101
FXUS02 KWBC 260700
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 AM 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 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
MODEL GUIDANCE AGREES ON A GENERAL SUMMERTIME UPPER-LEVEL PATTERN
CONSISTING OF UPPER RIDGING ACROSS THE SOUTHERN TIER AND THE
STRONGER UPPER-LEVEL FLOW SHUNTED TO THE NORTH, WITH SOME SMALLER
SCALE DIFFERENCES. RECENT MODELS ARE PRETTY AGREEABLE IN RIDGING
COMBINING FROM THE SOUTHWESTERN U.S. AND FROM THE WESTERN ATLANTIC
TO STRETCH ACROSS THE SOUTHERN TIER AS THE PERIOD BEGINS SATURDAY.
WITH TIME THE TWO MAY BREAK APART AND COMBINE AGAIN AND PERHAPS
COMBINE AGAIN, WITH LESS CERTAINTY. WITH THE 12/18Z MODEL CYCLE,
THOUGH THE 12Z CMC WAS A MINOR OUTLIER IN HANGING THE WESTERN PART
OF THE RIDGE/HIGH BACK WEST COMPARED TO OTHER GUIDANCE, BUT THE
INCOMING 00Z GUIDANCE AS A WHOLE IS ACTUALLY MORE LIKE THAT WITH A
SLOWER DRIFT OF THE HIGH EASTWARD.
IN THE NORTHERN STREAM, MODELS HAVE GOOD CONSENSUS WITH A SLOWLY
DEEPENING TROUGH AXIS OVER THE EAST THIS WEEKEND INTO EARLY NEXT
WEEK, BUT VARY SOMEWHAT ON HOW DEEP AND WITH THE ASSOCIATED
FRONTAL POSITION. THE 12Z CMC WAS ESPECIALLY DEEP WITH THE TROUGH
BUT THE NEWER 00Z RUN HAS BACKED OFF SOME. THE GFS AND ECMWF RUNS
SHOWED BETTER CONSENSUS THAN A COUPLE DAYS AGO CERTAINLY THOUGH.
THE EASTERN PACIFIC TO THE NORTHWEST IS ANOTHER AREA THAT COULD
SEE SOME TROUGHING, THOUGH SMALLER-SCALE AND THUS LESS CERTAIN.
MODELS HAVE BEEN WAFFLING WITH HOW QUICKLY TO BRING ENERGY
EASTWARD INTO BRITISH COLUMBIA OR SO THIS WEEKEND, WITH NEWER 00Z
RUNS LOOKING SLOWER TO DO SO, WHICH IS ALSO CONSISTENT WITH THE
UPPER HIGH'S SLOWER MOVEMENT WITH ITS RIDGE EXTENDING NORTH JUST
EAST OF THIS ENERGY. THUS THIS IS STILL AN AREA OF UNCERTAINTY
THAT WILL AFFECT TEMPERATURES AND PERHAPS PRECIPITATION FORECASTS
IN THE NORTHWESTERN AND NORTH-CENTRAL U.S.
THE WPC FORECAST WAS BASED ON A DETERMINISTIC BLEND OF THE 12/18Z
GUIDANCE FAVORING THE ECMWF AND GFS EARLY IN THE PERIOD, GRADUALLY
REDUCING AND ELIMINATING THE CMC AND THE TIME-LIMITED UKMET WITH
TIME. ENSEMBLE MEANS FROM THE GEFS AND EC WERE USED IN THEIR PLACE
AND EVENTUALLY ENDED UP WITH AN EQUAL BLEND OF THE 18Z GFS AND
GEFS MEAN AND THE 12Z ECMWF AND EC MEAN BY DAY 7.
..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 IS IN PLACE ACROSS
THE NORTHEAST TO MID-ATLANTIC AS A STARTING POINT IN THE DAY 4 ERO
SATURDAY. THE RISK AREA IS BROADER/FARTHER SOUTH 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. BUT THE AREA
COVERED BY THE MARGINAL MAY BE ABLE TO NARROW SOME WITH TIME IF
MODELS COME INTO BETTER AGREEMENT WITH PLACEMENT OF HIGHER QPF.
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. 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 NORTH CAROLINA 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.
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 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 BUT
LIKELY WIDESPREAD RECORD WARM MINIMUM TEMPERATURES. 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.
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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