948
FXUS02 KWBC 130701
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 AM EDT SUN AUG 13 2023
VALID 12Z WED AUG 16 2023 - 12Z SUN AUG 20 2023
...HEAT WAVE TO PREVAIL ACROSS THE SOUTH-CENTRAL U.S. THROUGH THE
PERIOD...
...HAZARDOUS HEAT ACROSS THE PACIFIC NORTHWEST AND THE SOUTHWEST
TO WANE BY LATE WEEK...
..OVERVIEW
THE UPPER FLOW PATTERN SHOULD BE FAIRLY AMPLIFIED ACROSS THE
NORTHERN TIER AND INTO PARTS OF THE EAST THIS WEEK AS AN INITIAL
SHORTWAVE EXITING THE NORTHEAST ON WEDNESDAY MAY GIVE WAY TO A
VIGOROUS SYSTEM THROUGH THE UPPER MIDWEST, GREAT LAKES, AND THE
NORTHEAST LATER THIS WEEK. MEANWHILE, HAZARDOUS HEAT WILL CONTINUE
ACROSS THE PACIFIC NORTHWEST AS WELL AS THE SOUTHWEST INTO THE
SOUTHERN PLAINS MUCH OF THIS WEEK. AMPLIFIED TROUGHING DOWN THE
WEST COAST BY NEXT WEEKEND SHOULD QUICKLY BRING TEMPERATURES BACK
TO NORMAL OR BELOW NORMAL ACROSS THE WEST AND SOUTHWEST, BUT HEAT
WILL CONTINUE ACROSS THE SOUTHERN PLAINS/GULF COAST AND EXPAND
NORTHWARD INTO THE CENTRAL STATES.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
AS THE MEDIUM RANGE PERIOD BEGINS WEDNESDAY, MODEL GUIDANCE IS IN
GOOD AGREEMENT REGARDING INITIAL ENERGY/TROUGHING EXITING THE EAST
AND STRONG RIDGING FROM THE SOUTHERN PLAINS TO THE NORTHWEST, AS
WELL AS WITH A LINGERING BROAD CLOSED LOW OFF THE CALIFORNIA
COAST. THE GREATEST UNCERTAINTIES ARISE AS EARLY AS THURSDAY AS
SHORTWAVE ENERGY (ORIGINATING FROM THE FAR NORTH PACIFIC) ROUNDS
THE TOP OF THE RIDGE INTO CENTRAL CANADA. THROUGH THE 18Z/12Z (AUG
12) MODEL RUNS, WHICH WERE THE LATEST RUNS AVAILABLE AT FORECAST
GENERATION TIME, THE GFS WAS SIGNIFICANTLY FLATTER AND FASTER WITH
THIS SYSTEM (A KNOWN BIAS OF THE GFS) BARELY SKIRTING THE NORTHERN
U.S. AND QUICKLY SHIFTING THROUGH EASTERN CANADA FRIDAY INTO
SATURDAY. MEANWHILE, THE NON-NCEP GUIDANCE WERE ALL MUCH MORE
AMPLIFIED, SPLITTING THE ENERGY ALLOWING IT TO DIVE SOUTH AND EAST
ACROSS THE GREAT LAKES/MIDWEST WITH SUGGESTIONS THAT A CLOSED LOW
CUTS OFF OVER THE OHIO VALLEY OR NORTHEAST LATER THIS WEEK.
UNCERTAINTY INCREASED EVEN MORE THOUGH WITH THIS SYSTEM AS THE
LATEST 00Z RUNS THOUGH AS THE CMC NOW LOOKS MORE LIKE THE GFS,
WHICH DID SLOW DOWN SOMEWHAT WITH THE NEW 00Z RUN. THE ECMWF AND
UKMET REMAIN RATHER AMPLIFIED LIKE THEIR PREVIOUS RUNS. IT'S
INTERESTING TO NOTE THE GFS HAS BEEN VERY CONSISTENT OVER THE PAST
SEVERAL RUNS WITH THIS FAST SOLUTION, WHILE THE ECMWF IS MORE
VARIABLE REGARDING SPEED AND STRENGTH. BASED ON SPAGHETTI PLOTS
WITH VARIOUS ENSEMBLE SOLUTIONS AND DETERMINISTIC SOLUTIONS, THERE
IS STILL MORE SUPPORT FOR SOMETHING SLOWER/MORE AMPLIFIED, THUS
THE WPC FORECAST FOR TONIGHT LEANED IN THAT DIRECTION. HOWEVER,
GIVEN LATEST 00Z RUNS, IT'S A HIGHLY UNCERTAIN FORECAST AND
WOULDN'T BE SURPRISED TO SEE THE FORECAST TREND FASTER WITH TIME.
THE WPC FORECAST LEANED VERY HEAVILY ON THE ECMWF THROUGH THE
PERIOD GIVEN IT WAS MORE IN THE MIDDLE WITH THE SHORTWAVE AS IT
MOVES INTO THE NORTHEAST LATER IN THE WEEK. EARLY PERIOD USED SOME
SMALLER PARTS OF THE UKMET AND CMC, FAVORING THE ENSEMBLE MEANS
(MORE ECENS MEAN) LATE IN THE PERIOD. OVERALL, THIS RESULTED IN A
FAIRLY CONSISTENT FORECAST (ALBEIT A BIT DEEPER/MORE AMPLIFIED)
WITH PREVIOUS WPC CONTINUITY.
..WEATHER/HAZARDS HIGHLIGHTS
FAIRLY QUIET IN TERMS OF SENSIBLE WEATHER THROUGH AT LEAST MID TO
LATE WEEK. SHOWERS AND STORM ASSOCIATED WITH A LINGERING FRONTAL
BOUNDARY OVER THE SOUTHEAST, COMBINED WITH ANOMALOUS MOISTURE, MAY
RESULT IN POCKETS OF HEAVY TO EXCESSIVE RAINFALL ALONG THE
SOUTHEAST COAST AND OVER THE FLORIDA PENINSULA. AS SUCH, A
MARGINAL RISK IN IN PLACE FOR THIS REGION ON BOTH THE DAY
4/WEDNESDAY AND DAY 5/THURSDAY EXCESSIVE RAINFALL OUTLOOKS.
FLORIDA LOOKS TO REMAIN WET INTO NEXT WEEKEND TOO. TO THE NORTH,
SHOWERS AND STORMS SHOULD ACCOMPANY THE SHORTWAVE THROUGH THE
GREAT LAKES INTO THE NORTHEAST WEDNESDAY-FRIDAY, BUT HIGHLY
UNCERTAIN ON EXACT AMOUNTS AND IMPACTS. MONSOONAL MOISTURE WILL
CONTINUE TO STREAM INTO THE FOUR CORNERS REGION THROUGH MID WEEK,
BUT MAY INCREASE WITH RAINFALL EXPANDING IN COVERAGE ACROSS PARTS
OF THE GREAT BASIN AND THE WEST LATER THIS WEEK AND NEXT WEEKEND
AS AMPLIFIED TROUGHING BECOMES ESTABLISHED OVER THE REGION.
THE BIG STORY DURING THE MEDIUM RANGE PERIOD THOUGH WILL CONTINUE
TO BE OPPRESSIVE HEAT LASTING INTO NEXT WEEKEND FROM THE CENTRAL
GULF COAST INTO THE SOUTHERN PLAINS. NUMEROUS DAILY RECORD HIGHS
AND WARM OVERNIGHT LOWS ARE LIKELY, AND THE COMBINATION OF HEAT
AND HUMIDITY WILL ALSO RESULT IN EXTREMELY DANGEROUS HEAT INDICES
IN EXCESS OF 110F IN MANY LOCATIONS. THE HEAT WAVE ACROSS THE
SOUTHWEST AND PACIFIC NORTHWEST WILL REMAIN THROUGH ABOUT MID-WEEK
WITH DAYTIME HIGHS 10 TO 20 DEGREES ABOVE NORMAL ACROSS THE
NORTHWEST THROUGH THURSDAY. HIGH TEMPERATURES IN THE 90S, 100S,
AND EVEN LOCALIZED 110S POSSIBLE ARE EXPECTED ACROSS WASHINGTON,
OREGON, AND THE INTERIOR VALLEY OF CALIFORNIA. EROSION OF THE WARM
CORE RIDGE ACROSS THE NORTHWEST WITH TIME SHOULD BEGIN TO MODERATE
TEMPERATURES BY FRIDAY. SEE KEY MESSAGES ISSUED BY WPC FOR
ADDITIONAL INFORMATION AND GRAPHICS RELATED TO THESE TWO HEAT
WAVES. BY LATE NEXT WEEK, TROUGHING COMING INTO THE WEST SHOULD
PUSH THE RIDGE EAST, PROMOTING WARMING TEMPERATURES ACROSS THE
CENTRAL U.S. BY THE WEEKEND. DAYTIME HIGHS IN THE 90S TO NEAR 100
LOOKS TO BUILD INTO THE CENTRAL PLAINS AND MIDWEST.
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
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