132
FXUS21 KWNC 271915
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EST DECEMBER 27 2023
SYNOPSIS: MID-LEVEL LOW PRESSURE IS EXPECTED TO TRACK INLAND INTO SOUTHERN
CALIFORNIA AND THE SOUTHWEST ON JANUARY 4. AS THIS MID-LEVEL LOW PRESSURE
PROGRESSES EASTWARD, A SURFACE LOW PRESSURE SYSTEM IS LIKELY TO DEVELOP ALONG
THE GULF COAST WITH A SUBSEQUENT TRACK NORTHEASTWARD NEAR THE EAST COAST. FROM
JANUARY 6 TO 10, MID-LEVEL LOW PRESSURE IS EXPECTED TO SHIFT EAST FROM THE WEST
COAST TO THE CENTRAL CONTIGUOUS U.S. (CONUS). MULTIPLE LOW PRESSURE SYSTEMS
COULD AFFECT THE EAST COAST FROM JANUARY 4 TO 10 BUT UNCERTAINTY REMAINS HIGH
ON THEIR EXACT TRACKS. DESPITE A NEGATIVE ARCTIC OSCILLATION (AO) DURING THE
NEXT TWO WEEKS, IT REMAINS UNCLEAR IF AND WHEN A SIGNIFICANT ARCTIC AIR
OUTBREAK WILL OCCUR.
HAZARDS
SLIGHT RISK OF HEAVY PRECIPITATION FOR PARTS OF SOUTHERN CALIFORNIA, THU, JAN
4.
SLIGHT RISK OF HEAVY SNOW FOR THE HIGHER ELEVATIONS OF ARIZONA, SOUTHWESTERN
COLORADO, AND NORTHERN NEW MEXICO, THU-FRI, JAN 4-5.
SLIGHT RISK OF HEAVY PRECIPITATION FOR NORTHERN CALIFORNIA AND THE PACIFIC
NORTHWEST, SAT-TUE, JAN 6-9.
SLIGHT RISK OF HEAVY SNOW FOR SIERRA NEVADA MOUNTAINS, KLAMATH MOUNTAINS, AND
CASCADES, SAT-TUE, JAN 6-9.
SLIGHT RISK OF HEAVY SNOW FOR PARTS OF THE GREAT BASIN AND CENTRAL TO NORTHERN
ROCKIES, SUN-TUE, JAN 7-9.
SLIGHT RISK OF HIGH WINDS FOR PARTS OF THE WEST AND HIGH PLAINS, THU-TUE, JAN
6-9.
SLIGHT RISK OF HEAVY PRECIPITATION FOR PARTS OF THE GULF COAST, SOUTHEAST, AND
EAST COAST, THU-WED, JAN 4-10.
SLIGHT RISK OF HIGH WINDS FOR THE ALEUTIANS, ALASKA PENINSULA, AND COASTAL
SOUTHWESTERN ALASKA, THU-FRI, JAN 4-5.
DETAILED SUMMARY
FOR SATURDAY DECEMBER 30 - WEDNESDAY JANUARY 03:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR THURSDAY JANUARY 04 - WEDNESDAY JANUARY 10: THE 0Z GEFS, ECMWF, AND
CANADIAN ENSEMBLE MEANS DEPICT A 500-HPA SHORTWAVE TROUGH TRACKING EASTWARD
ACROSS SOUTHERN CALIFORNIA AND THE SOUTHWEST DURING THE MIDDLE PART OF NEXT
WEEK. THIS SHORTWAVE TROUGH ALONG WITH THE GEFS AND ECMWF PROBABILISTIC
EXTREMES TOOLS (PETS) SUPPORT A SLIGHT RISK OF HEAVY PRECIPITATION FOR SOUTHERN
CALIFORNIA ON JANUARY 4 ALTHOUGH THE HEAVIEST PRECIPITATION MAY BEGIN TO TIME
OFF. AS THIS SHORTWAVE TROUGH PROGRESSES EASTWARD, THERE IS AN INCREASED RISK
OF HEAVY SNOW FOR THE HIGHER ELEVATIONS OF THE FOUR CORNERS REGION. DUE TO THE
DRIER GEFS MODEL SOLUTION, ONLY SLIGHT RISKS OF HEAVY PRECIPITATION AND SNOW
ARE POSTED WITH THIS SOUTHERN STREAM SHORTWAVE TROUGH.
ENSEMBLE MEAN SOLUTIONS MAY BE CONVERGING ON A COMMON SOLUTION DURING WEEK-2
WITH AN AMPLIFIED 500-HPA TROUGH SHIFTING INLAND FROM THE WEST COAST TO THE
ROCKIES FROM JANUARY 6 TO 9. THEREFORE, PARTS OF THE GREAT BASIN AND CENTRAL TO
NORTHERN ROCKIES ARE DESIGNATED WITH A SLIGHT RISK OF HEAVY SNOW, VALID FOR
JANUARY 7 TO 9. GIVEN THE BETTER MODEL AGREEMENT ON THE EVOLVING LONGWAVE
PATTERN, THE SLIGHT RISK OF HIGH WINDS IS EXPANDED EAST FROM THE WEST COAST TO
THE ROCKIES AND HIGH PLAINS, JAN 6-9. ADDITIONALLY, ENHANCED ONSHORE FLOW AND
THE GEFS PET SUPPORT A SLIGHT RISK OF HEAVY PRECIPITATION ACROSS THE PACIFIC
NORTHWEST AND NORTHERN CALIFORNIA WITH A SLIGHT RISK OF HEAVY SNOW POSTED FOR
THE CASCADES, KLAMATH MOUNTAINS, AND SIERRA NEVADA MOUNTAINS FOR THE SAME
PERIOD AS THE HIGH WIND RISK. THE HEAVIEST PRECIPITATION IS EXPECTED TO BE ON
JANUARY 6 AND 7. HOWEVER, A MODERATE RISK IS NOT WARRANTED SINCE THE GEFS AND
ECMWF ENSEMBLE MEANS HAVE LIMITED PROBABILITIES OF INTEGRATED VAPOR TRANSPORT
VALUES EXCEEDING 250 KG/M/S.
MULTIPLE INDIVIDUAL SHORTWAVE TROUGHS ARE LIKELY TO EMERGE FROM THE LONGWAVE
TROUGH UPSTREAM AND INCREASE THE CHANCE FOR PERIODS OF MODERATE TO HEAVY
PRECIPITATION ACROSS THE GULF COAST, SOUTHEAST, AND EAST COAST. BASED ON THE
UNCALIBRATED 24-HOUR PRECIPITATION AMOUNTS FROM THE ECMWF ENSEMBLE MEAN, A
SLIGHT RISK OF HEAVY PRECIPITATION IS POSTED FOR A LARGE SPATIAL AREA
THROUGHOUT THE ENTIRETY OF WEEK-2 DUE TO UNCERTAINTY ON SURFACE LOW TRACKS AND
TIMING. THE SPATIAL COVERAGE OF THIS PRECIPITATION HAZARD IS CONSISTENT WITH
THE BACKGROUND EL NIñO. THE ECMWF ENSEMBLE MEMBERS DEPICT THREE POTENTIAL
WINDOWS FOR AN EAST COAST STORM INCLUDING: JANUARY 4, 7-8, AND 10. SINCE THE
GEFS MODEL SHOWS THE 500-HPA TROUGH AXIS FURTHER EAST, IT WOULD FAVOR A MORE
OFFSHORE TRACK OF ANY LOW PRESSURE SYSTEM AND YIELDS A DRIER OUTCOME FOR THE
EAST COAST. SUBSEQUENT OUTLOOKS WILL CLOSELY MONITOR THE POTENTIAL FOR AN EAST
COAST STORM DURING EARLY JANUARY AS TEMPERATURES MAY BE COLD ENOUGH TO SUPPORT
HEAVY SNOW ACROSS THE HIGHER ELEVATIONS OR INLAND AREAS OF THE MID-ATLANTIC AND
NORTHEAST.
A STRONG LOW PRESSURE SYSTEM IS FORECAST TO DEVELOP OVER THE BERING SEA NEXT
WEEK. BASED ON GOOD MODEL AGREEMENT AND CONTINUITY WITH THE STRENGTH OF THIS
LOW PRESSURE SYSTEM (SUB 960-HPA), A SLIGHT RISK OF HIGH WINDS IS POSTED FOR
THE ALEUTIANS, ALASKA PENINSULA, AND COASTAL SOUTHWESTERN ALASKA ON JANUARY 4
AND 5. ALTHOUGH ABOVE-NORMAL PRECIPITATION IS FAVORED ACROSS SOUTHEASTERN
ALASKA, PRECIPITATION AMOUNTS ARE EXPECTED TO REMAIN BELOW HAZARDS THRESHOLDS.
FORECASTER: BRAD PUGH
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