810
FXUS02 KWBC 161939
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
338 PM EDT WED AUG 16 2023
VALID 12Z SAT AUG 19 2023 - 12Z WED AUG 23 2023
...SIGNIFICANT SOUTHWEST U.S./CALIFORNIA EXCESSIVE RAINFALL/RUNOFF
THREAT FUELED BY DEEP TROPICAL MOISTURE IN ADVANCE OF HILARY...
...HEAT WAVE EXPANDING ACROSS THE CENTRAL TO EAST-CENTRAL U.S.
THIS WEEKEND THROUGH EARLY-MID NEXT WEEK...
..OVERVIEW
A VERY ACTIVE WEATHER PATTERN IS SET TO EMERGE. A VIGOROUS
SHORTWAVE WITH EMBEDDED CLOSED LOW WILL SHIFT OUT OF THE NEW
ENGLAND THIS WEEKEND AS AN ANOMALOUSLY STRONG/MASSIVE UPPER
RIDGE/CLOSED HIGH EXPANDS ACROSS THE CENTRAL TO EAST-CENTRAL U.S.
BRINGING A RESURGENCE OF EXCESSIVE HEAT THROUGH AT LEAST THE
MIDDLE OF NEXT WEEK. TROUGHING OVER THE WEST COAST LOOKS TO REMAIN
INTACT THROUGH THE PERIOD RENEWED BY SHORTWAVES OUT OF THE GULF OF
ALASKA AND INTO SOUTHWEST CANADA. CONFIDENCE CONTINUES TO TO
INCREASE ON A HEAVY RAINFALL AND POTENTIALLY HIGH IMPACT EVENT TO
UNFLOLD AND FOCUS ACROSS PARTS OF THE SOUTHWEST AND CALIFORNIA
SATURDAY TO MONDAY ASSOCIATED WITH A DEEP LEAD MOISTURE PLUME AND
FAVORABLE INGREDIENTS IN ADVANCE OF THE FORECAST APPROACH OF
EXTRATROPICALLY TRANSITIONING HURRICANE HILARY OUT FROM THE
TROPICAL EAST PACIFIC AS PER THE LATEST FROM THE NATIONAL
HURRICANE CENTER.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
THE WPC MEDIUM RANGE PRODUCT SUITE WAS PRIMARILY DERIVED FROM THE
01 UTC NATIONAL BLEND OF MODELS ALONG WITH ADDED INFORMATION FROM
WPC/NDFD CONTINUITY AND THE MOST COMPATIBLE GEFS/ECMWF ENSEMBLE
MEANS WHOSE COMPOSITE SEEMS TO PROVIDE A REASONABLE FORECAST BASIS
ACROSS MUCH OF THE NATION, BUT IN PARTICULAR SEEMS MOST IN LINE
WITH THE LATEST NHC HILARY FORECAST.
..WEATHER/HAZARDS HIGHLIGHTS
DEEP MONSOONAL/TROPICAL MOISTURE CHANNELING NORTHWARD AHEAD OF
EAST PACIFIC/WEST COAST UPPER TROUGHING AND ON THE WESTERN
PERIPHERY OF A DOWNSTREAM CENTRAL U.S. UPPER RIDGE WILL INCREASING
MAKE MUCH OF THE INTERIOR WEST THEN NORTHERN ROCKIES WET THIS
PERIOD. HEAVIEST RAINFALL AMOUNTS WILL ESPECIALLY FOCUS OVER PARTS
OF THE SOUTHWEST U.S./SOUTHERN CALIFORNIA, BUT REMAIN LOCALLY
UNCERTAIN AS DEPENDENT ON THE ULTIMATE TRACK OF HILARY. HOWEVER,
MODELS DO CONTINUE TO TREND TOWARDS A SIGNFICANT EXCESSIVE
RAINFALL THREAT AND CONFIDENCE/MODEL AGREEMENT IS HIGH ENOUGH TO
MAINTAIN A SLIGHT RISK ACROSS ACROSS PORTIONS OF SOUTHEAST
CALIFORNIA, SOUTHERN NEVADA, AND WESTERN ARIZONA ON BOTH THE DAYS
4 AND 5 (SATURDAY AND SUNDAY) WPC EXCESSIVE RAINFALL OUTLOOKS.
HEAVY RAINFALL MAY ALSO LIFT ACROSS SOUTH-CENTRAL CALIFORNIA AS
WELL INTO EARLY NEXT WEEK. TO THE NORTH, MOISTURE WILL INTERACT
WITH A FRONTAL BOUNDARY ACROSS THE NORTHWEST/NORTHERN ROCKIES
PROVIDING SOME ENHANCEMENT OF RAINFALL TO THAT REGION. BROAD
MARGINAL RISKS ARE DEPICTED ON THE EXCESSIVE RAINFALL OUTLOOKS.
MUCH OF THE REST OF THE COUNTRY LOOKS TO REMAIN MOSTLY DRY UNDER
THE EXPANSIVE UPPER RIDGE, WITH THE EXCEPTION OF FLORIDA AND THE
GULF COAST AS TROPICAL MOISTURE SHIFTS WESTWARD ACROSS FLORIDA AND
THE GULF OF MEXICO. THIS COULD ALSO BRING SOME RAINFALL INTO
SOUTHERN TEXAS NEXT TUESDAYWEDNESDAY.
A HEAT WAVE WILL BUILD OVER THE SOUTHERN AND CENTRAL U.S. INTO THE
MIDWEST WITH DAYTIME HIGHS 10-20 DEGREES ABOVE NORMAL IN SOME
PLACES. THIS EQUATES TO DAYTIME HIGHS NEAR 100 DEGREES POSSIBLE AS
FAR NORTH AS THE UPPER MIDWEST STATES, WITH DAILY RECORD HIGHS
POSSIBLE, AND SOME LOCATIONS IN THE MIDWEST SEEING THEIR HOTTEST
DAY OF THE YEAR SO FAR. HUMIDITY LEVELS WILL SEND HEAT INDICES
INTO THE 100S FOR MANY. SEE KEY MESSAGES ISSUED BY WPC FOR
ADDITIONAL DETAILS AND GRAPHICS RELATED TO THIS HEAT WAVE. HEAT
MAY ALSO BUILD BACK INTO THE SOUTHEAST BY THE MIDDLE OF NEXT WEEK,
AND POSSIBLY BEYOND PER THE LATEST FORECASTS FROM THE CLIMATE
PREDICTION CENTER. ELSEWHERE, UPPER TROUGHING OUT WEST SHOULD KEEP
HIGHS GENERALLY 5-15 DEGREES BELOW NORMAL WITH PARTS OF THE
SOUTHWEST 15-20 DEGREES BELOW NORMAL ESPECIALLY SUNDAY AND MONDAY
AS A RESULT OF THE INCREASED CLOUD COVER AND HEAVY PRECIPITATION
THREAT.
SCHICHTEL/SANTORELLI
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 FORECAST, EXCESSIVE RAINFALL OUTLOOK,
WINTER WEATHER OUTLOOK PROBABILITIES, HEAT INDICES AND KEY
MESSAGES 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
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=OVW
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page