408
FXUS02 KWBC 090701
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
201 AM EST THU NOV 09 2023
VALID 12Z SUN NOV 12 2023 - 12Z THU NOV 16 2023
...MOISTURE DIRECTED INTO CALIFORNIA COULD LEAD TO HEAVY RAIN AND
SNOW TUESDAY-THURSDAY...
..OVERVIEW
GUIDANCE GENERALLY SHOWS THE UPPER PATTERN TRANSITIONING FROM
FAIRLY LOW AMPLITUDE MEAN FLOW WITH PROGRESSIVE SHORTWAVES TOWARD
A MORE AMPLIFIED REGIME CONSISTING OF A DEEP EASTERN PACIFIC
TROUGH, A BROAD RIDGE ALIGNED OVER THE CENTRAL U.S., AND A TROUGH
REACHING THE WESTERN ATLANTIC. THIS EVOLUTION WILL FAVOR DRY
WEATHER OVER A MAJORITY OF THE LOWER 48 AND A TREND TO WELL ABOVE
NORMAL TEMPERATURES OVER THE NORTHERN TWO-THIRDS OF THE CENTRAL
U.S. INTO MIDWEST. THE MOST LIKELY AREAS OF PRECIPITATION FOCUS
DURING THE PERIOD WILL BE ALONG THE WEST COAST, WITH GRADUALLY
INCREASING COVERAGE AND INTENSITY AHEAD OF THE AMPLIFYING PACIFIC
TROUGH THAT SHOULD EVENTUALLY DIRECT AN ATMOSPHERIC RIVER INTO
CALIFORNIA IN PARTICULAR, AND ACROSS THE SOUTHERN TIER/GULF COAST
STATES WHERE MOISTURE SHOULD OVERRUN A SLOW-MOVING FRONT OVER THE
GULF OF MEXICO. A SOUTHERN STREAM SHORTWAVE/UPPER LOW EJECTING
FROM NORTHWESTERN MEXICO AFTER SUNDAY SHOULD CONTRIBUTE TO THIS
ACTIVITY. SOUTHERN TEXAS MAY SEE THE HIGHEST RAINFALL TOTALS WITH
THIS, BUT THERE IS STILL CONSIDERABLE UNCERTAINTY WITH HOW MUCH
RAIN FALLS ONSHORE VERSUS OFFSHORE AND HOW MUCH INSTABILITY WILL
BE IN PLACE TO ENHANCE RAIN RATES. ALONG THE EASTERN SEABOARD, ONE
OR MORE SHORTWAVES PUSHING THROUGH THE NORTHERN TIER OF THE
COUNTRY EARLY NEXT WEEK AND FORMING THE MIDWEEK ATLANTIC TROUGH
WILL LEAD TO COOLER THAN AVERAGE TEMPERATURES BEFORE A MODERATING
TREND AS THE WEEK PROGRESSES.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
AS THE MEDIUM RANGE PERIOD BEGINS SUNDAY, A SHORTWAVE MOVING
THROUGH THE NORTHERN TIER SHOWS SOME DIFFERENCES BETWEEN MODELS,
MADE MORE COMPLEX BY SPLIT FLOW OVER THE GREAT LAKES AS THERE ARE
VARIATIONS IN MODELS WITH WHERE THE TROUGHING FARTHER SOUTH IN THE
MIDWEST SPLITS WITH RIDGING FARTHER NORTH INTO SOUTHERN CANADA.
MOST MODELS SEEMED REASONABLY AGREEABLE WITH THIS FEATURE NOW,
WITH THE EXCEPTION OF THE 12Z UKMET THAT INDICATED TROUGHING WHERE
OTHER GUIDANCE SHOWS RIDGING. WHILE THIS WAS RELATIVELY MINOR,
SINCE IT WAS AN OUT OF PHASE DIFFERENCE THAT COULD NOT BE BLENDED
EASILY, DID LEAVE THE UKMET OUT OF THE MODEL BLEND FOR THIS
REASON. RECENT MODEL CYCLES ARE BECOMING MORE AGREEABLE WITH THE
TROUGH AMPLITUDE AND TIMING AS IT CROSSES THE EAST INTO THE
ATLANTIC AS THE WEEK PROGRESSES, WHERE A DETERMINISTIC AND
ENSEMBLE MODEL BLEND WORKED WELL.
EARLY IN THE WEEK, SHORTWAVE ENERGY WILL BE LOCATED OVER NORTHERN
MEXICO AND LIKELY TRACK NORTHEAST INTO THE SOUTHERN U.S. EMBEDDED
SOUTH OF THE UPPER RIDGE BY TUESDAY-THURSDAY, WITH SOME QUESTIONS
WITH THE TIMING/TRACK SPECIFICS AND WHEN THE FEATURE ERODES.
RELATIVELY SMALL DIFFERENCES WERE SEEN WITH THE FEATURE INITIALLY
ALOFT, BUT THESE DIFFERENCES CONTRIBUTE TO EVEN MORE SPREAD FOR
QPF DETAILS ACROSS THE FAR SOUTHERN TIER THAN WHAT MIGHT BE
SUGGESTED BY THE COMPARISONS ALOFT. ECMWF RUNS HAVE BEEN
PARTICULARLY HEAVY ALONG AND INLAND FROM THE GULF COAST WHILE THE
GFS IS MOST SUPPRESSED WITH THE MOISTURE, WITH THE CMC AND UKMET
IN BETWEEN. BY MIDWEEK INTO THURSDAY, 12/18Z GFS RUNS HAD THE
SHORTWAVE DISAPPEARING/ABSORBED WHILE THE NON-NCEP KEPT SOME
SEMBLANCE OF IT. FAVORED THE LATTER AND FORTUNATELY THE 00Z GFS
CAME IN WITH KEEPING THE FEATURE EXISTING LONGER.
REGARDING THE LARGER-SCALE FLOW, FOR SEVERAL DAYS MODELS HAVE
SHOWN THE HIGH LIKELIHOOD FOR AMPLIFIED TROUGHING TO DEVELOP OVER
THE EASTERN PACIFIC AND AFFECT THE WEST COAST, WITH A
CORRESPONDING INCREASE OF PRECIPITATION OVER THE WESTERN U.S. AND
IN PARTICULAR CALIFORNIA TOWARD MIDWEEK. HOWEVER THERE HAS BEEN
QUITE A BIT OF SPREAD AND RUN-TO-RUN VARIABILITY FOR DETAILS
WITHIN THE OVERALL TROUGH, THUS LIMITING CONFIDENCE IN SPECIFICS
OF PRECIPITATION TIMING/COVERAGE/AMOUNTS. THESE DETAILS INCLUDE
THE DISTRIBUTION OF ENERGY WITHIN THE TROUGH AND POTENTIAL FOR
UPPER LOW(S) FORMATION. BUT MODELS HAVE AT LEAST CONVERGED BETTER
OVER THE PAST DAY OVERALL REGARDING THE AXIS OF THE TROUGH,
INCLUDING THE ECMWF SUITE SLOWING SOMEWHAT TO BE MORE SIMILAR TO
THE OTHER GUIDANCE, SO A BLEND OF THE DETERMINISTIC AND ENSEMBLE
GUIDANCE SEEMED TO PROVIDE A GOOD MIDDLE GROUND SOLUTION FOR THE
TROUGH AND THE DOWNSTREAM RIDGE. HOWEVER, THE NEWER 00Z GUIDANCE
HAS OVERALL COME IN A LITTLE FASTER/FARTHER EAST WITH THE TROUGH
THAN THE 12/18Z SUITE USED FOR THE FORECAST.
THUS THE WPC FORECAST CONTINUED THE APPROACH OF TRANSITIONING FROM
A MULTI-MODEL DETERMINISTIC BLEND (18Z GFS, 12Z ECMWF, AND 12Z
CMC) EARLY IN THE PERIOD TOWARD A MIX OF MODELS AND MEANS (18Z
GEFS AND 12Z ECENS) TO DOWNPLAY SOME OF THE LESS CONFIDENT
INDIVIDUAL MODEL DIFFERENCES WHILE CAPTURING THE OVERALL PATTERN.
..WEATHER/HAZARDS HIGHLIGHTS
MOISTURE OVERRUNNING THE COLD FRONT THAT IS FORECAST TO STALL OVER
THE NORTHWESTERN GULF (BUT TRACK A BIT MORE PROGRESSIVELY THROUGH
FLORIDA) WILL LEAD TO SOME RAIN ACROSS THE SOUTH-CENTRAL TO
SOUTHEASTERN QUADRANT OF THE U.S. CONTINUING INTO THE FIRST HALF
OF NEXT WEEK. THE HIGHEST RAINFALL TOTALS ARE LIKELY TO BE OVER
SOUTHERN TEXAS AND PERHAPS SHIFTING INTO SOUTHERN LOUISIANA NEAR A
MEANDERING SURFACE LOW ALONG THE FRONT, WITH EASTERN PACIFIC AND
GULF MOISTURE COMBINING. NOT MUCH INSTABILITY WILL BE IN PLACE
THROUGH EARLY NEXT WEEK SINCE THE REGION WILL BE IN A POST-FRONTAL
AIRMASS, SO RAIN RATES SHOULD NOT BE TOO HIGH. BY MONDAY THOUGH,
THERE MAY BE MORE SUPPORT FOR CONVECTION FROM TEXAS INTO THE LOWER
MISSISSIPPI VALLEY AS MID-UPPER LEVEL ENERGY APPROACHES AND
POSSIBLY INCREASES INSTABILITY. BUT ON BOTH DAYS, THERE IS
CONSIDERABLE UNCERTAINTY WITH HOW MUCH RAIN SPREADS INLAND, WITH
RAIN TOTALS MAXIMIZED OVER THE GULF. THUS THERE ARE NO FLASH
FLOODING RISK AREAS DELINEATED IN THE EXCESSIVE RAINFALL OUTLOOK
FOR SUNDAY AND MONDAY, BUT THIS POTENTIAL RAINFALL EVENT WILL
CONTINUE TO BE MONITORED.
ROUNDS OF FRONTAL SYSTEMS AND SHORTWAVES PUSHING THROUGH THE
NORTHWEST WILL MAINTAIN PRECIPITATION CHANCES ACROSS THE PACIFIC
NORTHWEST AND THE NORTHERN ROCKIES THROUGH EARLY NEXT WEEK.
MODERATE TO HEAVY AMOUNTS MAY BE DIRECTED INTO THE NORTHERN PARTS
OF THE OLYMPICS AND CASCADES, WITH LOWER ELEVATION RAIN AND HIGHER
ELEVATION SNOW. STARTING MONDAY AND ESPECIALLY BY
TUESDAY-THURSDAY, UPPER TROUGHING WILL DEEPEN OVER THE EASTERN
PACIFIC AND DIRECT MOISTURE PLUMES/ATMOSPHERIC RIVERS INTO THE
WEST, ESPECIALLY CALIFORNIA. EXPECT HEAVY LOWER ELEVATION RAIN AND
HIGHER ELEVATION SNOW. WHILE CONFIDENCE IS SOMEWHAT ABOVE AVERAGE
IN A PERIOD OF ENHANCED PRECIPITATION ASSOCIATED WITH THE OVERALL
UPPER TROUGH, IT IS MUCH LOWER IN TERMS OF SPECIFICS (TIMING,
COVERAGE, AMOUNTS OVER PARTICULAR LOCATIONS) DUE TO MODEL SPREAD
AND VARIABILITY FOR INDIVIDUAL COMPONENTS OF THE TROUGH.
ON SUNDAY, MUCH OF THE EAST WILL BE UNDER A POST-FRONTAL COOL HIGH
PRESSURE SYSTEM, WITH TEMPERATURES NEAR TO BELOW AVERAGE, BUT
WARMING CLOSER TO NORMAL TUESDAY-WEDNESDAY AND PERHAPS REACHING
ABOVE NORMAL BY THURSDAY. THE EXCEPTION WILL BE THE FLORIDA
PENINSULA, WITH HIGHS WELL INTO THE 80S ON SUNDAY MODERATING
GRADUALLY CLOSER TO NORMAL AFTER THE COLD FRONT PRESSES THROUGH.
AS UPPER RIDGING BUILDS ACROSS THE NORTH-CENTRAL U.S. EARLY NEXT
WEEK, ABOVE NORMAL TEMPERATURES BY AROUND 10-20F WILL OVERSPREAD
THE CENTRAL AND NORTHERN PLAINS INTO THE MIDWEST, WITH ABOVE
AVERAGE POCKETS EXTENDING BACK INTO THE GREAT BASIN AS WELL.
MEANWHILE BELOW NORMAL HIGHS SHOULD LINGER IN THE SOUTH-CENTRAL
U.S. WITH LOWER HEIGHTS OVERHEAD AND CLOUDS AND RAIN POSSIBLE, AND
INTERESTINGLY LEAD TO THE WARMEST HIGHS (NEARING 70F) IN THE
CENTRAL PLAINS RATHER THAN FARTHER SOUTH.
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, 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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