186
FXUS02 KWNH 060701
PREEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
259 AM EDT TUE MAY 6 2025
VALID 12Z FRI MAY 09 2025 - 12Z TUE MAY 13 2025
...DAILY HEAVY RAINFALL POTENTIAL ACROSS THE SOUTHEAST ALONG A
STATIONARY FRONT...
..OVERVIEW
ENERGY DRIFTING FROM THE MID-MISSISSIPPI VALLEY WILL STALL OVER
THE SOUTHEAST, SUPPORTING DAILY HEAVY RAINFALL THREATS THROUGH AT
LEAST THE WEEKEND. TO THE NORTH, A NORTHERN STREAM SHORTWAVE WILL
CLOSE OFF AN UPPER LOW OVER THE NORTHEAST, BUT STILL WITH SOME
UNCERTAINTY IN HOW MUCH RAINFALL WILL BE ASSOCIATED WITH THIS.
ELONGATED 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 NEXT SUNDAY, WITH CLOSED LOW DEVELOPMENT OFF THE
NORTHWEST COAST. THIS MAY EVENTUALLY PUSH INLAND BY NEXT TUESDAY.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE LATEST MODEL GUIDANCE CONTINUES TO SHOW RELATIVELY GOOD
AGREEMENT WITH REGARDS TO THE LARGE SCALE PATTERN THROUGH THE
MEDIUM RANGE PERIOD, BUT A LOT OF UNCERTAINTY IN THE DETAILS. THE
MODELS ARE STARTING TO COME INTO BETTER AGREEMENT WITH A CLOSED LOW
MOVING OVER THE NORTHEAST LATER THIS WEEK, BUT A LOT OF
UNCERTAINTY STILL IN THE TIMING. THE ECMWF REMAINS ON THE SLOWER
SIDE OF THE GUIDANCE, WITH THE UKMET THE QUICKEST. ENSEMBLE MEANS
AND LATEST AI GUIDANCE WOULD SUGGEST SOMETHING MORE IN THE MIDDLE.
THAT BEING SAID, A GENERAL MODEL COMPROMISE ACTUALLY WORKED WELL AS
A STARTING POINT FOR THIS FEATURE. THE WEAK UPPER LOW SETTLING
INTO THE SOUTHEAST SHOWS SOME UNCERTAINTY STILL IN THE DISTRIBUTION
OF ENERGY WHICH HAS IMPLICATIONS FOR QPF AMOUNTS ACROSS THE
SOUTHEAST THROUGH THE WEEKEND. TIMING BECOMES A QUESTION BY EARLY
NEXT WEEK FOR THE TROUGH INTO THE WEST COAST, WHICH SHOULD BE
ASSOCIATED WITH SOME SORT OF CLOSED LOW. THE CMC IS THE QUICKEST TO
BRING THIS INLAND, WITH THE ECMWF AND ENSEMBLE MEANS A GOOD MIDDLE
GROUND.
..WEATHER/HAZARDS HIGHLIGHTS
A STATIONARY FRONTAL BOUNDARY THROUGH THE SOUTHEAST WILL CONTINUE
TO SUPPORT A HEAVY RAINFALL THREAT AS ANOMALOUS MOISTURE POOLS
ALONG THE BOUNDARY. MODEL SPREAD, DRIER ANTECEDENT CONDITIONS, AND
HIGHER FLASH FLOOD GUIDANCE MAY LIMIT THE OVERALL FLASH FLOODING
POTENTIAL AND AT THIS POINT WARRANTS ONLY MARGINAL RISKS ON THE
DAYS 4 AND 5 EROS (FRIDAY AND SATURDAY). AREAS OF RAIN ARE ALSO
POSSIBLE IN THE NORTHEASTERN U.S. AT TIMES LATER THIS WEEK INTO THE
WEEKEND, BUT AMOUNTS ARE HIGHLY DEPENDENT ON UPPER LOW EVOLUTION.
RAIN AND VERY HIGH ELEVATION SNOWS MAY MOVE BACK INTO THE WEST BY
ABOUT SUNDAY OR MONDAY ASSOCIATED WITH UPPER TROUGHING.
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
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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