981
FXUS02 KWBC 021905
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
205 PM EST SUN FEB 2 2025
VALID 12Z WED FEB 05 2025 - 12Z SUN FEB 09 2025
...ANOTHER ROUND OF POTENTIALLY HEAVY PRECIPITATION FOR CALIFORNIA
AROUND THURSDAY...
..OVERVIEW
LATEST MODELS AND ENSEMBLES CONTINUE TO SHOW NEARLY ZONAL FLOW
ACROSS MOST OF THE LOWER 48 MID-LATE WEEK, FOLLOWED BY A TREND
TOWARD BROAD MEAN TROUGHING FROM NORTHEASTERN CANADA INTO THE
WESTERN U.S. NEXT WEEKEND AS ALASKA UPPER RIDGING REGAINS
AMPLITUDE. THIS TREND SHOULD FINALLY LEAD TO A DRIER PATTERN FOR
CALIFORNIA AFTER A SYSTEM BRINGS ANOTHER EPISODE OF SIGNIFICANT
RAIN AND SNOW AROUND THURSDAY. MOISTURE FARTHER INLAND WILL
SUPPORT PRECIPITATION ACROSS THE GREAT BASIN AND ROCKIES, WITH
SIGNIFICANT SNOW POSSIBLE FOR HIGHER ELEVATIONS. THE EASTERN HALF
OF THE COUNTRY WILL LIKELY SEE TWO EVENTS WITH THE FULL RANGE OF
PRECIPITATION TYPES, ONE AROUND WEDNESDAY-THURSDAY AND THEN ANOTHER
NEXT WEEKEND. EACH SYSTEM MAY PRODUCE SOME AREAS OF MODERATE TO
HEAVY RAIN AND/OR SNOW (POSSIBLY SEPARATED BY A WINTRY MIX)
DEPENDING ON LATITUDE AND SYSTEM DETAILS. THE SOUTHERN TIER WILL
SEE THE MOST PERSISTENT WARMTH DURING THE PERIOD. INDIVIDUAL WAVES
WILL BRIEFLY PULL WELL ABOVE NORMAL TEMPERATURES SOMEWHAT FARTHER
NORTHWARD, ESPECIALLY THE WEDNESDAY-THURSDAY ONE. THE EVOLVING
UPPER PATTERN AND CANADIAN SURFACE HIGH PRESSURE SHOULD PROMOTE
BELOW NORMAL TEMPERATURES FROM THE NORTHWEST INTO THE NORTHERN
PLAINS WITH THE COLDEST ANOMALIES CENTERED OVER MONTANA AROUND
MIDWEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MOST GUIDANCE CONTINUES TO SHOW GOOD AGREEMENT FOR THE LARGE SCALE
PATTERN EVOLUTION THROUGH THE PERIOD. HOWEVER THERE ARE ONGOING
MEANINGFUL DIFFERENCES FOR THE EASTERN U.S. SYSTEM WEDNESDAY-
THURSDAY WHILE SOLUTIONS ARE STILL WORKING OUT SPECIFICS OF THE
SYSTEM FORECAST TO REACH CALIFORNIA AROUND THURSDAY. AS EASTERN
PACIFIC/WEST COAST DYNAMICS PROGRESS INLAND LATE WEEK THROUGH THE
WEEKEND AND BROAD TROUGHING TAKES SHAPE OVER THE WEST BY NEXT
WEEKEND, TYPICAL DIFFERENCES ARISE FOR EASTERN U.S. LOW PRESSURE BY
NEXT SUNDAY WHILE SOME SPREAD DEVELOPS FOR THE CHARACTER OF FLOW
OVER THE NORTHWEST U.S. AND WESTERN CANADA.
THE WEDNESDAY-THURSDAY SYSTEM FEATURES TWO PERSISTENT CLUSTERS,
ONE CONSISTING OF THE WEAK/SUPPRESSED GFS AND MULTIPLE RUNS OF MOST
MACHINE LEARNING (ML) MODELS AND THE OTHER COMPOSED OF
ECMWF/UKMET/CMC RUNS AND TO A FAIR DEGREE THE ICON. THESE
DIFFERENCES ARE A RESULT OF FAIRLY MODEST DIFFERENCES IN STRENGTH
OF THE UPPER LEVEL SHORTWAVE. CONTINUED FAVORING OF THE WEAK SIDE
OF THE SPREAD IN THE ML GUIDANCE LEADS TO KEEPING THE FORECAST
CLOSE TO CONTINUITY BY WAY OF A COMPROMISE THAT REFLECTS A SOMEWHAT
MORE INLAND WAVE THAN THE GFS BUT WITH A DEPTH WEAKER THAN THE
OTHER MODELS.
GUIDANCE CONTINUES TO IMPROVE ITS CLUSTERING FOR THE SYSTEM
TRACKING INTO CALIFORNIA AROUND THURSDAY, THOUGH WITH SOME
CONTINUED DIFFERENCES FOR TRACK/DEPTH/TIMING. THE 06Z GFS LOOKED A
LITTLE FAST/WEAK WHILE LATEST ECMWF RUNS ARE A BIT ON THE SLOW
SIDE. THE 12Z UKMET/CMC ARE DEEPEST. AN INTERMEDIATE SOLUTION LOOKS
GOOD AT THIS TIME. AS THIS SYSTEM CONTINUES EASTWARD, THE ENSEMBLE
MEANS ACHIEVE REMARKABLY GOOD AGREEMENT NEAR THE EAST COAST BY NEXT
SUNDAY. MOST OPERATIONAL MODELS ARE FAIRLY CLOSE AS WELL BUT THE ML
MODELS SHOW A LOT MORE SPREAD, SUGGESTING POTENTIAL FOR MORE
DIVERGENCE IN FUTURE MODEL RUNS. THE FASTER TREND IN THE 12Z GFS IS
AN INITIAL EXAMPLE OF THIS. THERE WAS MINIMAL SUPPORT FOR THE
STRONGER ECMWF/UKMET, WITH THE NEW 12Z ECMWF ADJUSTING WEAKER.
THE 00Z ECMWF/CMC SUGGESTED POTENTIAL FOR SOME WESTWARD ELONGATION
OF UPPER FLOW OVER/OFFSHORE SOUTHWESTERN CANADA BY NEXT SUNDAY.
MOST ML MODELS DID NOT SUPPORT THAT IDEA AND THE NEW 12Z ECMWF/CMC
HAVE REVERTED BACK TO MORE NORTHWESTERLY FLOW AS RECOMMENDED BY
MOST OTHER MODELS/MEANS.
PREFERENCES IN THE EARLY-MIDDLE PART OF THE PERIOD LED TO STARTING
THE FORECAST WITH 60 PERCENT GFS (SPLIT BETWEEN THE 00Z AND 06Z
RUNS) WITH THE REMAINDER COMPRISING 20 PERCENT EACH OF THE 00Z
ECMWF AND CMC. THE FORECAST NEXT WEEKEND INCORPORATED 30-50 PERCENT
OF THE ENSEMBLE MEANS (06Z GEFS/00Z ECENS) WHILE REMOVING THE 00Z
GFS (STRAYED SLOW WITH THE WESTERN TROUGH). THROUGHOUT THE FORECAST
THIS APPROACH KEPT SIGNIFICANT SYSTEMS CLOSE TO CONTINUITY WHILE
AWAITING ANY MORE PRONOUNCED TRENDS.
..WEATHER/HAZARDS HIGHLIGHTS
THE LONG-LASTING ATMOSPHERIC RIVER (AR) TAKING AIM AT CALIFORNIA
WILL FINALLY WEAKEN AND MOVE SOUTH BY WEDNESDAY, LEADING TO REDUCED
RAIN AMOUNTS. LIGHT TO MODERATE SHOWERS COULD LINGER OVER SOUTHERN
CALIFORNIA, BUT THESE LOOK TO STAY UNDER ANY FLOODING THRESHOLDS
EVEN FOR THE SENSITIVE BURN SCARS IN THAT REGION. THUS THE DAY
4/WEDNESDAY ERO DOES NOT DEPICT ANY RISK AREA, BUT WILL CONTINUE
TO MONITOR GUIDANCE FOR ANY TRENDS. MEANWHILE LOWER ELEVATION
RAIN/HIGHER ELEVATION SNOW COULD REACH OREGON INTO NORTHERN
CALIFORNIA WEDNESDAY AND INCREASE IN MAGNITUDE IN CALIFORNIA ON
THURSDAY AS ANOTHER AR STRENGTHENS WITH THE APPROACH/ARRIVAL OF LOW
PRESSURE. THIS AR EVENT SHOULD BE SHORTER-LIVED THAN THE NEAR
TERM/SHORT RANGE AR, BUT SOME LOCALLY HEAVY RAIN AMOUNTS ARE
POSSIBLE OVER AREAS THAT WILL HAVE QUITE WET ANTECEDENT CONDITIONS
BY THAT TIME. LATEST GUIDANCE PROVIDES GOOD SUPPORT FOR A DAY
5/THURSDAY MARGINAL RISK AREA VERY CLOSE TO THAT PROPOSED IN THE
PREVIOUS CYCLE FOR NORTHERN/CENTRAL CALIFORNIA. GUIDANCE STILL
SUGGESTS THAT FASTER MOVEMENT OF THE AR SHOULD TEMPER AMOUNTS SOME,
PRECLUDING AN EMBEDDED SLIGHT RISK AREA FOR NOW. RISK UPGRADES MAY
STILL BE POSSIBLE AS GUIDANCE BETTER REFINES SYSTEM DETAILS IN THE
SHORTER RANGE. LIGHTER PRECIPITATION SHOULD PERSIST INTO FRIDAY
OVER CALIFORNIA BUT THEN THE PATTERN EVOLUTION WILL LIKELY SHIFT
THE BEST POTENTIAL FOR ORGANIZED (BUT FAIRLY LIGHT) ACTIVITY INTO
THE PACIFIC NORTHWEST DURING THE WEEKEND.
SNOW WILL ALSO BE LIKELY FROM HIGHER ELEVATIONS OF THE CASCADES
AND SIERRA NEVADA ACROSS MUCH OF THE INTERMOUNTAIN WEST INTO THE
NORTHERN/CENTRAL ROCKIES. THE HEAVIEST SNOW AMOUNTS ARE LIKELY IN
HIGHER ELEVATIONS, BUT THE NORTHERN GREAT BASIN MAY SEE SNOW AS
WELL. THE THURSDAY AR MAY PRODUCE A BETTER DEFINED PERIOD OF
ENHANCED SNOWFALL IN THE SIERRA NEVADA. 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, SIGNIFICANT MOISTURE (WITH PRECIPITABLE
WATER VALUES AT LEAST 2-3 STANDARD DEVIATIONS ABOVE CLIMATOLOGY)
WILL BE PRESENT BY WEDNESDAY-THURSDAY IN THE EAST-CENTRAL U.S. AS
A DEVELOPING FRONTAL WAVE SHOULD REACH THE OHIO VALLEY/GREAT LAKES
BY EARLY THURSDAY. AN EXPANDING AREA OF PRECIPITATION WILL DEVELOP,
PARTICULARLY ACROSS OR SOMEWHAT NORTH OR SOUTH OF THE OHIO VALLEY.
THERE CONTINUES TO BE SOME THREAT FOR FLOODING SOMEWHERE WITHIN
THE OHIO VALLEY/CENTRAL OR SOUTH-CENTRAL APPALACHIANS AS
INSTABILITY COULD REACH SUFFICIENTLY FAR NORTH. ALSO, DEPENDING ON
SURFACE WAVE STRENGTH (ESPECIALLY ON THE WEAKER SIDE OF THE
SPREAD) THERE COULD BE STRONG WESTERLY FLOW AT LOW LEVELS JUST
ABOVE THE SURFACE TO PROMOTE SOME TRAINING AND TERRAIN ENHANCEMENT.
THERE IS STILL SIGNIFICANT SPREAD FOR SURFACE DETAILS AND QPF
PLACEMENT WITH THIS SYSTEM. HOWEVER IT SEEMS THAT ENOUGH GUIDANCE
CLUSTERING EXISTS (INCLUDING RECENT ML MODEL RUNS AND FIRST-GUESS
ERO FIELDS) OVER AREAS OF WET ANTECEDENT CONDITIONS TO FAVOR THE
INTRODUCTION OF A MARGINAL RISK AREA CENTERED MAINLY OVER WEST
VIRGINIA AND THE EASTERN TWO-THIRDS OF KENTUCKY IN THE DAY
4/WEDNESDAY ERO.
THIS WEDNESDAY-THURSDAY SYSTEM WILL ALSO BRING THE POTENTIAL FOR
WINTRY WEATHER TO THE NORTHEAST AND NORTHERN MID-ATLANTIC. A
TRANSITION ZONE OF SLEET AND/OR FREEZING RAIN MAY EXIST BETWEEN THE
SNOW OVER FAR NORTHERN AREAS AND THE RAIN TO THE SOUTH. ENERGY
EJECTING FROM THE WEST NEXT WEEKEND WILL LIKELY PRODUCE ANOTHER
SURFACE SYSTEM REACHING THE EAST BY EARLY NEXT SUNDAY, SPREADING
SNOW ACROSS NORTHERN LATITUDES AND RAIN FARTHER SOUTH. AS WITH THE
PRIOR SYSTEM, A BAND OF WINTRY MIX MAY SEPARATE THE TWO PRIMARY
PRECIPITATION TYPES.
COLDER THAN AVERAGE TEMPERATURES ARE FORECAST FOR NORTHWESTERN AND
NORTH-CENTRAL PARTS OF THE LOWER 48 THROUGH THE PERIOD. 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 WEDNESDAY. THESE AREAS WILL LIKELY REMAIN BELOW AVERAGE BUT
WITH SOME MODERATION LATER THIS WEEK. MEANWHILE, OTHER AREAS FROM
THE FOUR CORNERS STATES THROUGH THE EAST SHOULD SEE ABOVE TO WELL
ABOVE NORMAL TEMPERATURES FOR MOST OF THE PERIOD. SOME AREAS WILL
LIKELY SEE ONE OR MORE DAYS OF MIN/MAX TEMPERATURES REACHING 20 OR
MORE DEGREES ABOVE NORMAL (PERHAPS EVEN A NARROW BAND OF PLUS 30F
OR GREATER ANOMALIES FOR MORNING LOWS OVER SOUTH-CENTRAL AREAS) AND
SOME DAILY RECORDS ARE LIKELY TO BE SET. LATEST FORECASTS CONTINUE
TO SHOW THE MOST NUMEROUS DAILY RECORDS AROUND WEDNESDAY-
THURSDAY. SOME SLIGHT COOLING IS POSSIBLE INTO FRIDAY-SATURDAY BUT
TEMPERATURES SHOULD REMAIN WELL ABOVE AVERAGE ACROSS THE SOUTHERN
TIER. UPPER TROUGHING AND A COLD FRONT WILL LIKELY FINALLY COOL THE
FOUR CORNERS TO PARTS OF THE SOUTH-CENTRAL U.S. BY NEXT SUNDAY.
RAUSCH/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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