333
FXUS02 KWBC 120700
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 AM EDT SAT APR 12 2025
VALID 12Z TUE APR 15 2025 - 12Z SAT APR 19 2025
..OVERVIEW
AS THE MEDIUM RANGE PERIOD BEGINS TUESDAY, UPPER TROUGHING IN THE
GREAT LAKES/OHIO VALLEY AND A COUPLE OF SURFACE COLD FRONTS WILL
LEAD TO SOME EASTERN U.S. PRECIPITATION, WITH POSSIBLE SNOW IN THE
HIGHER ELEVATIONS OF THE INTERIOR NORTHEAST IN GENERALLY COOLER
THAN AVERAGE TEMPERATURES. MEANWHILE SOUTHERN STREAM UPPER ENERGY
IN THE EASTERN PACIFIC AND CALIFORNIA COULD PRODUCE SOME LIGHT
SCATTERED PRECIPITATION IN CALIFORNIA TO THE FOUR CORNERS STATES
AND THEN SOME MODEST RAIN IN THE CENTRAL PLAINS/MIDDLE MISSISSIPPI
VALLEY MIDWEEK. FARTHER NORTH, MODEL GUIDANCE HAS SHOWN AMPLE
SPREAD IN THE EVOLUTION OF NORTHERN STREAM TROUGHING IN
SOUTHWESTERN CANADA MIDWEEK, WITH SOME MODELS DIVING THE
TROUGH/EMBEDDED UPPER LOW MORE SOUTH AND SOME SHIFTING IT MORE
EAST, LEADING TO SIGNIFICANT SENSIBLE WEATHER DIFFERENCES. THIS
FORECAST TRENDED TOWARD THE TROUGH DEEPENING SOUTHWARD, ALLOWING
FOR MORE NOTABLE PRECIPITATION IN THE ROCKIES WEDNESDAY-FRIDAY, AND
SLOWER PROGRESSION OF A COLD FRONT AND ITS BROAD PRECIPITATION
SHIELD THROUGH THE CENTRAL U.S. THURSDAY TOWARD THE EAST-CENTRAL
U.S. FRIDAY.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE FIRST TROUGH TRACKING THROUGH THE EAST-CENTRAL AND EASTERN U.S.
TUESDAY-WEDNESDAY CONTINUES TO SHOW GOOD MODEL AGREEMENT. INITIAL
WEAKENING TROUGHING IN SOUTHERN CALIFORNIA TUESDAY AND THE PRIMARY
UPPER LOW IN THE EASTERN PACIFIC HAVE SOME WEST-EAST SPREAD
INITIALLY, BUT OVERALL A MULTI-MODEL BLEND WORKED WELL. THUS THE
MAIN MODEL DIAGNOSTIC CONCERN IS REGARDING THE NEXT NORTHERN STREAM
UPPER TROUGH AND ITS PLACEMENT BEYOND MIDWEEK. MODELS FROM A DAY
AGO HEAVILY FAVORED THIS TROUGH SKIRTING EASTWARD, BUT IN THE PAST
COUPLE OF MODEL CYCLES MORE SPREAD HAS ARISEN. OVERALL, THERE HAS
BEEN A SLOWER TREND FOR THE TROUGH MOVING EAST IN MODELS AND
ENSEMBLES. SOME DETERMINISTIC MODELS DIVE ENERGY SOUTHWARD THROUGH
THE GREAT BASIN OR SO THURSDAY-FRIDAY, ENOUGH TO FORM A CLOSED LOW
THERE. THESE INCLUDE THE 12Z ECMWF AND CMC, AS WELL AS THE 18Z GFS
IN A SIGNIFICANT FLIP FROM THE 12Z GFS THAT HAD THE UPPER
TROUGH/LOW TRACKING EAST LIKE OLDER GUIDANCE. HOWEVER, AI/ML MODELS
FROM THE 12Z/18Z CYCLE DID NOT SHOW THE TROUGHING DIGGING AS FAR
WEST AS THIS CLUSTER OF DETERMINISTIC MODELS. THEY GENERALLY SHOWED
A CENTRAL U.S. TROUGH, WHICH WAS STILL SLOWER WITH THE TROUGH THAN
SOME PREVIOUS FORECASTS. THIS FORECAST ISSUANCE WAS NOT VERY
CONFIDENT IN THE SOLUTION PRESENTED BY THE 12Z EC/CMC AND 18Z GFS.
THE FORECAST BLEND QUICKLY RAMPED UP THE PROPORTION OF ENSEMBLE
MEANS DAY 5 AND USED THE 18Z GEFS/12Z ECENS MEANS ALONE BY DAYS 6-7
GIVEN THE LOW CONFIDENCE IN THE CHANGING FORECAST PATTERN. EVEN
THIS BLEND OF THE ENSEMBLE MEANS WAS A NOTABLE CHANGE FROM THE
PREVIOUS FORECAST, SLOWING DOWN THE TROUGH AND COLD FRONT AND
PRODUCING MUCH MORE PRECIPITATION ACROSS THE INTERIOR WEST. NOW THE
NEWER 00Z MODEL CYCLE HAS COME IN WITH A SIMILAR PATTERN FOR UPPER
TROUGHING TO DIVE SOUTH THROUGH THE GREAT BASIN OR SO, AND NOW
SHOWS THE ORIGINALLY EASTERN PACIFIC ENERGY PHASING IN BY LATE WEEK
TO FORM A SOUTHWEST UPPER LOW. THIS INCLUDES THE 00Z AIFS IN A BIG
CHANGE FROM ITS 18Z RUN. SO THERE IS MORE CONFIDENCE THAT THIS MUCH
FARTHER WEST TROUGHING DEVELOPING IS REASONABLE. THUS EVEN THOUGH
FORECAST CHANGES IN THIS CYCLE WERE NOTABLE, EXPECT MORE IN THE
NEXT FORECAST. IT APPEARS THE ENERGY THAT WILL EVENTUALLY FORM THIS
TROUGH/UPPER LOW IS CURRENTLY SPINNING OVER THE BERING SEA AND
VICINITY, SO HOPEFULLY AS IT TRACKS INTO AREAS WITH MORE OBSERVED
DATA FOR BETTER MODEL INITIALIZATION SOON AND CONTINUED STABILITY
IN THE FORECAST.
..WEATHER/HAZARDS HIGHLIGHTS
A SURFACE LOW TRACKING THROUGH SOUTHEASTERN CANADA TUESDAY AND ITS
TRAILING COLD FRONT WILL SUPPORT SOME PRECIPITATION ACROSS THE
GREAT LAKES TO EASTERN SEABOARD TUESDAY AND LINGERING ACROSS THE
INTERIOR NORTHEAST WEDNESDAY. ON THE BACKSIDE OF THE LOW,
TEMPERATURES COULD BE COLD ENOUGH FOR SNOW IN HIGHER ELEVATIONS OF
THE ADIRONDACKS AND GREEN AND WHITE MOUNTAINS INTO TUESDAY. GUSTY
WINDS ARE ALSO POSSIBLE.
A WEAKENING UPPER LOW REACHING THE SOUTHWEST BY TUESDAY MAY
PRODUCE SOME VERY SCATTERED AND LIGHT PRECIPITATION. THEN AS
SURFACE LOW PRESSURE DEVELOPS IN THE CENTRAL HIGH PLAINS AND MOVES
EAST, RAIN IS FORECAST TO SPREAD ACROSS THE CENTRAL PLAINS TO
MIDDLE MISSISSIPPI VALLEY FOR MIDWEEK. RECENT MODELS SHOW THIS RAIN
REMAINING PRETTY MODEST, SO NO EXCESSIVE RAINFALL AREAS ARE IN
PLACE FOR THE DAY 4-5 (TUESDAY/WEDNESDAY) EROS. THEN FARTHER NORTH,
THIS FORECAST ISSUANCE HAS TRENDED TOWARD SHOWING GREATER COVERAGE
OF RAIN AND HIGHER ELEVATION SNOW OVER PARTS OF THE WEST/ROCKIES
UNDER THE DIGGING UPPER TROUGH. PRECIPITATION LOOKS TO SPREAD FROM
THE NORTHERN ROCKIES/HIGH PLAINS WEDNESDAY A BIT SOUTH CENTERED
OVER WYOMING THURSDAY AND INTO COLORADO FRIDAY. POSSIBLE
INTERACTION WITH THE SOUTHERN STREAM TROUGH TRACKING EAST FROM THE
EASTERN PACIFIC COULD SUPPORT PRECIPITATION ACROSS PARTS OF
CALIFORNIA/GREAT BASIN/SOUTHWEST. A LOW PRESSURE/FRONTAL SYSTEM
TRACKING EASTWARD ALONG WITH SOME UPPER-LEVEL SUPPORT COULD LEAD TO
RAIN AND PERHAPS FAR NORTHERN TIER SNOW IN THE MIDWEST THURSDAY
AND SHIFTING INTO THE GREAT LAKES/OHIO VALLEY AND NORTHEAST ON
FRIDAY. THE FRONTAL SYSTEM AND PRECIPITATION HAVE TRENDED SLOWER
THAN THE PREVIOUS FORECAST. THEN DEPENDING ON IF AND HOW
TROUGHING/AN UPPER LOW DEVELOPS OVER THE SOUTHWEST LATE WEEK,
MOISTURE STREAMING INTO THE SOUTHERN PLAINS COULD ALLOW FOR
INCREASING RAIN CHANCES THERE. OVERALL, RECOMMEND CONTINUING TO
MONITOR FORECAST UPDATES UNTIL THE FORECAST STABILIZES.
INITIAL MEAN RIDGING ALOFT IN THE WEST WILL ALLOW FOR ABOVE NORMAL
TEMPERATURES THERE, SPREADING INTO THE PLAINS BY MIDWEEK.
GENERALLY TEMPERATURES ARE FORECAST TO BE 10-20 DEGREES ABOVE
NORMAL, ALLOWING FOR HIGHS IN THE 90S IN THE DESERT SOUTHWEST AND
THEN ACROSS MUCH OF TEXAS BY THURSDAY. COOLER THAN AVERAGE
TEMPERATURES ARE LIKELY IN THE GREAT LAKES AND OHIO VALLEY TUESDAY
INTO THE EASTERN U.S. WEDNESDAY AND POSSIBLY INTO THURSDAY. LOWS
SHOULD GENERALLY BE 5-10F BELOW AVERAGE AND HIGHS AROUND 10-15F
BELOW AVERAGE. AFTER THAT, THE TEMPERATURE FORECAST BECOMES MORE
UNCERTAIN DEPENDENT ON THE UPPER PATTERN. THE INTERIOR WEST LOOKS
TO GRADUALLY COOL INTO LATE WEEK, THOUGH THE NORTHWEST COULD STAY A
BIT ABOVE AVERAGE WITH POSSIBLE UPPER RIDGING POKING IN. THE
SOUTHEASTERN U.S. MAY WARM TO ABOVE NORMAL LATE 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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