651
FXUS02 KWBC 271859
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
158 PM EST SAT JAN 27 2024
VALID 12Z TUE JAN 30 2024 - 12Z SAT FEB 3 2024
...LARGE SCALE SYSTEM LIKELY TO SPREAD PRECIPITATION ACROSS MUCH
OF THE WEST NEXT WEEK WITH HIGHEST TOTALS EXPECTED OVER
CALIFORNIA...
19Z UPDATE: THE MAIN FEATURE OF INTEREST NEXT WEEK CONTINUES TO
BE THE AMPLIFYING UPPER TROUGH ACROSS THE WESTERN U.S. AND THE
PATTERN CHANGE THAT WILL COMMENCE WITH IT. THE 12Z MODEL GUIDANCE
SUITE IS GENERALLY IN VERY GOOD AGREEMENT ON AN ATMOSPHERIC RIVER
EVENT ACROSS THE WEST COAST STARTING WEDNESDAY AND THEN MOISTURE
MOVING INLAND ACROSS THE INTERMOUNTAIN WEST AND ROCKIES LATER IN
THE WEEK. HOWEVER, THE 12Z CMC CONTINUES TO BE A MORE PROGRESSIVE
SOLUTION WITH ARRIVAL OF RAIN AND MOUNTAIN SNOW ACROSS CALIFORNIA
COMPARED TO THE UKMET/GFS/ECMWF AND THE ENSEMBLE MEANS, SO A
NON-CMC BLEND WAS INCORPORATED BEYOND TUESDAY TO ACCOUNT FOR THIS.
BY NEXT SATURDAY, THE LOW IS EXPECTED TO REACH THE WESTERN HIGH
PLAINS AND BEGIN TAPPING INTO GULF OF MEXICO MOISTURE THAT WILL
FUEL INCREASING COVERAGE OF SHOWERS AND THUNDERSTORMS, SOME OF
WHICH COULD BE STRONG TO SEVERE ACROSS PORTIONS OF TEXAS.
OVERALL, THE ECMWF IS GENERALLY A LITTLE FASTER IN BRINGING THE
SURFACE LOW OUT ACROSS THE SOUTHERN PLAINS SATURDAY NIGHT, AND THE
CMC SLOWER, WHEREAS THE ENSEMBLE MEANS SUGGEST THE LOW SHOULD BE
NEAR THE TEXAS PANHANDLE BY 00Z SUNDAY. ACROSS THE EASTERN U.S.,
MODEL DIFFERENCES ARE MORE EVIDENT WITH SHORTWAVES AND CLOSED LOWS
TO THE EAST OF THE UPPER RIDGE AXIS. THE CMC IS MUCH FASTER AND
WEAKER WITH THE TROUGH OVER NEW ENGLAND BY NEXT FRIDAY, WHEREAS
THE ECMWF SUPPORTS A CLOSED LOW OVER THE OHIO VALLEY AND THE GFS
SHOWS AN ELONGATED TROUGH AXIS OVER THE GREAT LAKES. TAKING THESE
FACTORS INTO ACCOUNT, THE UPDATED WPC FRONTS/PRESSURES FORECAST
WAS PRIMARILY DERIVED FROM A GFS/ECMWF/ECENS/GEFS BLEND ALONG WITH
ABOUT 20% OF PREVIOUS WPC CONTINUITY FOR THE SECOND HALF OF THE
FORECAST PERIOD, WITH GRADUALLY INCREASING PERCENTAGES OF THE
MEANS BY FRIDAY AND SATURDAY. THE PREVIOUS FORECAST DISCUSSION IS
APPENDED BELOW FOR REFERENCE. /HAMRICK
--------------------------
..OVERVIEW
LATEST MODELS AND ENSEMBLES GENERALLY SUGGEST THAT THE LARGE SCALE
PATTERN WILL TAKE ON AN INCREASINGLY BLOCKY LOOK WITH TIME. THIS
EVOLUTION WILL FEATURE AN INITIAL ROCKIES UPPER RIDGE SETTLING
OVER THE CENTRAL U.S. AND EXTENDING NORTH INTO CANADA WHILE A
PACIFIC UPPER TROUGH REACHING THE WEST EVENTUALLY BECOMES
NEGATIVELY TILTED AND EAST COAST MEAN TROUGHING WILL COMPRISE ONE
SHORTWAVE PASSING THROUGH AROUND MIDWEEK AND THEN REINFORCING
ENERGY FARTHER NORTH TOWARD THE END OF THE WEEK. CONTINUE TO
EXPECT STRONG AND MOIST SOUTHERLY FLOW AHEAD OF THE PACIFIC TROUGH
TO SUPPORT AN ATMOSPHERIC RIVER EVENT WHOSE FOCUS SHOULD PROGRESS
SOUTHWARD ALONG THE WEST COAST OVER THE COURSE OF THE WEEK. A
BROAD SHIELD OF RAIN/SNOW WILL LIKELY EXTEND FARTHER INLAND OVER
THE WEST AFTER WEDNESDAY AND RAIN SHOULD DEVELOP OVER PARTS OF THE
PLAINS BY FRIDAY OR SATURDAY. OVER THE EAST, AN AREA OF LIGHT TO
PERHAPS MODERATE RAIN/SNOW SHOULD ACCOMPANY A MIDWEEK SYSTEM WHILE
THE NORTHEAST COULD SEE SOME SNOW LATE IN THE WEEK AS REINFORCING
ENERGY ALOFT SETTLES INTO THE MEAN TROUGH POSITION.
..GUIDANCE/PREDICTABILITY ASSESSMENT
WITH RESPECT TO THE LARGER SCALE ASPECTS OF THE FORECAST, GUIDANCE
HAS GENERALLY BEEN MORE AGREEABLE AND CONSISTENT WITH THE INCOMING
WESTERN U.S. UPPER TROUGH VERSUS THE TWO PRIMARY FEATURES
COMPRISING THE EAST COAST MEAN TROUGH. CONTINUE TO FAVOR A
CONSENSUS/AVERAGE FORECAST OVER THE WEST WHERE THERE IS A
PERSISTENT SPREAD FOR TIMING OF THE LEADING HEIGHT FALLS (GFS
SLOW, CMC FAST) WITH NO PRONOUNCED CLUSTERING THUS FAR AND
DIFFERENCES WELL WITHIN TYPICAL GUIDANCE ERROR AT THAT TIME FRAME.
WHAT TRENDS EXIST OVER THE PAST DAY ARE JUST SLIGHTLY SLOWER AS
OF MIDWEEK. THE NEW 00Z GFS HAS ADDED A NEW WRINKLE IN THE
SURFACE FORECAST OFF THE PACIFIC NORTHWEST COAST, EJECTING THE
LEADING DEEP SURFACE LOW NORTH OF OTHER GUIDANCE AND THEN TRACKING
A TRAILING WAVE CLOSER TO THE COAST THAN OTHER GUIDANCE ON
WEDNESDAY. MODEL/ENSEMBLE CONSENSUS AGREES UPON THE INCREASINGLY
NEGATIVE TILT OF THE UPPER TROUGH BY FRIDAY-SATURDAY WITH TYPICAL
DETAIL UNCERTAINTIES.
OVER THE EAST, THE LEADING SYSTEM STILL EXHIBITS SIGNIFICANT
SPREAD BUT WITH RECENT TRENDS GRAVITATING MORE TOWARD THE
SLOWER/CLOSED UPPER DYNAMICS INITIALLY ADVERTISED BY GFS RUNS.
THE NEW 00Z UKMET IS A FAST/OPEN EXTREME WHILE THE NEW 00Z ECMWF
HAS ADJUSTED A LITTLE FASTER THAN THE 00Z GFS/GEFS/CMC AND 12Z
ECENS MAJORITY. THEN GUIDANCE HAS BEEN SHOWING A LOT OF SPREAD
AND VARIABILITY WITH UPSTREAM ENERGY LIKELY TO AMPLIFY INTO THE
NORTHEAST AND VICINITY TOWARD THE END OF THE WEEK. THROUGH THE
12Z/18Z CYCLES, SOLUTIONS VARIED AMONG OPEN TROUGHING OR A CLOSED
LOW WITH MOST NOT NOTABLY DEEP. IN CONTRAST, 12Z
ECMWF-INITIALIZED MACHINE LEARNING MODELS GENERALLY SUGGESTED THE
POTENTIAL FOR THIS TROUGHING TO DEVELOP UP TO A DAY EARLIER AND IN
DEEPER FASHION (AND MOST WITH A CLOSED LOW) THAN THE GFS/ECMWF AND
THEIR MEANS (WITH THE CMC/CMCENS A LITTLE FARTHER EAST). NEW 00Z
MODEL TRENDS SEEM TO BE SUPPORTING A DEEPER UPPER LOW OVER OR NEAR
THE NORTHEAST.
GUIDANCE COMPARISONS LED TO UPDATING THE FORECAST WITH A 12Z/18Z
OPERATIONAL MODEL COMPOSITE EARLY WITH GRADUALLY INCREASING INPUT
FROM THE 18Z GEFS/12Z ECMWF MEANS TO YIELD A HALF MODEL/HALF MEAN
MIX BY THE END OF THE PERIOD NEXT SATURDAY.
..WEATHER/HAZARDS HIGHLIGHTS
GUIDANCE HAS MADE ONLY INCREMENTAL ADJUSTMENTS FOR THE BROAD AREA
OF PRECIPITATION EXPECTED TO SPREAD ACROSS THE WEST FROM TUESDAY
ONWARD. INITIAL APPROACH OF THE PACIFIC UPPER TROUGH
TUESDAY-THURSDAY WILL SUPPORT A STRONG SOUTHERLY FLOW OF ENHANCED
MOISTURE AND LIKELY BRING A PERIOD OF SIGNIFICANT RAINFALL AND
HIGH ELEVATION SNOW TO THE WEST COAST STATES. DURING THE PERIOD
COVERED BY THE DAYS 4-5 EXCESSIVE RAINFALL OUTLOOKS (EARLY TUESDAY
THROUGH WEDNESDAY NIGHT), EXPECT THE HEAVIEST RAINFALL TO REACH
NORTHERN CALIFORNIA AROUND WEDNESDAY WHEN A SLIGHT RISK AREA
REMAINS IN THE UPDATED DAY 5 OUTLOOK, WITH ONLY MINIMAL
ADJUSTMENTS NEEDED. THIS OUTLOOK AREA CORRESPONDS TO THE BEST
OVERLAP OF GUIDANCE SIGNALS WITHIN PERSISTENT TIMING SPREAD (GFS
SLOWEST, CMC FASTEST) THAT AFFECTS THE SOUTHWARD EXTENT OF
PRECIPITATION. THE SURROUNDING MARGINAL RISK AREA REFLECTS AN
INTERMEDIATE TIMING OF SIGNIFICANT BUT LESS EXTREME RAINFALL
POTENTIAL. THE AVERAGE OF GUIDANCE HAS NUDGED A LITTLE SLOWER
WITH THE ARRIVAL OF THIS MOISTURE LATE IN THE DAY 4 PERIOD. THIS
REDUCES CONFIDENCE IN THE ESTABLISHED DAY 4 MARGINAL RISK AREA,
BUT FOR NOW IT IS BEING MAINTAINED FOR THE UPDATED OUTLOOK. THERE
IS A MARGINAL RISK AREA OVER THE OLYMPIC PENINSULA IN WESTERN
WASHINGTON ON BOTH DAYS. MOISTURE ANOMALIES AND THEIR PERSISTENCE
ARE BETTER DURING DAY 4 BUT GUIDANCE STILL SHOWS SOME RELATIVE QPF
MAXIMA INTO DAY 5 WITH EXISTING WET CONDITIONS. FROM THURSDAY
ONWARD, MOISTURE WILL PUSH FARTHER SOUTH THROUGH CALIFORNIA WITH
SOME HEAVY PRECIPITATION, AS WELL AS THROUGH MUCH OF THE INTERIOR
WEST/SOUTHWEST/ROCKIES WITH RAIN AND HIGHER ELEVATION SNOW BEING
ENHANCED OVER SOUTHWARD FACING TERRAIN. EXPECT SOME RAIN OF
VARYING INTENSITY TO DEVELOP OVER PORTIONS OF THE CENTRAL U.S. BY
FRIDAY OR SATURDAY.
THE SYSTEM CROSSING THE EAST TUESDAY-WEDNESDAY WILL PRODUCE AN
AREA OF PRECIPITATION (EXACT RAIN/SNOW LINE SOMEWHAT UNCERTAIN AT
THE MOMENT) THAT SHOULD BE MOSTLY IN THE LIGHT TO MODERATE RANGE.
THEN UPPER TROUGHING AND POTENTIAL SURFACE DEVELOPMENT MAY PRODUCE
SOME SNOW OVER THE NORTHEAST BY FRIDAY-SATURDAY.
THE NORTHERN-CENTRAL PLAINS INTO UPPER MIDWEST WILL SEE WELL ABOVE
NORMAL TEMPERATURES THROUGH THE PERIOD, WITH NORTHERN AREAS
TENDING TO SEE THE BEST CHANCE FOR MULTIPLE DAYS OF MIN/MAX
TEMPERATURES AT LEAST 20F ABOVE NORMAL. SOME MORNING LOWS COULD
BE UP TO 25-30F OR SO ABOVE NORMAL AND A FEW DAILY RECORDS WILL BE
POSSIBLE. THE WEST WILL BE WARM EARLY IN THE WEEK WITH SOMEWHAT
LESS EXTREME ANOMALIES (GENERALLY UP TO PLUS 10-20F), BUT THAT MAY
STILL BE WARM ENOUGH TO PRODUCE SOME DAILY RECORDS. THE UPPER
TROUGH MOVING IN SHOULD BRING A COOLING TREND FOR THE LATTER HALF
OF THE WEEK WITH HIGHS OVER CALIFORNIA AND AN EXPANDING PORTION OF
THE SOUTHWESTERN U.S. TRENDING BELOW NORMAL THURSDAY-SATURDAY.
PARTS OF THE SOUTHWEST MAY SEE HIGHS 10-15F BELOW NORMAL BY THE
END OF THE WEEK. THE ABOVE NORMAL MIN TEMPERATURES WILL TAKE
LONGER TO TREND TOWARD NORMAL DUE TO CLOUDS AND PRECIPITATION.
OVER THE EAST, THE FLORIDA PENINSULA SHOULD SEE TEMPERATURES UP TO
5-10F BELOW NORMAL TUESDAY-WEDNESDAY AND COASTAL NEW ENGLAND
SHOULD SEE SIMILAR ANOMALIES FOR HIGHS ON TUESDAY. OTHERWISE
EXPECT NEAR TO ABOVE NORMAL TEMPERATURES, ALBEIT WITH SOME
UNCERTAINTY FOR HIGHS OVER THE NORTHEAST BY FRIDAY-SATURDAY
DEPENDING ON DEPTH OF UPPER TROUGHING.
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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