELY FROM THE MIDWEST TO THE EAST COAST
INTO LATE WEEK, BECOMING MORE LIMITED TO THE CENTRAL U.S. BY NEXT
WEEK...
..OVERVIEW
THE PERSISTENT UPPER HIGH THAT HAS STAYED ATOP THE SOUTHERN
ROCKIES FOR WEEKS NOW IS FORECAST TO COMBINE WITH RIDGING COMING
IN FROM THE WESTERN ATLANTIC AND DRIFT EASTWARD ATOP THE
SOUTH-CENTRAL TO SOUTHEASTERN U.S. INTO NEXT WEEK. THIS SHOULD
FINALLY BRING TEMPERATURES IN THE DESERT SOUTHWEST CLOSER TO
NORMAL (THOUGH STILL HOT) AS THE PERIOD PROGRESSES. THE FLOW
PATTERN OF RIDGING STRETCHING NORTH WILL ALSO PROMOTE ABOVE NORMAL
TEMPERATURES ACROSS THE CENTRAL PLAINS TO MID-MISSISSIPPI VALLEY
WITH THE SOUTHEAST ALSO LIKELY TO WARM ABOVE NORMAL, WITH HIGH
HEAT INDICES. LATE WEEK WARM TEMPERATURES ARE FORECAST INTO THE
OHIO VALLEY TO THE NORTHEAST/MID-ATLANTIC, AHEAD OF A COLD FRONT
AND TROUGH AXIS PRESSING INTO THOSE REGIONS BY EARLY NEXT WEEK.
THIS FRONT SHOULD ALSO FOCUS CONVECTION MOVING THROUGH THE
NORTH-CENTRAL TO EASTERN U.S., WITH SOME RISK OF HEAVY RAINFALL
AND FLASH FLOODING, THOUGH CONFIDENCE REMAINS LOW IN THE DETAILS.
DIURNALLY DRIVEN SHOWERS AND THUNDERSTORMS WILL BE POSSIBLE OVER
AND NEAR THE FOUR CORNERS STATES THROUGH LATE WEEK INTO NEXT WEEK
WITH MONSOONAL MOISTURE INCOMING UNDER THE RIDGE.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
MODEL GUIDANCE INDICATES OVERALL SUMMERTIME UPPER-LEVEL PATTERN
CONTINUES WITH A PERSISTENT HIGH ACROSS PORTIONS OF THE SOUTHERN
TIER OF THE COUNTRY AND STRONGER UPPER-LEVEL FLOW SHUNTED TO THE
NORTH. HEIGHT RISES LOOK TO INCREASE MORE BROADLY INITIALLY OVER
THE SOUTHEAST/MID-ATLANTIC AS AN UPPER-LEVEL HIGH OVER THE
ATLANTIC COMBINES WITH A STUBBORN UPPER-LEVEL HIGH OVER THE
SOUTHERN ROCKIES/PLAINS LATE WEEK/EARLY WEEKEND. STRONGER
UPPER-LEVEL FLOW SHOULD THEN SHIFT BACK SOUTHWARD OVER THE
NORTHEAST/MID-ATLANTIC ROTATING AROUND AN UPPER-LEVEL LOW OVER
HUDSON BAY. UPPER-LEVEL RIDGING WILL THEN BUILD A BIT NORTHWARD
LATE THIS WEEKEND INTO EARLY NEXT WEEK OVER THE EASTERN GREAT
BASIN/ROCKIES/PLAINS AS THE OVERALL PATTERN AMPLIFIES EVER SO
SLIGHTLY WITH DEEPER TROUGHING OVER THE NORTHEAST/MID-ATLANTIC.
THE UPPER-LEVEL HIGH CENTERED OVER THE SOUTHERN ROCKIES/PLAINS
ALSO LOOKS TO SHIFT EASTWARD WITH TIME. SHORTWAVE ENERGY OVER THE
NORTHEASTERN PACIFIC WILL DROP SOUTHWARD OVER THE PACIFIC
NORTHWEST BEFORE UPPER-LEVEL RIDGING LOOKS TO EXPAND EVEN FURTHER
NORTHWESTWARD INTO THE REGION NEXT WEEK AS WELL. SUBTLE SHORTWAVE
IMPULSES WILL LIKELY IMPACT THE LOCATION/COVERAGE OF ORGANIZED
CONVECTION IN THE NORTHWESTERLY FLOW CENTERED OVER THE NORTHERN
PLAINS/MIDWEST/NORTHEAST, BUT HAVE VERY LOW PREDICTABILITY AT THIS
TIME RANGE.
A GENERAL DETERMINISTIC GUIDANCE BLEND OF THE 00Z ECMWF/CMC/UKMET
AND 06Z GFS IS USED FOR THE UPDATED WPC FORECAST GIVEN GENERAL
LARGE-SCALE AGREEMENT BETWEEN THE MODELS AND GOOD RUN-TO-RUN
CONTINUITY OVER THE LAST FEW CYCLES. CONTRIBUTIONS FROM THE 00Z
ECENS MEAN AND 06Z GEFS MEAN ARE INCREASED AS THE FORECAST
TIME-LIMITED UKMET IS REMOVED BY THE MIDDLE OF THE PERIOD. THE
CONTRIBUTION FROM THE 00Z CMC IS ALSO REDUCED GIVEN A BIT MORE
AMPLIFICATION WITH THE FLOW OVER THE NORTHERN TIER THAT IS AN
OUTLIER COMPARED TO BOTH THE DETERMINISTIC GFS/ECMWF AND THEIR
RESPECTIVE SYSTEM MEANS. GIVEN THE GENERALLY GOOD LARGER-SCALE
AGREEMENT IN THE GUIDANCE THIS UPDATE FOLLOWS CONTINUITY FROM THE
PRIOR FORECAST.
..WEATHER/HAZARDS HIGHLIGHTS
SHOWERS AND THUNDERSTORMS LOOK LIKELY ACROSS PARTS OF THE
NORTH-CENTRAL AND MUCH OF THE EASTERN U.S. THROUGH THE LATTER PART
OF THE WEEK AND INTO NEXT WEEK IN GENERALLY WESTERLY TO
NORTHWESTERLY FLOW ON THE NORTH SIDE OF THE UPPER HIGH, WITH UPPER
TROUGHING EDGING INTO THE EAST AND A FRONTAL BOUNDARY OR TWO
HELPING TO FOCUS CONVECTION. EVEN WITH THE FRONTAL SYSTEMS, THERE
HAS BEEN CONSIDERABLE UNCERTAINTY OVER THE PRECISE EAST-WEST
TIMING AND SOUTHWARD EXTENT--KEEPING CONFIDENCE LOWER THAN
DESIRED. BUT FOR FRIDAY AND SATURDAY FOR THE DAYS 4 AND 5 EROS,
THE INGREDIENTS ARE IN PLACE FOR SOME FOCUSED HEAVY RAINFALL THAT
COULD CAUSE FLASH FLOODING DESPITE THE LOCATION DIFFERENCES.
CONVECTION WILL BE MORE STRONGLY FORCED IN THE EAST WITH
SHORTWAVES ALOFT AND FOCUSED NEAR THE COLD FRONT WITH A GENERAL
WEST-EAST ORIENTATION ALLOWING FOR TRAINING/REPEAT ACTIVITY IN A
MOIST AND UNSTABLE ENVIRONMENT. GIVEN THE LOCATION DIFFERENCES,
RELATIVELY BROAD MARGINAL RISKS ARE IN PLACE FRIDAY-SATURDAY IN
THE EROS AS A STARTING POINT, WHICH MAY BE ABLE TO NARROW IN
FUTURE FORECASTS IF MODELS COME INTO BETTER AGREEMENT WITH THE
FRONTAL AND THUS THE QPF TIMING, AND FUTURE SLIGHT RISKS CANNOT BE
RULED OUT. THE FOCUS OF HEAVY RAINFALL IN THE EAST SHOULD DROP
SOUTHWARD SOMEWHAT EACH DAY THIS WEEKEND AND INTO EARLY NEXT WEEK
AS THE COLD FRONT SLOWLY PROGRESSES. THE NORTH-CENTRAL U.S. CAN
ALSO EXPECT SCATTERED STORMS AS SHORTWAVES TRACK THROUGH THE
REGION AND MOISTURE INCREASES. ANY HEAVY RAIN/FLASH FLOODING
THREAT WILL LIKELY BE TIED TO THE POTENTIAL FOR ORGANIZED
CONVECTIVE SYSTEMS IN NORTHWESTERLY FLOW, WITH THIS POTENTIAL
APPARENT OVERNIGHT FRIDAY AND AN ASSOCIATED DAY 4 MARGINAL RISK
ERO. RAINFALL AMOUNTS/COVERAGE LOOK TO INCREASE EARLY NEXT WEEK
AFTER A LULL OVER THE WEEKEND.
ELSEWHERE, THE FOUR CORNERS STATES ARE LIKELY TO SEE DIURNALLY
DRIVEN CONVECTION EACH DAY AS MONSOONAL MOISTURE COMES IN
UNDERNEATH THE SOUTHERN ROCKIES UPPER RIDGE. THE EROS DEPICT A
MARGINAL RISK AREA ON BOTH DAYS 4 AND 5. AS THE RIDGE SHIFTS
EASTWARD NEXT WEEK, THIS MAY INCREASE MOIST SOUTHERLY FLOW AND
ALLOW FOR SHORTWAVE ENERGY TO COME IN, 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 FRIDAY AND SATURDAY 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
PLUME OF MOISTURE SHOULD SHIFT WEST WITH TIME.
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 THE CENTER OF THE UPPER HIGH FORECAST TO DRIFT EAST. FARTHER
NORTHEAST, TEMPERATURES APPROACHING OR OVER 100F ARE LIKELY ACROSS
THE CENTRAL PLAINS TO THE MIDDLE 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 ON
FRIDAY. SOME RECORD TEMPERATURES FOR HIGHS AND WARM LOWS ARE
POSSIBLE AND MAY BE MOST FOCUSED ACROSS THE EAST. TEMPERATURES IN
MOST OF THESE AREAS SHOULD MODERATE BY THE WEEKEND AS UPPER-LEVEL
TROUGHING BEGINS TO SHIFT SOUTHWARD AND 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 INCREASING
TEMPERATURES INTO THE WEEKEND AND EARLY NEXT WEEK UNDER RIDGING
ALOFT THAT BUILDS WEST FROM THE ATLANTIC AND SOUTHEAST FROM THE
PLAINS, AND HEAT INDICES COULD RISE ABOVE 110F AS THE WARMTH
COMBINES WITH HIGH DEWPOINTS. 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, AND TEMPERATURES LOOK
TO REBOUND A BIT EARLY NEXT WEEK AS UPPER-LEVEL RIDGING BUILDS
NORTHWARD. COOLER TRENDS OVER THE NORTHEAST UNDER UPPER TROUGHING
COULD NUDGE HIGHS A LITTLE BELOW NORMAL BY EARLY NEXT WEEK.
PUTNAM/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 MIDWEST AND CENTRAL
PLAINS, FRI-TUE, JUL 28-AUG 1.
- HAZARDOUS HEAT ACROSS PORTIONS OF THE MID-MISSISSIPPI VALLEY AND
MID-SOUTH, SUN-TUE, JUL 30-AUG 1.
- HAZARDOUS HEAT ACROSS PORTIONS OF THE NORTHEAST AND
MID-ATLANTIC, FRI-SAT, JUL 28-JUL 29.
- HAZARDOUS HEAT ACROSS PORTIONS OF THE SOUTHEAST AND THE
MID-ATLANTIC, SAT-TUE, JUL 29-AUG 1.
- HAZARDOUS HEAT ACROSS PORTIONS OF THE SOUTHEAST, MON-TUE, JUL
31-AUG 1.
- HEAVY RAIN ACROSS PORTIONS OF SOUTHWESTERN ALASKA, FRI-SAT, JUL
28-JUL 29.
- HAZARDOUS HEAT ACROSS PORTIONS OF MAINLAND ALASKA, FRI, JUL 28.
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
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page