522
FXUS02 KWBC 230629
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
129 AM EST THU JAN 23 2025
VALID 12Z SUN JAN 26 2025 - 12Z THU JAN 30 2025
..OVERVIEW
THE START OF THE PERIOD ON SUNDAY WILL FEATURE AN UPPER LEVEL
CLOSED LOW DIVING SOUTHWARD ALONG THE CALIFORNIA COAST, AND ONLY
VERY SLOWLY MOVING EASTWARD WITH TIME NEXT WEEK. THIS SHOULD BRING
BENEFICIAL PRECIPITATION TO PARTS OF SOUTHERN CALIFORNIA THAT HAVE
BEEN DEALING WITH DEVASTATING WILDFIRES. ORGANIZED RAINS/TERRAIN
SNOWS SHOULD MAKE THEIR WAY DOWNSTREAM INTO THE SOUTHWEST AS WELL.
MEANWHILE, NORTHERN STREAM MEAN TROUGHING, AND REINFORCING
SHORTWAVES WILL CROSS FROM THE NORTHERN PLAINS INTO THE GREAT LAKES
AND NORTHEAST INTO NEXT WEEK. MODERATE TO LOCALLY HEAVY RAINFALL
WILL DEVELOP TO THE SOUTH ACROSS THE LOWER MISSISSIPPI VALLEY
SUNDAY AND MONDAY AS A SLOW MOVING FRONTAL BOUNDARY MOVES THROUGH
THE REGION. ADDITIONAL FRONTAL WAVE GENESIS OVER THE SOUTHERN
PLAINS INTO THE MIDDLE OF NEXT WEEK GIVEN SOUTHWEST LOW SLOW
APPROACH MAY AGAIN INCREASE LEAD RETURN FLOW AND EMERGING RAINFALL
TO MONITOR.
..GUIDANCE/PREDICTABILITY ASSESSMENT
ON THE LARGE SCALE, THE GUIDANCE CONTINUES TO SHOW REASONABLE
AGREEMENT, BUT THERE REMAINS PLENTY OF UNCERTAINTY IN THE DETAILS
AND TIMING OF INDIVIDUAL SYSTEMS. THROUGH EARLY NEXT WEEK, MODELS
SHOW GOOD CLUSTERING OF THE LOW AS IT SLOWLY MOVES SOUTH THROUGH
CALIFORNIA. AFTER TUESDAY THOUGH, THERE IS SOME UNCERTAINTY IN
TIMING INTO THE SOUTHWEST/FOUR CORNERS AND ALSO WITH LESS
PREDICTABLE ENERGY THAT MAY SHEAR OFF FROM THE LOW. ENSEMBLE MEAN
GUIDANCE PROVIDES A GOOD MIDDLE GROUND FOR THIS FEATURE IN THE LATE
PERIOD. TO THE NORTH, MEAN NORTHERN STREAM TROUGHING OVER THE
NORTHERN PLAINS- GREAT LAKES-NORTHEAST CONTINUES TO SHOW
UNCERTAINTY IN THE AMPLITUDE OF INDIVIDUAL SHORTWAVES DROPPING
THROUGH, ESPECIALLY NEXT WEDNESDAY AND THURSDAY.
ACCORDINGLY, WPC GUIDANCE USED A GENERAL MODEL BLEND FOR THE FIRST
HALF OF THE PERIOD. FOR DAYS 6 AND 7, TRANSITIONED TO A 60/40
SPLIT BETWEEN THE ENSEMBLE MEANS AND THE DETERMINISTIC GFS AND
ECMWF WHICH SEEMED TO PROVIDE THE BEST STARTING POINT AMIDST THE
UNCERTAINTIES.
..WEATHER/HAZARDS HIGHLIGHTS
THE SLOW MOVING UPPER LOW THROUGH CALIFORNIA ON SUNDAY WILL
CONTINUE TO ALLOW FOR MUCH NEEDED RAIN TO SOUTHERN CALIFORNIA. EVEN
THOUGH QPF AMOUNTS ARE NOT TOO HIGH, GIVEN SENSITIVITY ESPECIALLY
IN FRESH BURN SCAR LOCATIONS, IT MAY NOT TAKE MUCH TO CAUSE
FLOODING CONCERNS. FOR THIS REASON, A SMALL MARGINAL RISK WAS ADDED
TO PARTS OF SOUTHERN CALIFORNIA ON THE DAY 4 EXCESSIVE RAINFALL
OUTLOOK. MODEST SNOWS ARE POSSIBLE ACROSS THE TERRAIN OF SOUTHERN
CALIFORNIA, WITH RAIN AND MOUNTAIN SNOW INTO PARTS OF THE SOUTHWEST
AS WELL. A TIGHTENED GRADIENT BEHIND THE COLD FRONT DROPPING SOUTH
MAY PRODUCE SOME GUSTY WINDS ALONG PARTS OF THE ROCKIES LATE THIS
WEEK AND CALIFORNIA AND NEVADA ON SATURDAY WITH OFFSHORE FLOW AND
MODESTLY FAVORABLE FIRE WEATHER CONDITIONS POSSIBLE AGAIN BEHIND
THE UPPER LOW NEXT WEEK TO KEEP AN EYE ON.
FARTHER EAST, GULF MOISTURE WILL INTERACT WITH A FRONT APPROACHING
THE LOWER MISSISSIPPI VALLEY TO TENNESSEE AND OHIO VALLEYS BY THIS
COMING WEEKEND/EARLY NEXT WEEK. LATEST GUIDANCE CONTINUES TO SHOW
HEAVY RAINFALL TOTALS OVER PARTS OF THE SOUTHERN U.S., WITH THE
POTENTIAL FOR HEAVY RAIN AND THUNDERSTORMS ON SUNDAY ACROSS THE
LOWER MISSISSIPPI VALLEY. A MARGINAL RISK WAS CARRIED INTO THE NEW
DAY 4/SUNDAY EXCESSIVE RAINFALL OUTLOOK FROM EASTERN TEXAS INTO
MISSISSIPPI WHERE STORMS MAY TRAIN ALONG A SLOW MOVING FRONTAL
BOUNDARY. SNOW OR A WINTRY MIX IS POSSIBLE ON THE NORTHERN SIDE OF
THIS PRECIPITATION SHIELD MAINLY OVER THE OHIO VALLEY, SOUTH-
CENTRAL APPALACHIANS, AND POSSIBLY THE TENNESSEE VALLEY AND
VICINITY. PRECIPITATION MAY SPREAD TOWARDS THE EAST COAST EARLY
NEXT WEEK AS THE FRONTAL SYSTEM PROGRESSES WITH SOME RAINFALL
REDEVELOPMENT ACROSS THE SOUTHERN PLAINS AND LOWER MISSISSIPPI
VALLEY AS WELL. THIS SIGNAL IS INCREASING WITH DEVELOPMENT OF AN
ORGANIZED FRONTAL WAVE WITH SOUTHWEST UPPER SYSTEM APPROACH.
MUCH OF THE EAST SHOULD FINALLY BE BACK UP TOWARDS NORMAL
TEMPERATURES EARLY NEXT WEEK, THOUGH READINGS A FEW DEGREES BELOW
NORMAL ARE POSSIBLE ACROSS THE SOUTHEAST. ANOMALOUSLY COLD
TEMPERATURES WILL ALSO DEVELOP IN THE HIGH PLAINS, ROCKIES, AND
MUCH OF THE WEST UNDER THE INFLUENCE OF UPPER TROUGHING. THE
COLDEST ANOMALIES WILL BE IN THE HIGH PLAINS AND ROCKIES TO
SOUTHERN HIGH PLAINS WHERE HIGH TEMPERATURES COULD BE 10-20 DEGREES
BELOW NORMAL. LATE PERIOD RIDGING OVER THE NORTHERN TIER COULD
ALLOW TEMPERATURES TO RISE ABOVE NORMAL NEXT WEEK, GRADUALLY
SHIFTING SOUTH AND EAST WITH TIME.
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 (QPF), EXCESSIVE RAINFALL
OUTLOOK (ERO), WINTER WEATHER OUTLOOK (WWO) PROBABILITIES, HEAT
INDICES, AND KEY MESSAGES CAN BE ACCESSED FROM:
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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