457
FXUS02 KWBC 021855
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
255 PM EDT TUE APR 2 2024
VALID 12Z FRI APR 05 2024 - 12Z TUE APR 09 2024
...MAJOR NEW ENGLAND COASTAL STORM WITH MARITIME HAZARDS AND HIGH
WIND/COASTAL FLOODING ALONG WITH HEAVY SNOW TO LINGER INTO FRIDAY...
...WIDESPREAD PRECIPITATION/COOLING PATTERN FOR THE WEST LATE THIS
WEEK AND FOR THE CENTRAL U.S. THIS WEEKEND/EARLY NEXT WEEK...
..PATTERN OVERVIEW
DURING THE MEDIUM RANGE PERIOD, AN OMEGA STYLE BLOCKING PATTERN IS
EXPECTED TO FORM OVER THE CONTINENTAL U.S. AND SLOWLY TRANSITION
OUT OF THE BLOCKING PATTERN BY EARLY NEXT WEEK. TWO CLOSED UPPER
LOWS WILL INITIALLY BE LOCATED OVER THE WEST COAST AND NORTHEAST
ON FRIDAY WITH A RIDGE STRENGTHENING OVER THE CENTRAL U.S. AND
SOUTHERN CANADA. THE LOW OVER THE NORTHEAST WILL SUPPORT AN
IMPACTFUL COASTAL STORM WHILE THE LOW OVER THE WEST COAST SUPPORTS
ANOTHER FRONTAL SYSTEM MOVING EAST ACROSS MUCH OF THE WEST. THE
NORTHEASTERN LOW WILL EXIT INTO THE ATLANTIC AND THE WESTERN NOW
WILL MOVE INTO THE CENTRAL U.S. OVER THE WEEKEND, PUSHING THE
FRONTAL SYSTEM ACROSS THE ROCKIES INTO THE PLAINS. ANOTHER UPPER
LOW WILL MOVE DOWN THE WEST COAST TO THE SOUTHWEST EARLY NEXT WEEK,
WHICH MAY BRING ANOTHER FRONTAL SYSTEM ACROSS THE SOUTHERN TIER OF
THE NATION.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODEL GUIDANCE IS IN GOOD AGREEMENT ON THE UPPER LEVEL PATTERN WITH
AN EXPECTED AMOUNT OF UNCERTAINTY AND MODEL SPREAD FOR THIS TIME
PERIOD. THE HIGHEST AMOUNT OF UNCERTAINTY WILL BE SURROUNDING THE
EVOLUTION OF THE WESTERN SYSTEM AS IT MOVES INTO THE CENTRAL U.S.
OVER THE WEEKEND INTO EARLY NEXT WEEK. THE EVOLUTION WILL
ULTIMATELY DEPEND ON INTERACTIONS OF UPPER LEVEL FEATURES (HOW HIGH
PRESSURE OVER SOUTHERN CANADA AFFECTS THE STRENGTH AND LOCATION OF
THE UPPER LOW) AND COMPLEX FRONTOGENESIS TRANSITIONS. THIS SYSTEM
WILL LIKELY HAVE IMPLICATIONS FOR FRONTS, PRECIPITATION, AND CLOUD
COVER, WHICH COULD AFFECT VIEWING CONDITIONS FOR THE TOTAL SOLAR
ECLIPSE ON MONDAY.
THE WPC FORECAST WAS MAINLY DERIVED FROM A MULTI-MODEL BLEND OF
THE 06 UTC GFS AND 00 UTC ECMWF/CMC/UKMET FOR MAXIMUM SYSTEM
DETAIL CONSISTENT WITH ABOVE NORMAL PREDICTABILITY FRIDAY INTO
SUNDAY. OPTED TO ADD THE 06 UTC GEFS AND 00 UTC ECMWF ENSEMBLE
MEANS FOR MONDAY AND TUESDAY ALONG WITH THE DETERMINISTIC GUIDANCE
TO REDUCE INDIVIDUAL MODEL DIFFERENCES BUT MAINTAIN SOME DEPTH OF
SYSTEMS. SLIGHTLY HIGHER WEIGHT WAS GIVEN TO THE ECMWF COMPARED TO
THE CMC AND GFS BECAUSE IS ALIGNED BETTER WITH THE ENSEMBLE MEAN
SOLUTIONS. THE LATEST 12 UTC MODEL AND ENSEMBLE SUITE REMAINS
MAINLY IN LINE.
..WEATHER/HAZARDS HIGHLIGHTS
THE RISK OF EXCESSIVE RAINFALL LEADING TO FLASH FLOODING IS LESS
THEN 5 PERCENT FOR DAYS 4 AND 5 (FRIDAY AND SATURDAY). THE MARGINAL
RISK AREA THAT WAS PREVIOUSLY IN THE DAY 5 OUTLOOK FOR PARTS OF
MONTANA, WYOMING, AND SOUTH DAKOTA WAS REMOVED BECAUSE RAINFALL
RATES WILL BE LIMITED DUE TO A LACK OF INSTABILITY AND
PRECIPITATION SHOULD SWITCH OVER TO SNOW AND MIXED PRECIPITATION
DURING THE OVERNIGHT HOURS. THERE MAY BE FLASH FLOODING CONCERNS
EARLY NEXT WEEK IN THE SOUTH-CENTRAL U.S.
POTENT CLOSED UPPER LOW ROTATION WILL SUPPORT A MAJOR NOR'EASTER
OFFSHORE NEW ENGLAND, WITH IMPACTS LINGERING INTO FRIDAY. THIS
SYSTEM WILL SUPPORT SIGNIFICANT WRAP-BACK EARLY SPRING HEAVY SNOWS
OVER THE NORTHEAST AS DEPICTED IN THE WPC WINTER WEATHER OUTLOOK.
WHILE SNOW WILL BE THE PRIMARY PRECIPITATION TYPE INLAND,
PROTRACTED FETCH OFF THE ATLANTIC WITH THIS DEEP LOW MAY KEEP NEAR
COASTAL AREAS WARM ENOUGH NEAR THE GROUND FOR SLEET AND RAIN
LEADING INTO THIS FORECAST PERIOD. THE HEAVIEST OF THE WET SNOW IS
EXPECTED TO FALL ACROSS THE HIGHER ELEVATIONS OF THE INTERIOR
NORTHEAST. ADDITIONALLY, THE DEEP SURFACE LOW SHOULD PRODUCE HIGH
WINDS THAT, FOR A TIME, SHOULD BE ONSHORE AND COULD LEAD TO COASTAL
FLOODING. LIGHTER SNOW WILL LIKELY LINGER IN INTO FRIDAY FOR THE
NORTHEAST, AND WESTERLY FLOW COULD CREATE UPSLOPE FLOW AND SNOW
ACROSS THE APPALACHIANS THURSDAY INTO FRIDAY AND ALSO ACROSS THE
LOWER GREAT LAKES WHERE THERE COULD BE SOME LAKE EFFECT
ENHANCEMENT. TEMPERATURES ARE FORECAST TO BE COOLER THAN AVERAGE
FOR THE EASTERN SEABOARD BEHIND THIS SYSTEM, GRADUALLY WARMING UP
EARLY NEXT WEEK.
IN THE WEST, THE STRONGLY AMPLIFYING UPPER TROUGH/CLOSED LOW AND
ASSOCIATED SURFACE FRONTAL SYSTEM WILL ACT TO COOL TEMPERATURES.
THIS MAY RISK RECORD COLD DAILY MAXIMUM TEMPERATURES IN SOUTHERN
CALIFORNIA. PRECIPITATION CHANCES WILL SPREAD ACROSS THE WEST LATE
THIS WEEK INTO THE WEEKEND, WITH PRECIPITATION FALLING AS RAIN AT
LOW ELEVATIONS AND MIXED PRECIPITATION AND SNOW AT HIGHER
ELEVATIONS. NO EXCESSIVE RAINFALL RISKS ARE IN PLACE, THOUGH THE
RISK MAY BE NONZERO IN SOUTHERN CALIFORNIA WHICH HAS SEEN A WET
PATTERN LATELY.
THE ENERGY WILL EJECT NORTHEASTWARD OVER THE CENTRAL U.S. SUNDAY
INTO MONDAY WITH MOIST RETURN FLOW FROM THE GULF OF MEXICO AHEAD OF
THE SYSTEM. THIS WILL INITIATE AND SPREAD ORGANIZED PRECIPITATION
ACROSS A BROAD REGION WITH CYCLOGENESIS/FRONTOGENESIS. SNOW WILL
ALSO BE POSSIBLE IN THE NORTHERN ROCKIES AND NEARBY VICINITY WITH
RAIN AND THUNDERSTORMS FARTHER SOUTH AND EAST. BEHIND THE SYSTEM,
HIGH WINDS AND CRITICAL FIRE DANGER WILL BE POSSIBLE IN THE
SOUTHERN AND CENTRAL PLAINS AS HUMIDITY DROPS AND WINDS INCREASE.
RENEWED LIGHT TO MODERATE PRECIPITATION IS POSSIBLE ALONG THE WEST
COAST EARLY NEXT WEEK AS A NEW PACIFIC UPPER TROUGH DIGS DOWN
TOWARDS THE SOUTHWEST, THEN THE FOCUS FOR PRECIPITATION WILL SHIFT
INTO THE SOUTH-CENTRAL U.S. ON TUESDAY AS THE SYSTEM PROGRESSES.
HEAVY RAINFALL MAY LEAD TO FLASH FLOODING CONCERNS FOR THE SOUTHERN
PLAINS AND LOWER MISSISSIPPI VALLEY MONDAY NIGHT THROUGH TUESDAY.
DOLAN/SCHICHTEL
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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