596
FXUS02 KWBC 270656
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
256 AM EDT WED MAR 27 2024
VALID 12Z SAT MAR 30 2024 - 12Z WED APR 03 2024
...HEAVY RAIN AND HIGH ELEVATION SNOW LIKELY ACROSS CALIFORNIA,
THE GREAT BASIN/SOUTHWEST, AND INTO THE ROCKIES...
...WINTRY PRECIPITATION POSSIBLE IN THE NORTH-CENTRAL PLAINS THIS
WEEKEND AND SPREADING ACROSS THE NORTHERN TIER EARLY NEXT WEEK...
..OVERVIEW
AN UPPER LOW IS FORECAST TO BE JUST OFFSHORE OF CALIFORNIA AS THE
MEDIUM RANGE PERIOD BEGINS SATURDAY AND MOVE EASTWARD INTO THE FOUR
CORNERS REGION EARLY NEXT WEEK. THIS FEATURE AND ITS SURFACE LOW
WILL DIRECT MOISTURE IN THE FORM OF A WEAK ATMOSPHERIC RIVER INTO
CALIFORNIA AND PRODUCE HEAVY RAIN AND HIGHER ELEVATION SNOW FOR
CALIFORNIA, MUCH OF THE SOUTHWEST/GREAT BASIN, AND INTO THE
ROCKIES. FARTHER DOWNSTREAM, INCREASING MOISTURE SHOULD COMBINE
WITH NORTHERN STREAM TROUGHING TO PRODUCE LOW PRESSURE THAT TRACKS
EAST FROM THE CENTRAL PLAINS SUNDAY THROUGH THE NORTHEAST TUESDAY-
WEDNESDAY. EXPANSIVE PRECIPITATION COVERAGE IS LIKELY WITH THIS
SYSTEM, WITH SNOW AND FREEZING RAIN POSSIBLE ON ITS NORTH SIDE.
..GUIDANCE/PREDICTABILITY ASSESSMENT
RECENT MODEL AGREEMENT IS QUITE GOOD THROUGH THIS WEEKEND, WITH
THE PATTERN CONSISTING OF AN UPPER LOW COMING INTO CALIFORNIA AND A
BROAD RIDGE EAST OF IT, WITH NORTHERN TIER SHORTWAVES AND AN UPPER
LOW PULLING AWAY FROM MAINE AND THE CANADIAN MARITIMES. A MULTI-
MODEL DETERMINISTIC BLEND WORKED WELL FOR THE EARLY PART OF THE
MEDIUM RANGE PERIOD.
INTO THE WORKWEEK, THERE START TO BE MORE DIFFERENCES REGARDING
THE TIMING OF THE WEST UPPER LOW PUSHING EASTWARD AND HOW IT
RELATES TO DEEPENING NORTHERN STREAM TROUGHING IN THE NORTH-CENTRAL
U.S. TO GREAT LAKES. MODELS (OPERATIONAL AND AI/MACHINE LEARNING)
VARY WITH THE POTENTIAL PHASING OF THESE FEATURES, OR AT LEAST
OPENING UP OF THE SOUTHERN STREAM LOW, AND WHETHER THE NORTHERN OR
SOUTHERN STREAM BECOMES MORE DOMINANT IF THERE IS LESS PHASING.
MOST GUIDANCE SHOWS SOME INTERACTION OF THE STREAMS, BUT GFS RUNS
FOR EXAMPLE PHASE SOME SOUTHERN ENERGY BUT LEAVE SOME BEHIND. AT
THE SURFACE, THE TIMING OF THESE FEATURES INFLUENCES THE SURFACE
LOW POSITION AND DEPTH, WHICH IS IMPORTANT FOR PRECIPITATION
PLACEMENT AND TYPE. FORTUNATELY THE ENSEMBLE MEANS' POSITION OF THE
SURFACE LOW WAS PRETTY AGREEABLE NEAR DETROIT EARLY TUESDAY AND
MOVING NORTHEAST INTO WEDNESDAY, THOUGH THE DETERMINISTIC MODELS
VARIED. UPSTREAM, MODELS GENERALLY SHOW TROUGHING MAKING ITS WAY
TOWARD THE PACIFIC NORTHWEST BY WEDNESDAY, BUT THE 00Z CMC WAS AN
OUTLIER WITH THIS, MUCH FASTER AND OUT OF PHASE. WITHOUT MUCH
CONSENSUS AMONG GUIDANCE FOR THE LATE PERIOD, THE WPC FORECAST
QUICKLY INCREASED THE AMOUNT OF ENSEMBLE MEANS IN THE BLEND TO OVER
HALF DAY 6-7 TO MINIMIZE INDIVIDUAL MODEL DIFFERENCES.
..WEATHER/HAZARDS HIGHLIGHTS
FOR THE WESTERN U.S., AN ACTIVE AND UNSETTLED WEEKEND IS EXPECTED
AS A PERSISTENT JET ON THE SOUTHEAST SIDE OF AN UPPER LOW DIRECTS
MOISTURE INTO CALIFORNIA EASTWARD. A MODEST ATMOSPHERIC RIVER
SHOULD TAKE AIM AT CALIFORNIA SATURDAY, WITH ANOMALOUS MOISTURE
POSSIBLY REACHING ABOVE THE 95TH PERCENTILE. NOTABLE UPSLOPE FLOW
INTO THE TRANSVERSE RANGES GENERALLY PERPENDICULAR TO THE
TOPOGRAPHY MEANS HEAVY RAINFALL COULD OCCUR, SO A SLIGHT RISK IS
CONTINUED IN THE EXCESSIVE RAINFALL OUTLOOK FOR THE URBAN COASTAL
AREAS INTO UPSLOPE PORTIONS OF THE TRANSVERSE RANGE BELOW THE SNOWY
HIGHER ELEVATIONS. A MARGINAL RISK EXTENDS EAST INTO PARTS OF THE
DESERT SOUTHWEST AS MOISTURE REACHES FARTHER INLAND. HEAVY SNOW IS
LIKELY TO CONTINUE SATURDAY FOR THE SIERRA NEVADA WHILE BEGINNING
IN THE INTERMOUNTAIN WEST AS WELL. BY SUNDAY, THE ATMOSPHERIC RIVER
WILL BE PUSHING EAST INTO THE SOUTHWEST, AND A MARGINAL RISK IS IN
PLACE FOR MUCH OF ARIZONA WHERE HEAVY RAINFALL MAY OCCUR.
ADDITIONALLY, THOUGH THE ATMOSPHERIC RIVER WILL HAVE PASSED BEYOND
SOUTHERN CALIFORNIA BY SUNDAY, CONVECTIVE RAINFALL COULD OCCUR AS
STEEPER LAPSE RATES COME IN WITH THE UPPER LOW OVERHEAD. THESE
SHOWERS MAY HAVE SOME HIGHER RAIN RATES THAT COULD CAUSE SOME
ISOLATED FLOODING CONCERNS ESPECIALLY AFTER A WET COUPLE OF DAYS,
SO A MARGINAL RISK IS DELINEATED IN SOUTHERN CALIFORNIA TOO. AMPLE
MOISTURE ACROSS MUCH OF THE WEST WILL ALSO PRODUCE MODERATE TO
HEAVY SNOW IN HIGHER ELEVATIONS OVER THE WEEKEND. A DRYING TREND IS
EXPECTED IN THE WEST MONDAY-TUESDAY, EXCEPT FOR THE PACIFIC
NORTHWEST THAT COULD SEE INCREASING SUPPORT FOR PRECIPITATION BY
TUESDAY.
FARTHER EAST, SHORTWAVES GENERALLY RIDING ALONG THE NORTHERN SIDE
OF A SOUTH-CENTRAL U.S. RIDGE COULD COMBINE WITH MOISTURE TO
PRODUCE SOME RAIN OVER THE WEEKEND ACROSS THE MIDWEST AND GREAT
LAKES REGION INTO THE OHIO VALLEY AND MID-ATLANTIC. FOR THE OHIO
VALLEY IN PARTICULAR, THERE MAY BE A SWATH OF RELATIVELY HEAVY RAIN
ON SUNDAY THAT COULD TRAIN BECAUSE OF THE WEST-EAST ORIENTATION,
BUT THE PLACEMENT SEEMS TOO UNCERTAIN TO DELINEATE ANY RISK IN THE
EXCESSIVE RAINFALL OUTLOOK AT THIS POINT. THEN WIDESPREAD
PRECIPITATION IS LIKELY TO DEVELOP WITH A LOW PRESSURE SYSTEM
TRACKING EAST FROM THE CENTRAL PLAINS THROUGH THE NORTHEAST SUNDAY-
WEDNESDAY. CHANCES FOR WINTRY PRECIPITATION ARE INCREASING ACROSS
THE NORTH-CENTRAL PLAINS BY THE WEEKEND, STRETCHING INTO THE UPPER
MIDWEST AND GREAT LAKES REGION MONDAY AND HIGHER ELEVATIONS OF THE
NORTHEAST ON MONDAY OR TUESDAY. HOWEVER, THERE IS STILL
CONSIDERABLE UNCERTAINTY IN THE PLACEMENT AND AMOUNTS OF SNOW AND
ICE, SO CONTINUE TO MONITOR FORECASTS.
CHILLY TEMPERATURES LINGER ACROSS THE NORTH-CENTRAL U.S. THROUGH
MONDAY, BUT FARTHER SOUTH FROM THE CENTRAL TO SOUTHERN
PLAINS/MISSISSIPPI VALLEY, NOTABLE WARMTH IS EXPECTED INTO THE
WEEKEND AS UPPER RIDGING BUILDS. TEMPERATURES OF 10-20 DEGREES
ABOVE AVERAGE WILL BECOME WIDESPREAD, WITH HIGHS IN THE 70S
REACHING KANSAS AND MISSOURI WHILE HIGHS CLIMB INTO THE 90S IF NOT
100F IN SOUTHERN TEXAS. THE ABOVE NORMAL TEMPERATURES ARE LIKELY TO
EXPAND EAST INTO THE OHIO/TENNESSEE VALLEYS, MID-ATLANTIC, AND
SOUTHEAST BY EARLY NEXT WEEK. A COLD FRONT IS FORECAST TO FINALLY
DROP TEMPERATURES IN THE SOUTH-CENTRAL U.S. BY TUESDAY, FOCUSING
THIS WARMTH IN THE SOUTHEAST BEFORE THE FRONT PUSHES THROUGH THERE
TOO BY MIDWEEK. MEANWHILE IN THE SOUTHWEST, COOLER THAN AVERAGE
TEMPERATURES PARTICULARLY IN TERMS OF HIGHS ARE LIKELY UNDERNEATH
THE UPPER LOW. THE PACIFIC NORTHWEST COULD SEE ABOVE AVERAGE
TEMPERATURES THOUGH, ESPECIALLY INTO EARLY NEXT WEEK.
TATE
ADDITIONAL 3-7 DAY HAZARD INFORMATION CAN BE FOUND ON THE WPC
MEDIUM RANGE HAZARDS OUTLOOK CHART AT:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
WPC MEDIUM RANGE 500MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,
QUANTITATIVE PRECIPITATION FORECAST (QPF), EXCESSIVE RAINFALL
OUTLOOK (ERO), WINTER WEATHER OUTLOOK (WWO) PROBABILITIES, HEAT
INDICES, AND KEY MESSAGES CAN BE ACCESSED FROM:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST500_WBG.GIF
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST_WBG_CONUS.GIF
HTTPS://WWW.WPC.NCEP.NOAA.GOV/5KM_GRIDS/5KM_GRIDSBODY.HTML
HTTPS://WWW.WPC.NCEP.NOAA.GOV/QPF/DAY4-7.SHTML
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=ERO
HTTPS://WWW.WPC.NCEP.NOAA.GOV/WWD/PWPF_D47/PWPF_MEDR.PHP?DAY=4
HTTPS://WWW.WPC.NCEP.NOAA.GOV/HEAT_INDEX.SHTML
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=OVW
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