251
FXUS02 KWBC 231844
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
144 PM EST SAT DEC 23 2023
VALID 12Z TUE DEC 26 2023 - 12Z SAT DEC 30 2023
...HEAVY RAIN THREAT REACHING THE MID-ATLANTIC BY TUESDAY AND
POSSIBLY EXTENDING NORTHEASTWARD INTO WEDNESDAY...
...TWO EPISODES OF ENHANCED PRECIPITATION POSSIBLE FOR THE CENTRAL
WEST COAST MID-LATE WEEK...
..OVERVIEW
LATEST GUIDANCE SHOWS THE LARGE SCALE PATTERN SETTLING INTO A
FAIRLY AMPLIFIED AND BLOCKY REGIME DOMINATED BY MEAN RIDGING OVER
THE WESTERN U.S. INTO WESTERN/WEST-CENTRAL CANADA, WHICH WILL
WEAKEN PACIFIC SHORTWAVES, AND TROUGHING OVER THE EASTERN HALF OF
NORTH AMERICA. AN INITIAL PLAINS/MIDWEST UPPER LOW WILL WORK TO
ESTABLISH THE EASTERN UPPER TROUGH, AND AN ASSOCIATED SURFACE
SYSTEM WILL SPREAD RAINFALL OF VARYING INTENSITY OVER THE EAST
EARLY-MID WEEK ALONG WITH THE POTENTIAL FOR LINGERING SNOW OVER
THE NORTH-CENTRAL PLAINS. PRECIPITATION OVER THE EAST SHOULD TREND
LIGHTER AND MORE SCATTERED LATER IN THE WEEK BUT WITH UNCERTAINTY
IN SPECIFICS. OVER THE WEST, MOST PRECIPITATION SHOULD FOCUS NEAR
THE WEST COAST WITH A COUPLE FRONTAL SYSTEMS TENDING TO PRODUCE
THE HIGHEST TOTALS OVER/NEAR NORTHERN CALIFORNIA.
..GUIDANCE/PREDICTABILITY ASSESSMENT
RECENT MULTI-DAY D+8 MEANS HAVE BEEN FAIRLY AGREEABLE IN SHOWING A
DOMINANT CORE OF POSITIVE HEIGHT ANOMALIES POSITIONED OVER CENTRAL
CANADA, WITH CORRESPONDING TELECONNECTIONS CONSISTENT FOR
SURROUNDING NEGATIVE HEIGHT ANOMALIES ASSOCIATED WITH MEAN
TROUGHING OVER THE EASTERN U.S. AND EASTERN PACIFIC. THIS ADDS TO
CONFIDENCE IN THE FORECAST LARGE SCALE PATTERN, BUT INDIVIDUAL
SOLUTIONS SUGGEST RAPIDLY INCREASING DETAIL UNCERTAINTIES FROM
MIDWEEK ONWARD, ESPECIALLY FOR THE EASTERN U.S. TROUGH.
MODEL GUIDANCE IS VERY AGREEABLE EARLY IN THE PERIOD WITH THE DEEP
UPPER LOW IN THE MIDWEST, BUT AGREEMENT DISSOLVES FROM THURSDAY
ONWARD AS DIGGING CANADIAN ENERGY INTERACTS WITH/REPLACES THE
INITIAL UPPER LOW. THE TRACK AND SPEED OF THE UPPER LOW/LOWS WILL
HAVE A CONSIDERABLE INFLUENCE ON THE SURFACE DETAILS. MODELS DO
SHOW AGREEMENT ON A WETTER PATTERN DEVELOPING IN THE EAST TUESDAY
TO THURSDAY AS THE MIDWEST SYSTEM WEAKENS AND MOVES TOWARDS THE
COAST. THERE MAY BE SOME RE-DEVELOPMENT OF THE SURFACE CYCLONE
SOMEWHERE ALONG THE COAST NEAR THE MID-ATLANTIC OR NORTHEAST NEAR
THE END OF THE WEEK.
FOR THE WESTERN U.S., MODEL GUIDANCE CONTINUES TO SHOW AGREEMENT
ON AN UPPER SHORTWAVE ARRIVING WEDNESDAY INTO THURSDAY, BUT THE
12Z UKMET CONTINUES TO TO BE SLOWER THAN OTHER GUIDANCE. SOLUTIONS
DO START TO DIVERGE LATER IN THE PERIOD, BUT THERE IS SOME GENERAL
AGREEMENT ON ANOTHER TROUGH MOVING TOWARDS THE COAST NEXT WEEKEND.
BASED ON 00Z/06Z GUIDANCE COMPARISONS, THE UPDATED FORECAST
STARTED WITH AN OPERATIONAL MODEL COMPOSITE EARLY BUT THEN PLACED
MORE EMPHASIS ON THE GFS/GEFS AND EC MEAN BY MID-LATE PERIOD.
..WEATHER/HAZARDS HIGHLIGHTS
THE SYSTEM FORECAST TO AFFECT THE CENTRAL AND EASTERN U.S.
MID-NEXT WEEK WILL SPREAD RAINFALL INTO THE EAST AND GREAT
LAKES/UPPER MIDWEST, AND SNOW SHOWERS WILL LINGER OVER THE
NORTH-CENTRAL PLAINS AND PARTS OF THE UPPER MIDWEST. RAINFALL MAY
BE LOCALLY HEAVY AT TIMES ALONG THE EAST COAST, AND THERE ARE
MARGINAL RISKS OF EXCESSIVE RAINFALL FOR PARTS OF THE MID-ATLANTIC
AND SOUTHEAST ON TUESDAY AND FOR THE COASTAL NORTHEAST AND
NORTHERN MID-ATLANTIC ON WEDNESDAY. SOUTHEASTERLY LOW LEVEL FLOW
MAY HELP TO ENHANCE TOTALS OVER FAVORED TERRAIN ALONG THE
APPALACHIANS WHILE POTENTIAL FOR SOME MODEST INSTABILITY MAY
CONTRIBUTE TO ANOTHER RELATIVE MAXIMUM NEAR THE COAST.
PRECIPITATION SHOULD BECOME LIGHTER AND MORE SCATTERED WITH TIME,
WITH A TENDENCY TOWARD LAKE EFFECT/TERRAIN ENHANCED SNOW AS
TEMPERATURES GRADUALLY DECLINE. LINGERING SNOW IN THE
NORTH-CENTRAL PLAINS MAY ALSO BE HEAVY AT TIMES ON TUESDAY, WHICH
MAY AFFECT POST-CHRISTMAS TRAVEL. LOWER SNOW TOTALS ARE EXPECTED
IN THE UPPER MIDWEST, BUT SNOW AND MIXED PRECIPITATION/FREEZING
RAIN WILL ALSO LIKELY AFFECT TRAVEL IN SOME CAPACITY.
ALONG THE WEST COAST, THE PRIMARY PRECIPITATION EVENTS SHOULD BE
OVER THE CENTRAL WEST COAST AROUND WEDNESDAY AND FRIDAY WITH THE
ARRIVAL OF UPPER SHORTWAVES AND ASSOCIATED SURFACE FRONTS. THERE
IS A MARGINAL RISK OF EXCESSIVE RAINFALL FOR PARTS OF NORTHERN
CALIFORNIA AND FAR SOUTHWESTERN OREGON ON WEDNESDAY, AND THE SAME
AREA WILL LIKELY BE HIT AGAIN WITH MORE PRECIPITATION ON FRIDAY.
IN BOTH EVENTS EXPECT SNOW OVER HIGHER ELEVATIONS. THE PACIFIC
NORTHWEST WILL LIKELY SEE SOME PRECIPITATION FROM THESE EVENTS BUT
WITH LIGHTER AMOUNTS.
IN TERMS OF TEMPERATURES, EXPECT UNSEASONABLY WARM CONDITIONS IN
THE EAST TUESDAY AND WEDNESDAY AHEAD OF THE APPROACHING FRONTAL
SYSTEM. MORNING LOWS SHOULD BE PARTICULARLY ANOMALOUS WITH
READINGS 20-30 DEGREES ABOVE NORMAL FOR MUCH OF THE EAST AND UPPER
MIDWEST. WARMER THAN NORMAL TEMPERATURES WILL LIKELY LINGER EVEN
LONGER IN THE NORTHEAST THROUGH THURSDAY OR FRIDAY. COOLER AIR
BEHIND THE SYSTEM WILL INITIALLY STILL BE ON THE MILD SIDE, WITH
ONLY SLIGHTLY BELOW NORMAL READINGS OVER THE CENTRAL-SOUTHERN
ROCKIES/PLAINS ON TUESDAY. AS UPPER TROUGHING BECOMES ESTABLISHED
OVER THE EAST LATER IN THE WEEK, THE SOUTHEAST AND VICINITY SHOULD
TREND COOLER WITH TEMPERATURES DROPPING TO 5-10 DEGREES OR SO
BELOW NORMAL. MUCH OF THE WEST SHOULD SEE MODERATELY ABOVE NORMAL
TEMPERATURES THROUGH THE PERIOD.
DOLAN/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
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page