431
FXUS02 KWBC 110701
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
301 AM EDT TUE JUL 11 2023
VALID 12Z FRI JUL 14 2023 - 12Z TUE JUL 18 2023
...HAZARDOUS TO EXTREME HEAT WILL BUILD ACROSS 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 THE NORTHEAST...
..OVERVIEW
THE UPPER LEVEL PATTERN OVER THE CONUS LATE THIS WEEK AND INTO THE
WEEKEND MAY TREND SLIGHTLY MORE AMPLIFIED WITH TIME AS TROUGHING
IS MAINTAINED ACROSS THE EASTERN U.S., AND UPPER LEVEL RIDGING
BUILDS INTO THE WEST. THE EASTERN TROUGH WILL BE ANCHORED BY A
DEEP UPPER LOW MEANDERING NEAR HUDSON BAY WITH MULTIPLE WAVES OF
ENERGY ROTATING THROUGH THE BASE DRIVING ROUNDS OF SHOWERS AND
STORMS ACROSS THE NATIONS MIDSECTION AND INTO THE NORTHEAST. A
POTENTIALLY DANGEROUS HEAT WAVE WILL BE TAMPING UP AS THE PERIOD
BEGINS FRIDAY ACROSS MUCH OF THE SOUTHERN TIER OF THE U.S. AND
BACK INTO THE SOUTHWEST LASTING THROUGH THE WEEKEND AND EVEN WELL
INTO NEXT WEEK, AS PER THE LATEST INFORMATION FROM THE CLIMATE
PREDICTION CENTER. THERE IS INCREASING CONFIDENCE THIS COULD BE A
LONG DURATION HEAT WAVE FOR MUCH OF THE SOUTH AND SOUTHWEST.
..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 MOVES
INTO BRITISH COLUMBIA EARLY NEXT WEEK. THE 12Z (JULY 10) CMC WAS
AN OUTLIER BRINGING THAT CLOSED LOW FARTHER SOUTH INTO THE PACIFIC
NORTHWEST AND WAS EXCLUDED FROM THE LATE PERIOD BLEND FOR TONIGHT.
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 BLEND FOR THE WPC FORECAST TONIGHT USED THE
DETERMINISTIC MODELS THROUGH DAY 5, WITH INCREASING CONTRIBUTIONS
FROM THE ENSEMBLE MEANS LATE PERIOD WITH THE ECMWF AND GFS.
..WEATHER/HAZARDS HIGHLIGHTS
A FRONTAL BOUNDARY DROPPING SLOWLY SOUTHWARD THROUGH THE MIDWEST
THIS WEEKEND WILL BE THE FOCUS FOR 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, BUT EXACT LOCATION REMAINS RATHER UNCERTAIN STILL.
THE BEST OVERLAP IN THE CURRENT AVAILABLE GUIDANCE POINTS TO THE
SOUTHERN MISSOURI TO KENTUCKY REGION, WHERE A SLIGHT RISK WAS
PLACED ON THE DAYS 4 EXCESSIVE RAINFALL OUTLOOK. THE NORTHERN
PORTION OF THIS FRONT WILL MOVE INTO THE NORTHEAST WITH ROUNDS OF
ADDITIONAL RAINFALL, AND GIVEN HOW SUSCEPTIBLE THIS REGION IS, A
SLIGHT RISK WAS MAINTAINED ON THE DAY 4 ERO FOR PORTIONS OF NEW
ENGLAND. BY NEXT WEEKEND, RAINFALL SHOULD DRIFT SOUTH WITH THE
FRONT MORE INTO PARTS OF THE SOUTH-CENTRAL PLAINS TO THE MID-SOUTH
AND THE NORTHEAST. A BROAD MARGINAL RISK WAS DRAWN ON THE DAY 5
ERO ALONG THE ENTIRE BOUNDARY. IT IS PLAUSIBLE EMBEDDED SLIGHT
RISKS WILL BE NEEDED CLOSER IN TIME, BUT THERE IS STILL A LOT OF
UNCERTAINTY IN EXACTLY WHERE TO PRECLUDE ANYTHING AT THIS TIME.
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.
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
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page