474
FXUS21 KWNC 181855
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT MARCH 18 2024
SYNOPSIS: BY EARLY NEXT WEEK, A POTENTIALLY POTENT LOW PRESSURE SYSTEM TRACKING
ACROSS THE MIDWEST LEADS TO AN INCREASED RISK FOR HEAVY PRECIPITATION ACROSS
THE MISSISSIPPI, TENNESSEE AND OHIO VALLEYS, ACCUMULATING HEAVY SNOWFALL, ALONG
WITH A WIDESPREAD THREAT FOR EPISODES OF HIGH WINDS FOR MUCH OF THE CENTRAL AND
EASTERN U.S. IN THE WAKE OF THE LOW PRESSURE SYSTEM, ANOMALOUSLY COLD AIR IS
FAVORED TO DIVE SOUTHEASTWARD RENEWING THE RISK OF EARLY SPRING FROST AND/OR
FREEZES FOR MANY PARTS OF THE SOUTHEASTERN CONUS. PREDICTED MID-LEVEL LOW
PRESSURE RETURNING ACROSS THE WEST PROMOTES THE RISK OF HIGH ELEVATION HEAVY
SNOW OVER PARTS OF CALIFORNIA AND OREGON.
HAZARDS
SLIGHT RISK OF HEAVY PRECIPITATION FOR PARTS OF THE MISSISSIPPI, TENNESSEE, AND
OHIO VALLEYS, AND SOUTHEAST, TUE-WED, MAR 26-27.
SLIGHT RISK OF HIGH WINDS FOR PARTS FOR MUCH OF THE MIDWEST, AND REGIONS EAST
OF THE MISSISSIPPI RIVER, TUE-THU, MAR 26-28.
SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES FOR PARTS OF THE GREAT PLAINS,
MISSISSIPPI, TENNESSEE, AND OHIO VALLEYS, AND THE SOUTHEAST, WED-FRI, MAR
27-29.
SLIGHT RISK OF HEAVY SNOW FOR THE NORTHERN AND CENTRAL ROCKIES, EASTWARD TO THE
GREAT LAKES, TUE-THU, MAR 26-27.
SLIGHT RISK OF HIGH ELEVATION HEAVY SNOW OF THE SIERRA NEVADA OF CALIFORNIA,
AND THE CASCADES OF THE PACIFIC NORTHWEST, WED-SAT, MAR 27-30.
DETAILED SUMMARY
FOR THURSDAY MARCH 21 - MONDAY MARCH 25:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR TUESDAY MARCH 26 - MONDAY APRIL 01: EARLY IN WEEK-2, DYNAMICAL MODELS ARE
IN FAIR AGREEMENT FEATURING AMPLIFIED RIDGING CENTERED OVER THE NORTHEASTERN
PACIFIC AND ALASKA, WITH DEEP TROUGHING DOWNSTREAM CONSISTING OF A BROAD
DISTRIBUTION OF NEGATIVE 500-HPA HEIGHTS OVERSPREADING MUCH OF THE WESTERN AND
CENTRAL CONUS. IN REGARDS TO THE RIDGING UPSTREAM, BOTH THE GEFS AND ECMWF
ENSEMBLES HAVE TRENDED MORE TOWARDS A MORE AMPLIFIED MEAN SOLUTION OVER THE
PAST FEW DAYS, RESULTING IN STRONGER NORTHWESTERLY FLOW AND THE POTENTIAL FOR
ANOMALOUS COLD AIR ADVECTION OVER THE CENTRAL CONUS BY EARLY NEXT WEEK.
ADDITIONALLY, LEE CYCLOGENESIS AND A FAIRLY POTENT LOW PRESSURE SYSTEM SHIFTING
INTO THE GREAT LAKES REMAINS FAVORED IN THE ENSEMBLES, WHICH IS EXPECTED TO
SUSTAIN THE INCREASED RISK OF HEAVY PRECIPITATION ACROSS THE SOUTHEASTERN
CONUS, WITH THE POTENTIAL FOR ACCUMULATING HEAVY SNOWFALL ON THE BACKSIDE OF
THE TRACKING LOW, ALONG WITH THE EPISODES OF HIGH WINDS.
TIED TO THE AMPLIFIED TROUGHING ALOFT BY THE OUTSET OF WEEK-2, THE GEFS, ECMWF
AND CANADIAN ENSEMBLES HAVE BEEN CONSISTENT WITH THE TIMING AND LOCATION OF
INCREASED DAILY PRECIPITATION AMOUNTS IN THE WARM SECTOR OF THE PREDICTED LOW
PRESSURE SYSTEM. A SLIGHT RISK OF HEAVY PRECIPITATION IS ISSUED OVER PORTIONS
OF THE MISSISSIPPI, TENNESSEE AND OHIO VALLEYS AND THE SOUTHEAST, WHERE
PROBABILISTIC EXTREMES TOOLS (PETS) SHOW AT LEAST A 20% CHANCE OF 3-DAY
ACCUMULATIONS EXCEEDING THE 85TH PERCENTILE AND 1 INCH. A MODERATE RISK WAS
CONSIDERED FOR ISSUANCE BASED ON THE ECMWF PET FAVORING HIGHER CHANCES (>40%)
FOR MEETING HAZARD CRITERIA OVER PARTS OF THE EASTERN GULF STATES, HOWEVER THIS
IS MUCH LESS SUPPORTED IN THE UNCALIBRATED DAILY GUIDANCE AND GEFS PET.
LOCALIZED FLOODING IS ALSO POSSIBLE ACROSS PARTS OF THE 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. LATER IN WEEK-2, THERE IS SOME SUPPORT IN THE PETS FOR
THE HEAVY PRECIPITATION RISK EMERGING OVER PARTS OF THE COASTAL MID-ATLANTIC
AND NORTHEAST ASSOCIATED WITH A SECONDARY SURFACE LOW DEVELOPING OVER THE
SOUTHEAST IN THE ECMWF, THOUGH THIS IS NOT WELL REPRESENTED IN THE GEFS AND
CANADIAN. AT THE BASE OF THE EASTWARD SHIFTING TROUGHING ALOFT, A SLIGHT RISK
OF HIGH WINDS IS ALSO POSTED OVER A BROAD AREA OF THE EASTERN CONUS FOR MAR
26-28 WHICH IS ALSO SUPPORTED BY PETS.
IN THE WAKE OF THE PREDICTED FRONTAL SYSTEM, THE UNCALIBRATED GEFS DEPICTS
STRONGER MEAN SURFACE HIGH PRESSURE COMPARED TO PREVIOUS RUNS, WITH NEGATIVE
TEMPERATURE DEPARTURES IN THE DOUBLE DIGITS (DEG F) OVER THE NORTHERN PLAINS
AND UPPER MIDWEST DURING THE FIRST FEW DAYS OF THE PERIOD. THESE TRENDS ARE
ALSO REFLECTED IN THE PETS, WHICH DEPICT ELEVATED CHANCES (40-60%) FOR MINIMUM
TEMPERATURES FALLING BELOW THE 15TH PERCENTILE OVER THE UPPER MIDWEST. DESPITE
THESE STRONG COLD SIGNALS, NO CORRESPONDING HAZARDS ARE ISSUED OVER THIS PART
OF THE COUNTRY, AS ACTUAL TEMPERATURES ARE NOT EXPECTED TO REACH HAZARD
CRITERIA (ESPECIALLY WITH HIGHER SUN ANGLES LATER IN MARCH). HOWEVER, AS THE
TROUGHING ALOFT SHIFTS EASTWARD WITH TIME, SO DOES THE ANOMALOUSLY COLD AIR
MASS, WHERE EARLY SPRING FROST AND/OR FREEZES MAY ADVERSELY IMPACT EMERGING
SPRING VEGETATION OVER PARTS OF THE PLAINS, MISSISSIPPI, TENNESSEE AND OHIO
VALLEYS AND THE SOUTHEAST. WEAKER SIGNALS ARE DEPICTED IN THE PETS AS THE COLD
AIR MIXES SOUTHEASTWARD BY THE MIDDLE OF NEXT WEEK, BUT THESE TOOLS MAINTAIN AT
LEAST A 20% CHANCE FOR MINIMUM TEMPERATURES FALLING BELOW THE 15TH PERCENTILE
AND 40 DEGREES F, SUPPORTING A SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES
MAR 27-29. WITH THE ANOMALOUS COLD IN PLACE, ACCUMULATING SNOWFALL LOOKS
INCREASINGLY LIKELY ON THE BACKSIDE OF THE LOW OVER NORTH-CENTRAL CONUS, AS
WELL AS FARTHER WEST ACROSS PORTIONS OF THE ROCKIES ASSOCIATED WITH UPSLOPE
FLOW. BASED ON THE UNCALIBRATED ECMWF AND THE GEFS SNOW WATER EQUIVALENT (SWE)
PET, A SLIGHT RISK OF HEAVY SNOW IS ISSUED (MAR 26-27) FROM THE ROCKIES TO THE
GREAT LAKES AND EXCLUDES PARTS OF THE NORTHERN PLAINS WHERE DRIER AIR IS
FAVORED.
AS MUCH OF THE ANOMALOUS TROUGHING WEAKENS AND BEGINS TO LIFT OUT BY THE MIDDLE
OF WEEK-2 OVER THE EASTERN CONUS, BOTH THE GEFS AND ECMWF ENSEMBLES CONTINUE TO
FEATURE ADDITIONAL 500-HPA TROUGHING ENCROACHING THE WEST COAST. WHILE MUCH
LESS AMPLIFIED IN COMPARISON TO THE TROUGHING DOWNSTREAM, ADDITIONAL SHORTWAVE
ACTIVITY IS EXPECTED TO PROMOTE THE RETURN OF ABOVE-NORMAL PRECIPITATION OVER
THE WESTERN CONUS, WITH POTENTIALLY HEAVY PRECIPITATION OVER PARTS OF
CALIFORNIA AND THE PACIFIC NORTHWEST. BOTH THE GEFS AND ECWMF PETS ARE IN
AGREEMENT DEPICTING A BROAD AREA WITH INCREASED CHANCES FOR 3-DAY AMOUNTS
EXCEEDING THE 85TH PERCENTILE WITH, WITH 30-40% CHANCES OVER THE CENTRAL WEST
COAST. HOWEVER, THE HEAVIEST TOTALS IN THE UNCALIBRATED TOOLS AND PETS APPEAR
LIMITED TO THE HIGHER ELEVATIONS OF CALIFORNIA AND OREGON. AS A RESULT, NO
CORRESPONDING RISK OF HEAVY PRECIPITATION IS ISSUED, BUT A SLIGHT RISK OF HIGH
ELEVATION SNOW IS POSTED OVER THESE AREAS FOR MAR 27-30.
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 THROUGH LATE MARCH. ENHANCED WIND SPEEDS ARE
POSSIBLE ASSOCIATED WITH DEVELOPING MEAN LOW PRESSURE OVER THE BERING SEA AND
GULF OF ALASKA, THOUGH WIND SPEEDS ARE NOT EXPECTED TO EXCEED HAZARD
THRESHOLDS.
FORECASTER: NICK NOVELLA
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page