828
FXUS21 KWNC 151815
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT MARCH 15 2024
SYNOPSIS: LATER IN MARCH, DYNAMICAL MODELS FAVOR A FAIRLY BUSY PATTERN
CONSISTING OF A SERIES OF MID-LEVEL LOWS, THOUGH THERE IS STILL A GOOD DEGREE
OF UNCERTAINTY IN REGARDS TO THE TIMING, LOCATION AND STRENGTH OF THESE
FEATURES DURING WEEK-2. SURFACE LOW PRESSURE DEVELOPMENT INCREASES CHANCES OF
HEAVY PRECIPITATION AND EPISODES OF HIGH WINDS OVER EASTERN AND CENTRAL
CONTIGUOUS U.S. (CONUS) THROUGH THE MIDDLE OF WEEK-2, WITH POSSIBLE HEAVY
ACCUMULATING SNOWFALL OVER THE HIGHER ELEVATIONS OF THE WEST AND THE MIDWEST.
AN INCREASING THREAT OF HEAVY PRECIPITATION AND HIGH ELEVATION ALSO EXISTS OVER
THE WEST COAST TIED TO MORE MID-LEVEL LOW PRESSURE FAVORED IN THE MODELS AND
ONSHORE FLOW.
HAZARDS
SLIGHT RISK OF HEAVY PRECIPITATION FOR PARTS OF THE EAST COAST, SAT-MON, MAR
23-25.
SLIGHT RISK OF HIGH WINDS FOR PARTS OF THE EAST COAST, AND OHIO AND TENNESSEE
VALLEYS, SAT-MON, MAR 23-25.
SLIGHT RISK OF HEAVY PRECIPITATION THROUGHOUT PARTS OF THE SOUTHERN AND CENTRAL
PLAINS, MISSISSIPPI, TENNESSEE AND OHIO VALLEYS, AND THE SOUTHEAST, SUN-WED,
MAR 24-27.
SLIGHT RISK OF HEAVY SNOW FOR THE NORTHERN AND CENTRAL ROCKIES, NORTHERN AND
CENTRAL PLAINS, UPPER MISSISSIPPI VALLEY, AND NORTHERN GREAT LAKES, SAT-WED,
MAR 23-27.
SLIGHT RISK OF HIGH WINDS FOR PARTS OF THE INTERIOR WEST AND THE HIGH PLAINS,
SAT-WED, MAR 23-27.
SLIGHT RISK OF HEAVY PRECIPITATION FOR MUCH OF CALIFORNIA, AND PARTS OF THE
PACIFIC NORTHWEST, SUN-WED, MAR 24-27.
SLIGHT RISK OF HIGH ELEVATION HEAVY SNOW OF THE SIERRA NEVADA OF CALIFORNIA,
AND THE CASCADES OF THE PACIFIC NORTHWEST, SUN-WED, MAR 24-27.
DETAILED SUMMARY
FOR MONDAY MARCH 18 - FRIDAY MARCH 22:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR SATURDAY MARCH 23 - FRIDAY MARCH 29: CONSISTENT WITH PREVIOUS ENSEMBLE
GUIDANCE, DYNAMICAL MODELS CONTINUE TO FEATURE A BROAD DISTRIBUTION OF FAIRLY
WEAK 500-HPA NEGATIVE HEIGHT DEPARTURES OVER MUCH OF THE CONUS, WITH MORE
AMPLIFIED MID-LEVEL FEATURES CENTERED OVER THE HIGHER LATITUDES OF NORTH
AMERICA IN THE WEEK-2 MEANS. DAILY ANALYSIS OF THE GEFS AND ECMWF ENSEMBLES
SUGGEST MUCH OF THE ANOMALOUS MEAN TROUGHING DEPICTED OVER THE LOWER 48
CONSISTS OF A SERIES OF SHORTWAVE DISTURBANCES, THOUGH THERE REMAINS A FAIR
AMOUNT OF UNCERTAINTY IN REGARDS TO TIMING, MAGNITUDE AND LOCATION OF SUCH
IMPULSES, THEREBY LIMITING FORECAST CONFIDENCE FOR A NUMBER OF WEATHER RELATED
HAZARDS IN TODAY'S OUTLOOK. NOTWITHSTANDING, THE TROPICS BEAR MENTIONING, AS
THERE EXISTS A ROBUST MADDEN-JULIAN OSCILLATION (MJO) EVENT WITH ITS ENHANCED
PHASE FAVORED TO PROPAGATE FROM THE WESTERN PACIFIC INTO THE WESTERN HEMISPHERE
DURING WEEK-2. COMBINED WITH CONSTRUCTIVELY INTERFERING EQUATORIAL KELVIN AND
ROSSBY WAVE ACTIVITY PREDICTED OVER THE TROPICAL AMERICAS, SOUTHERN STREAM
ENERGY IS LIKELY TO REMAIN ACTIVE DURING THE PERIOD, WITH BROAD SCALE ENHANCED
DIVERGENCE ALOFT CONDUCIVE FOR ABOVE-NORMAL PRECIPITATION THROUGHOUT MUCH OF
THE CONUS LATER IN MARCH.
LATE NEXT WEEK AND HEADING INTO NEXT WEEKEND, ENSEMBLES CONTINUE TO FEATURE A
MEAN SURFACE LOW DEVELOPMENT ACROSS THE SOUTHEAST WITH INCREASED PRECIPITATION
AMOUNTS ALONG THE EASTERN SEABOARD. WHILE BOTH THE GEFS AND ECMWF ENSEMBLES
DEEPEN THE MEAN LOW AS IT MOVES OFFSHORE OF THE CAROLINAS, SOLUTIONS VARY IN
REGARDS TO THE LOCATION OF THE HEAVIEST PRECIPITATION AMOUNTS, WITH THE GEFS
DEPICTING A MORE SUPPRESSED TRACK LIKELY DUE TO STRONGER MID-LEVEL RIDGING
FAVORED TO THE NORTH. THE UNCALIBRATED ECMWF POSES THE BIGGEST PRECIPITATION
THREAT, WHICH DEPICTS GREATER THAN 40% (20%) CHANCES FOR 3-DAY PRECIPITATION
AMOUNTS EXCEEDING ONE (TWO) INCHES FROM THE MID-ATLANTIC TO THE NORTHEAST.
HOWEVER, PROBABILISTIC EXTREMES TOOLS (PET) GUIDANCE FROM THE GEFS AND ECMWF
ARE MUCH LESS BULLISH, AND MAINTAIN THE HIGHEST PRECIPITATION SIGNALS OFFSHORE.
TO RECONCILE THESE DIFFERENCES, A SLIGHT RISK OF HEAVY PRECIPITATION IS ISSUED
FROM THE SOUTHEAST TO NEW ENGLAND FOR MAR 23-25. A SLIGHT RISK OF HIGH WINDS
FOR A SIMILAR REGION INCLUDING THE OHIO AND TENNESSEE VALLEYS IS LIKEWISE
ISSUED FOR THE SAME PERIOD GIVEN THE POTENTIAL FOR STRENGTHENING PRESSURE
GRADIENTS AND SOME SUPPORT FROM THE PETS.
NEARLY CONCURRENT WITH THE LOW PRESSURE SYSTEM LIFTING OUT OVER THE EASTERN
CONUS EARLY IN WEEK-2, ADDITIONAL SURFACE LOW DEVELOPMENT IS FAVORED IN THE LEE
OF THE ROCKIES TIED TO A DEEPENING TROUGH FAVORED IN THE ENSEMBLES. THE 0Z GEFS
IS CONSIDERABLY MORE VIGOROUS WITH THE DEVELOPMENT OF THE UPSTREAM MEAN LOW
COMPARED TO THE ECMWF, AND FEATURES THE RETURN OF ENHANCED PRECIPITATION
AMOUNTS AS SOON AS DAY 9 (MAR 24) THROUGHOUT THE SOUTHERN AND CENTRAL PLAINS
AND MISSISSIPPI VALLEY. THE ECMWF IS SLOWER TO EVOLVE THE SYSTEM, BUT
NONETHELESS FAVORS MORE GULF RETURN FLOW WITH INCREASED CHANCES (>20%) FOR
3-DAY TOTALS EXCEEDING AN INCH THROUGHOUT SOUTHEASTERN CONUS IN THE
UNCALIBRATED GUIDANCE. THE HEAVY PRECIPITATION POTENTIAL IS SUPPORTED IN BOTH
THE GEFS AND ECMWF PETS, WHICH ALSO DEPICT A LARGE COVERAGE OF THE CENTRAL AND
EASTERN CONUS HAVING AT LEAST A 20% CHANCE OF 3-DAY AMOUNTS EXCEEDING THE 85TH
PERCENTILE CLIMATOLOGICALLY. THEREFORE, A BROAD SLIGHT RISK AREA OF HEAVY
PRECIPITATION IS POSTED OVER THE SOUTHEASTERN CONUS AND VALID FOR DAYS MAR
24-27 TO ACCOUNT FOR MODEL DIFFERENCES IN THE TIMING, STRENGTH, AND EVENTUAL
TRACK OF THE SURFACE LOW. ALONG THE SOUTHWESTERN PERIPHERY OF THE HAZARD,
THUNDERSTORM ACTIVITY IS POSSIBLE GIVEN STRONG MOISTURE ADVECTION IN THE GEFS
AND ANY DRYLINE THAT DEVELOPS OVER EASTERN TEXAS. ADDITIONALLY, LOCALIZED
FLOODING IS ALSO POSSIBLE ACROSS PARTS OF THE EASTERN GULF STATES DUE TO
ABOVE-NORMAL PRECIPITATION RECEIVED DURING THE PAST TWO WEEKS LEAVING SEVERAL
LOCATIONS AT MINOR FLOOD STAGE, AND ENHANCED PRECIPITATION FAVORED IN THE
REGION DURING WEEK-1. AS THE LOW TRACKS EASTWARD LATER IN WEEK-2, THERE IS SOME
SUPPORT IN THE GEFS FOR THE HEAVY PRECIPITATION RISK RETURNING TO THE
MID-ATLANTIC AND NORTHEAST, BUT SIGNIFICANT MODEL DIFFERENCES AT THIS LEAD
PRECLUDE ANY CORRESPONDING HAZARDS AT THIS TIME.
WITH ANOMALOUSLY COLD AIR FAVORED FARTHER NORTH TIED TO THE BROAD 500-HPA
TROUGH, PERIODS OF ACCUMULATING SNOW REMAIN POSSIBLE OVER PARTS TO THE ROCKIES,
THE ADJACENT HIGH PLAINS, ACROSS MUCH OF THE MIDWEST AND INTO THE GREAT LAKES
ON THE BACKSIDE OF THE TRACKING LOW. THE GEFS SNOW WATER EQUIVALENT (SWE) PET
SUPPORTS A SLIGHT RISK OF HEAVY SNOW (MAR 23-27) ACROSS THIS REGION, AS DOES
THE EUROPEAN ENSEMBLE MEAN. A SLIGHT RISK OF HIGH WINDS ALSO REMAINS ISSUED
(MAR 23-27), WHERE RELATIVE TO YESTERDAY, BOTH THE SNOW AND WIND HAZARDS HAVE
BEEN EXPANDED TO INCLUDE MORE OF THE HIGHER ELEVATIONS OF THE WEST GIVEN
STRONGER TROUGHING FAVORED AND TRENDS IN THE GUIDANCE. IT SHOULD BE NOTED
EPISODES OF HIGH WINDS MAY EXACERBATE ONGOING WILDFIRE ACTIVITY OVER SEVERAL
LOCATIONS IN THE SOUTHERN HIGH PLAINS AND FOUR CORNERS REGION.
FURTHER WEST, THE LARGEST HEIGHT PATTERN DIFFERENCES RESIDE OVER THE EASTERN
PACIFIC AMONG THE MODELS. THE ECMWF FAVORS MORE OF A POLEWARD RETREAT OF A
500-HPA RIDGE EARLY IN WEEK-2, ALLOWING FOR MORE ANOMALOUS TROUGHING EXTENDING
INTO THE WEST COAST. AS A RESULT, A SHARP INCREASE IN DAILY PRECIPITATION
AMOUNTS ARE SEEN IN THE RAW GUIDANCE, WITH 20-40% CHANCES OF 3-DAY AMOUNTS
EXCEEDING 2 INCHES ACROSS PARTS OF THE PACIFIC NORTHWEST AND CALIFORNIA THROUGH
THE MIDDLE OF WEEK-2. THE GEFS IS MORE MUTED WITH THIS PATTERN TRANSITION, BUT
DOES SHOW SOME SIGN OF TROUGH DEVELOPMENT OFF THE WEST COAST WITH INCREASED
PRECIPITATION AMOUNTS BY THE MIDDLE OF WEEK-2. IN LIGHT OF THESE DIFFERENCES,
THERE IS SUPPORT IN THE CANADIAN FOR ENHANCED PRECIPITATION AMOUNTS EARLY IN
WEEK-2, THUS A SLIGHT RISK OF HEAVY PRECIPITATION IS ISSUED OVER PARTS OF
CALIFORNIA AND THE PACIFIC NORTHWEST FOR MAR 24-27 GIVEN THE TREND TOWARDS
WETTER CONDITIONS OUT WEST. A CORRESPONDING HIGH ELEVATION HEAVY SNOW SHAPE IS
ALSO ISSUED FOR PARTS OF THE SIERRA NEVADA'S AND CASCADES.
NO HAZARDS ARE ISSUED OVER ALASKA AS MUCH OF THE STATE IS FAVORED TO BE UNDER
THE INFLUENCE OF A STRONG 500-HPA RIDGE. WHILE THIS RIDGE IS FAVORED TO
GRADUALLY DEAMPLIFY LATER IN WEEK-2, MUCH OF THE MAINLAND AND SOUTHEAST ARE
EXPECTED TO BE UNSEASONABLY WARM AND DRY THROUGH LATE MARCH.
FORECASTER: NICK NOVELLA
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