644
FXUS02 KWBC 301900
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
200 PM EST THU JAN 30 2025
VALID 12Z SUN FEB 02 2025 - 12Z THU FEB 06 2025
...PROLONGED ATMOSPHERIC RIVER EVENT EXPECTED FOR THE PACIFIC
NORTHWEST THIS WEEKEND INTO NEXT WEEK...
..OVERVIEW
GUIDANCE SHOWS FAIRLY ZONAL MEAN FLOW ALOFT ACROSS MUCH OF THE
CONTINENTAL U.S. DURING SUNDAY-THURSDAY. CYCLONIC FLOW OVER CANADA
WILL HELP TO PUSH COLD AIR INTO THE NORTHERN ROCKIES/PLAINS AND
TEMPERATURES WILL BE BELOW NORMAL ALONG THE WEST COAST, BUT
OTHERWISE THE LOW-AMPLITUDE FLOW AND POTENTIAL INFLUENCE OF A
BAHAMAS/CUBA UPPER RIDGE ON THE FAR SOUTHERN TIER AT TIMES WILL
SUPPORT ABOVE NORMAL TEMPERATURES OVER A MAJORITY OF THE COUNTRY.
MEANWHILE A SLOW MOVING UPPER LEVEL LOW DRIFTING NEAR/OFFSHORE
VANCOUVER ISLAND AND THE PACIFIC NORTHWEST ALONG WITH THE FAST
FLOW/SHORTWAVES TO THE SOUTH WILL SUSTAIN A PROLONGED ATMOSPHERIC
RIVER EVENT ACROSS NORTHERN CALIFORNIA AND VICINITY WITH POTENTIAL
FOR HEAVY RAINFALL. MOISTURE STREAMING INLAND WILL PRODUCE SNOW
OVER THE NORTHERN HALF OF THE ROCKIES. FARTHER EAST, SOUTHERN
CANADA/NORTHERN TIER LOW PRESSURE SHOULD SPREAD AN AREA OF SNOW
ACROSS THE UPPER GREAT LAKES AND NORTHEAST SUNDAY INTO MONDAY AND
A LINGERING FRONT WITH EMBEDDED DEVELOPING WAVE IN THE EAST MAY
PRODUCE ANOTHER AREA OF PRECIPITATION AROUND WEDNESDAY-THURSDAY.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODELS AND ENSEMBLES CONTINUE TO SHOW FAIRLY GOOD AGREEMENT FOR
THE LARGE SCALE PATTERN BUT DIFFER WITH VARIOUS DETAILS. OF
PARTICULAR INTEREST ARE THE SPECIFICS OF THE UPPER LOW AND
TROUGHING TO THE SOUTH (AFFECTING THE EXACT FOCUS OF THE WEST
COAST ATMOSPHERIC RIVER) PLUS EVENTUAL EJECTION OF SOME OVERALL
TROUGH ENERGY, AND THE RELATIVE INFLUENCE OF CANADIAN CYCLONIC
FLOW VERSUS LOWER LATITUDE RIDGING (DETERMINING THE POSITION OF
THE SURFACE FRONT OVER THE EASTERN HALF OF THE COUNTRY). THERE ARE
ALSO SOME LINGERING DIFFERENCES WITH LOW PRESSURE TRACKING ACROSS
THE NORTHERN TIER/SOUTHERN CANADA AROUND THE START OF NEXT WEEK.
LATEST SPREAD FOR THE NORTHERN TIER/SOUTHERN CANADA SYSTEM
RECOMMENDS AN INTERMEDIATE SOLUTION AT THIS TIME. LATEST MACHINE
LEARNING (ML) MODELS ARE GENERALLY IN THE FASTER HALF OF THE
DYNAMICAL GUIDANCE SPREAD AND THEIR AVERAGE DEPTH IS A LITTLE
WEAKER THAN THE DYNAMICAL RUNS BY EARLY MONDAY. LOWER
PREDICTABILITY SHORTWAVE DETAILS WILL STILL TAKE SOME TIME TO BE
RESOLVED.
ML MODELS SUPPORT THE MAJORITY GUIDANCE CLUSTER THAT HAS THE WEST
COAST UPPER LOW EVENTUALLY DRIFTING A LITTLE OFFSHORE VANCOUVER
ISLAND AND THE PACIFIC NORTHWEST, POSSIBLY EVEN GETTING A LITTLE
FARTHER WEST THAN CONSENSUS BY NEXT THURSDAY. AMONG LATEST
SOLUTIONS, THE 12Z UKMET BECOMES FARTHEST SOUTH BY WEDNESDAY WHILE
THE CMC HAS BEEN MOST INCONSISTENT--BRINGING IT MORE INLAND THAN
OTHER GUIDANCE IN THE 00Z RUN (THOUGH NOW NEARLY MATCHED BY THE NEW
12Z ECMWF) BUT HOLDING IT FARTHEST OFFSHORE IN THE NEW 12Z RUN.
PREFER AN EMPHASIS ON RECENT GFS/ECMWF RUNS AND THEIR MEANS
OVERALL, THOUGH WITH SOME ASPECTS OF OTHER GUIDANCE AS WELL FOR QPF
PURPOSES.
FARTHER EAST, TRENDS OVER THE PAST COUPLE DAYS HAVE GENERALLY BEEN
TOWARD A LITTLE MORE INFLUENCE OF LOWER LATITUDE UPPER RIDGING
WHICH HOLDS THE EASTERN U.S. SURFACE FRONT SOMEWHAT FARTHER
NORTHWARD BY NEXT TUESDAY. GFS RUNS HAVE STILL BEEN LEANING ON THE
SOUTHERN SIDE OF THE SPREAD FOR THE FRONT AT THAT TIME BUT ML
MODELS HAVE REFLECTED THE TRENDS OF MOST OTHER GUIDANCE. ON THE
OTHER HAND, CMC RUNS HAVE BEEN A NORTHERN EXTREME. TOWARD NEXT
THURSDAY MOST GUIDANCE IS SIGNALING THAT EJECTING TROUGH ENERGY
UPSTREAM SHOULD DEVELOP A SURFACE WAVE WHOSE TRACK COULD BE
ANYWHERE BETWEEN THE OHIO VALLEY/MID-ATLANTIC AND SOUTHERN CANADA.
AN OPERATIONAL MODEL/ENSEMBLE MEAN BLEND PROVIDES A REASONABLE
STARTING POINT FOR DEPICTING THIS POTENTIAL SYSTEM.
..WEATHER/HAZARDS HIGHLIGHTS
THE MOST IMPACTFUL WEATHER EVENT DURING THIS FORECAST PERIOD WILL
BE THE PROLONGED ATMOSPHERIC RIVER THAT WILL BRING EXTENDED
PERIODS OF MODERATE TO HEAVY RAINFALL FOR NORTHERN INTO CENTRAL
CALIFORNIA. AN ANOMALOUS MOISTURE FLUX ORIENTED NEARLY ORTHOGONAL
TO THE TERRAIN AHEAD OF A SLOW MOVING FRONT WILL LIKELY SUPPORT
MULTI-INCH RAINFALL TOTALS DURING THE DAY 4 PERIOD SUNDAY, MERITING
A SLIGHT RISK AREA IN THE EXCESSIVE RAINFALL OUTLOOK OVER PARTS OF
NORTHERN CALIFORNIA FROM THE COAST TO THE FOOTHILLS OF THE
NORTHERN SIERRA NEVADA. THIS PATTERN CONTINUES INTO MONDAY (DAY 5)
OVER A SIMILAR OR SLIGHTLY FARTHER SOUTH LATITUDE. AFTER MONDAY,
ADDITIONAL HEAVY RAINFALL IS LIKELY ACROSS THE STATE AS THE
MOISTURE MOVES VERY SLOWLY SOUTHWARD BUT WITH THE FOCUS POSSIBLY
BECOMING A LITTLE BROADER/LESS FOCUSED. GUIDANCE CONTINUES TO SHOW
MEANINGFUL VARIATIONS IN THE EXACT LOCATION OF BEST MOISTURE FOCUS,
SO CONTINUE TO MONITOR FORECASTS FOR ADJUSTMENTS IN RAINFALL AND
ERO PRODUCTS.
AS FOR OTHER ASPECTS OF THE FORECAST OVER THE WEST, A BROADER AREA
OF RAIN AND HIGHER ELEVATION SNOW WILL EXTEND FROM THE PACIFIC
NORTHWEST INTO THE NORTHERN HALF OF THE ROCKIES, WITH THE NORTH-
CENTRAL INTERMOUNTAIN WEST AND ROCKIES LIKELY SEEING THE HEAVIEST
SNOW. EARLY NEXT WEEK THE PACIFIC NORTHWEST MAY BE COLD ENOUGH TO
SUPPORT SOME SNOW REACHING DOWN TO FAIRLY LOW ELEVATIONS. OVER
CALIFORNIA, SNOW LEVELS WILL INITIALLY BE RATHER HIGH BUT THEY
SHOULD FALL A LITTLE TOWARDS MIDWEEK WITH HEAVY SNOW BECOMING MORE
LIKELY FOR THE HIGHER TERRAIN OF THE SIERRA NEVADA. THE OVERALL
PATTERN MAY PRODUCE AREAS OF STRONG WINDS OVER SOME AREAS FROM THE
WEST COAST THROUGH THE ROCKIES.
THERE WILL BE TWO SYSTEMS OF NOTE OVER THE EAST. SOUTHERN
CANADA/NORTHERN TIER LOW PRESSURE WILL BRING AN AREA OF LIGHT TO
MODERATE SNOW FROM THE NORTHERN GREAT LAKES THROUGH THE NORTHEAST
SUNDAY INTO EARLY MONDAY. THE TRAILING COLD FRONT WILL STILL OVER
THE EASTERN HALF OF THE COUNTRY BY TUESDAY-WEDNESDAY, WITH A
POTENTIAL EMBEDDED WAVE DEVELOPING AND LIFTING NORTHEASTWARD BY
THURSDAY. THESE FEATURES MAY SUPPORT AN EXPANDING AREA OF
PRECIPITATION OF VARYING TYPES BY WEDNESDAY-THURSDAY. BEST
POTENTIAL FOR SOME WINTRY WEATHER WILL BE OVER THE NORTHEAST, WHILE
RAINFALL OF VARYING INTENSITY WILL BE POSSIBLE FARTHER SOUTH.
THE PRIMARY FOCUS FOR COLD WEATHER DURING THE PERIOD WILL BE OVER
THE NORTHERN TIER, ESPECIALLY MONTANA AND THE DAKOTAS. COLDEST
ANOMALIES OF 20-35 DEGREES BELOW NORMAL ARE LIKELY DURING THE FIRST
HALF OF THE WEEK. THE NORTHWEST WILL BE BELOW NORMAL AS WELL, BUT
WITH LESS EXTREME ANOMALIES, WHILE THE NORTHEAST SHOULD START OUT
CHILLY EARLY SUNDAY BUT WITH NEAR TO ABOVE NORMAL READINGS
THEREAFTER. 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 WILL BE POSSIBLE NEXT WEEK.
RAUSCH/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 (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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