939
FXUS02 KWBC 262042
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
441 PM EDT FRI MAY 26 2023
VALID 12Z MON MAY 29 2023 - 12Z FRI JUN 02 2023
...COASTAL LOW WITH HEAVY RAIN AND COASTAL/MARITIME THREATS FOR
THE SOUTHEAST/MID-ATLANTIC DURING THE WEEKEND TO TRACK OFFSHORE
NEXT WEEK...
...BROAD MULTI-DAY THUNDERSTORM AND LOCAL HEAVY RAIN THREAT
CONTINUES FOR THE PLAINS...
..OVERVIEW
OVER THE COURSE OF NEXT WEEK EXPECT AN INITIAL REX BLOCK PATTERN
OVER THE EAST TO TRANSITION TOWARD MORE OF AN OMEGA BLOCK AS GREAT
LAKES AND SOUTHERN ROCKIES UPPER RIDGES ULTIMATELY MERGE/AMPLIFY
OVER CENTRAL CANADA AND THE MISSISSIPPI VALLEY. A CALIFORNIA UPPER
LOW SHOULD ANCHOR WEST COAST MEAN TROUGHING TO START AND THEN A
NORTHEASTERN PACIFIC/PACIFIC NORTHWEST TROUGH SHOULD BECOME BETTER
DEFINED BY MID-LATE WEEK. THE LINGERING SYSTEM NEAR THE CAROLINAS
SHOULD WEAKEN AS IT DRIFTS OFFSHORE. PRECIPITATION OVER THE
MID-ATLANTIC WILL WANE THROUGH THE COMING WEEK AS RESULT. THE
FORECAST PATTERN WILL SUPPORT PERIODS OF RAINFALL FROM THE SIERRA
NEVADA THROUGH THE GREAT BASIN AND NORTHERN ROCKIES, WHILE
PORTIONS OF THE PLAINS WILL SEE POTENTIAL FOR LOCALLY HEAVY
RAINFALL. ONE OR MORE FRONTS SHOULD PROVIDE ADDED FOCUS OVER THE
NORTHERN PLAINS AND A SHORTWAVE TRAVERSING THE SOUTHERN TIER COULD
ENHANCE ACTIVITY OVER THE SOUTHERN PLAINS. EXPECT TEMPERATURES TO
BE ABOVE NORMAL OVER A MAJORITY OF THE NORTHERN U.S. WHILE NEAR TO
MODERATELY BELOW NORMAL READINGS SHOULD PREVAIL ACROSS THE
SOUTHERN TIER.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
THE LATEST RUNS OF GUIDANCE CONTINUE TO SHOW FAIRLY GOOD AGREEMENT
WITH THE LARGE-SCALE PATTERN AS IT TRANSITIONS FROM A BLOCKY
REGIME OVER THE EASTERN U.S. TO ANOTHER BLOCKY REGIME. ONCE AGAIN,
THE GFS IS FAVORING A A FASTER/EASTWARD POSITION WITH THE INITIAL
LOW EJECTING FROM CALIFORNIA INTO THE SOUTHERN STREAM. TREND HAS
PERSISTED NOW WITH THE PAST FOUR RUNS, HOWEVER BY THE MIDDLE OF
THE EXTENDED PERIOD IT FLIPS TO THEN BECOME THE SLOWER/WEST SIDE
OF THE CLUSTER BY THE END OF THE PERIOD. THE GEFS MEAN REMAINS
CLOSER TO THE CLUSTER. THERE CONTINUES TO BE VARIATIONS IN THE THE
DETAILS WITH THE EASTERN CANADA/NEW ENGLAND UPPER TROUGHING THAT
SHOULD BEGIN TO TAKE SHAPE IN RESPONSE TO CENTRAL CANADA RIDGING.
DIFFERENCES FOR THE SHORTWAVE TRACKING ACROSS THE SOUTHERN TIER
FALL WITHIN TYPICAL RANGES FOR THE TIME FRAME INVOLVED. THE WPC
SUITE OF PRODUCTS USED A COMPOSITE OF THE NBM, CONTINUITY, A
GENERAL BLEND OF THE 00Z ECWMF/UKMET/CMC/GFS/GEFS/EC ENSEMBLE
MEANS AND THE 06Z/12Z GFS.
..WEATHER/HAZARDS HIGHLIGHTS
HOLIDAY WEEKEND HAZARDS OF HEAVY RAIN AND GUSTY WINDS ASSOCIATED
WITH THE SYSTEM INITIALLY FORECAST TO BE NEAR THE SOUTHERN
MID-ATLANTIC COAST IS EXPECTED TO THE DECREASE THROUGH THE NEXT
WEEK AS THE COASTAL SYSTEM WEAKENS AND TRACKS FURTHER FROM THE
EASTERN SEABOARD. THE POTENTIAL FOR PERIODS OF HEAVY RAIN AND
ISOLATED FLOODING WILL REMAIN ELEVATED ALONG THE MID-ATLANTIC
COAST ON DAY 4 (12Z MONDAY-12Z TUESDAY) AS THIS IS WHERE TRAINING
OF THUNDERSTORMS ALONG AN AXIS OF INSTABILITY. THEREFORE, A
MARGINAL RISK FOR EXCESSIVE RAINFALL WILL REMAIN IN EFFECT. THE
THREAT WILL LESSEN BY DAY 5 (12Z TUESDAY-12Z WEDNESDAY) AS THE
SYSTEM SHIFTS FURTHER OFFSHORE, THUS NO HIGHLIGHTED RISK AREAS FOR
THIS PERIOD AT THIS TIME. EVEN AS THE SYSTEM ITSELF WEAKENS,
NORTHEASTERLY WINDS ALONG THE COAST COULD STILL REBOUND FOR A TIME
AS HIGH PRESSURE DROPS INTO THE NORTHEAST/MID-ATLANTIC BY
TUESDAY-WEDNESDAY.
SHOWERS AND THUNDERSTORMS ARE EXPECTED TO BREAK OUT ACROSS THE
SOUTHERN PLAINS ON A DAILY CADENCE DUE TO A PERSISTENT PATTERN
BRINGING IN LOW LEVEL MOISTURE FROM THE GULF OF MEXICO AND LEADING
TO UPSLOPE FLOW OVER THE HIGH PLAINS. A SOUTHERN TIER SHORTWAVE
MAY ALSO ENHANCE ACTIVITY DURING THE FIRST HALF OF THE WEEK, AND
HEIGHT FALLS EMERGING FROM THE WEST MAY INCREASE
COVERAGE/INTENSITY AGAIN TOWARD THE END OF THE WEEK. SOME OF THE
HIGHER QPF MAY FOCUS OVER TEXAS THUS THE DAYS 4-5 EXCESSIVE
RAINFALL OUTLOOKS REFLECT THE EARLY-WEEK POTENTIAL WITH MARGINAL
RISK. FURTHER NORTH OVER THE NORTHERN PLAINS, ONE OR MORE FRONTS
MAY FOCUS RAIN AND THUNDERSTORM ACTIVITY WITH SOME SIGNAL IN THE
GUIDANCE FOR LOCALLY HEAVY RAINFALL OVER PARTS OF THE EASTERN
DAKOTAS INTO MINNESOTA. MUCH OF THIS PART OF THE COUNTRY HAS BEEN
RECENTLY DRY, SO SOIL SATURATION IS LOW AS WELL AS THE THREAT FOR
FLOODING. HOWEVER,
SOME COMBINATION OF IMPROVED GUIDANCE AGREEMENT/HIGHER TOTALS
COULD EVENTUALLY SUPPORT AN AREA. AREAS OVER AND JUST NORTH OF THE
SIERRA NEVADA THROUGH THE GREAT BASIN INTO THE NORTHERN ROCKIES
WILL SEE MULTIPLE DAYS OF SHOWERS AND THUNDERSTORMS AHEAD OF THE
CALIFORNIA UPPER LOW AND TROUGH EVOLVING NEAR THE PACIFIC
NORTHWEST COAST. CURRENT GUIDANCE SIGNALS ARE DO NOT APPEAR
SUFFICIENTLY ORGANIZED TO DEPICT A LARGE SCALE RISK AREA IN THE
EXCESSIVE RAINFALL OUTLOOK BUT AN ISOLATED INSTANCE OR TWO OF
FLASH FLOODING IN TERRAIN SENSITIVE AREAS OR BURN SCARS WILL
REMAIN POSSIBLE.
MUCH OF THE NORTHERN PART OF THE COUNTRY AND THE MIDDLE
MISSISSIPPI VALLEY WILL SEE ABOVE NORMAL TEMPERATURES THROUGH NEXT
WEEK, WITH AREAS FROM THE NORTHERN PLAINS THROUGH GREAT LAKES AND
NORTHEAST MOST LIKELY TO SEE MULTIPLE DAYS OF PLUS 10-20F
ANOMALIES. MODERATELY ABOVE NORMAL READINGS OVER THE NORTHWEST
EARLY IN THE WEEK SHOULD TREND CLOSER TO NORMAL AS THE UPPER
TROUGH REACHES THE PACIFIC NORTHWEST COAST MID-LATE WEEK.
MEANWHILE MUCH OF THE SOUTHERN TIER WILL TEND TO SEE NEAR TO
MODERATELY BELOW NORMAL TEMPERATURES.
CAMPBELL/RAUSCH
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 SOUTHERN PLAINS, MON-TUE, MAY
29-MAY 30.
- HEAVY RAIN ACROSS PORTIONS OF THE SOUTHERN PLAINS, FRI, JUN 2.
- FLOODING POSSIBLE ACROSS PORTIONS OF THE NORTHERN PLAINS.
- 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, AND THE NORTHERN GREAT BASIN.
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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