614
FXUS02 KWBC 111859
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
259 PM EDT THU APR 11 2024
VALID 12Z SUN APR 14 2024 - 12Z THU APR 18 2024
...DEEPENING PLAINS SURFACE LOW LIKELY TO BRING SEVERE AND HEAVY
RAINFALL THREATS AHEAD OF IT AND STRONG WINDS AND NOTABLE SNOW
BEHIND...
..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 LOW PRESSURE SYSTEM OVER THE
PLAINS BY EARLY NEXT WEEK. VARIOUS HAZARDS ARE LIKELY WITH THIS
STORM SYSTEM, INCLUDING SEVERE WEATHER AND BANDS OF HEAVY RAINFALL
ON THE WARM SIDE 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 FOR ABOVE
NORMAL TEMPERATURES.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODEL AGREEMENT IS RATHER GOOD EARLY NEXT WEEK, INDICATING AN
UPPER LOW ATOP CALIFORNIA/NEVADA AS THE PERIOD BEGINS SUNDAY AND
ITS EASTWARD PROGRESSION TOWARD THE CENTRAL U.S. BY EARLY TUESDAY.
THERE ARE SOME SLIGHT DIFFERENCES IN THE SURFACE LOW POSITION AND
DEPTH AS IT CONSOLIDATES LATE MONDAY INTO TUESDAY, BUT NOTHING TOO
EGREGIOUS. BY WEDNESDAY GFS RUNS HAVE BEEN ON THE DEEP SIDE OF THE
SPREAD FOR THE SURFACE LOW AS IT REACHES NEAR THE CANADIAN BORDER,
BUT THE NEWER 12Z RUN SEEMS IN BETTER AGREEMENT.
THE SECOND UPPER TROUGH/LOW OF NOTE WILL BE THE TROUGH DIGGING IN
THE NORTHWEST BY TUESDAY AND DEEPENING/EXPANDING SOUTHEAST
WEDNESDAY-THURSDAY. THIS FEATURE SHOWS RELATIVELY MORE SPREAD IN
AMPLITUDE AS WELL AS THE LOCATION AND DURATION OF ANY EMBEDDED
UPPER LOW. THE 00Z GFS SEEMED A LITTLE EAST/FAST WITH THE FEATURE
TUESDAY-THURSDAY, BUT THE 06Z WAS MORE IN LINE WITH OTHER GUIDANCE.
BY WEDNESDAY AND ESPECIALLY THURSDAY, INCREASING SPREAD IS NOTED
WITH WITH HOW MUCH ENERGY MAKES ITS WAY EAST TOWARD THE FIRST UPPER
LOW (OVER THE GREAT LAKES AT THAT TIME) AND HOW MUCH STAYS PUT OR
DIGS IN THE WEST, WHILE ENERGY POTENTIALLY DIVING SOUTHWARD FROM
NORTH-CENTRAL CANADA COMPLICATES MATTERS. THE 00Z ECMWF AND CMC
WERE FARTHER SOUTH WITH THE DEPTH OF THE TROUGHING IN THE WEST
COMPARED TO THEIR NEWER 12Z RUNS.
FOR THE EARLY PART OF THE PERIOD, WPC MAINTAINED A MULTI-MODEL
BLEND OF THE DETERMINISTIC GUIDANCE FAVORING THE 00Z ECMWF AND 06Z
GFS. GRADUALLY TRANSITIONED TO A BLEND OF HALF MODELS/HALF ENSEMBLE
MEANS (ECMWF AND GEFS) BY DAY 7 AMID INCREASING SPREAD AND
UNCERTAINTY.
..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 HIGH WINDS
ARE POSSIBLE OVER PARTS OF SOUTHERN CALIFORNIA AND NEVADA 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 SURFACE LOW MONDAY-TUESDAY. THE STORM PREDICTION CENTER IS
ALREADY HIGHLIGHTING AREAS OF SEVERE POTENTIAL FOR THE PLAINS ON
MONDAY AND FOR THE MID-MISSISSIPPI TO WESTERN OHIO VALLEY ON
TUESDAY GIVEN THE ABUNDANT INSTABILITY AND MOISTURE. THESE
INGREDIENTS COULD ALSO PRODUCE HEAVY RAINFALL WITH INTENSE RATES
THAT COULD CAUSE FLASH FLOODING CONCERNS OVER PARTS OF THE MIDWEST
AND PLAINS. GUIDANCE SHOWS A FAIR AMOUNT OF SCATTER WITH THE
DETAILS, AND SOME AREAS HAVE DRY ANTECEDENT CONDITIONS THAT COULD
LIMIT FLOOD POTENTIAL, BUT THE OVERALL THREAT REMAINS SUFFICIENT TO
SHOW 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. AN EMBEDDED
SLIGHT RISK COULD BE ADDED IF AND WHEN MODELS NARROW IN ON A FOCUS
FOR HEAVY RAINFALL. CONTINUED NORTHEASTWARD PROGRESSION OF THE
STORM SHOULD CONCENTRATE HEAVIEST RAINFALL OVER THE UPPER MIDWEST
BY TUESDAY. BEHIND THE LOW, THE STORM SHOULD PRODUCE A BROAD AREA
OF GUSTY WINDS, ESPECIALLY OVER THE SOUTHERN/CENTRAL HIGH PLAINS
MONDAY AND INTO THE NORTH-CENTRAL HIGH PLAINS TUESDAY.
THE NEXT UPPER TROUGH DIGGING INTO THE WESTERN U.S. AND EVENTUALLY
EXTENDING INTO THE NORTHERN PLAINS EARLY-MID WEEK, ALONG WITH
ANOTHER FRONTAL BOUNDARY, SHOULD TEND TO FOCUS PRECIPITATION OVER
THE NORTHERN HALF OR SO OF THE ROCKIES AND HIGH PLAINS FOR A FEW
DAYS. THUS ON THE BACKSIDE OF THE CENTRAL U.S. SURFACE LOW,
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. BY NEXT THURSDAY OR SO,
THE SURFACE FRONT AHEAD OF THIS TROUGH MAY BECOME PARALLEL TO THE
UPPER LOW OVER THE CENTRAL U.S. 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 IN THE
EASTERN U.S. 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. THEN 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 MAY EXTEND FARTHER SOUTHWESTWARD.
TATE/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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