666
FXUS02 KWBC 110659
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
259 AM EDT THU APR 11 2024
VALID 12Z SUN APR 14 2024 - 12Z THU APR 18 2024
...DEEPENING PLAINS STORM EARLY NEXT WEEK LIKELY TO BRING A SEVERE
WEATHER THREAT ALONG WITH STRONG WINDS AND AREAS OF HEAVY
RAINFALL...
..OVERVIEW
WITH SOME CONTINUED SPREAD IN THE DETAILS, GUIDANCE AGREES IN
PRINCIPLE FOR A DEEP UPPER LOW TO BE CROSSING CALIFORNIA AROUND
THE START OF THE PERIOD EARLY SUNDAY. CONTINUED PROGRESSION OF
THIS FEATURE SHOULD SUPPORT A DEEPENING STORM SYSTEM OVER THE
PLAINS BY EARLY NEXT WEEK, WITH VARIOUS HAZARDS INCLUDING SEVERE
WEATHER AND BANDS OF HEAVY RAINFALL ALONG WITH A BROAD AREA OF
GUSTY WINDS. BEHIND THIS STORM, AN UPPER TROUGH DIGGING DOWN FROM
BRITISH COLUMBIA INTO THE NORTHWEST U.S. EARLY NEXT WEEK SHOULD
ULTIMATELY EVOLVE INTO A BROADER POSITIVELY TILTED MEAN TROUGH
FROM SOUTH- CENTRAL CANADA THROUGH THE WEST. EXPECT THIS TROUGH TO
BRING COLDER TEMPERATURES AND MULTIPLE DAYS OF SNOW POTENTIAL
ESPECIALLY TO THE NORTHERN HALF OF THE ROCKIES/HIGH PLAINS.
MEANWHILE UPPER RIDGING OVER THE PLAINS ON SUNDAY WILL SHIFT
EASTWARD AND SETTLE NEAR THE EAST COAST TUESDAY-THURSDAY, LEADING
TO A CORRESPONDING SHIFT IN EMPHASIS FOR ABOVE NORMAL TEMPERATURES.
..GUIDANCE/PREDICTABILITY ASSESSMENT
AFTER SOME WAFFLING IN THE GUIDANCE OVER THE PAST DAY, NEW RUNS
SEEM TO BE IMPROVING THEIR CLUSTERING WITH SOME ASPECTS OF THE
FORECAST WHILE MAINTAINING SPREAD WITH OTHERS. FOR THE CALIFORNIA
INTO PLAINS UPPER LOW/STORM DEVELOPMENT, SOME MODELS HAD NUDGED A
LITTLE FASTER RECENTLY WHILE THE GFS STAYED ON THE SLOWER SIDE, BUT
ADDING IN THE NEW 00Z RUNS THERE SEEMS TO BE IMPROVED CLUSTERING
BETWEEN THE TWO SIDES. AMONG THE 12Z/18Z RUNS, A COMPOSITE OF
OPERATIONAL RUNS (MORE GFS/ECMWF RELATIVE TO THE UKMET/CMC)
PROVIDED A GOOD INTERMEDIATE SOLUTION WITH REASONABLE CONTINUITY.
ECMWF-INITIALIZED MACHINE LEARNING MODELS (MLS) ON AVERAGE CONTINUE
TO SUPPORT LOW PRESSURE HAVING A CENTRAL DEPTH IN THE MID-UPPER
980S MB EARLY TUESDAY, WHICH IS A LITTLE WEAKER THAN WHAT SOME
DYNAMICAL MODEL RUNS ARE SHOWING. GFS RUNS HAVE BEEN ON THE DEEP
SIDE OF THE SPREAD FOR THE SURFACE LOW AS IT REACHES NEAR THE
CANADIAN BORDER BY WEDNESDAY.
DETAIL DIFFERENCES CONTINUE FOR THE DIGGING WESTERN TROUGH,
INCLUDING ITS AMPLITUDE AT A SPECIFIC POINT IN TIME AS WELL AS THE
LOCATION AND DURATION OF ANY EMBEDDED UPPER LOW. A GENERAL MODEL
BLEND, WITH MODEST ENSEMBLE MEAN INCLUSION LATE IN THE PERIOD,
OFFERS A GOOD INTERMEDIATE STARTING POINT GIVEN THE SPREAD. NOTE
THAT THE NEW 00Z GFS SEEMS TO EXTEND ITS NORTHERN TIER TROUGH AXIS
EAST OF CONSENSUS LATE IN THE PERIOD.
AFTER A REBOUND IN SPREAD IN YESTERDAY'S 00Z RUNS, GUIDANCE HAS
RETURNED TO PRIOR CONSENSUS FOR THE GENERAL EVOLUTION OF THE WEAK
WAVE EMERGING FROM THE GREAT LAKES ON SUNDAY, ALONG WITH SOME
LINGERING NORTHEAST UPPER TROUGHING IN ITS WAKE WHICH SHOULD
SUPPORT THE TRAILING FRONT SETTLING INTO THE MID-ATLANTIC.
..WEATHER/HAZARDS HIGHLIGHTS
THE UPPER LOW CROSSING CALIFORNIA AROUND SUNDAY SHOULD PRODUCE SOME
AREAS OF LIGHT TO LOCALLY MODERATE RAIN AND HIGH ELEVATION SNOW
FROM CALIFORNIA INTO THE NORTHERN ROCKIES, WHILE STRONG WINDS ARE
POSSIBLE OVER SOME AREAS AS THE FEATURE PASSES THROUGH. THEN EXPECT
MULTIPLE HAZARDS OVER THE CENTRAL U.S. EARLY NEXT WEEK AS THE
UPPER LOW HELPS TO DEEPEN A PLAINS SYSTEM MONDAY-TUESDAY. THE STORM
PREDICTION CENTER IS ALREADY HIGHLIGHTING AN AREA OF SEVERE
POTENTIAL OVER THE PLAINS WHILE THE STORM SHOULD PRODUCE A BROAD
AREA OF GUSTY WINDS, ESPECIALLY OVER THE CENTRAL-SOUTHERN HIGH
PLAINS. MEANWHILE ABUNDANT MOISTURE AND INSTABILITY ASSOCIATED WITH
THIS DYNAMIC STORM SHOULD PRODUCE SOME AREAS OF INTENSE RAINFALL
OVER PARTS OF THE MIDWEST AND PLAINS. GUIDANCE SHOWS A FAIR AMOUNT
OF SCATTER WITH THE DETAILS AND SOME AREAS HAVE DRY ANTECEDENT
CONDITIONS, BUT THE OVERALL THREAT APPEARS SUFFICIENT TO INTRODUCE
A MARGINAL RISK AREA IN THE DAY 5 (MONDAY-MONDAY NIGHT) EXCESSIVE
RAINFALL OUTLOOK, EXTENDING FROM PARTS OF THE UPPER MIDWEST/EASTERN
DAKOTAS INTO THE SOUTH-CENTRAL PLAINS. CONTINUED NORTHEASTWARD
PROGRESSION OF THE STORM SHOULD CONCENTRATE HEAVIEST RAINFALL OVER
THE UPPER MIDWEST BY TUESDAY.
THE UPPER TROUGH DIGGING INTO THE WESTERN U.S. AND EVENTUALLY
EXTENDING INTO THE NORTHERN PLAINS EARLY-MID WEEK SHOULD TEND TO
FOCUS PRECIPITATION OVER THE NORTHERN HALF OR SO OF THE ROCKIES AND
HIGH PLAINS FOR TWO OR THREE DAYS. MEANINGFUL SNOW WILL BE
POSSIBLE OVER AT LEAST THE HIGHER ELEVATIONS AND SOME SNOW MAY
EXTEND INTO THE HIGH PLAINS BY MIDWEEK AS COLDER AIR REACHES THE
REGION. THE SURFACE FRONT AHEAD OF THIS TROUGH MAY BECOME PARALLEL
TO THE UPPER LOW OVER THE CENTRAL U.S. AROUND THE END OF THE PERIOD
NEXT THURSDAY. THE COMBINATION OF DECELERATING PROGRESSION AND SOME
GULF INFLOW MAY LEAD TO INCREASING RAINFALL NEAR THE FRONT AROUND
THAT TIME.
OVER THE EAST, A GREAT LAKES WAVE AND FRONTAL SYSTEM ON SUNDAY MAY
PRODUCE AN AREA OF RAINFALL OVER PARTS OF THE EASTERN GREAT
LAKES, UPPER OHIO VALLEY, AND NORTHERN MID-ATLANTIC/FAR SOUTHERN
NEW ENGLAND. THIS ACTIVITY MAY PRODUCE SOME POCKETS OF MODERATE TO
HEAVY RAIN BUT SO FAR IT APPEARS SUFFICIENTLY PROGRESSIVE AND
LOCALIZED NOT TO WARRANT AN AREA IN THE ERO. THEN MOSTLY LIGHT RAIN
MAY REACH THE NORTHEAST BY TUESDAY-WEDNESDAY AHEAD OF A WARM FRONT
ANCHORED BY THE PLAINS STORM.
PLAINS/MISSISSIPPI VALLEY UPPER RIDGING WILL SUPPORT WELL ABOVE
NORMAL TEMPERATURES ACROSS THE CENTRAL U.S. SUNDAY-MONDAY WITH SOME
NORTHERN/CENTRAL AREAS SEEING HIGHS 20-25F ABOVE NORMAL.
THEREAFTER, THE PATTERN EVOLUTION WILL LEAD TO A BROAD AREA OF
ABOVE NORMAL TEMPERATURES OVER THE EASTERN HALF OF THE COUNTRY INTO
THE SOUTHERN PLAINS, WITH ADVANCING FRONTAL SYSTEMS SLOWLY TRIMMING
THE WESTERN SIDE OF THE WARMTH. EXPECT HIGHS TO BE UP TO 10-15F OR
SO ABOVE NORMAL WITH ANOMALIES FOR MORNING LOWS TENDING TO BE
SEVERAL DEGREES HIGHER. THE SOUTHWESTERN U.S. WILL SEE BELOW NORMAL
HIGHS SUNDAY INTO MONDAY WITH THE UPPER LOW CROSSING THE REGION.
THE UPPER TROUGH DIGGING INTO THE WEST AND THEN INCLUDING THE
NORTHERN PLAINS WILL LIKELY START TO BRING BELOW NORMAL HIGHS INTO
THE NORTHWEST EARLY NEXT WEEK AND FOLLOWED BY READINGS 10-20F
BELOW AVERAGE OVER THE NORTHERN ROCKIES/HIGH PLAINS BY NEXT
WEDNESDAY-THURSDAY. LESS EXTREME COOL ANOMALIES WOULD EXTEND
FARTHER SOUTHWESTWARD.
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 (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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