885
FXUS21 KWNC 191922
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT MARCH 19 2024
SYNOPSIS: EARLY WEEK-2, A POTENTIALLY POTENT LOW PRESSURE SYSTEM TRACKING
THROUGH THE EAST LEADS TO AN INCREASED RISK FOR HEAVY PRECIPITATION FROM THE
LOWER MISSISSIPPI, TENNESSEE AND OHIO VALLEYS NORTHWARD ALONG THE EASTERN
SEABOARD. HIGH PRESSURE MOVING IN BEHIND THE EXITING SYSTEM ENHANCES THE RISK
OF HIGH WINDS FOR MOST AREAS EAST OF THE MISSISSIPPI RIVER, AND THOSE WINDS ARE
EXPECTED TO BRING COLD CANADIAN AIR SOUTHWARD, INCREASING THE POTENTIAL FOR
RENEWED EARLY SPRING FROST AND/OR FREEZING CONDITIONS IN PARTS OF THE PLAINS
AND THE SOUTHEASTERN CONUS. LATER IN WEEK-2, ANOTHER STORM SYSTEM COULD AFFECT
THE SOUTHEAST, RENEWING THE RISK OF HEAVY PRECIPITATION OVER THIS PART OF THE
COUNTRY . FARTHER WEST, PREDICTED MID-LEVEL LOW PRESSURE IS EXPECTED TO BRING
HEAVY PRECIPITATION, INCLUDING HEAVY HIGHER-ELEVATIONS SNOWFALL, TO MOST OF
CALIFORNIA AND ADJACENT OREGON DURING THE FIRST HALF OF THE PERIOD.
HAZARDS
SLIGHT RISK OF HEAVY PRECIPITATION FOR PARTS OF THE MISSISSIPPI, TENNESSEE, AND
OHIO VALLEYS, AND INTERIOR SOUTHEAST, WED-THU MAR 27-28, AND SUN-TUE, MAR
31-APR 2.
SLIGHT RISK OF HEAVY PRECIPITATION OVER EASTERN SEABOARD, WED-FRI, MAR 27-29.
SLIGHT RISK OF HEAVY PRECIPITATION OVER MUCH OF CALIFORNIA ADJACENT OREGON,
WED-SAT, MAR 27-30.
SLIGHT RISK OF HIGH WINDS FOR MOST REGIONS EAST OF THE MISSISSIPPI RIVER,
WED-FRI, MAR 27-29.
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 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 FRIDAY MARCH 22 - TUESDAY MARCH 26:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
FOR WEDNESDAY MARCH 27 - TUESDAY APRIL 02: EARLY IN WEEK-2, MODELS ARE IN FAIR
AGREEMENT FEATURING AMPLIFIED MID-LEVEL RIDGING CENTERED OVER MOST OF ALASKA,
WITH ANOMALOUSLY POSITIVE 500-HPA HEIGHTS ACROSS THE NORTHERN TIER OF CANADA.
FARTHER SOUTH, A MID-LEVEL TROUGH OF MODERATE STRENGTH IS CENTERED OFF THE WEST
COAST, WITH ANOTHER COVERING MUCH OF THE CENTRAL CONUS WITH AN AXIS NEAR THE
MISSISSIPPI RIVER. MODELS ARE CONSISTENT IN SHOWING THAT THE PATTERN WILL BE
PROGRESSIVE, WITH THE CENTRAL CONUS MID-LEVEL TROUGH MOVING TO OR OFF THE EAST
COAST BY THE END OF WEEK-2 WHILE THE TROUGH NEAR THE WESTERN CONUS MOVES
INLAND, APPROACHING THE GREAT PLAINS BY THE END OF THE PERIOD. HOWEVER, THE
MODELS ARE NOT IN GOOD AGREEMENT ON THE STRENGTH AND SPEED OF THESE TROUGHS AS
THEY PROGRESS OVER THE COURSE OF WEEK-2, AND THIS LEADS TO UNCERTAINTIES IN THE
PLACEMENT OF SURFACE FEATURES AND RESULTING SENSIBLE WEATHER, REDUCING
CONFIDENCE IN THE FORECAST. IN GENERAL, THE EUROPEAN ENSEMBLE MEANS ARE
CONSISTENTLY MORE AMPLIFIED THAN THE GEFS AND CANADIAN ENSEMBLE MEANS.
THE FIRST MID-LEVEL TROUGH CENTERED NEAR THE CENTRAL CONUS IS EXPECTED TO
TRIGGER SOUTHERLY SURFACE FLOW IN THE SOUTHEAST AHEAD OF LEE CYCLOGENESIS
FARTHER WEST, AND THE RESULTING ADVECTION OF WARM, MOIST AIR FROM THE GULF OF
MEXICO UNDERNEATH CYCLONIC MID-LEVEL FLOW ENHANCES THE RISK OF HEAVY
PRECIPITATION EARLY IN THE PERIOD ACROSS THE SOUTHEAST. SOME TOOLS, ESPECIALLY
THE EUROPEAN OPERATIONAL MODEL, DEVELOP A SURFACE LOW PRESSURE SYSTEM NEAR THE
SOUTHEAST THAT TRACKS NORTHWARD ALONG THE ATLANTIC SEABOARD. THIS SCENARIO
WOULD BRING HEAVY PRECIPITATION FARTHER NORTH THAN ANTICIPATED YESTERDAY, INTO
THE MID-ATLANTIC AND THE NORTHEASTERN CONUS. GIVEN THE INCREASED POTENTIAL FOR
AN EAST COAST LOW PRESSURE SYSTEM, THE ENHANCED RISK OF HEAVY PRECIPITATION IS
EXTENDED FARTHER NORTH THAN YESTERDAY, COVERING THE MID-ATLANTIC REGION AND THE
NORTHEASTERN CONUS. CONDITIONS SHOULD CLEAR OUT AS THE MID-LEVEL TROUGH PUSHES
EASTWARD OFF THE ATLANTIC COAST, BUT THE SECOND SYSTEM INITIALLY OFF THE WEST
COAST IS EXPECTED TO REACH THE GREAT PLAINS LATER WEEK-2, BRINGING A RENEWED
RISK OF HEAVY RAINFALL TO PARTS OF THE SOUTHEAST TOWARD THE END OF THE PERIOD.
IN THE WAKE OF THE EAST COAST TROUGH, SURFACE HIGH PRESSURE IS EXPECTED TO PUSH
SOUTHWARD FROM CANADA INTO THE CENTRAL AND EASTERN CONUS, INCREASING THE ODDS
FOR TWO HAZARDS. FIRST, THE PRESSURE GRADIENT BETWEEN THIS HIGH PRESSURE SYSTEM
AND THE DEPARTING STORM SYSTEM IN THE EASTERN CONUS INCREASES THE RISK FOR HIGH
WINDS OVER A BROAD AREA COVERING MOST OF THE CONUS EAST OF THE MISSISSIPPI
RIVER. IN ADDITION, THIS HIGH PRESSURE SYSTEM IS EXPECTED TO DRIVE COLD
CANADIAN AIR INTO THE CENTRAL AND SOUTHEASTERN CONUS. TEMPERATURES ARE EXPECTED
TO BE WELL BELOW NORMAL ACROSS THIS AREA FOR A FEW DAYS, BUT POTENTIALLY
IMPACTFUL COLD SHOULD BE RESTRICTED TO THE SOUTHERN AREAS AFFECTED BY THE COLD
OUTBREAK, WHERE THERE WILL BE AN ELEVATED RISK OF FROST AND/OR FREEZING
CONDITIONS THAT COULD IMPACT EARLY-SPRING FLORA DEVELOPMENT. THUS, A SLIGHT
RISK FOR MUCH BELOW NORMAL TEMPERATURES IS POSTED FROM PORTIONS OF THE CENTRAL
AND SOUTHERN GREAT PLAINS EASTWARD THROUGH THE LOWER OHIO VALLEY AND INTERIOR
SOUTHEAST. THE ECMWF PROBABILISTIC EXTREMES TOOL (PET) BRINGS GREATER THAN 50
PERCENT CHANCES FOR TEMPERATURES TO DROP BELOW 40 DEG. F AS FAR SOUTH AS
SOUTHERN MISSISSIPPI, AND NON-TRIVIAL ODDS FOR SUBFREEZING WEATHER IS NOTED AS
FAR SOUTH AS SOUTHERN OKLAHOMA, CENTRAL ARKANSAS, AND NORTHERN ALABAMA. LATER
WEEK-2, AS SURFACE LOW PRESSURE APPROACHES THE REGION, SOUTHERLY WINDS ARE
EXPECTED TO SCOUR OUT THE COLD AIR, ENDING THE SLIGHT RISK OF MUCH BELOW NORMAL
TEMPERATURES.
FARTHER WEST, A MID-LEVEL TROUGH WILL BE WEST OF THE REGION AT THE START OF
WEEK-2, SLOWLY MOVING EASTWARD AS THE WEEK PROGRESSES. FOR AS LONG AS THE
TROUGH REMAINS WEST OF THE CONUS, MID-LEVEL SHORTWAVES EJECTED OUT OF THE MAIN
TROUGH WILL PUT THE REGION UNDER CYCLONIC MID-LEVEL FLOW WHILE ROBUST WESTERLY
WINDS DRIVE MOIST PACIFIC AIR INTO THE REGION. THESE CONDITIONS FAVOR ONE OR
MORE PERIODS OF HEAVY PRECIPITATION IN THE FAR WEST. A SLIGHT RISK FOR HEAVY
PRECIPITATION IS POSTED FOR AREAS WHERE THE GEFS AND EUROPEAN ENSEMBLE PETS
SHOW ENHANCED CHANCES FOR PRECIPITATION ABOVE THE 20TH PERCENTILE AND TOTALS
EXCEEDING ONE INCH OVER A THREE-DAY PERIOD, PRIMARILY ACROSS MOST OF CALIFORNIA
AND SOUTHERN OREGON. IN THE HIGHER ELEVATIONS, MOST OF THIS PRECIPITATION WILL
FALL AS SNOW, SO A SLIGHT RISK OF HEAVY SNOW IS POSTED FOR THE HIGHER
ELEVATIONS OF THE SOUTHERN CASCADES, NORTHERN CALIFORNIA COASTAL RANGES, AND
THE SIERRA NEVADA. THE THREAT ENDS AROUND MID-WEEK, WHEN THE MID-LEVEL TROUGH
IS FORECAST TO MOVE EAST OF THE REGION.
NO HAZARDS ARE ISSUED OVER ALASKA. A SUBSTANTIAL 500-HPA RIDGE IS EXPECTED
ACROSS MOST OF THE STATE AS WEEK-2 STARTS. LATER IN THE WEEK, THE ENSEMBLE
MEANS ALL SHOW THE RIDGE DEAMPLIFYING WHILE A MID-LEVEL TROUGH MOVES EASTWARD
TOWARD THE STATE, BECOMING ESTABLISHED NEAR THE ALEUTIANS BY THE END OF WEEK-2.
THIS PATTERN IS LIKELY TO INDUCE CYCLOGENESIS NEAR SOUTHERN ALASKA AFTER
MID-WEEK, WHICH COULD RESULT IN STIFF WINDS AND PRECIPITATION NEAR THE
SOUTH-CENTRAL AND SOUTHEASTERN PARTS OF THE STATE, BUT THE PETS SHOW VERY
LITTLE CHANCE THAT CONDITIONS WILL REACH HAZARDS THRESHOLDS.
FORECASTER: RICH TINKER
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