101
FXUS02 KWBC 271825
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
224 PM EDT SAT MAY 27 2023
VALID 12Z TUE MAY 30 2023 - 12Z SAT JUN 03 2023
...WELL ABOVE NORMAL TO NEAR RECORD TEMPERATURES FROM THE UPPER
MIDWEST TO THE NORTHEAST NEXT WEEK...
...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 AND SOUTHEASTERN 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 REMAINS IN GOOD
AGREEMENT FOR THE INITIAL MID-ATLANTIC SYSTEM AS IT SLOWLY
WOBBLES/DRIFTS EASTWARD BY MIDWEEK. WITHIN DEVELOPING EASTERN
CANADA/NORTHEASTERN U.S. MEAN TROUGHING, ENSEMBLES CONTINUE TO
TREND DEEPER (THOUGH WITH SOME OSCILLATION) IN RESPONSE TO A BIT
NARROWER UPPER RIDGE AXIS IN THE MIDDLE OF THE CONTINENT.
ENSEMBLES AND SOME DETERMINISTIC RUNS HAVE HINTED AT SOME AREA OF
LOW PRESSURE IN THE GULF MIDWEEK NEXT WEEK THAT MAY MOVE EASTWARD
IN TANDEM WITH THE UPPER TROUGH, BUT CONFIDENCE IS LOW IN ANY
SPECIFICS. OVERALL A MULTI-MODEL/ENSEMBLE BLEND SERVED WELL AS A
STARTING POINT, WITH THE EXCEPTION OF THE 00Z UKMET IN THE GULF
AROUND DAY 4-5 (TOO STRONG WITH LOW PRESSURE), AND THE 00Z
CANADIAN OFF FL/THE SOUTHEAST AROUND DAY 6-7 (LIKELY TOO
DEVELOPED/NORTH WITH ANY FEATURE). OTHERWISE, THE RECENT GFS/ECMWF
RUNS AND THEIR ENSEMBLE MEANS WERE GENERALLY AN ACCEPTABLE BLEND.
..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 EXPERIMENTAL 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. 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. HIGH TEMPERATURES WILL LIKELY BE WELL INTO THE 80S TO
LOW 90S WHICH COULD NEAR OR EXCEED DAILY RECORD HIGHS. 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 (ESPECIALLY PARTS OF
SOUTHERN CA/DESERT SOUTHWEST), AS WELL AS MID-ATLANTIC FOR HIGHS
EARLY IN THE PERIOD, WILL TEND TO SEE NEAR TO MODERATELY BELOW
NORMAL TEMPERATURES.
FRACASSO/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
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