125
FXUS02 KWBC 200641
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
240 AM EDT SAT MAY 20 2023
VALID 12Z TUE MAY 23 2023 - 12Z SAT MAY 27 2023
...HEAVY RAIN THREAT POSSIBLE LATER NEXT WEEK FOR THE
SOUTHEAST/FLORIDA...
..PATTERN OVERVIEW AND GUIDANCE/PREDICTABILITY ASSESSMENT
MODELS AND ENSEMBLES NOW GENERALLY AGREE THAT A WARMING UPPER
RIDGE NEXT WEEK WILL SHIFT SLOWLY EASTWARD OVER THE PLAINS BEFORE
NUDGING INTO THE MISSISSIPPI VALLEY/MIDWEST. EARLY-MID NEXT WEEK
WILL ALSO SEE AN UPSTREAM UPPER TROUGH FORM OVER THE NORTHWEST AS
A NORTHEAST U.S. UPPER TROUGH LIFTS INTO THE CANADIAN MARITIMES IN
RESPONSE TO THE APPROACH OF A NEW DIGGING EAST-CENTRAL CANADIAN
UPPER TROUGH. SEPARATED SOUTHERN STREAM UPPER TROUGH ENERGIES WILL
MEANWHILE SETTLE DOWN NEAR CALIFORNIA AND WELL DOWNSTREAM IN THIS
FLOW OVER THE SOUTHEAST/FLORIDA. 12 UTC ECMWF/UKMET SOLUTIONS SEEM
THE MOST REASONABLE FIT WITH THE OVERALL PATTERN ACROSS MUCH OF
OUR FINE NATION AND CLUSTER BEST WITH GEFS/ECMWF ENSEMBLES FOR
TUESDAY INTO WEDNESDAY MORNING. THE NEWER 00 UTC ECMWF AND UKMET
RUNS REMAIN IN LINE AND THE 00 UTC CANADIAN HAS ALSO COME INTO THE
FOLD. HOWEVER, RECENT CANADIAN RUNS HAVE BEEN PRODUCING SCATTERED
AND RUN TO RUN INCONSISTENT EXCESSIVE SMALL SCALE QPF MAXES. WHILE
THESE BULLSEYES MAY REPRESENT LOCAL POTENTIAL GIVEN THE SLOWED AND
AMPLIFIED WARM SEASON FLOW PATTERN, PREDICTABILITY DOES NOT SEEM
TO WARRANT SUCH PRECISION, ESPECIALLY INTO LONGER TIME FRAMES.
DISCOUNTED PAST GFS RUNS THAT HAVE BEEN OFFERING LESS LIKELY UPPER
TROUGH/LOW STREAM PHASING SCENARIOS OVER THE CANADIAN PLAINS AND
TOO SLOW SUBSEQUENT DOWNSTREAM PROGRESSIONS THROUGH EARLY-MID NEXT
WEEK. HOWEVER, THE 18 UTC GFS AND NOW ESPECIALLY THE LATEST 00 UTC
GFS HAS BACKED OFF FROM THIS LESS LIKELY SCENARIO, BOLSTERING
FORECAST CONFIDENCE.
LATER, THE 12 UTC ECMWF MODEL THEN BECOMES A LESS LIKELY OUTLIER
BRINGING MUCH MORE AMPLE UPPER TROUGH ENERGY EASTWARD FROM THE
NORTHWEST TO THE PLAINS LATER NEXT WEEK THAN THE FULL ENVELOPE OF
ENSEMBLE AND MODEL SOLUTIONS THAT INSTEAD DIG HEIGHT FALLS MORE
INTO A WESTERN U.S. UPPER TROUGH POSITION. THE LATEST 00 UTC ECMWF
MODEL HAS TRENDED STRONGLY AWAY FROM THE PRIOR 12 UTC ECMWF RUN.
MEANWHILE, THE ECMWF ENSEMBLE MEAN WESTERN U.S. UPPER TROUGH BY
THEN IS MUCH DEEPER THAN THE ECMWF MODEL, BUT NOT QUITE AS DEEP AS
THE GEFS MEAN. PREFER A GEFS/ECMWF ENSEMBLE MEAN BLENDED SOLUTION
IN THIS LATER TIME FRAME. OTHERWISE OVER THE COUNTRY, OPTED TO
APPLY LESS BLEND WEIGHTING TO THE GEFS MEAN TO ADD EMPHASIS TO THE
ECMWF ENSEMBLE MEAN SOLUTION THAT BOTH OFFERS A SEEMINGLY
FAVORABLE FASTER PROGRESSION OF LEADING FRONTAL RAINS/COOLING
THURSDAY INTO NEW ENGLAND AND ALSO SHOWS A DEEPER LINGERING
SOUTHEAST U.S. UPPER TROUGH BEST CONSISTENT WITH EARLIER WEEK
TRENDS.
..WEATHER/HAZARDS HIGHLIGHTS
A SLOW-MOVING AND SOUTHERN STREAM SEPARATED UPPER TROUGH OVER
SOUTHEAST U.S. NEXT WEEK SEEMS TO BROADLY FAVOR PERIODS OF HEAVY
MARITIME RAINS BUT ALSO ONSHORE FROM MAINLY ATLANTIC COASTAL
PORTIONS OF THE SOUTHEAST/FLORIDA AS SERIES OF SURFACE FRONTAL
LOWS ROTATE IN PROXIMITY TO TAP DEEPENED POOLED MOISTURE, BUT
DETAILS REMAIN UNCERTAIN. STRONG ONSHORE FLOW CAN BE EXPECTED TO
SET UP NORTH OF THESE SURFACE LOWS UNDER SUCH SCENARIO, BUT NO
EXPERIMENTAL WPC DAY 4/5 ERO THREAT AREAS ARE PLANNED TO BE ISSUED
AT THIS TIME. THERE ARE ALSO SOME GUIDANCE INDICATED SCENARIOS
THAT SHOW LESS LIKELY COASTAL WAVE DEVELOPMENTS FARTHER UP/OFF THE
EAST COAST, BUT WITH PLENTY OF UNCERTAINTY. OTHERWISE, THE
AFOREMENTIONED MAIN UPPER RIDGE POSITION SLOW TRANSLATION SHOULD
SUPPORT SUMMERTIME TEMPERATURES WITH VALUES UPWARDS TO 15-20
DEGREES ABOVE NORMAL INTO EARLY-MID NEXT WEEK THAT SHOULD SPREAD
SLOWLY EAST WITH TIME ACROSS THE NORTH-CENTRAL U.S. TO THE MIDWEST
INTO LATER NEXT WEEK, ALL ONLY TEMPERED LOCALLY BY SCATTERED AND
POTENTIALLY STRONG THUNDERSTORM ACTIVITY BOTH WITH EJECTION OF
IMPULSES FROM THE WEST AND INTERACTION WITH NORTHERN STREAM
SYSTEM/FRONTAL APPROACHES FROM SOUTHERN CANADA. LOCALLY HEAVY
THUNDERSTORM ACTIVITY MAY ALSO FOCUS HEAVY LOCAL DOWNPOURS DOWN
OVER THE SOUTHERN 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 NEXT 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 UNCERTAIN LATER NEXT WEEK
UPPER TROUGH POSITION.
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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