535
FXUS02 KWBC 101900
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
200 PM EST SUN NOV 10 2024
VALID 12Z WED NOV 13 2024 - 12Z SUN NOV 17 2024
... ANOTHER ATMOSPHERIC RIVER TO BRING HEAVY RAIN AND MOUNTAIN
SNOW THREATS TO PARTS OF THE NORTHWEST MIDWEEK...
..OVERVIEW
A FAIRLY PROGRESSIVE PATTERN IS FORECAST THROUGH LATER WEEK AND
INTO NEXT WEEKEND. A SOMEWHAT AMPLIFIED TROUGH WILL PUSH FROM THE
CENTRAL TO EASTERN U.S. WEDNESDAY-FRIDAY, WITH INCREASING CHANCES
FOR THIS TROUGH TO TAP INTO TROPICAL GULF MOISTURE AND CAUSE HEAVY
RAINFALL FOR PORTIONS OF THE SOUTHEASTERN QUADRANT OF THE COUNTRY
MIDWEEK, WITH LIGHT TO MODERATE MUCH-NEEDED PRECIPITATION FARTHER
NORTH IN THE MIDWEST TO MID-ATLANTIC/NORTHEAST. UPPER RIDGING ON
EITHER SIDE OF THIS TROUGH WILL PROMOTE PERIODS OF WARMER
TEMPERATURES ACROSS THE EASTERN HALF OF THE NATION THROUGH THE
PERIOD. MEANWHILE OUT WEST, AN ATMOSPHERIC RIVER WILL IMPACT PARTS
OF THE NORTHWEST AROUND MIDWEEK BRINGING HEAVY RAIN AND SNOW
THREATS, WITH ADDITIONAL ROUNDS OF PRECIPITATION LATER IN THE WEEK
WITH TROUGH RELOADING ALONG THE COAST. THIS POSITIVELY TILTED
TROUGH IS FORECAST TO SET UP OVER THE WEST WHILE RIDGING BUILDS
ATOP THE EAST NEXT WEEKEND.
..GUIDANCE/PREDICTABILITY ASSESSMENT
WHILE MODEL GUIDANCE IS REASONABLY AGREEABLE WITH THE OVERALL
PATTERN, EVEN EARLY ON THERE ARE SOME MODEL DIFFERENCES REGARDING
THE TIMING AND AMPLITUDE OF UPPER TROUGHS AND RIDGES THAT HAVE
SENSIBLE WEATHER IMPACTS. FIRST, THE TROUGH WITH ITS AXIS OVER THE
PLAINS TO START THE PERIOD WEDNESDAY CONTINUES TO SHOW BASICALLY
TWO CAMPS: SLOWER AND DEEPER NON-NCEP GUIDANCE (ECMWF, CMC, EC
MEAN, AND AI/ML MODELS, ALONG WITH THE UKMET THAT MAY EVEN BE TOO
SLOW), AND FASTER AND SHALLOWER NCEP GUIDANCE (GFS, GEFS MEAN, AND
THE TAIL END OF THE NAM'S FORECAST). THE SLOWER AND DEEPER TROUGH
LEADS TO MORE MOISTURE INFLOW FROM THE GULF FOR HEAVIER RAINFALL IN
THE SOUTHEASTERN CONUS. WITH THE BULK OF THE GUIDANCE INDICATING A
SLOWER/DEEPER TROUGH, AND CONSIDERING THE GFS'S PROPENSITY TOWARD
FASTER TROUGH PROGRESSION, FAVORED MORE OF AN ECMWF/CMC TYPE OF
SOLUTION WITH THIS TROUGH. FOR THE MOST PART, NEWER 12Z NON-NCEP
MODELS HAVE TRENDED A BIT SHALLOWER/FASTER WITH THE TROUGH THOUGH
(GFS/GEFS ARE STILL FARTHER EAST). SO THERE IS STILL SOME
UNCERTAINTY WITH THE DETAILS BUT PERHAPS MODELS ARE CONVERGING
TOWARD A MIDDLE GROUND SOLUTION.
MODELS SHOW THE GENERAL IDEA OF AN UPPER RIDGE BEHIND THIS TROUGH
RELATIVELY WELL, BUT THERE IS MORE SPREAD WITH THE NEXT TROUGH
COMING INTO THE WEST. DIFFERING DISTRIBUTIONS OF VORTICITY WITHIN
THIS TROUGH LEAD TO MODEL DIFFERENCES WITH POSSIBLE
NORTHERN/SOUTHERN STREAM SEPARATION BY THE WEEKEND, WHICH AFFECTS
THE TROUGH PROGRESSION. THE 00Z ECMWF WAS PARTICULARLY AGGRESSIVE
IN DEPICTING A CLOSED LOW WELL OFFSHORE OF MEXICO IN THE SOUTHERN
STREAM BUT THE 12Z ECMWF HAS BACKED OFF ON THIS.
THE WPC FORECAST FAVORED THE ECMWF WITH LESSER PROPORTIONS OF THE
GFS, CMC, AND ENSEMBLE MEANS EARLY IN THE PERIOD. GRADUALLY
INCREASED THE PROPORTION OF ENSEMBLE MEANS IN THE BLEND TO HALF DAY
6 AND MORE DAY 7 AMID INCREASING SPREAD ESPECIALLY WITH THE SECOND
TROUGH.
..WEATHER/HAZARDS HIGHLIGHTS
A MODEST ATMOSPHERIC RIVER WILL CONTINUE TO IMPACT THE PACIFIC
NORTHWEST INTO NORTHERN CALIFORNIA INTO THE BEGINNING OF THE PERIOD
WEDNESDAY. ABOVE NORMAL MOISTURE AND SOME INSTABILITY ALONG THE
COAST COULD LEAD TO HEAVY RAIN THAT MAY CREATE MINOR FLOODING
CONCERNS ESPECIALLY CONSIDERING THERE IS ANOTHER AR SET TO IMPACT
THE REGION IN THE SHORT RANGE PERIOD. THUS A MARGINAL RISK REMAINS
IN PLACE FOR WESTERN WASHINGTON/OREGON AND INTO NORTHWEST
CALIFORNIA ON THE DAY 4/WEDNESDAY ERO. SNOW MAY BE HEAVY IN THE
MOUNTAINS, PARTICULARLY THE CASCADES AS THE WEEK PROGRESSES, WITH
SOME MODEST SNOW AMOUNTS INTO THE NORTHERN ROCKIES AS WELL. AFTER
WEDNESDAY, PRECIPITATION SHOULD TREND LIGHTER AS THE MOISTURE MOVES
INLAND, BUT SOME LINGERING PRECIPITATION ALONG THE COAST MAY BE
POSSIBLE AS WEAKER ENERGY RELOADS INTO THE LARGER SCALE TROUGH.
MEANWHILE ADDITIONAL SNOW IS POSSIBLE IN THE NORTHERN ROCKIES TO
PERHAPS THE NORTHERN HIGH PLAINS.
TROPICAL GULF MOISTURE STREAMING AHEAD OF A CENTRAL U.S. TROUGH
AND COLD FRONT, AS WELL AS COASTAL FRONT INTERACTION AND POSSIBLY
EVEN SOME REMNANT ENERGY FROM WHAT WAS RAFAEL, COULD LEAD TO HEAVY
RAIN FROM THE CENTRAL GULF COAST TO MID-SOUTH WEDNESDAY. CURRENT
MODEL DIFFERENCES LIMIT CONFIDENCE IN PLACEMENT OF THE HEAVIEST QPF
THOUGH. MODELS INCLUDING THE 00Z ECMWF AND RECENT AIFS/CMC/UKMET
RUNS SHOWED GOOD CLUSTERING IN THE HEAVIEST RAIN OVER
NORTHERN/CENTRAL MISSISSIPPI AND VICINITY, BUT THE NEW 12Z ECMWF
COMING IN FARTHER SOUTH NEAR SOUTHERN ALABAMA/FLORIDA PANHANDLE
LIMITS CONFIDENCE IN THAT POSITION. THUS MAINTAINED THE BROAD
MARGINAL RISK FOR THE REGION BUT EXPECT LOCALLY EXCESSIVE RAIN
TOTALS. IF AND WHEN MODEL GUIDANCE BECOMES MORE AGREEABLE, THIS
SETUP DOES SEEM FAVORABLE FOR AN EMBEDDED SLIGHT RISK IN FUTURE
FORECASTS. FARTHER NORTH, LIGHT TO MODERATE PRECIPITATION IS
FORECAST ACROSS THE MIDWEST. RAINFALL SHOULD PIVOT INTO THE EAST
THURSDAY WHILE LIGHTENING OVERALL. MOST OF THIS PRECIPITATION LOOKS
TO FALL AS RAIN GIVEN THE WARMER THAN NORMAL TEMPERATURES, BUT
SOME ICE AND SNOW ARE POSSIBLE IN HIGHER ELEVATIONS OF THE INTERIOR
NORTHEAST, THOUGH THIS FORECAST SHOWED A DECREASE IN FORECAST
PRECIPITATION THERE.
WHILE SYSTEM PROGRESSION WILL PROVIDE SOME DAY-TO-DAY VARIABILITY,
MOST OF THE LOWER 48 TO THE EAST OF THE ROCKIES SHOULD SEE AROUND
NORMAL TO ABOVE NORMAL TEMPERATURES MUCH OF THE WEEK. MEANWHILE
LINGERING SNOW COVER IN THE CENTRAL/SOUTHERN ROCKIES WILL PROMOTE
COOLER THAN NORMAL HIGHS THERE THROUGH WEDNESDAY OR THURSDAY WHILE
THE WEST OTHERWISE SHOULD TREND COLDER WITH MORE AMPLIFIED
TROUGHING MOVING INTO THE REGION LATE WEEK AND INTO NEXT WEEKEND.
TATE/SANTORELLI
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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