285
FXUS02 KWBC 191859
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
258 PM EDT MON JUN 19 2023
VALID 12Z THU JUN 22 2023 - 12Z MON JUN 26 2023
...PROLONGED HEAT WAVE CONTINUES ACROSS THE TEXAS AND SOUTHEASTERN
NEW MEXICO THROUGHOUT THIS WEEK AND EVEN INTO EARLY NEXT WEEK...
...HEAVY RAIN AND FLOODING POTENTIAL LINGERS ACROSS THE
SOUTHEAST/SOUTHERN APPALACHIANS FOR THE LATTER PART OF THE WEEK...
19Z UPDATE: THE 12Z MODEL GUIDANCE SUITE HAS A VERY GOOD OVERALL
DEPICTION OF THE LARGE SCALE PATTERN ACROSS THE CONTINENTAL U.S.
THROUGH LATE FRIDAY, SO A MULTI-DETERMINISTIC MODEL BLEND SUFFICES
AS A GOOD STARTING POINT IN THE FORECAST PROCESS. MORE NOTEWORTHY
MODEL DIFFERENCES EMERGE BY EARLY SUNDAY WITH THE CLOSED LOW
ACROSS MONTANA AND THEN EXITING ACROSS THE DAKOTAS, WITH THE UKMET
CONSIDERABLY WEAKER THAN THE GFS/CMC, AND THE ECMWF IS MORE
AMPLIFIED WITH IT AS IT REACHES THE UPPER MIDWEST LATE SUNDAY. BY
NEXT MONDAY, THE GFS IS MORE PROGRESSIVE WITH THE WEST COAST
TROUGH/UPPER LOW MOVING INLAND, WHEREAS THE ECENS/CMC/EC KEEP IT
FARTHER BACK TO THE NORTHWEST. THE GFS/GEFS IS DISPLACED EAST
WITH THE UPPER RIDGE AXIS OVER THE SOUTHERN PLAINS, WHEREAS THE
CMC/ECMWF KEEPS THE CORE OF THE HIGH OVER NORTHWESTERN MEXICO, BUT
AGREES FAIRLY WELL ACROSS THE EASTERN U.S. IN TERMS OF THE
EXCESSIVE RAINFALL OUTLOOKS FOR DAYS 4 AND 5, NO MAJOR CHANGES
WERE WARRANTED FOR THIS FORECAST UPDATE. THE PREVIOUS DISCUSSION
IS APPENDED BELOW FOR REFERENCE. /HAMRICK
-----------------------
..OVERVIEW
THE MEDIUM RANGE PERIOD WILL BEGIN THURSDAY WITH AN AMPLIFIED AND
BLOCKY UPPER PATTERN ACROSS THE LOWER 48, INCLUDING A DEEP
POSITIVELY-TILTED TROUGH ACROSS THE NORTHWESTERN U.S., A WARM
RIDGE TO REMAIN ANCHORED OVER TEXAS/NORTHERN MEXICO, AND A REX
BLOCK IN THE EAST AS AN UPPER LOW SITS ATOP THE TENNESSEE VALLEY
WHILE AN UPPER HIGH PREVAILS TO THE NORTH. WIDESPREAD SHOWERS AND
THUNDERSTORMS ARE LIKELY FOR THE SOUTHEAST AND SOUTHERN
APPALACHIANS GIVEN THE UPPER LOW, WHICH AFTER A WET SHORT RANGE
PERIOD COULD CAUSE ADDITIONAL FLOODING CONCERNS. MEANWHILE A LOW
PRESSURE/FRONTAL SYSTEM SET UP IN THE NORTH-CENTRAL PLAINS COULD
LEAD TO FLASH FLOODING CONCERNS WITH THUNDERSTORMS FOCUSING THERE.
THE UPPER PATTERN LOOKS TO RELAX A BIT AS THE PERIOD PROGRESSES,
BUT MAINTAIN THE GENERAL PATTERN OF WESTERN TROUGHING/CENTRAL U.S.
RIDGING/EASTERN TROUGHING--MAINTAINING CONTINUED HEAT CONCERNS
ACROSS TEXAS IN PARTICULAR AND INTO SOUTHEASTERN NEW MEXICO. RAIN
CHANCES LOOK TO SPREAD UP THE EAST INTO THE WEEKEND.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
FOR THE LATTER PART OF THIS WEEK, MODEL GUIDANCE CONTINUES TO SHOW
FAIRLY GOOD AGREEMENT WITH THE OVERALL BLOCKY SYNOPTIC PATTERN,
PARTICULARLY WITH THE TROUGH IN THE NORTHWEST AND THE UPPER HIGH
MEANDERING NEAR THE RIO GRANDE. THERE HAS BEEN MORE WAFFLING WITH
THE POSITIONING OF THE EASTERN UPPER LOW AND ITS EVENTUAL DRIFT
NORTH AND PHASING WITH THE NORTHERN STREAM FLOW BY THE WEEKEND. IN
TERMS OF THE 12/18Z MODEL CYCLE AVAILABLE FOR FORECAST PRODUCTION,
THE 12Z CMC SEEMED TO BE A NORTHEASTERN OUTLIER IN THIS LOW'S
POSITION EVEN FOR DAY 3/THURSDAY, AND THE NEWER 00Z CMC COMES INTO
BETTER ALIGNMENT WITH THE OTHER MODELS. THOUGH THE DIFFERENCES
APPEAR SOMEWHAT MINOR, SMALL DIFFERENCES IN THE POSITION AND
EVOLUTION OF THE UPPER LOW HAVE BIG IMPLICATIONS FOR THE QPF. A
MODEL BLEND FAVORING THE ECMWF/GFS WITH SOME INCLUSION OF THE
UKMET AND ONLY A SMALL PERCENTAGE OF THE CMC SEEMED TO WORK WELL
FOR THE EARLY PART OF THE FORECAST PERIOD.
INTO THE WEEKEND AND EARLY NEXT WEEK, THE EASTERN UPPER LOW SHOULD
OPEN INTO A TROUGH AND PHASE WITH THE NORTHERN STREAM, AS THE
INITIAL UPPER HIGH OVER SOUTHEASTERN CANADA HAS QUICKLY EXITED TO
THE EAST. BUT BEHIND THIS FEATURE, ANOTHER SHORTWAVE LOOKS TO
TRACK FROM THE WEST ACROSS THE NORTH-CENTRAL U.S. THAT SHOULD ALSO
PUSH A SURFACE LOW/FRONTAL SYSTEM EASTWARD THAT HAD BEEN STALLED
THROUGH LATE WEEK. THESE TROUGHING FEATURES MAY ALL COMBINE
SOMEHOW EARLY NEXT WEEK BUT STILL WITH SOME UNCERTAINTY AT THIS
POINT. MEANWHILE MODELS SHOW GOOD AGREEMENT THAT THE UPPER HIGH
OVER WESTERN TEXAS/NORTHERN MEXICO WILL CONTINUE TO HOLD ON, WHILE
RIDGING MAY POKE NORTHWARD INTO THE FOUR CORNERS STATES AND
BEYOND, BUILDING AHEAD OF AN UPPER TROUGH AND EMBEDDED LOW IN THE
EASTERN PACIFIC. GUIDANCE IS PERSISTENT WITH SHOWING THIS LOW BUT
WITH VARIATIONS IN ITS POSITION THAT ARE WITHIN REASON FOR THIS
LEAD TIME. THE WPC FORECAST TRENDED TOWARD INCLUDING MORE ENSEMBLE
MEANS IN THE BLEND FOR THE MID-LATE FORECAST PERIOD AMID
INCREASING MODEL SPREAD, TO ABOUT HALF OF THE BLEND BY DAY
7/MONDAY.
..WEATHER/HAZARDS HIGHLIGHTS
THE UPPER LOW MEANDERING OVER THE SOUTHEAST/TENNESSEE VALLEY OR SO
WILL PROVIDE SUPPORT FOR MULTIPLE ROUNDS OF RAIN AND THUNDERSTORMS
FOR THE SOUTHEASTERN QUADRANT OF THE COUNTRY THROUGH MUCH OF THIS
WEEK. INTO THE MEDIUM RANGE PERIOD STARTING THURSDAY, A SLIGHT
RISK OF EXCESSIVE RAINFALL IS ONCE AGAIN IN PLACE FOR THE SOUTHERN
APPALACHIANS INTO THE PIEDMONT GIVEN THE ADDITIONAL RAINFALL
POTENTIAL OVER WHAT WILL BE INCREASINGLY MOIST/SENSITIVE SOILS
FROM RAIN DURING THE SHORT RANGE PERIOD. THE WPC DAY 1-5 QPF
INDICATES 7-10 INCHES OF RAIN AS AN AREAL AVERAGE IN THE SOUTHERN
APPALACHIANS WHERE UPSLOPE FLOW SHOULD ENHANCE TOTALS, AND THERE
WILL LIKELY BE LOCALLY HIGHER AMOUNTS. ADDITIONALLY ON THURSDAY,
MAINTAINED A SLIGHT RISK ACROSS PARTS OF THE FLORIDA PANHANDLE
WHERE A STATIONARY FRONT COULD FOCUS MOISTURE AND THUS
RAIN/STORMS. SOME ADDITIONAL ENHANCED RAINFALL BEYOND THURSDAY IS
POSSIBLE FOR THE SOUTHEAST/SOUTHERN APPALACHIANS GIVEN THE SLOW
PREDICTED MOVEMENT OF THE UPPER LOW TOGETHER WITH PLENTY OF
ANTECEDENT MOISTURE TO WORK WITH. MOST MODEL GUIDANCE HAS
LESSENING RAINFALL AMOUNTS FORECAST BY FRIDAY, WITH THE MAIN
EXCEPTION OF THE ECMWF RUNS, BUT HAVE A MARGINAL RISK IN THE DAY 5
ERO TO COVER THE POTENTIAL FOR ADDITIONAL FLOODING CONCERNS. BY
LATE WEEK INTO NEXT WEEKEND, RAIN AND THUNDERSTORMS ARE LIKELY TO
SPREAD FARTHER NORTH UP THE EAST COAST INTO THE MID-ATLANTIC AND
NORTHEAST.
UPPER TROUGHING WITH EMBEDDED UPPER LOWS IN THE WEST WILL CAUSE A
LOW PRESSURE AND FRONTAL SYSTEM TO STALL THROUGH LATE WEEK
STRETCHED ACROSS THE NORTH-CENTRAL U.S. AND PROVIDE A FOCUS FOR
THUNDERSTORMS. THERE SHOULD BE AMPLE INSTABILITY IN THIS AREA AND
THUS POTENTIAL FOR HIGH RAIN RATES. A SLIGHT RISK IN THE DAY
4/THURSDAY ERO HAS BEEN MAINTAINED IN THE CENTRAL HIGH PLAINS
WHERE THE FRONT COULD STALL BUT SHIFTED A BIT SOUTHWEST INTO AREAS
MORE PRONE TO FLOODING FROM WETTER ANTECEDENT CONDITIONS AND MORE
SUSCEPTIBLE SOILS. THERE IS STILL UNCERTAINTY IN WHERE THE
HEAVIEST RAIN WILL SET UP THOUGH, AND ADDITIONAL SHIFTS MAY BE
NEEDED IN FUTURE CYCLES. THEN BY DAY 5/FRIDAY, THE UPPER-LEVEL
SUPPORT STARTS TO LOOK FAVORABLE ACROSS THE NORTHERN PLAINS,
NAMELY WITH THE POTENTIAL FOR A COUPLED UPPER JET (RIGHT
ENTRANCE/LEFT EXIT REGION COMBINATION). A BROAD SLIGHT RISK IS IN
PLACE THERE AS WELL. THE FRONTAL SYSTEM LOOKS TO START MOVING
FASTER BY THE WEEKEND/EARLY NEXT WEEK AHEAD OF AN UPPER LOW,
PUSHING RAIN CHANCES EASTWARD.
MEANWHILE, THE EXCESSIVE HEAT WILL CONTINUE THROUGH THIS WEEK
ACROSS MUCH OF TEXAS AND INTO SOUTHEASTERN PORTIONS OF NEW MEXICO,
WITH WIDESPREAD 100S AND EVEN SOME 110S ACROSS CENTRAL AND
SOUTHERN PORTIONS OF TEXAS, AND 90S WITH HEAT INDICES WELL OVER
100F ELSEWHERE. MANY DAILY RECORD HIGH TEMPERATURES ARE POSSIBLE,
AND SOME MONTHLY RECORDS MAY EVEN BE CHALLENGED. AS MEAN UPPER
RIDGING EXPANDS FARTHER NORTH, HIGHS IN THE 90S ARE LIKELY ACROSS
MUCH OF THE PLAINS AND MISSISSIPPI VALLEY, WHILE 80S AND LOW 90S
IN THE UPPER MIDWEST/GREAT LAKES REGION WILL BE 10-15F ABOVE
NORMAL. MEANWHILE THE WEST SHOULD SEE COOLER THAN NORMAL
TEMPERATURES PARTICULARLY FOR HIGHS WITH THE BOUTS OF UPPER
TROUGHING ALOFT, WHILE COOLER THAN AVERAGE TEMPERATURES WILL ALSO
BE PRESENT IN THE SOUTHEASTERN U.S. GIVEN THE CLOUDINESS/RAIN
CHANCES AND THE UPPER LOW.
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, EXPERIMENTAL EXCESSIVE RAINFALL
OUTLOOK, WINTER WEATHER OUTLOOK PROBABILITIES AND HEAT INDICES 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
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