670
FXUS02 KWBC 281900
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 PM EDT MON APR 28 2025
VALID 12Z THU MAY 01 2025 - 12Z MON MAY 05 2025
..OVERVIEW
IT OVERALL REMAINS THE CASE THAT BEHIND A DEVELOPING STORM SYSTEM
TRACKING FROM THE MIDWEST THROUGH THE GREAT LAKES AND SOUTHEASTERN
CANADA LATE THIS WEEK (WITH ASSOCIATED FRONTS AND RAINFALL OF
VARYING INTENSITY), GUIDANCE CONTINUES TO SHOW A LOWER 48 PATTERN
ALOFT THAT BECOMES MORE BLOCKY HEADING INTO THE WEEKEND AND EARLY
NEXT WEEK. AN UPPER TROUGH REACHING THE WEST COAST BY SATURDAY
WILL DISPLACE A LEADING WEAK UPPER LOW CROSSING THE SOUTHWEST AND
SHOULD ULTIMATELY CLOSE OFF A FAIRLY DEEP LOW BY SUNDAY-MONDAY,
WHILE A RIDGE LIKELY SETS UP OVER THE PLAINS AND THEN MISSISSIPPI
VALLEY. THIS PATTERN WILL FAVOR A BROAD AREA OF RAIN AND HIGHER
ELEVATION SNOW MOVING ACROSS THE WEST WHILE PARTS OF THE SOUTHERN
HALF OF THE PLAINS SHOULD SEE MULTIPLE DAYS WITH EPISODES OF
RAIN/THUNDERSTORMS. IN CONTRAST TO THE RELATIVE CONSENSUS OVER THE
WESTERN-CENTRAL U.S. LATE IN THE PERIOD, MODELS AND ENSEMBLES ARE
ALL OVER THE PLACE REGARDING HOW MUCH TROUGHING WITH AN EMBEDDED
UPPER LOW OVER THE EAST.
..GUIDANCE/PREDICTABILITY ASSESSMENT
A MAIN UPPER TROUGH THAT REACHES INTO THE EAST SHOWS DECENT
CLUSTERING INTO EARLY SATURDAY, BUT SOLUTIONS WITH RECENT GUIDANCE
RUNS THEN RAPIDLY DIVERGE WITH DIFFERENCES IN THE CHARACTER OF
UPSTREAM ENERGY STREAMING INTO THE MEAN TROUGH. THE 00 UTC
ECMWF/GFS SHOW RAPID PROGRESSION OF THE SATURDAY TROUGH IN FAVOR OF
MUCH MORE SHALLOW CYCLONIC FLOW OVER NEW ENGLAND THEREAFTER. ON
THE OTHER EXTREME, THE 00/12 UTC CMC/UKMET DROP AN UPPER LOW INTO
THE NORTHEAST/MID-ATLANTIC. THE LATEST 12 UTC GFS/ECMWF HAVE NOW
TRENDED MORE INTO THIS CAMP. THE FULL ENSEMBLE SPREAD IS QUITE
VARIED AS WELL, BUT WITH THE RESULTING MEANS HOLDING ONTO EAST
COAST TROUGHING INTO NEXT MONDAY. RECENT ML MODELS DIFFER AS WELL,
BUT WITH A RELATIVE MAJORITY SUPPORTING A TROUGH WITH POSSIBLE
UPPER LOW. THE 00 UTC AIFS SHOWS AN UPPER LOW JUST OFF THE NEW
JERSEY COAST FOR EARLY MONDAY, BUT THE 12 UTC AIFS HAS A CLOSED
LOW WAY BACK NEAR THE APPALACHIANS. PUTTING THIS TOGETHER THE
TREND THEME OF ML GUIDANCE, PLUS TELECONNECTION SUPPORT FOR SOME
DEGREE OF TROUGHING ALIGNED NEAR THE EAST COAST BASED ON A POSITIVE
HEIGHT ANOMALY CENTER LIKELY TO BE JUST WEST OF LAKE SUPERIOR BY
THE END OF THE PERIOD, PREFERENCE NOW FAVORS THE EAST COAST TROUGH
OF AT LEAST/MORE THAN ENSEMBLE MEANS AMPLITUDE. THE MORNING WPC
MEDIUM RANGE PRODUCT SUITE MAINTAINED WPC CONTINUITY GIVEN
UNCERTAINTIES, BUT GIVEN AMPLIFIED 12 UTC GUIDANCE TRENDS THIS NOW
PROVE QUITE CONSERVATIVE IN THAT IT KEEPS THE UPPER LOW ONLY UP
NEAR MAINE.
OVERALL MOST OF THE GUIDANCE IS MUCH BETTER BEHAVED FOR THE UPPER
TROUGH REACHING THE WEST COAST BY AROUND EARLY SATURDAY AND THEN
CLOSING OFF AN UPPER LOW THAT DRIFTS OVER THE SOUTHERN/CENTRAL
PARTS OF THE WEST BY SUNDAY-MONDAY. SOME ML MODELS SUGGEST THAT
THE UPPER LOW COULD TAKE A SLIGHTLY FARTHER SOUTH TRACK THAN THE
AVERAGE OF DYNAMICAL MODELS/MEANS. THIS TRENDS WELL INTO WPC
CONTINUITY THAT WAS STRONGLY MAINTAINED.
..WEATHER/HAZARDS HIGHLIGHTS
SURFACE LOW/FRONTAL PROGRESSION ACROSS THE EASTERN HALF OF THE
COUNTRY THURSDAY-FRIDAY WILL BRING A BROAD AREA OF RAINFALL WITH
VARYING INTENSITY, BUT GENERALLY WITH LIGHTER TOTALS THAN EXPECTED
ON PRIOR DAYS OVER THE PLAINS. ADEQUATE INSTABILITY AND MOISTURE
MAY STILL PRODUCE SOME POCKETS OF RAIN RATES GREAT ENOUGH TO CAUSE
RUNOFF ISSUES, ESPECIALLY WHERE THERE ARE WETTER GROUND CONDITIONS
LEADING INTO THE EVENT. THE DAY 4 EXCESSIVE RAINFALL OUTLOOK
MAINTAINS A BROAD MARGINAL RISK AREA FROM PARTS OF THE LOWER
MISSISSIPPI VALLEY AND TENNESSEE VALLEY INTO THE GREAT LAKES. WHAT
THREAT OF EXCESSIVE RAINFALL EXISTS FARTHER EAST BY DAY 5 WILL BE
MORE NARROW, WITH BEST RELATIVE POTENTIAL OVER THE CENTRAL AND
NORTHERN APPALACHIANS WHERE GROUND CONDITIONS ARE ON THE WETTER
SIDE AND A SUBSET OF GUIDANCE SHOWS LOCALLY ENHANCED RAINFALL. A
MARGINAL RISK COVERS THIS AREA OF INTEREST. SOME CONVECTION MAY
ALSO EXTEND NEAR THE GULF COAST BUT WITH POOR AGREEMENT FOR
COVERAGE AND AMOUNTS. MOST OF THE EAST SHOULD TREND DRIER BY THE
WEEKEND BUT AN UNCERTAIN LINGERING UPPER TROUGH COULD PRODUCE SOME
CLOUDS/SHOWERS IF IT IS SUFFICIENTLY DEEP.
MULTIPLE DAYS OF LOW LEVEL FLOW COMING IN FROM THE GULF, ALONG WITH
SOME WEAK SHORTWAVE ENERGY APPROACHING FROM THE SOUTHWEST AND
EVENTUALLY HEIGHT FALLS AHEAD OF THE DEEPER WESTERN UPPER LOW, WILL
SUPPORT MULTIPLE EPISODES OF RAINFALL OVER PORTIONS OF THE SOUTHERN
AND EVENTUALLY ALSO CENTRAL PLAINS. GUIDANCE SIGNALS ARE
SUFFICIENTLY GOOD TO SUPPORT A MARGINAL RISK AREA OVER MUCH OF THE
SOUTHWESTERN TWO-THIRDS OF TEXAS INTO FAR SOUTHEAST NEW MEXICO ON
DAY 5/FRIDAY. SOME LOCALLY HEAVY TOTALS ARE POSSIBLE THEREAFTER,
WITH MORE ORGANIZED HEAVY RAINFALL BECOMING POSSIBLE EARLY NEXT
WEEK DEPENDING ON THE EASTWARD DRIFT OF THE WESTERN UPPER LOW.
THE PACIFIC SYSTEM MOVING INTO THE WEST WILL BRING RAIN AND HIGH
ELEVATION SNOW INTO THE NORTHWEST AROUND FRIDAY, WITH PRECIPITATION
THEN CONTINUING ACROSS THE SIERRA NEVADA/GREAT BASIN AND INTO THE
NORTHERN-CENTRAL ROCKIES. HIGHEST TOTALS WILL BE DEPENDENT ON THE
EXACT TRACT OF THE FORECAST EVOLVING UPPER LOW, AND ARE CURRENTLY
MOST LIKELY TO BE OVER THE GREAT BASIN AND NORTHERN ROCKIES.
LEADING WEAK SHORTWAVE/UPPER LOW ENERGY MAY PRODUCE LIGHTER
PRECIPITATION FROM THE SIERRA NEVADA EAST INTO THE ROCKIES
THURSDAY-FRIDAY.
MOST OF THE EAST EXCEPT FOR FAR NORTHERN AREAS SHOULD SEE ABOVE
NORMAL TEMPERATURES LATE THIS WEEK WITH SOME PLUS 10-15F
ANOMALIES. COLD FRONTAL PASSAGE AND ARRIVAL OF UPPER TROUGHING
SHOULD BRING NEAR TO BELOW NORMAL TEMPERATURES EASTWARD FROM THE
CENTRAL U.S. INTO THE EAST BY THE WEEKEND. MEANWHILE ABOVE NORMAL
TEMPERATURES WILL MIGRATE FROM THE NORTHWEST INTO THE
NORTHERN/CENTRAL PLAINS DURING THE PERIOD, CORRESPONDING TO
MOVEMENT OF AN UPPER RIDGE. PLUS 10-20F OR SO ANOMALIES WILL BE
POSSIBLE OVER NORTHERN LOCATIONS WITH WARMEST READINGS LIKELY TO BE
DURING FRIDAY-SUNDAY. THEN THE WEST WILL TREND SIGNIFICANTLY
COLDER NEXT WEEKEND INTO MONDAY WITH THE ARRIVAL OF THE DEEP UPPER
TROUGH/LOW, BRINGING HIGHS DOWN TO 5-20F BELOW NORMAL. THE MOST
EXTREME ANOMALIES ARE FOR THE SOUTHERN GREAT BASIN AND SOUTHWEST.
RAUSCH/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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