386
FXUS02 KWBC 311925
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
225 PM EST FRI JAN 31 2025
VALID 12Z MON FEB 03 2025 - 12Z FRI FEB 07 2025
...PROLONGED ATMOSPHERIC RIVER EVENT WILL LAST INTO NEXT WEEK FOR
CALIFORNIA...
..OVERVIEW
QUASI-ZONAL FLOW IS FORECAST ACROSS MUCH OF THE LOWER 48 NEXT
WEEK. SUBTROPICAL RIDGING NEAR THE BAHAMAS/CUBA WILL PROMOTE ABOVE
NORMAL TEMPERATURES ACROSS A MAJORITY OF THE COUNTRY, WHILE BROAD
CYCLONIC FLOW ALLOWS ARCTIC AIR TO OOZE SOUTHWARD ACROSS THE
NORTHERN TIER. MEANWHILE, A SLOW MOVING UPPER LOW DRIFTING
NEAR/OFFSHORE VANCOUVER ISLAND AND THE PACIFIC NORTHWEST WILL
SUSTAIN A PROLONGED ATMOSPHERIC RIVER ACROSS NORTHERN CALIFORNIA
MONDAY INTO TUESDAY BEFORE GRADUALLY DRIFTING SOUTH LATER IN THE
WEEK. SNOW IS LIKELY FARTHER INLAND ALONG WITH THE POTENTIAL FOR
SIGNIFICANT SNOWFALL ACCUMULATIONS, PARTICULARLY ACROSS THE HIGHER
ELEVATIONS. PERSISTENT MOISTURE WILL LIKELY LEAD TO ADDITIONAL
ROUNDS OF PRECIPITATION FOR MUCH OF THE INTERMOUNTAIN WEST THROUGH
MOST OF NEXT WEEK. FARTHER EAST, MOISTURE RETURN AND A
STRENGTHENING LOW PRESSURE SYSTEM WILL LEAD TO INCREASING
PRECIPITATION CHANCES ACROSS THE EASTERN THIRD OF THE CONTINENTAL
U.S. MID TO LAKE WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE SYNOPTIC EVOLUTION FROM MONDAY INTO TUESDAY REMAINS IN GOOD
MODEL AGREEMENT AMONGST THE LATEST GUIDANCE, WITH DETERMINISTIC
SOLUTIONS HAVING A SOLID HANDLE ON THE ONGOING PATTERN. AS SUCH, A
GENERAL MODEL BLEND FEATURING THE 00Z ECMWF/GFS/CMC WAS FAVORED
WITH MORE WEIGHT PLACED ON THE ECMWF AND THE GFS. FROM WEDNESDAY
ONWARD, THE AFOREMENTIONED DETERMINISTIC BLEND SHIFTED TO A BLEND
THAT WAS HEAVILY WEIGHTED TOWARDS THE 00Z EPS AND 06Z GEFS ENSEMBLE
MEANS AND THE 00Z ECMWF GIVEN STARK DIFFERENCES IN TIMING AND
STRENGTH OF SYNOPTIC FEATURES, PARTICULARLY ACROSS THE WESTERN HALF
OF THE CONTINENTAL U.S. THE 00Z CANADIAN AND ESPECIALLY THE 06Z
GFS WAS GIVEN MINIMAL CONSIDERATION, MAINLY DUE TO HOW THOSE RUNS
HANDLED THE EVOLUTION OF THE UPPER LOW OFF THE PACIFIC NORTHWEST,
PHASING WITH A MID-LATITUDE WAVE FARTHER WEST AND DEVELOPING A
MUCH STRONGER SURFACE LOW OFF THE COAST OF CALIFORNIA LATER IN THE
PERIOD. THAT BEING SAID, A SUBSET OF THE LATEST MACHINE LEARNING
(ML) MODELS AT LEAST HINTED AT THIS EVOLUTION BEING A POSSIBLE
OUTCOME. SO UNCERTAINTY REMAINS HIGH AND A MORE STABLE SOLUTION
ANCHORED BY THE ENSEMBLE MEANS AND THE SIMILAR DETERMINISTIC RUN OF
THE ECWMF IS A GOOD MEDIUM GROUND SOLUTION FOR NOW.
ACROSS THE EAST, MODEL SPREAD REGARDING THE POSITION OF A
STRENGTHENING LOW PRESSURE SYSTEM CONTINUES TO SHRINK, WITH MOST
GUIDANCE SHOWING A LOCATION ACROSS THE EAST-CENTRAL GREAT LAKES BY
DAY 6 ON THURSDAY. THE REMAINING UNCERTAINTY WITH THIS SYSTEM IS
NOW MOSTLY CONFINED TO THE STRENGTH OF THE LOW PRESSURE, WITH THE
LATEST 12Z UKMET NOW SUB-990MB, THE ECMWF AND CMC SUB-1000MB, AND
THE THE GFS AND ICON WERE WEAKER AND ABOVE 1000MB.
..WEATHER/HAZARDS HIGHLIGHTS
A STRONG AND LONG-LASTING ATMOSPHERIC RIVER TAKING AIM AT NORTHERN
CALIFORNIA WILL BE ONGOING AS THE PERIOD BEGINS MONDAY. AFTER A
FEW VERY WET DAYS IN A ROW, MULTI-INCH RAINFALL TOTALS WILL AGAIN
BE A CONCERN. AS A RESULT, A SLIGHT RISK REMAINS DELINEATED IN THE
DAY 4 EXCESSIVE RAINFALL OUTLOOK FROM THE COAST INTO THE SIERRA
NEVADA FOOTHILLS. DEPENDING ON HOW MUCH RAIN FALLS IN PREVIOUS DAYS
IN SIMILAR LOCATIONS, THIS MAY BE CONSIDERED A HIGHER-END SLIGHT
RISK AND FUTURE UPGRADES ARE NOT OUT OF THE QUESTION. BY TUESDAY,
THE ATMOSPHERIC RIVER FINALLY STARTS TO SHIFT SOUTHWARD AND THUS
THE HEAVIEST RAIN WILL FOLLOW SUIT ACROSS CALIFORNIA. THE DAY
5/TUESDAY ERO MAINTAINS A MARGINAL RISK ACROSS CENTRAL CALIFORNIA
GIVEN A FOCUS FOR HEAVIER RAINS THERE DURING THIS PERIOD. WHILE
THAT ASPECT OF THE FORECAST HASN'T CHANGED, DID DECIDE TO NUDGE THE
MARGINAL RISK FARTHER SOUTH ALONG THE SOUTHERN CALIFORNIA COAST,
WHICH NOW INCLUDES THE NORTHWESTERN LOS ANGELES SUBURBS. GIVEN A
MULTI-MODEL SIGNAL FOR HEAVIER RAINS OVER SENSITIVE TERRAIN FROM
RECENT BURN SCARS, CONFIDENCE WAS HIGH ENOUGH TO MAKE THIS CHANGE
ON DAY 5. IT'S ALSO POSSIBLE THAT AN EXPANSION EVEN FARTHER SOUTH
TO INCLUDE ALL OF LOS ANGELES IS WARRANTED WITH FUTURE UPDATES.
SNOW WILL ALSO BE LIKELY ACROSS MUCH OF THE INTERMOUNTAIN WEST
WITH THIS SYSTEM. EARLY NEXT WEEK, HEAVIEST SNOW AMOUNTS ARE
FORECAST ACROSS THE SIERRA NEVADA (AS SNOW LEVELS COME DOWN AFTER
THE WEEKEND) 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. 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, SOME LINGERING RAIN/SNOW IS POSSIBLE
ACROSS THE INTERIOR NORTHEAST ON MONDAY AS A FRONTAL SYSTEM EXITS.
THEN MOISTURE IS FORECAST TO RETURN FOR 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 WHERE THERE'S A
GROWING SIGNAL FOR WIDESPREAD MODERATE TO PERHAPS HEAVY RAINFALL.
THE BEST POTENTIAL FOR SOME WINTRY WEATHER WILL BE OVER THE
NORTHEAST WHERE THE COLD AIR HANGS ON THE LONGEST. PRECIPITATION
POTENTIAL THEN SHIFTS SOUTH AND EASTWARD ON FRIDAY AS A COLD FRONT
PUSHES INTO THE REGION.
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 EARLY
IN THE WEEK. 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 WILL BE POSSIBLE NEXT
WEEK. A COLD FRONT COMING THROUGH THE CENTRAL U.S. WILL CAUSE
TEMPERATURES TO MODERATE THERE BY LATE WEEK.
MILLER/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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