868
FXUS21 KWNC 201823
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT MARCH 20 2024
SYNOPSIS: EARLY IN WEEK-2, SURFACE LOW PRESSURE IS FAVORED TO TRACK
NORTHEASTWARD FROM THE SOUTHEAST SUSTAINING AN INCREASED RISK OF HEAVY
PRECIPITATION AND EPISODES OF HIGH WINDS FOR MUCH OF THE EASTERN SEABOARD.
MODELS SHOW SIGNS FOR STRONGER MID-LEVEL LOW PRESSURE ENCROACHING THE WEST
COAST, ELEVATING THE RISK OF HEAVY PRECIPITATION, SNOW, AND HIGH WINDS FOR
PARTS OF CALIFORNIA AND THE PACIFIC NORTHWEST. AS THIS MID-LEVEL LOW PRESSURE
SHIFTS INLAND, ADDITIONAL SURFACE LOW FORMATION IS FAVORED IN THE LEE OF THE
ROCKIES, BRINGING A RENEWED RISK FOR HEAVY PRECIPITATION ACROSS THE
SOUTHEASTERN CONTIGUOUS U.S. (CONUS), AS WELL AS THE POTENTIAL FOR HEAVY SNOW
ACROSS THE NORTHERN TIER OF THE U.S. LATER IN WEEK-2.
HAZARDS
SLIGHT RISK OF HEAVY PRECIPITATION OVER MUCH OF THE EASTERN SEABOARD, THU-FRI,
MAR 28-29.
SLIGHT RISK OF HIGH WINDS FOR MUCH OF THE NORTHEASTERN CONUS, THU-SUN, MAR
28-31.
SLIGHT RISK OF HEAVY PRECIPITATION OVER MUCH OF CALIFORNIA AND ADJACENT OREGON,
THU-SAT, MAR 28-30.
SLIGHT RISK OF HEAVY SNOW OVER THE HIGHER ELEVATIONS OF THE SIERRA NEVADA RANGE
OF CALIFORNIA, AND THE CASCADES OF THE PACIFIC NORTHWEST, THU-SAT, MAR 28-30.
SLIGHT RISK OF HIGH WINDS OF PORTIONS OF THE WEST COAST, THU-SAT, MAR 28-30.
SLIGHT RISK OF HEAVY PRECIPITATION FOR PARTS OF THE MISSISSIPPI, TENNESSEE, AND
OHIO VALLEYS, AND SOUTHEAST, SUN-TUE, MAR 31-APR 2.
SLIGHT RISK OF HEAVY SNOW OVER PORTIONS OF THE ROCKIES, NORTHERN AND CENTRAL
PLAINS, UPPER MISSISSIPPI VALLEY, AND GREAT LAKES, SAT-TUE, MAR 30-APR 2.
DETAILED SUMMARY
FOR SATURDAY MARCH 23 - WEDNESDAY MARCH 27:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR THURSDAY MARCH 28 - WEDNESDAY APRIL 03: DYNAMICAL MODELS CONTINUE TO
ADVERTISE PREDOMINATELY BELOW NORMAL 500-HPA HEIGHTS OVERSPREADING MUCH OF THE
CONUS, WHILE KEEPING MUCH OF ANOMALOUS MID-LEVEL RIDGING CONFINED TO THE HIGHER
LATITUDES OF NORTH AMERICA IN THE MEAN WEEK-2 HEIGHT FIELDS. THE HEIGHT PATTERN
OVER THE CONUS IS ANTICIPATED TO REMAIN PROGRESSIVE NEXT WEEK, CONSISTING OF A
SERIES OF SHORTWAVE DISTURBANCES PROPAGATING EASTWARD TO MAINTAIN AN INCREASED
RISK OF POTENTIALLY IMPACTFUL WEATHER DURING THE PERIOD. A KEY CHANGE IS
APPARENT IN BOTH THE 0Z GEFS AND CANADIAN ENSEMBLES, WHICH NOW FAVOR STRONGER
500-HPA TROUGHING OVER THE EASTERN CONUS EARLY IN WEEK-2, FALLING MORE IN LINE
WITH PREVIOUS RUNS OF THE ECMWF ENSEMBLE.
THE ANOMALOUS TROUGHING FEATURED IN THE MODELS OVER THE EAST TRANSLATES INTO
BETTER MODEL AGREEMENT FOR A SECONDARY SURFACE LOW FORMING ON THE TAIL END OF A
FRONTAL BOUNDARY OVER THE SOUTHEAST, WITH A NOR-EASTER-LIKE STORM TRACK
POTENTIALLY PRODUCING HEAVY PRECIPITATION AND HIGH WINDS AFFECTING THE EASTERN
SEABOARD LATE NEXT WEEK. HOWEVER, MODEL DIFFERENCES REMAIN IN REGARDS TO THE
EVOLUTION OF THE STORM TRACK, AND ENSEMBLES GENERALLY KEEP THE MEAN LOW CENTER
AND HIGHEST DAILY PRECIPITATION AMOUNTS OFFSHORE. A SLIGHT RISK OF HEAVY
PRECIPITATION REMAINS ISSUED FOR MUCH OF THE EASTERN SEABOARD WHERE
PROBABILISTIC EXTREMES TOOLS (PETS) DEPICT 20% CHANCES FOR 3-DAY AMOUNTS
EXCEEDING THE 85TH PERCENTILE. THE UNCALIBRATED ECMWF SUGGESTS A HIGHER RISK
DESIGNATION IS WARRANTED WITH HIGHER CHANCES (40-50%) FOR AMOUNTS EXCEEDING AN
INCH OVER PARTS OF THE MID-ATLANTIC AND THE NORTHEAST, THOUGH THE DRIER
SOLUTION IN THE UNCALIBRATED GEFS AND PETS ARE MUCH MORE SUPPORTIVE OF A SLIGHT
RISK DESIGNATION AT THIS TIME. IN REGARDS TO HIGH WIND POTENTIAL, BETTER MODEL
AGREEMENT EXISTS IN THE AMPLIFICATION OF THE 500-HPA MEAN TROUGH AND A DEEPER
SURFACE MEAN LOW AT THE SURFACE THAT SLOWS OVER THE CANADIAN MARITIMES TOWARDS
THE MIDDLE OF THE PERIOD. A SLIGHT RISK OF HIGH WINDS REMAINS ISSUED OVER A
BROAD AREA OVER THE NORTHEASTERN CONUS BUT IS NOW EXTENDED THROUGH DAY 11 (MAR
31) BASED ON MODEL TRENDS. SIMILAR TO PRECIPITATION, A MODERATE RISK WAS
CONSIDERED OVER THE NORTHEAST, BUT THERE IS LITTLE SUPPORT IN THE PETS OVER
THIS REGION FOR WINDS EXCEEDING THE 85TH PERCENTILE.
FARTHER WEST, MODELS HAVE BEEN CONSISTENT WITH ANOTHER 500-HPA TROUGH UPSTREAM
ENCROACHING THE WEST COAST EARLY IN WEEK-2. THE ENHANCED ONSHORE FLOW IS
EXPECTED TO SUSTAIN AN INCREASED RISK OF HEAVY PRECIPITATION AND HIGH ELEVATION
SNOWFALL, AND THE CORRESPONDING SLIGHT RISK AREAS REMAIN POSTED OVER PARTS OF
CALIFORNIA AND THE PACIFIC NORTHWEST, BOTH VALID THROUGH MAR 30. OF NOTE, THE
ECMWF HAS BECOME MORE PRONOUNCED WITH THE TROUGHING ALOFT, RESULTING IN HIGHER
CHANCES FOR 3-DAY AMOUNTS EXCEEDING THE 85TH PERCENTILE AND 2 INCHES OVER THE
HIGHER ELEVATIONS OF CALIFORNIA, SUPPORTIVE OF A MODERATE RISK FOR HEAVY SNOW.
HOWEVER, SOME OF THIS INFLATION IN PERCENTILE SPACE IS, IN PART, ATTRIBUTED TO
A DRIER CLIMATOLOGY FOR LATE MARCH, AND DUE TO GENERALLY DRIER AMOUNTS DEPICTED
IN THE GEFS WITH LARGE ENSEMBLE SPREAD, ONLY A SLIGHT RISK REMAINS ISSUED. THE
STRONGER TROUGHING FAVORED ALSO SUPPORTS THE ADDITION OF A SLIGHT RISK OF HIGH
WINDS OVER THE WEST COAST, WHERE BOTH THE GEFS AND ECWMF PETS SHOW AT LEAST A
20% CHANCE OF WINDS EXCEEDING THE 85TH PERCENTILE.
AS THE MID-LEVEL TROUGH OVER THE WEST COAST IS FORECAST TO MOVE EAST INTO THE
INTERIOR WEST, LEE CYCLOGENESIS REMAINS FAVORED TOWARDS THE MIDDLE OF WEEK-2.
THERE IS FAIR AGREEMENT IN THE ENSEMBLES IN REGARDS TO THE TIMING OF SURFACE
LOW FORMATION, WITH INCREASING PRECIPITATION AMOUNTS OVERSPREADING THE PLAINS
AND MISSISSIPPI VALLEY BY DAYS 11 TO 12 (MAR 31-APR 1). GIVEN GOOD CONTINUITY
IN THE GUIDANCE AND SUPPORT FROM THE PETS, A SLIGHT RISK OF HEAVY PRECIPITATION
REMAINS POSTED FOR MAR 31-APR 2, AND IS EXPANDED TO INCLUDE MORE OF THE
MISSISSIPPI AND OHIO VALLEYS RELATIVE TO YESTERDAY'S OUTLOOK BASED ON
UNCALIBRATED TOOLS. WHILE THE DETAILS OF THE STORM TRACK ARE QUITE UNCERTAIN AT
THIS LEAD, ACCUMULATING SNOWFALL IS FAVORED ON THE BACKSIDE OF THE LOW WHERE
ANOMALOUSLY COLD AIR IS EXPECTED TO BE ESTABLISHED. BOTH THE GEFS BASED SNOW
WATER EQUIVALENT (SWE) PET AND UNCALIBRATED ECMWF SUPPORT AN INCREASED
POTENTIAL FOR HEAVY SNOW, AND A BROAD SLIGHT RISK AREA FOR HEAVY SNOW IS ISSUED
FROM THE ROCKIES TO THE UPPER MIDWEST FOR MAR 30-APR 2.
TIED TO THE FRONTAL SYSTEM OVER THE EASTERN CONUS, ANOTHER ROUND OF COLD AIR
ADVECTION IS FAVORED WITH SURFACE HIGH PRESSURE DESCENDING INTO THE PLAINS AND
MISSISSIPPI VALLEY THROUGH THE MIDDLE OF WEEK-2. THE STRONGEST NEGATIVE
TEMPERATURE DEPARTURES REMAIN FORECAST OVER THE NORTH-CENTRAL CONUS, HOWEVER
THERE IS MORE UNCERTAINTY AS TO HOW COLD TEMPERATURES WILL BE FURTHER SOUTH
WHERE SOME REGIONS ARE MORE VULNERABLE FOR FROSTS AND/OR FREEZES ADVERSELY
IMPACTING EMERGING SPRING VEGETATION. DIFFERENCES EXIST BETWEEN THE GEFS AND
ECMWF PETS IN REGARDS TO THE STRENGTH OF THE COLD SIGNALS SHIFTING
SOUTHEASTWARD IN TIME, AND GIVEN THE POTENTIAL FOR THE AFOREMENTIONED LEE
CYCLOGENESIS OVER THE PLAINS WHERE MUCH OF THE CENTRAL CONUS COULD BE BACK IN
THE WARM SECTOR, ANY ANOMALOUS COLD APPEARS TO BE MORE SHORT-LIVED. THEREFORE,
THE SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES IS REMOVED FROM TODAY'S
OUTLOOK.
STRONG 500-HPA RIDGING IS EXPECTED ACROSS MOST OF ALASKA FOLLOWED BY MORE
ANOMALOUS TROUGHING DEVELOPING OVER THE ALEUTIANS TO INDUCE MORE ONSHORE FLOW.
ABOVE-NORMAL TEMPERATURES REMAIN PREDOMINANTLY FAVORED THROUGHOUT THE PERIOD,
WITH ABOVE-NORMAL PRECIPITATION BEGINNING AROUND SOUTHERN MAINLAND AND
SOUTHEAST TOWARD THE MIDDLE OF WEEK-2. BY THIS TIME, MORE UNSETTLED WEATHER IS
REFLECTED IN THE PRECIPITATION AND WIND PETS, HOWEVER CONDITIONS ARE NOT
EXPECTED TO REACH HAZARD THRESHOLDS.
FORECASTER: NICK NOVELLA
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