055
FXUS02 KWBC 220701
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 AM EDT SAT JUL 22 2023
VALID 12Z TUE JUL 25 2023 - 12Z SAT JUL 29 2023
...DANGEROUS HEAT WILL CONTINUE ACROSS THE SOUTHWEST AND BUILD
FARTHER INTO THE NORTH-CENTRAL AND NORTHEASTERN U.S. 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 OVER THE EAST-CENTRAL U.S.
EARLY IN THE WEEK SHOULD GRADUALLY DEAMPLIFY AND EVENTUALLY ALLOW
FOR AN ATLANTIC UPPER RIDGE TO BUILD OVER FLORIDA AND THE
SOUTHEAST LATE IN THE WEEK. THIS SHOULD RAISE TEMPERATURES TO WELL
ABOVE NORMAL IN THE OHIO VALLEY/GREAT LAKES AND
NORTHEAST/MID-ATLANTIC FOR THE LATTER PART OF THE WORKWEEK BEFORE
A COLD FRONT MODERATES TEMPERATURES THERE BY NEXT SATURDAY.
MEANWHILE 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 ADDITIONAL TROUGHING
LIKELY TO REMAIN IN PLACE NEAR THE PACIFIC NORTHWEST MID-LATE
WEEK. 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
WITH THE MODEL/ENSEMBLE GUIDANCE AGREEING FAIRLY WELL FOR THE
ROCKIES/PLAINS UPPER HIGH AND WEAKENING EASTERN U.S. TROUGH, THE
MAIN MODEL DIFFERENCES CONTINUE TO INVOLVE THE EVENTUAL
TIMING/MOVEMENT OF THE UPPER LOW CENTERED ATOP BRITISH COLUMBIA AT
THE START OF THE PERIOD TUESDAY, AND ADDITIONAL ENERGY COMING IN
BEHIND TO PRODUCE ANOTHER ROUND OF TROUGHING NEAR THE PACIFIC
NORTHWEST FOR THE LATTER PART OF THE WEEK. WITH THE FIRST FEATURE,
THE 12/18Z MODEL CYCLE SEEMED TO BE GENERALLY IN BETTER AGREEMENT
THAN IN PREVIOUS DAYS WITH THE TIMING OF ITS EJECTION EASTWARD.
THE MAIN EXCEPTION WAS THE 12Z UKMET THAT WAS SLOWER AND MERGED IT
WITH UPSTREAM ENERGY. HOWEVER, THE INCOMING 00Z MODEL CYCLE HAS
TRENDED SLOWER OVERALL WITH THE UPPER AND SURFACE LOWS COMPARED TO
THE PREVIOUS CYCLE, AFFECTING ASSOCIATED FRONTAL POSITIONS AS
WELL. THEN WITH THE ENERGY UPSTREAM, MODEL GUIDANCE HAS BEEN
CONSISTENT WITH FORMING ANOTHER TROUGH AND POSSIBLY A CLOSED LOW
CENTERED NEAR THE PACIFIC NORTHWEST INTO LATE WEEK. THE NEWER 00Z
MODEL CYCLE MAINTAINS THIS BUT IS OVERALL A LITTLE WEAKER AND
FASTER WITH ITS TRACK EASTWARD/INLAND BY FRIDAY-SATURDAY, SO THERE
ARE STILL SOME DETAILS TO FIGURE OUT.
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 (LIKELY TRENDING MORE ZONAL WITH
TIME) IN THE NORTH-CENTRAL U.S. EXACT FRONTAL POSITIONS AND EVEN
SMALLER-SCALE BOUNDARIES CAN INFLUENCE THE QPF AMOUNTS AND
PLACEMENT CONSIDERABLY. EVEN IN THE ENSEMBLE MEANS THERE ARE
CONSIDERABLE DIFFERENCES IN ANY QPF FOCUS--FOR EXAMPLE, THE 12Z EC
ENSEMBLE MEAN HAD NO QPF FROM AROUND THE TENNESSEE VALLEY TO THE
CENTRAL APPALACHIANS IN BETWEEN AREAS OF LIGHT QPF, WHILE IN THE
GEFS MEAN QPF IS MAXIMIZED THERE (THOUGH STILL LIGHT, GENERALLY A
TENTH TO QUARTER INCH). THE WPC QPF CONTINUES TO SHOW SOMEWHAT
BROADER 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 STARTED
WITH A BLEND OF THE 12Z ECMWF, 18Z GFS, AND 12Z CMC DETERMINISTIC
MODELS, INCORPORATING THE GEFS AND EC ENSEMBLE MEANS IN THE BLEND
BY DAYS 5-7.
..WEATHER/HAZARDS HIGHLIGHTS
AT THE BEGINNING OF THE PERIOD TUESDAY, MOIST INFLOW INTO THE MEAN
BUT ERODING UPPER TROUGH ATOP THE NORTH-CENTRAL TO NORTHEASTERN
U.S., ALONG WITH FRONTS AT THE SURFACE, WILL LEAD TO THE
POSSIBILITY OF CONVECTION FROM THE NORTHWEST FLOW PATTERN IN THE
MID-MISSISSIPPI VALLEY EASTWARD INTO THE OHIO VALLEY AND INTO THE
NORTHEAST AHEAD OF THE TROUGH AXIS. MODEL GUIDANCE IS STILL QUITE
VARIABLE WITH THE PLACEMENT OF STORMS AND RAINFALL AMOUNTS, SO
MAINTAINED THE MARGINAL RISK IN THE EXCESSIVE RAINFALL OUTLOOK FOR
DAY 4/TUESDAY WITH THE EXPANSION WESTWARD INTO THE MID-MISSISSIPPI
VALLEY FOR POSSIBLE TUESDAY MORNING ACTIVITY LINGERING FROM DAY 3
AS WELL AS PERHAPS ANOTHER ROUND OF STORMS LATER TUESDAY IN THAT
REGION. PARTS OF THE NORTHEAST REMAIN SUSCEPTIBLE TO FLOODING WITH
ANY ADDITIONAL RAINFALL DUE TO VERY WET ANTECEDENT CONDITIONS, SO
FORECAST RAINFALL AMOUNTS WILL BE CLOSELY MONITORED FOR THAT AREA
IN CASE THE RISK LEVEL MAY NEED TO BE UPGRADED. BY DAY 5/WEDNESDAY
THERE IS EVEN MORE SPREAD IN ANY SIGNAL FOR FOCUSED RAINFALL
ACROSS THE EAST. DID NOT INTRODUCE ANY EXCESSIVE RAINFALL AREAS AT
THIS TIME DUE TO THE UNCERTAINTY IN THE PLACEMENT OF STORMS, BUT
CONVECTION THAT DOES FORM COULD CONTAIN HEAVY RAINFALL AMOUNTS
GIVEN THE INSTABILITY IN PLACE. A LOW PRESSURE SYSTEM TRACKING
THROUGH SOUTHERN CANADA COULD HELP FOCUS RAIN/STORMS IN THE UPPER
MIDWEST ON WEDNESDAY WITH SOME PREDICTABILITY, SO PLAN TO
INTRODUCE A MARGINAL RISK THERE. BY LATER IN THE WEEK THE COLD
FRONT ASSOCIATED WITH THIS LOW PRESSURE SYSTEM LOOKS TO PROVIDE A
CLEARER FOCUS FOR CONVECTION GENERALLY ACROSS THE MIDWEST TO GREAT
LAKES REGION AND THE NORTHEAST. MEANWHILE OVER THE 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. FLORIDA AND PARTS OF THE GULF COAST MAY SEE SOME
SCATTERED SHOWERS AND THUNDERSTORMS AS WELL.
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 ABOVE 110F DURING PEAK
AFTERNOON HEATING AS HIGH DEWPOINTS COMBINE WITH THE HOT
TEMPERATURES, ESPECIALLY ON TUESDAY BEFORE SOME MINOR MODERATING
OF THE TEMPERATURES. A FEW DAILY RECORD HIGHS WILL BE POSSIBLE
MAINLY OVER AND NEAR THE SOUTHERN HIGH PLAINS INTO MIDWEEK, WITH
SOME DAILY RECORD WARM LOWS ALSO POSSIBLE OVER SOME OF THE ABOVE
REGIONS. 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 (BY 5-15F) 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. THE HEAT MAY BE RELATIVELY
SHORT-LIVED IN PORTIONS OF THOSE REGIONS THOUGH AS A COLD FRONT
LOOKS TO PUSH SOUTH THROUGH THOSE AREAS NEXT WEEKEND. 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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