406
FXUS02 KWBC 110649
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
148 AM EST WED JAN 11 2023
VALID 12Z SAT JAN 14 2023 - 12Z WED JAN 18 2023
...UNSETTLED AND ACTIVE PATTERN CONTINUES FOR WESTERN U.S. WITH
FOCUS ON CALIFORNIA ATMOSPHERIC RIVERS...
..OVERVIEW AND GUIDANCE/PREDICTABILITY ASSESSMENT
THE LATEST GUIDANCE CONTINUES TO SHOW GOOD AGREEMENT ON THE
OVERALL FLOW PATTERN ACROSS THE U.S. STAYING FAIRLY AMPLIFIED
DURING THE MEDIUM RANGE PERIOD (SATURDAY-WEDNESDAY). THIS FEATURES
AN INITIAL TROUGH EXITING THE EAST COAST THIS WEEKEND WITH
SECONDARY LOW PRESSURE DEVELOPMENT EXPECTED TO BE WELL OFF THE
COAST WITH LITTLE IMPACT TO PARTS OF THE NORTHEAST. OUT WEST, THE
PARADE OF UPPER SHORTWAVES INTO THE WEST WILL CONTINUE WITH THESE
SYSTEMS EXPECTED TO MOVE INLAND ACROSS THE SOUTHWEST WITH LIKELY
DOWNSTREAM CYCLOGENESIS ACROSS THE CENTRAL PLAINS. THIS DEEPENED
LOW SHOULD TRACK GENERALLY INTO THE MIDWEST AND THEN THE GREAT
LAKES EARLY NEXT WEEK. THE NEXT SYSTEM INTO THE WEST, POSSIBLY
MORE AMPLIFIED THAN THE FIRST, IS ALSO EXPECTED TO SPAWN ANOTHER
AREA OF LOW PRESSURE IN THE CENTRAL PLAINS BY NEXT WEDNESDAY.
MOST OF THE GUIDANCE DIFFERENCES RIGHT NOW RESIDE IN THE TIMING
AND DETAILS OF THESE INDIVIDUAL SHORTWAVES INTO THE WEST COAST,
AND CONTINUE TO SHOW A LOT OF RUN TO RUN VARIABILITY, LENDING TO
LOW CONFIDENCE FORECASTS. THERE IS GOOD AGREEMENT WITH THE FIRST
SHORTWAVE INTO CALIFORNIA THIS WEEKEND, BUT QUESTIONS AS IT MOVES
DOWNSTREAM ON STRENGTH. THE NEXT SYSTEM MOVES INTO THE WEST AROUND
MONDAY, WITH GREATER QUESTIONS ON PLACEMENT AND TIMING OF LOW
PRESSURE ALONG THE COAST AND INLAND. THROUGH THE 12Z/18Z GUIDANCE
(YESTERDAY...JAN 10), THE ECMWF WAS THE MOST AMPLIFIED COMING
INLAND AND CONSEQUENTLY FARTHER SOUTH WITH THE SURFACE LOW. THE
GFS AND CMC, ALONG WITH THE ENSEMBLE MEANS, SUGGEST THIS SYSTEM IS
DISPLACED A LITTLE FARTHER NORTH. THESE KINDS OF DIFFERENCES DO
HAVE BIG IMPLICATIONS FOR LATE PERIOD RAINFALL INTO THE NORTHWEST
AND CALIFORNIA. LOTS OF TIMING QUESTIONS AS THE SHORTWAVE
PROGRESSES INTO THE SOUTHWEST/SOUTHERN PLAINS NEXT
TUESDAY-WEDNESDAY, AS WELL AS A LOT OF UNCERTAINTY SURROUNDING
ANOTHER POSSIBLE SHORTWAVE TOWARDS THE NORTHWEST NEXT WEDNESDAY. A
QUICK LOOK AT THE NEW 00Z GUIDANCE (AVAILABLE AFTER FORECAST
GENERATION TIME) SHOWS GENERALLY THE SAME PATTERN/ISSUES AS
DESCRIBED ABOVE AND PROVIDE LITTLE IN THE WAY OF ANY KIND OF
TRENDS. THE WPC FORECAST USED A EQUAL BLEND OF THE DETERMINISTIC
SOLUTIONS THROUGH DAY 5/MONDAY WHICH HELPED TO SMOOTH OUT SOME OF
THE SMALLER SCALE DETAILS. FOR DAYS 6 AND 7, TRENDED MORE TOWARDS
THE MOSTLY AGREEABLE ENSEMBLE MEANS TO HELP MITIGATE SOME OF THE
LARGER SCALE DIFFERENCES. THIS APPROACH MAINTAINED GOOD CONTINUITY
WITH THE PREVIOUS WPC FORECAST AS WELL.
..WEATHER/HAZARD HIGHLIGHTS
UNSETTLED AND ACTIVE WEATHER IS EXPECTED TO CONTINUE ACROSS
PORTIONS OF THE WEST AS A SERIES OF ATMOSPHERIC RIVERS MOVE
ONSHORE. THE FIRST IN THIS SERIES OF EXTENDED RANGE STORMS WILL
ARRIVE THIS WEEKEND, AND IS EXPECTED TO BRING ANOTHER ROUND OF
WIDESPREAD HEAVY RAIN ACROSS NORTHERN AND COASTAL CALIFORNIA WITH
HEAVY SNOWFALL INTO THE SIERRA MOUNTAINS AS WELL. WORSENING
FLOODING OR DELAYED IMPROVEMENT OF ONGOING ISSUES IS POSSIBLE
ACROSS THIS VERY OVER-SATURATED COASTAL CENTRAL TO SOUTHERN
CALIFORNIA. AS THE ENERGY MOVES INLAND ON SUNDAY, RAIN AND HIGHER
ELEVATION SNOWS ARE POSSIBLE IN THE SOUTHWEST, AND EVENTUALLY
RETURN FLOW OUT OF THE GULF OF MEXICO MAY INCREASE PRECIPITATION
CHANCES INTO THE PLAINS/MIDWEST AS WELL. AN ALMOST CONSTANT FETCH
OF ONSHORE MOISTURE INTO THE NORTHWEST AND PARTS OF THE CALIFORNIA
THROUGH THE PERIOD WILL KEEP RAINFALL, THOUGH LESS INTENSE, IN THE
FORECAST EARLY NEXT WEEK BEFORE ANOTHER POSSIBLE HEAVIER STORM
ARRIVES AROUND NEXT TUESDAY. IN THE EAST, PRECIPITATION AHEAD OF
THE TROUGH SHOULD BE WELL OFF THE COAST BY THIS WEEKEND, EXCEPT
FOR SOME POSSIBLY LIGHT WRAP BACK SNOWS ACROSS NORTHERN NEW
ENGLAND WHICH IS DEPENDENT ON PROXIMITY OF SECONDARY LOW
DEVELOPMENT TO THE COAST.
ABOVE NORMAL TEMPERATURES WILL MOVE EAST WITH TIME FROM THE
CENTRAL U.S. THIS WEEKEND INTO THE MIDWEST AND EVENTUALLY THE EAST
EARLY NEXT WEEK. THE GREATEST ANOMALIES SHOULD FOCUS ACROSS THE
DEEP SOUTH INTO THE MIDWEST WITH DAYTIME HIGHS 10 TO 20 DEGREES F
ABOVE NORMAL. EVEN MORE IMPRESSIVE WILL BE THE VERY WARM NIGHTTIME
LOWS, WITH READINGS 20 TO 25 DEGREES F ABOVE NORMAL GENERALLY
ACROSS THE SAME REGION FROM SUNDAY ONWARD. DAYTIME HIGHS ACROSS
THE WEST AND SOUTHWEST SHOULD BE NEAR OR BELOW NORMAL AMIDST
PLENTY OF CLOUDS AND RAINY CONDITIONS.
SANTORELLI
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, EXPERIMENTAL EXCESSIVE RAINFALL
OUTLOOK, WINTER WEATHER OUTLOOK PROBABILITIES AND HEAT INDICES 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
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