678
FXUS02 KWBC 131832
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
131 PM EST TUE FEB 13 2024
VALID 12Z FRI FEB 16 2024 - 12Z TUE FEB 20 2024
***MAJOR ATMOSPHERIC RIVER EVENT POSSIBLE FOR PORTIONS OF
CALIFORNIA SUNDAY INTO MONDAY WITH HEAVY RAIN AND SIERRA SNOW***
..GENERAL OVERVIEW
BROAD CYCLONIC FLOW ALOFT IS EXPECTED ACROSS THE NORTH-CENTRAL
U.S. FOR THE END OF THE WEEK, AND MAINLY ZONAL FLOW ACROSS MUCH OF
THE COUNTRY EAST OF THE ROCKIES WITH A RIDGE AXIS OVER THE
INTERMOUNTAIN WEST. THE TROUGH OVER THE GREAT LAKES AMPLIFIES
FURTHER GOING INTO THE WEEKEND, AND A SOUTHERN STREAM UPPER TROUGH
IS PROGGED TO ENTER THE GULF REGION BY SATURDAY AND INDUCE A
RELATIVELY WEAK SURFACE LOW THAT SHOULD TRACK ACROSS FLORIDA AND
THEN OFFSHORE. MEANWHILE, A BIG SURFACE HIGH FROM CANADA WILL BE
SETTLING SOUTHWARD ACROSS THE PLAINS AND THEN EVENTUALLY THE DEEP
SOUTH REGION BY LATE SUNDAY WITH COLDER TEMPERATURES ACCOMPANYING
IT. THE WEST COAST WILL LIKELY BECOME QUITE UNSETTLED GOING INTO
THE WEEKEND AND NEXT MONDAY WITH INCREASING CHANCES OF A MAJOR
ATMOSPHERIC RIVER EVENT FOR PORTIONS OF CENTRAL AND SOUTHERN
CALIFORNIA.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE MAIN FEATURES OF INTEREST IN THE GUIDANCE AT THE START OF THE
MEDIUM RANGE PERIOD (FRIDAY FEB 16) ARE A COUPLE SHORTWAVES IN AN
ENERGETIC NORTHERN STREAM FLOW PATTERN OVER THE NORTHERN TIER OF
THE EASTERN/CENTRAL U.S., A SOUTHERN STREAM SHORTWAVE OVER MEXICO
SHIFTING EASTWARD OVER THE GULF, AND A HIGHLY AMPLIFIED RIDGE OVER
THE WEST WITH A CLOSED HIGH WELL INTO CANADA. THE GUIDANCE IS IN
RELATIVELY GOOD AGREEMENT WITH THE OVERALL PLACEMENT AND EVOLUTION
OF THE MAIN FEATURES THROUGH THE MIDDLE OF THE PERIOD. ONE
NOTABLE DIFFERENCE IS A TREND IN THE GFS FOR A SLOWER AND STRONGER
NORTHERN STREAM SHORTWAVE DROPPING SOUTHWARD ACROSS THE MIDWEST
AND TOWARDS THE EAST COAST/SOUTH WHICH WOULD HELP ENHANCE
PRECIPITATION CHANCES ALONG THE GULF COAST AND INTO FLORIDA
FRIDAY/SATURDAY IN COMBINATION WITH THE SOUTHERN STREAM SYSTEM.
THIS ALSO ADDS SOME UNCERTAINTY TO WINTRY PRECIPITATION CHANCES
FROM THE GREAT LAKES TO NEW ENGLAND, WITH MUCH MORE WIDESPREAD
SNOWFALL IF THE GFS WERE RIGHT, BUT IT REMAINS THE OUTLIER FOR
NOW. THUS, OPTED TO BEGIN THE UPDATED FORECAST BLEND WITH A LEAN
TOWARDS THE 00Z ECMWF/CMC OVER THE 06Z GFS/00Z UKMET. ATTENTION
THEN TURNS TO THE WEST COAST FOR THE LATTER PART OF THE PERIOD
SUNDAY INTO EARLY NEXT WEEK AS ANOTHER ATMOSPHERIC RIVER EVENT IS
ON THE HORIZON. ALL THE GUIDANCE IS IN AGREEMENT ON AN INITIAL
SHORTWAVE PASSING THROUGH THE WEST COAST SATURDAY/SUNDAY, WITH THE
UKMET WEAKEST WITH THIS FEATURE. SUBSEQUENT HEIGHT RISES
IMMEDIATELY FOLLOW IN ITS THE WAKE AS AN INFLUX OF WARM, MOIST AIR
FROM THE PACIFIC PROCEEDS A CLOSED UPPER-LOW APPROACHING THE
COAST. ONE NOTABLE TREND IN BOTH THE MORE RECENT GFS AND ECMWF
GUIDANCE, PARTICULARLY IN THE ECMWF, IS FOR A SLOWER AND MORE
NORTHERLY APPROACH OF THE CLOSED LOW. EARLIER RUNS HAD THIS SYSTEM
ONSHORE BY TUESDAY WHEREAS IT NOW LINGERS ALONG AND OFF THE COAST.
THE CMC REMAINS A MORE DISTINCT OUTLIER WITH A MORE NORTHERLY
TRACK LIFTING TOWARDS BRITISH COLUMBIA, THOUGH A SUBSEQUENT
SHORTWAVE HELPS TO REINFORCE TROUGHING OFF THE WEST COAST THAT
BETTER ALIGNS WITH THE MEAN AXIS IN THE OTHER GUIDANCE. SHIFTED
THE FORECAST BLEND TO A MIX OF THE 06Z GFS/00Z ECMWF ALONG WITH AN
INCREASE IN THE 00Z ECENS AND GEFS MEANS WHILE REMOVING THE CMC
FOR THE LATTER HALF OF THE FORECAST PERIOD. WHILE THE SLOWER
TREND DOES BRING THE GFS/ECMWF CLOSER TO THE CMC, IT STILL REMAINS
MORE OF AN OUTLIER AND THIS KEEPS BETTER CONTINUITY WITH THE PRIOR
FORECAST GIVEN THE TREND OVERALL HAS STILL RESULTED IN A BIT OF A
SHIFT IN THE TRACK/EVOLUTION OF THE SYSTEM. THE GREATEST
CONTRIBUTION COMES FROM THE 00Z ECENS MEAN WITH A MEAN TROUGH AXIS
THAT PROVIDES THE BEST COMPROMISE BETWEEN THE GFS AND ECMWF
SOLUTIONS. DESPITE SOME OF THE SHIFTS IN THE GUIDANCE, THE
GFS/ECMWF AND GEFS/ECENS ALL STILL INDICATE A MULTI-DAY HEAVY
RAIN/SNOW EVENT FOR CALIFORNIA WITH SMALLER-SCALE TIMING/LOCATION
DIFFERENCES.
..WEATHER/HAZARDS HIGHLIGHTS
THE LOW PRESSURE SYSTEM DEVELOPING OVER THE GULF FRIDAY NIGHT HAS
GRADUALLY TRENDED SOUTH OVER THE PAST FEW DAYS OF MODEL RUNS, WITH
CONSEQUENTIAL RAINFALL MAINLY CONFINED TO THE TEXAS COASTAL REGION
AND NORTHERN FLORIDA. ALTHOUGH RAINFALL TOTALS ARE GENERALLY
EXPECTED TO BE UNDER TWO INCHES FOR BOTH OF THESE AREAS, THERE MAY
BE JUST ENOUGH HIGHER RAINFALL RATES TO WARRANT A MARGINAL RISK
AREA FOR SOUTHERN TEXAS ON FRIDAY, AND POTENTIAL EPISODES OF
TRAINING CONVECTION ACROSS NORTHERN FLORIDA ON SATURDAY TO JUSTIFY
A MARGINAL RISK THERE.
FOR THE WEST COAST REGION, MOST OF THE RAINFALL WILL LIKELY REMAIN
OFFSHORE UNTIL THE 6-12Z TIME PERIOD SATURDAY MORNING, BUT THERE
ARE SOME MODEL DIFFERENCES IN ARRIVAL OF THE HEAVIER RAINFALL, SO
THE MARGINAL RISK AREA IS MAINTAINED FOR THE DAY 4 PERIOD
FRIDAY-FRIDAY NIGHT FOR COASTAL PORTIONS OF NORTHWESTERN
CALIFORNIA. A MORE SUBSTANTIAL AXIS OF HEAVIER RAINFALL IS
BECOMING MORE LIKELY ACROSS THIS REGION AND INLAND INTO UPSLOPE
AREAS OF THE SOUTHERN CASCADES/NORTHERN SIERRA GOING INTO SATURDAY
AND SATURDAY NIGHT WITH SOME RAINFALL TOTALS APPROACHING TWO
INCHES, AND THEREFORE GREATER CONFIDENCE IN HAVING A MARGINAL RISK
FOR THE DAY 5 PERIOD. LOOKING AHEAD TO SUNDAY AND MONDAY, A MAJOR
ATMOSPHERIC RIVER EVENT IS BECOMING MORE EVIDENT IN THE LATEST
MODEL GUIDANCE AS A SLOW MOVING PACIFIC LOW APPROACHES CALIFORNIA,
WITH ANOMALOUS MOISTURE FLUX DIRECTED TOWARDS THE COASTAL TERRAIN
AND A HIGH CHANCE FOR HEAVY RAINFALL GRADUALLY SHIFTING SOUTHWARD
SUNDAY INTO MONDAY, AND POTENTIALLY CONTINUING INTO TUESDAY.
RIGHT NOW, IT APPEARS THE HIGHEST RAINFALL TOTALS LATE IN THE
FORECAST PERIOD WOULD BE MOST FAVORED FOR THE TRANSVERSE RANGES
WHERE SEVERAL INCHES OF RAINFALL IS A GOOD POSSIBILITY, SO THIS
WILL CONTINUE TO BE MONITORED CLOSELY. HEAVY SNOW IS ALSO LIKELY
FOR THE SIERRA AND NORTHERN CALIFORNIA MOUNTAINS DURING THIS TIME
PERIOD.
THE SURFACE HIGH SETTLING SOUTH FROM WESTERN CANADA WILL LIKELY BE
ACCOMPANIED WITH TEMPERATURES RUNNING ABOUT 10-20 DEGREES BELOW
MID-FEBRUARY AVERAGES ACROSS MUCH OF THE NORTH-CENTRAL U.S. ON
FRIDAY BEHIND THE COLD FRONT. HOWEVER, IT APPEARS THAT THIS
AIRMASS WILL NOT BE AS COLD AS THE ARCTIC AIR INTRUSION BACK IN
MID-JANUARY. THIS AIRMASS THEN SETTLES ACROSS THE SOUTH-CENTRAL
U.S. AND INTO THE OHIO VALLEY GOING INTO SATURDAY WITH HIGHS
GENERALLY 5-15 DEGREES BELOW AVERAGE, BUT A WARMER TREND ACROSS
THE NORTHERN PLAINS AND MIDWEST AS THE AIRMASS MODIFIES BY SUNDAY
AND INTO EARLY NEXT WEEK. IN FACT, MOST OF THE NATION SHOULD BE
BE WARMER THAN AVERAGE BY NEXT TUESDAY EAST OF THE ROCKIES,
PERHAPS UP TO 20 DEGREES ABOVE ACROSS PORTIONS OF THE CENTRAL AND
SOUTHERN PLAINS, AND SLIGHTLY BELOW AVERAGE FOR THE WEST COAST.
PUTNAM/HAMRICK
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
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page