027
FXUS02 KWBC 250701
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 AM 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 CONTINUES TO SHOW THE BEST AGREEMENT WITH THE UPPER
HIGH INITIALLY ATOP THE SOUTHERN ROCKIES GENERALLY TRENDING
EASTWARD WITH TIME, WITH SOME MINOR MODEL DIFFERENCES REGARDING
POTENTIAL INTERACTION/COMBINATION WITH RIDGING FARTHER EAST. A
GENERAL BLEND OF MODELS AND ENSEMBLES WAS ABLE TO HANDLE THAT
SUFFICIENTLY. THE FLOW PATTERN FARTHER NORTH HAS BEEN MUCH MORE
UNCERTAIN, GENERALLY LOW AMPLITUDE WITH SMALL-SCALE FEATURES
HAVING LOW PREDICTABILITY. FORTUNATELY IN THE LAST FEW MODEL
CYCLES OVERALL THERE SEEMS TO BE BETTER AGREEMENT AS LARGER SCALE
TROUGHING DEEPENS SLIGHTLY INTO THE NORTHEAST WITH TIME. THERE ARE
STILL SOME DIFFERENCES IN THE DEPTH OF THE TROUGH ON EACH DAY,
AFFECTING THE FRONTAL AND QPF PLACEMENT, BUT RUN-TO-RUN CONTINUITY
HAS BEEN RELATIVELY BETTER, ESPECIALLY WITH THE GFS AND ECMWF
RUNS. THE 12Z UKMET WAS NOT FAVORED AS THE WESTERN ATLANTIC RIDGE
SEEMED TO OVERPOWER THE TROUGH PRESSING INTO THE EAST AND THUS DID
NOT DEEPEN THE TROUGH LIKE OTHER GUIDANCE, WHILE THE 12Z CMC ENDED
UP LOOKING TOO FAST/EAST WITH THE EASTERN TROUGH NEXT WEEK. THEN
THERE ARE STILL SOME NOTABLE DIFFERENCES WITH FLOW FARTHER WEST
INTO THE EASTERN PACIFIC AND SOUTHWESTERN CANADA WHERE SHORTWAVES
ARE LIKELY, WITH THE 12Z UKMET LOOKING OFF AND NOW THE NEWER 00Z
GFS LOOKING A BIT SUSPECT WITH HOW FAST A SHORTWAVE TRACKS EAST
AND ERODES RIDGING IN THE NORTHERN ROCKIES OR SO EARLY NEXT WEEK.
SO THIS IS AN AREA THAT STILL REMAINS UNCERTAIN. THE WPC FORECAST
PREFERENCES FAVORED AN 18Z GFS AND 12Z EC AND CMC BLEND EARLY ON
WITH SMALLER COMPONENTS OF THE ENSEMBLE MEANS, REMOVING THE CMC
WITH TIME AND GRADUALLY INCREASING THE ENSEMBLE MEANS TO HALF BY
THE LATTER PART OF THE PERIOD. QPF 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
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 SHOULD 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 INTO EARLY NEXT WEEK AS
THE COLD FRONT MOVES SOUTH. THE NORTH-CENTRAL U.S. CAN ALSO EXPECT
SCATTERED STORMS STARTING LATE WEEK AND POSSIBLY INCREASING IN
COVERAGE/RAIN AMOUNTS INTO EARLY NEXT WEEK AS SHORTWAVES TRACK
THROUGH THE REGION AND MOISTURE INCREASES.
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 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 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.
COOLER TRENDS OVER THE NORTHEAST UNDER UPPER TROUGHING COULD NUDGE
HIGHS A LITTLE BELOW NORMAL BY EARLY NEXT WEEK.
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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