769
FXUS02 KWBC 102045
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
444 PM EDT WED MAY 10 2023
VALID 12Z SAT MAY 13 2023 - 12Z WED MAY 17 2023
***FLASH FLOODING A GROWING CONCERN ACROSS PORTIONS OF TEXAS THIS
WEEKEND WITH A MODERATE RISK OF EXCESSIVE RAINFALL ON SATURDAY,
AND AN EARLY SEASON HEATWAVE ACROSS THE PACIFIC NORTHWEST***
..SYNOPTIC SCALE OVERVIEW
THE LOW PRESSURE SYSTEM OVER THE MIDWEST ON SATURDAY, ASSOCIATED
WITH A DECAYING UPPER LEVEL LOW, WILL CONTINUE WEAKENING GOING
THROUGH THE WEEKEND, WITH A SWATH OF MODERATE TO HEAVY RAIN ACROSS
PORTIONS OF THE UPPER MIDWEST. THE TRAILING COLD FRONT FROM THIS
STORM SYSTEM WILL SLOW DOWN ACROSS TEXAS FOR A WHILE, AND IN
COMBINATION WITH SHORTWAVE ENERGY ALOFT AND COPIOUS MOISTURE
TRANSPORT FROM THE WESTERN GULF OF MEXICO, SHOULD HELP TO FOCUS
AREAS OF HEAVY RAIN ACROSS MUCH OF CENTRAL TEXAS INTO THE WEEKEND.
MEANWHILE, A BUILDING NORTHWESTERN U.S./SOUTHWESTERN CANADA UPPER
RIDGE WILL LIKELY CLOSE OFF A HIGH OVER SOUTHWESTERN CANADA BY
SUNDAY AND THEN POSSIBLY OPEN UP AGAIN WHILE PERSISTING OVER
WESTERN CANADA. AT THE SAME TIME AN UPPER LOW MAY RETROGRADE
ACROSS THE GREAT BASIN AND PACIFIC NORTHWEST, WITH SOME DEGREE OF
MEAN RIDGING POSSIBLY BUILDING OVER THE WEST IN ITS WAKE. THIS
PATTERN WILL PROMOTE MUCH ABOVE NORMAL TEMPERATURES OVER THE
NORTHWEST AND TO A LESSER EXTREME OVER OTHER PARTS OF THE WEST.
DOWNSTREAM MEAN TROUGHING THAT DEVELOPS IN RESPONSE TO THE WESTERN
CANADA RIDGE WILL TEND TO FAVOR COOLER CONDITIONS AND LOWER
HUMIDITY OVER THE EAST DURING THE FIRST HALF OF NEXT WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
COMPARING GUIDANCE FROM THE 00Z/06Z CYCLE, THE MOST PROMINENT
DISCREPANCIES INVOLVE THE GFS RUNS IN A COUPLE RESPECTS.
CONTINUING A TRAIT THAT BECAME MORE PRONOUNCED FROM AROUND
YESTERDAY'S 12Z RUN, THE MODEL IS STILL SLOWER THAN MOST OTHER
GUIDANCE (INCLUDING THE GEFS MEAN) WITH THE SOUTHEASTWARD
PROGRESSION OF SHORTWAVE ENERGY FROM THE GREAT LAKES THROUGH
MID-ATLANTIC FROM LATE WEEKEND INTO EARLY NEXT WEEK. THIS LEADS
THE GFS TO MAINTAIN A FARTHER NORTH SURFACE WAVE/FRONT OVER THE
EAST INTO MONDAY VERSUS RECENT MAJORITY CLUSTER TRENDS THAT HAVE
BEEN TOWARD A MORE SUPPRESSED DEPICTION. THIS CONFLICT BETWEEN
THE GFS AND OTHER GUIDANCE PERSISTS INTO THE 12Z CYCLE. THEN BY
THE LATTER HALF OF THE PERIOD THE GFS SIGNIFICANTLY BREAKS DOWN
THE WESTERN CANADA RIDGE IN CONTRAST TO THE GEFS MEAN AND MOST
OTHER GUIDANCE HOLDING ONTO A FAIRLY STRONG RIDGE THROUGH DAY 7
WEDNESDAY. THE 06Z GFS WAS MORE EXTREME/QUICKER WITH ITS
BREAKDOWN VERSUS THE 00Z RUN. THE 12Z GFS STILL BREAKS DOWN THE
CANADIAN RIDGE BY DAY 7, AND WHILE THE 12Z CMC BRINGS A COMPACT
FEATURE INTO WESTERN CANADA IT STILL MAINTAINS MORE RIDGING THAN
THE GFS BY THE END OF THE PERIOD. FROM DAY 4 SUNDAY ONWARD,
VARIOUS LOW PREDICTABILITY SMALL-MEDIUM SCALE DIFFERENCES ALOFT
DEVELOP OVER THE CENTRAL U.S. WITH AN INFLUENCE ON QPF DETAILS
WITHIN AN OVERALL TREND FOR LOWER COVERAGE/AMOUNTS NEXT WEEK AFTER
THE HEAVY RAINFALL EXPECTED OVER THE SOUTHERN PLAINS DURING THE
WEEKEND. FORECAST CONSIDERATIONS LED TO STARTING THE LATEST
UPDATE WITH AN OPERATIONAL MODEL BLEND FOR THE FIRST HALF OF THE
PERIOD BUT WITH SLIGHTLY LESS THAN TYPICAL GFS WEIGHT. THEN THE
BLEND REPLACED THE GFS WITH THE GEFS MEAN AND OVERALL STEADILY
INCREASED GEFS/ECMWF/CMC MEAN INPUT WHILE PHASING OUT THE
OPERATIONAL 00Z CMC BY DAY 7 WEDNESDAY DUE TO DEVELOPING
DIFFERENCES ALONG THE U.S.-CANADIAN BORDER. THIS YIELDED A 75
PERCENT MEANS TO 25 PERCENT 00Z ECMWF WEIGHT BY DAY 7.
..WEATHER/HAZARDS HIGHLIGHTS
A HIGH IMPACT HEAVY RAIN EVENT IS LOOKING INCREASINGLY LIKELY
ACROSS MUCH OF CENTRAL AND SOUTHERN TEXAS GOING INTO THE UPCOMING
WEEKEND, IN ADDITION TO THE RAIN ALREADY EXPECTED DURING THE SHORT
RANGE PERIOD. A FAVORABLE COMBINATION OF A STALLING FRONT,
MULTIPLE WEAK SHORTWAVE IMPULSES PASSING ALOFT, SUSTAINED DEEP
MOISTURE FLUX FROM THE WESTERN GULF OF MEXICO, AND APPRECIABLE LOW
LEVEL INSTABILITY SOUTH OF THE FRONT WILL SET THE STAGE FOR
MULTIPLE MESOSCALE CONVECTIVE SYSTEMS WITH TRAINING THUNDERSTORMS
AND HIGH RAINFALL RATES. THIS UNSETTLED PATTERN GOING INTO THE
DAY 4 PERIOD SATURDAY WILL LIKELY RESULT IN 2-5 INCHES OF RAINFALL
WITH LOCALLY HIGHER TOTALS POSSIBLE ACROSS MUCH OF CENTRAL AND
SOUTHERN TEXAS. SINCE THIS HEAVY RAINFALL ON DAY 4 WILL BE
FALLING ON ALREADY HIGHLY SATURATED GROUNDS FROM THE PREVIOUS
DAYS, A MODERATE RISK REMAINS IN EFFECT ACROSS PORTIONS OF
SOUTH-CENTRAL TEXAS, INCLUDING THE GREATER SAN ANTONIO AREA.
THERE WILL LIKELY BE SOME CHANGES TO THIS RISK AREA IN FUTURE
FORECAST UPDATES ONCE THE MODEL SIGNAL BECOMES MORE REFINED.
EXPECT SOME ADDITIONAL HEAVY RAIN GOING INTO DAY 5 AS WELL ACROSS
PARTS OF TEXAS AND OKLAHOMA, AND A SLIGHT RISK IS MAINTAINED FROM
FAR SOUTHERN KANSAS TO THE RIO GRANDE TO COVER THIS POTENTIAL,
ALTHOUGH THE HEAVIEST RAINFALL SHOULD BE WANING BY THIS TIME.
GUIDANCE OFFERS MIXED MESSAGES FOR HEAVY RAINFALL POTENTIAL OVER
SURROUNDING AREAS INCLUDING THE HIGH PLAINS, DUE TO DIFFERENCES IN
UPPER LEVEL DETAILS THAT HAVE FAIRLY LOW PREDICTABILITY SEVERAL
DAYS OUT IN TIME. FARTHER NORTH ACROSS THE UPPER MIDWEST, SOME
LINGERING THUNDERSTORM COMPLEXES ARE A GOOD POSSIBILITY GOING INTO
SATURDAY IN ASSOCIATION WITH THE WEAKENING UPPER TROUGH/SURFACE
LOW. SOME LIGHTER RAINFALL MAY EXTEND FARTHER EAST/SOUTHEAST AS
THE WEAKENING WAVE AND LEADING FRONT DROP SOUTHWARD. DRIER
WEATHER WILL ARRIVE IN TIME FOR MOTHER'S DAY ACROSS MUCH OF THE
NORTH-CENTRAL U.S., AND COVERAGE OF SHOWERS AND STORMS SHOULD
DECREASE OVER CENTRAL/EASTERN AREAS GOING INTO EARLY NEXT WEEK.
MEANWHILE LARGE SCALE EASTERLY FLOW ALOFT TO THE SOUTH OF THE
SOUTHWESTERN CANADA RIDGE SHOULD BRING INCREASING 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
IMPULSES, COULD PRODUCE SCATTERED AREAS OF RAINFALL. MOST
ACTIVITY SHOULD BE ON THE LIGHT SIDE BUT LOCALIZED HIGHER TOTALS
COULD BE POSSIBLE GIVEN THE MOISTURE ANOMALIES FOR THE TIME OF
YEAR.
THE OTHER STORY THAT WILL BE MAKING WEATHER HEADLINES WILL BE THE
EARLY SEASON HEATWAVE CENTERED OVER THE PACIFIC NORTHWEST STARTING
THIS WEEKEND AND PERSISTING INTO EARLY NEXT WEEK AS THE ANOMALOUS
UPPER HIGH BECOMES ANCHORED IN PLACE OVER SOUTHERN BRITISH
COLUMBIA. 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 SET DAILY HIGH
TEMPERATURE RECORDS. OVERNIGHT LOWS WILL ALSO BE QUITE WARM WITH
READINGS ONLY FALLING INTO THE 60S FOR MANY OF THESE SAME AREAS.
WHILE THE BEST POTENTIAL FOR HIGHS UP TO 20-25F ABOVE NORMAL WILL
BE SATURDAY-MONDAY (WITH SOME DEPENDENCE ON THE UPPER LOW THAT
COULD TRACK OVER THE REGION), LOW TEMPERATURES OVER THE NORTHWEST
AND SOME NEARBY AREAS COULD REMAIN WARM ENOUGH TO CHALLENGE DAILY
RECORDS THROUGH AT LEAST MIDWEEK. 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, THE HEAT AND HUMIDITY
ACROSS 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.
COOLER WEATHER OWING TO CLOUD COVER AND RAINFALL WILL LIKELY BE
THE CASE ACROSS MUCH OF THE SOUTHERN PLAINS WITH HIGHS RUNNING
5-15 DEGREES BELOW AVERAGE MOST DAYS.
RAUSCH/HAMRICK
HAZARDS:
- HEAVY RAIN ACROSS PORTIONS OF THE CENTRAL AND SOUTHERN PLAINS,
SAT-SUN, MAY 13-MAY 14.
- HEAVY RAIN ACROSS PORTIONS OF THE SOUTHERN PLAINS, SAT-TUE, MAY
13-MAY 16.
- FLOODING POSSIBLE ACROSS PORTIONS OF THE UPPER MISSISSIPPI
VALLEY, THE NORTHERN PLAINS, THE NORTHERN ROCKIES, AND THE
NORTHERN GREAT BASIN.
- FLOODING OCCURRING OR IMMINENT ACROSS PORTIONS OF THE MID- AND
UPPER MISSISSIPPI VALLEY, THE NORTHERN PLAINS, THE NORTHERN
ROCKIES, AND INTERIOR OREGON.
- FLOODING LIKELY ACROSS PORTIONS OF THE NORTHERN AND CENTRAL
GREAT BASIN, THE NORTHERN PLAINS, THE CENTRAL ROCKIES, THE GREAT
LAKES, AND THE SOUTHWEST.
- MUCH ABOVE NORMAL TEMPERATURES ACROSS THE WESTERN PORTION OF THE
PACIFIC NORTHWEST, SAT-MON, MAY 13-MAY 15.
- MUCH ABOVE NORMAL TEMPERATURES ACROSS THE INTERIOR VALLEYS OF
CALIFORNIA, AND THE INTERIOR PORTION OF THE PACIFIC NORTHWEST,
SAT-WED, MAY 13-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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