713
FXUS02 KWBC 191900
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
259 PM EDT WED JUL 19 2023
VALID 12Z SAT JUL 22 2023 - 12Z WED JUL 26 2023
***DANGEROUS HEAT WAVE PERSISTS ACROSS THE SOUTHWESTERN U.S.
THROUGH EARLY NEXT WEEK, AND HEAT BUILDS FARTHER NORTH ACROSS THE
NORTHERN HIGH PLAINS AND EVENTUALLY EXTENDING INTO THE MIDWEST***
..GENERAL OVERVIEW
GUIDANCE AGREES WELL UPON A PERSISTENTLY STRONG FOUR CORNERS UPPER
HIGH WITH A RIDGE EXTENDING NORTH INTO SOUTHERN CANADA, WHILE A
DOWNSTREAM EASTERN U.S. UPPER TROUGH ACHIEVES ITS GREATEST
DEPTH/AMPLITUDE DURING THE WEEKEND BEFORE TRENDING SOMEWHAT MORE
SHALLOW NEXT MONDAY-WEDNESDAY. THE NORTHEASTERN
PACIFIC/NORTHWESTERN NORTH AMERICA PATTERN SHOULD TAKE ON A REX
BLOCK APPEARANCE, WITH SOME HEIGHT FALLS POSSIBLY REACHING THE
NORTHWESTERN U.S. AS THE PACIFIC UPPER LOW DRIFTS TOWARD/INTO
BRITISH COLUMBIA. THE FOUR CORNERS UPPER HIGH/RIDGE SHOULD
SUPPORT CONTINUATION OF THE INTENSE HEAT WAVE OVER THE DESERT
SOUTHWEST AND A REBOUND OF HEAT OVER THE SOUTHERN ROCKIES/HIGH
PLAINS AFTER THE WEEKEND, WHILE THE PATTERN EVOLUTION WILL LIKELY
HELP TO SPREAD HOT TEMPERATURES INTO THE NORTHERN ROCKIES/HIGH
PLAINS DURING THE WEEKEND AND EXTENDING FARTHER EASTWARD INTO THE
MIDWEST NEXT WEEK. MEANWHILE, A FRONTAL BOUNDARY SETTLING INTO
THE SOUTH WILL BRING EPISODES OF POTENTIALLY HEAVY RAINFALL AND
STRONG STORMS ACROSS MUCH OF THE GULF COAST REGION AND THE FLORIDA
PENINSULA, AND ALSO HELP TO TEMPER THE ONGOING SOUTHERN TIER HEAT
WAVE.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
FORECAST ISSUES WITHIN THE AGREEABLE LARGE SCALE PATTERN HAVE NOT
CHANGED MUCH OVER THE PAST DAY. GUIDANCE IS GRADUALLY TRYING TO
CONVERGE FOR THE SPECIFICS OF SHORTWAVE ENERGY AND ASSOCIATED
SURFACE EVOLUTION AFFECTING THE NORTHEAST INTO THE WEEKEND, WHILE
PREDICTABILITY IS LOW FOR TRAILING SHORTWAVES THAT WILL INFLUENCE
SPECIFICS OF THE WAVY FRONT THAT SHOULD LINGER OVER THE WESTERN
ATLANTIC INTO THE SOUTHERN TIER STATES THROUGH THE FIRST PART OF
NEXT WEEK. DETAILS ARE STILL SOMEWHAT AMBIGUOUS AND VARIABLE FOR
SHORTWAVE ENERGY DROPPING INTO THE WESTERN SIDE OF THE MEAN
TROUGH, TEMPERING CONFIDENCE FOR DETAILS OF A FRONT THAT MAY REACH
THE MIDWEST/GREAT LAKES EARLY NEXT WEEK. IN DIFFERING WAYS THE
06Z/12Z GFS RUNS ARE SOMEWHAT ON THE EXTREME SIDE OF GUIDANCE IN
BEING FASTER TO BRING THE PACIFIC UPPER LOW/SURROUNDING FLOW INTO
WESTERN NORTH AMERICA. THE 06Z GFS WAS THE MORE EXTREME OF THE
TWO IN TERMS OF HEIGHT FALLS REACHING THE NORTHWESTERN U.S. BASED
ON THE 00Z/06Z GUIDANCE COMPARISONS, THE UPDATED FORECAST STARTED
WITH A 00Z/06Z OPERATIONAL MODEL BLEND EARLY IN THE PERIOD. 06Z
GFS ISSUES OVER THE NORTHWEST FAVORED SWAPPING IN THE 00Z VERSION
FOR GFS INPUT BY DAYS 5-7 MONDAY-WEDNESDAY, WHILE ADDING IN SOME
GEFS/ECENS/CMCENS MEAN GUIDANCE DURING THE LATTER HALF OF THE
PERIOD HELPED TO DOWNPLAY LOWER CONFIDENCE DETAILS THAT ARISE BY
THAT TIME.
..WEATHER/HAZARDS HIGHLIGHTS
THE WAVY FRONT SETTLING INTO THE SOUTH THIS WEEKEND ALONG WITH ANY
SEA BREEZE BOUNDARIES SHOULD PROVIDE A FOCUS FOR SHOWERS AND
THUNDERSTORMS THAT MAY PRODUCE SOME LOCALLY HEAVY RAINFALL DUE TO
THEIR SLOW MOVEMENT OR REPEATING OVER THE SAME AREA. THE DAYS 4-5
EXCESSIVE RAINFALL OUTLOOKS THAT COVER THE SATURDAY-SUNDAY NIGHT
PERIOD DEPICT A MARGINAL RISK AREA FOR FLOODING POTENTIAL FROM THE
CENTRAL GULF COAST REGION TO NORTHERN FLORIDA/SOUTHEAST COAST
WHERE THE BEST COMBINATION OF MOISTURE, FORCING, AND INSTABILITY
WILL EXIST. AN EMBEDDED SLIGHT RISK AREA COULD EVENTUALLY ARISE
IF SHORTER TERM GUIDANCE CLUSTERS SUFFICIENTLY IN TERMS OF
LOCATION AND QPF MAGNITUDE, BUT FOR NOW THE SIGNAL DOES NOT APPEAR
STRONG ENOUGH TO INTRODUCE SUCH AN AREA YET. ACROSS THE WESTERN
U.S., A MARGINAL RISK AREA IS VALID FOR BOTH DAYS 4 AND 5 FROM
SOUTHEASTERN COLORADO ACROSS MUCH OF NEW MEXICO AND INTO EASTERN
PORTIONS OF ARIZONA. WITH THE CORE OF THE UPPER HIGH EXPECTED TO
BE OVER THE FOUR CORNERS REGION, THIS WILL RESULT IN SOME
ADVECTION OF MONSOONAL MOISTURE FROM WESTERN MEXICO NORTHWARD
ACROSS THE SOUTHERN ROCKIES, RESULTING IN ISOLATED TO PERHAPS
SCATTERED COVERAGE OF SLOW MOVING THUNDERSTORMS THAT CAN BE
EXPECTED MAINLY DURING THE AFTERNOON AND EVENING HOURS. AFTER
SUNDAY EXPECT LINGERING SHOWERS AND THUNDERSTORMS ACROSS THE GULF
COAST REGION TO BECOME MORE SCATTERED WITH TIME AS THE FRONT TO
THE NORTH WEAKENS. MEANWHILE ONE OR MORE EPISODES OF
SHOWERS/STORMS WILL BE POSSIBLE OVER THE MIDWEST AND EVENTUALLY
EXTENDING INTO THE EAST DUE TO A COMBINATION OF SHORTWAVES WITHIN
THE UPPER TROUGH AND A FRONT PUSHING SOUTHEAST FROM CANADA. IT
WILL TAKE ADDITIONAL TIME TO RESOLVE COVERAGE AND TOTALS FROM THIS
POTENTIAL ACTIVITY. ISOLATED MONSOONAL SHOWERS/STORMS ARE LIKELY
TO CONTINUE ACROSS PARTS OF THE FOUR CORNERS REGION.
THE FOUR CORNERS UPPER RIDGE WILL MAINTAIN THE EXTREME HEAT OVER
THE SOUTHWEST THROUGH THE WEEKEND AND EARLY NEXT WEEK.
TEMPERATURES OF 5-15 DEGREES ABOVE AVERAGE FOR BOTH HIGHS AND LOWS
OVER THE DESERT SOUTHWEST AS OF SATURDAY MAY DECLINE A BIT TO 5-10
DEGREES ABOVE NORMAL FOR HIGHS THEREAFTER BUT THIS HEAT WILL
REMAIN HAZARDOUS. THIS WILL EQUATE TO HIGHS WELL INTO THE 110S
FOR THE LOWER ELEVATIONS OF EASTERN CALIFORNIA, SOUTHERN ARIZONA,
AND SOUTHERN NEVADA, WITH THE POTENTIAL FOR ADDITIONAL RECORD HIGH
TEMPERATURES BEING ESTABLISHED AND RECORD LONG STREAKS OF 110+
DEGREE READINGS FOR SOME ARIZONA LOCATIONS. MEANWHILE
TEMPERATURES OVER THE SOUTHERN HIGH PLAINS/ROCKIES SHOULD REBOUND
TO 5-10F ABOVE NORMAL AFTER A BRIEF TIME NEAR NORMAL ON SATURDAY.
FARTHER NORTH, THE INTERMOUNTAIN WEST INTO NORTHERN ROCKIES SHOULD
SEE HIGHS/LOWS 5-15F ABOVE NORMAL DURING THE WEEKEND FOLLOWED BY
GRADUAL MODERATION AS THE NORTHERN AREA OF ANOMALOUS HEAT SHIFTS
ITS FOCUS FROM THE NORTHERN HIGH PLAINS (ALREADY STARTING BY THE
WEEKEND) TOWARD THE MIDWEST. BY NEXT WEDNESDAY, HIGHS FROM THE
NORTHERN HALF OF THE PLAINS INTO PARTS OF THE MIDWEST SHOULD BE
5-15F ABOVE NORMAL (90S TO AROUND 100). THESE MAY APPROACH OR
EXCEED THE HIGHEST TEMPERATURES OF THE SUMMER SO FAR AT SOME
LOCATIONS. PARTS OF THE SOUTH SHOULD SEE A REPRIEVE FROM THIS
WEEK'S INTENSE HEAT AS A FRONTAL BOUNDARY STALLS OVER THE REGION.
IT WILL STILL BE QUITE HOT AND HUMID FOR SOUTHERN TEXAS WHERE HEAT
INDICES MAY EXCEED 110 DEGREES DURING PEAK AFTERNOON HEATING AND
THE FLORIDA PENINSULA MAY SEE HAZARDOUS HEAT INDICES AS WELL.
MOST AREAS EAST OF THE MISSISSIPPI RIVER SHOULD GENERALLY BE
WITHIN A FEW DEGREES OF LATE JULY AVERAGES WITH NO MAJOR HEAT
WAVES.
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
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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