561
FXUS02 KWBC 210700
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
259 AM EDT FRI JUL 21 2023
VALID 12Z MON JUL 24 2023 - 12Z FRI JUL 28 2023
...DANGEROUS HEAT WILL CONTINUE ACROSS THE SOUTHWEST AND BUILD
FARTHER NORTH AND EAST INTO THE PLAINS/MIDWEST AS NEXT WEEK
PROGRESSES...
..OVERVIEW
A STRONG AND PERSISTENT UPPER RIDGE/HIGH ANCHORED OVER THE
SOUTHERN ROCKIES WILL KEEP HOTTER THAN USUAL TEMPERATURES ACROSS
THE SOUTHWEST NORTHEASTWARD INTO THE PLAINS AND MIDWEST UNDER THE
RIDGE AXIS. DOWNSTREAM, AN UPPER TROUGH IS FORECAST ATOP THE
EAST-CENTRAL U.S. EARLY IN THE WEEK, WHICH SHOULD GRADUALLY
DEAMPLIFY AND ALLOW FOR HOTTER THAN NORMAL TEMPERATURES TO SPREAD
INTO THE OHIO VALLEY/GREAT LAKES AND NORTHEAST/MID-ATLANTIC BY
LATE NEXT WEEK. FARTHER WEST, AN EASTERN PACIFIC UPPER LOW (PART
OF A REX BLOCK CONFIGURATION INCLUDING AN ALASKA/NORTHWESTERN
CANADA RIDGE) MAY EJECT EAST ACROSS SOUTHERN CANADA AND DROP
FRONTS INTO THE NORTHWESTERN TO NORTH-CENTRAL U.S., WITH POTENTIAL
FOR TROUGHING TO BUILD INTO THAT REGION ONCE AGAIN. SOME DIURNALLY
FAVORED SHOWERS AND THUNDERSTORMS WILL BE POSSIBLE OVER THE FOUR
CORNERS STATES WHILE FRONTS/UPPER SHORTWAVES MAY PRODUCE SOME
EPISODES OF CONVECTION OVER THE EASTERN HALF OF THE COUNTRY, BUT
OVERALL THE COVERAGE OF HEAVY RAINFALL THREATS SHOULD BE LESS THAN
AVERAGE FOR THE MIDDLE OF SUMMER.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
MODEL GUIDANCE IS IN PRETTY GOOD AGREEMENT WITH THE SYNOPTIC SCALE
PATTERN DESCRIBED ABOVE, ESPECIALLY THE PERSISTENT UPPER HIGH AND
THE TROUGHING ACROSS THE EAST GRADUALLY FILLING WITH TIME. THE
MAIN MODEL DIFFERENCES ARE WITH THE EVENTUAL TIMING/MOVEMENT OF
THE UPPER LOW IN THE EASTERN PACIFIC AT THE START OF THE PERIOD
MONDAY. GFS RUNS HAVE BEEN CONSISTENTLY ON THE FASTER SIDE WITH
THE UPPER AND ASSOCIATED SURFACE LOW TRACK EASTWARD BY
WEDNESDAY/DAY 5 OR SO, WHILE CMC RUNS ARE ON THE SLOWER SIDE. THE
12Z ECMWF WAS IN BETWEEN AND WAS THE MOST AGREEABLE WITH THE
ENSEMBLE MEANS, SO THE WPC FORECAST PREFERRED ITS DEPICTION. THE
NEWER 00Z GFS AND ECMWF ARE FORTUNATELY SHOWING BETTER CONSISTENCY
WITH THE TIMING, THOUGH THE 00Z CMC IS STILL SLOW AND MAKES THE
PATTERN IN SOUTH-CENTRAL AND SOUTHEASTERN CANADA OUT OF PHASE.
WHILE MODELS AGREE FAIRLY WELL ON THE LARGER SCALE, THEY CONTINUE
TO SHOW AMPLE DIFFERENCES IN TERMS OF QPF ESPECIALLY IN THE
UNCERTAIN NORTHWEST FLOW PATTERN IN THE NORTH-CENTRAL U.S. OVERALL
THE WPC QPF BROADENED THE COVERAGE OF LIGHT AMOUNTS IN THE
NORTH-CENTRAL U.S. COMPARED TO THE NBM USING A MULTI-MODEL AND
ENSEMBLE BLEND TO PROVIDE SOME DEPICTION OF THE RAINFALL
POTENTIAL, BUT THESE RAINFALL FORECASTS COULD CHANGE NOTABLY WITH
TIME IF/AS MODELS START TO CONVERGE. FOR THE MASS FIELDS THE WPC
FORECAST USED A BLEND HEAVY ON THE 12Z ECMWF ALONG WITH SOME
12/18Z GFS AND 12Z CMC AND UKMET EARLY IN THE PERIOD, GRADUALLY
ADDING IN AND INCREASING THE GEFS/EC ENSEMBLE MEAN PROPORTION TO
ALMOST HALF WITH TIME AMID INCREASING MODEL DIFFERENCES.
..WEATHER/HAZARDS HIGHLIGHTS
SHOWERS AND STORMS ARE LIKELY IN THE EAST EARLY IN THE WORKWEEK
WITH MOIST INFLOW AHEAD OF THE UPPER TROUGH AXIS. WITH SCATTERED
HEAVY AMOUNTS POSSIBLE, A MARGINAL RISK IS DELINEATED FOR MONDAY'S
EXCESSIVE RAINFALL OUTLOOK FOR GENERALLY THE APPALACHIANS REGION
INTO THE CAROLINAS AND FLORIDA. ON TUESDAY THE HEAVIEST RAIN
TOTALS LOOK TO FOCUS ACROSS THE NORTHEASTERN U.S. AHEAD OF AN
UPPER SHORTWAVE AND COLD FRONT. A MARGINAL RISK IS IN PLACE FOR
THE NORTHERN MID-ATLANTIC INTO THE INTERIOR NORTHEAST FOR THIS
ACTIVITY. IF RAIN AMOUNTS MORE AGREEABLY TREND UPWARD, HIGHER
EXCESSIVE RAINFALL RISK LEVELS ARE POSSIBLE THERE CONSIDERING THE
VERY WET ANTECEDENT CONDITIONS. FARTHER SOUTH, A LINGERING FRONT
ACROSS THE GULF COAST COULD SPARK SOME CONVECTION PARTICULARLY ON
MONDAY-TUESDAY BEFORE THE FRONT DISSIPATES. UNCERTAINTY WHETHER
THE RAIN WILL FOCUS ON- OR OFFSHORE PRECLUDES A MARGINAL RISK
FARTHER WEST OF FLORIDA AT THIS TIME (SOUTHEASTERN LOUISIANA MAY
BE THE MOST LIKELY PLACE FOR HEAVY RAIN TO END UP ONSHORE).
MEANWHILE INTO THE NORTHERN HALF OF THE PLAINS/MISSISSIPPI VALLEY
INTO THE MIDWEST/GREAT LAKES REGION, GENERAL NORTHWEST FLOW AND A
COUPLE OF FRONTAL SYSTEMS COULD PRODUCE SHOWERS AND THUNDERSTORMS,
PERHAPS WITH LOCALLY HEAVY RAINFALL. AT THIS POINT MODEL GUIDANCE
SHOWS TOO MUCH VARIATION IN LOCATION OF ENHANCED AMOUNTS TO DEPICT
ANY RISK AREAS IN THE EROS. SHORTER TERM GUIDANCE MAY EVENTUALLY
PROVIDE ENOUGH FOCUS TO DEFINE REGIONS WITH RELATIVELY GREATER
HEAVY RAINFALL POTENTIAL. THESE AREAS COULD CONTINUE TO SEE
CONVECTION INTO THE LATTER HALF OF NEXT WEEK AS WELL. THEN FARTHER
WEST, THE FOUR CORNERS STATES ARE LIKELY TO SEE DIURNALLY DRIVEN
CONVECTION EACH DAY NEXT WEEK AS MONSOONAL MOISTURE COMES IN
UNDERNEATH THE SOUTHERN ROCKIES UPPER RIDGE. THE EROS DEPICT A
MARGINAL RISK AREA ON BOTH DAYS.
THE RELENTLESS UPPER HIGH CENTERED OVER THE SOUTHERN ROCKIES WILL
KEEP TEMPERATURES IN THE DESERT SOUTHWEST AROUND 5-10F ABOVE
AVERAGE FOR HIGHS IN THE 110S. THOUGH THESE ANOMALIES ARE A LITTLE
LESS EXTREME THAN IN THE SHORTER TERM, THE HEAT WILL CONTINUE TO
BE HAZARDOUS INTO NEXT WEEK. HIGHS OVER 100F ARE FORECAST TO
STRETCH INTO MUCH OF TEXAS AS WELL, AND EASTERN TEXAS NEAR THE
GULF COAST CAN EXPECT HEAT INDICES WELL OVER 110F DURING PEAK
AFTERNOON HEATING AS HIGH DEWPOINTS COMBINE WITH THE HOT
TEMPERATURES. UPPER RIDGING EXTENDING TO THE NORTH WILL ALSO ALLOW
FOR THE PLAINS AND MIDWEST TO WARM TO GENERALLY 10-15F ABOVE
NORMAL THROUGH MUCH OF NEXT WEEK, REACHING THE 100F MARK AT SOME
LOCATIONS. WARMER THAN NORMAL TEMPERATURES ARE LIKELY TO EXPAND
EAST INTO THE OHIO VALLEY, GREAT LAKES, AND MID-ATLANTIC/NORTHEAST
REGIONS BY THE LATTER PART OF NEXT WEEK AFTER THE UPPER TROUGHING
ERODES. MEANWHILE THE ONLY NOTABLE AREA OF POTENTIALLY BELOW
NORMAL TEMPERATURES WILL BE THE PACIFIC NORTHWEST GIVEN THE ROUNDS
OF TROUGHING ALOFT IN THE VICINITY.
TATE
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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