966
FXUS02 KWBC 281901
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
200 PM EST THU DEC 28 2023
VALID 12Z SUN DEC 31 2023 - 12Z THU JAN 04 2024
..OVERVIEW
THE LATEST MODELS AND ENSEMBLES STILL ADVERTISE A PATTERN
TRANSITION TOWARD A SERIES OF PACIFIC SHORTWAVES (SOME WITH AN
EMBEDDED UPPER LOW) AFFECTING SOME LOCATIONS NEAR THE WEST COAST
AND THEN TRACKING ACROSS THE SOUTHERN TIER. AFTER A LEADING
TROUGH PASSES THROUGH THE EASTERN U.S. EARLY NEXT WEEK, WESTERN
CANADA MEAN RIDGING SHOULD BE PERSISTENT ENOUGH TO SUPPORT A
DOWNSTREAM TROUGH EXTENDING INTO THE NORTHEASTERN QUADRANT OF THE
LOWER 48 BY MID-LATE WEEK. THIS PATTERN SHOULD CONFINE THE
MAJORITY OF PRECIPITATION AND SOMEWHAT BELOW NORMAL HIGH
TEMPERATURES TO PARTS OF THE WEST COAST AND THE GULF COAST
STATES/SOUTHEAST. THE GREAT LAKES COULD SEE SOME LIGHT SNOW
AROUND SUNDAY AND WEDNESDAY-THURSDAY. WARMEST TEMPERATURE
ANOMALIES WILL LIKELY BE NEAR THE CANADIAN BORDER.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE MOST UNCERTAINTY DURING THE MEDIUM RANGE PERIOD WAS IN THE
WEST. A GENERAL MODEL BLEND CONSISTING OF THE 00Z EC/CMC/UKMET AND
06Z GFS, WITH MORE WEIGHTING TOWARD THE 00Z EC, WAS USED ON DAY 3.
A MORE EVENLY DISTRIBUTED GENERAL MODEL BLEND WAS IMPLEMENTED ON
DAY 4 DUE TO SPREAD IN THE GUIDANCE REGARDING YET ANOTHER WEST
COAST SYSTEM. IT'S WORTH NOTING THAT THE EURO HAS TRENDED CLOSER
TO THE COAST AND CLOSER IN LINE WITH WHAT THE GFS HAS BEEN
SIGNALING OVER THE LAST 24 HOURS REGARDING THE WEST COAST LOW.
THIS EVEN DISTRIBUTION CONTINUES INTO DAY 5 WHEN THE 06Z GEFS AND
00Z ECENS MEANS WERE INTRODUCED. THE CANADIAN ENSEMBLE WAS LEFT
OUT DUE TO IT'S MORE PROGRESSIVE SOLUTION WITH RESPECT TO THE
CENTRAL U.S. TROUGH. THE 06Z GFS HAD A DEEPER UPPER LOW OVER THE
ROCKIES/PLAINS THAN THE REST OF THE GUIDANCE AS WELL. THERE'S A
LOT OF ENSEMBLE SPREAD REGARDING THE EARLY-MID WEEK TROUGH
ENTERING THE WEST ON DAYS 6 AND 7.
..WEATHER/HAZARDS HIGHLIGHTS
THE WEAK SYSTEM CROSSING THE GREAT LAKES THROUGH SUNDAY MAY
PRODUCE A LITTLE LIGHT SNOW NEAR ITS PATH. THE TRAILING FRONT MAY
PRODUCE AREAS OF RAIN ACROSS THE GULF COAST/SOUTHEAST
SUNDAY-MONDAY BUT WITH CONTINUED UNCERTAINTY OVER COVERAGE/AMOUNTS
DUE TO DETAIL DIFFERENCES IN THE GUIDANCE FOR SOUTHERN STREAM
ENERGY EMERGING FROM THE SOUTHWEST AND THE ORIENTATION/TIMING OF
NORTHERN STREAM ENERGY. AT THE VERY LEAST, THIS ACTIVITY SHOULD
BE PROGRESSIVE ENOUGH TO KEEP MOST TOTALS IN THE LIGHT TO MODERATE
RANGE. ANOTHER WEAK WAVE AND TRAILING CYCLONIC FLOW MAY PRODUCE A
LITTLE LAKE EFFECT SNOW BY MID-LATE WEEK.
IT WILL BE A CLOSE CALL AS TO WHETHER A SYSTEM BRUSHING SOUTHERN
CALIFORNIA WILL BRING ANY MOISTURE TO THAT PART OF THE STATE. AS
THE UPPER TROUGH CONTINUES EASTWARD, EXPECT SOME RAIN TO SPREAD
ALONG AND NEAR THE GULF COAST BY MIDWEEK, WITH UNCERTAIN NORTHWARD
COVERAGE BY THE TIME THE MOISTURE REACHES THE EAST COAST BY
THURSDAY. CURRENTLY EXPECT MOST OF THIS MOISTURE TO STAY FAR
ENOUGH SOUTH TO MAINTAIN RAIN AS THE PRIMARY PRECIPITATION TYPE.
A BETTER DEFINED SYSTEM FORECAST TO APPROACH THE WEST COAST BY
WEDNESDAY AND MOVE INTO THE SOUTHWEST BY THURSDAY MAY BRING
ORGANIZED PRECIPITATION TO THE WEST COAST AND SOME AREAS FARTHER
INLAND, WITH RELATIVELY HIGHER TOTALS MOST LIKELY OVER FAVORED
TERRAIN IN PORTIONS OF CALIFORNIA.
THE GREATEST TEMPERATURE ANOMALIES DURING THE PERIOD SHOULD BE OF
THE ABOVE NORMAL VARIETY ACROSS THE FAR NORTHERN TIER NEAR THE
CANADIAN BORDER WITH SOME LOCATIONS SEEING MULTIPLE DAYS WITH
READINGS 10-20F OR SO ABOVE NORMAL. MORNING LOWS WILL TEND TO BE
FARTHER ABOVE NORMAL THAN DAYTIME HIGHS. ON THE OTHER HAND, ASIDE
FROM THE SOUTHERN PLAINS BEING ABOVE NORMAL ON SUNDAY AHEAD OF A
FRONT, MOST AREAS FROM CALIFORNIA EASTWARD ACROSS THE SOUTHERN
TIER SHOULD SEE NEAR TO BELOW NORMAL HIGH TEMPERATURES DURING THE
PERIOD. LOW TEMPERATURES WILL ALSO BE BELOW NORMAL ON SOME DAYS,
SUCH AS SUNDAY MORNING WHEN READINGS IN THE LOW TO MID 30S MAY
LEAD TO FROST OR FREEZES OVER PORTIONS OF NORTHERN FLORIDA.
KEBEDE/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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