098
FXUS02 KWBC 010716
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
216 AM EST SAT FEB 1 2025
VALID 12Z TUE FEB 04 2025 - 12Z SAT FEB 08 2025
...ATMOSPHERIC RIVER EVENT LIKELY TO LAST INTO TUESDAY FOR
CALIFORNIA, WITH ADDITIONAL ROUNDS OF PRECIPITATION ACROSS THE
WEST THROUGH MUCH OF NEXT WEEK...
..OVERVIEW
LOW AMPLITUDE UPPER FLOW IS FORECAST ACROSS MUCH OF THE LOWER 48
NEXT WEEK, BUT A COUPLE OF FEATURES WILL CAUSE IMPACTFUL WEATHER
REGARDLESS. A SLOW MOVING UPPER LOW DRIFTING NEAR/OFFSHORE
VANCOUVER ISLAND AND THE PACIFIC NORTHWEST WILL SUSTAIN A STRONG
ATMOSPHERIC RIVER INTO CALIFORNIA AS THE PERIOD BEGINS TUESDAY AND
GRADUALLY DRIFTING SOUTH. PERSISTENT MOISTURE WILL LEAD TO
ADDITIONAL ROUNDS OF PRECIPITATION FOR MUCH OF THE INTERMOUNTAIN
WEST THROUGH MOST OF NEXT WEEK. THIS INCLUDES SNOW WITH THE
POTENTIAL FOR SIGNIFICANT SNOWFALL ACCUMULATIONS, PARTICULARLY
ACROSS THE HIGHER ELEVATIONS. FARTHER EAST, MOISTURE RETURN AND A
STRENGTHENING LOW PRESSURE SYSTEM WILL LEAD TO INCREASING
PRECIPITATION CHANCES ACROSS THE EASTERN THIRD OF THE LOWER 48 MID
TO LATE WEEK, INCLUDING POSSIBLE WINTER WEATHER FOR THE NORTHEAST.
THE QUASI-ZONAL FLOW PATTERN WITH SUBTROPICAL RIDGING NEAR THE
BAHAMAS/CUBA WILL PROMOTE ABOVE NORMAL TEMPERATURES ACROSS A
MAJORITY OF THE COUNTRY, THOUGH A CANADIAN SURFACE HIGH NUDGING
INTO THE NORTHWESTERN TO NORTH-CENTRAL U.S. SHOULD LEAD TO MUCH
BELOW NORMAL TEMPERATURES THERE WITH COLDEST ANOMALIES TUESDAY-
WEDNESDAY.
..GUIDANCE/PREDICTABILITY ASSESSMENT
WHILE MODEL AGREEMENT IN THE LARGE SCALE PATTERN IS REASONABLY
GOOD, DIFFERENCES ON SMALLER SCALES ARE YET TO BE RESOLVED AND
COULD HAVE SENSIBLE WEATHER IMPACTS. THE FIRST MODEL DIFFERENCE OF
NOTE IS THE AXIS OF THE AR INTO CALIFORNIA AT THE START OF THE
PERIOD TUESDAY, AS MODELS VARY ON THE TIMING OF THE AR'S SOUTHWARD
SHIFT. THE GFS/GEFS SUITE WAS GENERALLY ON THE SLOWER SIDE OF THE
ENVELOPE, MAINTAINING STRONG IVT INTO AREAS OF NORTHERN/CENTRAL
CALIFORNIA THAT SHOULD SEE THE HEAVIEST RAINFALL FOCUS OVER THE
WEEKEND/MONDAY, ASIDE FROM THE 18Z DETERMINISTIC GFS THAT WAS
FASTER/FARTHER SOUTH. MOST OTHER GUIDANCE SHOWED RAIN FOCUSING FROM
THE BAY AREA SOUTH (THOUGH PERHAPS FARTHER NORTH OF THE BAY'S
LATITUDE FARTHER INLAND IN THE SIERRA FOOTHILLS) TOWARD PARTS OF
SOUTHERN CALIFORNIA. HOWEVER, THE NEW 00Z ECMWF DID SHIFT NORTH
SOMEWHAT AND ALIGNS WELL WITH THE 18Z AIFS PRECIPITATION, SO THESE
MAY BE A GOOD MIDDLE GROUND SOLUTION. THE TIMING/PLACEMENT OF THE
AR AXIS WILL MATTER FOR FLOODING CONCERNS.
ENERGY FROM THE EASTERN PACIFIC UPPER LOW PERHAPS COMBINING WITH
CENTRAL CANADIAN ENERGY WILL PUSH A SHORTWAVE ACROSS THE NORTHERN
TIER WEDNESDAY-THURSDAY AND DRAW A SURFACE LOW NORTHEASTWARD INTO
THE GREAT LAKES. 12Z ECMWF GUIDANCE INCLUDING THE CONTROL AND
ENSEMBLE MEMBERS WERE STRONGEST WITH THIS LOW, WHILE SOME AI/ML
MODELS AND THE 12Z UKMET HINTED AT SIMILAR LOW PLACEMENT THOUGH
WERE NOT AS STRONG AS THE 991MB OPERATIONAL 12Z ECMWF. THE 12Z CMC
AND MANY OF ITS ENSEMBLE MEMBERS WERE A BIT EAST AND WEAKER, BUT
THE 18Z GFS WERE WEST AND WEAKER. A MIDDLE GROUND SOLUTION SIMILAR
TO THE EC PLACEMENT BUT NOT AS DEEP SEEMED TO WORK FOR THE
FORECAST. THE INCOMING 00Z GUIDANCE IS TRENDING A BIT SOUTHEAST FOR
THE LOW POSITION 12Z THURSDAY, BUT THE 00Z EC HAS ADJUSTED TO A
MORE REASONABLE CENTRAL PRESSURE.
THE EVOLUTION OF THE WESTERN UPPER TROUGH PIVOTING SOUTH AND EAST
INTO LATE WEEK CONTINUES TO BE A CHALLENGING ASPECT OF THE
FORECAST. CMC RUNS CONSISTENTLY PULL THE UPPER LOW FARTHER
WEST/OFFSHORE AND THEN END UP SLOW AS IT PIVOTS EAST. THE 00Z
GFS/ECMWF SEEM TO BE IN BETTER ALIGNMENT WITH THE TROUGH AS IT
MOVES INTO THE INTERIOR WEST. REGARDING AN ASSOCIATED SURFACE LOW,
THE 18Z GFS WAS A QUITE STRONG OUTLIER NEAR THE CA/OR BORDER EARLY
FRIDAY.
THE WPC FORECAST USED A BLEND OF DETERMINISTIC GUIDANCE FAVORING
THE EC AND GFS EARLY IN THE PERIOD. QUICKLY TRANSITIONED TO A
MOSTLY ENSEMBLE MEAN BLEND BY DAYS 6-7 GIVEN THE INCREASING SPREAD
PARTICULARLY WITH THE WESTERN TROUGH.
..WEATHER/HAZARDS HIGHLIGHTS
A STRONG AND LONG-LASTING ATMOSPHERIC RIVER TAKING AIM AT
CALIFORNIA WILL BE ONGOING AS THE PERIOD BEGINS TUESDAY. HOWEVER,
THERE IS CONSIDERABLE UNCERTAINTY IN WHEN AND HOW FAST THIS AR
SHIFTS SOUTHWARD ACROSS THE STATE, AS DISCUSSED IN THE PREVIOUS
SECTION. MAINTAINED A MARGINAL RISK IN THE DAY 4/TUESDAY ERO
BECAUSE OF LOW CONFIDENCE IN THE PLACEMENT OF HEAVY RAIN. IF THE
HEAVY RAINFALL AXIS ENDS UP ON THE NORTHERN SIDE OVER AREAS THAT
RECEIVE MULTIPLE INCHES OF RAIN DURING THE SHORT RANGE PERIOD, OR
FOCUSES OVER THE URBAN BAY AREA WITH HEAVY RATES, EITHER/BOTH
SCENARIOS COULD WARRANT A SLIGHT RISK UPGRADE IN FUTURE CYCLES.
EXPECT THE AR TO CONTINUE TO WEAKEN AS IT SHIFTS SOUTHWARD INTO
WEDNESDAY, LEADING TO REDUCED RAIN AMOUNTS. THERE IS SOME POTENTIAL
FOR RAIN TO LINGER ACROSS AREAS OF SOUTHERN CALIFORNIA OVER RECENT
BURN SCARS THAT WOULD BE SENSITIVE TO MODERATE RAIN, BUT MODEL
GUIDANCE VARIES. HAVE NO MARGINAL RISK OUTLOOKED FOR THIS AREA IN
THIS FORECAST CYCLE BECAUSE OF THE MODEL SPREAD (WITH SOME
INDICATING NO PRECIP), BUT WILL CONTINUE TO MONITOR. ADDITIONAL
ROUNDS OF COASTAL/LOW ELEVATION RAIN COULD CONTINUE INTO LATER NEXT
WEEK.
SNOW WILL ALSO BE LIKELY ACROSS MUCH OF THE INTERMOUNTAIN WEST
WITH THIS SYSTEM. INTO TUESDAY, THE HEAVIEST SNOW AMOUNTS ARE
FORECAST ACROSS THE SIERRA NEVADA INTO THE NORTHERN ROCKIES, WHILE
THE NORTHERN GREAT BASIN ALSO RECEIVES SNOW. SOME SNOW SHOULD
EXTEND INTO THE WASATCH AND CENTRAL ROCKIES FOR MIDWEEK AND BEYOND
WHILE SOME MODERATE SNOWS LAST IN THE SIERRA, CASCADES, AND
NORTHERN ROCKIES. THE PATTERN WILL ALSO PROMOTE STRONG WINDS
ESPECIALLY ON MOUNTAIN RIDGES LIKE THE SIERRA AND CENTRAL ROCKIES,
BUT SOME GUSTY CONDITIONS MAY REACH LOWER ELEVATIONS OF THE GREAT
BASIN AND FOUR CORNERS TOO.
MEANWHILE FARTHER EAST, MOISTURE IS FORECAST TO RETURN LATE
TUESDAY AND ESPECIALLY WEDNESDAY-THURSDAY IN THE EAST-CENTRAL U.S.
AS STRENGTHENING LOW PRESSURE SYSTEM AND ITS ATTENDANT WARM FRONT
LIFTS NORTHWARD. AS THIS SYSTEM EVOLVES, AN EXPANDING AREA OF
PRECIPITATION WILL DEVELOP, PARTICULARLY ACROSS THE OHIO VALLEY.
THERE MAY BE A NONZERO THREAT FOR FLOODING AS INSTABILITY COULD
REACH PRETTY FAR NORTH, BUT HELD OFF ON ANY DAY 5/WEDNESDAY ERO
BECAUSE OF UNCERTAINTY IN THE FRONTAL PLACEMENT AND THUS QPF
PLACEMENT, WHICH VARIED ACROSS THE LOWER OR UPPER OHIO VALLEY. THE
NORTHEAST AND NORTHERN MID-ATLANTIC HAVE POTENTIAL FOR WINTRY
WEATHER ON WEDNESDAY-THURSDAY WHERE COLD AIR HANGS ON.
COLDER THAN AVERAGE TEMPERATURES ARE FORECAST FOR NORTHWESTERN AND
NORTH-CENTRAL PARTS OF THE LOWER 48 NEXT WEEK. MONTANA TO THE
DAKOTAS WILL BE PARTICULARLY COLD, WITH ANOMALIES OF 20-35 DEGREES
BELOW NORMAL AND HIGHS BARELY REACHING 0F IN SOME LOCATIONS INTO
TUESDAY-WEDNESDAY. THESE AREAS WILL LIKELY REMAIN BELOW AVERAGE BUT
WITH SOME MODERATION LATER NEXT WEEK. MEANWHILE, OTHER AREAS FROM
THE FOUR CORNERS STATES THROUGH THE EAST SHOULD SEE ABOVE TO WELL
ABOVE NORMAL TEMPERATURES DURING THE PERIOD. SOME AREAS WILL LIKELY
SEE ONE OR MORE DAYS OF MIN/MAX TEMPERATURES REACHING 20 OR MORE
DEGREES ABOVE NORMAL AND SOME DAILY RECORDS ARE LIKELY TO BE SET
NEXT WEEK. SOME SLIGHT COOLING IS POSSIBLE INTO LATE WEEK BUT
TEMPERATURES SHOULD REMAIN ABOVE AVERAGE IN THE SOUTHERN TIER.
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 (QPF), EXCESSIVE RAINFALL
OUTLOOK (ERO), WINTER WEATHER OUTLOOK (WWO) PROBABILITIES, HEAT
INDICES, AND KEY MESSAGES CAN BE ACCESSED FROM:
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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