799
FXUS02 KWBC 170651
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
250 AM EDT WED MAY 17 2023
VALID 12Z SAT MAY 20 2023 - 12Z WED MAY 24 2023
...WARMER THAN AVERAGE TEMPERATURES WILL PERSIST ACROSS THE
NORTHWEST THROUGH THIS WEEKEND...
..OVERVIEW
STRONG UPPER RIDGING ACROSS THE WEST WILL CONTINUE TO CAUSE WARM
TO HOT TEMPERATURES THERE THROUGH THE WEEKEND, BEFORE AN UPPER
TROUGH FINALLY SHIFTS INTO THE NORTHWEST NEXT WEEK AND SHIFTS
WARMER THAN NORMAL TEMPERATURES INTO THE NORTH-CENTRAL CONUS. A
MONSOONAL PATTERN WILL BE IN PLACE ACROSS THE WEST WITH
ANOMALOUSLY HIGH MOISTURE UNDERNEATH THE RIDGE, WITH SCATTERED
SHOWERS AND THUNDERSTORMS LIKELY. FARTHER EAST, A COLD FRONT WILL
PUSH A ROUND OF RAIN THROUGH THE EAST THIS WEEKEND, AND THEN
ADDITIONAL FRONTAL SYSTEMS MAY SPARK SHOWERS AND THUNDERSTORMS
ACROSS FLORIDA IN PARTICULAR THROUGH MUCH OF NEXT WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
WHILE RECENT MODEL GUIDANCE CONTINUES TO BE AGREEABLE WITH THE
WESTERN U.S. RIDGING LATE WEEK, DOWNSTREAM THERE ARE STILL TIMING
DIFFERENCES OF A POTENT SHORTWAVE OR COMPACT UPPER LOW TRACKING
NEAR THE GREAT LAKES WITH A SURFACE LOW REFLECTION AND THE
ASSOCIATED FRONTAL TIMING EVEN BY DAY 3/SATURDAY. THROUGH THE
12/18Z MODEL CYCLE, GFS RUNS AND THE GEFS ENSEMBLE MEMBERS
REMAINED FASTER THAN THE OVERALL NOW BETTER CLUSTERED ECMWF, CMC,
AND UKMET. LEANING MORE TOWARD THE LATTER CLUSTER SEEMED PRUDENT
AS THE MAJORITY SOLUTION AND AS ITS TIMING WAS FAIRLY CONSISTENT
WITH THE PREVIOUS FORECAST. THE INCOMING 00Z MODELS LOOK PRETTY
SIMILAR ON TIMING TO THE PREVIOUS RUNS, WITH THE GFS STAYING ON
THE FASTER SIDE. THE PROGRESSION OF THESE FEATURES MAY ALSO IMPACT
A SHORTWAVE FARTHER SOUTH ATOP THE SOUTHEAST/MID-ATLANTIC OR
NEARBY WESTERN ATLANTIC AND SOME POTENTIAL SURFACE LOW REFLECTION
INTO SATURDAY. THESE RELATIVELY WEAK AND SMALL LOWS STILL HAVE LOW
PREDICTABILITY AT THIS POINT, SO ADDITIONAL REFINEMENT IS LIKELY.
IN THE WEST, ENERGY SPILLING IN FROM THE NORTHEAST PACIFIC COULD
FINALLY SPIN SOME TROUGHING TOWARD AND INTO THE NORTHWEST THROUGH
THE FIRST HALF OF NEXT WEEK. FOR THE MOST PART THERE ARE SOME
FAIRLY TYPICAL MODEL DIFFERENCES WITH THE TIMING AND DEPTH OF THIS
TROUGHING. THE MAIN OUTLIER APPEARED TO BE THE 12Z GFS, WHICH
PROGRESSED STRONGER ENERGY MORE QUICKLY EASTWARD BY SUNDAY-MONDAY
COMPARED TO OTHER GUIDANCE, PRODUCING TROUGHING OVER THE
NORTH-CENTRAL U.S. BY TUESDAY-WEDNESDAY OUT OF PHASE WITH THE
OTHER GUIDANCE. THE 18Z GFS SEEMED REASONABLE THOUGH, THOUGH
FARTHER EAST IT MAY BE MAINTAINING TOO MUCH SEPARATION IN UPPER
TROUGHING IN THE NORTHEAST BY AROUND TUESDAY. THERE ARE SOME
VARIATIONS IN THE PATTERN IN THE EAST NEXT WEEK DEPENDENT ON
TIMING AND DEPTH OF SHORTWAVES MOVING THROUGH THE MEAN TROUGHING
PATTERN. THE GEFS AND EC ENSEMBLE MEANS AT LEAST WERE FAIRLY
SIMILAR WITH THE PATTERN ACROSS THE COUNTRY, THOUGH THE EC MEAN
MAINTAINED A BIT DEEPER TROUGH IN THE EAST TUESDAY-WEDNESDAY
COMPARED TO THE GEFS MEAN.
THUS THE WPC FORECAST WAS BASED ON A BLEND FAVORING THE 12Z ECMWF
WITH LOWER PROPORTIONS OF THE 18Z GFS, 12Z UKMET, AND 12Z CMC
EARLY IN THE PERIOD. THEN INTRODUCED AND INCREASED THE GEFS AND EC
ENSEMBLE MEAN PROPORTIONS IN THE BLEND AMID INCREASING SPREAD IN
THE INDIVIDUAL MODELS, REACHING A LITTLE OVER HALF IN THE BLEND
FOR THE MASS FIELDS BY THE END OF THE PERIOD.
..WEATHER/HAZARDS HIGHLIGHTS
A COLD FRONT IS FORECAST TO TRACK THROUGH THE EAST THIS WEEKEND
AND PRODUCE WIDESPREAD RAIN ALONG AND AHEAD OF IT. THERE IS A
CHANCE OF LOCALLY HEAVY RAIN ACROSS THE NORTHEAST ON SATURDAY AS
ATLANTIC MOISTURE AND PERHAPS ANOTHER SURFACE SYSTEM COULD ENHANCE
TOTALS, BUT FLASH FLOODING IS NOT EXPECTED TO BE A BIG THREAT DUE
TO THE ONGOING DRYNESS IN THE REGION. THE BACK END OF THE FRONT
STALLING NEAR THE CENTRAL RIO GRANDE VALLEY COULD FOCUS MOISTURE
AND INSTABILITY THERE THAT COULD PRODUCE SOME HEAVY RAIN RATES
ATOP MOIST SOILS FROM RECENT RAINFALL. A MARGINAL RISK WAS
MAINTAINED FOR PARTS OF SOUTHWESTERN TEXAS FOR THIS FORECAST CYCLE
FOR DAY 4/SATURDAY. MEANWHILE, SCATTERED SHOWERS AND THUNDERSTORMS
ARE ALSO POSSIBLE IN THE WEST AT TIMES THIS WEEKEND INTO NEXT WEEK
ESPECIALLY IN THE AFTERNOONS/EVENINGS WITH A COMMON DIURNAL CYCLE,
AS A MONSOON-LIKE PATTERN SETS UP WITH ANOMALOUSLY HIGH MOISTURE
REMAINING OVER A LARGE PORTION OF THE WESTERN U.S., FIRST UNDER
THE UPPER RIDGE AXIS AND THEN AS TROUGHING EDGES INTO THE
NORTHWEST. CHANCES FOR SHOWERS AND THUNDERSTORMS MAY INCREASE IN
THE PLAINS BY TUESDAY-WEDNESDAY. MEANWHILE MULTIPLE FRONTAL
SYSTEMS COULD MOVE THROUGH THE SOUTHEASTERN U.S. INCLUDING
FLORIDA, WHICH COULD PROVIDE FOCUS FOR AMPLE MOISTURE AND ENHANCE
DAILY DIURNALLY-DRIVEN SHOWERS AND THUNDERSTORMS.
COASTAL AREAS OF THE PACIFIC NORTHWEST CAN EXPECT TEMPERATURES TO
REMAIN WARMER THAN NORMAL BY AROUND 10-15 DEGREES ON SATURDAY,
BEFORE MODERATING TO AROUND NORMAL NEXT WEEK AS UPPER TROUGHING
AND A COLD FRONT OR TWO MOVE IN. INTERIOR AREAS LIKE THE GREAT
BASIN ARE LIKELY TO SEE ABOVE AVERAGE TEMPERATURES BY 15-25F
UNDERNEATH THE UPPER RIDGE AXIS, WITH HIGHS IN THE 90S THAT COULD
BE RECORD-SETTING ON SATURDAY. LOW TEMPERATURES IN THE 50S AND 60S
COULD ALSO BREAK RECORDS FOR WARM MINIMUM TEMPERATURES ACROSS
WIDESPREAD AREAS OF THE WEST OVER THE WEEKEND. THEN UPPER
TROUGHING COMING INTO THE NORTHWEST SHOULD SHIFT WARMER THAN
AVERAGE TEMPERATURES EASTWARD INTO THE NORTH-CENTRAL U.S. THROUGH
MONDAY-WEDNESDAY, MODERATING A BIT WITH ANOMALIES AROUND 10-15F
ABOVE NORMAL. MEANWHILE FARTHER SOUTH, POST-FRONTAL COOLER AIR AND
PERIODS OF RAIN AND CLOUDS COULD LEAD TO SLIGHTLY BELOW AVERAGE
TEMPERATURES FOR PARTS OF THE PLAINS AT TIMES THROUGH EARLY NEXT
WEEK.
TATE
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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