346
FXUS02 KWBC 090740
PMDEPD
EXTENDED FORECAST DISCUSSION...AMENDED
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
339 AM EDT TUE MAY 9 2023
VALID 12Z FRI MAY 12 2023 - 12Z TUE MAY 16 2023
***FLASH FLOODING A GROWING CONCERN ACROSS PORTIONS OF TEXAS
FRIDAY AND INTO THE WEEKEND WITH A MODERATE RISK OF EXCESSIVE
RAINFALL ON SATURDAY, AND AN EARLY SEASON HEATWAVE ACROSS THE
PACIFIC NORTHWEST***
..SYNOPTIC SCALE OVERVIEW
A SLOW MOVING LOW PRESSURE SYSTEM SITUATED OVER THE
CENTRAL/NORTHERN PLAINS ON FRIDAY, ASSOCIATED WITH A UPPER LEVEL
LOW, WILL TRACK ACROSS THE MIDWEST STATES WHILE WEAKENING GOING
INTO THE WEEKEND, WITH WIDESPREAD RAIN ACROSS THE DAKOTAS AND
EASTERN PORTIONS OF WYOMING AND MONTANA. THE TRAILING COLD FRONT
FROM THIS STORM SYSTEM IS EXPECTED TO SLOW DOWN CONSIDERABLY
ACROSS TEXAS, AND IN COMBINATION WITH SHORTWAVE ENERGY ALOFT AND
COPIOUS MOISTURE TRANSPORT FROM THE WESTERN GULF OF MEXICO, AREAS
OF HEAVY RAIN ARE BECOMING LIKELY ACROSS MUCH OF CENTRAL TEXAS
GOING INTO THE WEEKEND. MEANWHILE, THE UPPER RIDGE CONTINUES TO
BUILD ACROSS THE NORTHWESTERN U.S. AND INTO BRITISH COLUMBIA AND
ALBERTA, WITH MUCH WARMER TEMPERATURES BECOMING WIDESPREAD. IN
RESPONSE TO THE BUILDING RIDGE WILL BE A DOWNSTREAM TROUGH THAT
DEVELOPS FURTHER FROM THE GREAT LAKES TO THE NORTHEAST AND
MID-ATLANTIC REGION WITH A RETURN TO COOLER CONDITIONS AND LOWER
HUMIDITY FOR THE BEGINNING OF NEXT WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE 00Z MODEL GUIDANCE SUITE HAS A GOOD OVERALL SYNOPTIC SCALE
DEPICTION OF THE UPPER LEVEL AND SURFACE PATTERN FOR THE END OF
THE WEEK AND INTO THE WEEKEND, WITH ABOVE AVERAGE CONFIDENCE FOR
MOST AREAS SO A MULTI-DETERMINISTIC MODEL BLEND SUFFICES AS A
STARTING POINT IN THE FORECAST PROCESS. THE MODELS AGREE WELL ON
A STRONG UPPER RIDGE BUILDING INTO SOUTHWESTERN CANADA, WASHINGTON
AND OREGON, AND THE UPPER LOW OVER THE DAKOTAS EVOLVING INTO AN
OPEN WAVE THAT MERGES WITH THE WESTERLIES. THERE IS ALSO BETTER
MODEL CONSENSUS ON THE AXIS AND MAGNITUDE OF THE HEAVY QPF
EXPECTED OVER TEXAS THIS WEEKEND, AND THE CMC AND GFS HAVE A
BETTER SIGNAL FOR A WEAK UPPER LOW OVER WESTERN TEXAS ON SATURDAY.
LOOKING AHEAD TO MONDAY, THERE ARE SOME AMPLITUDE DIFFERENCES
WITH THE SHORTWAVE BUILDING ACROSS THE EASTERN U.S. AND ALSO FOR
THE NEXT SHORTWAVE DROPPING SOUTH FROM CENTRAL CANADA ON TUESDAY
WHERE THE CMC IS STRONGEST WITH THAT FEATURE. THE 12Z ECMWF WAS
QUICKEST IN BREAKING DOWN THE NORTHWESTERN UPPER RIDGE, BUT THE
00Z ECMWF MAINTAINS IT LONGER. TO ACCOUNT FOR THE INCREASING
MODEL DIFFERENCES BY DAYS 6 AND 7, USE OF THE ENSEMBLE MEANS
INCREASED TO ABOUT 50% FOR THE END OF THE FORECAST PERIOD.
..WEATHER/HAZARDS HIGHLIGHTS
A HIGH IMPACT HEAVY RAIN EVENT IS LOOKING INCREASINGLY LIKELY
ACROSS MUCH OF CENTRAL AND SOUTHERN TEXAS GOING INTO FRIDAY AND
CONTINUING THROUGH MUCH OF THE UPCOMING WEEKEND. 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. A BROAD
SLIGHT RISK AREA OF EXCESSIVE RAINFALL IS CURRENTLY WARRANTED FOR
THE DAY 4 PERIOD ACROSS MAINLY CENTRAL TEXAS TO THE RIO GRANDE
WITH A STRONG MODEL SIGNAL FOR 3-6 INCH TOTALS DURING THIS TIME
PERIOD. THE UNSETTLED PATTERN REMAINS UNABATED GOING INTO THE DAY
5 PERIOD SATURDAY WITH AN ADDITIONAL 3-6 INCHES LIKELY WITH
LOCALLY HIGHER TOTALS POSSIBLE. SINCE THIS HEAVY RAINFALL ON DAY
5 WILL BE FALLING ON ALREADY HIGHLY SATURATED GROUNDS FROM THE
PREVIOUS DAYS, A COORDINATED MODERATE RISK WAS INTRODUCED 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. ELSEWHERE ACROSS THE CONTINENTAL U.S.,
WIDESPREAD LIGHT TO MODERATE RAIN WILL LIKELY BE ONGOING ACROSS
THE DAKOTAS ON FRIDAY IN ASSOCIATION WITH THE UPPER LOW CROSSING
THAT REGION, WITH AMOUNTS GENERALLY IN THE HALF TO ONE INCH RANGE.
THIS THEN REACHES THE UPPER MIDWEST ON SATURDAY AND SHRINKS SOME
IN COVERAGE, AND THEN DRIER WEATHER ARRIVES IN TIME FOR MOTHER'S
DAY ACROSS MUCH OF THE NORTH-CENTRAL U.S. AND SCATTERED SHOWERS
OVER THE NORTHEASTERN U.S.
IN TERMS OF TEMPERATURES, HIGHS WILL LIKELY BE RUNNING 10 TO 15
DEGREES ABOVE MID MAY AVERAGES FROM THE UPPER MIDWEST TO THE GREAT
LAKES AND NORTHEAST STATES TO CLOSE OUT THE WORK WEEK, AND THEN
TRENDING COOLER GOING INTO THE WEEKEND AS AN UPPER-LOW OVER CANADA
BUILDS SOUTHWARD AND MULTIPLE COLD FRONTS LIKELY PASS THROUGH THE
REGION. ANOMALOUS EARLY SEASON HEAT WILL BUILD ACROSS THE PACIFIC
NORTHWEST BY FRIDAY AND ESPECIALLY INTO THE WEEKEND WITH HIGHS
REACHING 15-25+ DEGREES ABOVE AVERAGE ACROSS MUCH OF WASHINGTON
AND OREGON. THE POTENTIAL EXISTS FOR HIGHS TO REACH INTO THE 90S
FOR SOME OF THE INLAND VALLEY LOCATIONS AND MAY CHALLENGE SOME
DAILY RECORD HIGHS. THE HEAT WAVE WILL LIKELY PERSIST GOING INTO
EARLY NEXT WEEK AS THE UPPER RIDGE REMAINS STRONG. LOWS MAY BE A
LITTLE LESS EXTREME BUT COULD STILL CHALLENGE A FEW DAILY RECORDS
FOR WARM LOWS BY THE WEEKEND. HIGHS WILL LIKELY BE SLIGHTLY BELOW
AVERAGE ACROSS MUCH OF NEW MEXICO, TEXAS, AND OKLAHOMA OWING TO
WIDESPREAD RAIN AND CLOUDY CONDITIONS, BUT OVERNIGHT LOWS SHOULD
BE NEAR AVERAGE. WARM AND HUMID CONDITIONS WILL LIKELY CONTINUE
FOR MUCH OF THE SOUTHEASTERN U.S. GOING INTO THE WEEKEND.
HAMRICK
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
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page