810
FXUS02 KWBC 111848
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
248 PM 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 INTO THE SOUTHEAST THROUGH THE WEEK TO NEXT WEEKEND...
..MID-MISSISSIPPI VALLEY HEAVY RAIN/RUNOFF THREAT BY MIDWEEK
..OVERVIEW
A SUMMERTIME UPPER RIDGING WILL BE IN PLACE ACROSS THE SOUTH-
CENTRAL U.S. FOR MUCH OF THE COMING WEEK, LEADING TO HIGH HEAT
INDICES THAT COULD BE HAZARDOUS ACROSS THE SOUTHERN PLAINS TO GULF
COAST INTO THE 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 GROWING SIGNAL IN SUPPORT OF ORGANIZED SURFACE LOW PRESSURE
SYSTEM CYCLOGENESIS 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 WESTERN ATLANTIC.
..GUIDANCE/PREDICTABILITY ASSESSMENT
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. GUIDANCE FORECAST SPREAD AND SYSTEM
UNCERTAINTY IN THIS PATTERN RECENTLY HAS TENDED TO RAMP UP
GENERALLY AFTER ONLY 4 DAYS FROM CURRENT. ACCORDINGLY, FELT
COMFORTABLE USING A GFS/ECMWF/UKMET/CANADIAN MODEL BLEND FOR MAX
DETAILS WEDNESDAY INTO EARLY THURSDAY. BEYOND THEN INTO LONGER TIME
FRAMES, PREFER TO GRAVIATE TO A BLEND WITH AN ENSEMBLE MEAN FOCUS
SUPPLIMENTED BY MODEL GUIDANCE ON THE LESS PROGRESSIVE/AMPLIFIED
SIDE OF THE FULL ENVELOPE OF SOLUTIONS FOR MID-LATITUDE FLOW. IN
THIS PERIOD THAT PLACED MORE EMPHASIS ON THE 00 UTC CANADIAN
ENSEMBLE MEAN AND TO A LESSER EXTENT THE 00 UTC CANADIAN MODEL AND
THE 06 UTC GFS MODEL. THIS SEEMS TO OVERALL BETTER ALIGN WITH
LATEST 12 UTC GUIDANCE TRENDS. HOWEVER IN CONTRAST, 00/12 UTC
ECMWF SYSTEM AND ASSOCIATED QPF PROGRESSION ACROSS THE EAST-CENTRAL
TO EASTERN U.S. SEEMS TOO FAST CONSIDERING AMPLE UPSTREAM
AMPLITUDE MORE LOCKED IN TO DEVELOP ACROSS THE WEST COAST.
..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 AN ENERGETIC SHORTWAVE PROVIDES SUPPORT FOR
THUNDERSTORMS LIKELY IN THE FORM OF MULTIPLE MESOSCALE CONVECTIVE
SYSTEMS TRACKING WEST-EAST OR NORTHWEST-SOUTHEAST ON WEDNESDAY AND
THURSDAY. A SLIGHT RISK DAY 4/WEDNESDAY ERO HAS BEEN INTRODUCED FOR
THE MID-MISSISSIPPI VALLEY GIVEN A STEADY/GROWING SIGNAL WITH WARM
FRONTAL AND UPPER SYSTEM APPROACH IN A FORECAST TIME PERIOD PRIOR
TO MOST GUIDANCE FORECAST SPREAD RECENTLY. BROAD MARGINAL RISKS
ALSO 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 FOR DAY
5/THURSDAY, BUT GIVEN THE POTENTIAL FOR HIGH RAIN RATES IN AN
UNSTABLE ENVIRONMENT, A SLIGHT RISK IN FUTURE CYCLES ARE CERTAINLY
A POSSIBILITY. RAIN IS ALSO POSSIBLE FARTHER NORTH INTO THE
NORTHERN PLAINS AND PORTIONS OF THE 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 EAST 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/SCHICHTEL
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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