488
FXUS21 KWNC 071857
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EST NOVEMBER 07 2023
SYNOPSIS: STRONG MID-LEVEL LOW PRESSURE IS FORECAST TO SHIFT INLAND TO THE WEST
FROM NOVEMBER 15 TO 17 WITH AN INCREASING RISK OF HEAVY PRECIPITATION ACROSS
CALIFORNIA AND HEAVY SNOW FOR THE SIERRA NEVADA MOUNTAINS. ACCUMULATING SNOW IS
LIKELY TO OVERSPREAD THE HIGHER ELEVATIONS OF THE GREAT BASIN AND CENTRAL
ROCKIES BY NOVEMBER 16. LOW PRESSURE DEVELOPMENT IS EXPECTED OVER THE GREAT
PLAINS LATER IN WEEK-2, BUT THE SUBSEQUENT TRACK OF THIS LOW PRESSURE SYSTEM
AND PRECIPITATION AMOUNTS ACROSS THE CENTRAL U.S. REMAIN UNCERTAIN. STRONG
MID-LEVEL LOW PRESSURE IS ALSO FORECAST OVER THE BERING SEA EARLY IN WEEK-2
WITH INCLEMENT WEATHER AFFECTING MUCH OF ALASKA.
HAZARDS
MODERATE RISK OF HEAVY PRECIPITATION FOR PARTS OF NORTHERN AND CENTRAL
CALIFORNIA, WED-THU, NOV 15-16.
SLIGHT RISK OF HEAVY PRECIPITATION FOR SOUTHWESTERN OREGON AND CALIFORNIA,
WED-FRI, NOV 15-17.
MODERATE RISK OF HEAVY SNOW FOR THE SIERRA NEVADA MOUNTAINS, WED-THU,, NOV
15-16..
SLIGHT RISK OF HEAVY SNOW FOR THE KLAMATH MOUNTAINS AND SIERRA NEVADA
MOUNTAINS, WED-FRI, NOV 15-17.
SLIGHT RISK OF HEAVY SNOW FOR THE HIGHER ELEVATIONS OF UTAH AND COLORADO,
WED-SAT, NOV 15-18.
SLIGHT RISK OF HIGH WINDS FOR MUCH OF THE WEST, WED-SAT, NOV 15-18.
SLIGHT RISK OF HIGH WINDS FOR THE ALEUTIANS, ALASKA PENINSULA, KODIAK ISLAND,
AND COASTAL WESTERN ALASKA, WED-FRI, NOV 15-17.
SLIGHT RISK OF HEAVY PRECIPITATION FOR THE KENAI PENINSULA AND PARTS OF
SOUTHEASTERN ALASKA, WED-FRI, NOV 15-17.
SLIGHT RISK OF HEAVY PRECIPITATION FOR EASTERN OKLAHOMA, EASTERN TEXAS, MIDDLE
TO LOWER MISSISSIPPI VALLEY, AND OHIO VALLEY, FRI-SUN, NOV 17-19.
DETAILED SUMMARY
FOR FRIDAY NOVEMBER 10 - TUESDAY NOVEMBER 14:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR WEDNESDAY NOVEMBER 15 - TUESDAY NOVEMBER 21: THE GEFS, ECMWF, AND CANADIAN
ENSEMBLE MEANS ARE IN GOOD AGREEMENT AND DEPICT A HIGHLY AMPLIFIED 500-HPA
TROUGH PROGRESSING EAST FROM THE NORTHEASTERN PACIFIC TO THE WESTERN CONTIGUOUS
(CONUS) EARLY IN WEEK-2. BASED ON AN IMPROVED SIGNAL FOR HEAVY PRECIPITATION
AMONG THE GEFS AND ECMWF PROBABILISTIC EXTREMES TOOLS (PETS) AND THE
UNCALIBRATED ECMWF MODEL OUTPUT, A MODERATE RISK OF HEAVY PRECIPITATION WAS
ADDED TO THE COASTAL RANGES OF NORTHERN CALIFORNIA AND THE SIERRA NEVADA
MOUNTAINS ON NOV 15 AND 16. THERE IS AN INCREASING CHANCE THAT THE NORTHERN
STREAM SHORTWAVE BRIEFLY INTERACTS WITH SUBTROPICAL MOISTURE WHICH COULD LEAD
TO A BRIEF PERIOD OF HEAVY PRECIPITATION. THE MODEL CONSENSUS CONTINUES TO
FAVOR A PROGRESSIVE PATTERN WITH TOTAL PRECIPITATION AMOUNTS EARLY IN WEEK-2
REMAINING BELOW 4 INCHES, LIQUID EQUIVALENT. A SLIGHT RISK OF HEAVY
PRECIPITATION IS VALID THROUGH NOV 17 AND ALSO EXTENDS TO SOUTHERN CALIFORNIA
WHERE PRECIPITATION AMOUNTS COULD LOCALLY EXCEED 1 TO 2 INCHES. SINCE THE NEXT
WEEK IS PREDICTED TO BE MOSTLY DRY AND 28-DAY AVERAGE STREAMFLOWS ARE MOSTLY
CLOSE TO AVERAGE ACROSS CALIFORNIA, THE FLOOD RISK APPEARS TO BE LOW.
FORECAST CONFIDENCE IS ALSO HIGHER TODAY THAT HEAVY SNOW AFFECTS THE SIERRA
NEVADA MOUNTAINS AS THE ANOMALOUS TROUGH SHIFTS INLAND AND SNOW LEVELS LOWER.
THEREFORE, A MODERATE RISK OF HEAVY SNOW IS POSTED FOR THE SIERRA NEVADA
MOUNTAINS ON NOV 15 AND 16. ACCUMULATING SNOWFALL, ALBEIT WITH LOWER AMOUNTS,
SUPPORTS A SLIGHT RISK OF HEAVY SNOW ACROSS THE HIGHER ELEVATIONS OF UTAH AND
COLORADO FROM NOV 15 TO 18. ALSO, DURING THIS TIME PERIOD, A SLIGHT RISK OF
HIGH WINDS (NOV 15-18) COVERS CALIFORNIA, THE GREAT BASIN, SOUTHWEST, CENTRAL
TO SOUTHERN ROCKIES, AND ADJACENT HIGH PLAINS BASED ON THE EVOLVING 500-HPA
PATTERN.
AN AMPLIFIED TROUGH IS LIKELY TO LEAD TO A SURFACE LOW PRESSURE OVER THE BERING
SEA, BUT ENSEMBLE SPREAD ON ITS STRENGTH AND TRACK HAS INCREASED FROM
YESTERDAY. BASED ON THE ENSEMBLE MEANS WHICH DEPICT A SURFACE LOW NEAR THE
BERING STRAIT, A SLIGHT RISK OF HIGH WINDS IS POSTED FOR COASTAL WESTERN
ALASKA, THE ALEUTIANS, ALASKA PENINSULA, AND KODIAK ISLAND FROM NOV 15 TO 17.
THE SIGNAL FOR HEAVY PRECIPITATION ACROSS SOUTHEASTERN ALASKA DIMINISHED AMONG
THE PETS DUE TO RISING 500-HPA HEIGHTS OVER THE GULF OF ALASKA. DUE TO
CONTINUITY AND MINOR SUPPORT FROM THE PRECIPITATION TOOLS, A SLIGHT RISK OF
HEAVY PRECIPITATION IS MAINTAINED FOR PARTS OF SOUTHEASTERN ALASKA BUT
DECREASED IN SPATIAL COVERAGE FROM YESTERDAY.
MODEL GUIDANCE CONTINUES TO DIFFER ON HOW MUCH PRECIPITATION OCCURS DURING
WEEK-2 ACROSS THE CENTRAL CONUS. THE ECMWF MODEL IS MUCH HEAVIER WITH
PRECIPITATION AMOUNTS WITH A MORE VIGOROUS SHORTWAVE TROUGH EJECTING FROM THE
WEST, WHILE THE GEFS DAMPENS THIS SHORTWAVE TROUGH. GIVEN THESE MODEL
DIFFERENCES, ONLY A SLIGHT RISK OF HEAVY PRECIPITATION IS POSTED FOR EASTERN
OKLAHOMA AND TEXAS, MIDDLE TO LOWER MISSISSIPPI VALLEY, AND OHIO VALLEY FROM
NOV 17 TO 19.
FORECASTER: BRAD PUGH
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