789
FXUS02 KWBC 051858
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
158 PM EST WED MAR 5 2025
VALID 12Z SAT MAR 08 2025 - 12Z WED MAR 12 2025
..OVERVIEW
GUIDANCE SHOWS A MODERATELY PROGRESSIVE PATTERN FROM THE WEEKEND
INTO THE MIDDLE OF NEXT WEEK, WITH THREE SIGNIFICANT SYSTEMS OF
NOTE. AN UPPER LOW EJECTING FROM THE SOUTHERN ROCKIES/HIGH PLAINS
EARLY SATURDAY MAY PRODUCE A SMALL AREA OF HIGH PLAINS SNOW AND
THEN OPEN UP AND DEVELOP A SURFACE WAVE ALONG WITH SOUTHEAST U.S.
ENHANCED RAINFALL. A TRAILING UPPER RIDGE BUILDING INTO THE WEST
SHOULD WEAKEN AS IT REACHES THE EASTERN STATES. THEN THE FOCUS
WILL TURN TO A COUPLE LOWS DEVELOPING OVER THE EAST PACIFIC, ONE
NEARING THE WEST COAST NEXT MONDAY (REACHING THE CENTRAL U.S.
WEDNESDAY) AND THE SECOND AROUND WEDNESDAY. BOTH WILL LIKELY BRING
SOME FOCUSED RAIN/MOUNTAIN SNOW TO THE WEST WITH THE LATTER STORM
EXPECTED TO BRING THE POTENTIAL FOR HEAVIER TOTALS. MEANWHILE,
GREAT LAKES/NORTHEAST UPPER TROUGHING SHOULD FLATTEN AFTER MONDAY
WHILE A WAVY MEAN FRONTAL BOUNDARY OVER SOUTHERN CANADA AND THE
NORTHEAST MAY DIP INTO THE NORTHERN TIER AS THE FIRST PACIFIC
SYSTEM MOVES INLAND.
..GUIDANCE/PREDICTABILITY ASSESSMENT
DYNAMICAL AND MACHINE LEARNING (ML) GUIDANCE AGREE FAIRLY WELL
WITH THE LARGE-SCALE ASPECTS OF THE PATTERN, BUT THERE ARE SOME
MEDIUM TO SMALLER SCALE DETAILS THAT ARE UP FOR DEBATE. AMONG THE
00Z/06Z RUNS, THE CMC WAS THE SLOW EXTREME WITH THE WEEKEND INTO
MONDAY SOUTHERN TIER SHORTWAVE WITH THE ML MODELS VARIED SOMEWHAT
FOR TIMING BUT ALSO NOT SUPPORTING THE SLOW CMC. FARTHER WEST,
GUIDANCE CLUSTERING IS IMPROVING FOR THE IDEA OF AMPLIFYING EASTERN
PACIFIC TROUGH ENERGY TO CLOSE OFF AN UPPER LOW OFFSHORE
CALIFORNIA BY EARLY MONDAY. HOWEVER THE 00Z UKMET STRAYED FAST/OPEN
(IMPROVING IN THE NEW 12Z RUN) WHILE THE 06Z GFS WOBBLED NORTHWEST
OF CONSENSUS FOR A TIME (00Z/12Z RUNS BETTER). THE UPPER SYSTEM
SHOULD REACH THE ROCKIES/PLAINS BY NEXT WEDNESDAY, WITH TYPICAL
SPREAD FOR EXACT TIMING. A MODEL/MEAN BLEND YIELDS A PLAINS/MIDWEST
SURFACE LOW DEPTH CLOSE TO THE AVERAGE OF ML MODELS. THERE IS
STILL A DECENT AMOUNT OF SPREAD FOR THE POTENTIAL WEDNESDAY SYSTEM
NEAR THE WEST COAST. SOME DYNAMICAL MODELS SHOW A RATHER VIGOROUS
SURFACE LOW, WHILE CMC RUNS ARE A FEW HOURS LATER TO DEVELOP THEIR
STRONGEST LOW. ML MODELS ARE GENERALLY WEAKER THAN THE DYNAMICAL
MODELS AT THE SURFACE (BUT AGREE REASONABLY WELL FOR THE ALIGNMENT
OF THE UPPER TROUGH) WITH VARIED IDEAS FOR SURFACE DETAILS. A
MODEL/ENSEMBLE MEAN BLEND MAINTAINS GOOD CONTINUITY FOR TRACK AND
AN INTERMEDIATE DEPTH OF THE SURFACE LOW WHILE AWAITING BETTER
DETAIL AGREEMENT.
GUIDANCE COMPARISONS LED TO STARTING WITH MOSTLY 00Z/06Z GFS AND
00Z ECMWF EMPHASIS, WITH A LITTLE 00Z UKMET, EARLY-MID PERIOD. THE
GFS COMPONENT SWITCHED ENTIRELY TO THE 00Z RUN AROUND MONDAY-
TUESDAY DUE TO POOR AGREEMENT NEAR THE WEST COAST IN THE 06Z RUN.
THE REST OF THE FORECAST INCORPORATED SOME OF THE 06Z GEFS/00Z
ECENS MEANS WITH THE GFS/ECMWF RUNS.
..WEATHER/HAZARDS HIGHLIGHTS
THE UPPER LOW FORECAST TO EJECT FROM THE SOUTHERN ROCKIES/HIGH
PLAINS ON SATURDAY MAY INITIALLY PRODUCE A NARROW BAND OF
MEANINGFUL SNOW. PROBABILITIES OF 0.25 INCH LIQUID IN THE FORM OF
SNOW ARE CURRENTLY ABOUT 10-35 PERCENT OVER NORTHEASTERN NEW
MEXICO AND FAR NORTHWESTERN TEXAS. THEN SHOWERS AND THUNDERSTORMS
WILL INCREASE IN COVERAGE OVER THE SOUTH AS THE UPPER SYSTEM OPENS
UP AND MOVES EASTWARD, SUPPORTING A SURFACE WAVE. THE DAY
4/SATURDAY EXCESSIVE RAINFALL OUTLOOK MAINTAINS A MARGINAL RISK
AREA OVER PARTS OF THE LOWER MISSISSIPPI VALLEY, GULF COAST, AND
SOUTHEAST. MOISTURE ANOMALIES REACH UP TO 2-2.5 STANDARD DEVIATIONS
ABOVE NORMAL AND THE SYNOPTIC SETUP APPEARS TO SUPPORT POTENTIAL
FOR SOME TRAINING OF CONVECTION. THE ONLY ADJUSTMENT IN THE
AFTERNOON UPDATE WAS TO NUDGE THE AREA A BIT SOUTHWARD, PER
ECMWF/ECENS/ICON GUIDANCE LEANING ON THAT SIDE OF THE ENVELOPE. ML
GUIDANCE FALLS BETWEEN THE ECMWF AND FARTHER NORTH GFS, WHILE
SUPPORT FOR THE NORTHERN SIDE OF THE SPREAD HAS WANED. BY DAY
5/SUNDAY, GUIDANCE REMAINS SPLIT REGARDING THE POTENTIAL FOR SOME
CONTINUATION OF TRAINING/HEAVY RAINFALL OVER NORTHERN FLORIDA.
PREFER TO MAINTAIN NO RISK AREA FOR NOW BUT ONE MAY BE NEEDED IF
FUTURE RUNS GRAVITATE MORE TO THE HEAVIER SIDE OF THE CURRENT
SPREAD.
FARTHER NORTH, THERE WILL BE STRONG AND GUSTY WINDS LINGERING
ACROSS THE NORTHEAST ON SATURDAY BEHIND EASTERN CANADA LOW
PRESSURE. WAVES ALONG A FRONT MAY BRING ONE OR MORE EPISODES OF
MOSTLY LIGHT SNOW TO THE NORTHERN GREAT LAKES/NORTHEAST FROM THE
WEEKEND INTO NEXT WEEK.
EASTERN PACIFIC UPPER TROUGHING DURING THE WEEKEND SHOULD INITIALLY
FOCUS AN ATMOSPHERIC RIVER INTO VANCOUVER ISLAND WITH SOME
PRECIPITATION EXTENDING INTO NORTHWESTERN WASHINGTON STATE. WITH AN
UPPER LOW POSSIBLY CLOSING OFF NEAR CALIFORNIA BY EARLY MONDAY
(WITH ASSOCIATED SURFACE DEVELOPMENT), IT MAY TAKE UNTIL EARLY NEXT
WEEK FOR AN ATMOSPHERIC RIVER EVENT TO BRING HEAVIER RAIN TO
PORTIONS OF CENTRAL AND SOUTHERN CALIFORNIA, ALONG WITH HEAVY SNOW
FOR THE SIERRA AND EVENTUALLY MOVING INLAND ACROSS THE HIGHER
TERRAIN OF THE INTERMOUNTAIN WEST. THIS LOOKS TO SET UP A
PARTICULARLY WINDY PATTERN FOR PARTS OF THE WEST AS WELL. WITH
UNCERTAIN DETAILS, ANOTHER SIGNIFICANT SYSTEM MAY AFFECT THE WEST
COAST BY WEDNESDAY. MOST GUIDANCE SUGGESTS THAT THIS STORM COULD
PRODUCE HEAVIER PRECIPITATION AND LOCALLY STRONGER WINDS THAN THE
FIRST ONE.
THE SOUTHERN ROCKIES/HIGH PLAINS UPPER LOW WILL SUPPORT WELL BELOW
NORMAL HIGHS (BY 15-20F OR SO) UNDERNEATH IT ON SATURDAY. ABOVE
AVERAGE TEMPERATURES WILL EXPAND SOUTHWARD/EASTWARD FROM THE
NORTHERN PLAINS FROM THE WEEKEND INTO NEXT WEEK. THE NORTHERN
PLAINS SHOULD RETURN CLOSER TO NORMAL BY NEXT WEDNESDAY AS A FRONT
SAGS SOUTH FROM CANADA. LOCATIONS FROM THE NORTHERN-CENTRAL PLAINS
THROUGH THE MIDWEST AND EVENTUALLY INTO THE NORTHERN MID-ATLANTIC
SHOULD SEE ONE OR MORE DAYS WITH HIGHS REACHING 15-30F ABOVE
EARLY MARCH AVERAGES. THIS WARMTH MAY PUSH HIGHS WELL INTO THE 60S
FROM THE DAKOTAS INTO IOWA AND INTO THE 70S AS FAR NORTH AS THE
MIDDLE MISSISSIPPI VALLEY AND PARTS OF THE MID-ATLANTIC.
RAUSCH/CAMPBELL
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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