687
FXUS02 KWBC 100659
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
259 AM EDT WED APR 10 2024
VALID 12Z SAT APR 13 2024 - 12Z WED APR 17 2024
..OVERVIEW
MOST GUIDANCE SHOWS A SIMILAR LARGE SCALE PATTERN EVOLUTION DURING
THE PERIOD. A DEEP NORTHEAST UPPER TROUGH SHOULD DEPART AFTER
SATURDAY, GIVING WAY TO WEAK SHORTWAVE ENERGY THAT MAY SUPPORT A
NORTHERN TIER WAVE DURING SATURDAY-MONDAY. ON THE OPPOSITE COAST,
EXPECT A STRONG UPPER LOW TO REACH CALIFORNIA THIS WEEKEND WITH A
BRIEF PERIOD OF PRECIPITATION AND CONTINUE TRACKING INLAND. THE
UPPER RIDGE TO THE EAST WILL SUPPORT WELL ABOVE NORMAL TEMPERATURES
OVER THE CENTRAL U.S. DURING THE WEEKEND. AS THE UPPER LOW REACHES
THE PLAINS NEXT WEEK, IT WILL LIKELY DEVELOP A STRONG SURFACE
SYSTEM AROUND TUESDAY AND CONTINUE NORTHEASTWARD INTO MIDWEEK.
UPPER TROUGHING FORECAST TO DIG INTO THE NORTHWEST NEXT WEEK ALONG
WITH ITS LEADING COLD FRONT WILL EVENTUALLY BRING A COOLER TREND TO
THAT REGION AND MAY HAVE SOME INFLUENCE ON THE PLAINS SYSTEM THAT
WILL SPREAD AN INCREASING AREA OF RAINFALL ACROSS THE CENTRAL U.S.
..GUIDANCE/PREDICTABILITY ASSESSMENT
SOME TIMING SPREAD PERSISTS FOR THE UPPER LOW REACHING CALIFORNIA
AND CONTINUE EASTWARD/NORTHEASTWARD THEREAFTER. RECENT GFS RUNS
HAVE BEEN LEANING A BIT ON THE SLOWER SIDE OF THE SPREAD WHILE SOME
OF THE OTHER OPERATIONAL DYNAMICAL MODELS HAVE BEEN TRENDING A
LITTLE FASTER OVER THE PAST DAY. 12Z ECMWF-INITIALIZED MACHINE
LEARNING MODELS (MLS) SHOW SOME TIMING SPREAD AS WELL BUT THE
MAJORITY FAVORS TIMING CLOSE TO CONTINUITY, BETWEEN THE GFS AND
ECMWF/OTHER FASTER MODELS. MOST OF THE NEW 00Z MODELS ARE SHOWING
SOMEWHAT OF A FASTER TREND THOUGH. ASSOCIATED PLAINS LOW PRESSURE
SHOULD BE DEEPEST AROUND TUESDAY WITH THE AVERAGE OF MLS
SUGGESTING A STRENGTH BETWEEN THE DEEPER GFS/ECMWF RUNS AND WEAKER
CMC/ENSEMBLE MEANS.
THERE IS A PERSISTENT SIGNAL FOR UPPER TROUGHING TO DIG INTO THE
WEST DURING THE FIRST HALF OF NEXT WEEK, BUT AGAIN WITH SPREAD FOR
THE DETAILS PLUS A SLIGHTLY SLOWER TREND FOR PROGRESSION OF LEADING
HEIGHT FALLS AND ASSOCIATED COLD FRONT. THE 12Z ECMWF SEEMED TO
HAVE LESS SOUTHWESTWARD EXTENT OF TROUGHING BY WEDNESDAY COMPARED
TO MOST OTHER GUIDANCE. THE MLS ALSO DISPLAY A MODERATE AMOUNT OF
SPREAD BUT WITH THEIR AVERAGE ENDING UP FAIRLY CLOSE TO THE
DYNAMICAL MODEL/MEAN CONSENSUS.
BY AROUND NEXT WEDNESDAY THERE IS A QUESTION OF HOW THE WESTERN
TROUGH MAY INTERACT WITH THE SYSTEM EMERGING INTO THE PLAINS. THE
OVERWHELMING MAJORITY OF GUIDANCE SAYS THE TWO FEATURES WILL STAY
SEPARATE, IN CONTRAST TO THE 12Z/09 GFS THAT MERGED THEM TO YIELD
A VERY DEEP SURFACE LOW.
DETAILS CONTINUE TO VARY FOR THE WAVE THAT IS MOST LIKELY TO TRACK
FROM THE NORTHERN PLAINS THROUGH THE NORTHEAST SATURDAY-MONDAY.
THE NEW 00Z UKMET/CMC HAVE ADDED TO THE UNCERTAINTY BY TRACKING
NOTICEABLY FARTHER NORTHWARD, WITH CORRESPONDING SIGNIFICANT
DIFFERENCES IN POSITION OF THE TRAILING FRONT. THE MLS GENERALLY
FAVORED A COMPOSITE OF 12Z/18Z GUIDANCE.
THE UPDATED FORECAST STARTED WITH A 12Z/18Z OPERATIONAL MODEL
COMPOSITE DURING THE FIRST HALF OF THE PERIOD TO REFLECT THE
DESIRED INTERMEDIATE SOLUTION/CONTINUITY FOR SIGNIFICANT FEATURES.
LATER IN THE PERIOD, A BLEND OF MODELS ALREADY TONED DOWN SOME
DETAIL DIFFERENCES WITHIN AN ENSEMBLE MEAN/ML FAVORED GENERAL
PATTERN, SO THE FORECAST ONLY NEEDED TO INCORPORATE A MODEST INPUT
OF THE 18Z GEFS/12Z ECENS MEANS.
..WEATHER/HAZARDS HIGHLIGHTS
THE DEEP UPPER LOW REACHING NEAR CALIFORNIA BY THE START OF THE
PERIOD EARLY SATURDAY MAY PRODUCE SOME BANDS OF LOCALLY
MODERATE TO HEAVY RAIN DURING THE DAY, THOUGH MOISTURE ANOMALIES
DO NOT APPEAR TOO EXTREME WITH THIS SYSTEM. THIS ACTIVITY COULD
LEAD TO SOME RUNOFF ISSUES GIVEN FAIRLY HIGH SOIL MOISTURE
ANOMALIES CURRENTLY EXISTING ALONG THE COAST. THUS THE DAY
4/SATURDAY EXCESSIVE RAINFALL OUTLOOK MAINTAINS A MARGINAL RISK
AREA ALONG THE CENTRAL/SOUTH-CENTRAL CALIFORNIA COAST WHERE THE
BEST AVERAGE OF GUIDANCE SUGGESTS POTENTIAL FOR RAINFALL
ENHANCEMENT. A SLIGHT EASTWARD ADJUSTMENT IN THE MODEL AVERAGE FOR
THE UPPER LOW HAS LED TO A MODEST TRIMMING OF THE NORTHERN SIDE OF
THE PRIOR RISK AREA. FARTHER INLAND, 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/MISSISSIPPI VALLEY DURING THE FIRST HALF
OF NEXT WEEK AS IT DEVELOPS POTENTIALLY STRONG LOW PRESSURE.
HIGHEST PRECIPITATION TOTALS WITH THIS SYSTEM SHOULD BE OVER THE
NORTHERN HALF OF THE PLAINS/MISSISSIPPI VALLEY. THIS STORM MAY
ALSO PRODUCE AN AREA OF STRONG WINDS WITH THE SOUTHERN HALF OF THE
HIGH PLAINS BEING ONE PARTICULAR AREA OF FOCUS.
THE UPPER TROUGH DIGGING INTO THE NORTHWEST DURING THE FIRST HALF
OF NEXT WEEK SHOULD ULTIMATELY INCREASE PRECIPITATION OVER/EAST OF
THAT REGION. MEANINGFUL SNOW WILL BE POSSIBLE OVER PORTIONS OF THE
NORTHERN HALF OF THE ROCKIES BY AROUND NEXT TUESDAY. WITH
DECREASING CONFIDENCE IN SPECIFICS FOR THE TIME BEING, A WEAK
WAVE/FRONTAL SYSTEM MAY PRODUCE SOME RAIN OVER PARTS OF THE GREAT
LAKES/OHIO VALLEY INTO THE NORTHERN MID-ATLANTIC/NORTHEAST DURING
AT LEAST A PART OF THE WEEKEND.
UPPER RIDGING OVER THE PLAINS AND VICINITY WILL SUPPORT WELL ABOVE
NORMAL TEMPERATURES ACROSS THE CENTRAL U.S. ESPECIALLY DURING THE
WEEKEND WHEN SOME NORTHERN-CENTRAL AREAS SHOULD SEE HIGHS UP TO
20-25F ABOVE NORMAL. EXPECT LESS EXTREME WARM ANOMALIES TO EXTEND
THROUGH THE EASTERN U.S. FROM SUNDAY ONWARD. MEANWHILE THE UPPER
LOW TRACKING INTO CALIFORNIA THIS WEEKEND WILL BRING A BELOW NORMAL
HIGHS TO THE SOUTHWESTERN U.S. SATURDAY INTO MONDAY AND THE UPPER
TROUGH/COLD FRONT MOVING INTO THE NORTHWEST PLUS THE DEVELOPING
PLAINS STORM WILL LIKELY BRING BELOW NORMAL HIGHS INTO THE
NORTHWEST AND NORTHERN HIGH PLAINS BY NEXT TUESDAY-WEDNESDAY. PARTS
OF THE NORTHEAST SHOULD SEE MODERATELY BELOW NORMAL HIGHS ON
SATURDAY FOLLOWED BY A WARMER TREND.
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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