330
FXUS02 KWBC 181901
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
200 PM 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 TO EASTERN 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 STILL SOME LINGERING DIFFERENCES
IN THE DETAILS, WHICH BECOME MORE NOTICEABLE WITH TIME (AS IS
TYPICAL). LINGERING WESTERN ATLANTIC TROUGHING SUNDAY WILL GET
SHUNTED AWAY AS THE UPSTREAM UPPER RIDGE MOVES INTO AND SETS UP
OVER THE EAST DURING THE WORKWEEK, LIKELY RELOADING WITH TIME AS
THE ATLANTIC SUBTROPICAL RIDGE SUPPORTS IT. MODELS/MEANS CONTINUE
TO AGREE WELL WITH THESE FEATURES. FARTHER WEST, MEAN TROUGHING
WILL PERSIST OVER THE WESTERN HALF OF THE LOWER 48 WITH RELATIVELY
MORE MODEL SPREAD. THE MOST NOTABLE DIFFERENCES ARISE THE SECOND
HALF OF NEXT WEEK AS SEPARATE SYSTEMS INTO THE WEST WORK TO
AMPLIFY/REINFORCE TROUGHING OVER THE WEST-CENTRAL U.S.. THIS LEADS
TO DIFFERENT DEGREES OF AMPLIFICATION AND PLACEMENT OF THE MEAN
TROUGH, THOUGH ALL WELL WITHIN THE REALM OF SOLUTIONS FOR A DAY 6
OR 7 FORECAST. ALSO SOME QUESTION IN THE STRENGTH AND POSITION OF
UPPER LEVEL RIDGING INTO THE WEST COAST NEXT THURSDAY.
WITH GOOD INITIAL MODEL AGREEMENT, THE WPC FORECAST USED A BLEND
OF THE LATEST DETERMINISTIC GUIDANCE FOR THE EARLY PART OF THE
PERIOD. INCORPORATED THE GEFS AND EC ENSEMBLE MEANS STARTING DAY 5
AND INCREASED THEIR PROPORTION TO 40 PERCENT BY DAY 7 AMID THE
INCREASING MODEL DIFFERENCES. THIS SERVED TO SMOOTH OUT INDIVIDUAL
MODEL DIFFERENCES BUT MAINTAIN SOME STRENGTH IN INDIVIDUAL
SYSTEMS. THE CMC WAS NOT PREFERRED LATE PERIOD DUE TO IT BEING
SLIGHTLY FASTER/FARTHER INLAND WITH RIDGING OVER THE WEST.
..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 INTO FAR SOUTHWEST OREGON 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, AS THE PACIFIC NORTHWEST LOOKS TO SEE PERIODIC PRECIPITATION
THROUGH THE WEEK. AMOUNTS FARTHER INLAND 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 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/GULF COAST,
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
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page