881
FXUS02 KWBC 290702
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
202 AM EST WED NOV 29 2023
VALID 12Z SAT DEC 02 2023 - 12Z WED DEC 06 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 WEATHER PATTERN IS UPCOMING THROUGH THE MEDIUM RANGE
TIME SCALES. AN AMPLIFIED TROUGH WILL BE REINFORCED BY A COUPLE OF
SHORTWAVES AS IT MOVES FROM THE INTERIOR WEST TO THE EAST COAST
SATURDAY-MONDAY. AMPLIFIED RIDGING BUILDS BEHIND THIS ACROSS THE
WEST AND EVENTUALLY THE PLAINS EARLY NEXT WEEK AS THE NEXT SYSTEM
MOVES IN TO THE WEST COAST FROM THE EAST PACIFIC NEXT WEDNESDAY.
THE GUIDANCE CONTINUES TO BE QUITE AGREEABLE ON THE LARGE
SCALE/SYNOPTIC PATTERN BUT STILL WITH A LOT OF UNCERTAINTY IN THE
DETAILS. RUN TO RUN VARIABILITY AND TIMING OF INDIVIDUAL
SHORTWAVES THROUGH THE MIDWEST AND EAST THIS WEEKEND/EARLY NEXT
WEEK, WHICH TRANSLATES TO EVEN SOME REGIONAL SENSIBLE
WEATHER/PRECIPITATION UNCERTAINTIES ESPECIALLY ACROSS THE EAST.
OUT WEST, MODELS AGREE THAT AN ATMOSPHERIC RIVER MAY IMPACT THE
WEST COAST THIS WEEKEND, BUT STILL SHOW CONSIDERABLE DIFFERENCES
IN PLACEMENT OF THE HEAVIEST QPF. THE LATEST NBM STILL SEEMS TOO
WET IN SPOTS, AND THE WPC FORECAST TEMPERED THAT DOWN SOMEWHAT.
THE WPC FORECAST TONIGHT USED A PURELY DETERMINISTIC MODEL BLEND
FOR DAYS 3 AND 4. AFTER THIS, BEGAN INCREASING USE OF THE ENSEMBLE
MEANS AMIDST DIFFERENCES IN TIMING OF SHORTWAVES INTO THE EAST AND
TROUGH AMPLIFICATION. THERE IS BETTER AGREEMENT ACTUALLY AS THE
NEXT TROUGH MOVES INTO THE EAST EARLY-MID NEXT WEEK, BUT LARGER
SCALE TIMING DIFFERENCES WITH THE NEXT TROUGH INTO THE WEST AT THE
SAME TIME NECESSITATED MORE INFLUENCE FROM THE ENSEMBLE MEANS DAYS
6-7, ALTHOUGH WITH STILL 50 PERCENT OF THE DETERMINISTIC GFS AND
ECMWF TO HELP MAINTAIN SYSTEM DEFINITION. THIS MAINTAINED PRETTY
GOOD CONTINUITY WITH THE PREVIOUS WPC FORECAST AS WELL.
..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 CONTINUE TO
SUPPORT A MODERATE TO HEAVY RAINFALL THREAT FOR THE GULF COAST AND
SOUTHEAST INTO SATURDAY, WHERE THERE IS A MARGINAL RISK FOR
EXCESSIVE RAINFALL WITHIN AN AREA OF ANOMALOUS MOISTURE (PWS 2-3
STANDARD DEVIATIONS ABOVE NORMAL) AND INSTABILITY. IT IS POSSIBLE
AN EMBEDDED SLIGHT RISK WILL BE NEEDED AT SOME POINT, BUT THERE IS
STILL SOME UNCERTAINTY ON EXACT AMOUNTS. RAINFALL MAY CONTINUE
INTO SUNDAY AND MONDAY AS WELL ACROSS THE SOUTHEAST, BUT SHOULD BE
LIGHTER IN INTENSITY. MUCH OF THE EASTERN U.S. LOOKS UNSETTLED
THROUGH NEXT WEEK, ALBEIT WITH HIGHER UNCERTAINTY ON RAINFALL
AMOUNTS GIVEN SHORTWAVE DIFFERENCES. SOME OF THE PRECIPITATION
COULD BE IN THE FORM OF SNOW ACROSS PARTS OF THE GREAT LAKES AND
NORTHEAST.
OUT WEST, PRECIPITATION WILL BE ONGOING AS THE PERIOD BEGINS
SATURDAY. SOME MODEST RAINFALL TOTALS ARE LIKELY ALONG THE COAST,
WITH SNOW FARTHER INLAND ACROSS THE HIGHER ELEVATIONS OF THE
CASCADES, NORTHERN SIERRAS, AND NORTHERN ROCKIES. A SMALL MARGINAL
RISK WAS ADDED TO TONIGHTS DAY 4/SATURDAY ERO ACROSS FAR NORTHWEST
CA/SOUTHWEST OR. THE STRONGER SYSTEM/POTENTIAL AR MOVES IN SUNDAY
AND WITH SNOW LEVELS RISING, COULD BRING A MORE WIDESPREAD HEAVY
RAINFALL THREAT ALONG THE OREGON COAST AND WESTERN SLOPES OF THE
CASCADES. A MARGINAL RISK WAS INCLUDED FOR THIS AREA ON THE DAY
5/SUNDAY ERO. THE NEXT SYSTEM IN THE EAST PACIFIC EARLY NEXT WEEK
BRINGS ANOTHER RAIN/MOUNTAIN SNOW THREAT, THOUGH AT THIS POINT
LOOKS TO FOCUS FARTHER NORTH ACROSS MAINLY WASHINGTON STATE.
TEMPERATURES ACROSS THE EAST THIS WEEKEND MAY BE MODERATELY ABOVE
NORMAL, WITH SLIGHTLY BELOW NORMAL TEMPERATURES ACROSS THE
INTERIOR SOUTHWEST. THE WESTERN U.S. SHOULD TREND WARMER WITH TIME
AND ESPECIALLY BY NEXT TUESDAY-WEDNESDAY IN THE NORTHERN HIGH
PLAINS/PLAINS WHERE DAYTIME HIGHS COULD BE 10 TO 20 DEGREES ABOVE
NORMAL. MEANWHILE, THE EASTERN U.S. SHOULD TREND BACK TOWARDS
NORMAL/SLIGHTLY COOLER THAN NORMAL NEXT WEEK AS REINFORCED
TROUGHING AFFECTS THE AREA.
SANTORELLI
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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