029
FXUS02 KWBC 061859
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
258 PM EDT SAT MAY 06 2023
VALID 12Z TUE MAY 09 2023 - 12Z SAT MAY 13 2023
..OVERVIEW
EXPECT PORTIONS OF THE CENTRAL U.S. TO SEE THE HEAVIEST RAINFALL
DURING THE TUESDAY-SATURDAY PERIOD, AS GUIDANCE SHOWS INITIAL WEST
COAST ENERGY CONSOLIDATING INTO AN UPPER LOW THAT SHOULD TRACK
INTO OR NEAR THE NORTHERN PLAINS WHILE A TRAILING TROUGH/WEAKNESS
MAY LINGER THROUGH THE SOUTHWEST. THIS LOW/TROUGH WILL LIKELY GET
STUCK BETWEEN A RIDGE BUILDING OVER THE NORTHWESTERN U.S. INTO
WESTERN CANADA, AHEAD OF A PERSISTENT UPPER LOW SOUTH OF ALASKA,
AND ANOTHER RIDGE SETTING UP OVER THE MIDWEST THROUGH SOUTHEAST.
THE SLOW EVOLUTION OF THE PATTERN BY LATE IN THE PERIOD COULD ADD
TO THE POTENTIAL FOR HEAVY RAINFALL OVER SOME LOCATIONS. CENTRAL
AND THEN WESTERN CANADA UPPER RIDGING WILL TEND TO FAVOR CYCLONIC
OR NORTHWESTERLY UPPER FLOW OVER THE NORTHEAST, LEADING TO
RELATIVELY DRIER CONDITIONS OVER THAT REGION.
..GUIDANCE/PREDICTABILITY ASSESSMENT
LATEST MODELS AND ENSEMBLES SHOW DECENT CLUSTERING AND CONTINUITY
FOR THE WESTERN UPPER TROUGH INTO ABOUT DAY 4 WEDNESDAY. THEN THE
00Z/06Z RUNS SHOW A PRONOUNCED TREND TOWARD THE IDEA OF A
CONSOLIDATING UPPER LOW TRACKING INTO THE VICINITY OF THE NORTHERN
PLAINS BY AROUND THE END OF THE WEEK. THIS IDEA HAS SHOWN UP IN
SOME PAST CYCLES BUT ALSO WITH THE POSSIBILITY THAT THE UPPER LOW
COULD REMAIN FARTHER SOUTHWEST. THERE ARE CORRESPONDING
SIGNIFICANT DIFFERENCES IN HOW THE RIDGE TO THE WEST EVOLVES.
EVEN WITH THE OVERWHELMING SHIFT IN MODELS/MEANS FOR THE PRIMARY
UPPER LOW, THERE IS STILL A DECENT SIGNAL IN THE GUIDANCE THAT
UPPER TROUGHING (AND PERHAPS EVEN ANOTHER LOW) COULD PERSIST BACK
THROUGH THE SOUTHWESTERN U.S. INTO THE WEEKEND. THE NEW 12Z
GUIDANCE SEEMS TO SUPPORT MOST OF THE 00Z/06Z CYCLE ADJUSTMENTS
WHILE THE GFS HAS MADE A FAVORABLE TREND TOWARD CONSENSUS VERSUS
THE 06Z RUN THAT TRACKED THE UPPER LOW SOMEWHAT FARTHER EAST. THE
12Z ECMWF HAS ADJUSTED A BIT NORTHWEST OF ESTABLISHED CONSENSUS.
MEANWHILE GUIDANCE AGREES FAIRLY WELL IN PRINCIPLE ON MEAN
TROUGHING CENTERED OVER EASTERN CANADA INTO THE NORTHEASTERN U.S.
AND/OR WESTERN ATLANTIC, BUT WITH SHORTWAVE DETAILS THAT DECREASE
IN PREDICTABILITY BY THE LATTER HALF OF THE PERIOD.
BASED ON THE CLUSTERING OF LATEST GUIDANCE, THE UPDATED FORECAST
INCORPORATED AN OPERATIONAL MODEL BLEND FOR THE FIRST HALF OF THE
PERIOD AND THEN STARTED TO ADD IN SOME OF THE 06Z GEFS/00Z ECMWF
MEANS WITH THE TYPICAL DECLINE OF CONFIDENCE IN DETAILS AT LATER
TIME FRAMES. AMONG THE MODELS, THE BLEND USED MORE 00Z ECMWF THAN
06Z GFS GIVEN THE LESS PREFERRED EASTERN TRACK OF THE
ROCKIES/PLAINS UPPER LOW IN THE LATTER.
..WEATHER/HAZARDS HIGHLIGHTS
SHOWERS AND STORMS SHOULD INCREASE IN COVERAGE ACROSS MUCH OF THE
PLAINS STATES GOING INTO THE TUESDAY-WEDNESDAY TIME PERIOD AS
MOISTURE ADVECTION FROM THE GULF OF MEXICO INCREASES AHEAD OF A
NEARLY STATIONARY FRONTAL SYSTEM OVER THE PLAINS AND THE FRONT
APPROACHING FROM THE WEST. THE DAY 4 (12Z TUESDAY-12Z WEDNESDAY)
EXCESSIVE RAINFALL OUTLOOK PLANS TO MAINTAIN A MARGINAL RISK AREA
OVER PARTS OF THE CENTRAL PLAINS, WITH A FOCUS NEAR THE INITIAL
WAVY FRONT, AND ALSO ACROSS MUCH OF CENTRAL AND SOUTHERN TEXAS IN
THE WARM SECTOR. THE HEAVIEST CONVECTION DURING THE DAY 5 (12Z
WEDNESDAY-12Z THURSDAY) PERIOD IS CURRENTLY FAVORED ACROSS
PORTIONS OF EASTERN TEXAS NORTHWARD THROUGH THE ARKLATEX REGION
INTO PARTS OF KANSAS/MISSOURI, PLUS THE NORTHERN HALF OF THE HIGH
PLAINS, WITH MARGINAL RISK AREAS MAINTAINED FOR BOTH OF THOSE
AREAS. THE POTENTIAL EXISTS FOR EVENTUAL SLIGHT RISKS ON EITHER
DAY IN FUTURE UPDATES ONCE GUIDANCE CLUSTERS BETTER FOR LOCATIONS
AND MAGNITUDE OF HIGHEST QPF. SPECIFICS OVER THE NORTHERN HIGH
PLAINS WILL DEPEND ON THE EXACT TRACK OF THE UPPER LOW EXPECTED TO
CROSS THE REGION. LOOKING BEYOND WEDNESDAY, AREAS OF HEAVY
RAINFALL COULD PERSIST INTO THURSDAY OR LATER OVER/NEAR THE
NORTHERN HIGH PLAINS GIVEN THE SLOWING PROGRESSION OF THE
SUPPORTING UPPER LOW. MEANWHILE THE SOUTHERN PLAINS MAY SEE
INCREASING POTENTIAL FOR HEAVIER RAINFALL, WITH SEVERAL INCHES OF
RAIN POSSIBLE IN SOME AREAS OF TEXAS. AS THE UPPER LOW CROSSES
THE GREAT BASIN AND ROCKIES, EXPECT SUFFICIENT COLD AIR TO SUPPORT
LATE SEASON HIGHER ELEVATION SNOW ESPECIALLY OVER WYOMING AND
MONTANA.
IN TERMS OF TEMPERATURES, HIGHS UP TO 10-15F ABOVE EARLY MAY
AVERAGES OVER THE CENTRAL/SOUTHERN PLAINS ON TUESDAY WILL MODERATE
THEREAFTER WHILE SIMILAR ANOMALIES SETTLE OVER THE MIDWEST AND
EXPAND ACROSS THE GREAT LAKES/OHIO VALLEY/NORTHEAST. WARMTH WILL
BUILD ACROSS THE PACIFIC NORTHWEST BY FRIDAY INTO SATURDAY WITH
HIGHS REACHING 10-20F ABOVE NORMAL. THE WEST COAST STATES AND
INTERMOUNTAIN WEST WILL LIKELY SEE SLIGHTLY BELOW AVERAGE HIGHS
THROUGH WEDNESDAY BEFORE A MODERATING TREND COMMENCES. OVERNIGHT
LOWS SHOULD BE CLOSER TO AVERAGE OVER THE WEST EARLY IN THE PERIOD
BEFORE TRENDING WARMER, AND GENERALLY ABOVE AVERAGE EAST OF THE
ROCKIES.
RAUSCH/HAMRICK
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, EXPERIMENTAL EXCESSIVE RAINFALL
OUTLOOK, WINTER WEATHER OUTLOOK PROBABILITIES AND HEAT INDICES ARE
AT:
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
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