469
FXUS02 KWBC 251935
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
334 PM EDT THU MAY 25 2023
VALID 12Z SUN MAY 28 2023 - 12Z THU JUN 01 2023
...COASTAL LOW OFFERS HEAVY RAIN AND COASTAL/MARITIME THREATS FOR
THE SOUTHEAST/MID-ATLANTIC...
...BROAD MULTI-DAY THUNDERSTORM AND LOCAL HEAVY RAIN THREAT
CONTINUES FOR THE PLAINS...
..PATTERN OVERVIEW AND GUIDANCE/PREDICTABILITY ASSESSMENT
INITIALLY, MUCH OF THE EASTERN HALF OF THE LOWER 48 IS IN A REX
BLOCK PATTERN (AS A CLOSED RIDGE SETTLES IN OVER THE GREAT LAKES
WHILE A CUTOFF LOW LINGERS OVER THE SOUTHEAST) AND WITH A TROUGH
OVER THE WEST. A LOW PRESSURE SYSTEM IS EXPECTED TO LIFT NORTHWARD
NEAR THE SOUTHEAST COAST WHICH WILL SPREAD HEAVY RAIN AND WIND TO
THE CAROLINAS. THE NATIONAL HURRICANE CENTER HAS BEEN MONITORING
THE FORECAST FOR THIS SYSTEM BUT KEEPS THE CHANCES OF ANY TROPICAL
DEVELOPMENT VERY LOW. MEAN TROUGHING WILL BE IN PLACE OVER
PORTIONS OF THE WEST, CENTERED ON THE WEST COAST, THROUGH AT LEAST
THE MID-PERIOD, WITH WEAK FLOW ALOFT OVER THE CENTER OF THE
COUNTRY WITH THE NORTHERN STREAM SHUNTED NORTHWARD INTO CANADA.
SUBTLE SHORTWAVES TRAVERSE THROUGH A WEAK SOUTHERN STREAM RIDGE
OVER THE SOUTHERN PLAINS, WHICH WILL LIKELY HELP PROMOTE SCATTERED
PRECIPITATION CHANCES ACROSS THE AREA. LATER IN THE PERIOD, THE
CUTOFF LOW OVER THE SOUTHEAST SLOWLY TRANSLATES NORTHEASTWARD UP
THE EAST COAST. THE MEAN TROUGHING OVER THE WEST COAST SHIFTS A
BIT WESTWARD AS THE NORTHERN STREAM AMPLIFIES NORTHWESTWARD WITH A
RIDGE BUILDING OVER THE NORTHERN ROCKIES.
THE LATEST GUIDANCE HAD A FAIR AMOUNT CLUSTERING DURING THE FIRST
FEW DAYS OF THE EXTENDED PERIOD AND THE OVERALL HANDLING OF HOW
EACH SYSTEM/FEATURE EVOLVES. THE WPC FORECAST WAS COMPRISED OF
DETERMINISTIC GFS/ECMWF/CMC/UKMET, ENSEMBLE MEAN (GEFS/ECENS)
GUIDANCE AND THE NBM.
..WEATHER/HAZARDS HIGHLIGHTS
HEAVY RAIN, GUSTY WINDS AND BEACH RELATED HAZARDS CAN BE EXPECTED
THIS HOLIDAY WEEKEND AS A LOW PRESSURE SYSTEM OFF THE SOUTHEAST
COAST TRACKS INLAND OVER THE CAROLINAS. RAIN PRIOR TO THE EXTENDED
PERIOD WILL LIKELY RAISE SOIL SATURATION AND INCREASE SENSITIVITY.
WITH RAIN LIKELY TO CONTINUE INTO EARLY NEXT WEEK THE DAY 4/5
MARGINAL RISKS OF EXCESSIVE RAINFALL WHERE MAINTAINED FOR THE
POTENTIAL FOR AT LEAST ISOLATED INSTANCES OF FLASH FLOODING.
THERE IS A DEGREE OF UNCERTAINTY WITH BOTH THE EXACT TRACK OF THE
LOW, AND THUS FOOTPRINT OF HEAVY RAINFALL, AS WELL AS WITH THE
EXPECTED AMOUNTS, AND IT IS POSSIBLE THAT A GREATER THREAT OF
FLASH FLOODING MAY CONTINUE FROM SATURDAY INTO SUNDAY.
TO THE NORTH, UPPER-LEVEL RIDGING OVER THE GREAT LAKES WILL PUSH
HIGH TEMPERATURES WELL ABOVE AVERAGE BY AS MUCH AS 15-20 DEGREES
FROM THE NORTHERN PLAINS THROUGH THE GREAT LAKES AND INTO THE
INTERIOR NORTHEAST NEXT WEEK, EVENTUALLY SPREADING FURTHER
EASTWARD INTO THE NORTHEAST AND MID-ATLANTIC. FRONTAL ACTIVITY
ALONG THE NORTHERN STREAM MAY BRING THE CHANCE FOR SOME ISOLATED
TO SCATTERED STORMS, PARTICULARLY FOR THE NORTHERN PLAINS/UPPER
MIDWEST, BUT CONDITIONS SHOULD OTHERWISE REMAIN DRY. DEPENDING ON
THE EVOLUTION OF BROADER HEIGHT RISES OVER THE CENTRAL/EASTERN
CONUS, TEMPERATURES COULD TREND EVEN WARMER MORE BROADLY OVER THE
EASTERN HALF OF THE COUNTRY.
DAILY ROUNDS OF SHOWERS AND THUNDERSTORMS ARE EXPECTED TO FIRE UP
ACROSS THE HIGH PLAINS/PLAINS WITHIN THE MOIST, SOUTHEASTERLY
UPSLOPE FLOW. SOME OF THESE STORMS MAY HAVE THE POTENTIAL TO
PRODUCE MODERATE TO HEAVY RAINFALL OVER THE REGION. A MARGINAL
RISK OF EXCESSIVE RAINFALL IS ALREADY IN EFFECT FOR SUNDAY AS
MOISTURE REMAINS ANOMALOUSLY HIGH OVER THE REGION AND WEAK FLOW
ALOFT LEADS TO SLOW STORM MOTIONS. A MARGINAL RISK WAS RAISED FOR
DAY 5 OVER PORTIONS OF TEXAS AND OKLAHOMA WHERE THERE WILL STILL
BE THE POTENTIAL FOR HIGHER RAINFALL INTENSITY/TOTALS GIVEN THE
ABUNDANT MOISTURE AND FORCING OVER THE REGION. THE SUBTLE HEIGHT
RISES MORE BROADLY OVER THE CENTRAL/EASTERN CONUS AND THE
TEMPERING OF LOW-LEVEL JET ACTIVITY OVERNIGHT SHOULD DECREASE
MOISTURE TRANSPORT AND STORM COVERAGE/INTENSITY, BRINGING DOWN THE
THREAT OF LOCALLY HEAVY RAINFALL NEXT WEEK. MEAN TROUGHING WILL
REMAIN OVER THE WEST AT THE START OF THE PERIOD, WITH THE
SUBSEQUENT STORMY PATTERN OVER THE NORTHERN ROCKIES/GREAT BASIN
THIS WEEK CONTINUING INTO THE WEEKEND AND NEXT WEEK. STORM
COVERAGE AND RAINFALL AMOUNTS SHOULD TREND DOWNWARD AS TROUGHING
ALOFT BEGINS TO SHIFT WEST AND RIDGING BUILDS NORTHWESTWARD OVER
THE NORTHERN ROCKIES, BUT AN ISOLATED INSTANCE OR TWO OF FLASH
FLOODING IN TERRAIN SENSITIVE AREAS OR BURN SCARS WILL REMAIN
POSSIBLE. HIGH TEMPERATURES ACROSS MOST OF THE WEST WILL REMAIN
AROUND AVERAGE BEFORE A WARMING TREND OVER THE NORTHWEST AS THE
RIDGING BUILDS IN OVER THE REGION. COASTAL CALIFORNIA WILL BE
COOLER AS A CUTOFF LOW SITS OVER THE COAST, WITH ONSHORE FLOW IN
PLACE.
CAMPBELL/PUTNAM
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
HAZARDS:
- HEAVY RAIN ACROSS PORTIONS OF THE MID-ATLANTIC, SUN, MAY 28.
- FLOODING POSSIBLE ACROSS PORTIONS OF THE NORTHERN ROCKIES.
- FLOODING OCCURRING OR IMMINENT ACROSS PORTIONS OF THE CENTRAL
ROCKIES, THE NORTHERN ROCKIES, AND
THE NORTHERN GREAT BASIN.
- FLOODING LIKELY ACROSS PORTIONS OF THE CENTRAL ROCKIES, THE
CENTRAL GREAT BASIN, THE NORTHERN
ROCKIES, THE NORTHERN GREAT BASIN, AND THE NORTHERN PLAINS.
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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