316
FXUS02 KWBC 161800
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
200 PM EDT FRI AUG 16 2024
VALID 12Z MON AUG 19 2024 - 12Z FRI AUG 23 2024
...HAZARDOUS HEAT LIKELY ACROSS THE SOUTHERN PLAINS AND CENTRAL
GULF COAST STATES INTO NEXT WEEK...
..OVERVIEW
A SLOW-MOVING UPPER PATTERN WILL BE IN PLACE NEXT WEEK AS AN UPPER
HIGH CENTERED OVER THE SOUTHERN HIGH PLAINS PROMOTES HAZARDOUS
HEAT OVER THE SOUTHERN PLAINS TO THE CENTRAL GULF COAST. AN UPPER
LOW/TROUGH IS FORECAST TO MEANDER JUST OFF THE WEST COAST, LEADING
TO A COOLER AND WETTER PATTERN FOR THE NORTHWEST. MEANWHILE, AN
UPPER TROUGH WILL TAKE HOLD FROM THE GREAT LAKES AND SOUTHWARD AND
SLOWLY MOVE EAST AND BE PERIODICALLY REINFORCED BY SHORTWAVE
ENERGIES AS NEXT WEEK PROGRESSES. THIS TROUGH AND A SURFACE LOW
PRESSURE/FRONTAL SYSTEM WILL PROMOTE SCATTERED TO WIDESPREAD
THUNDERSTORMS WITH THE POTENTIAL FOR HEAVY RAIN ACROSS THE
NORTHEAST U.S. INTO EARLY NEXT WEEK. HURRICANE ERNESTO IS FORECAST
TO TRACK NORTH OVER THE WESTERN ATLANTIC AND REMAIN OFFSHORE OF THE
U.S. EAST COAST.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODELS AND ENSEMBLES CONTINUE TO SHOW ABOVE NORMAL PREDICTABILITY
AND AGREEMENT IN THE LARGE SCALE UPPER PATTERN NEXT WEEK, BUT
PLENTY OF UNCERTAINTY IN THE DETAILS. SOME QUESTION ON SMALLER
SCALE MESOSCALE SYSTEMS ROTATING AROUND THE NORTHERN SIDE OF THE
RIDGE THROUGH THE NORTHERN PLAINS/MIDWEST WHICH LIKELY TAKE UNTIL
SHORT RANGE TO FULLY RESOLVE ANYWAYS. AGREEMENT HAS IMPROVED WITH
RESPECT TO AN UPPER SHORTWAVE ACROSS SOUTH-CENTRAL CANADA, BUT SOME
UNCERTAINTY ON HOW MUCH, IF AT ALL, THIS SUPPRESSES RIDGING ACROSS
THE NORTH- CENTRAL U.S.. OUT WEST, AN ADDITIONAL UPPER LOW LOOKS
TO DROP FROM THE GULF OF ALASKA DISPLACING THE UPPER LOW OFF THE
NORTHWEST COAST THAT WILL BE IN PLACE EARLY NEXT WEEK, BUT PLENTY
OF UNCERTAINTY ON THE TIMING AND STRENGTH OF THIS EVOLUTION. THE
WPC PROGS FOR TODAY USED AN EQUAL BLEND OF THE DETERMINISTIC
GUIDANCE THE FIRST HALF OF THE PERIOD, INCREASING THE ENSEMBLE
MEANS BY THE LATTER HALF IN AN ATTEMPT TO SMOOTH OUT SOME OF THE
SMALLER SCALE INCONSISTENCIES. OVERALL, MAINTAINED GOOD CONTINUITY
WITH THE PREVIOUS WPC FORECAST.
..WEATHER/HAZARDS HIGHLIGHTS
A GREAT LAKES/EASTERN U.S. UPPER TROUGH AND SURFACE LOW
PRESSURE/FRONTAL SYSTEM WILL PROVIDE FORCING FOR RAIN AND
THUNDERSTORMS ACROSS THE EASTERN U.S. INTO EARLY NEXT WEEK.
INSTABILITY AND ABOVE NORMAL MOISTURE WILL BE IN PLACE AND COULD
LEAD TO LOCALLY HEAVY RAIN. A WPC MARGINAL RISK OF EXCESSIVE
RAINFALL REMAINS OVER THE NORTHEAST DAY 4/MONDAY. WHILE WIDESPREAD
HEAVY RAIN IS NOT PARTICULARLY LIKELY, EMBEDDED HEAVY TOTALS COULD
CAUSE FLOODING CONCERNS ESPECIALLY CONSIDERING WET ANTECEDENT
CONDITIONS IN MUCH OF THE REGION AND THE MULTIPLE DAYS IN A ROW OF
RAIN. RAIN IS EXPECTED TO TAPER OFF IN THE NORTHEAST TUESDAY-
WEDNESDAY AS SURFACE HIGH PRESSURE BUILDS IN BEHIND THE COLD
FRONT(S) AND IN THE WAKE OF ERNESTO LIFTING WELL OFFSHORE. HOWEVER,
TRAILING FRONTS SLATED TO STALL FARTHER SOUTH ACROSS FLORIDA WILL
MAINTAIN SEVERAL DAYS OF THUNDERSTORM CHANCES THERE. FLOODING
ISSUES ARE A POSSIBILITY IF HEAVY RAIN FALLS IN URBAN AREAS. THIS
FRONT MOVES SLOWLY AS IT BENDS BACK TO THE WEST ATOP THE CENTRAL
GULF COAST AND BACK NORTH INTO THE PLAINS. SCATTERED STORMS ARE
POSSIBLE NEAR THE FRONT AS IMPULSES "RIDE THE RIDGE" ALOFT, BUT
WITH GENERALLY LOW CONFIDENCE IN PLACEMENT STILL AT THIS TIME.
MONSOONAL CONVECTION WILL AFFECT THE FOUR CORNERS STATES NORTHWARD
INTO EARLY NEXT WEEK WITH MOIST SOUTHERLY FLOW WEST OF THE UPPER
RIDGE AXIS. MARGINAL RISKS ARE SLOWLY SPREAD MONDAY-TUESDAY OVER
PORTIONS OF ARIZONA, UTAH, SOUTHEAST CALIFORNIA, SOUTHERN NEVADA
AND COLORADO. STORMS WITH EMBEDDED HEAVY RAIN COULD CAUSE ISOLATED
FLOODING, PARTICULARLY IN VULNERABLE AREAS LIKE THE SLOT CANYONS OF
SOUTHERN UTAH. MONSOONAL CONVECTION LOOKS TO GRADUALLY REDUCE IN
SCOPE INTO MIDWEEK. SOME RAIN IS ALSO FORECAST TO MOVE ACROSS THE
NORTHERN TIER AS THE WEEK PROGRESSES. SOME CONVECTION MAY BREAK OUT
ALONG A SLOW MOVING WARM FRONT ACROSS THE NORTHEAST PLAINS EARLY
WEEK AS WELL, BUT GIVEN DRY ANTECEDENT CONDITIONS, AND A LOT OF
UNCERTAINTY ON PLACEMENT AND AMOUNTS, OPTED TO HOLD OFF ON A
MARGINAL RISK IN THE ERO AT THIS TIME ACROSS THE REGION.
UPPER RIDGING OVER THE SOUTH-CENTRAL U.S. WILL MAINTAIN ABOVE
NORMAL TEMPERATURES BY 5-15 DEGREES FROM THE HIGH PLAINS EAST INTO
THE CENTRAL GULF COAST. HIGHS WELL INTO THE 100S IN MUCH OF TEXAS
COULD SET DAILY RECORDS. FROM EASTERN TEXAS INTO THE LOWER
MISSISSIPPI VALLEY, HOT TEMPERATURES AND HIGH DEWPOINTS SHOULD
PRODUCE HEAT INDICES LIKELY ABOVE 110 DEGREES. LOW TEMPERATURES IN
THE UPPER 70S TO LOW 80S WILL EXACERBATE HEAT STRESS AND COULD SET
RECORDS FOR WARM MINIMUM TEMPERATURES. EXPERIMENTAL HEATRISK
CONTINUES TO SHOW MAJOR TO EXTREME IMPACTS FROM THIS LENGTHY HEAT
WAVE. NORTH OF THIS REGION, MOST AREAS SHOULD SEE NEAR TO SLIGHTLY
BELOW NORMAL HIGHS, WITH SOME BELOW NORMAL LOWS AS WELL FOR THE
OHIO VALLEY, WHILE THE INTERMOUNTAIN WEST CAN EXPECT ABOVE AVERAGE
LOWS. THE PACIFIC NORTHWEST INTO NORTHERN CALIFORNIA SHOULD SEE
TEMPERATURES A BIT BELOW NORMAL IN RESPONSE TO THE LOW ALOFT.
SANTORELLI/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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