199
FXUS02 KWBC 101903
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
303 PM 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
THERE'S REASONABLE AGREEMENT AMONG THE NON-GFS GUIDANCE AS IT
PERTAINS TO THE SYNOPTIC EVOLUTION OF THE WESTERN UPPER-TROUGH
PATTERN DURING THE MEDIUM RANGE PERIOD. ELSEWHERE, THE GFS CLUSTERS
WELL WITH THE OTHER MODELS. AN UNUSUAL AMOUNT OF TIMING SPREAD
EXISTS WITHIN THE GEFS/ECE/CMCE MEMBERS FOR THE WEST COAST SYSTEM
AT THE BEGINNING OF DAY 3 (12Z 04/13). A SIGNIFICANT NUMBER OF
ENSEMBLE MEMBERS SEEM TO SUGGEST THAT THE APPROACHING MID-LEVEL
CUT-OFF LOW WILL BE SLOWER/DISPLACED TO THE WEST COMPARED TO THEIR
RESPECTIVE MEANS. THIS DIFFUSION IN THE ENSEMBLE MEMBERS ONLY
WORSENS AS THE SYSTEM MOVES INLAND IN THE SUBSEQUENT DAYS.
ON DAYS 3 AND 4, A GENERAL MODEL BLEND CONSISTING OF THE
DETERMINISTIC 00Z EC/UKMET/CMC AND 06Z GFS WERE USED. WEIGHTING
FAVORED THE 00Z MODELS SINCE THE GFS IS MUCH SLOWER WITH THE CUT-
OFF LOW IN THE WEST. THE NON-GRAPHCAST (GFS BASED AI) MODELS
PRODUCED SOMETHING SIMILAR TO THAT OF THE 00Z OPERATIONAL GUIDANCE.
THE DESCENDING TROUGH FROM WESTERN CANADA INTRODUCES ANOTHER AREA
OF UNCERTAINTY ON DAY 5. THAT BEING SAID, THE NON-GFS GUIDANCE
CONTINUES TO CLUSTER RELATIVELY WELL COMPARATIVELY REGARDING THE
TIMING ASPECT OF THE WESTERN TROUGH. DESPITE THAT THE EC DIVERGES A
BIT FROM THE UK AND CMC'S LONGWAVE ENERGY ACROSS THE UPPER
MIDWEST/GREAT LAKES. THUS, THE 00Z ECE WAS INTRODUCED TO THE BLEND
FOR DAY 5.
THE GFS AND UKMET ARE PHASED OUT OF THE BLEND ON DAY 6 AND ARE
REPLACED WITH THE 00Z CMCE AND 06Z GEFS. THE ONCE WESTERN LOW MOVES
INTO THE GREAT PLAINS AND BEGINS TO TILT NEGATIVELY ON DAY 6.
THERE'S SPREAD ON HOW QUICKLY THIS OCCURS. THE GEFS AND GFS APPEAR
TO BE A SLIGHTLY SLOWER AND DEEPER THAN THE EURO AND CANADIAN BASED
GUIDANCE WITH THIS SYSTEM, WHICH IS REFLECTED IN IT'S ENHANCED QPF
FOOTPRINT OVER THE UPPER MIDWEST ON TUESDAY. THE INCLUSION OF THE
GEFS HELPS TO ACCOUNT FOR AREAS FARTHER WEST OVER MINNESOTA THAT
MAY BE IMPACTED BY HEAVY RAINFALL THAT DAY.
THE MID-LEVEL TROUGH IN THE NORTHWEST CARRIES QUITE A BIT OF
ENSEMBLE SPREAD WITH IT, POTENTIALLY DUE IN PART TO ANY INTERACTION
IT MAY HAVE WITH THE PLAINS SYSTEM. THE ECE APPEARS TO HAVE THE
LEAST AMOUNT OF SPREAD BETWEEN THE ENSEMBLES ON DAY 7, WITH THE
UPPER-TROUGH ENTERING THE INTERMOUNTAIN WEST. THEREFORE, THE
ENSEMBLE MEANS WITH WEIGHTING TOWARD THE ECE WAS PREFERRED ON THE
DAY 7 BLEND.
..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.
KEBEDE/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
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page