005
FXUS02 KWBC 131859
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
258 PM EDT SAT MAY 13 2023
VALID 12Z TUE MAY 16 2023 - 12Z SAT MAY 20 2023
...WARMER THAN AVERAGE TEMPERATURES WILL PERSIST ACROSS THE
NORTHWEST...
..OVERVIEW
THE OVERALL WEATHER PATTERN THROUGH NEXT WEEK WILL CONSIST OF AN
ANOMALOUSLY STRONG UPPER RIDGE OVER THE WESTERN HALF OF THE U.S.
AND INTO WESTERN CANADA THAT WILL BE PERSISTENT ASIDE FROM AN
UPPER LOW GRADUALLY SHEARING OUT/WEAKENING ATOP THE NORTHWEST
THROUGH AROUND MIDWEEK. THIS PATTERN WILL MAINTAIN WARM TO HOT
TEMPERATURES ACROSS THE NORTHWEST AND TO A LESSER EXTENT OVER
OTHER PARTS OF THE WEST. DOWNSTREAM, MEAN TROUGHING IS LIKELY
ACROSS EASTERN NORTH AMERICA, WITH INDIVIDUAL SHORTWAVES
SUPPORTING COLD FRONTS THAT SHOULD PUSH SOUTHEASTWARD TO THE EAST
OF THE ROCKIES AND PRODUCE AREAS OF SHOWERS AND THUNDERSTORMS.
MEANWHILE MOIST INFLOW CONTINUES INTO THE SOUTHERN PLAINS,
MAINTAINING SOME RISK OF EXCESSIVE RAINFALL THERE, THOUGH THE
THREAT OF WIDESPREAD FLASH FLOODING SHOULD DECREASE THROUGH NEXT
WEEK GIVEN LESS UPPER-LEVEL SUPPORT COMPARED TO THE NEAR TERM AND
SHORT RANGE PERIOD. HOWEVER THE SOUTH-CENTRAL ROCKIES/HIGH PLAINS
COULD SEE AN INCREASE OF RAINFALL AROUND THE END OF THE WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
LATEST MODELS AND ENSEMBLES STILL SHOW SOME DETAIL DIFFERENCES AND
ADJUSTMENTS WITHIN THE AGREEABLE LARGE SCALE PATTERN. WITH THE
DETAILS OF THE STRONG UPPER TROUGH CROSSING THE NORTHEAST AROUND
WEDNESDAY BECOMING MORE STABLE, THE PRIMARY LARGE SCALE FOCUS FROM
THE MODEL DIAGNOSTICS PERSPECTIVE IS THE ULTIMATE TRACK AND
EVOLUTION OF A POTENT SHORTWAVE/POSSIBLE EMBEDDED UPPER LOW ALONG
WITH A SURFACE LOW REFLECTION REACHING SOUTH-CENTRAL CANADA BY
EARLY WEDNESDAY AND CONTINUING FARTHER EASTWARD THEREAFTER. THE
00Z/06Z GUIDANCE AS A WHOLE GENERALLY NUDGED TOWARD SOMEWHAT
FASTER SYSTEM/FRONTAL TIMING VERSUS THE PREVIOUS MAJORITY, WITH
THE 00Z CMC BEING A SLOWER HOLDOUT. NEW 12Z MODELS THUS FAR SHOW
IMPROVED CLUSTERING, BOTH IN TERMS OF A SURFACE LOW TRACK NEAR
LAKE SUPERIOR BY EARLY DAY 6 FRIDAY AS WELL AS FOR TIMING WITH THE
CMC ADJUSTING FASTER. SOME TYPICAL DIFFERENCES REMAIN WITH AN
AVERAGE PROVIDING A REASONABLE REFLECTION OF CONSENSUS. MEANWHILE,
LOWER PREDICTABILITY SMALL-MEDIUM SCALE ISSUES CONTINUE TO PLAGUE
THE FORECAST FROM THE SOUTHERN HALF OF THE PLAINS EASTWARD. IN THE
LATEST MODEL RUNS THROUGH 12Z, THE CMC/UKMET AND TO SOME DEGREE
00Z ECMWF SUGGEST A WEAK UPPER TROUGH/LOW REACHING TEXAS IN SOME
FASHION BY THE START OF THE PERIOD ON TUESDAY AND THEN PROGRESSING
EASTWARD WHILE THE GFS SUPPRESSES/SHEARS OUT THIS FEATURE IN FAVOR
OF A COMPACT CENTRAL PLAINS INTO SOUTHEAST FEATURE. THE 12Z UKMET
OFFERS POTENTIAL FOR SOME INTERACTION AMONG THE TWO. A BLENDED
APPROACH YIELDS A DISCERNIBLE BUT STILL CONSERVATIVE SOUTHERN
STREAM SHORTWAVE. GUIDANCE COMPARISONS LED TO UPDATING THE
FORECAST WITH A 00Z/06Z OPERATIONAL MODEL COMPOSITE ON DAYS 3-4
TUESDAY-WEDNESDAY, FOLLOWED BY REMOVAL OF THE SLOW 00Z CMC FOR THE
NORTHERN TIER SYSTEM BY DAY 5 THURSDAY AND THAN SOME INCORPORATION
OF THE 06Z GEFS/00Z ECMWF MEANS (PLUS SPLITTING GFS INPUT AMONG
THE 00Z AND 06Z RUNS) BY DAYS 6-7 FRIDAY-SATURDAY.
..WEATHER/HAZARDS HIGHLIGHTS
PERSISTENT MOIST INFLOW IS LIKELY TO CONTINUE INTO THE SOUTHERN
PLAINS THROUGH MUCH OF NEXT WEEK. THOUGH RAIN AMOUNTS SHOULD NOT
BE AS HIGH AS WITH RECENT EVENTS AND IN THE SHORT TERM ACROSS
TEXAS, SOME RAINFALL CONTINUING OVER WHAT IS LIKELY TO BE
EXTREMELY WET GROUND HAS LED TO MARGINAL RISKS IN THE EXCESSIVE
RAINFALL OUTLOOK CONTINUING INTO DAYS 4-5/TUESDAY-WEDNESDAY, WITH
SOME EASTWARD SHIFT FOR WEDNESDAY COMPARED TO TUESDAY. THERE IS
STILL A FAIR AMOUNT OF MODEL SPREAD WITH PLACEMENT OF ANY HEAVIER
TOTALS THAT MAY NOT BE RESOLVED UNTIL THE SHORT TERM OR NEAR TERM,
DEPENDING IN PART ON THE EVOLUTION/PROGRESSION OF FEATURES ALOFT.
BASED ON THE RELATIVE CLUSTERING AMONG NON-GFS SOLUTIONS FOR A
POSSIBLE UPPER TROUGH/LOW OVER TEXAS, EXPECT THE UPDATED DAY 4 ERO
TO REFLECT SOMEWHAT OF AN EASTWARD/NORTHEASTWARD SHIFT AND
EXPANSION OF THE MARGINAL RISK AREA OVER TEXAS WHILE THE PLAN FOR
THE DAY 5 ERO IS AN EASTWARD EXPANSION OF THE MARGINAL RISK (WHILE
MAINTAINING THE ORIGINAL AREA AS-IS) TO INCLUDE THE GULF COAST
REGION BASED ON THE POTENTIAL FOR SOME AREAS OF HEAVY RAINFALL
NEAR/AHEAD OF THE UPPER FEATURE. THERE COULD ALSO BE THE POTENTIAL
FOR SOME AREAS OF ENHANCED RAINFALL TO EXTEND FARTHER EASTWARD
THROUGH THE SOUTHEAST COAST ALONG A WAVY FRONT (AND OTHER DROPPING
DOWN FROM THE NORTH TO REPLACE IT). FOR NOW THE UNCERTAINTY OVER
THIS REGION IS GREATER THAN DESIRED FOR ADDING TO THE MARGINAL
RISK AREA AS WELL.
RETURNING WESTWARD, ANOTHER UNCERTAINTY IS THE EXTENT AND
MAGNITUDE OF LOCALLY HEAVIER RAINFALL EXTENDING BACK THROUGH NEW
MEXICO AND ARIZONA. LATEST ECMWF/GFS RUNS HAVE ESSENTIALLY FLIPPED
AS FAR AS WHICH REFLECTS THE HEAVIER MAXIMA, BUT REMAINING MODELS
AND ENSEMBLE PROBABILITIES SUGGEST LIGHTER ACTIVITY. MIXED
MESSAGES BETWEEN MODEL/ENSEMBLE GUIDANCE VERSUS AN OVERALL
BACKGROUND OF ANOMALOUSLY HIGH PRECIPITABLE WATER VALUES WITHIN A
MONSOON-LIKE PATTERN THAT SETS UP HAVE FAVORED NOT YET REFLECTING
ANY RISK AREAS IN THE ERO BUT REQUIRES CONTINUED MONITORING. AREAS
OF RAIN FARTHER NORTH IN THIS MONSOONAL TYPE OF PATTERN WITH
MOISTURE COMING IN UNDERNEATH GREAT BASIN RIDGING ALOFT ARE ALSO
UNCERTAIN IN TERMS OF PLACEMENT AND AMOUNTS. BUT BY THE LATTER
PART OF NEXT WEEK, A LOW PRESSURE SYSTEM MOVING ACROSS SOUTHERN
CANADA AND POSSIBLY AS FAR SOUTH AS THE GREAT LAKES SHOULD BRING A
COLD FRONT ACROSS MUCH OF THE CENTRAL U.S., SERVING TO FOCUS RAIN
AND THUNDERSTORMS ALONG AND AHEAD OF IT WITH SLIGHTLY MORE
PREDICTABILITY, WITH RAIN CHANCES GRADUALLY PROGRESSING SOUTH AND
EAST WITH TIME COINCIDENT WITH THE FRONT'S MOVEMENT. THIS FRONT
AND TRAILING HIGH PRESSURE COULD BRING SOME UPSLOPE FLOW OVER
PARTS OF THE SOUTH-CENTRAL ROCKIES/HIGH PLAINS, ENHANCING
POTENTIAL RAINFALL AMOUNTS THERE. THE NORTHEAST COULD SEE A ROUND
OF RAIN WITH A LEADING COLD FRONT ON TUESDAY BUT THEN IS LIKELY TO
SEE DRY CONDITIONS UNTIL MOISTURE IS DRAWN INTO THE EAST LATE WEEK
AHEAD OF THE NEXT COLD FRONT THAT WILL BE APPROACHING FROM THE
CENTRAL U.S.
TEMPERATURE-WISE, EXPECT WARM TO HOT TEMPERATURES TO PERSIST
ACROSS THE WEST AS LARGE SCALE UPPER RIDGING PREVAILS ON THE
WHOLE. THE NORTHWEST (THE PACIFIC NORTHWEST INTO THE GREAT BASIN)
IS LIKELY TO SEE THE HIGHEST TEMPERATURE ANOMALIES OF 10-20
DEGREES OR SO ABOVE AVERAGE PERSIST THROUGH MUCH OF THE WEEK,
THOUGH WITH PERHAPS SOME SLIGHT MODERATION LATE WEEK FOR THE
PACIFIC NORTHWEST WHILE AREAS FARTHER INLAND MAY TREND SLIGHTLY
WARMER. THE HIGHEST POTENTIAL FOR RECORD HIGHS HAS NOW PHASED INTO
THE SHORT RANGE PERIOD, BUT RECORD HIGH MINIMUM TEMPERATURES IN
THE 50S AND 60S COULD CONTINUE TO BE WIDESPREAD THROUGH MID- AND
LATE WEEK ACROSS THE WEST, PERHAPS EVEN CHALLENGING MONTHLY
RECORDS. THE WARMING TREND OVER THE NORTHERN GREAT BASIN BY
FRIDAY-SATURDAY MAY ONCE AGAIN REACH RECORD HIGHS THOUGH. FARTHER
SOUTH, HIGHS IN THE 90S ARE LIKELY IN THE CALIFORNIA CENTRAL
VALLEY WITH HIGHS ABOVE 100F IN THE DESERT SOUTHWEST (THOUGH THE
LATTER IS LESS ANOMALOUS FOR MAY). WARMER THAN AVERAGE
TEMPERATURES SHOULD EXPAND ACROSS MUCH OF THE NORTHERN TIER
EARLY-MID WEEK, FOLLOWED BY A COOLING TREND THURSDAY-SATURDAY
AFTER THE FRONTAL PASSAGE. THE NORTHEAST TO MID-ATLANTIC SHOULD
SEE VARIABLE ABOVE OR BELOW NORMAL TEMPERATURES DEPENDING ON
FRONTAL PROGRESSION. CURRENTLY ANTICIPATE THE MOST NOTABLE
ANOMALIES BEING ON THE COOL SIDE OF NORMAL BY 5-15F OVER THE
NORTHEAST DURING WEDNESDAY INTO EARLY THURSDAY AFTER A TUESDAY
FRONTAL PASSAGE. THE CLOUDY AND RAINY CONDITIONS OVER THE SOUTHERN
HIGH PLAINS SHOULD KEEP HIGHS 5-15F BELOW NORMAL ESPECIALLY FOR
THE FIRST HALF OF THE WEEK, FOLLOWED BY A BRIEF REBOUND CLOSE TO
NORMAL. FRONTAL PASSAGE AND A REBOUND IN CLOUDS/RAINFALL MAY DROP
THE REGION'S HIGHS BELOW NORMAL AGAIN BY FRIDAY-SATURDAY.
RAUSCH/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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