497
FXUS02 KWBC 281902
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
201 PM EST TUE NOV 28 2023
VALID 12Z FRI DEC 01 2023 - 12Z TUE DEC 05 2023
...WET PATTERN FOR THE NORTHWEST TO INCLUDE HEAVY SNOW THREATS
INLAND FROM THE CASCADES TO THE NORTH-CENTRAL INTERMOUNTAIN
WEST/ROCKIES...
..OVERVIEW AND GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
AN ACTIVE AND TRICKY WEATHER PATTERN IS UPCOMING THROUGH MEDIUM
RANGE TIME SCALES, WITH LARGER SCALE FLOW NOW SET TO TRANSITION
FROM OVERALL SPLIT FLOW TO ONE WITH MORE NORTHERN STREAM DOMINATED
POSITIVE PNA PATTERN IN ABOUT A WEEK. MOST GUIDANCE IS ACTUALLY
QUITE AGREEABLE WITH RESPECT TO EVENTUAL POSITIVE PNA DEVELOPMENT
TO BE MAINLY COMPRISED OF AN AMPLIFIED UPPER RIDGE OVER WESTERN
NORTH AMERICA AND AN AMPLIFIED UPPER TROUGH OVER EAST-CENTRAL
U.S.. HOWEVER, GUIDANCE GET THERE IN DIFFERENT WAYS, SHOWING
SIGNIFICANT RUN TO RUN AND MODEL TO MODEL DIFFERNENCES FROM THE
WEEKEND INTO EARLY NEXT WEEK WITH FLOW EMBEDDED SYSTEMS ALOFT AND
ESPECIALLY THE OFTEN COMPLEX SURFACE SYSTEM REFLECTION.
ACCORDINGLY, THERE IS QUITE A BIT OF UNCERTAINTY WITH SENSIBLE
WEATHER LOCAL AND EVEN REGIONAL FOCI. IN PARTICULAR, THERE IS MORE
THAN NORMAL DIFFERENCES WITH EVEN MID-LARGER SCALE AREAS OF
PRECIPITATION OVER THE EAST-CENTRAL U.S., BUT ALSO IN THE WET
PATTERN TO/INLAND FROM THE NORTHWEST. SEEMINGLY HEAVY NBM QPF
AMOUNTS WERE OVERALL LESSENED GIVEN UNCERTAINTIES AND AS MACHINE
LEARNING TOOLS SHED FURTHER DOUBT ON MID-LATER FORECAST PERIOD
QPF.
ACCORDINGLY, THE WPC MEDIUM RANGE PRODUCT SUITE WAS PRIMARILY
DERIVED FROM A COMPOSITE OF BEST CLUSTERED GUIDANCE OF THE 06 UTC
GFS/GEFS MEAN, 00 UTC ECMWF/UKMET/ECMWF ENSEMBLE MEAN, THE 13 UTC
NATIONAL BLEND OF MODELS (NBM) AND WPC CONTINUITY FOR FRIDAY INTO
EARLY SATURDAY TO SMOOTH OUT THE EMBEDDED FEATURE VARIANCES
CONSISTENT WITH A PATTERN WITH SEEMINGLY LESS THAN AVERAGE
PREDICTABILITY. OPTED TO BLEND THE GEFS/ECMWF ENSEMBLE MEANS
ONWARD THROUGH THE WEEKEND INTO EARLY NEXT WEEK ALONG WITH INPUT
FROM THE NBM.
..WEATHER/HAZARDS HIGHLIGHTS
UPPER-LEVEL SHORTWAVE ENERGY WILL MOVE OVER THE MID-SOUTH WHILE A
WARM FRONT LIFTS NORTH OUT OF THE GULF OF MEXICO LATE THIS WEEK,
AND AN AMPLIFIED TROUGH SHIFTS OUT OF THE WEST THIS WEEKEND
PROVIDING A RENEWED SURGE OF MOISTURE. THIS WILL SUPPORT DAILY
WIDESPREAD MODERATE TO HEAVY RAINFALL FOR THE GULF COAST AND
SOUTHEAST. THERE IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR THIS
REGION VALID DAYS 4 AND 5 (FRIDAY AND SATURDAY) AS ANOMALOUS
MOISTURE (PWS 2-3 STANDARD DEVIATIONS ABOVE NORMAL) AND
INSTABILITY WILL BE PRESENT. IT IS POSSIBLE AN EMBEDDED SLIGHT
RISK WILL BE NEEDED AT SOME POINT, BUT THERE IS STILL SOME
UNCERTAINTY ON EXACT AMOUNTS. THE HEAVY RAINFALL THREAT ACROSS THE
SOUTHEAST MAY LINGER INTO SUNDAY AS WELL, WITH RAINFALL ALSO
LIFTING NORTHWARD UP THE EAST COAST INTO MONDAY, ALBEIT ALL WITH
HIGH UNCERTAINTY AT THESE LONGER TIME FRAMES. EVEN SO, THERE DOES
SEEM TO BE SEVERAL UNCERTAIN OPPORTUNITIES FOR HEAVY RAIN OVER THE
SOUTHEAST TO MONITOR ALONG WITH MODERATE SWATHS OF NORTHERN
PERIPHERY SNOW INTO THE NORTHEAST AND VICIITY. STRONGER
CYCLOGENESIS WITH EXPECTED NORTHERN STEAM AMPLIFCATION INTO NEXT
WEEK WITH AFOREMENTIONED POSITIVE PNA PATTERN DEVELOPMENT MAY THEN
ALSO LEAD TO WIDESPREAD/LARGER SCALE PRECIPITATION TO EMERGE.
OUT WEST, PRECIPITATION WILL INCREASE THURSDAY THROUGH THE WEEKEND
AS A COUPLE DYNAMIC SHORTWAVES MOVE THROUGH THE REGION, WITH SOME
PRECIPITATION REACHING SOUTHWARD INTO CALIFORNIA BY
FRIDAY-SATURDAY AND POSSIBILITY FOR ACCUMULATING SNOWS IN THE
HIGHER ELEVATIONS. THE HEAVIEST PRECIPITATION (COASTAL RAIN AND
MOUNTAIN SNOW) WILL BE ACROSS THE WASHINGTON/OREGON COAST AND
CASCADES SUNDAY INTO MONDAY, WHERE SOME MODELS INDICATE A
POTENTIAL ATMOSPHERIC RIVER TO IMPACT THE REGION. MODEST TO HEAVY
SNOWFALL LOOKS TO PERIODICALLY IMPACT PARTS OF THE NORTH-CENTRAL
INTERMOUNTAIN WEST/ROCKIES AS WELL THIS WEEKEND INTO EARLY NEXT
WEEK.
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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