119
FXUS02 KWBC 121901
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 PM EDT SAT AUG 12 2023
VALID 12Z TUE AUG 15 2023 - 12Z SAT AUG 19 2023
...HEAT WAVE TO PREVAIL FROM THE CENTRAL GULF COAST WESTWARD INTO
THE SOUTHWEST...
...HAZARDOUS HEAT ACROSS THE PACIFIC NORTHWEST INTO MID-NEXT
WEEK...
..OVERVIEW
THE UPPER FLOW PATTERN SHOULD BE FAIRLY AMPLIFIED ACROSS THE
NORTHERN TIER AND INTO PARTS OF THE EAST NEXT WEEK AS A VIGOROUS
INITIAL SHORTWAVE MOVING THROUGH THE NORTHEAST TUESDAY INTO
WEDNESDAY COULD GIVE WAY TO ANOTHER STRONG SYSTEM INTO THE UPPER
MIDWEST, GREAT LAKES, AND THE NORTHEAST LATE WEEK. THIS EASTERN
U.S. TROUGHING SHOULD FINALLY ERODE HEAT ACROSS THE SOUTHEAST, BUT
HAZARDOUS HEAT IS EXPECTED TO PERSIST THROUGH THE SOUTHERN PLAINS
INTO THE SOUTHWEST ALL OF NEXT WEEK. A HEAT WAVE ACROSS THE
PACIFIC NORTHWEST REGION STARTING THIS WEEKEND SHOULD LAST THROUGH
ABOUT MIDWEEK BEFORE LOWER HEIGHTS MOVE BACK INTO THE REGION.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
AS THE MEDIUM RANGE PERIOD BEGINS TUESDAY, MODEL GUIDANCE IS IN
GOOD AGREEMENT REGARDING THE INITIAL STRONG SHORTWAVE MOVING FROM
THE GREAT LAKES REGION QUICKLY INTO THE NORTHEAST, THE RESULTANT
TROUGH AXIS PUSHING INTO THE SOUTHEAST, AND RIDGING PERSISTING
ACROSS THE SOUTH-CENTRAL U.S. WHILE AFFECTING THE NORTHWEST AS
WELL. HOWEVER, SOME MODELS SIGNIFICANTLY DIVERGE WITH THE
POTENTIAL FOR ANOTHER POSSIBLY STRONG SHORTWAVE COMING INTO THE
NORTH-CENTRAL TO NORTHEASTERN U.S. BEHIND THIS FIRST ONE. GFS RUNS
SPECIFICALLY, INSTEAD OF DIGGING ENERGY SOUTHEASTWARD INTO THE
NORTH-CENTRAL U.S. AND CAUSING AMPLIFIED TROUGHING TO SHIFT SLOWLY
EAST LIKE THE NON-NCEP GUIDANCE, TRACK ENERGY STRAIGHT EAST ACROSS
CANADA MUCH MORE PROGRESSIVELY AND END UP OUT OF PHASE. THERE ARE
A FEW REASONS TO LEAN AWAY FROM THE GFS-TYPE SOLUTIONS. SOME OF
THESE GFS RUNS HAVE BEEN FLATTER AND MORE PROGRESSIVE WITH ANY
TROUGHING EVEN COMPARED TO THE MAJORITY OF ITS ENSEMBLE MEMBERS
AND THE GEFS ENSEMBLE MEANS. THE GFS HAS ALSO EXHIBITED THIS
FASTER/PROGRESSIVE TYPE OF BIAS WITH TROUGHS GENERALLY OVER THE
YEARS. ADDITIONALLY, LEANING AWAY FROM THE GFS LEADS TO A FORECAST
CLOSER TO CONTINUITY. HOWEVER, THE PERSISTENCE OF THE GFS SHOWING
THIS FOR FOUR OR FIVE RUNS DOES LEAD TO SOME LOWERING OF
CONFIDENCE IN THE EVENTUAL PATTERN. SO DOES THE ORIGINS OF THE
ENERGY THAT COULD FORM THIS TROUGH FEATURE, WAY OUT IN THE
NORTHERN PACIFIC ROUNDING AN ALEUTIANS UPPER LOW. THUS THOUGH IT
SEEMED PRUDENT TO PREFER OTHER GUIDANCE, CONFIDENCE IS NOT EXACTLY
HIGH AT THIS POINT. THE WPC FORECAST FAVORED A BLEND OF THE 00Z
ECMWF, CMC, AND UKMET (THROUGH ITS TIME PERIOD), WITH SOME 00Z
GEFS MEAN COMPONENT THAT WASN'T QUITE AS FAST AS THE DETERMINISTIC
GFS RUNS. AS USUAL INCREASED THE PORTION OF GEFS AND EC ENSEMBLE
MEANS WITH TIME. INCOMING 12Z RUNS ARE MUCH LIKE EACH MODEL'S
OLDER 00Z ONES, EXCEPT THAT THE 12Z CMC SEEMS TO BECOME QUITE SLOW
WITH THE TROUGH/LOW BY LATE NEXT WEEK.
..WEATHER/HAZARDS HIGHLIGHTS
A LOW PRESSURE SYSTEM MOVING QUICKLY THROUGH THE NORTHEAST ON
TUESDAY MAY BRING SOME THREAT FOR SHOWERS AND THUNDERSTORMS AHEAD
OF IT. GIVEN SENSITIVITY TO RAINFALL ACROSS PORTIONS OF THE
NORTHEAST, A LOW END MARGINAL RISK REMAINS IN THAT REGION ON THE
DAY 4/TUESDAY EXCESSIVE RAINFALL OUTLOOK. THE ASSOCIATED COLD
FRONT SHOULD SLOW/STALL AS IT WEAKENS ACROSS THE SOUTHEAST INTO
THE MIDDLE OF THE WEEK, PROVIDING A FOCUS FOR ANOMALOUS MOISTURE
AND INSTABILITY TO POOL THERE AND STRETCHING SOUTHWARD INTO
FLORIDA, FOR SOME EXCESSIVE RAINFALL POTENTIAL. MARGINAL RISKS ARE
IN PLACE FOR PARTS OF THE CENTRAL GULF COAST, SOUTHEAST, AND
CAROLINAS TUESDAY AND WEDNESDAY. FLORIDA AT LEAST LOOKS TO REMAIN
IN A WET PATTERN THROUGH MUCH OF THE WEEK. THE NEXT POTENTIAL
SHORTWAVE AND SURFACE LOW/FRONTAL REFLECTION COULD BRING ANOTHER
ROUND OF RAIN AND STORMS TO THE MIDWEST/GREAT LAKES INTO THE
NORTHEAST. GIVEN MODEL UNCERTAINTY AND THE POTENTIAL FOR ANY HEAVY
RAIN TO BE FAST-MOVING, HELD OFF ON ANY EXCESSIVE RAINFALL RISK
AREA FOR THIS ACTIVITY. MEANWHILE, MONSOONAL MOISTURE IS LIKELY TO
STAY ENHANCED ACROSS THE FOUR CORNERS STATES THROUGH TUESDAY, WITH
A MARGINAL RISK INDICATED ON THE DAY 4 ERO. SHOWERS MAY EXPAND
ACROSS PARTS OF THE GREAT BASIN AND WEST LATER NEXT WEEK AS WEAK
UPPER TROUGHING MOVES NORTHWARD OFF CALIFORNIA.
THE BIG STORY DURING THE MEDIUM RANGE PERIOD 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. HAZARDOUS HEAT THIS WEEKEND INTO
EARLY NEXT WEEK ACROSS THE SOUTHEAST SHOULD GRADUALLY MODERATE
TUESDAY WITH NEAR NORMAL TEMPERATURES BY WEDNESDAY AS TROUGHING
DROPS INTO THE REGION. MEANWHILE, A SECOND AREA OF HEAT IS
FORECAST TO LAST THROUGH TUESDAY-THURSDAY ACROSS MUCH OF THE
NORTHWEST, WITH DAYTIME HIGHS 10 TO 20 DEGREES ABOVE NORMAL
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 ON THURSDAY AND ESPECIALLY FRIDAY. SEE KEY MESSAGES
ISSUED BY WPC FOR ADDITIONAL INFORMATION AND GRAPHICS RELATED TO
THESE TWO HEAT WAVES. RECORD HIGH MAXIMUM AND MINIMUM TEMPERATURES
ARE LIKELY TO BE WIDESPREAD. BY LATE NEXT WEEK, TROUGHING COMING
INTO THE WEST SHOULD PUSH THE RIDGE EAST, PROMOTING TEMPERATURES
AROUND 10 TO 15 DEGREES ABOVE AVERAGE IN THE NORTH-CENTRAL U.S.
FRIDAY-SATURDAY.
TATE/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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