430
FXUS02 KWBC 111905
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 PM EDT TUE JUL 11 2023
VALID 12Z FRI JUL 14 2023 - 12Z TUE JUL 18 2023
...HAZARDOUS TO EXTREME HEAT IS FORECAST FOR MUCH OF THE SOUTHERN
U.S. AND INTO THE SOUTHWEST THROUGH EARLY NEXT WEEK AND BEYOND...
...HEAVY RAIN CONCERNS LIKELY TO FOCUS FROM THE CENTRAL PLAINS
EASTWARD TO PORTIONS THE NORTHEAST...
..OVERVIEW
THE PREVAILING UPPER LEVEL PATTERN OVER THE CONUS IN THE
MEDIUM-RANGE WILL FEATURE PERIODIC INTRUSIONS OF COOL AIR FROM
CENTRAL CANADA INTO THE NORTHERN TIER STATES. THIS PATTERN WILL
TEND TO ANCHOR AN UPPER-LEVEL TROUGH NEAR THE EASTERN SEABOARD AS
A WARM UPPER RIDGE CENTERED OVER THE SOUTHWEST IS FORECAST TO
BUILD FURTHER INLAND TOWARD THE FOUR CORNERS REGION. ROUNDS OF
SHOWERS AND STORMS BETWEEN THESE SYNOPTIC SYSTEMS WILL LIKELY
CONTINUE ACROSS THE MIDSECTION OF THE COUNTRY, WITH UNSETTLED
WEATHER MOVING ONCE AGAIN INTO THE NORTHEAST WHERE A COUPLE ROUNDS
OF ENHANCED RAINFALL ARE POSSIBLE. MEANWHILE, A POTENTIALLY
DANGEROUS HEAT WAVE IS FORECAST TO OVERSPREAD THE ENTIRE SOUTHERN
TIER OF THE U.S. AND ESPECIALLY THE SOUTHWEST THROUGH THE WEEKEND
AND EVEN WELL INTO NEXT WEEK.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
THE LATEST GUIDANCE REMAINS IN REASONABLE AGREEMENT REGARDING THE
OVERALL SYNOPTIC PATTERN ACROSS THE CONUS DURING THE MEDIUM RANGE,
THOUGH CONTINUES TO OFFER TYPICAL DIFFERENCES IN THE DETAILS. SOME
UNCERTAINTIES SURROUNDING IMPULSES ROUNDING THROUGH THE MIDWEST,
WHICH HAVE SIGNIFICANT IMPLICATIONS FOR SURFACE FEATURES AND
SENSIBLE WEATHER, INCLUDING POTENTIAL HEAVY RAINFALL/FLOODING,
ESPECIALLY ACROSS PARTS OF THE MID-MISSISSIPPI VALLEY AND MIDWEST,
AND INTO THE NORTHEAST. UPPER RIDGING OVER THE NORTHWEST EARLY IN
THE PERIOD SHOULD SHIFT EAST WITH TIME AS A CLOSED UPPER LOW OVER
THE NORTHEASTERN PACIFIC MOVES INTO BRITISH COLUMBIA EARLY NEXT
WEEK. THE CMC HAS GONE BACK-AND-FORTH BETWEEN A FAST AND A SLOW
SOLUTION WITH THIS CLOSED LOW. THE GFS AND ECMWF ALSO HAD A
SIMILAR TIMING ISSUE BUT NOT AS SEVERE AS THE CMC. THE ENSEMBLE
MEANS ARE IN MUCH BETTER AGREEMENT IN THIS REGARD. OTHERWISE,
EVEN LATE IN THE PERIOD, THERE IS RELATIVELY EXCELLENT AGREEMENT
ON AN ANOMALOUSLY STRONG UPPER HIGH BUILDING AND HOLDING STRONG
OVER THE SOUTHWEST U.S. AND THE UPPER LOW NEAR HUDSON BAY DROPPING
SLOWLY SOUTHWARD AND GRAZING THE UPPER GREAT LAKES NEXT TUESDAY.
THE WPC FORECASTS MEDIUM-RANGE THIS MORNING WERE BASED ON A
COMPOSITE BLEND OF 40% 00Z ECMWF, 40% 06Z GFS, AND 20% FROM THE
00Z CMC THROUGH DAY 5, WITH INCREASING CONTRIBUTIONS FROM THE
ENSEMBLE MEANS LATE PERIOD FROM THE 00Z EC MEAN AND THE 06Z GEFS.
..WEATHER/HAZARDS HIGHLIGHTS
A FRONTAL BOUNDARY DROPPING SLOWLY SOUTHWARD THROUGH THE MIDWEST
THIS WEEKEND WILL BE THE FOCUS FOR MORE DAILY ROUNDS OF SHOWERS
AND STORMS. GIVEN AVAILABLE MOISTURE AND INSTABILITY, HEAVY
RAINFALL SEEMS A GOOD BET FOR PORTIONS OF THE MID-MISSISSIPPI
VALLEY INTO THE MIDWEST. THE BEST OVERLAP IN THE CURRENT AVAILABLE
GUIDANCE POINTS TO THE SOUTHERN MISSOURI TO KENTUCKY REGION, WHERE
A SLIGHT RISK WAS MAINTAINED ON THE DAYS 4 EXCESSIVE RAINFALL
OUTLOOK. THE NORTHERN PORTION OF THIS FRONT WILL MOVE INTO THE
NORTHEAST WITH ROUNDS OF ADDITIONAL RAINFALL. A LOW PRESSURE WAVE
TRACKING UP THE EAST COAST COULD HELP FOCUS AN INITIAL ROUND OF
HEAVY RAIN LATE FRIDAY INTO EARLY SATURDAY ACROSS CENTRAL TO
SOUTHEASTERN NEW ENGLAND. A SLIGHT RISK WAS MAINTAINED ON THE DAY
4 ERO FOR THE REGION GIVEN HOW SENSITIVE TO HEAVY RAIN THIS AREA
ALREADY IS. THERE COULD BE ANOTHER ROUND OF ENHANCED RAINFALL
MOVING INTO NEW ENGLAND LATER IN THE WEEKEND ASSOCIATED WITH
ANOTHER COASTAL LOW PRESSURE WAVE. MORE ROUNDS OF ENHANCED
RAINFALL ARE POSSIBLE FOR NEW ENGLAND INTO EARLY NEXT WEEK AS THE
UPPER TROUGH IS FORECAST TO AMPLIFY. MEANWHILE, NEAR AND ALONG
THE TRAILING PORTION OF THE FRONT, RAINFALL SHOULD DRIFT FARTHER
SOUTH INTO PARTS OF THE SOUTH-CENTRAL PLAINS TO THE MID-SOUTH AND
THE NORTHEAST. A BROAD MARGINAL RISK WAS MAINTAINED ON THE DAY 5
ERO NEAR AND AHEAD OF THE ENTIRE BOUNDARY, WITH A SLIGHT RISK
BEING INTRODUCED ACROSS OKLAHOMA INTO THE TEXAS PANHANDLE WHERE
MODELS ARE IN GOOD AGREEMENT FOR THE NEXT IMPULSE TO EJECT FROM
THE CENTRAL ROCKIES AND INTERACT WITH THE FRONT. ELSEWHERE,
SHOWERS SHOULD LINGER EARLY NEXT WEEK ACROSS PARTS OF THE GULF
COAST INTO THE SOUTHEAST AND MID-ATLANTIC REGION.
HAZARDOUS HEAT IS EXPECTED TO EXPAND ACROSS THE SOUTHERN TIER
THROUGH AT LEAST THIS COMING WEEKEND (AND LIKELY BEYOND PER LATEST
CPC FORECASTS) AS THE UPPER RIDGE STRENGTHENS OVER THE SOUTHWEST
AND INTO MUCH OF THE SOUTH. MUCH ABOVE NORMAL TEMPERATURES WILL
EXPAND FROM THE SOUTHERN HIGH PLAINS INTO THE SOUTHWEST AND
CALIFORNIA, WITH POTENTIAL FOR NUMEROUS RECORD DAILY DAYTIME HIGHS
AND WARM OVERNIGHT LOWS POSSIBLE. FARTHER EAST, THE MAIN STORY
WILL BE OPPRESSIVE HUMIDITY LEADING TO HEAT INDICES OF 105-115
(LOCALLY HIGHER) FOR A LARGE PORTION THE SOUTH FROM EASTERN TEXAS
INTO THE SOUTHEAST AND FLORIDA. AGAIN, SOME DAILY TEMPERATURE
RECORDS ARE POSSIBLE. SEE KEY MESSAGES ISSUED BY WPC FOR
ADDITIONAL INFORMATION AND GRAPHICS RELATED TO THIS HEAT WAVE.
ELSEWHERE, A COLD FRONT DROPPING SOUTH FROM CANADA SHOULD BRING
TEMPERATURES DOWN TO 5-15F BELOW AVERAGE OVER PARTS OF THE
NORTHERN AND CENTRAL PLAINS THROUGH SUNDAY WITH SOME MODERATION
EARLY NEXT WEEK AS UPPER RIDGING TRIES TO BUILD IN.
KONG/SANTORELLI
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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