987
FXUS02 KWBC 202008
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
407 PM EDT THU JUL 20 2023
VALID 12Z SUN JUL 23 2023 - 12Z THU JUL 27 2023
***DANGEROUS HEAT WAVE PERSISTS ACROSS THE SOUTHWESTERN U.S.
THROUGH THE MIDDLE OF NEXT WEEK, AND HEAT BUILDS FARTHER NORTH
ACROSS THE NORTHERN HIGH PLAINS AND EVENTUALLY EXTENDING INTO THE
MIDWEST***
..OVERVIEW
A STRONG AND PERSISTENT UPPER RIDGE/HIGH ANCHORED OVER THE
SOUTHERN ROCKIES WILL KEEP HOTTER THAN USUAL TEMPERATURES ACROSS
THE SOUTHWEST INTO THE SOUTHERN PLAINS. AWAY FROM THE UPPER HIGH,
THE AMPLIFIED RIDGE-TROUGH PATTERN OVER THE LOWER 48 AS OF SUNDAY
SHOULD TREND STEADILY LESS AMPLIFIED OVER THE COURSE OF NEXT WEEK
AS A NORTHEASTERN PACIFIC UPPER LOW (PART OF A REX BLOCK
CONFIGURATION INCLUDING AN ALASKA/NORTHWESTERN CANADA RIDGE)
TRACKS INTO WESTERN CANADA AND FLOW TO ITS SOUTH BECOMES MORE
PROGRESSIVE ACROSS SOUTHERN CANADA AND THE FAR NORTHERN TIER OF
THE U.S. THE INITIAL EASTERN TROUGH SHOULD BECOME JUST A MODEST
WEAKNESS BY NEXT THURSDAY. THIS PATTERN EVOLUTION WILL LIKELY
SPREAD A NORTHERN AREA OF HEAT FROM THE NORTHERN ROCKIES/HIGH
PLAINS TOWARD THE MIDWEST. SOME DIURNALLY FAVORED SHOWERS AND
THUNDERSTORMS WILL BE POSSIBLE OVER THE FOUR CORNERS STATES AND
FRONTS/UPPER SHORTWAVES MAY PRODUCE SOME EPISODES OF CONVECTION
OVER THE EASTERN HALF OF THE COUNTRY, BUT OVERALL THE COVERAGE OF
HEAVY RAINFALL THREATS SHOULD BE LESS THAN AVERAGE FOR THE MIDDLE
OF SUMMER.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
WITHIN WHAT CONTINUES TO BE AN AGREEABLE PATTERN EVOLUTION AMONG
THE GUIDANCE, THE MOST CONTENTIOUS PART OF THE FORECAST STILL
INVOLVES WHAT HAPPENS TO THE NORTHEASTERN PACIFIC UPPER LOW AND
ITS SURROUNDING FLOW AFTER EARLY NEXT WEEK. GFS RUNS OVER THE
PAST DAY HAVE BECOME RATHER CONSISTENT IN BEING ON THE FASTER SIDE
OF THE GUIDANCE SPREAD FOR THE UPPER LOW BY DAYS 6-7
WEDNESDAY-THURSDAY, AND WHILE THE 12Z RUN HAS SLOWED A BIT VERSUS
00Z/06Z RUNS, THE 12Z UKMET IS SIMILAR TO THE 12Z GFS AND THIS
SCENARIO IS WITHIN THE REALM OF ENSEMBLE POSSIBILITIES. ECMWF/CMC
RUNS ARE STILL SOMEWHAT SLOWER WITH THE UPPER LOW. EITHER WAY,
CONSENSUS SUGGESTS THAT A WEAK TROUGH MAY LINGER NEAR THE PACIFIC
NORTHWEST COAST INTO NEXT THURSDAY. FARTHER EAST, THE
MODELS/MEANS AGREE THAT THE SOUTHERN ROCKIES UPPER RIDGE SHOULD
GRADUALLY EXTEND ITS REACH FARTHER EASTWARD ACROSS THE
SOUTH-CENTRAL PLAINS AS THE EASTERN TROUGH ALOFT FILLS. BY
MIDWEEK THE 12Z CMC IS SLOWER TO WEAKEN THE TROUGH VERSUS OTHER
GUIDANCE, WITH RECENT TRENDS ACTUALLY LEANING TOWARD SLIGHTLY
QUICKER WEAKENING OF THE TROUGH. A 00Z/06Z OPERATIONAL MODEL
BLEND EARLY AND A TRANSITION TO AN EVEN MODEL/ENSEMBLE MEAN WEIGHT
BY DAY 7 THURSDAY PROVIDED A GOOD REFLECTION OF CONSENSUS EARLY
AND DOWNPLAYED DETAILS THAT HAVE LOWER CONFIDENCE LATE IN THE
PERIOD.
..WEATHER/HAZARDS HIGHLIGHTS
THE COMBINATION OF THE FRONT LIKELY STALLING OVER THE SOUTH AND
LOCALIZED SEA BREEZE BOUNDARIES MAY HELP TO FOCUS SCATTERED TO
NUMEROUS SHOWERS AND STORMS NEAR THE GULF COAST REGION AND
SOUTHEAST THROUGH AT LEAST LATE WEEKEND, WITH COVERAGE/TOTALS
LIKELY DECREASING SOMEWHAT THEREAFTER. THE DAY 4 (SUNDAY-SUNDAY
NIGHT) EXCESSIVE RAINFALL OUTLOOK MAINTAINS A MARGINAL RISK AREA
FROM THE CENTRAL GULF COAST TO SOUTHEASTERN COAST. BY DAY 5
(MONDAY-MONDAY NIGHT), THE LOCALIZED HEAVY RAINFALL THREAT OVER
THE SOUTHERN TIER SHOULD BE CONFINED MORE TO THE SOUTHEAST COAST
BUT APPROACHING SHORTWAVE ENERGY COULD PROMOTE LOCALIZED HEAVY
RAINFALL FARTHER NORTH OVER PARTS OF THE
MID-ATLANTIC/APPALACHIANS. A MARGINAL RISK ENCOMPASSES THESE
AREAS. MEANWHILE DIURNALLY FAVORED CONVECTION MAY BE LOCALLY
HEAVY OVER PORTIONS OF THE FOUR CORNERS STATES DURING DAYS 4-5,
POSSIBLY EXPANDING NORTHWEST INTO SOME OF THE GREAT BASIN BY DAY 5
IN ASSOCIATION WITH MOISTURE AND SHORTWAVE ENERGY FLOWING AROUND
THE WESTERN PERIPHERY OF THE SOUTHERN ROCKIES UPPER RIDGE. THE
OUTLOOKS DEPICT A MARGINAL RISK AREA ON BOTH DAYS.
A FRONT DROPPING INTO THE MIDWEST/GREAT LAKES BY EARLY NEXT WEEK
AND LIKELY WEAKENING AS IT CONTINUES EASTWARD, ALONG WITH A
SEPARATE FRONT OVER THE PLAINS, MAY PRODUCE SHOWERS AND
THUNDERSTORMS AT TIMES THROUGH THE PERIOD. SOME OF THE RAINFALL
COULD BE LOCALLY HEAVY BUT GUIDANCE SIGNALS WITH RESPECT TO
LOCATION AND QPF MAGNITUDE APPEAR TOO DIFFUSE TO DEPICT ANY RISK
AREAS IN THE OUTLOOKS THROUGH DAY 5 FOR NOW. SHORTER TERM
GUIDANCE MAY EVENTUALLY PROVIDE ENOUGH FOCUS TO DEFINE REGIONS
WITH RELATIVELY GREATER HEAVY RAINFALL POTENTIAL. THE FOUR
CORNERS STATES WILL LIKELY SEE DIURNAL SHOWERS/STORMS CONTINUE
THROUGH THE END OF THE FORECAST PERIOD NEXT THURSDAY, WITH THE
SAME BEING THE CASE FOR THE FLORIDA PENINSULA.
THE STRONG UPPER RIDGE OVER THE SOUTHERN ROCKIES SHOULD KEEP
TEMPERATURES 5-10F ABOVE NORMAL OVER LOCATIONS FROM THE SOUTHWEST
INTO THE SOUTHERN HIGH PLAINS THROUGH THE PERIOD. EVEN IF THE
ANOMALIES OVER THE SOUTHWEST WILL BE A LITTLE LESS EXTREME THAN IN
THE SHORTER TERM, THE HEAT WILL CONTINUE TO BE HAZARDOUS INTO NEXT
WEEK. FLOW AROUND THE UPPER RIDGE WILL ALSO EXTEND HOT
TEMPERATURES (5-15F ABOVE NORMAL) INTO THE GREAT BASIN INTO
NORTHERN ROCKIES/HIGH PLAINS BY SUNDAY. THE GREAT BASIN SHOULD
TREND CLOSER TO NORMAL THEREAFTER, WHILE THE NEXT WORK WEEK SHOULD
SEE NORTHERN TIER HEAT SPREADING FORM THE NORTHERN PLAINS INTO THE
MIDWEST WITH HIGHS 10-15F ABOVE NORMAL. FLATTENING OF THE UPPER
FLOW OVER THE EAST MAY EVENTUALLY ALLOW FOR PLUS 5-10F ANOMALIES
TO REACH THE GREAT LAKES/OHIO VALLEY/NORTHEAST BY NEXT
WEDNESDAY-THURSDAY. SHOWER/THUNDERSTORM UNCERTAINTIES TEMPER
CONFIDENCE IN SOME TEMPERATURE DETAILS THOUGH. AWAY FROM THE
SOUTHWEST, THE HIGHEST HEAT INDEX VALUES (POSSIBLY REACHING OR
EXCEEDING 110F DURING PEAK AFTERNOON HEATING) SHOULD BE OVER
SOUTHERN TEXAS/WESTERN GULF COAST AND THE FLORIDA PENINSULA GIVEN
THE HIGH DEWPOINTS OVER THOSE AREAS. THE PACIFIC NORTHWEST WILL
TEND TO SEE HIGHS NEAR OR MODERATELY BELOW NORMAL DUE TO THE
PROXIMITY OF UPPER TROUGHING.
RAUSCH/HAMRICK
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:
- HEAVY RAIN ACROSS PORTIONS OF THE CENTRAL GULF COAST, SUN, JUL
23.
- HAZARDOUS HEAT ACROSS PORTIONS OF THE LOWER MISSISSIPPI VALLEY,
THE CENTRAL GREAT BASIN, THE
NORTHERN PLAINS, THE SOUTHERN PLAINS, THE NORTHERN ROCKIES, THE
CENTRAL ROCKIES, CALIFORNIA, THE
NORTHERN GREAT BASIN, THE SOUTHEAST, THE PACIFIC NORTHWEST, AND
THE SOUTHWEST, SUN-WED, JUL 23-JUL
26.
- HAZARDOUS HEAT ACROSS PORTIONS OF THE CENTRAL PLAINS, THE
CENTRAL ROCKIES, THE CENTRAL GREAT
BASIN, THE SOUTHERN ROCKIES, THE SOUTHERN PLAINS, AND THE
SOUTHWEST, MON-WED, JUL 24-JUL 26.
- HAZARDOUS HEAT ACROSS PORTIONS OF THE CENTRAL PLAINS, THE LOWER
MISSISSIPPI VALLEY, THE TENNESSEE
VALLEY, THE MIDDLE MISSISSIPPI VALLEY, THE SOUTHEAST, AND THE
SOUTHERN PLAINS, TUE-WED, JUL 25-JUL
26.
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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