979
FXUS02 KWBC 140659
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
157 AM EST WED FEB 14 2024
VALID 12Z SAT FEB 17 2024 - 12Z WED FEB 21 2024
***MULTIPLE ATMOSPHERIC RIVER EVENTS POSSIBLE FOR PORTIONS OF
CALIFORNIA WITH HEAVY RAIN AND SIERRA SNOW***
..GENERAL OVERVIEW
BROAD CYCLONIC FLOW ALOFT IS EXPECTED ACROSS THE NORTH-CENTRAL
U.S. FOR THE WEEKEND, AND AN AMPLIFIED UPPER RIDGE AXIS ACROSS THE
ROCKIES AND INTERMOUNTAIN WEST. THE TROUGH OVER THE GREAT LAKES
GRADUALLY LIFTS NORTH INTO CANADA GOING INTO EARLY NEXT WEEK AND A
SUBSEQUENT ABATEMENT IN THE COLDER TEMPERATURES, AND A SOUTHERN
STREAM UPPER TROUGH IS PROGGED TO CROSS THE GULF ON SATURDAY AND
INDUCE A RELATIVELY WEAK SURFACE LOW THAT SHOULD TRACK ACROSS
FLORIDA AND THEN OFFSHORE. MEANWHILE, A BIG SURFACE HIGH FROM
CANADA WILL INITIALLY BE SITUATED ACROSS THE SOUTHERN PLAINS AND
THE DEEP SOUTH REGION THIS WEEKEND, WITH CHILLY CONDITIONS ON
SATURDAY FOLLOWED BY A WARMING TREND. THE WEST COAST WILL LIKELY
BECOME QUITE UNSETTLED GOING INTO THE WEEKEND AND ESPECIALLY INTO
EARLY NEXT WEEK WITH INCREASING CHANCES OF MULTIPLE ATMOSPHERIC
RIVER EVENTS FOR PORTIONS OF CENTRAL AND SOUTHERN CALIFORNIA.
..GUIDANCE/PREDICTABILITY ASSESSMENT
OVERALL, THE 00Z MODEL GUIDANCE SUITE IS IN DECENT SYNOPTIC SCALE
AGREEMENT TO BEGIN THE PERIOD ON SATURDAY. AT THE TIME OF
FRONTS/PRESSURES COMPILATION, THE 12Z CMC WAS OUT OF PHASE ACROSS
PORTIONS OF THE CENTRAL AND EASTERN U.S. AND DID NOT FIT THE
BETTER CLUSTERED GFS/ECMWF/UKMET/ICON SOLUTIONS AND THE ENSEMBLE
MEANS, SO A NON-CMC BLEND WAS USED AS A STARTING POINT IN THE
FORECAST PROCESS. HOWEVER, THE 00Z CMC IS IN BETTER AGREEMENT
OVERALL COMPARED TO ITS PREVIOUS RUN. GOING INTO EARLY NEXT WEEK,
THE FRONTS/PRESSURES WERE PRIMARILY DERIVED FROM A
GFS/ECMWF/PREVIOUS WPC BLEND WITH STEADILY INCREASING
CONTRIBUTIONS FROM THE ENSEMBLE MEANS, WHICH ACCOUNTED FOR ABOUT
40-50% OF THE FORECAST BLEND GOING INTO EARLY-MID NEXT WEEK DUE TO
THE GREATER MESOSCALE DIFFERENCES.
..WEATHER/HAZARDS HIGHLIGHTS
THE LOW PRESSURE SYSTEM DEVELOPING OVER THE GULF SATURDAY MORNING
HAS MAINTAINED SOME CONTINUITY NOW OVER THE PAST FEW MODEL RUNS,
WITH CONSEQUENTIAL RAINFALL MAINLY CONFINED TO NORTHERN FLORIDA ON
SATURDAY AND THEN SOUTH FLORIDA ON SUNDAY. ALTHOUGH RAINFALL
TOTALS ARE GENERALLY EXPECTED TO BE ON THE ORDER OF 1 TO 2.5
INCHES, THERE MAY BE POTENTIAL EPISODES OF TRAINING CONVECTION
ACROSS NORTHERN FLORIDA ON SATURDAY TO JUSTIFY A MARGINAL RISK
THERE. SOME SLOWER MOVING CELLS MAY DEVELOP ACROSS THE METRO
AREAS OF PALM BEACH, BROWARD, AND MIAMI-DADE COUNTIES, AND THIS
MAY LOCALLY PRODUCE ENOUGH HEAVY RAINFALL ON SUNDAY TO WARRANT A
MARGINAL RISK AREA FOR DAY 5.
A MORE SUBSTANTIAL AXIS OF HEAVIER RAINFALL IS BECOMING MORE
LIKELY ACROSS THE NORTHERN HALF OF CALIFORNIA GOING INTO SATURDAY
AND EXTENDING INLAND ACROSS UPSLOPE AREAS OF THE NORTHERN SIERRA,
WITH SOME RAINFALL TOTALS APPROACHING TWO INCHES, AND THEREFORE
ENOUGH CONFIDENCE IN HAVING A MARGINAL RISK FOR THE DAY 4 PERIOD.
THE AXIS OF HIGHEST PW ANOMALIES WILL LIKELY BE ORIENTED TOWARDS
THE HIGHER TERRAIN OF THE COASTAL MOUNTAIN RANGES BETWEEN SAN
FRANCISCO AND EUREKA, WHERE A SLIGHT RISK OF EXCESSIVE RAINFALL IS
PLANNED FOR THE DAY 4 PERIOD. LOOKING AHEAD TO SUNDAY, ANOTHER
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
OF CENTRAL CALIFORNIA. IT APPEARS THE HIGHEST RAINFALL TOTALS
WILL BE ON TUESDAY 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 ACROSS THE SOUTHERN TIER STATES
THIS WEEKEND WILL LIKELY BE ACCOMPANIED WITH TEMPERATURES RUNNING
ABOUT 5-15 DEGREES BELOW MID-FEBRUARY AVERAGES FROM TEXAS TO THE
OHIO VALLEY ON SATURDAY BEHIND THE COLD FRONT. A WARMER TREND
COMMENCES ACROSS THE 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 THE MIDDLE OF NEXT WEEK EAST
OF THE ROCKIES, PERHAPS UP TO 20 DEGREES ABOVE AVERAGE ACROSS
PORTIONS OF THE CENTRAL AND SOUTHERN PLAINS, AND SLIGHTLY BELOW
AVERAGE FOR THE WEST COAST WHERE CLOUDS AND PRECIPITATION WILL
KEEP TEMPERATURES IN CHECK.
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