519
FXUS02 KWBC 140737
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
336 AM EDT SUN MAY 14 2023
VALID 12Z WED MAY 17 2023 - 12Z SUN MAY 21 2023
...WARMER THAN AVERAGE TEMPERATURES WILL PERSIST ACROSS THE
NORTHWEST...
...THE SOUTH-CENTRAL ROCKIES/PLAINS COULD SEE HEAVY RAINFALL
AROUND THURSDAY-FRIDAY...
..OVERVIEW
THE OVERALL WEATHER PATTERN THROUGH THE WEEK INTO NEXT WEEKEND
SHOULD REMAIN FAIRLY STAGNANT ACROSS THE COUNTRY. AN ANOMALOUSLY
STRONG UPPER RIDGE OVER THE WESTERN HALF OF THE U.S. AND INTO
WESTERN CANADA WILL BE PERSISTENT ASIDE FROM AN UPPER LOW
GRADUALLY SHEARING OUT/WEAKENING ATOP THE NORTHWEST THROUGH AROUND
MIDWEEK. THIS PATTERN WILL MAINTAIN WARM TO HOT TEMPERATURES
ACROSS THE NORTHWEST AND TO A LESSER EXTENT OVER OTHER PARTS OF
THE WEST. DOWNSTREAM, MEAN TROUGHING IS LIKELY ACROSS EASTERN
NORTH AMERICA, WITH INDIVIDUAL SHORTWAVES SUPPORTING COLD FRONTS
THAT SHOULD PUSH SOUTHEASTWARD TO THE EAST OF THE ROCKIES AND
PRODUCE AREAS OF SHOWERS AND THUNDERSTORMS, INCLUDING THE
POSSIBILITY FOR SOME ENHANCED RAINFALL AMOUNTS IN THE
SOUTH-CENTRAL ROCKIES/HIGH PLAINS LATE THIS WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODEL GUIDANCE CONTINUES TO SHOW GENERAL AGREEMENT ON THE LARGE
SCALE BUT LINGERING DIFFERENCES IN THE MIDDLE AND SMALLER SCALES
OF THE UPPER-LEVEL AND SURFACE FEATURES. AS ONE SPOKE OF UPPER
TROUGHING LIFTS OUT OF THE NORTHEAST ON WEDNESDAY, ANOTHER COMPACT
UPPER LOW IS LIKELY TO DROP THROUGH SOUTH-CENTRAL CANADA AND ATOP
THE GREAT LAKES LATE THURSDAY INTO FRIDAY. THERE REMAIN SOME MINOR
TIMING DIFFERENCES IN THE 12/18Z MODEL CYCLE WITH THIS FEATURE AND
ITS SURFACE LOW REFLECTION--THE GFS RUNS AND THE 12Z CMC WERE A
BIT SLOWER THAN THE UKMET AND ECMWF. AS ALL WERE WITHIN THE SPREAD
OF THE ENSEMBLE MEMBERS ENVELOPE, A MIDDLE GROUND FOR TIMING
SEEMED BEST. THE 12Z CMC AND THE NEWER 00Z CMC RUN OPEN UP THE
UPPER LOW MORE QUICKLY AND THE 00Z SHOWS MORE PHASING THAN THE
OTHER GUIDANCE BY FRIDAY-SATURDAY, WHICH AFFECTS THE TIMING OF THE
SHORTWAVE EASTWARD OVER THE WEEKEND.
MEANWHILE LOW PREDICTABILITY SMALLER-SCALE FEATURES CONTINUE TO
PLAGUE THE FORECAST FROM THE SOUTHERN HALF OF THE PLAINS EASTWARD.
OVERALL, RECENT MODELS HAVE TRENDED TOWARD A SHORTWAVE MOVING MORE
QUICKLY EASTWARD MIDWEEK COMPARED TO PREVIOUS CYCLES, LESSENING
QPF OVER THE THE SOUTH-CENTRAL U.S. AND RAISING IT INTO THE
SOUTHEAST FOR WEDNESDAY. ADDITIONAL REFINEMENTS WILL LIKELY BE
NEEDED EVEN INTO THE SHORT TERM WITH THE SMALL-SCALE ELEMENTS OF
THE FORECAST CAUSING QPF AND OTHER DIFFERENCES THROUGH THE PERIOD.
THEN MODELS HANDLE THE POTENTIAL FOR UPPER TROUGHING INFLUENCE TO
APPROACH THE NORTHWEST THIS WEEKEND DIFFERENTLY, WITH LOW
CONFIDENCE ON ANY PARTICULAR SOLUTION.
THE WPC FORECAST WAS BASED ON A MULTI-MODEL DETERMINISTIC BLEND OF
THE 12Z AND 18Z MODEL GUIDANCE EARLY IN THE PERIOD. GRADUALLY
INCREASED THE GEFS AND EC ENSEMBLE MEANS THROUGH THE LATTER PART
OF THE PERIOD TO JUST OVER HALF BY DAY 7 GIVEN INCREASING
UNCERTAINTY.
..WEATHER/HAZARDS HIGHLIGHTS
AS A WEST-EAST FRONTAL BOUNDARY LINGERS NEAR THE GULF COAST ON
WEDNESDAY, SCATTERED THUNDERSTORMS ARE POSSIBLE FROM THE
SOUTH-CENTRAL U.S. INTO THE SOUTHEAST. THIS FORECAST FAVORED MORE
RAINFALL FARTHER EAST ACROSS THE SOUTHEAST RATHER THAN BACK ACROSS
TEXAS PER THE NEWER MODEL GUIDANCE. WITH AMOUNTS TRENDING DOWN
CONSIDERABLY IN TEXAS, THE MARGINAL RISK WAS ELIMINATED THERE.
AREAS FARTHER EAST SHOULD BE LESS SENSITIVE TO RAIN SINCE THE
RECENT PATTERN HAS BEEN DRIER AND FLASH FLOOD GUIDANCE IS HIGH
ESPECIALLY CLOSE TO THE COAST. PLUS, THIS TREND FOR HEAVIER QPF
THERE IN THE SOUTHEAST IS SOMEWHAT NEW, SO DID NOT WANT TO ADD ANY
ERO RISK AT THIS LEAD TIME. HOWEVER, INSTABILITY AND MOISTURE IN
PLACE MEANS RAIN RATES COULD BE HIGH, AND ISOLATED FLASH FLOODING
CANNOT BE COMPLETELY RULED OUT, SO A MARGINAL RISK MAY HAVE TO BE
ADDED THERE IN THE FUTURE. NOT HAVING AN ERO AREA FOR DAY 4 IS
MORE ABOUT THE PREDICTABILITY BEING TOO LOW RATHER THAN A ZERO
CHANCE OF FLASH FLOODING.
FARTHER NORTH, SHOWERS AND STORMS ARE LIKELY TO OCCUR AHEAD OF A
COLD FRONT DROPPING SOUTH INTO THE NORTH-CENTRAL CONUS. ON
WEDNESDAY STORMS LOOK PROGRESSIVE ENOUGH THAT THEY MAY NOT CAUSE
FLASH FLOODING ISSUES IN THE NORTHERN PLAINS, BUT BY THURSDAY THE
FRONT COULD HANG UP A BIT IN THE SOUTH-CENTRAL ROCKIES/HIGH
PLAINS. THIS STALLING FRONT AND MOISTURE ANOMALIES THAT COULD BE
ABOVE THE 90TH PERCENTILE COULD LEAD TO SOME FLASH FLOODING
ISSUES, ESPECIALLY WHERE UPSLOPE FLOW COULD ENHANCE RAIN AMOUNTS
IN THE HIGHER ELEVATIONS OF THE CENTRAL ROCKIES. THIS WOULD ALSO
BE ATOP WET GROUND WITH HIGH STREAMFLOWS THAT COULD EXACERBATE THE
RISK. THE PATTERN BY DAY 5/THURSDAY IN SOME WAYS SEEMS MORE
PREDICTABLE THAN THE SHORT RANGE INTO DAY 4 SINCE IT IS DRIVEN BY
THE RELATIVELY LARGER-SCALE FEATURES OF THE UPPER LOW AND SURFACE
FRONTAL SYSTEM. THUS THERE SEEMS TO BE ENOUGH CONFIDENCE FOR A
SLIGHT RISK IN THE DAY 5 ERO FOR THE CENTRAL ROCKIES WITH A
MARGINAL RISK EXTENDING INTO MUCH OF THE SOUTH-CENTRAL PLAINS AND
SOUTHERN ROCKIES DOWNSTREAM. SOME RAIN COULD LINGER IN THOSE AREAS
INTO FRIDAY AS WELL, WHILE FARTHER NORTH THE COLD FRONT SHOULD BE
MORE PROGRESSIVE TOWARD THE EAST, PUSHING RAIN CHANCES INTO THE
EAST-CENTRAL U.S. ON FRIDAY AND INTO THE EASTERN SEABOARD ON
SATURDAY. SCATTERED SHOWERS MAY ALSO BE POSSIBLE FOR PARTS OF THE
INTERIOR WEST BY LATE WEEK.
TEMPERATURE-WISE, EXPECT WARM TO HOT TEMPERATURES TO PERSIST
ACROSS THE WEST AS LARGE SCALE UPPER RIDGING PREVAILS ON THE
WHOLE. THE PACIFIC NORTHWEST SHOULD SEE HIGH TEMPERATURES AROUND
15-25 DEGREES ABOVE AVERAGE FOR WEDNESDAY-THURSDAY ALONG WITH LOWS
IN THE 50S AND 60S THAT COULD SET RECORD HIGH MINIMUM
TEMPERATURES. THESE COASTAL AREAS COULD SEE SOME GRADUAL
MODERATION CLOSER TO NORMAL FOR LATE WEEK INTO THE WEEKEND, BUT
INTERIOR AREAS LIKE THE GREAT BASIN CAN EXPECT MUCH ABOVE AVERAGE
TEMPERATURES TO PERSIST INTO THE WEEKEND, WITH HIGHS INTO THE 90S
POSSIBLY SETTING RECORDS AS WELL. HIGHS IN THE 90S AND EVEN
NEARING 100F ARE POSSIBLE IN THE CALIFORNIA CENTRAL VALLEY, WITH
HIGHS ABOVE 100F IN THE DESERT SOUTHWEST ON WEDNESDAY (THOUGH THE
LATTER IS LESS ANOMALOUS FOR MAY). THE NORTH-CENTRAL U.S. COULD
SEE ABOVE AVERAGE TEMPERATURES BY ABOUT 10F ON WEDNESDAY, FOLLOWED
BY A COOLER TREND THURSDAY-FRIDAY AFTER THE FRONTAL PASSAGE, BUT
POSSIBLY WARMING UP AGAIN BY THE WEEKEND. THE SOUTHERN TIER
HOWEVER MAY SEE TEMPERATURES AROUND TO SLIGHTLY BELOW AVERAGE
GIVEN THE PERIODIC RAIN CHANCES. THE NORTHEAST COULD SEE A COOL
WEDNESDAY AND THURSDAY MORNING WITH TEMPERATURES AROUND 10-15F
BELOW NORMAL, BUT SHOULD MODERATE TO NEAR NORMAL AFTER THAT.
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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