189
FXUS02 KWBC 081940
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
338 PM EDT TUE AUG 08 2023
VALID 12Z FRI AUG 11 2023 - 12Z TUE AUG 15 2023
...HEAT WAVE TO PERSIST OVER THE SOUTH INTO THE SOUTHWEST THROUGH
EARLY NEXT WEEK...
19Z UPDATE: THE 12Z MODEL GUIDANCE SUITE IS INITIALLY WELL
CLUSTERED ACROSS THE CONTINENTAL U.S. FOR THE END OF THE WEEK,
WITH SOME TIMING DIFFERENCES WITH A SHORTWAVE TROUGH CROSSING
SOUTH-CENTRAL CANADA SINCE THE GFS IS SLOWER AND A LITTLE
STRONGER. GOING INTO THE WEEKEND, MORE NOTABLE DIFFERENCES WITH
THE GFS ARE EVIDENT ACROSS SOUTHERN CANADA AND ACROSS THE NORTHERN
PLAINS/UPPER MIDWEST, BUT IT IS RELATIVELY IN LINE WITH THE OTHER
GUIDANCE ELSEWHERE. BY EARLY NEXT WEEK, THE GFS IS A LITTLE
WEAKER WITH THE DEGREE OF UPPER LEVEL RIDGING ACROSS THE
NORTHWESTERN U.S. WHICH COULD HAVE SOME IMPACT ON THE MAGNITUDE OF
THE HOT TEMPERATURES EXPECTED. ALL OF THE MODEL GUIDANCE AGREES
WELL ON MAINTAINING THE SOUTHERN PLAINS/GULF COAST UPPER RIDGE,
AND THIS RESULTS IN HIGH CONFIDENCE OF THE ONGOING HEAT AND
OPPRESSIVE HUMIDITY CONTINUING UNABATED FOR MANY OF THESE AREAS
GOING INTO THE MIDDLE OF AUGUST. IN TERMS OF THE DAY 4 AND 5
EXCESSIVE RAINFALL OUTLOOK, THERE IS STILL NOT A CLEAR ENOUGH
SIGNAL FOR ANY SLIGHT RISK AREAS AT THIS TIME. THE
FRONTS/PRESSURES FORECAST WAS WEIGHTED SLIGHTLY MORE TOWARDS THE
ECMWF/CMC ALONG WITH SOME PREVIOUS WPC CONTINUITY THROUGH SUNDAY,
AND THEN INCREASING USE OF THE ENSEMBLE MEANS TO ABOUT 40% BY NEXT
TUESDAY. THE PREVIOUS FORECAST DISCUSSION IS APPENDED BELOW FOR
REFERENCE. /HAMRICK
-------------------------
..OVERVIEW
LATEST GUIDANCE IS SUGGESTING THAT THE UPPER RIDGE INITIALLY
CENTERED FROM THE FAR SOUTHERN PLAINS THROUGH THE FLORIDA
PENINSULA SHOULD EXPAND ACROSS THE SOUTHERN AND WESTERN U.S. FROM
LATE THIS WEEK INTO EARLY NEXT WEEK. THE WESTERN PART OF THIS
RIDGE COULD ULTIMATELY CONNECT WITH A SEPARATE RIDGE FORECAST TO
BUILD OVER THE NORTHEASTERN PACIFIC. THE EXPANDING RIDGE WILL
MAINTAIN THE SOUTHERN TIER HEAT WAVE WITH DAILY RECORD HIGH
TEMPERATURES POSSIBLE EVERY DAY OF THE FORECAST PERIOD, WITH THE
MOST ANOMALOUS TEMPERATURES LIKELY TO BE OVER TEXAS INTO THE
CENTRAL GULF COAST REGION. TEMPERATURES WILL ALSO GRADUALLY
INCREASE OVER THE SOUTHWEST WHILE VERY WARM TO HOT TEMPERATURES
BECOME ESTABLISHED OVER THE PACIFIC NORTHWEST. MEANWHILE BROAD
CYCLONIC FLOW WILL PREVAIL OVER THE NORTHERN HALF OR SO OF THE
LOWER 48 EAST OF THE ROCKIES. A SUCCESSION OF EMBEDDED SHORTWAVES
SHOULD SUPPORT SURFACE WAVES/FRONTAL SYSTEMS THAT MAY BE CAPABLE
OF PRODUCING EPISODES OF LOCALLY HEAVY RAINFALL, BUT THESE
FEATURES HAVE LOWER PREDICTABILITY SEVERAL DAYS OUT SO CONFIDENCE
IN IMPORTANT DETAILS IS NOT VERY HIGH. WHILE FORMER TROPICAL
STORM EUGENE IN THE EASTERN PACIFIC HAS WEAKENED TO A REMNANT LOW,
THE SYSTEM'S REMAINING UPPER LEVEL ENERGY AND POSSIBLY SOME
MOISTURE COULD GET INCORPORATED INTO AN UPPER TROUGH/LOW FORECAST
TO EVOLVE NEAR THE CALIFORNIA COAST. THIS FEATURE MAY RETROGRADE
EARLY NEXT WEEK AS UPPER RIDGING BUILDS IN FROM THE EAST.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
WITHIN THE BROAD CYCLONIC NORTHERN STREAM FLOW, MOST GUIDANCE IS
STILL SIGNALING A SEQUENCE OF DISTINCT SYSTEMS BUT WITH ONGOING
DETAIL DIFFERENCES. AS OF THE START OF THE PERIOD EARLY FRIDAY,
THE NEW 00Z UKMET DIFFERS FROM MOST OTHER GUIDANCE BY SHOWING LESS
PHASING OF A SHORT RANGE MID-LATITUDE U.S. WAVE AND THE UPPER LOW
GETTING CLOSE TO MAINE. BEHIND THIS SYSTEM, THERE IS STILL A
LOOSE CLUSTERING FOR AN AREA OF LOW PRESSURE TO TRACK ACROSS THE
NORTHERN TIER, GREAT LAKES, AND SOUTHEASTERN CANADA/NEW ENGLAND
DURING FRIDAY-SUNDAY. THERE ARE STILL NOTABLE DETAIL DIFFERENCES
WHILE GFS RUNS HAVE RANGED BETWEEN STRONG/FAST SOLUTIONS A DAY OR
SO AGO TO THE NEW 00Z RUN THAT BECOMES WEAKER/MORE DISJOINTED WITH
THE SURFACE SYSTEM COMPARED TO MOST OTHER GUIDANCE. YET ANOTHER
FRONTAL SYSTEM SHOWS UP OVER THE NORTHERN PLAINS BY SUNDAY, BUT
CONSENSUS SO FAR SUGGESTS IT WILL BE WEAKER THAN ITS PREDECESSOR
(BUT THE NEW 00Z ECMWF HAS TRENDED MUCH STRONGER). BY THE LATTER
HALF OF THE PERIOD THE MODELS HAVE BEEN DIFFERING ON HOW
NORTHEASTERN PACIFIC/GULF OF ALASKA ENERGY MAY TRAVEL AROUND THE
NORTHERN PERIPHERY OF RIDGING TO THE SOUTH, WITH SOME EVENTUAL
INFLUENCE ON THE SUNDAY NORTHERN PLAINS SYSTEM. SPORADIC GFS
RUNS, INCLUDING THE 18Z VERSION, HAVE BEEN MORE AMPLIFIED THAN
MOST OTHER SOLUTIONS WITH THE ENERGY ROUNDING THE RIDGE. THE NEW
00Z GFS COMPARES MUCH BETTER TO CONSENSUS, AS DID THE 12Z RUN.
CMC RUNS HAVE AT TIMES BEEN A BIT ON THE AMPLIFIED SIDE WITH
SHORTWAVES REACHING THE NORTHERN PLAINS AND BEYOND. FARTHER
SOUTH, THERE HAVE BEEN SOME VARIATIONS IN SPECIFICS FOR THE
SOUTHERN TIER UPPER RIDGE FROM DAY TO DAY, AFFECTING DETAILS OF
TEMPERATURE FORECASTS AT SOME LOCATIONS. THE MOST NOTABLE TREND
LATELY IS FOR STRONGER RIDGING TO HOLD ON OVER THE GULF COAST AND
FLORIDA IN ADDITION TO THE STRONGEST RIDGING THAT HAS BEEN MORE
CONSISTENTLY DEPICTED OVER THE SOUTHERN PLAINS/ROCKIES. CURRENT
CLUSTERING LOOKS GOOD FOR THE UPPER LOW THAT SHOULD BE NEAR THE
CALIFORNIA COAST FRIDAY-SUNDAY AND THEN RETROGRADE OFFSHORE.
BASED ON THE 12Z/18Z GUIDANCE AVAILABLE FOR THE LATEST FORECAST
UPDATE, PREFERENCE INCORPORATED A 12Z/18Z MODEL BLEND EARLY AND
THAN TRANSITIONED TOWARD SOMEWHAT MORE 18Z GEFS/12Z ECMWF MEAN
INPUT LATE. GFS INPUT EVENTUALLY SWITCHED EXCLUSIVELY TO THE 12Z
RUN DUE TO COMPARING BETTER TO CONSENSUS OVER WESTERN NORTH
AMERICA EARLY NEXT WEEK.
..WEATHER/HAZARDS HIGHLIGHTS
THERE WILL BE TWO GENERAL AREAS OF INTEREST FOR LOCALLY HEAVY
RAINFALL DURING THE FRIDAY-SATURDAY NIGHT PERIOD COVERED BY THE
DAYS 4-5 EXCESSIVE RAINFALL OUTLOOKS, BOTH DENOTED BY A MARGINAL
RISK. ONE EXTENDS FROM THE SOUTHEAST INTO PARTS OF THE
MISSISSIPPI/TENNESSEE VALLEYS, AND NORTH INTO THE UPPER
MIDWEST/CENTRAL GREAT LAKES (DAY 4) OR INTO THE CENTRAL
APPALACHIANS/GREAT LAKES (DAY 5). NORTHERN TIER AREAS WILL SEE
RAINFALL FOCUSED BY SURFACE LOW PRESSURE AND ASSOCIATED FRONTAL
SYSTEM ALONG WITH SUPPORTING UPPER DYNAMICS, WITH MODERATE
PROGRESSION AND A MIX OF ANTECEDENT GROUND CONDITIONS CONTINUING
TO SUPPORT THE MARGINAL RISK DESIGNATION. CENTRAL AND SOUTHERN
PARTS OF THIS OUTLOOK AREA MAY HAVE A MORE FAVORABLE COMBINATION
OF INSTABILITY AND MOISTURE BUT GUIDANCE THUS FAR HAS BEEN VERY
INCONSISTENT AMONG EACH OTHER AND FROM RUN TO RUN IN DEPICTING
WHERE HEAVIEST TOTALS MAY BE. THUS WILL MAINTAIN THE MARGINAL
RISK WHILE AWAITING ANY EVENTUAL IMPROVED FOCUS THAT COULD WARRANT
ONE OR MORE EMBEDDED SLIGHT RISK AREAS. MEANWHILE FARTHER WEST,
GUIDANCE AGREES IN PRINCIPLE THAT FLOW BETWEEN THE CALIFORNIA
COAST UPPER LOW AND SOUTHERN TIER RIDGE SHOULD BEGIN TO DIRECT
SHORTWAVE ENERGY AND MOISTURE ALONG THE ARIZONA/NEW MEXICO BORDER
DURING DAY 4 AND EXPANDING NORTHEASTWARD INTO DAY 5, POSSIBLY
INTERACTING WITH A FRONT THAT REACHES THE CENTRAL HIGH PLAINS.
GUIDANCE HAS NOT YET COME INTO AGREEMENT FOR QPF SPECIFICS BUT THE
GENERAL PATTERN APPEARS SUFFICIENTLY FAVORABLE TO MERIT A MARGINAL
RISK AREA THAT FITS THAT EVOLUTION.
FROM DAYTIME SUNDAY THROUGH NEXT TUESDAY, CONTINUED PROGRESSION OF
WAVES/FRONTAL SYSTEMS WILL PRODUCE EPISODES OF SHOWERS AND
THUNDERSTORMS OF VARYING INTENSITY FROM PORTIONS OF THE
NORTHERN/CENTRAL PLAINS THROUGH THE EASTERN U.S. EXPECT FLORIDA
TO SEE AN INCREASE OF RAINFALL THIS WEEKEND AS AN AREA OF ENHANCED
MOISTURE MOVES IN FROM THE EAST. THE FOUR CORNERS/SOUTHWEST AND
HIGHER TERRAIN OF CALIFORNIA SHOULD SEE DIURNALLY FAVORED EPISODES
OF CONVECTION, THOUGH WITH SOME CONTINUED UNCERTAINTY OVER
SPECIFICS INVOLVING MOISTURE AND SHORTWAVE IMPULSES AT ANY
PARTICULAR LOCATION.
EXPECT THE HEAT ACROSS THE SOUTHERN TIER TO CONTINUE INTO NEXT
WEEK WITH THE GREATEST EMPHASIS OVER THE SOUTHERN PLAINS THROUGH
CENTRAL GULF COAST REGION WHERE HIGHS WILL LIKELY BE 5-10F OR SO
ABOVE NORMAL NEARLY EVERY DAY. SOME LOCATIONS IN FLORIDA SHOULD
SEE HIGHS SEVERAL DEGREES ABOVE NORMAL AS WELL, WHILE WESTWARD
EXPANSION OF THE UPPER RIDGE AS CURRENTLY FORECAST WOULD ALSO
RAISE TEMPERATURES IN THE SOUTHWEST UP TO 5-10F ABOVE NORMAL BY
NEXT MONDAY-TUESDAY (LEADING TO SOME HIGHS EXCEEDING 110F). DAILY
RECORD HIGHS WILL BE MOST LIKELY OVER THE SOUTHERN PLAINS, CENTRAL
GULF COAST, AND FLORIDA. HIGH HUMIDITY SHOULD LEAD TO MAXIMUM
HEAT INDICES AT LEAST IN THE 110-115F RANGE ALONG AND NEAR THE
WESTERN HALF OF THE GULF COAST, AND PERHAPS AT SCATTERED LOCATIONS
FARTHER EAST. RECORD WARM LOWS WILL BE POSSIBLE ACROSS A BROAD
PORTION OF THE SOUTHERN TIER EACH NIGHT. MEANWHILE STRENGTHENING
UPPER RIDGING SHOULD BRING HIGHER TEMPERATURES TO THE PACIFIC
NORTHWEST DURING THE WEEKEND AND EARLY NEXT WEEK, WITH HIGHS
REACHING 10F OR MORE ABOVE NORMAL OVER SOME LOCATIONS. VERY WARM
TO HOT TEMPERATURES MAY EXTEND BEYOND THE MEDIUM RANGE FORECAST
PERIOD. SOME RECORD WARM LOWS MAY BE POSSIBLE BY EARLY NEXT WEEK
BUT FORECAST HIGHS ARE NOT YET REACHING DAILY RECORD VALUES. IN
CONTRAST, LOCATIONS FROM THE NORTHERN ROCKIES INTO THE MIDWEST
SHOULD SEE VARIABLE TEMPERATURES WITH SOME AREAS SEEING ONE OR
MORE DAYS OF SLIGHTLY BELOW NORMAL HIGHS. THE UPPER TROUGH/LOW
NEAR CALIFORNIA SHOULD KEEP HIGHS OVER MOST OF THE STATE NEAR OR
SLIGHTLY BELOW NORMAL THROUGH LATE WEEK, FOLLOWED BY A WARMER
TREND AS THE FEATURE DRIFTS WESTWARD.
RAUSCH
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
HAZARDS:
- HAZARDOUS HEAT ACROSS PORTIONS OF CALIFORNIA, THE PACIFIC
NORTHWEST, AND THE NORTHERN GREAT
BASIN, SUN-TUE, AUG 13-AUG 15.
- HAZARDOUS HEAT ACROSS PORTIONS OF CALIFORNIA AND THE SOUTHWEST,
MON-TUE, AUG 14-AUG 15.
- HAZARDOUS HEAT ACROSS PORTIONS OF THE SOUTHEAST, THE LOWER
MISSISSIPPI VALLEY, THE SOUTHERN
PLAINS, AND THE TENNESSEE VALLEY, FRI-TUE, AUG 11-AUG 15.
- HAZARDOUS HEAT ACROSS PORTIONS OF THE SOUTHERN PLAINS, FRI-SAT,
AUG 11-AUG 12.
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
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