125
FXUS02 KWBC 220648
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
247 AM EDT MON MAY 22 2023
VALID 12Z THU MAY 25 2023 - 12Z MON MAY 29 2023
...WATCHING COASTAL FRONT/LOW FOR THE POSSIBILITY OF BRINGING
HEAVY RAIN TO THE EAST COAST/FLORIDA...
..PATTERN OVERVIEW AND GUIDANCE/PREDICTABILITY ASSESSMENT
MODELS AND ENSEMBLES REMAIN IN DECENT AGREEMENT THAT A WARM UPPER
RIDGE WILL SHIFT VERY SLOWLY EASTWARD OVER THE PLAINS BEFORE
NUDGING TOWARD THE MISSISSIPPI VALLEY/MIDWEST BY THE WEEKEND.
MEANWHILE, FAIRLY AMPLIFIED TROUGHS WILL BE ANCHORED ALONG BOTH
THE WEST AND THE EAST COASTS, RESULTING IN LITTLE OVERALL MOTION
TO THE ENTIRE SYNOPTIC PATTERN ACROSS THE U.S. IN THIS BLOCKY
PATTERN, RECENT TRENDS SHOW A NEW CLOSED LOW FORMS BETWEEN THE
GREAT LAKES AND NEW ENGLAND FROM LATE WEEK INTO THE WEEKEND. THE
PRESENCE OF THIS UPPER LOW ENHANCES THE FRONTAL CHARACTERISTICS
ALONG THE EAST COAST AND INCREASES THE CHANCE OF INTERACTION WITH
ANOTHER UPPER LOW THAT IS FORECAST TO FORM IN THE VICINITY OF THE
SOUTHEAST/FLORIDA LATE THIS WEEK. WHILE UNCERTAINTY REMAINS TOO
HIGH TO PROVIDE THE SPECIFICS, STREAM INTERACTION OFFERS INCREASED
POSSIBILITIES THAT ENHANCED RAINFALL JUST OFFSHORE WITH COASTAL
LOW GENESIS COULD WORK ONSHORE FROM THE EAST COAST OF FLORIDA TO
THE SOUTHEAST AND POSSIBLY FARTHER UP/OFF THE EAST COAST AS WE
HEAD INTO THE MEMORIAL DAY WEEKEND. THIS SYSTEM IS ALSO BEING
MONITORRED BY THE NATIONAL HURRICANE CENTER FOR ANY
NON-EXTRATROPICAL DEVELOPMENT.
ALONG THE WEST COAST, MODELS HAVE SETTLED INTO THE IDEA OF A
CLOSED LOW MOVING SLOWLY ACROSS CALIFORNIA FOR THE LATTER HALF OF
THIS WEEK. HOWEVER, ALL BETS ARE OFF WITH ANOTHER UPPER TROUGH/LOW
IS FORECAST TO REACH THE PACIFIC NORTHWEST BY THE MEMORIAL DAY
WEEKEND. THERE HAS BEEN QUITE A BIT OF UNCERTAINTY IN ITS DEPTH,
AND LATEST RUNS EVEN IT'S EXISTENCE WITH GUIDANCE TRENDING
ERATICALLY DIFFERENT WITH ENERGY TRACKS OUT FROM THE GULF OF
ALASKA LEADING TO HORRENDOUS RUN TO RUN CONTINUITY AND
PREDICTABILITY. THIS HAS NOT HAD AS LARGE AN IMPACT ON THE
LOCATION OF THE WEST COAST MEAN TROUGH AXIS ON THE ENSEMBLE MEANS
HOWEVER, AND THAT GENERAL FLOW REGIME WOULD ALLOW FOR A CONTINUED
MOIST/WET AND UNSETTLED PATTERN ACROSS MUCH OF THE INTERMOUNTAIN
WEST TO THE ROCKIES.
OVERALL, THE WPC MEDIUM RANGE PRODUCT SUITE WAS PRIMARILY DERIVED
FROM A COMPOSITE BLEND OF LOOSELY CLUSTERED GUIDANCE OF THE 18 UTC
GFS/GEFS, 12 UTC ECMWF/UKMET/CANADIAN AND A COMPATIBLE 01 UTC
NATIONAL BLEND OF MODELS (NBM) FOR MID-LATER THIS WEEK IN A
PATTERN WITH BELOW AVERAGE PREDICTABILITY. SWITCHED GUIDANCE
PREFERENCE INCREASINGLY TO A BLEND OF BROADLY COMPATIBLE BLEND OF
THE GEFS/ECMWF ENSEMBLE MEANS AND NBM BY THE WEEKEND AMID EVEN
MORE RAPIDLY GROWING FORECAST SPREAD. DESPITE UNCERTAINTIES, THIS
SOLUTION OFFERS A REASONABLY GOOD MATCH WIH WPC PRODUCT CONTINUITY
FOR MUCH OF THE LOWER 48 AND LENDS WELL WITH LATEST NHC/WPC
OFFSHORE SYSTEM COLLABORATIONS AND EXPECTATIONS. THAT SAID, STRONG
TRENDS FROM THE NEWER 00 UTC MODELS, ESPECIALLY THE GFS/CANADIAN,
ARE NOW FAVORING A MORE NORTHWARD LIFT UP OVER THE EAST OF MORE
AMPLE SOUTHEAST CLOSED UPPER SYSTEM ENERGIES THAN THE ENSEMBLE
MEANS, NOW MORE IN LINE WITH THE 12 AND NOW 00 UTC ECMWF. THIS
FURTHER OPENS THE DOOR FOR A CLOSER OFFSHORE FRONT/LOW AND
RAINFALL SCENARIO TO MONITOR.
..WEATHER/HAZARDS HIGHLIGHTS
AN UPPER LOW BETWEEN THE GREAT LAKES AND NEW ENGLAND OFFERS A
POSSIBILITY OF LINGERING RAIN ACROSS NORTHERN NEW ENGLAND INTO
THURSDAY. MEANWHILE WELL TO THE SOUTH, A SLOW-MOVING AND SOUTHERN
STREAM SEPARATED UPPER TROUGH OVER SOUTHEAST THIS WEEK WILL FAVOR
PERIODS OF HEAVY MARITIME RAIN JUST OFFSHORE THE SOUTHEAST, BUT
ALSO ONSHORE FROM MAINLY ATLANTIC COASTAL PORTIONS OF THE
SOUTHEAST/FLORIDA AS SURFACE FRONTAL LOWS ROTATE IN PROXIMITY TO
TAP DEEPENED POOLED MOISTURE. DETAILS REMAIN UNCERTAIN AND THE NHC
IS ADDITIONALLY MONITORING POTENTIAL FOR ANY NON-FRONTAL LOW
DEVELOPMENTS WITH DEEPER TROPICAL MOISTURE. STRONG ONSHORE FLOW
COULD BE EXPECTED TO SET UP NORTH OF SURFACE LOWS WITH SUFFICIENT
DEVELOPMENT. IT REMAINS QUITE RUN TO RUN UNCERTAIN IN GUIDANCE AS
TO THE POTENTIAL FOR THE INTERACTION OF THESE TWO MAIN SYSTEMS
THAT COULD LEAD TO EJECTION OF THE SOUTHEAST CLOSED LOW AND THE
NORTHWARD TRACK OFF THE EAST COAST OF ORGANIZED LOW PRESSURE
SYSTEMS AND ASSOCIATED WRAPPING RAINS AND UNSETTLED MARITIME
CONDITIONS.
OTHERWISE, THE AFOREMENTIONED MAIN UPPER RIDGE POSITION SLOW
TRANSLATION SHOULD SUPPORT SUMMERTIME TEMPERATURES WITH VALUES
UPWARDS TO 15-20 DEGREES ABOVE NORMAL INTO LATER WEEK THAT SHOULD
PROVE SLOW TO SPREAD SLOWLY EAST WITH TIME ACROSS THE
NORTH-CENTRAL U.S. TO THE MIDWEST. THE HEAT MAY BE TEMPERED
LOCALLY BY SCATTERED AND POTENTIALLY STRONG THUNDERSTORM ACTIVITY
BOTH WITH EJECTION OF IMPULSES FROM THE WEST AND WITH INTERACTION
WITH NORTHERN STREAM SYSTEM/FRONTAL APPROACHES FROM SOUTHERN
CANADA. LOCALLY HEAVY THUNDERSTORM ACTIVITY MAY ALSO FOCUS HEAVY
LOCAL DOWNPOURS DOWN OVER THE CENTRAL TO SOUTHERN ROCKIES/PLAINS
AS WELL WITH MOISTURE/INSTABILITY POOLING WITH SOUTHERN STREAM
IMPULSES. ABOVE TO MUCH ABOVE NORMAL OVERNIGHT TEMPERATURES AND A
PATTERN FAVORING SCATTERED TO WIDESPREAD SHOWERS AND THUNDERSTORMS
ARE ALSO EXPECTED TO LINGER ALL WEEK OVER MUCH OF INTERIOR WEST
THROUGH THE ROCKIES IN MOISTENED FLOW CHANNELED BETWEEN WEST COAST
UPPER TROUGHING AND THE DOWNSTREAM CENTRAL U.S. UPPER RIDGE, WITH
DETAILS/LOCAL FOCUS DEPENDENT ON THE ULTIMATE SHAPE OF THE STILL
QUITE UNCERTAIN LATER WEEK UPPER TROUGH POSITIONS AND FLOW
INTERACTIONS.
SCHICHTEL
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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