623
FXUS02 KWBC 261901
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 PM EDT WED JUL 26 2023
VALID 12Z SAT JUL 29 2023 - 12Z WED AUG 02 2023
...THE BEST POTENTIAL FOR HAZARDOUS HEAT SHOULD SHIFT INTO THE
CENTRAL PLAINS/MID-MISSISSIPPI VALLEY AND THE SOUTHEAST THIS
WEEKEND INTO 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 EVENTUALLY 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. RIDGING
STRETCHING NORTH FROM THE UPPER HIGH 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. A "RING OF FIRE" TYPE OF PATTERN IS LIKELY IN
THE PRECIPITATION FORECAST, AS MONSOONAL MOISTURE LEADS TO
DIURNALLY DRIVEN CONVECTION IN THE FOUR CORNERS STATES AND
VICINITY, SHORTWAVES PUSH THROUGH NORTHWEST FLOW AND SPARK
THUNDERSTORMS IN THE NORTH-CENTRAL U.S., AND A COLD FRONT PRESSING
SOUTH AND THEN STALLING HELPS TO FOCUS RAIN AND STORMS ALONG THE
EASTERN SEABOARD. THERE IS A RISK OF HEAVY RAINFALL AND FLASH
FLOODING IN THESE AREAS WHERE HIGH RAIN RATES OCCUR AND WHERE
STORMS TRAIN/OCCUR OVER THE SAME AREAS.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
LATEST MODEL GUIDANCE HAS REMAINED MOSTLY CONSISTENT ON THE
OVERALL UPPER-LEVEL PATTERN THROUGH MUCH OF THE MEDIUM RANGE
PERIOD. A BROAD UPPER-LEVEL HIGH OVER THE SOUTHERN TIER IS
FORECAST TO CONSOLIDATE ONCE AGAIN OVER THE
SOUTHWEST/SOUTH-CENTRAL U.S., AS HAS BEEN THE CASE FOR MUCH OF THE
LAST FEW WEEKS. MEAN TROUGHING WILL BUILD IN OVER THE NORTHEAST
FOLLOWING THIS CONSOLIDATION WITH ANOTHER TROUGH LOCATED ALONG
PACIFIC NORTHWEST COAST, WITH THE MAIN UPPER-LEVEL FLOW OVER THE
U.S. OVER THE NORTHERN TIER. THE UPPER HIGH IS EXPECTED TO SHIFT
SLOWLY EASTWARD OVER THE SOUTH-CENTRAL U.S. MID-PERIOD AND
EVENTUALLY TOWARDS THE SOUTHEASTERN U.S. AS THE OVERALL PATTERN
AMPLIFIES A BIT. RIDGING WILL BUILD SOMEWHAT NORTHWARD STRETCHING
FROM THE PACIFIC NORTHWEST THROUGH THE NORTHERN ROCKIES AND PLAINS
AS THE TROUGH OVER THE EAST DIPS SOUTHWARD. THE NORTHERN STREAM
HAS TRENDED SLIGHTLY MORE AMPLIFIED DURING THE FORECAST PERIOD,
MOST NOTICEABLE RUN-TO-RUN IN THE GFS, CULMINATING WITH THE 06Z
RUN, AND TO A LESSER EXTENT THE 00Z RUN. HOWEVER, THE GUIDANCE
REMAINS IN GENERALLY GOOD AGREEMENT OVERALL ON THE LARGE-SCALE
THROUGH THE MID-PERIOD, WITH THE MOST NOTICEABLE DIFFERENCES
RELATED TO THE TIMING AND STRENGTH OF EMBEDDED WAVES IN THE FLOW
REGIME ACROSS THE WEST AND NORTHERN TIER OF THE COUNTRY
SURROUNDING THE SOUTHERN UPPER HIGH.
PREDICTABILITY DECREASES IN THE LATE PERIOD AS DISAGREEMENT ARISES
OVER HOW FAR EAST THE UPPER-HIGH SHIFTS, AND CONSEQUENTLY THE
EVOLUTION OF MEAN TROUGHING OVER THE NORTHEASTERN U.S., WHICH
WOULD EITHER WEAKEN AND/OR SHIFT EASTWARD UNDER THIS SCENARIO. THE
MOVEMENT OF THE UPPER HIGH NOTABLY TRENDED SLOWER ACROSS THE
GUIDANCE RUN-TO-RUN AS WELL. THE 00Z/06Z GFS RUNS ARE BOTH
FURTHEST EAST WITH THE UPPER HIGH, WITH THE 06Z GEFS AND 00Z ECENS
MEANS A BIT FURTHER WEST, FOLLOWED BY THE 00Z ECMWF AND 00Z CMC.
THE GFS HAS ALSO TRENDED TOWARDS MORE EMBEDDED UPPER ENERGY OVER
THE WEST COMPARED TO THE ECMWF/CMC OR ENSEMBLE MEANS, WHICH WILL
HAVE IMPLICATIONS ON MONSOON/OVERALL PRECIPITATION ACTIVITY OVER
THE REGION.
WITH GOOD OVERALL LARGE-SCALE AGREEMENT EARLY IN THE PERIOD A
GENERAL MODEL BLEND IS INITIALLY USED FOR THE UPDATED WPC
FORECAST. CONTRIBUTIONS FROM THE CMC AND GFS ARE REDUCED GIVEN
NOTED FORECAST DIFFERENCES LATER IN THE PERIOD, WITH THE MEANS AND
ECMWF OFFERING A GOOD COMPROMISE BETWEEN THE UPPER-HIGH PLACEMENT.
THIS ALSO AVOIDS TRENDING TOO MUCH TOWARDS DEPICTING EMBEDDED
ENERGY OVER THE WEST AS INDICATED BY THE GFS UNTIL IT BECOMES A
MORE RELIABLE PATTERN ACROSS THE GUIDANCE, UNLIKELY UNTIL FORECAST
LEAD-TIME DECREASES. THE NOTED DISAGREEMENT OVER THE UPPER-HIGH
PLACEMENT IN THE GUIDANCE LED TO THE BIGGEST DIFFERENCES WITH THE
PRIOR FORECAST, AND WILL HAVE IMPLICATIONS ON PRECIPITATION
CHANCES AND HIGH TEMPERATURES OVER THE SOUTHEAST, WITH
TEMPERATURES TRENDING COOLER IN THIS FORECAST CYCLE, PARTICULARLY
FOR THE CAROLINAS.
..WEATHER/HAZARDS HIGHLIGHTS
SHOWERS AND THUNDERSTORMS LOOK LIKELY ACROSS MUCH OF THE
NORTH-CENTRAL AND EASTERN U.S. THROUGH THE WEEKEND 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 FORCE CONVECTION. MORE
SPECIFICALLY, A COLD FRONT PRESSING SOUTHWARD ACROSS THE NORTHEAST
ON SATURDAY AND THE MID-ATLANTIC ON SUNDAY SHOULD FOCUS STORMS
ALONG AND AHEAD OF IT. WITH SHORTWAVES ALOFT AND THE COLD FRONT
SHOWING A GENERAL WEST-EAST ORIENTATION ALLOWING FOR
TRAINING/REPEAT ACTIVITY, A BROAD MARGINAL RISK HAS BEEN
MAINTAINED ACROSS THE NORTHEAST TO MID-ATLANTIC FOR THE DAY 4 ERO
(SATURDAY JULY 29). THE RISK AREA IS BROADER/FARTHER SOUTH INTO
THE TENNESSEE VALLEY/CAROLINAS THAN JUST THE FRONTAL CONVECTION
ITSELF SINCE THE ENVIRONMENT TO THE SOUTH OF THE FRONT WILL BE
UNSTABLE AND HIGH RAIN RATES ARE LIKELY, PLUS THE FRONT WILL BE
MOVING SOUTH THROUGH THE DAY. THERE IS ALSO STILL SIGNIFICANT
MODEL DISAGREEMENT IN THE LOCATION OF HIGHER RAINFALL AMOUNTS,
WITH SOME STRONG SIGNALS PRESENT BUT SIGNIFICANT AREAL
DISPLACEMENT. FUTURE SLIGHT RISKS CANNOT BE RULED OUT WITHIN THIS
BROAD MARGINAL. ONE SUCH AREA WHERE A SLIGHT RISK WAS CONSIDERED
WAS ACROSS WEST VIRGINIA, WHERE UPSLOPE FLOW COULD ENHANCE RAIN
TOTALS AND IT TENDS TO BE MORE SENSITIVE IN THE VARYING TERRAIN.
ANOTHER AREA OF CONCERN IS OVER NEW ENGLAND, ESPECIALLY IF
CONFIDENCE GROWS FOR PORTIONS OF INTERIOR NEW ENGLAND THAT ARE
SENSITIVE GIVEN RECENT SIGNIFICANT RAINFALL EVENTS. HOWEVER, GIVEN
THE SIGNIFICANT DISAGREEMENT IN AREAL COVERAGE AND HIGH FFGS NEAR
THE COAST WHERE SOME OF THE STRONGER QPF SIGNALS ARE PRESENT, A
MARGINAL RISK REMAINS SUFFICIENT FOR NOW. BY THE DAY 5 ERO
TIMEFRAME SUNDAY, THE NORTHEAST SHOULD BE POST-FRONTAL AND DRY
WHILE CONVECTION FOCUSES FARTHER SOUTH. A MARGINAL RISK COVERS
VIRGINIA AND THE CAROLINAS GENERALLY, AND BACK INTO THE SOUTHERN
APPALACHIANS IN CASE HEAVY RAIN FALLS IN SENSITIVE MOUNTAINOUS
AREAS. THE COLD FRONT SHOULD PUSH EVEN FARTHER SOUTH MONDAY FOR A
CONVECTIVE FOCUS OVER THE SOUTHEAST, BUT THE FRONT LIFTING AND/OR
REFORMING BY TUESDAY-WEDNESDAY COULD PUT RAIN CHANCES IN THE
NORTHEAST TO MID-ATLANTIC BY THEN, WITH PRECIPITATION CHANCES
TRENDING UPWARD ACROSS THE REGION.
MEANWHILE, THE NORTH-CENTRAL U.S. CAN ALSO EXPECT SCATTERED STORMS
AS SHORTWAVES TRACK THROUGH THE REGION AND MOISTURE INCREASES. A
HEAVY RAIN/FLASH FLOODING THREAT WILL LIKELY BE TIED TO THE
POTENTIAL FOR ORGANIZED CONVECTIVE SYSTEMS IN NORTHWESTERLY FLOW.
DAY TO DAY POSITIONS OF HEAVY RAIN AND MCSS ARE UNCERTAIN AND VARY
SOMEWHAT AMONG MODEL GUIDANCE, BUT MARGINAL RISKS COVER THIS
POTENTIAL OVER THE WEEKEND. THE FOUR CORNERS STATES ARE LIKELY TO
SEE DIURNALLY DRIVEN CONVECTION EACH DAY AS MONSOONAL MOISTURE
COMES IN UNDERNEATH THE SOUTHERN ROCKIES UPPER RIDGE. AS THE RIDGE
SHIFTS EASTWARD NEXT WEEK, THIS MAY INCREASE MOIST SOUTHERLY FLOW
AND ALLOW FOR ADDITIONAL SHORTWAVE ENERGY TO COME IN, SO RAINFALL
TOTALS MAY BECOME MORE WIDESPREAD AND LOCALLY HEAVIER AS THE WEEK
PROGRESSES. FLORIDA AND PARTS OF THE GULF COAST SHOULD SEE SOME
SCATTERED SHOWERS AND THUNDERSTORMS AS WELL, AND A MARGINAL RISK
IS IN PLACE ON DAY 4/SATURDAY ACROSS THE WEST COAST OF THE FLORIDA
PENINSULA BEFORE A PLUME OF WELL ABOVE (ALREADY HIGH) AVERAGE
PRECIPITABLE WATER VALUES THAT COULD PRODUCE HEAVY RAINFALL RATES
EXITS TO THE WEST. URBAN AREAS WILL BE PARTICULARLY SENSITIVE TO
HEAVY RAIN POTENTIAL.
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 SATURDAY. BY EARLY NEXT
WEEK, HIGHS SHOULD FINALLY EASE TO NEAR NORMAL THERE WITH THE
CENTER OF THE UPPER HIGH FORECAST TO DRIFT EAST, THOUGH THIS IS
STILL OVER 100F IN MANY AREAS. FARTHER EAST, TEMPERATURES
APPROACHING OR OVER 100F ARE LIKELY ACROSS THE CENTRAL/SOUTHERN
PLAINS INTO THE MIDDLE/LOWER MISSISSIPPI VALLEY FOR THE WEEKEND
INTO NEXT WEEK WITH TEMPERATURES AROUND 10-15F ABOVE NORMAL. IN
SOME AREAS, THE EXACT LOCATIONS SEEING NEAR NORMAL OR ABOVE NORMAL
TEMPERATURES WILL DEPEND ON THE AXIS OF A FRONT MEANDERING FROM
DAY TO DAY, AS WELL AS DETAILS OF CONVECTION AND RESIDUAL CLOUD
COVER. THE SAME IS TRUE ACROSS THE EAST--ANOTHER WARMER THAN
AVERAGE DAY LOOKS LIKELY ON SATURDAY IN THE OHIO AND TENNESSEE
VALLEYS TO MID-ATLANTIC, WITH A FEW RECORD HIGHS POSSIBLE AND
WIDESPREAD RECORD WARM MINIMUM TEMPERATURES LIKELY. THE COLD FRONT
SHOULD PUT THESE AREAS CLOSER TO NORMAL BY EARLY NEXT WEEK, AND
TEMPERATURES MAY EVEN BE A FEW DEGREES BELOW NORMAL IN THE
NORTHEAST. MEANWHILE THE SOUTHEAST/GULF COAST SHOULD SEE GREATER
PERSISTENCE OF ABOVE NORMAL TEMPERATURES BY 5-10 DEGREES WHILE
HEAT INDICES SOAR ABOVE 105F, EVEN ABOVE 110F IN SOME AREAS, AS
THE WARMTH COMBINES WITH HIGH DEWPOINTS. MEAN TROUGHING OVER THE
NORTHWEST WILL KEEP TEMPERATURES A BIT BELOW AVERAGE THROUGH THE
WEEKEND BEFORE UPPER-RIDGING BEGINS TO BUILD IN AND TEMPERATURES
PUSH ABOVE AVERAGE BY THE MIDDLE OF NEXT WEEK.
PUTNAM/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
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page