921
FXUS02 KWBC 271845
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
245 PM 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 GUIDANCE CONTINUES TO BE IN FAIRLY GOOD AGREEMENT
THROUGH AT LEAST THE WEEKEND ON THE PATTERN CONSISTING OF AN UPPER
LOW COMING INTO CALIFORNIA, A BROAD RIDGE AHEAD OF IT ACROSS THE
SOUTHEAST, AN UPPER LOW EXITING THE NORTHEAST, AND NORTHERN STREAM
SHORTWAVES THROUGH THE FAR NORTHERN TIER. A MULTI-MODEL BLEND OF
THE DETERMINISTIC MODELS WORKED WELL FOR THE FIRST HALF OF THE
MEDIUM RANGE PERIOD.
BY MONDAY-TUESDAY, THERE ARE MORE DIFFERENCES WHICH ARISE AS THE
WESTERN LOW MOVES INLAND AND ENERGY COMBINES/INTERACTS WITH A
NORTHERN SYSTEM DROPPING INTO THE GREAT LAKES. THE DETAILS OF
POSSIBLE PHASING OF THIS SYSTEM ARE VERY UNCERTAIN, WITH THE CMC
SUGGESTING THE LEAST AMOUNT OF PHASING WITH A FASTER NORTHERN
STREAM UPPER LOW THROUGH THE GREAT LAKES/NORTHEAST TUESDAY-
WEDNESDAY. GFS AND ECMWF ARE SIMILAR ENOUGH, BUT 06Z GFS WAS
DISPLACED MORE SOUTH WITH THE UPPER LOW THAN THE ECMWF (WHICH HAD
BETTER SUPPORT FROM THE ENSEMBLE MEANS AND THE AI MODEL). 12Z GFS
CAME IN TO BETTER AGREEMENT WITH THE ECMWF. ELSEWHERE, THERE ARE
ALSO TIMING DIFFERENCES WITH THE NEXT SHORTWAVE INTO THE THE
NORTHWEST. THE LATE PERIOD BLEND HEAVILY FAVORED THE ECMWF WITH
GREATER CONTRIBUTIONS FROM THE ENSEMBLE MEANS IN AN ATTEMPT TO
MITIGATE DETAIL DIFFERENCES. THIS MAINTAINED GOOD CONTINUITY FROM
THE PREVIOUS WPC FORECAST AS WELL.
..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 AND EASTWARD. A MODEST ATMOSPHERIC RIVER
SHOULD TAKE AIM AT CALIFORNIA SATURDAY, WITH ANOMALOUS MOISTURE
POSSIBLY REACHING ABOVE THE 95TH PERCENTILE. FAVORABLE UPSLOPE
FLOW INTO THE TRANSVERSE RANGES WILL LIKELY BRING A PERIOD OF HEAVY
TO EXCESSIVE RAINFALL, 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 NORTH AND 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 SOUTHEAST 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. AS THE UPPER LOW SHIFTS INLAND SUNDAY-MONDAY, AND WITH
DEVELOPING LOW PRESSURE IN THE CENTRAL U.S., A PERIOD OF GUSTY
WINDS ARE POSSIBLE ACROSS MUCH OF NEW MEXICO AND SOUTHWEST TEXAS. 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 THERE REMAINS ENOUGH UNCERTAINTY STILL TO PRECLUDE ANY RISK IN
THE EXCESSIVE RAINFALL OUTLOOK AT THIS POINT. MORE WIDESPREAD,
POSSIBLY HEAVY, PRECIPITATION IS LIKELY MONDAY-WEDNESDAY FROM THE
OHIO/TENNESSEE VALLEYS AND EASTWARD WITH A DEVELOPING LOW PRESSURE
SYSTEM. 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.
SANTORELLI/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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