575
FXUS02 KWBC 260700
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
259 AM 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 SYSTEM LINGERING OVER THE
CAROLINAS INTO MONDAY SHOULD WEAKEN AS IT DRIFTS OFFSHORE, LEADING
TO A LIGHTER TREND FOR RAINFALL OVER THE MID-ATLANTIC AFTER THE
START OF THE WEEK. 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 MODELS AND ENSEMBLES GENERALLY AGREE ON THE TRANSITION FROM
ONE BLOCKY REGIME TO ANOTHER, BUT SHOW TYPICAL DIFFERENCES IN SOME
DETAILS. FOR EXAMPLE THE 18Z AND NEW 00Z GFS RUNS STRAY TO THE
FAST SIDE IN EJECTING THE INITIAL CALIFORNIA UPPER LOW AHEAD OF
INCOMING SOUTHERN STREAM ENERGY, WITH THE GEFS RUNS SIDING MORE TO
THE SLOWER MAJORITY CLUSTER. THERE IS INCREASING SPREAD FOR
TIMING OF THE EAST COAST UPPER LOW'S DEPARTURE (GEFS MEAN SLOWEST,
12Z ECMWF/00Z UKMET FASTEST) WITH NO CLEAR CLUSTERING, AND BY THE
END OF THE PERIOD THERE IS TYPICAL VARIATION FOR 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 UPDATED FORECAST STARTED WITH AN OPERATIONAL MODEL COMPOSITE
(GFS INPUT SPLIT BETWEEN THE 18Z AND 12Z RUNS) FOR THE FIRST HALF
OF THE PERIOD AND THEN STARTED TO INCORPORATE THE 18Z GEFS/00Z
ECMWF MEANS ON THE WAY TO AN EVEN MODEL/MEAN WEIGHT BY DAY 7
FRIDAY. THIS SOLUTION REPRESENTED THE MAJORITY OR INTERMEDIATE
IDEAS DEPENDING ON THE FEATURE OF INTEREST.
..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 SHOULD DECREASE NEXT WEEK AS THE SYSTEM
WEAKENS. THE DAY 4 (12Z MONDAY-12Z TUESDAY) EXCESSIVE RAINFALL
OUTLOOK WILL LIKELY MAINTAIN A MARGINAL RISK AREA WHERE POTENTIAL
EXISTS FOR SOME TRAINING OF RAINFALL ALONG AN AXIS OF INSTABILITY.
HEAVIEST RAINFALL SHOULD REMAIN OFFSHORE BY THE DAY 5 (12Z
TUESDAY-12Z WEDNESDAY) TIME FRAME, BUT FUTURE MODEL RUNS WILL HAVE
TO BE MONITORED AS FAIRLY MODEST CHANGES COULD ALTER THAT
SCENARIO. 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.
EXPECT DAILY ROUNDS OF SHOWERS AND THUNDERSTORMS ACROSS THE
SOUTHERN PLAINS 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. THE DAYS 4-5 EXCESSIVE RAINFALL
OUTLOOKS REFLECT THE EARLY-WEEK POTENTIAL WITH MARGINAL RISK AREAS
CENTERED OVER TEXAS. ONE OR MORE FRONTS MAY FOCUS RAIN AND
THUNDERSTORM ACTIVITY ACROSS THE NORTHERN TIER, WITH SOME SIGNAL
IN THE GUIDANCE FOR LOCALLY HEAVY RAINFALL OVER PARTS OF THE
EASTERN DAKOTAS INTO MINNESOTA. INITIALLY DRY GROUND CONDITIONS
YIELDED A PREFERENCE FOR NO RISK AREA AT THIS TIME BUT SOME
COMBINATION OF IMPROVED GUIDANCE AGREEMENT/HIGHER TOTALS COULD
EVENTUALLY SUPPORT AN AREA. MEANWHILE, 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.
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
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
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page