547
FXUS02 KWNH 210701
PREEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
200 AM EST FRI FEB 21 2025
VALID 12Z MON FEB 24 2025 - 12Z FRI FEB 28 2025
..WET PACIFIC NORTHWEST PATTERN LASTS INTO MONDAY
..OVERVIEW
THE UPPER FLOW PATTERN SHOULD REMAIN RATHER PROGRESSIVE THROUGH
MUCH OF THE MEDIUM RANGE PERIOD. BY MONDAY, A NORTHERN STREAM
SHORTWAVE WILL SHIFT THROUGH THE NORTHEAST, WITH A SOUTHERN STREAM
WAVE THROUGH THE GULF AND FLORIDA. MEANWHILE, A STRONG SHORTWAVE
WILL MOVE ONSHORE IN THE PACIFIC NORTHWEST ON TUESDAY, WITH
GUIDANCE SUGGESTING IT EVENTUALLY AMPLIFIES OVER THE EAST BY LATE
NEXT WEEK. THIS IN TURN LEADS TO AN AMPLIFYING RIDGE OVER THE WEST
WITH A TROUGH OR CUT OFF LOW REACHING THE WEST COAST BY NEXT
FRIDAY. THE INITIAL SHORTWAVE INTO THE WEST WILL BE ASSOCIATED WITH
AN ONGOING ATMOSPHERIC RIVER AND HEAVY RAIN THREAT THAT LASTS
THROUGH ABOUT MONDAY.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODELS AND ENSEMBLES SHOW FAIRLY GOOD AGREEMENT ON THE LARGE SCALE
PATTERN THROUGH MUCH OF NEXT WEEK, THOUGH STILL CONSIDERABLE
VARIABILITY IN THE DETAILS OF INDIVIDUAL SYSTEMS. THERE WAS ENOUGH
AGREEMENT THE FIRST HALF OF THE PERIOD FOR A MULTI-MODEL BLEND. TWO
AREAS OF UNCERTAINTY TO NOTE THE SECOND HALF OF NEXT WEEK. THE
FIRST BEING UNCERTAINTY IN STREAM FLOW SEPARATIONS AND PATTERN
AMPLIFICATION OVER THE EAST LATE NEXT WEEK, WHICH TRANSLATES TO
CONSIDERABLE DIFFERENCES IN THE PRECIPITATION DISTRIBUTION AND
AMOUNTS IN THE EAST. THE SECOND AREA IS OUT WEST WITH AN
APPROACHING UPPER TROUGH/CUT OFF LOW NEXT THURSDAY-FRIDAY. THE 18Z
GFS IS CONSIDERABLY SLOWER THAN THE ECMWF AND CMC, HOLDING THE
UPPER LOW WELL OFFSHORE. WPCS FORECAST FAVORED THE ECMWF AND CMC
WITH THE ENSEMBLE MEANS, WHICH RESULTED IN A POSITION OVER SOUTHERN
CALIFORNIA NEXT FRIDAY. THE NEW 00Z GUIDANCE TONIGHT (AVAILABLE
AFTER THE WPC FORECAST WENT OUT) CONTINUES TO SHOW VARIABILITY,
WITH THE GFS CONSIDERABLY FASTER AND THE ECMWF/CMC SLOWER THAN
THEIR PREVIOUS RUNS. WPC LEANED MORE HEAVILY TOWARDS THE ENSEMBLE
MEANS LATE PERIOD.
..WEATHER/HAZARDS HIGHLIGHTS
A CONSISTENT FEED OF MOISTURE WILL BE ONGOING INTO THE PACIFIC
NORTHWEST AS THE PERIOD BEGINS MONDAY, WITH MODERATE TO HEAVY LOWER
ELEVATION RAIN AND HIGH ELEVATION/MOUNTAIN SNOWS. ENHANCED SNOWS
WILL ALSO WORK INLAND OVER THE NORTHERN INTERMOUNTAIN WEST/ROCKIES
WITH DOWNSTREAM SYSTEM TRANSLATION. EXPECT HIGHEST PRECIPITATION
TOTALS OVER THE FAVORED TERRAIN AND COASTAL AREAS OF WESTERN
WASHINGTON/OREGON AND INTO NORTHWEST CALIFORNIA. THE DAY 4 WPC
EXCESSIVE RAINFALL OUTLOOK VALID FOR MONDAY CONTINUES A MARGINAL
RISK THREAT AREA GIVEN THE CUMULATIVE EFFECT OF THE MULTI-DAY
EPISODE WHICH BEGINS IN THE SHORT RANGE PERIOD. THE NORTHWEST
SHOULD TREND DRIER MIDWEEK AS A DYNAMIC MONDAY- TUESDAY SYSTEM
DEPARTS AND UPPER RIDGING BUILDS IN.
DOWNSTREAM, SHORTWAVE ENERGY OVER THE GULF AND FLORIDA MAY SUPPORT
PERIODS OF MODERATE RAINFALL ACROSS SOUTH FLORIDA ON MONDAY.
DIGGING OF NORTHERN STREAM SHORTWAVE ENERGY INTO EARLY NEXT WEEK
WILL SPREAD LIGHT PRECIPITATION (MOSTLY SNOW) FROM THE GREAT LAKES
REGION THROUGH NEW ENGLAND. LATEST GUIDANCE IS NOT TOO ENTHUSIASTIC
ABOUT POTENTIAL FOR WRAPBACK COASTAL LOW LINKAGE OVER THE
NORTHEAST TO ENHANCE ACTIVITY EARLY- MID NEXT WEEK, BUT IT REMAINS
WORTH MONITORING IN FUTURE RUNS. MODERATE CYCLOGENESIS AND
FRONTOGENESIS MAY DEVELOP OVER THE PLAINS/MISSISSIPPI VALLEY NEXT
WEDNESDAY AND WORK INTO THE EASTERN U.S. BY THURSDAY AND FRIDAY.
THE WARMER PATTERN BY THEN SHOULD MOSTLY FAVOR AN EMERGING AREA OF
MODERATE WRAPPING RAINS WITH RETURN GULF MOISTURE FLOW ASIDE FROM A
LITTLE WINTRY WEATHER ON THE FAR NORTH COOL SIDE OF THE LOW.
BY EARLY NEXT WEEK MOST, LOCATIONS WEST OF THE MISSISSIPPI RIVER
WILL WARM TO MUCH ABOVE NORMAL WITH DECENT COVERAGE OF PLUS 10-25
DEGREE ANOMALIES. BEST POTENTIAL FOR HIGHEST ANOMALIES WILL BE NEAR
THE NORTHERN PLAINS. THE EAST SHOULD ALSO WARM TO ABOVE NORMAL
EARLY TO MID WEEK, BEFORE COOLING OFF AGAIN BACK TO NORMAL (OR
SLIGHTLY BELOW) LATE WEEK UNDERNEATH OF TROUGHING.
SANTORELLI
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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