095
FXUS02 KWBC 240714
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
313 AM 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
(THOUGH STILL HOT) TEMPERATURES 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 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
MODEL GUIDANCE HAS REMAINED CONSISTENT AND AGREEABLE WITH THE
SOUTHWESTERN TO SOUTH-CENTRAL U.S. UPPER HIGH THROUGH THIS WEEK,
THOUGH BY THE WEEKEND INTO EARLY NEXT WEEK THERE IS SOME SLIGHT
DIVERGENCE IN SOLUTIONS WITH ITS CENTROID AS WESTERN ATLANTIC
RIDGING MAY STRETCH WEST AND INFLUENCE/COMBINE WITH IT,
PARTICULARLY SHOWN BY THE ECMWF AND CMC RUNS. THE NEWER 00Z ECMWF
LOOKS MORE IN LINE WITH OTHER GUIDANCE WITH DRIFTING THE HIGH EAST
COMPARED TO ITS 12Z RUN. FARTHER NORTH, THE LOW AMPLITUDE FLOW
CONTINUES TO PRESENT AN INCREDIBLY CHALLENGING FORECAST WHERE
SHORTWAVE DETAILS AND THE DEPTH OF ASSOCIATED TROUGHING ARE BOTH
UNCERTAIN, LEADING TO DIFFERENCES IN FRONTAL POSITIONS AND QPF.
WITHIN A TREND TOWARD MORE TROUGHINESS IN THE NORTHEAST AS THE
PERIOD PROGRESSES, IN TERMS OF THE 12Z/18Z GUIDANCE, THE GFS RUNS
SEEMED MOST AMPLIFIED WITH TROUGHING OVER THE NORTHEAST BY
FRIDAY-SATURDAY AND MANY (BUT NOT ALL) ENSEMBLE MEMBERS THAT WERE
AMPLIFIED WERE FROM THE GEFS AS WELL. A 12Z ECMWF/CMC TYPE OF
SOLUTION SEEMED MORE IN LINE WITH THE ENSEMBLE MEANS AND SO THIS
WAS MORE PREFERRED. THE 12Z UKMET BECAME OUT OF PHASE IN AREAS OF
SOUTHERN CANADA AND THE NORTHERN U.S. AND WAS NOT FAVORED. WITH
THE INCOMING 00Z MODEL CYCLE, THE ECMWF WAS EVEN LESS AMPLIFIED
THAN THE PREVIOUS RUN WHILE THE GFS IS PERHAPS MORE AMPLIFIED.
THIS IS CASTING EVEN MORE DOUBT ON THE ALREADY UNCERTAIN TIMING OF
THE COLD FRONT DROPPING SOUTH INTO THE NORTH-CENTRAL TO
NORTHEASTERN U.S. THAT COULD PRODUCE HEAVY QPF. UPSTREAM THERE ARE
MODEL DIFFERENCES TOO WITH TIMING OF ADDITIONAL ENERGIES/LOWS IN
THE EASTERN PACIFIC TO NORTHWEST. THE WPC FORECAST BEGAN WITH A
BLEND OF DETERMINISTIC AND ENSEMBLE GUIDANCE EARLY IN THE PERIOD
AND WITH TIME SHIFTED THE BALANCE TO OVER HALF ENSEMBLE MEANS TO
PROVIDE AN INTERMEDIATE SOLUTION. FOR QPF, ONCE 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 IS A LOT OF UNCERTAINTY
OVER THE PRECISE EAST-WEST TIMING AND SOUTHWARD EXTENT--KEEPING
CONFIDENCE LOW. THIS IS PARTICULARLY TRUE ON THURSDAY FOR THE DAY
4 ERO, WHERE THERE IS CONSIDERABLE UNCERTAINTY WITH PLACEMENT OF
HEAVY RAINFALL WITHIN THE GENERAL AREA OF THE NORTHERN TWO-THIRDS
OF THE PLAINS AND MISSISSIPPI VALLEY INTO THE APPALACHIANS AND
MID-ATLANTIC/NORTHEAST AHEAD OF FRONTAL BOUNDARIES. THERE DOES
SEEM TO BE SOME EMERGING FOCUS IN THE MODEL GUIDANCE FOR RAIN IN
AND AROUND THE LOWER GREAT LAKES REGION, BUT GIVEN THE UNCERTAINTY
WITH AMOUNTS AND PLACEMENT, CONTINUED TO HOLD OFF ON INTRODUCING
ANY MARGINAL RISK AREA. BY THE DAY 5 ERO TIMEFRAME FRIDAY,
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 THAT COULD LEAD TO FLOODING
ISSUES. TRAINING/REPEAT ACTIVITY IS ALSO LIKELY TO BECOME MORE OF
A FACTOR WITH THE FRONT TAKING ON A WEST-EAST ORIENTATION. THUS A
MARGINAL RISK IS IN PLACE ACROSS MUCH OF THE OHIO VALLEY TO
NORTHEAST FOR FRIDAY. HOWEVER THERE IS THE POSSIBILITY THAT SOME
GUIDANCE SHOWS WHERE THE FRONT IS SLOWER AND THE FRONT AND
THUNDERSTORMS ARE FOCUSED IN CANADA UNTIL SATURDAY, SO THIS WILL
CONTINUE TO BE MONITORED. RAIN AND THUNDERSTORMS LOOK 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 PLACEMENT AND AMOUNTS OF RAINFALL.
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. 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
CENTERED IN THE MID-MISSISSIPPI VALLEY, WITH LOW CONFIDENCE. THE
SOUTHEAST COULD SEE SLIGHTLY INCREASING TEMPERATURES INTO THE
WEEKEND AND EARLY NEXT WEEK UNDERNEATH SOME POTENTIAL RIDGING
INFLUENCE FROM THE WEST AND EAST. 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 ONLY NOTABLE AREA
OF POTENTIALLY BELOW NORMAL TEMPERATURES, THOUGH STILL WITH HIGHS
NO COOLER THAN A FEW DEGREES BELOW AVERAGE.
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
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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