745
FXUS02 KWNH 310703
PREEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
302 AM EDT MON MAR 31 2025
VALID 12Z THU APR 03 2025 - 12Z MON APR 07 2025
...MULTI-DAY AND SIGNIFICANT HEAVY RAIN/FLOODING AND SEVERE THREAT
LIKELY FOR LOWER/MIDDLE MISSISSIPPI, TENNESSEE, AND OHIO VALLEYS
THROUGH NEXT SATURDAY...
..OVERVIEW
THE MEDIUM RANGE UPPER PATTERN WILL BE AMPLIFIED, BLOCKY, AND
ACTIVE THROUGH THE PERIOD. A FRONTAL BOUNDARY WILL REMAIN PARKED
OVER THE OHIO VALLEY TO SOUTHERN PLAINS IN BETWEEN AN AMPLIFIED
WESTERN TROUGH AND STRONG ATLANTIC TO GULF UPPER RIDGE. THIS
PATTERN SETS THE STAGE FOR A MULTI-DAY HEAVY RAIN AND SEVERE
WEATHER EVENT WHICH SHOULD BE ONGOING BY THE START OF THE PERIOD ON
THURSDAY FROM THE LOWER MISSISSIPPI INTO THE OHIO VALLEY, WITH
SIGNIFICANT FLOODING INCREASINGLY LIKELY. AN UPPER TROUGH INTO THE
EAST NEXT WEEKEND MAY FINALLY HELP PUSH OUT THE FRONTAL BOUNDARY.
THE WEST SHOULD STAY RELATIVELY COOL UNDERNEATH PERSISTENT
TROUGHING WITH SOME PROGRESSION EASTWARD EARLY NEXT WEEK INTO THE
CENTRAL U.S., WHILE ABOVE NORMAL TEMPERATURES REMAIN LATE WEEK FOR
MUCH OF THE EAST BEFORE MODERATING.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODEL GUIDANCE IS RELATIVELY AGREEABLE ON THE LARGE SCALE PATTERN
MIDWEEK INTO NEXT WEEKEND, BUT STILL UNCERTAIN WITH SOME OF THE
DETAILS, WHICH COULD HAVE SENSIBLE WEATHER IMPACTS. A BUILDING AND
BLOCKY RIDGE OVER THE ATLANTIC TO GULF SHOULD HELP AMPLIFY
TROUGHING OVER THE WEST THROUGH THE PERIOD. SHORTWAVES WITHIN THAT
TROUGH SHOW MORE SPREAD, AND MAY PLAY A ROLE IN EXACTLY WHERE THE
HEAVIEST RAINFALL OCCURS. EITHER WAY, MODELS HAVE BEEN EXTREMELY
CONSISTENT IN SHOWING A POTENTIALLY SIGNIFICANT FLOODING EVENT FROM
THE LOWER MISSISSIPPI VALLEY INTO THE OHIO VALLEY. BY FRIDAY AND
INTO THE WEEKEND, THERE IS SOMEWHAT MORE UNCERTAINTY IN THE DETAILS
OF ANOTHER SHORTWAVE DIGGING THROUGH THE WESTERN SIDE OF THE
TROUGH AND HOW MUCH OF THIS EVENTUALLY EJECTS EASTWARD NEXT
WEEKEND. THE MAIN MODEL OUTLIER HERE IS THE GFS WHICH IS A LITTLE
FASTER WITH THIS SCENARIO, WHILE THE ECMWF AND CMC (AND ENSEMBLE
MEANS) HOLD BACK THE MAIN ENERGY A LITTLE LONGER ACROSS THE WEST. A
NORTHERN STREAM SHORTWAVE SHOWS SOME TIMING/DEPTH ISSUES, BUT
OTHERWISE GUIDANCE AGREES THIS SHOULD AMPLIFY OVER THE GREAT LAKES
AND MOVE INTO THE NORTHEAST EARLY NEXT WEEK, AND FINALLY HELP PUSH
THE WAVY SURFACE FRONT EASTWARD.
THE WPC FORECAST WAS ABLE TO UTILIZE A DETERMINISTIC MODEL BLEND
THROUGH DAY 5. AFTERWARDS, INCORPORATED SOME ENSEMBLE MEAN GUIDANCE
TO HELP TEMPER THE DETAIL DIFFERENCES, WHILE REDUCING THE
PROPORTION OF OPERATIONAL MODELS (ESPECIALLY THE 18Z/MAR 30 GFS) IN
FAVOR OF OVER HALF MEANS BY DAY 7. THIS APPROACH MAINTAINED
RELATIVELY GOOD AGREEMENT WITH THE PREVIOUS WPC FORECAST.
..WEATHER/HAZARDS HIGHLIGHTS
A SURFACE LOW EXITING THE GREAT LAKES ON THURSDAY WILL LEAVE
BEHIND A WAVY FRONTAL BOUNDARY THAT ESSENTIALLY BECOMES STUCK
BETWEEN A STRONG UPPER RIDGE TO THE EAST AND AMPLIFIED TROUGHING
OVER THE WEST. MOIST AND UNSTABLE INFLOW POOLING ALONG THE FRONT
WILL LEAD TO WIDESPREAD SEVERE WEATHER AND FLASH FLOODING CONCERNS
WHICH SHOULD BEGIN DURING THE SHORT RANGE PERIOD AND CONTINUE FOR
SEVERAL DAYS. SPC SHOWS SEVERE PROBABILITIES FROM THE LOWER
MISSISSIPPI VALLEY INTO THE OHIO VALLEY. THE GREATEST CONCERN FOR
FLASH FLOODING FOR THURSDAY WILL STRETCH ACROSS A SIMILAR AREA, AS
THE FRONT ANCHORS STORMS FOR SIGNIFICANT TRAINING CONCERNS. FOR
SEVERAL DAYS NOW, MODELS HAVE BEEN INDICATING SEVERAL INCH RAINFALL
TOTALS, ESPECIALLY ACROSS ARKANSAS INTO WESTERN KENTUCKY WHERE
24-HOUR TOTALS IN EXCESS OF 5-8 INCHES COULD BE REALIZED IN SOME
SPOTS (AND THIS IS ON TOP OF SEVERAL INCHES OF RAINFALL IN THE
SHORT RANGE AS WELL). AS SUCH, A MODERATE RISK IS IN PLACE FOR THIS
REGION FOR THE DAY 4/THURSDAY ERO. THE HEAVY RAINFALL AXIS SHOULD
REMAIN OVER THE SAME AREAS INTO FRIDAY AS WELL, WITH A SLIGHT SHIFT
TO THE SOUTH AND WEST. ANOTHER MODERATE RISK IS IN EFFECT ON THE
DAY 5 ERO FROM NORTHEAST TEXAS TO SOUTHEAST MISSOURI. HIGH RISKS
ARE NOT OUT OF THE QUESTION IN FUTURE EROS AS THE EVENT DRAWS
NEARER AND IT BECOMES CLEARER HOW THE DETAILS COULD EVOLVE,
ESPECIALLY INTO THE TIMEFRAME OF THE CAMS. HEAVY RAINFALL IS LIKELY
TO CONTINUE INTO SATURDAY AS WELL FOR ROUGHLY THE SAME AREAS,
LEADING TO THE POTENTIAL FOR HIGH IMPACT AND LIFE- THREATENING
FLOODING AND FLASH FLOODING OVER THE COURSE OF SEVERAL DAYS. BY
SUNDAY, THE HEAVY RAIN THREAT SHOULD FINALLY BEGIN TO SHIFT
EASTWARD WITH MODERATE TO HEAVY RAINS POSSIBLE ACROSS THE GULF
COAST STATES INTO THE SOUTHEAST, AND MORE WIDESPREAD RAIN ALSO
MOVING INTO THE EAST.
AS TROUGHING SETS UP OVER THE WEST WITH MULTIPLE SHORTWAVES MOVING
THROUGH, ROUNDS OF PRECIPITATION ARE POSSIBLE FROM THE WEST COAST
INTO THE INTERMOUNTAIN WEST AND ROCKIES. GENERALLY LOWER ELEVATION
RAIN AND HIGHER ELEVATION SNOW ARE EXPECTED, WITH MAINLY LIGHT TO
MODEST AMOUNTS. INTO LATE WEEK, A POSSIBLE UPPER LOW IN THE FOUR
CORNERS REGION COULD LEAD TO ENHANCED PRECIPITATION TOTALS ACROSS
THE SOUTHERN AND CENTRAL ROCKIES AND PLAINS. SNOW IS LIKELY IN
HIGHER ELEVATIONS OF THE ROCKIES IN COLORADO AND NORTHERN NEW
MEXICO, WITH UNCERTAINTY AT THIS POINT IN IF/HOW MUCH SNOW COULD
SPILL INTO LOWER ELEVATIONS OF THE HIGH PLAINS.
ABOVE NORMAL TEMPERATURES WILL LINGER ACROSS MUCH OF THE EAST
THROUGH THE WEEKEND WITH DAYTIME HIGHS 10 TO 20 DEGREES ABOVE
NORMAL, ESPECIALLY FOR PORTIONS OF THE SOUTHEAST AND SOUTHERN MID-
ATLANTIC. TEMPERATURES SHOULD MODERATE EARLY NEXT WEEK AS THE UPPER
RIDGE SHIFTS EASTWARD AND TROUGHING MOVES INTO THE EAST.
MEANWHILE, THE WEST SHOULD TREND AND STAY COOLER UNDERNEATH UPPER
TROUGHING THROUGH FRIDAY. BY NEXT WEEKEND, TEMPERATURES MAY
MODERATE SOMEWHAT ALONG THE WEST COAST WHILE EASTERN PACIFIC UPPER
RIDGING MOVES IN. THIS SHIFTS COOLER TEMPERATURES EASTWARD, AND
DAYTIME HIGHS ACROSS PARTS OF THE SOUTHERN ROCKIES COULD BE 10 TO
20 DEGREES BELOW NORMAL NEXT WEEKEND. BELOW NORMAL TEMPERATURES
ALSO SHIFT INTO THE CENTRAL U.S. AND MIDWEST BY NEXT MONDAY.
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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