031
FXUS02 KWBC 271900
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 PM EDT SAT JUL 27 2024
VALID 12Z TUE JUL 30 2024 - 12Z SAT AUG 03 2024
...HAZARDOUS HEAT TO SHIFT FROM THE SOUTH-CENTRAL PLAINS EARLY
PERIOD TO THE NORTHWEST LATER NEXT WEEK...
..OVERVIEW
GUIDANCE CONTINUES TO SHOW THE PATTERN EVOLVING TOWARD A
STRENGTHENING SOUTHERN ROCKIES/PLAINS UPPER RIDGE WHICH WILL BUILD
BACK AND AMPLIFY ACROSS THE WEST LATER NEXT WEEK. THIS SHOULD HELP
SET UP A PROLONGED PERIOD OF HOT WEATHER OVER MANY AREAS WITH THE
MOST ANOMALOUS HEAT EXPECTED OVER CENTRAL PARTS OF THE PLAINS EARLY
TO MIDWEEK. WARMER THAN NORMAL TEMPERATURES ARE FORECAST TO EXPAND
NORTH TOWARD THE U.S./CANADIAN BORDER LATER IN THE WEEK, DESPITE
SHORTWAVE ENERGY MOVING THROUGH THE MIDWEST AND EVENTUALLY
DEVELOPING MEAN TROUGHING OVER THE EASTERN U.S. THAT WILL SUPPORT A
BROAD AREA OF SHOWERS/THUNDERSTORMS DRIFTING ACROSS THE EASTERN
HALF OF THE COUNTRY.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODEL GUIDANCE IS AT LEAST AGREEABLE ON THE LARGE SCALE REGARDING
THE INITIALLY SOUTHERN TIER RIDGE SHIFTING AND BUILDING OVER THE
WEST LATER NEXT WEEK. THE MAIN MODEL UNCERTAINTIES ARE WITH THE
PATTERN TO THE NORTH, WITH TIMING AND STRENGTH DIFFERENCES OF
SHORTWAVES EVEN EARLY IN THE FORECAST PERIOD. THE MODEL SPREAD IN
THE DETAILS MADE IT DIFFICULT TO DETERMINE OUTLIERS, BUT THOUGHT
THE 00Z CMC WAS A BIT FAST WITH AN INITIAL GREAT LAKES SHORTWAVE
AND A NORTHWEST SHORTWAVE INTO TUESDAY, SO FAVORED OTHER GUIDANCE
INSTEAD. THEN BY THE LATTER PART OF THE WEEK, THE 00Z ECMWF (AND
THE NEWER 12Z ECMWF AS WELL) WERE ON THE SLOWER SIDE OF THE
ENVELOPE WITH A NORTH-CENTRAL U.S. SHORTWAVE AND A SURFACE
LOW/FRONTAL SYSTEM. EVEN THE ECMWF-BASED AI/MACHINE LEARNING MODELS
WERE FASTER, SO THIS PROVIDED CONFIDENCE TO LEAN AWAY FROM THE
SLOWER OPERATIONAL EC SOLUTION.
ANOTHER FEATURE TO WATCH BY THE END OF THE PERIOD IS THE POTENTIAL
FOR A TROPICAL CYCLONE TO APPROACH THE FORECAST AREA. MODELS HAVE
SHOWN AMPLE SPREAD IN THE PLACEMENT AND EVEN THE EXISTENCE OF THIS
LOW. THE DETERMINISTIC ECMWF AND THE EC ENSEMBLE MEMBERS HAVE BEEN
SHOWING IT MOST CONSISTENTLY. OPERATIONAL RUNS HAVE BEEN TRACKING
THE TROPICAL LOW TO THE EAST OF FLORIDA BUT SOME OF ITS ENSEMBLE
MEMBERS TAKE IT WEST OF FLORIDA INTO THE GULF OF MEXICO. RECENT GFS
RUNS HAD BEEN SHOWING A TROPICAL LOW AS WELL (INTO THE GULF),
UNTIL THE 12Z GFS DROPS IT COMPLETELY. THE EC-BASED AI/ML MODELS
VARY FROM NOT HAVING A LOW, TO HAVING A WEAK ONE ON EITHER SIDE OF
FLORIDA, WHILE THE AIFS IS SIMILAR TO THE OPERATIONAL ECMWF. CMC
RUNS ARE SLOWER BUT SHOW A GULF LOW. OVERALL, SOMETHING TO WATCH
BUT LOW CONFIDENCE OF WHAT ENDS UP OCCURRING.
THE WPC FORECAST USED A DETERMINISTIC BLEND EARLY IN THE PERIOD,
WITH LESS WEIGHTING FOR THE CMC AND EVENTUALLY ELIMINATING THE
ECMWF GOING FORWARD IN TIME, IN FAVOR OF THE GEFS AND EC ENSEMBLE
MEANS.
..WEATHER/HAZARDS HIGHLIGHTS
A WET PATTERN IS LIKELY FROM THE MIDWEST TO THE EASTERN SEABOARD
NEXT WEEK WITH AMPLE MOISTURE AND INSTABILITY IN PLACE AS WELL AS
MEAN TROUGHING ALOFT AND SURFACE FRONTAL SYSTEMS FOR SCATTERED
THUNDERSTORMS. THUS THE DAYS 4-5 EXCESSIVE RAINFALL OUTLOOKS
COVERING TUESDAY- WEDNESDAY NIGHT SHOW FAIRLY BROAD MARGINAL RISKS
ACROSS PARTS OF THE MIDWEST TO THE NORTHEAST. MODELS CONTINUE TO
SHOW A FOCUS FOR POTENTIALLY MULTIPLE ROUNDS OF STORMS AFFECTING
EASTERN PARTS OF THE OHIO VALLEY INTO THE CENTRAL/SOUTHERN
APPALACHIANS, WHICH IS ALSO AN AREA WITH RELATIVELY LOW FLASH FLOOD
GUIDANCE, SO AN EMBEDDED SLIGHT RISK REMAINS IN PLACE THERE FOR
TUESDAY. BY WEDNESDAY, MODEL GUIDANCE HAS TRENDED DRIER IN THAT
REGION, SO REMOVED THE DAY 5 SLIGHT RISK FROM THE APPALACHIANS THAT
WAS IN THE PREVIOUS ISSUANCE. HOWEVER, MODEL GUIDANCE IS KEYING IN
ON A LIKELY MESOSCALE CONVECTIVE SYSTEM WITH HEAVY RAIN RATES
MOVING ON THE CUSP OF THE INSTABILITY GRADIENT IN NORTHWEST MEAN
FLOW THAT SHOULD AFFECT PARTS OF THE MIDWEST DURING THAT PERIOD.
THERE IS SOME PLACEMENT SPREAD WITH THIS, BUT THE ANTECEDENT WET
CONDITIONS FOR MUCH OF THE AREA AND THE HEAVY RAINFALL POTENTIAL
SEEMS TO WARRANT A DAY 5/WEDNESDAY SLIGHT RISK ACROSS THE MIDWEST,
THOUGH THE AREA WILL LIKELY BE ADJUSTED IN FUTURE FORECASTS IF/WHEN
MODELS CONVERGE. MUCH OF THE NORTH-CENTRAL U.S. TO THE EASTERN
THIRD OF THE COUNTRY SHOULD REMAIN GENERALLY UNSETTLED THE REST OF
THE WEEK AS A UPPER TROUGH IS SLOW TO BUDGE OUT OF THE REGION WHILE
IT GENERALLY WEAKENS.
ELSEWHERE, MONSOONAL CONVECTION OVER THE SOUTHWEST SHOULD STAY
CONFINED TO SOUTHERN AREAS THROUGH MIDWEEK, AND MARGINAL RISKS
REMAIN REASONABLE FOR THE DAYS 4-5 EROS. CHANCES FOR CONVECTION MAY
EXPAND NORTHEASTWARD INTO LATER WEEK DEPENDING ON THE SHAPE OF THE
SOUTHERN ROCKIES/PLAINS RIDGE AND UPPER LEVEL ENERGY ROTATING
AROUND ITS WESTERN PERIPHERY. SOME RAIN IS FORECAST FOR THE
NORTHWEST INTO TUESDAY WITH AN INITIAL SHORTWAVE. ALSO ON TUESDAY,
ABOVE NORMAL PRECIPITABLE WATER VALUES SHOULD LEAD TO WIDESPREAD
RAIN/STORMS ACROSS THE FLORIDA PENINSULA, SO A MARGINAL RISK STILL
LOOKS ON TRACK THERE FOR THE DAY 4 ERO BEFORE MOISTURE LESSENS
MIDWEEK.
THE FORECAST PATTERN EVOLUTION WILL SUPPORT AN EXPANDING AREA OF
WARMER THAN AVERAGE TEMPERATURES ACROSS THE LOWER 48. THE MOST
SIGNIFICANT HIGH TEMPERATURE ANOMALIES SHOULD BE OVER THE CENTRAL
PLAINS EARLY ON WHERE SOME LOCATIONS SHOULD SEE MULTIPLE DAYS WITH
HIGHS 10-15F OR SO ABOVE NORMAL AND HIGH TEMPERATURES BROACH 105F.
THE EXPERIMENTAL HEATRISK LIKEWISE REFLECTS AN EXPANDING AREA OF
MODERATE TO MAJOR RISKS OF HEAT-RELATED IMPACTS THROUGH NEXT
WEDNESDAY, AND EVEN SOME POCKETS IN THE EXTREME CATEGORY IN THE
SOUTH-CENTRAL PLAINS. AN INCOMING FRONT WILL CAUSE SOME EASING OF
THE HEAT LATE NEXT WEEK IN THAT REGION. MUCH OF THE WEST WILL
LIKELY SEE NEAR TO SLIGHTLY BELOW NORMAL HIGHS THROUGH THE FIRST
HALF OF NEXT WEEK BEFORE THE STRENGTHENING RIDGE PUSHES
TEMPERATURES ABOVE NORMAL BY NEXT THURSDAY, AND MORE SIGNIFICANTLY
SO NEXT FRIDAY INTO SATURDAY WITH LOWER ELEVATIONS SEEING 100F+
HIGH TEMPERATURES. THE OHIO VALLEY TO MID-ATLANTIC AND NORTHEAST
SHOULD ALSO TREND WARMER WITH TIME NEXT WEEK.
TATE/SANTORELLI
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 (QPF), EXCESSIVE RAINFALL
OUTLOOK (ERO), WINTER WEATHER OUTLOOK (WWO) PROBABILITIES, HEAT
INDICES, AND KEY MESSAGES CAN BE ACCESSED FROM:
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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