438
FXUS02 KWBC 100657
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
156 AM EST TUE JAN 10 2023
VALID 12Z FRI JAN 13 2023 - 12Z TUE JAN 17 2023
...UNSETTLED AND ACTIVE PATTERN CONTINUES FOR WESTERN U.S. WITH
FOCUS ON CALIFORNIA ATMOSPHERIC RIVERS...
..OVERVIEW AND GUIDANCE/PREDICTABILITY ASSESSMENT
THE OVERALL FLOW PATTERN OVER THE CONUS LATER THIS WEEK THROUGH
EARLY NEXT WEEK WILL REMAIN MOSTLY AMPLIFIED, BUT PROGRESSIVE. AT
THE START OF THE PERIOD (FRIDAY), A STRONG RIDGE OF HIGH PRESSURE
WILL BUILD INTO THE PLAINS WHILE DOWNSTREAM OVER THE MIDWEST, AN
ELONGATED AMPLIFIED TROUGH OR CLOSED LOW WILL BE PUSHING A STRONG
SURFACE LOW THROUGH THE LOWER GREAT LAKES AS A COLD FRONT PUSHES
OFF THE EAST COAST. VERY UNCERTAIN DEEPENING LOW PRESSURE OFF THE
MID-ATLANTIC COULD BRING SOME POTENTIAL FOR WRAPAROUND
PRECIPITATION/SNOWS TO PARTS OF MAINLY THE INTERIOR NORTHEAST.
BACK TO THE WEST, ONE ATMOSPHERIC RIVER WILL BE ONGOING ACROSS THE
NORTHWEST, BUT SHOULD LARGELY SPARE OVER SATURATED CALIFORNIA FROM
MORE RAIN, AT LEAST UNTIL THE WEEKEND WHEN THE NEXT SYSTEM PUSHES
ASHORE. A BRIEF RIDGE MAY BUILD ON SUNDAY, BUT THE NEXT IN THIS
RELENTLESS PARADE OF STORMS EARLY NEXT WEEK WILL BRING ANOTHER
ROUND OF RAIN AND HEAVY MOUNTAIN SNOWS TO CALIFORNIA.
FOR THE EASTERN U.S. SYSTEM, THERE REMAINS A LOT OF VARIABILITY IN
THE DETAILS, ESPECIALLY THIS WEEKEND AS SOUTHERN STREAM ENERGY
DRIVES ADDITIONAL SURFACE LOW CYCLOGENESIS OFF THE MID-ATLANTIC
COAST. THE DETERMINISTIC MODELS EXHIBIT QUITE A BIT OF SPREAD BOTH
WITH RESPECT TO TIMING AND PROXIMITY OF THE LOW TO THE COAST WHICH
HAS BIG IMPLICATIONS FOR POSSIBLE WRAP BACK SNOWS ACROSS THE
NORTHEAST AND POSSIBLY INTO PARTS OF THE MID-ATLANTIC. THE 18Z
(JAN 9) GFS WAS NOT USED AFTER DAY 4 BECAUSE IT WAS MUCH TOO FAST
AND WELL EAST WITH THE SYSTEM OFF THE COAST, WHILE THE BETTER BULK
OF GUIDANCE SUGGESTED THE LOW PULLS MORE NORTHWARD. A QUICK LOOK
AT THE NEW 00Z GUIDANCE COMING IN (AVAILABLE AFTER THE FORECAST
PRODUCTION TIME) SHOWS AGAIN A LOT OF VARIABILITY IN THIS SYSTEM
ONCE IT GETS OFF THE COAST SUGGESTING A VERY LOW CONFIDENCE
FORECAST AFTER DAY 4. OUT WEST, AN INITIAL SHORTWAVE INTO THE WEST
COAST WHICH DRIFTS EAST INTO THE PLAINS THIS WEEKEND AND
EVENTUALLY THE MIDWEST BY EARLY NEXT WEEK SHOWS FAIRLY GOOD
AGREEMENT IN THE MODELS, THOUGH WITH SOME MINOR TIMING/STRENGTH
DIFFERENCES. A GENERAL MODEL BLEND TOOK CARE OF THESE ISSUES. BY
MONDAY, A COMPACT CLOSED LOW LOOKS TO APPROACH THE NORTHWEST COAST
AND MOVE INLAND OVER THE INTERMOUNTAIN WEST ON TUESDAY AND THERE
ARE SOME GREATER UNCERTAINTIES NOTED HERE WITH TIMING, STRENGTH,
AND INTERACTIONS BETWEEN NORTHERN AND SOUTHERN STREAM ENERGIES.
THE WPC FORECAST FOR TONIGHT USED A GENERAL MODEL BLEND DAYS 3-4,
BUT QUICKLY TRENDED TOWARDS THE ENSEMBLE MEANS THE SECOND HALF OF
THE PERIOD IN AN ATTEMPT TO MITIGATE THE DETAIL DIFFERENCES IN THE
DETERMINISTIC MODELS. THIS GENERALLY LINED UP WELL WITH THE
PREVIOUS SHIFT CONTINUITY 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 HIGHLY AMPLIFIED PATTERN MENTIONED ABOVE WILL HELP
FOCUS THE BEST MOISTURE TRANSPORT AND RAINFALL ALONG THE IMMEDIATE
NORTHWEST CALIFORNIA COAST INTO FRIDAY, AND FURTHER UP THE PACIFIC
NORTHWEST COAST AFFECTING COASTAL REGIONS OF OREGON AND
WASHINGTON. HOWEVER, BY THIS WEEKEND, ANOTHER STRONG WEATHER
SYSTEM APPROACHES CENTRAL CALIFORNIA AND WILL BRING ANOTHER ROUND
OF WIDESPREAD PRECIPITATION. THIS SYSTEM WILL IMPACT A LARGER AREA
OF CALIFORNIA WITH EVEN MORE HEAVY RAINFALL THREATS. WORSENING
FLOODING OR DELAYED IMPROVEMENT OF ONGOING ISSUES IS POSSIBLE
AGAIN ACROSS A VERY OVER-SATURATED COASTAL CENTRAL TO SOUTHERN
CALIFORNIA WHILE THE HIGHER ELEVATIONS OF THE SIERRA SEE HEAVY
SNOWFALL. 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/LOWER MISSISSIPPI VALLEY AS WELL.
MEANWHILE, BACK TO THE EAST, MOST OF THE PRECIPITATION WILL LIKELY
HAVE EXITED THE EAST COAST BY EARLY FRIDAY, EXCEPT FOR SOME
LINGERING, AND LOCALLY HEAVY, RAINFALL ALONG THE NEW ENGLAND
COAST. ANY SNOWFALL WITH THIS SYSTEM LIKELY REMAINS CONFINED TO
HIGHER ELEVATIONS AND LOCATIONS WELL INLAND. AS A SECONDARY LOW
PRESSURE AREA DEVELOPS OFF THE NORTHEAST COAST, THERE IS SOME
POTENTIAL FOR WRAP BACK SNOWS ACROSS PARTS OF THE NORTHEAST INTO
SATURDAY, BUT THIS EVOLUTION AND THREAT IS HIGHLY UNCERTAIN AND
DEPENDENT ON EXACT PROXIMITY OF THE LOW TO THE COAST.
PARTS OF THE NORTHEAST COULD BE WELL ABOVE NORMAL TO START ON
FRIDAY, BUT SHOULD TREND BACK TO NORMAL THIS WEEKEND. GENERALLY
WARMER THAN NORMAL TEMPERATURES ARE EXPECTED ACROSS THE CENTRAL
U.S. THROUGH THE PERIOD, PARTICULARLY BY LATER THIS WEEKEND INTO
EARLY NEXT WEEK WHERE PARTS OF THE PLAINS AND INTO THE MIDWEST
COULD SEE HIGH TEMPERATURES 15 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 ACROSS THE MISSISSIPPI
VALLEY AND INTO THE MIDWEST MONDAY-TUESDAY.
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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