510
FXUS02 KWBC 160700
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
200 AM EST FRI FEB 16 2024
VALID 12Z MON FEB 19 2024 - 12Z FRI FEB 23 2024
...ATMOSPHERIC RIVER TO BRING HEAVY RAIN AND MOUNTAIN SNOW TO
CALIFORNIA EARLY NEXT WEEK...
..OVERVIEW
UPPER-LEVEL AND SURFACE LOWS OVER THE EASTERN PACIFIC EARLY NEXT
WEEK WILL STEER A STREAM OF PACIFIC MOISTURE INTO CALIFORNIA AND
PRODUCE HEAVY RAINFALL WITH FLOODING POTENTIAL AND HEAVY MOUNTAIN
SNOW. THESE FEATURES SHOULD WEAKEN BY MIDWEEK WHILE SHORTWAVE
ENERGY PUSHES EASTWARD. THIS SHORTWAVE LOOKS TO COMBINE WITH
NORTHERN STREAM ENERGY AND HELP FORM A LOW PRESSURE/FRONTAL SYSTEM
IN THE CENTRAL U.S. THAT PUSHES INTO THE EASTERN U.S. BY THE
LATTER PART OF NEXT WEEK, SPREADING RAIN AND NORTHERN TIER SNOW TO
SOME AREAS. AHEAD OF THE UPPER TROUGH AND COLD FRONT, TEMPERATURES
ARE FORECAST TO BE ABOVE AVERAGE IN THE CENTRAL U.S. EARLY-MID
NEXT WEEK AND SHIFTING INTO THE EASTERN U.S. MID-LATE NEXT WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
AS THE MEDIUM RANGE PERIOD BEGINS MONDAY, MODEL AGREEMENT IS
INITIALLY QUITE GOOD IN SHOWING A CLOSED UPPER LOW ACROSS THE
EASTERN PACIFIC, RIDGING ATOP THE INTERMOUNTAIN WEST, AND LOW
AMPLITUDE TROUGHING WITH EMBEDDED SHORTWAVES ACROSS THE CENTRAL
AND EASTERN CONUS. BUT 12/18Z MODELS START TO DIVERGE BY TUESDAY
WITH THE POSITIONING OF THE UPPER LOW AND THUS THE SURFACE LOW
OVER THE EASTERN PACIFIC. GFS RUNS TOOK A SOUTHWARD DIVE,
ESPECIALLY IN THE 18Z RUN, WHILE THE NON-NCEP GUIDANCE SHIFTED IT
NORTH WITH A LITTLE MORE PHASING IN THE MID-UPPER LEVELS. THE 12Z
CMC IN PARTICULAR MIGRATED THE LOW NORTHWESTWARD, WHICH WAS NOT
FAVORED. THE ECMWF SEEMED BEST ALIGNED WITH THE ENSEMBLE MEANS.
FORTUNATELY THE INCOMING 00Z MODEL SUITE SEEMS TO SHOW SOMEWHAT
BETTER AGREEMENT WITH THE POSITIONING OF THESE UPPER AND SURFACE
LOW FEATURES.
BY WEDNESDAY-THURSDAY THERE ARE SOME MODEL DIFFERENCES IN THE
PACIFIC NORTHWEST/BRITISH COLUMBIA REGION WITH THE POTENTIAL FOR
SHORTWAVE ENERGY TO DISRUPT A ROUND OF RIDGING AHEAD OF ANOTHER
UPPER LOW TRACKING THROUGH THE PACIFIC. HOWEVER, FARTHER EAST
MODELS SHOW REASONABLE AGREEMENT ON THE LARGE SCALE WITH THE
PHASING OF THE NORTHERN AND SOUTHERN STREAMS TO FORM TROUGHING,
THOUGH THE SMALLER SCALE DETAILS ARE YET TO BE DETERMINED, AND
THESE DIFFERENCES DO AFFECT THE POSITIONING OF THE DEVELOPING
CENTRAL TO EASTERN U.S. SURFACE LOW AND FRONTS.
THE WPC FORECAST WAS BASED ON A BLEND OF MAINLY DETERMINISTIC
GUIDANCE OF THE 12/18Z GFS AND 12Z ECMWF/CMC/UKMET EARLY ON, BUT
ELIMINATED THE CMC AND UKMET BY DAY 5 WHILE REDUCING OTHER
DETERMINISTIC MODELS IN FAVOR OF THE EC AND GEFS ENSEMBLE MEANS.
THE MEANS REACHED HALF OF THE BLEND DAY 5 AND MORE BY DAYS 6-7 AS
SPREAD INCREASED.
..WEATHER/HAZARDS HIGHLIGHTS
AN ATMOSPHERIC RIVER WITH AMPLE PACIFIC MOISTURE WILL CAUSE ROUNDS
OF PRECIPITATION THAT WILL BE HEAVY ACROSS CALIFORNIA INTO MONDAY
AND TUESDAY. FOR COASTAL/LOWER ELEVATION AREAS, THE DAY 4 AND 5
EXCESSIVE RAINFALL OUTLOOKS INDICATE SLIGHT RISKS ACROSS CENTRAL
TO SOUTHERN PARTS OF CALIFORNIA FOR THE FLOODING POTENTIAL.
RAINFALL RATES IN THIS REGION HAVE THE POTENTIAL TO REACH 0.5-1"
PER HOUR, WITH OVER 1"/HOUR RATES POSSIBLE, AND SOME AREAS ARE
LIKELY STILL SENSITIVE FROM AR EVENTS EARLY IN THE MONTH/COOL
SEASON. THE SLIGHT RISK MONDAY IS LIKELY MORE ON THE HIGHER END OF
THE PROBABILITY RANGE FOR A SLIGHT ACROSS THE LOS ANGELES METRO,
WHILE TUESDAY'S SLIGHT IS LOWER-END AS THE EXPECTED RAINFALL
DECREASES, WITH SOME SHIFT SOUTH AS WELL. BROADER MARGINAL RISKS
COVER MUCH OF THE STATE FARTHER NORTH AND EAST, UNTIL THE HIGHER
ELEVATIONS OF THE SIERRA NEVADA ARE REACHED WHERE THE
PRECIPITATION WILL BE IN THE FORM OF HEAVY SNOW, POSSIBLY REACHING
MULTIPLE FEET. FARTHER EAST, MODERATE SNOW IS LIKELY IN THE HIGHER
ELEVATIONS OF THE INTERMOUNTAIN WEST AND ROCKIES.
PRECIPITATION CHANCES ARE LIKELY TO INCREASE IN THE OHIO VALLEY TO
GREAT LAKES WEDNESDAY-THURSDAY UNDER THE INFLUENCE OF A COUPLE OF
LOW PRESSURE/FRONTAL SYSTEMS. PRECIPITATION IS MOST LIKELY TO BE
RAIN EXCEPT IN THE FAR NORTHERN TIER. THE PRECIPITATION SHOULD
REACH THE EAST THURSDAY-FRIDAY WITH SOME SNOW POSSIBLE IN PARTS OF
THE NORTHEAST. CONTINUE TO MONITOR FORECASTS AS THE DETAILS ARE
YET TO BE DETERMINED.
UPPER RIDGING TRAVERSING THE INTERIOR WEST TO THE CENTRAL AND THEN
EASTERN U.S. THROUGH NEXT WEEK WILL PROMOTE ABOVE NORMAL
TEMPERATURES IN THOSE AREAS. TEMPERATURES AROUND 10-20F ABOVE
NORMAL WILL RISE TO 15-25F ABOVE NORMAL ACROSS THE PLAINS TO
MIDWEST ON TUESDAY AND WEDNESDAY. HIGHS ARE FORECAST TO BE INTO
THE 80S FOR PARTS OF TEXAS WITH 70S STRETCHING INTO THE SOUTHEAST.
TEMPERATURES SHOULD MODERATE CLOSER TO NORMAL AFTER THE COLD FRONT
COMES THROUGH BUT MAY STILL REMAIN ABOVE NORMAL IN THE CENTRAL
U.S., ESPECIALLY FOR LOWS. BY THURSDAY THE ABOVE NORMAL
TEMPERATURES ARE FORECAST TO PUSH INTO THE EAST WITH WARM
ANOMALIES OF 10-20F, ALSO MODERATING THERE BY FRIDAY. MEANWHILE
THE WEST COAST SHOULD BE NEAR AVERAGE FOR HIGHS BUT SOMEWHAT ABOVE
NORMAL FOR LOWS.
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, EXCESSIVE RAINFALL OUTLOOK,
WINTER WEATHER OUTLOOK PROBABILITIES, HEAT INDICES AND KEY
MESSAGES ARE AT:
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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