338
FXUS02 KWBC 061901
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
301 PM EDT TUE MAY 6 2025
VALID 12Z FRI MAY 09 2025 - 12Z TUE MAY 13 2025
..MULTI-DAY SOUTHEAST U.S. HEAVY RAINFALL/FLOODING THREAT
..OVERVIEW
CLOSED LOW ENERGY DRIFTING FROM THE MID-MISSISSIPPI VALLEY WILL
STALL OVER THE SOUTHEAST, SUPPORTING DAILY HEAVY RAINFALL THREATS
THROUGH THE WEEKEND AND EARLY NEXT WEEK. TO THE NORTH, A NORTHERN
STREAM SHORTWAVE WILL CLOSE OFF A NEW COMPACT UPPER LOW OVER THE
NORTHEAST. ELONGATED UPPER TROUGHING OFF THE WEST COAST, STEMMING
FROM AN UPPER LOW MOVING OUT OF THE GULF OF ALASKA, WILL SEND AN
INITIAL SHORTWAVE INTO THE WEST/NORTHWEST SUNDAY. UPSTREAM CLOSED
LOW DEVELOPMENT OFF THE NORTHWEST COAST WILL LEAD INTO AN AMPLIFIED
UPPER TROUGH SLOW PUSH INLAND OVER THE WEST COAST BY NEXT TUESDAY.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE OVERALL PATTERN HAS TENDED TO PROVE SLOW TO PROGRESS COMPARED
TO A CONSENSUS OF GUIDANCE OVER THE PAST WEEK. EXPECT THIS TREND
WILL CONTINUE GIVEN PROPENSITY FOR THE DEVELOPMENT OF EMBEDDED
CLOSED LOWS. ACCORDINGLY, THE WPC MEDIUM RANGE PRODUCT SUITE WAS
PRIMARILY DERIVED FROM A COMPOSITE OF 00 UTC GFS/ECMWF/CANADIAN MODEL
AND ENSEMBLE GUIDANCE THAT WAS BEST CLUSTERED ON THE SLOWER SIDE
OF THE FULL ENVELOPE OF SOLUTIONS FOR SUNDAY-NEXT TUESDAY VERSUS
THE 06 UTC GFS/GEFS MEAN THAT WERE MORE PROGRESSIVE, ESPECIALLY
INTO THE WEST. THE NEWER 12 UTC GFS/GEFS MEAN TRENDED FAVORABLE
TOWARD THE LESS PROGRESSIVE SOLUTION CLUSTER WHILE THE REST OF
GUIDANCE HELD SERVICE, BOLSTERING FORECAST CONFIDENCE. MANUALLY
ADJUSTED 13 UTC NBM GUIDANCE TOWARD FAVORED GUIDANCE AS WELL.
..WEATHER/HAZARDS HIGHLIGHTS
WAVY FRONTAL SYSTEM AND CLOSED UPPER TROUGH/LOW STAGNATION OVER THE
SOUTHEAST WILL CONTINUE TO SUPPORT A MULTI-DAY HEAVY
RAINFALL/RUNOFF THREAT AS FUELED BY POOLING ANOMALOUS MOISTURE.
RELATIVELY DRY ANTECEDENT CONDITIONS AND HIGHER FLASH FLOOD
GUIDANCE MAY LIMIT THE OVERALL FLASH FLOODING POTENTIAL INITIALLY.
OPTED TO MAINTAIN WPC EXCESSIVE RAINFALL OUTLOOK MARGINAL RISKS
FOR DAYS 4/5 (FRIDAY/SATURDAY) FOR NOW, BUT REPEAT CELLS/TRAINING
ALONG WITH SUBSEQUENT CUMULATIVE EFFECTS MAY LEAD TO THREAT LEVEL
UPGRADES AS THE SUPPORTING GUIDANCE SIGNAL CONTINUES TO INCREASE.
AREAS OF RAIN ARE ALSO POSSIBLE IN THE NORTHEASTERN U.S. AT TIMES
LATER THIS WEEK INTO THE WEEKEND WITH AN INITIAL ENERGY PUSH INLAND.
INCREASINGLY WIDESPREAD RAIN AND VERY HIGH ELEVATION SNOWS MAY
MOVE BACK INTO THE WEST WITH MORE GUSTY INTO NEXT WEEK ASSOCIATED
WITH AMPLIFIED UPPER TROUGHING AND SURFACE SYSTEM APPROACH.
GENERAL TROUGHING FROM THE NORTHEAST TO THE SOUTH WILL KEEP
TEMPERATURES NEAR OR BELOW NORMAL AT LEAST THROUGH THE WEEKEND.
MEANWHILE OUT WEST, UPPER RIDGING WILL SUPPORT MUCH ABOVE NORMAL
TEMPERATURES WITH DAYTIME HIGHS 10-20+ DEGREES ABOVE NORMAL
PROGRESSING FROM THE NORTHWEST INTO THE NORTHERN PLAINS. PARTS OF
THE SOUTHWEST SHOULD APPROACH 100 DEGREES.
SANTORELLI/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 FORECAST (QPF), EXCESSIVE RAINFALL
OUTLOOK (ERO), WINTER WEATHER OUTLOOK (WWO) PROBABILITIES, HEAT
INDICES, AND KEY MESSAGES CAN BE ACCESSED FROM:
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
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=OVW
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