615
FXUS02 KWBC 110700
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 AM EDT SUN AUG 11 2024
VALID 12Z WED AUG 14 2024 - 12Z SUN AUG 18 2024
...EXCESSIVE HEAT LIKELY ACROSS THE SOUTHERN PLAINS AND CENTRAL
GULF COAST/SOUTHEAST THROUGH THE WEEK INTO NEXT WEEKEND...
..OVERVIEW
UPPER RIDGING WILL BE IN PLACE ACROSS THE SOUTH-CENTRAL U.S.
THROUGH MUCH OF THE WEEK, LEADING TO HIGH HEAT INDICES THAT COULD
BE HAZARDOUS ACROSS THE SOUTHERN PLAINS TO GULF COAST/SOUTHEAST. AN
UPPER LOW IS FORECAST TO DIG INTO THE EASTERN PACIFIC AND WEST
COAST LATE WEEK INTO THE WEEKEND, LEADING TO A COOLER AND WETTER
PATTERN FOR THE NORTHWEST WHILE THE SOUTHERN STREAM RIDGE MAY
RETROGRADE A BIT IN RESPONSE. SHORTWAVE ENERGY AND A SURFACE LOW
PRESSURE SYSTEM WILL PROMOTE SCATTERED TO WIDESPREAD THUNDERSTORMS
ACROSS THE CENTRAL U.S., SHIFTING INTO THE EAST LATE WEEK.
MEANWHILE, A TROPICAL SYSTEM THAT IS LIKELY TO DEVELOP PER NHC WILL
CONTINUE TO BE MONITORED, BUT FORTUNATELY MOST MODELS AND LATEST
NHC GUIDANCE CONTINUE TO TAKE THE LOW SYSTEM EAST OF THE LOWER 48
INTO THE ATLANTIC.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODEL GUIDANCE REMAINS GENERALLY AGREEABLE REGARDING THE LARGE
SCALE PATTERN, INCLUDING THE SOUTHERN STREAM RIDGE LIKELY
REBUILDING FARTHER WEST WITH TIME AS AN UPPER LOW WITH OKAY
PLACEMENT/TIMING AGREEMENT COMES INTO THE EASTERN PACIFIC AND
NORTHWEST. BUT A POSSIBLE SHORTWAVE MOVING THROUGH THE NORTHERN
TIER AND ITS ASSOCIATED SURFACE LOW/FRONTAL SYSTEM IS THE TRICKIEST
MODEL DIAGNOSTICS FEATURE. THE 12Z ECMWF/CMC HAS THE SHORTWAVE
TRACKING ACROSS THE NORTH-CENTRAL U.S. THURSDAY-FRIDAY AND INTO THE
GREAT LAKES BY SATURDAY, SIMILAR TO EARLIER MODEL CONSENSUS.
AI/MACHINE LEARNING MODELS ALSO SHOW A SHORTWAVE WITH REASONABLY
SIMILAR TIMING/PLACEMENT. HOWEVER, THE 12/18Z GFS RUNS PRETTY MUCH
DROPPED THIS SHORTWAVE FEATURE AFTER SHOWING IT A DAY AGO,
MAINTAINING RIDGING. LEANED AWAY FROM THESE GFS RUNS TO BE MORE
CONSISTENT WITH PREVIOUS FORECASTS AND THE NON-NCEP GUIDANCE.
FORTUNATELY THE NEWER 00Z GFS RUN HAS BROUGHT THE SHORTWAVE BACK.
THERE IS SOME UNCERTAINTY WITH HOW THIS SHORTWAVE INTERACTS WITH
TROUGHING THAT IS ALONG THE EAST COAST AT THE START OF THE PERIOD.
THE PATTERN ACROSS THE EAST WILL AFFECT THE TRACK OF THE TROPICAL
SYSTEM THAT IS LIKELY TO FORM. THE BULK OF THE MODEL AND ENSEMBLE
GUIDANCE CONTINUES TO SHOW THE SYSTEM TURNING NORTHEASTWARD ENOUGH
TO TAKE IT OUT TO SEA RATHER THAN INTO THE U.S., OTHER THAN THE
ROGUE 12/18Z GFS RUNS THAT WERE NOT PREFERRED.
THUS THE WPC FORECAST BLEND LEANED HEAVILY ON THE 12Z ECMWF AND
CMC AND EC ENSEMBLE MEAN, WITH SOME INCORPORATION OF THE 12Z GEFS
MEAN, DUE TO AFOREMENTIONED ISSUES WITH THE 12/18Z DETERMINISTIC
GFS RUNS.
..WEATHER/HAZARDS HIGHLIGHTS
INTO MIDWEEK, MONSOONAL MOISTURE WILL FLOW INTO THE ROCKIES FOR
SOME SCATTERED STORMS. OVERALL COVERAGE AND RAINFALL AMOUNTS SHOULD
BE LOWER THAN IN THE SHORT RANGE PERIOD, BUT LIKELY STILL
SUFFICIENT FOR A MARGINAL RISK FROM EASTERN ARIZONA INTO NEW MEXICO
AND COLORADO FOR THE DAY 4/WEDNESDAY ERO. A RELATIVE BREAK IN
MONSOONAL CONVECTION IS POSSIBLE ON THURSDAY, BUT BY FRIDAY AND
ESPECIALLY SATURDAY SOME RENEWED MOISTURE COULD COME INTO THE FOUR
CORNERS STATES, FOCUSING WESTWARD A BIT COMPARED TO EARLIER IN THE
WEEK AS THE UPPER RIDGE RETROGRADES.
MEANWHILE, PACIFIC AND GULF MOISTURE WILL LIKELY COMBINE ACROSS
THE CENTRAL U.S. WHILE A SHORTWAVE PROVIDES SUPPORT FOR
THUNDERSTORMS LIKELY IN THE FORM OF MULTIPLE MESOSCALE CONVECTIVE
SYSTEMS TRACKING WEST-EAST OR NORTHWEST-SOUTHEAST ON WEDNESDAY AND
THURSDAY. BROAD MARGINAL RISKS REMAIN IN PLACE IN THE DAY 4-5 EROS
FOR CENTRAL PARTS OF THE PLAINS INTO THE MID-MISSISSIPPI VALLEY AND
EAST INTO PARTS OF THE OHIO VALLEY BY THURSDAY FOR FLOODING
THREATS WITH THESE STORMS. AFOREMENTIONED MODEL DIFFERENCES WITH
THE SUPPORTING SHORTWAVE LESSENED CONFIDENCE IN EXACT LOCATION OF
HEAVY RAINS, BUT GIVEN THE POTENTIAL FOR HIGH RAIN RATES IN AN
UNSTABLE ENVIRONMENT, SLIGHT RISKS IN FUTURE CYCLES ARE CERTAINLY A
POSSIBILITY, ESPECIALLY ACROSS THE MIDDLE MISSISSIPPI VALLEY--
THOUGH RECENT MODELS ARE FOCUSING THE HEAVIEST RAIN A BIT NORTH OF
A DAY AGO. RAIN IS ALSO POSSIBLE FARTHER NORTH INTO THE NORTHERN
PLAINS AND UPPER MIDWEST, WHERE A MARGINAL RISK EXTENDS FOR DAY
4/WEDNESDAY ACROSS AREAS THAT STILL HAVE WET ANTECEDENT CONDITIONS
REMAIN FROM HEAVY RAINS EARLIER THIS SUMMER. THUNDERSTORM CHANCES
SHOULD SHIFT INTO THE EAST- CENTRAL U.S. ON FRIDAY AND INTO THE
EASTERN SEABOARD OVER THE WEEKEND.
SCATTERED STORMS ARE POSSIBLE IN THE SOUTHEAST AS A FRONT WORKS
ITS WAY THROUGH FLORIDA. COVERAGE OF STORMS MAY BE MAXIMIZED ON
THURSDAY IN THE FLORIDA PENINSULA WHERE ABOVE NORMAL MOISTURE
POOLS, BUT HELD OFF FROM ANY RISK AREA IN THE ERO SINCE MOST OF
FLORIDA IS NOT SENSITIVE TO FLOODING UNLESS THERE ARE EXCEPTIONALLY
HEAVY RAIN RATES/TOTALS, AND THERE IS NOT CONFIDENCE OF THAT
OCCURRING. LIGHT TO MODEST SHOWERS ARE FORECAST IN THE NORTHEAST
WEDNESDAY-THURSDAY AHEAD OF MORE WIDESPREAD RAIN APPROACHING INTO
THE WEEKEND. AND IN THE NORTHWEST, COVERAGE AND AMOUNTS OF RAIN
WILL INCREASE LATE WEEK INTO THE WEEKEND AS THE LOW/TROUGH ALOFT
PROVIDES SUPPORT.
THE UPPER RIDGE AXIS OVER THE SOUTH-CENTRAL U.S. WILL MAINTAIN
TEMPERATURES UP TO 10F ABOVE (ALREADY HOT) NORMAL VALUES ACROSS THE
SOUTHERN PLAINS INTO THE CENTRAL GULF COAST. COMBINED WITH THE
HIGH DEWPOINTS IN MOST AREAS, HEAT INDICES ABOVE 110F ARE POSSIBLE,
AND EXPERIMENTAL HEATRISK SHOWS MAJOR TO EXTREME IMPACTS. LOW
TEMPERATURES IN THE UPPER 70S TO NEAR 80 WILL EXACERBATE HEAT
STRESS AND COULD SET RECORDS FOR WARM MINIMUM TEMPERATURES. NORTH
OF THIS REGION THOUGH, MOST AREAS SHOULD SEE NEAR TO SLIGHTLY BELOW
NORMAL HIGHS FROM THE WESTERN TO NORTH-CENTRAL TO EASTERN U.S.,
WITH A COOLING TREND IN THE NORTHWEST LATE WEEK-WEEKEND IN RESPONSE
TO THE LOW ALOFT. LOW TEMPERATURES SHOULD BE NEAR TO A BIT ABOVE
AVERAGE IN MOST AREAS.
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 (QPF), EXCESSIVE RAINFALL
OUTLOOK (ERO), WINTER WEATHER OUTLOOK (WWO) PROBABILITIES, HEAT
INDICES, AND KEY MESSAGES CAN BE ACCESSED FROM:
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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