162
FXUS02 KWBC 270700
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 AM EDT SAT MAY 27 2023
VALID 12Z TUE MAY 30 2023 - 12Z SAT JUN 03 2023
..EAST COAST SYSTEM TO WEAKEN AND TRACK OFFSHORE
...BROAD MULTI-DAY THUNDERSTORM AND LOCAL HEAVY RAIN THREAT
CONTINUES FOR THE PLAINS...
..OVERVIEW
GUIDANCE CONTINUES TO SHOW A TRANSITION FROM ONE BLOCKING PATTERN
TO ANOTHER NEXT WEEK AS A REX BLOCK PATTERN INITIALLY OVER THE
EAST GIVES WAY TO AN OMEGA BLOCK, WITH GREAT LAKES AND SOUTHERN
ROCKIES UPPER RIDGES ULTIMATELY MERGING/AMPLIFYING OVER CENTRAL
CANADA AND THE MISSISSIPPI VALLEY/EASTERN PLAINS. WESTERN
U.S./EASTERN PACIFIC TROUGHING WILL CONSIST OF AN INITIAL
CALIFORNIA UPPER LOW, SOME ENERGY IMMEDIATELY UPSTREAM, A
SHORTWAVE REACHING/EJECTING FROM THE PACIFIC NORTHWEST, AND THEN A
TROUGH RELOADING MORE OFFSHORE. MEANWHILE THE BUILDING CENTRAL
CANADA UPPER RIDGE WILL LIKELY FORCE TROUGHING INTO THE NORTHEAST
TOWARD THE END OF NEXT WEEK. THE FORECAST PATTERN WILL SUPPORT
RAINFALL OF VARYING INTENSITY 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 NEAR
THE GULF COAST AND EVENTUALLY INTO THE FLORIDA PENINSULA.
RAINFALL OVER THE MID-ATLANTIC SHOULD TREND LIGHTER WITH TIME AS
THE EAST COAST SYSTEM WEAKENS AND DEPARTS. 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 ENSEMBLE MEANS CONTINUE TO DEPICT A SIMILAR LARGE
SCALE PATTERN EVOLUTION THROUGH THE PERIOD BUT WITH SOME TYPICAL
EMBEDDED DETAIL ISSUES AND TRENDS/REFINEMENT. RECENT GFS RUNS
HAVE BEEN ON THE FASTER SIDE OF THE SPREAD FOR THE UPPER LOW
INITIALLY FORECAST TO BE OVER/NEAR CALIFORNIA AND EVENTUALLY OPEN
UP OVER THE WEST AS IT CONTINUES INLAND, WITH LEADING HEIGHT FALLS
ALSO ADVANCING FARTHER EAST INTO THE PLAINS THAN MOST OTHER
SOLUTIONS. BEHIND THIS FEATURE, GUIDANCE GENERALLY SUGGESTS THAT
UPSTREAM ENERGY WILL HELP TO MAINTAIN A DIFFUSE TROUGH WITH A
NEUTRAL OR NEGATIVE TILT INTO DAYS 6-7 FRIDAY-SATURDAY. OVER THE
NORTHEASTERN PACIFIC/PACIFIC NORTHWEST, GUIDANCE IS REFINING THE
FORECAST TOWARD A DEFINED SHORTWAVE ARRIVING INTO THE PACIFIC
NORTHWEST BY AROUND DAY 5 THURSDAY FOLLOWED BY EJECTION OF THIS
SHORTWAVE AND FARTHER WEST TROUGH EMPHASIS IN RESPONSE TO DIGGING
OF ENERGY FROM THE EASTERN BERING SEA/SOUTHWESTERN ALASKA.
FARTHER EAST, GUIDANCE HAS COME INTO MUCH BETTER AGREEMENT FOR THE
INITIAL EAST COAST SYSTEM VERSUS 24 HOURS AGO WITH TIMING ON THE
SLOWER SIDE OF THE PRIOR SPREAD (WHICH WAS REPRESENTED BY THE GEFS
MEAN). WITHIN DEVELOPING EASTERN CANADA/NORTHEASTERN U.S. MEAN
TROUGHING, THE 18Z/00Z GFS RUNS DIFFER FROM MOST OTHER GUIDANCE
FOR HOW AN INITIAL UPPER LOW NEAR NEWFOUNDLAND MAY INTERACT WITH
UPSTREAM ENERGY BUT AT LEAST THE END RESULT IS A TROUGH EITHER
WAY. THE NEW 00Z CMC IS THE EXTREME SOLUTION AT THE MOMENT AS IT
DOES NOT DEVELOP THIS TROUGH. FINALLY, GUIDANCE EXHIBITS TYPICAL
SPREAD FOR THE UPPER FEATURE TRACKING ALONG THE GULF COAST GIVEN
THE FORECAST TIME FRAME AND MEDIUM SCALE THAT CAN SOMETIMES TEMPER
PREDICTABILITY. GUIDANCE PREFERENCE GENERALLY REFLECTED AN
OPERATIONAL MODEL EMPHASIS EARLY AND A MODEL/MEAN BLEND LATER IN
THE PERIOD, THOUGH WITH SOME GEFS INPUT EVEN EARLY IN THE FORECAST
TO MITIGATE LESS CONFIDENT ASPECTS OF THE GFS IN THE WEST.
..WEATHER/HAZARDS HIGHLIGHTS
EXPECT RAINFALL OVER THE MID-ATLANTIC TO DECREASE IN COVERAGE AND
INTENSITY FROM TUESDAY ONWARD AS THE UPPER LOW AND SURFACE SYSTEM
INITIALLY AFFECTING THE REGION WEAKEN AS THEY TRACK EASTWARD.
FARTHER WEST, THE PATTERN EVOLUTION WILL FAVOR MULTIPLE DAYS OF
SHOWERS AND THUNDERSTORMS FROM THE SIERRA NEVADA INTO THE NORTHERN
ROCKIES/MONTANA AS WELL AS PORTIONS OF THE PLAINS AND UPPER
MIDWEST. BY DAY 5 (12Z WEDNESDAY-12Z THURSDAY) THE SIERRA NEVADA
THROUGH MONTANA AXIS MAY SEE SUFFICIENT LOCALIZED ENHANCEMENT
AFTER SOMEWHAT MORE MODEST ACTIVITY FROM PRIOR DAYS TO MERIT A
MARGINAL RISK AREA IN THE EXCESSIVE RAINFALL OUTLOOK FOR THAT TIME
FRAME. ALSO DURING THAT PERIOD THERE IS A SIGNAL FOR INCREASING
COVERAGE/INTENSITY OF RAINFALL OVER THE SOUTHERN HIGH PLAINS WITH
THE APPROACH/ARRIVAL OF HEIGHT FALLS FROM THE WEST, WITH A
MARGINAL RISK INDICATED OVER THAT REGION AS WELL. A WAVY FRONT
MAY PRODUCE SOME LOCALLY HEAVY RAINFALL OVER THE EASTERN
DAKOTAS/MINNESOTA TUESDAY-WEDNESDAY BUT THIS AREA HAS HAD BELOW
AVERAGE RAINFALL OVER THE PAST COUPLE WEEKS AND GUIDANCE HAS
CONTINUED TO DISAGREE ON SPECIFICS, SO OUTLOOKS DO NOT SHOW ANY
RISK AREA THUS FAR. IMPROVED GUIDANCE CLUSTERING AND/OR A HEAVIER
CONSENSUS COULD EVENTUALLY FAVOR ONE THOUGH. RAINFALL MAY TREND
HEAVIER AND MORE EXPANSIVE OVER THE HIGH PLAINS AND VICINITY
TOWARD THE END OF NEXT WEEK. MEANWHILE THE DAY 4 OUTLOOK HOLDS
ONTO A SMALLER MARGINAL RISK AREA ALONG THE WESTERN GULF COAST
WITH THE POSSIBILITY FOR LINGERING ACTIVITY WITH THE SOUTHERN TIER
UPPER SHORTWAVE, WITH GUIDANCE TRENDS REDUCING THE NORTHWESTWARD
EXTENT VERSUS CONTINUITY. THROUGH THE REST OF THE PERIOD AS THE
SHORTWAVE DRIFTS EASTWARD, GUIDANCE DIVERGES CONSIDERABLY
REGARDING HOW MUCH RAIN MAY FALL ALONG THE GULF COAST. THERE IS A
LITTLE BETTER SIGNAL FOR INCREASING MOISTURE TO LIFT NORTHWARD
THROUGH FLORIDA LATE IN THE WEEK, LEADING TO POTENTIAL FOR HEAVIER
RAINFALL AT THAT TIME.
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. THE NORTHWEST SHOULD SEE MODERATELY ABOVE NORMAL
READINGS EARLY IN THE WEEK, FOLLOWED BY A TREND TOWARD NORMAL AS
AN UPPER SHORTWAVE REACHES THE REGION MID-LATE WEEK AND THEN A
REBOUND AS IT DEPARTS. THE NORTHEAST SHOULD BECOME NOTICEABLY
COOLER BY NEXT SATURDAY BEHIND A PASSING COLD FRONT SUPPORTED BY
AN AMPLIFYING UPPER TROUGH. MEANWHILE MUCH OF THE SOUTHERN TIER,
AS WELL AS MID-ATLANTIC FOR HIGHS EARLY IN THE PERIOD, 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