536
FXUS02 KWBC 090659
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
259 AM EDT TUE APR 9 2024
VALID 12Z FRI APR 12 2024 - 12Z TUE APR 16 2024
..OVERVIEW
THE VIGOROUS STORM SYSTEM AFFECTING THE EAST AT THE START OF THE
FORECAST PERIOD ON FRIDAY WILL CONTINUE TO TRACK OVER EASTERN
CANADA AND PUSH ITS TRAILING FRONT EASTWARD AS THE SUPPORTING
UPPER TROUGH LIFTS NORTHEASTWARD. SOME AREAS OF RAIN AND SNOW MAY
LINGER OVER THE NORTHEAST INTO SATURDAY. A TRAILING ROCKIES/PLAINS
UPPER RIDGE WILL BRING INITIAL WESTERN WARMTH INTO THE CENTRAL
U.S. WITH PARTS OF THE PLAINS SEEING HIGHS 15-25F ABOVE NORMAL
DURING THE WEEKEND. GUIDANCE IS STARTING TO STABILIZE FOR THE DEEP
UPPER LOW DROPPING INTO THE EASTERN PACIFIC DURING FRIDAY-SATURDAY,
BRINGING A BRIEF PERIOD OF PRECIPITATION INTO CALIFORNIA DURING
THE WEEKEND. HOWEVER AFTER SATURDAY THERE IS STILL TIMING SPREAD
FOR THE UPPER LOW BETWEEN CALIFORNIA AND THE PLAINS, WITH SOME
INFLUENCE FROM DIFFERENCES IN UPPER TROUGHING EXPECTED TO PUSH
GRADUALLY INTO THE NORTHWEST. THIS UPPER LOW WILL MOST LIKELY REACH
THE PLAINS BY NEXT TUESDAY AND SUPPORT A FAIRLY STRONG SURFACE LOW
AT THAT TIME.
..GUIDANCE/PREDICTABILITY ASSESSMENT
WITH GUIDANCE SHOWING REASONABLE AGREEMENT FOR THE DEPARTING
EASTERN SYSTEM, ATTENTION TURNS FARTHER WEST TO THE UPPER LOW
DROPPING OVER THE EASTERN PACIFIC AND THEN TRACKING INLAND PLUS
NORTHERN STREAM FLOW THAT MAY BRING A WAVE/FRONTAL SYSTEM ACROSS
THE NORTHERN/EASTERN U.S. A TRAILING TROUGH MAY PUSH INTO THE
NORTHWEST EARLY NEXT WEEK.
GUIDANCE IS AT LEAST CONSOLIDATING TOWARD THE IDEA OF A DEEP UPPER
LOW REACHING OFFSHORE CALIFORNIA BY SATURDAY, WITH A GENERAL MODEL
COMPOSITE LOOKING REASONABLE UP TO THAT TIME. THEN AS SPREAD
DEVELOPS FOR EASTWARD PROGRESSION, MOST OF THE RECENT RUNS OF ECMWF-
INITIALIZED MACHINE LEARNING MODELS (MLS) OFFER THE BEST SUPPORT
FOR CONTINUITY, WHICH WOULD BRING THE UPPER LOW CENTER TO THE
CALIFORNIA COAST BY EARLY SUNDAY AND THE HIGH PLAINS BY EARLY NEXT
TUESDAY. RELATIVE TO THIS SCENARIO, THE NEW 00Z GFS HAS TRENDED
SLOWER WHILE THE UKMET HAS STRAYED SOMEWHAT FASTER. RECENT ECMWF
RUNS HAVE TENDED TO STRAY ON THE FAST SIDE (PRIMARILY BY NEXT
TUESDAY IN THE 12Z VERSION) BUT THE NEW 00Z RUN HAS NUDGED SLOWER
TOWARD THE GFS (WHICH CATCHES UP BY THAT TIME) AND THE CMC.
SOME OF THIS TIMING SPREAD IS RELATED TO THE UPPER TROUGH EXPECTED
TO PUSH INTO SOUTHWESTERN CANADA AND THE NORTHWESTERN U.S. BY EARLY
NEXT WEEK. THERE HAS BEEN A SOMEWHAT SLOWER TREND FOR THE ARRIVAL
OF THIS TROUGH (AND A CORRESPONDING TREND FOR THE LEADING SURFACE
FRONT) BUT MOST DYNAMICAL MODELS/MEANS AND MLS SUGGEST MORE
NORTHWEST TROUGHING THAN FORECAST BY THE GFS--THUS LOWERING
CONFIDENCE IN THE SLOWEST SIDE OF THE SPREAD FOR THE UPPER LOW.
MEANWHILE THE GUIDANCE VARIES WITH LESS-DEFINED DETAILS OF NORTHERN
STREAM ENERGY THAT MAY SUPPORT A WEAK WAVE AND FRONTAL SYSTEM FROM
THE NORTHERN PLAINS INTO THE EAST SATURDAY ONWARD. THE MOST COMMON
THEME IS FAIRLY CLOSE TO CONTINUITY, WITH THIS WAVE REACHING THE
UPPER MIDWEST/GREAT LAKES BY SUNDAY AND THEN THE NORTHEAST/EASTERN
CANADA BY NEXT MONDAY. THE TRAILING COLD FRONT SHOULD EXTEND INTO
THE OHIO VALLEY/MID-ATLANTIC BUT WITH A MODERATE AMOUNT OF
UNCERTAINTY. MOST GUIDANCE SUGGESTS THAT ENOUGH UPPER RIDGING
SHOULD PERSIST OVER CENTRAL NORTH AMERICA TO SUPPORT SOME LINGERING
UPPER TROUGHING OVER THE NORTHEAST EARLY NEXT WEEK.
GUIDANCE COMPARISONS THROUGH THE 12Z/18Z CYCLES LED TO AN UPDATED
FORECAST USING A BLEND OF OPERATIONAL MODELS EARLY-MID PERIOD AND
THEN A RAPID TREND TO A MODEL/MEAN MIX LATE IN THE PERIOD.
..WEATHER/HAZARDS HIGHLIGHTS
THE WINDY SYSTEM TRACKING OUT OF THE GREAT LAKES AS OF EARLY FRIDAY
WILL STILL SUPPORT ANOMALOUS MOISTURE OVER THE NORTHEAST IN THE
STRONG SOUTHERLY FLOW ALONG/AHEAD OF THE COLD FRONT SWEEPING
THROUGH THE REGION DURING THE DAY. A MARGINAL RISK HAS BEEN
MAINTAINED IN THE DAY 4 EXCESSIVE RAINFALL OUTLOOK FOR SOME PARTS
OF NORTHERN NEW YORK THROUGH THE NORTHERN HALF OR SO OF NEW ENGLAND
GIVEN THE POTENTIAL FOR LOCALLY ENHANCED RAINFALL RATES AND
SENSITIVITY DUE TO SNOW COVER LIKELY TO MELT OVER THE COMING DAYS.
COLDER AIR WILL FILTER IN WITH THE PASSAGE OF THE FRONT WHICH MAY
RESULT IN AREAS OF MIXED PRECIPITATION TYPE OR CHANGEOVER TO ALL
SNOW BY FRIDAY NIGHT AND PERSISTING INTO SATURDAY.
THE UPPER LOW DROPPING SOUTHWARD OVER THE EASTERN PACIFIC LATE THIS
WEEK SHOULD APPROACH/REACH CALIFORNIA DURING THE WEEKEND. WHILE
MOISTURE ANOMALIES DO NOT APPEAR TOO EXTREME WITH THIS SYSTEM, THE
DEPTH OF THE UPPER SYSTEM OFFERS POTENTIAL FOR SOME LOCALIZED
MODERATE TO HEAVY RAIN BANDS. SUCH ACTIVITY COULD LEAD TO SOME
RUNOFF ISSUES GIVEN FAIRLY HIGH SOIL MOISTURE ANOMALIES CURRENTLY
EXISTING ALONG THE COAST. THUS THE DAY 5/SATURDAY ERO DEPICTS A
MARGINAL RISK AREA ALONG APPROXIMATELY THE CENTRAL HALF OF THE
CALIFORNIA COAST WHERE THE BEST AVERAGE OF GUIDANCE SUGGESTS
POTENTIAL FOR RAINFALL ENHANCEMENT. SOME PRECIPITATION IN THE
SIERRA NEVADA MAY BE IN THE FORM OF SNOW. AS THE UPPER LOW
PROGRESSES EASTWARD, IT SHOULD PRODUCE PRECIPITATION OF VARYING
INTENSITY ACROSS THE GREAT BASIN AND FOUR CORNERS STATES, FOLLOWED
BY INCREASING COVERAGE/INTENSITY OF RAINFALL OVER THE PLAINS BY
NEXT TUESDAY AS IT DEVELOPS POTENTIALLY STRONG LOW PRESSURE. THE
NORTHWEST MAY SEE SOME LIGHT PRECIPITATION LATE THIS WEEK AND
PERHAPS ANOTHER PERIOD OF RAIN/MOUNTAIN SNOW EARLY NEXT WEEK WITH
THE ARRIVAL OF AN UPPER TROUGH. FARTHER EAST, A WEAK WAVE/FRONTAL
SYSTEM MAY PRODUCE SOME RAIN OVER PARTS OF THE OHIO VALLEY/GREAT
LAKES THROUGH MID-ATLANTIC DURING AT LEAST A PART OF THE WEEKEND.
THE NORTHEAST WILL SEE UNSEASONABLY WARM LOWS EARLY FRIDAY AHEAD OF
THE COLD FRONT CROSSING THE REGION DURING THE DAY. BEHIND THE
FRONT, PARTS OF THE OHIO VALLEY/GREAT LAKES INTO CENTRAL-NORTHERN
APPALACHIANS WILL SEE A BRIEF PERIOD OF COOL DAYTIME HIGHS FRIDAY-
SATURDAY. FARTHER WEST, FROM FRIDAY THROUGH THE WEEKEND AN AREA OF
ABOVE NORMAL TEMPERATURES WILL SHIFT FROM THE WEST/HIGH PLAINS
INTO THE CENTRAL U.S. HIGHS SHOULD REACH UP TO 10-20F ABOVE NORMAL
ON FRIDAY WHILE PARTS OF THE NORTHERN/CENTRAL PLAINS MAY SEE PLUS
15-25F ANOMALIES DURING THE WEEKEND. SOME OF THIS WARMTH WITH
LESSER ANOMALIES (PLUS 5-15F) WILL LIKELY SPREAD INTO MOST OF THE
EAST FROM SUNDAY ONWARD. PERSISTENCE OF A MEAN TROUGH ALOFT MAY
HOLD DAYTIME HIGHS CLOSER TO NORMAL OVER THE NORTHEAST THOUGH. THE
UPPER LOW TRACKING IN FROM THE EASTERN PACIFIC WILL BRING BELOW
NORMAL HIGHS INTO CALIFORNIA AND THE SOUTHWEST DURING SUNDAY-
TUESDAY WHILE FARTHER NORTH AN UPPER TROUGH AND LEADING COLD FRONT
SHOULD PROMOTE MODESTLY BELOW NORMAL READINGS OVER THE NORTHWEST
BY EARLY NEXT WEEK.
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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