085
FXUS02 KWBC 122221
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
620 PM EDT WED JUL 12 2023
VALID 12Z SAT JUL 15 2023 - 12Z WED JUL 19 2023
...HAZARDOUS TO EXTREME HEAT IS FORECAST FOR THE ENTIRE SOUTHERN
TIER OF THE U.S. THROUGH EARLY NEXT WEEK AND BEYOND...
...HEAVY RAIN LIKELY TO FOCUS ACROSS THE CENTRAL PLAINS AS WELL AS
PORTIONS OF THE NORTHEAST...
..OVERVIEW
THE PREVAILING UPPER LEVEL PATTERN OVER THE CONUS IN THE
MEDIUM-RANGE WILL CONTINUE TO FEATURE PERIODIC INTRUSIONS OF COOL
AIR FROM CENTRAL CANADA INTO THE NORTHERN TIER STATES. THIS
PATTERN WILL TEND TO MAINTAIN BROAD TROUGHING ACROSS THE EASTERN
TWO-THIRDS OF THE COUNTRY WITH THE MAIN TROUGH AXIS EDGES TOWARD
THE EAST COAST WITH TIME AS AN ANOMALOUSLY STRONG UPPER RIDGE
BUILDS EASTWARD ACROSS 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 HEAVY RAIN IS POSSIBLE
LATER IN THE WEEKEND OVER NEW ENGLAND. MEANWHILE, THE NEXT UPPER
TROUGH IS FORECAST TO MOVE THROUGH THE PACIFIC NORTHWEST AND
NORTHERN ROCKIES EARLY NEXT WEEK, PERHAPS SLIGHTLY WEAKEN THE
UPPER RIDGE THAT IS FORECAST TO BRING A DANGEROUS HEAT WAVE FOR
THE ENTIRE SOUTHERN TIER OF THE U.S. ESPECIALLY THE
SOUTHWEST/CALIFORNIA THROUGH THE WEEKEND AND EVEN WELL INTO NEXT
WEEK.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
OVERALL, THE LATEST GUIDANCE REMAINS IN EXCELLENT AGREEMENT ON THE
OVERALL SYNOPTIC PATTERN THROUGH THE PERIOD, THOUGH CONTINUES TO
OFFER TYPICAL DIFFERENCES IN THE SMALLER SCALE 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. MODEL AGREEMENT CONTINUES TO IMPROVE
REGARDING THE TIMING OF THE UPPER TROUGH/LOW MOVING ONSHORE INTO
BRITISH COLUMBIA AND THE PACIFIC NORTHWEST EARLY NEXT WEEK.
OTHERWISE, EVEN LATE IN THE PERIOD, THERE IS VERY GOOD AGREEMENT
ON AN ANOMALOUSLY STRONG UPPER HIGH BUILDING AND HOLDING STRONG
OVER THE SOUTHWEST U.S. THROUGH TUESDAY, AND THEN LIKELY SHIFTING
BACK TO THE EAST NEXT WEDNESDAY. THE WPC FORECASTS WERE BASED ON A
COMPOSITE BLEND OF THE DETERMINISTIC AND ENSEMBLE SOLUTIONS FROM
THE 06Z GFS/GEFS, 00Z ECMWF/EC MEAN, AND 00Z CMC/CMC MEAN THROUGH
DAY 5, WITH A HIGHER PERCENTAGE FROM THE ENSEMBLE MEANS FOR DAYS 6
AND 7. THIS MAINTAINS GOOD CONTINUITY WITH THE PREVIOUS WPC
FORECAST AS WELL.
..WEATHER/HAZARDS HIGHLIGHTS
SHOWERS AND THUNDERSTORMS SHOULD INITIALLY FOCUS SATURDAY FROM THE
SOUTH-CENTRAL PLAINS INTO THE MID-SOUTH, OHIO VALLEY, AND THE
MID-ATLANTIC/NORTHEAST. GIVEN AVAILABLE MOISTURE AND INSTABILITY,
AT LEAST LOCALLY HEAVY RAINFALL SEEMS A GOOD BET FOR MANY
LOCATIONS. THE BEST OVERLAP IN THE CURRENT AVAILABLE GUIDANCE
CONTINUES TO POINT TO THE TEXAS PANHANDLE INTO WESTERN OKLAHOMA
WHERE A SMALL SLIGHT RISK WAS MAINTAINED ON THE DAY 4 ERO GIVEN
VERY WET ANTECEDENT CONDITIONS. THE RAINFALL AXIS SHOULD SHIFT
SOUTH AND EAST BY DAY 5/SUNDAY WHERE A MARGINAL RISK INCLUDES THE
CENTRAL AND EASTERN GULF COAST STATES FOR LOCALLY HEAVY RAIN
ASSOCIATED WITH SCATTERED THUNDERSTORMS. MEANWHILE, THE NORTHEAST
IS LOOKING AT YET ANOTHER ROUND OF HEAVY RAIN AS ANOMALOUS
PRECIPITABLE WATER VALUES ASSOCIATED WITH A LOW PRESSURE WAVE
STREAM NORTHWARD AHEAD OF A COLD FRONT. A SLIGHT RISK WAS
MAINTAINED ON DAY 5 FOR EASTERN PORTIONS OF NEW ENGLAND GIVEN HOW
SUSCEPTIBLE PARTS OF THIS REGION IS RIGHT NOW DUE TO RECENT VERY
HEAVY RAINFALL. SCATTERED SHOWERS AND EMBEDDED THUNDERSTORMS
APPEAR TO LINGER NEAR THE EAST COAST THROUGH AT LEAST TUESDAY AS
THE NEXT PUSH OF COOL AIR FROM SOUTHERN CANADA MOVES INTO THE
GREAT LAKES. ROUNDS OF ENHANCED RAINFALL APPEAR POSSIBLE AHEAD OF
THE COLD FRONT, BUT THIS TIME FARTHER NORTH FROM THE CENTRAL HIGH
PLAINS TOWARD THE MIDWEST AND INTO THE OHIO/TENNESSEE VALLEY FROM
EARLY TO MIDDLE OF NEXT WEEK.
HAZARDOUS TO POTENTIALLY DANGEROUS HEAT WILL IMPACT MUCH OF THE
SOUTHWEST/CALIFORNIA EASTWARD INTO THE SOUTHERN STATES (AND LIKELY
BEYOND PER LATEST CPC FORECASTS). NUMEROUS DAILY HIGH
TEMPERATURES, INCLUDING THE ALL-TIME HIGH TEMPERATURE IN LAS
VEGAS, NV, AND WARM OVERNIGHT LOW RECORDS ARE THREATENED THIS
WEEKEND ACROSS THIS REGION. 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. MUCH ABOVE
NORMAL TEMPERATURES ACROSS THE NORTHWEST THIS WEEKEND SHOULD
MODERATE AND SHIFT EAST AS HEIGHTS LOWER EARLY NEXT WEEK OVER THIS
REGION. HEAT MAY EXPAND NORTHWARD INTO PARTS OF THE CENTRAL PLAINS
AND MISSISSIPPI VALLEY AND POINTS EAST EARLY NEXT WEEK.
KONG/SANTORELLI
HAZARDS:
- HEAVY RAIN ACROSS PORTIONS OF THE CENTRAL PLAINS, THE LOWER
MISSISSIPPI VALLEY, AND THE SOUTHERN PLAINS, SAT, JUL 15.
- HEAVY RAIN ACROSS PORTIONS OF THE MID-ATLANTIC AND THE
NORTHEAST, SUN, JUL 16.
- FLOODING POSSIBLE ACROSS PORTIONS OF THE NORTHERN PLAINS.
- FLOODING OCCURRING OR IMMINENT ACROSS PORTIONS OF THE NORTHEAST.
- FLOODING LIKELY ACROSS PORTIONS OF THE NORTHEAST.
- HAZARDOUS HEAT ACROSS PORTIONS OF THE CENTRAL PLAINS, THE
CENTRAL ROCKIES, THE LOWER MISSISSIPPI VALLEY, THE CENTRAL GREAT
BASIN, THE TENNESSEE VALLEY, THE SOUTHERN ROCKIES, THE MIDDLE
MISSISSIPPI VALLEY, THE MID-ATLANTIC, CALIFORNIA, THE SOUTHEAST,
THE SOUTHERN APPALACHIANS, THE SOUTHERN PLAINS, THE OHIO VALLEY,
AND THE SOUTHWEST, SAT-WED, JUL 15-JUL 19.
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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