122
FXUS02 KWBC 311859
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
158 PM EST WED JAN 31 2024
VALID 12Z SAT FEB 03 2024 - 12Z WED FEB 07 2024
...SYSTEM EMERGING FROM THE WEST TO SPREAD SIGNIFICANT
PRECIPITATION ACROSS THE NORTHERN-CENTRAL ROCKIES PLUS THE PLAINS
AND GULF COAST/SOUTHEAST THROUGH THE WEEKEND...
...ANOTHER STRONG WEATHER SYSTEM INCREASINGLY LIKELY TO IMPACT
CALIFORNIA BY EARLY NEXT WEEK...
..OVERVIEW
LATEST GUIDANCE CONTINUES TO SHOW AN ACTIVE WEATHER PATTERN FOR
THE WEST FOR THE FIRST HALF OF NEXT WEEK. INITIAL UPPER TROUGHING
NEAR THE PACIFIC NORTHWEST SHOULD INTERACT WITH AN INCOMING
SOUTHERN STREAM SYSTEM TO PRODUCE A LARGE SCALE POSITIVELY TILTED
MEAN TROUGH THAT WILL PROMOTE A STRONG SOUTHWESTERLY FLOW OF
MOISTURE INTO THE WEST OVER A MULTI-DAY TIME FRAME, WITH HEAVIEST
RAIN/MOUNTAIN SNOW LIKELY TO FOCUS OVER CALIFORNIA. MEANWHILE AN
UPPER LOW TRACKING FROM THE SOUTHERN HALF OF THE ROCKIES THROUGH
THE SOUTHEAST DURING THE WEEKEND AND EARLY NEXT WEEK WILL SUPPORT
A STRONG SURFACE SYSTEM AND A HEAVY RAINFALL THREAT ACROSS THE
SOUTHERN TIER. ADDITIONALLY, A STRONG UPPER RIDGE CENTERED OVER
THE UPPER MIDWEST/GREAT LAKES FROM THE WEEKEND INTO MONDAY SHOULD
MERGE WITH ANOTHER RIDGE BUILDING IN ACROSS THE SOUTHWEST TO YIELD
A SOUTHERN PLAINS INTO NORTHEAST RIDGE BY NEXT WEDNESDAY. THESE
RIDGES WILL SUPPORT WELL ABOVE NORMAL TEMPERATURES OVER MUCH OF
THE CENTRAL U.S. THE RIDGE THAT EVENTUALLY REACHES THE NORTHEAST
BY WEDNESDAY WILL DISPLACE A CANADIAN MARITIMES UPPER TROUGH/LOW
THAT WILL PROMOTE NORTHWESTERLY FLOW ALOFT OVER THE NORTHEAST FROM
THE WEEKEND INTO EARLY NEXT WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODEL GUIDANCE CONTINUES TO SHOW REASONABLE AGREEMENT IN THE LARGE
SCALE PATTERN DESCRIBED ABOVE, WHILE DIFFERENCES IN THE DETAILS
PERSIST. THE SOUTHERN TIER UPPER LOW AND ASSOCIATED SURFACE LOWS
SHOWED TYPICAL LEVELS OF SPREAD THROUGH EARLY NEXT WEEK. GENERALLY
FAVORED THE 06Z GFS AND 00Z ECMWF THAT WERE WELL CLUSTERED, WHILE
THE 00Z CMC WAS DISPLACED A LITTLE WEST/SLOW. BY TUESDAY-WEDNESDAY
THE LOW TRACK BECOMES MORE QUESTIONABLE AS THE DETERMINISTIC ECMWF
RUNS LINGER FARTHER SOUTHWEST IN THE WESTERN ATLANTIC COMPARED TO
OTHER GUIDANCE. THE 00Z EC ENSEMBLE MEAN (AND THE SIMILAR PLACED
CMC MEAN) MAY BE A GOOD MIDDLE GROUND BETWEEN THE SLOWER
DETERMINISTIC EC AND THE FASTER GFS/GEFS SOLUTIONS. SOME OF THE
TYPICALLY HIGHER PERFORMING EC-BASED AI MODELS ARE SOMEWHAT
SIMILAR TO THE EC MEAN AS WELL.
FARTHER WEST, THE UPPER TROUGHING AND EMBEDDED UPPER LOW AND
SURFACE LOWS ARE A CONCERN ACROSS THE EASTERN PACIFIC TO WEST
COAST. THE 12Z CMC HAS FINALLY ALIGNED BETTER WITH OTHER GUIDANCE
ALOFT AFTER SEVERAL RUNS OF SHOWING LESS PHASING BETWEEN THE
PACIFIC ENERGY DROPPING SOUTH AND PACIFIC ENERGY TRACKING EAST
EARLY NEXT WEEK, DISPLACING THE CENTROID OF THE UPPER LOW TO THE
SOUTHWEST. HOWEVER, THE 12Z CMC SURFACE LOW IS FARTHER WEST OF
CONSENSUS AND IS STILL SLOW TO BRING PRECIPITATION INTO
CALIFORNIA, SO A GFS/ECMWF AND ENSEMBLE MEAN BLEND IS STILL
PREFERRED. BY TUESDAY-WEDNESDAY, NORTHERN STREAM ENERGY ARISING
FROM THE FAR NORTHERN PACIFIC/ALASKA SHOWS MODEL SPREAD AND COULD
IMPACT POSITIONING OF THE LARGER TROUGH/LOW. THE DIFFERENCES ALOFT
LEAD TO SURFACE POSSIBILITIES FROM A FAIRLY PROGRESSIVE LEADING
LOW AFTER SUNDAY-MONDAY TO PERSISTENCE OF THIS LOW OFF THE WEST
COAST (WHETHER MEANDERING IN PLACE OR EVEN DROPPING SOUTHWARD)
THROUGH WEDNESDAY. ANY FRONTAL WAVES OFFER ADDITIONAL UNCERTAINTY.
GIVEN THESE CONSIDERATIONS, THE WPC FORECAST USED A DETERMINISTIC
BLEND OF GUIDANCE FAVORING THE 06Z GFS/00Z ECMWF EARLY.
INCORPORATED SOME OF THE GEFS AND EC ENSEMBLE MEANS BY DAY 5 AND
RAMPED UP THEIR PERCENTAGES FAIRLY QUICKLY GIVEN THE INCREASING
SPREAD BY LATE PERIOD. THIS MAINTAINED REASONABLE CONTINUITY FROM
THE PREVIOUS SHIFT.
..WEATHER/HAZARDS HIGHLIGHTS
UPPER TROUGH ENERGY OVER THE WEST/ROCKIES TO BEGIN THE WEEKEND
WILL PRODUCE A BROAD AREA OF MODERATE TO HEAVY SNOW OVER THE
NORTHERN AND CENTRAL ROCKIES ON SATURDAY WITH LIGHTER ACTIVITY
LINGERING INTO SUNDAY. PRECIPITATION OVER THE HIGH PLAINS MAY FALL
AS RAIN AND/OR SNOW DEPENDING ON LOCATION, WITH RELATIVELY BETTER
POTENTIAL FOR SOME MEANINGFUL SNOW OVER PARTS OF THE NORTHERN AND
CENTRAL HIGH PLAINS. THE UPPER LOW BREAKING OFF FROM THE SOUTHERN
PART OF THE TROUGH ALONG WITH THE ASSOCIATED SURFACE SYSTEM MAY
LEAD TO A PERIOD OF EASTERLY PRECIPITATION ENHANCEMENT ALONG THE
CENTRAL ROCKIES AS WELL. RAIN NORTH AND THUNDERSTORMS FARTHER
SOUTH SHOULD ALREADY BE IN PROGRESS FROM THE CENTRAL PLAINS
SOUTH-SOUTHEAST TO THE GULF COAST AS OF EARLY SATURDAY, WITH
EASTWARD PROGRESSION OF THE SYSTEM OVER THE WEEKEND SPREADING SOME
HEAVY RAINFALL ACROSS THE GULF COAST STATES AND SOUTHEAST. THE DAY
4 EXCESSIVE RAINFALL OUTLOOK VALID SATURDAY-SATURDAY NIGHT
MAINTAINS A SLIGHT RISK AREA ALONG THE CENTRAL GULF COAST WHERE
THE BEST INSTABILITY AND ENSEMBLE PROBABILITIES OF HIGHEST
RAINFALL TOTALS OVERLAP, WITH OPERATIONAL MODEL RUNS SHOWING HEAVY
RAINFALL POTENTIAL AS WELL, LIKELY IN THE FORM OF A SQUALL LINE
MARCHING EASTWARD WITH HIGH RAINFALL RATES. MODEL TRENDS FOR THE
PAST COUPLE OF CYCLES HAVE SHOWN LINGERING CONVECTION BACK INTO
SOUTHEAST TEXAS, NECESSITATING SOME WESTWARD EXPANSION OF THE
SLIGHT RISK. THE SURROUNDING MARGINAL RISK AREA EXTENDS
NORTH-NORTHWEST INTO SOUTHWESTERN MISSOURI AND EASTERN KANSAS, FOR
SOMEWHAT LOWER RAINFALL TOTALS BUT WITH GROUND CONDITIONS STARTING
OUT ON THE DAMP SIDE. WE CONTINUE TO MONITOR A POSSIBLE SECONDARY
MAXIMUM OF HEAVY RAINFALL AROUND TEXARKANA, WHERE A TONGUE OF
INSTABILITY STRETCHES AND THE FRONT/SURFACE LOW TRACK COULD BE
SLOWER MOVING FOR MULTIPLE HOURS OF CONVECTION, WHICH COULD
PRODUCE FLOODING ISSUES CONSIDERING THOSE WET ANTECEDENT
CONDITIONS. MODELS CONTINUE TO WAFFLE WITH PLACEMENT AND OVERALL
THE MODEL RAINFALL AMOUNTS HAVE TRENDED SOMEWHAT DOWN, SO
CONTINUED TO HOLD OFF ON A NORTHERN EXPANSION OF THE SLIGHT RISK.
HEAVY RAINFALL POTENTIAL SHOULD CONTINUE EASTWARD INTO THE
SOUTHEAST/CAROLINAS BY SUNDAY-MONDAY. THE DAY 5 ERO CONTINUES TO
DEPICT A BROAD MARGINAL RISK AREA OVER THE SOUTHEAST, WITH CURRENT
SIGNALS SOMEWHAT DIFFUSE FOR WHERE BEST RAINFALL FOCUS WILL BE,
PRECLUDING INTRODUCTION OF ANY EMBEDDED SLIGHT RISK. ONE REGION OF
POTENTIALLY GREATER INTEREST MAY BE OVER PARTS OF GEORGIA/SOUTH
CAROLINA WHICH WILL BE JUST TO THE NORTH OF ONE OR MORE FRONTS
THAT COULD HELP TO FOCUS HEAVIER RAINFALL, WITH AT LEAST THE ECMWF
SHOWING SOME INSTABILITY CROSSING THIS AREA AS WELL. FARTHER
SOUTH, EXPANDED THIS MARGINAL RISK TO INCLUDE SOUTHERN FLORIDA AS
SOME GUIDANCE HAS A FOCUS FOR CONVECTION THERE OVER SOME SENSITIVE
URBAN AREAS. SOME HEAVY RAINFALL COULD LINGER INTO MONDAY OVER OR
NEAR THE CAROLINAS, WHILE DEPARTURE OF THE SURFACE SYSTEM MAY LEAD
TO A PERIOD OF STRONG WINDS ALONG/OFFSHORE THE SOUTHEAST COAST.
WHILE SPECIFICS ARE STILL NOT UNANIMOUS IN THE GUIDANCE, THE
MAJORITY OF GUIDANCE SUGGESTS STEADILY INCREASING CONFIDENCE IN A
MULTI-DAY ATMOSPHERIC RIVER EVENT AFFECTING CALIFORNIA FROM AROUND
SUNDAY INTO THE NEXT WORKWEEK. A POTENTIALLY STRONG SYSTEM THAT
MAY PRODUCE GUSTY WINDS SHOULD TRACK TO A POSITION JUST OFFSHORE
NORTHERN CALIFORNIA BY EARLY MONDAY, BRINGING THE LEADING SURGE OF
MOISTURE. SLOW MOVEMENT OF THE SUPPORTING UPPER TROUGH MAY PRODUCE
A CONTINUED SOUTHWESTERLY FLOW OF MOISTURE INTO THE REGION THROUGH
AT LEAST TUESDAY (WITH PRECIPITATION ENHANCEMENT POSSIBLY
GENERATED BY ONE OR MORE TRAILING FRONTAL WAVES) WHILE THE LEADING
EDGE OF THE MOISTURE BEGINS TO PUSH INTO THE SOUTHWEST/GREAT
BASIN. FOLLOWING THE GUIDANCE MAJORITY THAT BRINGS IN MOISTURE
EARLIER THAN CMC RUNS, THE DAY 5 ERO INDICATES A SLIGHT RISK
ACROSS MUCH OF COASTAL CALIFORNIA. THE SLIGHT WAS EXPANDED
NORTHWARD FROM THE PREVIOUS ISSUANCE, AS MODEL GUIDANCE GENERALLY
HAS MODERATE TO HEAVY RAIN ARRIVING IN NORTHERN CALIFORNIA FIRST
FOR A LONGER DURATION OF RAIN SUNDAY THERE, THOUGH PERHAPS WITH
WEAKER RAIN RATES THAN FARTHER SOUTH. THE MARGINAL RISK EXPANDS
FARTHER INLAND, BUT OF COURSE NOT TO HIGHER ELEVATION AREAS OF THE
SIERRA NEVADA WHERE HEAVY SNOW IS LIKELY. PRECIPITATION SHOULD
PERSIST ESPECIALLY FOR SOUTHERN PORTIONS OF CALIFORNIA WELL INTO
THE WORKWEEK. THIS EVENT STILL APPEARS LIKELY TO PRODUCE GREATER
LOW ELEVATION RAIN/MOUNTAIN SNOW TOTALS THAN THE PRECEDING EVENT
DUE TO A LONGER DURATION OF SOUTHWESTERLY FLOW ALOFT AND A MORE
DIRECT CONNECTION WITH LOWER LATITUDE MOISTURE. CONTINUE TO
MONITOR FORECASTS FOR THIS TIME FRAME AS SPECIFICS GRADUALLY
BECOME BETTER RESOLVED.
THE UPPER RIDGE INITIALLY OVER AND NEAR THE UPPER MIDWEST AND THEN
BECOMING ALIGNED FROM FROM THE SOUTHERN PLAINS THROUGH GREAT LAKES
WILL SUPPORT A BROAD AREA OF UNSEASONABLY WARM TEMPERATURES OVER
THE CENTRAL U.S. THROUGH THE PERIOD. CONTINUE TO EXPECT THE
GREATEST ANOMALIES TO BE OVER/NEAR THE UPPER MIDWEST WHERE MORNING
LOWS MAY BE AS WARM AS 25-35F ABOVE NORMAL AND EXCEEDING DAILY
RECORDS FOR MULTIPLE DAYS, WHILE DAYTIME HIGHS SHOULD BE A LITTLE
LESS EXTREME, UP TO 15-25F ABOVE NORMAL. IN CONTRAST, THE
SOUTHWEST U.S./CALIFORNIA SHOULD SEE COOL DAYTIME HIGHS THROUGH
THE PERIOD WITH SOME LOCALIZED AREAS UP TO 10-15F BELOW NORMAL.
CLOUDS/PRECIPITATION OVER THE WEST SHOULD KEEP MORNING LOWS NEAR
TO ABOVE NORMAL. FLORIDA SHOULD SEE A COUPLE COOL DAYS WITH HIGHS
5-10F BELOW NORMAL BY TUESDAY-WEDNESDAY AFTER PASSAGE OF THE
SOUTHEAST SYSTEM.
TATE/RAUSCH
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
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