578
FXUS02 KWBC 180659
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
159 AM EST THU JAN 18 2024
VALID 12Z SUN JAN 21 2024 - 12Z THU JAN 25 2024
...MULTIPLE ROUNDS OF POTENTIALLY HEAVY PRECIPITATION WILL AFFECT
THE WEST...
...HEAVY RAIN AND FLOODING POTENTIAL INCREASE ACROSS THE
SOUTH-CENTRAL U.S. NEXT WEEK...
..OVERVIEW
THE LARGE SCALE PATTERN NEXT WEEK WILL SHIFT NOTABLY FROM THIS
WEEK'S COLD PATTERN, AS AN UPPER RIDGE AXIS SHIFTS FROM THE
CENTRAL U.S. INTO THE EAST AND MEAN TROUGHING GETS ESTABLISHED IN
THE WESTERN TO CENTRAL U.S. EARLY TO MID-NEXT WEEK. THIS WILL
PROMOTE WARM AND MOIST INFLOW LIKELY FROM BOTH THE PACIFIC AND THE
GULF, WARMING TEMPERATURES IN THE EASTERN HALF OF THE COUNTRY
AFTER A CHILLY SUNDAY IN SOME AREAS. MULTIPLE DAYS OF HEAVY RAIN
AND POTENTIAL FOR FLASH FLOODING ARE EXPECTED ACROSS THE
SOUTH-CENTRAL U.S. NEXT WEEK AMID THE STALLING UPPER FLOW PATTERN
AND INCREASING MOISTURE. AS SHORTWAVES TRACK THROUGH THE WESTERN
TROUGH, MULTIPLE ROUNDS OF PRECIPITATION ARE LIKELY IN THE WEST
INTO NEXT WEEK, WITH HEAVY RAIN ACROSS CALIFORNIA IN PARTICULAR.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODEL AGREEMENT ON THE SYNOPTIC SCALE REMAINS REASONABLY GOOD
THROUGH THE PERIOD, THOUGH WITH INCREASING DIFFERENCES FURTHER OUT
IN TIME (AS IS TYPICAL). LINGERING WESTERN ATLANTIC TROUGHING
SUNDAY WILL GET SHUNTED AWAY AS THE UPSTREAM UPPER RIDGE TRACKS
EAST AND SETS UP OVER THE EAST DURING THE WORKWEEK, LIKELY
RELOADING WITH TIME AS THE ATLANTIC SUBTROPICAL RIDGE SUPPORTS IT.
MODELS/MEANS AGREE WELL WITH THESE FEATURES. FARTHER WEST, MEAN
TROUGHING WILL PERSIST OVER THE WESTERN HALF OF THE LOWER 48 WITH
RELATIVELY MORE MODEL SPREAD. FIRST, THERE ARE SOME DIFFERENCES IN
THE TIMING AND POSITION OF SHORTWAVES WITHIN THE BROAD TROUGH
EARLY NEXT WEEK, BUT THESE DIFFERENCES FALL WELL WITHIN TYPICAL
SPREAD EXPECTED IN THE MEDIUM RANGE PERIOD. IN FACT THE INCOMING
00Z MODEL GUIDANCE, AT LEAST THE ECMWF AND GFS, LOOKS PRETTY
AGREEABLE EVEN WITH THESE SHORTWAVES.
BY DAY 5/TUESDAY AND ESPECIALLY WEDNESDAY, ENERGY MAY CONSOLIDATE
TO DEVELOP AN UPPER LOW IN THE SOUTHWEST, POSSIBLY TEMPORARILY
SPLITTING AWAY FROM THE TROUGH INTO THE SOUTHERN STREAM. MODELS
VARY WITH THE POTENTIAL AND TIMING OF THIS STREAM SEPARATION. ONE
COMPLICATING FACTOR IS A SHORTWAVE UPSTREAM DIRECTED AT THE
PACIFIC NORTHWEST AROUND WEDNESDAY. THE 12Z ECMWF WAS AGGRESSIVE
WITH THIS FEATURE COMPARED TO OTHER MODEL GUIDANCE AND WAS NOT
FAVORED. FORTUNATELY IN THE 00Z CYCLE, MODEL RUNS ARE MORE
AGREEABLE IN SHOWING A POSITION OF THE SHORTWAVE/SMALL CLOSED LOW
AS WELL AS THE SURFACE LOW FARTHER NORTH TOWARD BRITISH
COLUMBIA/SOUTHEAST ALASKA, NOT DIRECTLY IMPACTING THE CONUS
PATTERN AS MUCH. DESPITE THE BETTER CONSENSUS, FURTHER CHANGES ARE
POSSIBLE GIVEN THESE FEATURES ARISE FROM THE DATA-POOR PACIFIC
OCEAN. GENERALLY MODELS SHOW A RIDGE AXIS REACHING THE WEST COAST
BY THURSDAY, THOUGH THE EXACT DETAILS WITH THE TROUGH FARTHER EAST
ARE STILL NEBULOUS.
WITH GOOD INITIAL MODEL AGREEMENT, THE WPC FORECAST USED A BLEND
OF THE DETERMINISTIC 18Z GFS AND 12Z ECMWF/CMC/UKMET FOR THE EARLY
PART OF THE PERIOD. INCORPORATED THE GEFS AND EC ENSEMBLE MEANS
STARTING DAY 5 AND INCREASED THEIR PROPORTION TO ABOUT HALF BY
DAYS 6-7 AMID THE INCREASING MODEL DIFFERENCES. THIS SERVED TO
SMOOTH OUT INDIVIDUAL MODEL DIFFERENCES BUT MAINTAIN SOME STRENGTH
IN INDIVIDUAL SYSTEMS.
..WEATHER/HAZARDS HIGHLIGHTS
THE WEST COAST STATES CAN EXPECT ROUNDS OF PRECIPITATION INTO NEXT
WEEK. EARLY IN THE WEEK, A LIKELY ATMOSPHERIC RIVER IS FORECAST TO
BRING MOISTURE TO CALIFORNIA AND SINK SOUTH GRADUALLY, WHILE A
POTENT SHORTWAVE AND THE LEFT EXIT REGION OF THE JET STREAM WILL
PROVIDE UPPER-LEVEL DYNAMICAL SUPPORT. THESE SHOULD COMBINE WITH
SOME INSTABILITY POSSIBLY SNEAKING ONSHORE, LEADING TO PERIODS OF
HIGH RAIN RATES LIKELY REACHING WELL OVER HALF AN INCH PER HOUR.
SLIGHT RISKS OF EXCESSIVE RAINFALL ARE INDICATED FOR SUNDAY AND
MONDAY GIVEN THIS SETUP, WITH SUNDAY'S ERO ENCOMPASSING NORTHERN
AND CENTRAL PARTS OF CALIFORNIA AND MONDAY'S FOCUSED ON SOUTHERN
CALIFORNIA. HOW FAR SOUTH TO EXTEND THE ERO ON SUNDAY REMAINS A
CHALLENGE AS MODEL GUIDANCE VARIES WITH AMOUNTS. THE SIERRA NEVADA
WILL LIKELY RECEIVE HEAVY SNOW WITH THE PRECIPITATION ACTIVITY
EARLY NEXT WEEK. RAIN AND SNOW ARE EXPECTED FARTHER EAST INTO THE
INTERMOUNTAIN WEST/SOUTHWEST AS WELL. MEANWHILE THE PACIFIC
NORTHWEST LOOKS TO SEE PERIODIC PRECIPITATION. AMOUNTS THERE COULD
ADD UP OVER MULTIPLE DAYS, BUT AT THIS POINT NO RISK AREAS ARE
INDICATED FOR FLOODING SINCE RAIN RATES DO NOT LOOK VERY HIGH
THERE AND THE REGION CAN TYPICALLY HANDLE QUITE A BIT OF RAIN.
PARTS OF THE INTERIOR NORTHWEST COULD HAVE SOME POSSIBLY
PERSISTENT FREEZING RAIN LASTING INTO SUNDAY.
INCREASING MOISTURE AHEAD OF THE WESTERN U.S. TROUGHING WILL START
TO SPREAD RAIN INTO THE SOUTHERN PLAINS ON SUNDAY. THE TREND HAS
BEEN FOR HEAVY RAIN TO START OVER SOUTH TEXAS LATE SUNDAY NIGHT,
SO A MARGINAL RISK AREA REMAINS IN PLACE THERE ON THE DAY 4
EXCESSIVE RAINFALL OUTLOOK. RAIN TOTALS ARE FORECAST TO QUICKLY
RAMP UP ON MONDAY AND LAST THROUGH TUESDAY-WEDNESDAY FOR PARTS OF
THE SOUTHERN PLAINS INTO THE LOWER MISSISSIPPI VALLEY, AND THESE
HEAVY TOTALS COULD PRODUCE FLASH FLOODING CONCERNS. AS A STARTING
POINT, A SLIGHT RISK IS DELINEATED FOR DAY 5/MONDAY IN THE
SOUTHEASTERN QUADRANT OF TEXAS INTO FAR SOUTHWESTERN LOUISIANA
WHERE THE BEST POTENTIAL FOR INSTABILITY TO PRODUCE HIGH RAIN
RATES IS, WITH A MARGINAL RISK EXTENDING FARTHER NORTH IN OKLAHOMA
AND THE LOWER MISSISSIPPI VALLEY. THE PRECIPITATION SHIELD WILL
GRADUALLY SPREAD NORTHEASTWARD ON MONDAY AND TUESDAY AND COULD
CAUSE SOME WINTRY WEATHER ON ITS NORTHERN SIDE. IN SOME AREAS
ACROSS THE MISSISSIPPI VALLEY INTO THE MIDWEST, PRECIPITATION MAY
START AS FREEZING RAIN OR MIXED PRECIPITATION BUT THEN TRANSITION
TO RAIN AS WARM AIR SPREADS FARTHER NORTH. THE GREAT LAKES
VICINITY IS MOST LIKELY TO SEE PERSISTENT WINTRY WEATHER OUT OF
THIS PRECIPITATION, BUT EVEN THERE IT LOOKS FAIRLY LIGHT AT THIS
POINT. PRECIPITATION MAY EVENTUALLY REACH THE EAST AROUND MIDWEEK
AFTER A DRY PERIOD THERE.
COLD AIR FROM AN ARCTIC HIGH WILL LINGER INTO SUNDAY ACROSS
PORTIONS OF THE MIDWEST, WHERE LOW TEMPERATURE ANOMALIES OF 15-25
DEGREES BELOW AVERAGE ARE POSSIBLE BEFORE QUICKLY WARMING TO NEAR
NORMAL FOR HIGHS. THE SOUTHERN PLAINS TO MID-SOUTH AND
SOUTHEASTERN U.S. LOOK TO SEE BELOW NORMAL LOWS AND HIGHS SUNDAY,
POSSIBLY PERSISTING INTO MONDAY IN SOME AREAS, BUT MODERATING
CLOSER TO NORMAL. THE WARMING TREND WILL CONTINUE FURTHER INTO
NEXT WEEK ACROSS THE EASTERN HALF OF THE U.S. UNDERNEATH THE UPPER
RIDGE ALLOWING FOR MORE SOUTHERLY FLOW. BY WEDNESDAY-THURSDAY, THE
EASTERN HALF OF THE COUNTRY SHOULD SEE ABOVE NORMAL TEMPERATURES,
AROUND 15-30F ABOVE AVERAGE FOR LOWS (LOCALLY HIGHER IN THE
MIDWEST) AND 10-20F ABOVE FOR HIGHS. FROM THE ROCKIES WESTWARD,
LOW TEMPERATURES AROUND 10-15F ABOVE NORMAL AND HIGH TEMPERATURES
GENERALLY WITHIN A FEW DEGREES OF NORMAL ARE EXPECTED.
TATE
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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