675
FXUS02 KWBC 180657
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
256 AM EDT THU MAY 18 2023
VALID 12Z SUN MAY 21 2023 - 12Z THU MAY 25 2023
...WARMER THAN AVERAGE TEMPERATURES WILL PUSH FROM THE NORTHWEST
EARLY THIS WEEK INTO THE NORTHERN PLAINS...
..OVERVIEW
AN UPPER RIDGE/HIGH WILL TRACK EASTWARD FROM THE INTERIOR WEST
ACROSS THE NORTHERN PLAINS AND INTO THE MIDWEST THROUGH NEXT WEEK,
WITH WARMER THAN NORMAL TEMPERATURES UNDERNEATH IT. A MONSOONAL
PATTERN WILL BE IN PLACE EARLY IN THE WEEK ACROSS THE WEST INTO
THE SOUTHERN HIGH PLAINS AS ANOMALOUSLY HIGH MOISTURE UNDERNEATH
THE RIDGE PROMOTES SCATTERED SHOWERS AND THUNDERSTORMS. AS
LOWERING HEIGHTS COME THROUGH THE NORTHWEST ACCOMPANIED BY A COLD
FRONT, INCREASING RAIN CHANCES ARE EXPECTED ACROSS MUCH OF THE
CENTRAL U.S. MEANWHILE, MULTIPLE FRONTAL SYSTEMS PUSHING THROUGH
THE SOUTHEAST MAY SPARK SHOWERS AND THUNDERSTORMS THAT COULD CAUSE
ISOLATED FLASH FLOODING CHANCES AT TIMES NEXT WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
AT THE BEGINNING OF THE PERIOD SUNDAY, MODELS GENERALLY AGREE WITH
THE UPPER-LEVEL SYNOPTIC PATTERN OF TROUGHING JUST EDGING INTO THE
PACIFIC NORTHWEST, A RIDGE/HIGH CENTERED JUST EAST IN THE INTERIOR
WEST/ROCKIES, AND TROUGHING OVER THE EAST. THE WESTERN TROUGH AND
THE RIDGE SHOULD PUSH EAST THROUGH THE PERIOD. THERE ARE SOME
MODEL VARIATIONS ON THE SMALLER SCALE BUT GENERALLY MOST SEEM
REASONABLE WITH NO NOTABLE OUTLIERS. BUT BY AROUND MIDWEEK THERE
START TO BE MORE DIFFERENCES WITH THE WESTERN TROUGH AND HOW IT
MAY MOVE/REORIENT WITH TIME, AS SOME ENERGY MAY SPLIT AND MOVE
EAST WHILE SOME IS REINFORCED ACROSS THE WEST. THOUGHT THE 12Z
ECMWF MAY HAVE BEEN A BIT FAST WITH TRACKING MOST ENERGY EASTWARD
NEAR THE U.S./CANADA BORDER COMPARED TO OTHER MODELS AND THE
ENSEMBLES OVERALL, AND THE INCOMING 00Z ECMWF DID SLOW DOWN
SOMEWHAT. WITH THE VARIOUS MODELS HANDLING THIS DIFFERENTLY,
FAVORED THE MORE AGREEABLE ENSEMBLE MEANS WITH THIS AND WITH SOME
DIFFERENCES IN THE EASTERN TROUGH AS WELL. THUS THE WPC FORECAST
BEGAN WITH A MULTI-MODEL DETERMINISTIC BLEND OF THE 12Z ECMWF/18Z
GFS/12Z CMC/12Z UKMET (FROM MOST TO LEAST WEIGHTING), BUT
GRADUALLY TRANSITIONED TO A BLEND OF ABOUT HALF GEFS/EC ENSEMBLE
MEANS BY THE END OF THE PERIOD AMID INCREASING UNCERTAINTY.
..WEATHER/HAZARDS HIGHLIGHTS
BY SUNDAY A COLD FRONT WILL HAVE CLEARED MOST OF THE EAST, WITH
THE EXCEPTION OF THE SOUTHEAST, PARTICULARLY SOUTHERN GEORGIA INTO
FLORIDA. THE FRONT PLUS ABOVE AVERAGE/AMPLE MOISTURE LEVELS COULD
SPARK THUNDERSTORMS WITH HIGH RAIN RATES. MARGINAL RISKS ARE
PLANNED FOR THE DAY 4 AND 5 (SUNDAY AND MONDAY) EROS NEAR THE
TRACK OF THIS FRONT, FIRST FOR SOUTHERN GEORGIA AND NORTHERN
FLORIDA ON SUNDAY AND FOR MUCH OF THE FLORIDA PENINSULA ON MONDAY.
THOUGH FLASH FLOOD GUIDANCE IS RELATIVELY HIGH, HIGH RAIN RATES
COULD OVERWHELM PARTICULARLY URBAN AREAS WITH POTENTIAL FOR FLASH
FLOODING. MEANWHILE, SCATTERED SHOWERS AND THUNDERSTORMS ARE ALSO
POSSIBLE IN THE WEST AT TIMES 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. AS TROUGHING EDGES IN. ONE AREA
THAT CONVECTION MAY BE MOST COMMON IS ACROSS THE SOUTHERN HIGH
PLAINS THROUGH MUCH OF THE WEEK. CHANCES FOR SHOWERS AND
THUNDERSTORMS WILL INCREASE ACROSS MUCH OF THE PLAINS BY
TUESDAY-THURSDAY AHEAD OF THE UPPER TROUGH AND A FRONTAL SYSTEM.
TEMPERATURES IN THE PACIFIC NORTHWEST WILL HAVE RETURNED CLOSER TO
NORMAL BY EARLY NEXT WEEK, BUT FOR INTERIOR AREAS LIKE THE GREAT
BASIN, TEMPERATURES OF 15-20F ABOVE AVERAGE WILL BE COMMON THROUGH
SUNDAY UNDER THE INFLUENCE OF THE UPPER RIDGE/HIGH. MOST OF THE
RECORD HIGH TEMPERATURE POTENTIAL HAS NOW PHASED INTO THE SHORT
RANGE PERIOD, BUT NOW TEMPERATURES IN THE 50S AND 60S COULD BREAK
RECORDS FOR WARM MINIMUM TEMPERATURES ACROSS WIDESPREAD AREAS OF
THE WEST ESPECIALLY SUNDAY. WARMTH SHOULD SHIFT EAST WITH TIME
INTO THE NORTHERN PLAINS AND EVENTUALLY THE MIDWEST (IN MODERATED
FORM) THROUGH THE WEEK, WITH SOME ABOVE NORMAL TEMPERATURES
REMAINING IN CALIFORNIA/NEVADA THOUGH. WARMER THAN NORMAL
TEMPERATURES MAY RETURN TO THE NORTHWEST LATER IN THE WEEK, BUT
NOT TO THE SAME MAGNITUDE OF ANOMALIES. NEAR TO SLIGHTLY BELOW
NORMAL TEMPERATURES ARE POSSIBLE ACROSS THE SOUTHERN TIER WITH
POST-FRONTAL COOLER AIR AND PERIODS OF RAIN AND CLOUDS.
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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