403
FXUS02 KWBC 112007
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
406 PM EDT THU MAY 11 2023
VALID 12Z SUN MAY 14 2023 - 12Z THU MAY 18 2023
...FLASH FLOODING POTENTIAL ACROSS TEXAS TO DECREASE GRADUALLY
FROM SUNDAY ONWARD...
..EARLY SEASON HEAT WAVE TO AFFECT THE PACIFIC NORTHWEST
..OVERVIEW
AN ANOMALOUSLY STRONG UPPER RIDGE/HIGH OVER SOUTHWESTERN CANADA AS
OF SUNDAY SHOULD ULTIMATELY WEAKEN SOMEWHAT AND OPEN UP BUT FAIRLY
STRONG RIDGING WILL LIKELY PERSIST OVER WESTERN CANADA THROUGH
MOST OF NEXT WEEK. MEANWHILE AN UPPER LOW RETROGRADING FROM THE
GREAT BASIN INTO THE PACIFIC NORTHWEST MAY SETTLE OVER/SHEAR OUT
NEAR THE CANADIAN BORDER AS IT BECOMES EMBEDDED WITHIN THE LARGER
SCALE RIDGE EVOLVING OVER WESTERN NORTH AMERICA. THIS PATTERN
WILL RESULT IN AN EARLY SEASON HEAT WAVE ACROSS THE NORTHWEST AND
TO A LESSER EXTENT OVER OTHER PARTS OF THE WEST. THE WESTERN
CANADA RIDGE WILL PROMOTE MEAN TROUGHING ALOFT OVER EASTERN NORTH
AMERICA WITH INDIVIDUAL SHORTWAVES SUPPORTING COLD FRONTS THAT
DROP INTO THE NORTHERN/EASTERN PARTS OF THE COUNTRY, WITH VARIABLE
TEMPERATURES AVERAGING CLOSE TO NORMAL. SOME RAINFALL MAY LINGER
OVER THE SOUTHERN PLAINS AND ROCKIES FOR A NUMBER OF DAYS FROM
SUNDAY ONWARD BUT IN A MORE SCATTERED/LESS INTENSE FASHION THAN
EXPECTED IN THE SHORT RANGE TIME FRAME (THROUGH SATURDAY).
..GUIDANCE/PREDICTABILITY ASSESSMENT
GUIDANCE GENERALLY AGREES WELL FOR THE OVERALL PATTERN EVOLUTION
BUT THERE ARE STILL THE TYPICAL EMBEDDED DETAIL DIFFERENCES. GFS
RUNS THROUGH THE 12Z CYCLE CONTINUE TO BE ON THE FLAT SIDE OF
GUIDANCE WITH SHORTWAVE ENERGY FORECAST TO DROP THROUGH THE GREAT
LAKES AND MID-ATLANTIC EARLY IN THE WEEK, CAUSING THE LEADING WAVY
FRONT PUSHING INTO THE SOUTHEAST QUADRANT OF THE LOWER 48 TO BE
SLOWER/NORTH VERSUS CONSENSUS. THE NEXT FRONT REACHING THE
NORTHEAST BY TUESDAY HAS EXHIBITED DECENT AGREEMENT/CONTINUITY
RECENTLY, THOUGH LATEST GUIDANCE HAS TRENDED TOWARD A STRONGER
WAVE DEVELOPING ALONG THE FRONT SOMEWHERE OVER/OFFSHORE NEW
ENGLAND OR THE CANADIAN MARITIMES LATE TUESDAY-WEDNESDAY. ANOTHER
FRONT MAY REACH THE NORTHERN TIER BY DAY 7 THURSDAY AS SHORTWAVE
ENERGY DROPS THROUGH CENTRAL CANADA. AMONG THE 00Z/06Z SOLUTIONS,
THE 06Z GFS IS MOST AMPLIFIED WITH THIS SHORTWAVE AND FARTHEST
SOUTH WITH THE FRONT, FAVORING MINIMAL INFLUENCE OF ITS SPECIFICS
IN THE FORECAST BY DAY 7. THE 12Z GFS IS LESS AMPLIFIED BUT AN
EASTERN EXTREME ALOFT.
FARTHER WEST, THE 00Z/06Z GFS ARE A LITTLE DEEPER AND SLOWER THAN
THE MAJORITY CLUSTER FOR THE GREAT BASIN/NORTHWEST UPPER LOW (12Z
GFS TRENDING FAVORABLY). LATEST GFS RUNS HAVE FINALLY REVERTED
BACK TO CONSENSUS THAT MAINTAINS A FAIRLY STRONG WESTERN CANADA
RIDGE THROUGH THE END OF THE PERIOD, AFTER HAVING A DAY OR SO OF
RUNS TRYING TO BREAK IT DOWN. NOW THE 12Z CMC IS THE SUSPICIOUS
MODEL, BRINGING A NORTHEAST PACIFIC UPPER TROUGH/LOW INTO THE
SOUTHWESTERN CANADA MEAN RIDGE POSITION. FINALLY, THERE ARE STILL
SOME SUBTLE BUT IMPORTANT DETAIL DIFFERENCES IN FLOW ALOFT OVER
THE SOUTHERN PLAINS/ROCKIES WITH LOW PREDICTABILITY SEVERAL DAYS
OUT IN TIME. THESE DIFFERENCES AFFECT THE DISTRIBUTION OF QPF,
WITH THE GFS RUNS TENDING TO BE SOMEWHAT DRIER THAN MOST OTHER
GUIDANCE OVER THE SOUTHERN HALF OF THE HIGH PLAINS.
A 00Z/06Z OPERATIONAL MODEL COMPOSITE WITH SLIGHTLY LESS THAN
TYPICAL GFS WEIGHT ACCOUNTED FOR THE ARRAY OF GUIDANCE DURING THE
FIRST HALF OF THE PERIOD. INCREASING DETAIL SPREAD FAVORED
INCORPORATING THE 06Z GEFS/00Z ECMWF MEANS ALONG WITH THE MODELS
BY DAYS 6-7 WEDNESDAY-THURSDAY, WITH THE MEANS REACHING HALF TOTAL
WEIGHT BY THE END OF THE PERIOD.
..WEATHER/HAZARDS HIGHLIGHTS
ALTHOUGH THE HEAVIEST RAINFALL IS LIKELY TO BE PRIOR TO SUNDAY
MORNING, STILL EXPECT SOME LINGERING AREAS OF MODERATE TO HEAVY
RAIN GOING INTO DAY 4 SUNDAY ACROSS CENTRAL PARTS OF TEXAS AND
INTO OKLAHOMA. THIS RAINFALL COMBINED WITH WET CONDITIONS FROM
RAIN OVER PREVIOUS DAYS SUPPORT HAVING THE DAY 4 EXCESSIVE
RAINFALL OUTLOOK MAINTAIN A SLIGHT RISK AREA FROM PORTIONS OF THE
RIO GRANDE TO THE VICINITY OF THE SOUTHWESTERN CORNER OF OKLAHOMA,
WITH THE AFTERNOON ISSUANCE REFLECTING A SLIGHT NORTHWESTWARD
EXPANSION BASED ON LATEST MODEL/ENSEMBLE GUIDANCE. GUIDANCE
CONTINUES TO SHOW VERY MIXED SIGNALS FOR HEAVY RAINFALL POTENTIAL
OVER SURROUNDING AREAS INCLUDING THE WESTERN HIGH PLAINS AND INTO
OKLAHOMA/KANSAS, OWING TO DIFFERENCES IN UPPER LEVEL DETAILS THAT
HAVE FAIRLY LOW PREDICTABILITY SEVERAL DAYS OUT IN TIME, FAVORING
PERSISTENCE OF A MARGINAL RISK ACROSS THOSE REGIONS. FOR DAY 5
TUESDAY THE AFTERNOON UPDATE PLANS TO INTRODUCE A SLIGHT RISK AREA
OVER SOUTHERN PARTS OF CENTRAL TEXAS, GIVEN SUFFICIENT GUIDANCE
SIGNALS FOR LOCALLY HEAVY RAINFALL OVER VERY WET GROUND. THIS IS
WITHIN A BROADER SOUTHERN PLAINS MARGINAL RISK AREA THAT
ENCOMPASSES THE RELATIVE MAJORITY OF STILL DIVERSE GUIDANCE FOR
WHERE HEAVIEST POCKETS OF RAINFALL MAY BE.
MEANWHILE LARGE SCALE EASTERLY FLOW ALOFT TO THE SOUTH OF THE
INITIAL SOUTHWESTERN CANADA RIDGE SHOULD ADVECT SOME OF THE
CENTRAL U.S. MOISTURE ACROSS PORTIONS OF THE WEST DURING THE
PERIOD. THE UPPER LOW FORECAST TO TRACK THROUGH THE GREAT BASIN
AND PACIFIC NORTHWEST DURING THE WEEKEND AND EARLY NEXT WEEK, AS
WELL AS OTHER POTENTIAL SMALLER SCALE IMPULSES, COULD PRODUCE
SCATTERED AREAS OF RAINFALL WITH TYPICAL DIURNAL ENHANCEMENT.
MOST AMOUNTS SHOULD BE LIGHT TO MODERATE BUT GUIDANCE IS SHOWING
SOME POCKETS OF ANOMALOUSLY HIGH MOISTURE FOR THE TIME OF YEAR (AT
LEAST 2-4 STANDARD DEVIATIONS ABOVE AVERAGE), SO THERE COULD BE
POTENTIAL FOR HEAVIER ACTIVITY ON A LOCALIZED BASIS. GOING INTO
THE MIDDLE OF THE WEEK, A DRIER WEATHER PATTERN IS LIKELY FROM THE
CENTRAL/NORTHERN PLAINS TO THE EAST COAST, BUT THERE WILL STILL BE
ENOUGH MOISTURE NEAR A WEAKENING COLD FRONT OVER THE GULF COAST
REGION TO GENERATE SCATTERED SHOWERS AND STORMS FROM TEXAS TO THE
SOUTHEAST STATES. THE COLD FRONT DROPPING INTO THE NORTHEAST BY
TUESDAY AND ANOTHER ONE REACHING THE NORTHERN TIER AROUND THURSDAY
MAY PRODUCE SCATTERED AREAS OF RAINFALL.
ANOTHER STORY MAKING WEATHER HEADLINES WILL BE THE EARLY SEASON
HEAT WAVE CENTERED OVER THE PACIFIC NORTHWEST STARTING THIS
WEEKEND AND PERSISTING INTO NEXT WEEK AS LARGE SCALE UPPER RIDGING
PREVAILS OVER WESTERN NORTH AMERICA (THOUGH WITH A WEAKENING
EMBEDDED UPPER LOW SETTLING OVER THE REGION). THE LATEST
TEMPERATURE FORECAST CALLS FOR HIGHS REACHING THE MIDDLE 80S TO
MIDDLE 90S FOR MANY OF THE LOWER ELEVATIONS IN WASHINGTON AND
OREGON, WHICH WOULD WOULD BE 20-25F ABOVE NORMAL AND SET DAILY
HIGH TEMPERATURE RECORDS. MORNING LOWS WILL ALSO BE QUITE WARM
WITH READINGS ONLY FALLING INTO THE 60S FOR MANY OF THESE SAME
AREAS. IN CONTRAST TO THE HIGHS THAT MAY MODERATE BELOW POTENTIAL
RECORD LEVELS AFTER MONDAY, MORNING LOWS COULD KEEP CHALLENGING
DAILY RECORDS FOR MOST OF NEXT WEEK--WITH A FEW MONTHLY RECORDS
POSSIBLE AS WELL. IT WILL ALSO BE QUITE WARM FOR THE CENTRAL
VALLEY OF CALIFORNIA WITH HIGHS WELL INTO THE 90S THERE AS WELL.
ELSEWHERE ACROSS THE NATION, HEAT AND HUMIDITY OVER THE CENTRAL
AND EASTERN U.S. SHOULD DECREASE SOME GOING INTO EARLY NEXT WEEK
AS A WEAK FRONTAL BOUNDARY CROSSES THE SOUTHERN TIER STATES, AND A
STRONGER COLD FRONT PASSES THROUGH THE GREAT LAKES AND NORTHEAST
BRINGING A MORE REFRESHING AIRMASS WITH A DAY OR SO OF MODERATELY
BELOW NORMAL HIGHS. CLOUD COVER AND RAINFALL WILL LIKELY KEEP
HIGHS 5-15F BELOW NORMAL OVER THE SOUTHERN PLAINS FOR MULTIPLE
DAYS, WITH VERY GRADUAL MODERATION OVER THE COURSE OF NEXT WEEK.
RAUSCH/HAMRICK
HAZARDS:
- HEAVY RAIN ACROSS PORTIONS OF THE CENTRAL AND SOUTHERN PLAINS,
SUN-MON, MAY 14-MAY 15.
- FLOODING POSSIBLE ACROSS PORTIONS OF THE UPPER MISSISSIPPI
VALLEY, THE SOUTHERN PLAINS, THE
NORTHERN ROCKIES, THE NORTHERN GREAT BASIN, AND THE NORTHERN
PLAINS.
- FLOODING OCCURRING OR IMMINENT ACROSS PORTIONS OF THE UPPER
MISSISSIPPI VALLEY, THE MIDDLE
MISSISSIPPI VALLEY, THE NORTHERN PLAINS, THE NORTHERN ROCKIES, AND
THE NORTHERN GREAT BASIN.
- FLOODING LIKELY ACROSS PORTIONS OF THE CENTRAL GREAT BASIN, THE
NORTHERN PLAINS, THE NORTHERN
GREAT BASIN, THE CENTRAL ROCKIES, THE SOUTHERN PLAINS, AND THE
SOUTHWEST.
- EXCESSIVE HEAT ACROSS PORTIONS OF THE PACIFIC NORTHWEST,
SUN-MON, MAY 14-MAY 15.
- MUCH ABOVE NORMAL TEMPERATURES ACROSS PORTIONS OF THE PACIFIC
NORTHWEST, THE NORTHERN GREAT
BASIN, AND CALIFORNIA, SUN-WED, MAY 14-MAY 17.
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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