052
FXUS02 KWBC 260728
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
328 AM EDT TUE MAR 26 2024
VALID 12Z FRI MAR 29 2024 - 12Z TUE APR 02 2024
...ROUNDS OF HEAVY RAIN AND SNOW LIKELY ACROSS CALIFORNIA AND INTO
THE INTERMOUNTAIN WEST...
..OVERVIEW
SNOW AND RAIN MAY CONTINUE INTO FRIDAY ACROSS THE NORTHEAST AS A
LOW PRESSURE SYSTEM LINGERS. MEANWHILE, AN UPPER TROUGH/LOW IN THE
EASTERN PACIFIC LATE THIS WEEK IS FORECAST TO SLOWLY MOVE INTO
CALIFORNIA AND THE SOUTHWEST BY EARLY NEXT WEEK. THIS FEATURE AND
ITS SURFACE LOW WILL DIRECT MOISTURE INTO CALIFORNIA EASTWARD AND
POTENTIALLY PRODUCE HEAVY RAIN AND SNOW FOR CALIFORNIA INTO THE
SOUTHWEST/GREAT BASIN AND ROCKIES. FARTHER EAST, INCREASING
MOISTURE SHOULD COMBINE WITH SHORTWAVES ROUNDING A SOUTH-CENTRAL
U.S. UPPER RIDGE TO PRODUCE ROUNDS OF PRECIPITATION FROM THE NORTH-
CENTRAL TO EAST-CENTRAL U.S. LATE THIS WEEK WITH INCREASING
COVERAGE EARLY NEXT WEEK. THERE IS STILL QUITE A BIT OF UNCERTAINTY
IN THE DETAILS OF PRECIPITATION COVERAGE, AMOUNTS, AND TYPE, BUT
SNOW AND FREEZING RAIN ARE POSSIBLE ACROSS THE NORTHERN TIER
STATES.
..GUIDANCE/PREDICTABILITY ASSESSMENT
OVERALL, THE LATEST DETERMINISTIC AND ENSEMBLE MODEL GUIDANCE
OFFERED REASONABLE AGREEMENT FOR THE SYNOPTIC PATTERN ACROSS THE
CONUS DURING THE MEDIUM RANGE PERIOD, THOUGH WITH TYPICAL
UNCERTAINTY IN THE DETAILS. THE FIRST FEATURE OF NOTE IS A LIFTING
NEGATIVELY TILTED TROUGH OVER THE NORTHEASTERN U.S. LATE WEEK AND
THE WESTERN ATLANTIC SURFACE LOW REFLECTION. SOME ECMWF RUNS HAVE
BEEN ON THE SLOW SIDE OF THE GUIDANCE ENVELOPE WITH THE SURFACE LOW
TRACK, INCLUDING THE 12Z. WEST-EAST WIGGLES IN THE LOW/FRONTAL
POSITION ARE GENERALLY SMALL BUT UNFORTUNATELY HAVE BIG
IMPLICATIONS FOR THE PRECIPITATION FORECAST IN NEW ENGLAND.
THROUGH LATE WEEK, THERE IS GOOD MODEL AGREEMENT AND HIGH
CONFIDENCE FOR MID-UPPER RIDGING ACROSS THE SOUTH-CENTRAL U.S., BUT
FARTHER NORTH MODELS VARY WITH EJECTING SHORTWAVES RIDING THE
RIDGE, IMPACTING PLACEMENT OF PRECIPITATION. THERE WERE NOT
NECESSARILY OUTLIERS WITHIN THE 12/18Z GUIDANCE ENVELOPE, BUT JUST
VARIATIONS THAT WILL HAVE TO BE RESOLVED AT SHORTER FORECAST
TIMESCALES.
MEANWHILE, A CLOSED UPPER LOW WILL SLOWLY MOVE EASTWARD TOWARD AND
INTO THE WEST COAST LATE WEEK INTO THE WEEKEND, SUPPORTING AN
ATMOSPHERIC RIVER OVER CALIFORNIA. BY THE EARLY PART OF NEXT WEEK,
MODELS VARY WITH THE TIMING OF THE TROUGH/LOW TRACKING EASTWARD,
WITH RELATION TO IT POSSIBLY PHASING WITH DEEPENING NORTHERN STREAM
TROUGHING IN THE NORTH-CENTRAL CONUS. SOME GUIDANCE FROM THE
12/18Z CYCLE STARTED TO SHOW MORE PHASING AFTER PREVIOUS RUNS KEPT
THE STREAMS SEPARATE THROUGH TUESDAY. THE 18Z AND NOW 00Z GFS AS
WELL AS THE ECMWF ARE ON THE PHASED SIDE. AI/MACHINE LEARNING
MODELS GENERALLY HAVE PHASING AS WELL. OVERALL THIS CAN BE A TRICKY
PATTERN THOUGH, SO THE PHASING/SEPARATION AND TIMING COULD
CERTAINLY CHANGE IN FUTURE UPDATES. THE 00Z GUIDANCE SUITE
GENERALLY HAS THE SOUTHERN STREAM WEST LOW MOVING MORE QUICKLY
EASTWARD, MAKING PHASING MORE LIKELY.
THE WPC FORECAST WAS BASED ON A MULTI-MODEL BLEND OF 12/18Z
DETERMINISTIC GUIDANCE THROUGH THE EARLY-MID MEDIUM RANGE PERIOD.
GIVEN THE INCREASING SPREAD INTO DAYS 6-7, QUICKLY INCREASED THE
AMOUNT OF GEFS AND EC ENSEMBLE MEANS IN THE BLEND TO OVER HALF BY
THE LATTER PART OF THE PERIOD.
..WEATHER/HAZARDS HIGHLIGHTS
SURFACE LOW PRESSURE IN THE WESTERN ATLANTIC TRACKING TOWARD THE
CANADIAN MARITIMES COULD CAUSE SOME PRECIPITATION TO LINGER ACROSS
NEW ENGLAND INTO FRIDAY. THE WESTWARD EXTENT OF THE PRECIPITATION,
ESPECIALLY ANY HEAVY AMOUNTS, REMAINS UNCERTAIN AS IT IS QUITE
DEPENDENT ON EXACT LOW TRACK. THERE IS SOME POTENTIAL FOR HEAVY
RAIN TO OCCUR OVER DOWNEAST MAINE THOUGH, AND A SURGE OF COLD AIR
ON THE BACKSIDE MAY ALLOW PRECIPITATION TO CHANGEOVER TO WET, HEAVY
SNOW ACROSS HIGHER ELEVATIONS FARTHER WEST ACROSS NEW ENGLAND.
HOWEVER, THERE IS ALSO SOME CHANCE THAT LITTLE TO NO PRECIPITATION
OCCURS IN NEW ENGLAND IF THE LOW IS FARTHER OFFSHORE, SO CONTINUE
TO MONITOR FUTURE FORECASTS. BRISK WINDS MAY ALSO OCCUR IN NEW
ENGLAND ON THE BACKSIDE OF THE LOW LATE WEEK.
FOR THE WESTERN U.S., AN ACTIVE AND UNSETTLED PERIOD IS EXPECTED
AS A PERSISTENT JET ON THE SOUTHEAST SIDE OF AN UPPER LOW DIRECTS
MOISTURE INTO CALIFORNIA EASTWARD. AT LEAST A WEAK ATMOSPHERIC
RIVER SHOULD START TO TAKE AIM AT CALIFORNIA ON FRIDAY AND PRODUCE
SOME LOCALLY HEAVY PRECIPITATION. A MARGINAL RISK LOOKS TO BE IN
GOOD SHAPE FOR FRIDAY'S EXCESSIVE RAINFALL OUTLOOK, FROM COASTAL
CALIFORNIA TOWARD THE FOOTHILLS OF THE SIERRA NEVADA, WHILE THE
HIGHER ELEVATIONS OF THE SIERRA CAN EXPECT HEAVY SNOW. BY SATURDAY,
ANOMALOUS MOISTURE LIKELY REACHING ABOVE THE 95TH PERCENTILE WILL
BE DIRECTED AT SOUTHERN CALIFORNIA. NOTABLE UPSLOPE FLOW INTO THE
TRANSVERSE RANGES MEANS HEAVY AMOUNTS COULD OCCUR, SO A SLIGHT RISK
IS PLANNED FOR URBAN AREAS TO THE UPSLOPE PORTIONS OF THE
TRANSVERSE RANGE BELOW THE SNOWY HIGHER ELEVATIONS FOR SATURDAY. A
MARGINAL RISK IS IN PLACE FARTHER EAST, STRETCHING INTO SOUTHWEST
NEVADA AS MOISTURE SPILLS WELL INLAND. AMPLE MOISTURE REMAINS IN
PLACE INTO SUNDAY-MONDAY ACROSS MUCH OF CALIFORNIA INTO THE DESERT
SOUTHWEST AND GREAT BASIN AND INTO THE ROCKIES. MODERATE TO HEAVY
SNOW IS LIKELY IN THE HIGHER ELEVATIONS OF THE INTERMOUNTAIN WEST.
FARTHER EAST, SHORTWAVES GENERALLY RIDING ALONG THE NORTHERN SIDE
OF A CENTRAL U.S. RIDGE COULD COMBINE WITH MOISTURE TO PRODUCE SOME
LIGHT TO MODERATE PRECIPITATION FRIDAY INTO THE WEEKEND ACROSS THE
NORTH-CENTRAL U.S. AND GREAT LAKES REGION INTO OHIO VALLEY.
PRECIPITATION LOOKS TO INCREASE IN COVERAGE AND AMOUNTS BY EARLY
NEXT WEEK. CONFIDENCE REMAINS LOWER THAN DESIRED FOR WHERE
PRECIPITATION WILL OCCUR AS WELL AS THE PRECIPITATION TYPES.
HOWEVER, CHANCES FOR WINTRY PRECIPITATION ARE INCREASING ACROSS THE
NORTHERN PLAINS AND UPPER MIDWEST BY THE WEEKEND, AND STRETCHING
INTO THE GREAT LAKES REGION AND HIGHER ELEVATIONS OF THE NORTHEAST
BY MONDAY.
SOME CHILLY TEMPERATURES MAY LINGER ACROSS THE NORTH-CENTRAL U.S.
THROUGH MUCH OF THE PERIOD, BUT FARTHER SOUTH FROM THE CENTRAL TO
SOUTHERN PLAINS/MISSISSIPPI VALLEY, A NOTABLE WARMING TREND IS
EXPECTED LATE WEEK INTO THE WEEKEND AS UPPER RIDGING BUILDS.
TEMPERATURES OF 10-20 DEGREES ABOVE AVERAGE WILL BECOME WIDESPREAD,
WITH HIGHS IN THE 70S AND 80S REACHING KANSAS AND MISSOURI WHILE
HIGHS CLIMB INTO THE 90S IF NOT 100F IN SOUTHERN TEXAS. THE ABOVE
NORMAL TEMPERATURES ARE LIKELY TO EXPAND EAST INTO THE
OHIO/TENNESSEE VALLEYS, MID-ATLANTIC, AND SOUTHEAST BY EARLY NEXT
WEEK. A COLD FRONT IS FORECAST TO FINALLY DROP TEMPERATURES IN THE
SOUTH-CENTRAL U.S. BY TUESDAY BEHIND A COLD FRONT, FOCUSING THIS
WARMTH IN THE SOUTHEAST. MEANWHILE IN THE WEST, NEAR TO ABOVE
NORMAL LOWS BUT NEAR TO BELOW NORMAL HIGHS ARE FORECAST, CONSISTENT
WITH THE CLOUDS AND PRECIPITATION THERE. ONE EXCEPTION MAY BE OVER
THE PACIFIC NORTHWEST WHERE ENOUGH UPPER RIDGING MAY BUILD IN TO
PUSH HIGHS A ABOVE NORMAL BY THE WEEKEND AND EARLY NEXT WEEK.
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 (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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