854
FXUS02 KWBC 101910
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
204 PM EST FRI NOV 10 2023
VALID 12Z MON NOV 13 2023 - 12Z FRI NOV 17 2023
...HEAVY RAINFALL POTENTIAL FOR THE WEST-CENTRAL GULF COAST MONDAY
AND TUESDAY...
...MOISTURE DIRECTED INTO CALIFORNIA COULD LEAD TO HEAVY RAIN AND
SNOW TUESDAY-THURSDAY...
..OVERVIEW
IT OVERALL REMAINS RELEVENT THAT RECENT GUIDANCE HAS BEEN SHOWING
AN 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 MAY 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, WITH MODELS CONTINUING TO
TREND WETTER IN THIS REGION. 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
MODEL AND ENSEMBLE SOLUTIONS REMAIN REASONABLY WELL CLUSTERED
DURING THE FIRST HALF OF THE WEEK WITH A SHORTWAVE EXITING THE
NORTHEAST AND ENERGY MOVING THROUGH THE SOUTHERN PLAINS/GULF
COAST. BY WEDNESDAY AND ESPECIALLY BEYOND, DETAILS OFF THE WEST
COAST BECOME INCREASINGLY MURKY. THE LATEST TREND IN GUIDANCE
SUGGESTS MORE SEPARATION BETWEEN NORTHERN STREAM ENERGY (WHICH
SLIDES THROUGH THE NORTHERN TIER OF THE U.S. THURSDAY-FRIDAY) AND
A DEEPENING UPPER LOW WHICH PARKS ITSELF OFF THE COAST OF
CALIFORNIA. MODEL ENSEMBLE PLOTS SUGGEST THERE IS STILL A FAIR BIT
OF UNCERTAINTY IN THE EVOLUTION OF WEST COAST/EAST PACIFIC
TROUGHING, BUT THE LATEST 12Z GFS, ECMWF, AND CMC HAVE CONTINUED
TO TREND IN THIS DIRECTION THIS AFTERNOON. THIS WOULD RESULT IN
FAR LESS PRECIPITATION ACROSS CALIFORNIA THAN PREVIOUSLY THOUGHT,
AND WILL CONTINUE TO BE MONITORED. THERE IS ALSO INCREASING
UNCERTAINTY IN THE TIMING AND DEPTH OF THE NORTHERN STREAM ENERGY
THROUGH THE DAKOTAS AND INTO THE GREAT LAKES THURSDAY-FRIDAY/DAY
6-7.
TODAYS UPDATED MEDIUM RANGE PROGS UTILIZED A DETERMINISTIC MODEL
BLEND FOR DAYS 3-5, WHICH SMOOTHED OUT ANY EARLY PERIOD SMALL
SCALE DIFFERENCES. GIVEN THE INCREASED UNCERTAINTY, TRENDED
QUICKLY TOWARDS A MAJORITY ENSEMBLE MEAN BLEND FOR DAYS 6 AND 7.
THIS GENERALLY MAINTAINS GOOD CONTINUITY WITH THE PREVIOUS
FORECAST, WITH SOME ADJUSTMENTS BASED ON LATEST TRENDS.
..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 NEXT WEEK. THE
HIGHEST RAINFALL TOTALS ARE LIKELY TO WORK ACROSS THE WEST-CENTRAL
GULF COAST MONDAY-TUESDAY AND POTENTIALLY EVEN INTO THE
SOUTHEAST/FLORIDA BY LATER NEXT WEEK, WITH EASTERN PACIFIC AND
GULF MOISTURE COMBINING. LIMITED 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, AND THE POTENTIAL FOR HEAVIER RAIN
TOTALS HAS TRENDED UPWARD AS THE GUIDANCE INDICATES THIS MID-UPPER
ENERGY MAY BE STRONGER AND TRACK SLOWER OVER THE REGION. SOME OF
THE DETERMINISTIC GUIDANCE HAS BECOME PARTICULARLY AGGRESSIVE WITH
RAINFALL TOTALS ALONG THE WEST-CENTRAL GULF COAST AROUND MONDAY.
HOWEVER, WITH THE HEAVIEST RAINFALL EXPECTED TO REMAIN ALONG THE
GULF COAST, AND ANTECEDENT CONDITIONS ALREADY VERY DRY, THE RISK
FOR FLASH FLOODING SHOULD REMAIN RELATIVELY LOW, BUT THERE HAS
BEEN AN INCREASE IN MODEL FORECAST TOTALS TO CONSIDER.
ACCORDINGLY, MARGINAL THREAT AREAS ONLY CONTINUE ON THE WPC
EXCESSIVE RAINFALL OUTLOOK FOR MONDAY AND TUESDAY TO CAPTURE SOME
THREAT FOR COASTAL COMMUNITIES.
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 MAY DIRECT MOISTURE PLUMES INTO THE WEST, ESPECIALLY
CALIFORNIA, BUT OVERALL PRECIPITATION TOTALS HAVE TRENDED LIGHTER
IN RECENT MODEL RUNS. 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 OF INDIVIDUAL SHORTWAVE ENERGIES AND LARGER SCALE
UPPER TROUGH PROGRESSINS AND STREAM PHASINGS.
SANTORELLI/SCHICHTEL
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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