793
FXUS02 KWBC 251748
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
148 PM EDT MON MAR 25 2024
VALID 12Z THU MAR 28 2024 - 12Z MON APR 01 2024
..HEAVY RAIN ACROSS THE EASTERN SEABOARD INTO THURSDAY
..ROUNDS OF HEAVY RAIN AND SNOW POSSIBLE ACROSS MUCH OF THE WEST
..OVERVIEW
A COLD FRONT OR TWO PUSHING AHEAD OF A BROAD UPPER TROUGH IN THE
CENTRAL-EASTERN U.S. AND EVENTUAL ATLANTIC SURFACE LOW DEVELOPMENT
WILL HELP FOCUS RAINFALL OVER PORTIONS OF THE EASTERN SEABOARD INTO
THURSDAY AND POSSIBLY LINGERING IN MAINE ON FRIDAY. MEANWHILE, ONE
OR MORE PACIFIC SYSTEMS WILL BRING MODERATE TO HEAVY RAIN AND
MOUNTAIN SNOW TO THE WEST COAST STATES (SHIFTING GRADUALLY SOUTH
WITH TIME) AND INTO THE ROCKIES LATER THIS WEEK INTO EARLY NEXT
WEEK. INCREASING MOISTURE MAY COMBINE WITH SHORTWAVES TO PRODUCE
SOME PRECIPITATION FROM THE NORTH-CENTRAL TO EAST-CENTRAL U.S.
FRIDAY-SUNDAY, THOUGH WITH AMPLE UNCERTAINTY IN THE DETAILS OF
COVERAGE/TOTALS AND TYPE.
..GUIDANCE/PREDICTABILITY ASSESSMENT
OVERALL, THE LATEST DETERMINISTIC AND ENSEMBLE MODEL GUIDANCE
OFFERED GOOD AGREEMENT AND RUN TO RUN CONSISTENCY FOR THE SYNOPTIC
FEATURES ACROSS THE CONUS DURING THE MEDIUM RANGE PERIOD. TROUGHING
WILL DEEPEN ALONG THE EAST COAST AS A QUICK MOVING STORM SYSTEM
LIFTS FROM THE SOUTHEAST TO NEW ENGLAND THURSDAY-FRIDAY. TRENDS IN
THE GUIDANCE HAVE BEEN FOR THE LOW PRESSURE TO TRACK SLIGHTLY
CLOSER TO THE COASTLINE, ESPECIALLY AS IT REACHES NEW ENGLAND. THE
06Z GFS (AND NOW 12Z GFS) CONTINUE TO LEAD THE WESTWARD TREND,
SPREADING PRECIPITATION FURTHER WEST/INLAND, WHICH WILL HAVE
IMPLICATIONS FOR HEAVY RAINFALL BUT ALSO WINTER WEATHER FOR THE
INTERIOR/HIGHER ELEVATIONS.
MEANWHILE, A CLOSED UPPER LEVEL LOW WILL SLOWLY MOVE SOUTHWARD
ALONG THE WEST COAST THROUGH THE WEEKEND, TAPPING INTO AN
ATMOSPHERIC RIVER BY LATE IN THE MEDIUM RANGE PERIOD OVER
CALIFORNIA. MODELS ARE IN DECENT AGREEMENT WITH THIS SYSTEM, WITH
THE TYPICAL MODEL BIAS/SPREAD EXPECTED BY DAY 6-7.
THERE IS GOOD MODEL AGREEMENT AND HIGH CONFIDENCE FOR MID-UPPER
RIDGING ACROSS THE SOUTH-CENTRAL U.S., BUT FARTHER NORTH MODELS
VARY WITH EJECTING SHORTWAVES RIDING THE RIDGE, IMPACTING PLACEMENT
OF PRECIPITATION. THERE WERE NOT NECESSARILY OUTLIERS WITHIN THE
12/18Z GUIDANCE ENVELOPE, BUT JUST VARIATIONS THAT WILL HAVE TO BE
RESOLVED AT SHORTER FORECAST TIMESCALES. HOWEVER, IN THE NEWER 00Z
GUIDANCE, THE CMC SEEMS QUITE AGGRESSIVE WITH A SHORTWAVE IN THE
NORTHERN PLAINS FRIDAY TRACKING EAST OVER THE WEEKEND, WHICH OTHER
GUIDANCE DOES NOT SHOW.
GIVEN THE GENERAL MODEL AGREEMENT ON THE LARGE SCALE, THE WPC
FORECAST WAS BASED ON A MULTI-MODEL BLEND OF DETERMINISTIC GUIDANCE
FAVORING THE GFS AND ECMWF. GRADUALLY INCORPORATED MORE GEFS AND
EC ENSEMBLE MEAN GUIDANCE AS THE PERIOD PROGRESSED, BUT WAS ABLE TO
MAINTAIN DETERMINISTIC MODELS AS OVER HALF THE BLEND THROUGH DAY
7.
..WEATHER/HAZARDS HIGHLIGHTS
LOW PRESSURE ORGANIZING THURSDAY ALONG THE COASTAL REGIONS OF SOUTH
AND NORTH CAROLINA WILL DEEPEN AS IT LIFTS NORTHEAST ALONG THE
MID-ATLANTIC AND NORTHEAST COASTS. FAVORABLE FORCING FOR ASCENT
PROVIDED BY A COUPLED JET STRUCTURE AND A PLUME OF MOISTURE LIFTING
NORTHWARD WILL ALLOW FOR WIDESPREAD MODERATE TO LOCALLY HEAVY
PRECIPITATION TO DEVELOP. THE LATEST TRENDS IN THE MODEL GUIDANCE
HAVE SHIFTED THE AXIS OF HEAVIEST PRECIPITATION SLIGHTLY WESTWARD,
BRINGING MORE COASTAL AREAS INTO THE EXCESSIVE RAINFALL RISK FROM
PORTIONS OF CENTRAL/NORTHEASTERN NORTH CAROLINA TO SOUTHERN NEW
ENGLAND. AS THE LOW DEEPENS FURTHER IN THE GULF OF MAINE ON FRIDAY,
A SURGE OF COLD AIR ON THE BACKSIDE MAY ALLOW PRECIPITATION TO
CHANGEOVER TO WET, HEAVY SNOW ACROSS PORTIONS OF VERMONT, NEW
HAMPSHIRE, AND MAINE THOUGH THERE ARE CONSIDERABLE UNCERTAINTIES IN
THE EVOLUTION OF THE LOW PRESSURE AND ASSOCIATED COLD AIR. BRISK
WINDS MAY ALSO OCCUR IN NEW ENGLAND ON THE BACKSIDE OF THE LOW LATE
WEEK.
FOR THE WEST COAST, AN ACTIVE AND UNSETTLED WEATHER PERIOD IS
EXPECTED. THE FIRST SYSTEM ARRIVES LATE WEDNESDAY INTO THURSDAY,
ESPECIALLY FOR THE PACIFIC NORTHWEST REGION WHERE HEAVY MOUNTAIN
SNOW IS POSSIBLE. A BRIEF BREAK FOR THE END OF THE WEEK BUT QUICK
ON ITS HEELS IS ANOTHER WEATHER SYSTEM PUSHING TOWARD COASTAL
NORTHERN CALIFORNIA BY LATE FRIDAY INTO SATURDAY. THIS SYSTEM WILL
BRING A PERIOD MODERATE TO LOCALLY HEAVY PRECIPITATION TO
CALIFORNIA THROUGH EARLY NEXT WEEK AT LEAST AS AN ATMOSPHERIC RIVER
IS INCREASINGLY LIKELY TO SET UP. BASED ON THE LATEST FORECAST,
MODERATE LEVELS OF IVT VALUES ARE FORECAST, ESPECIALLY FOR
CENTRAL/SOUTHERN CALIFORNIA BY DAYS 6-7. WHILE HEAVY RAINFALL LOOKS
TO PEAK IN SOUTHERN CALIFORNIA ON DAY 6/SATURDAY, THERE SEEMS TO
BE ENOUGH MOISTURE COMING IN BY DAY 5/FRIDAY TO START TO DELINEATE
A MARGINAL RISK FROM COASTAL CALIFORNIA EAST TOWARD THE FOOTHILLS
OF THE SIERRA.
FARTHER EAST, SHORTWAVES GENERALLY RIDING ALONG THE NORTHERN SIDE
OF A CENTRAL U.S. RIDGE COULD COMBINE WITH MOISTURE TO PRODUCE SOME
LIGHT TO MODERATE PRECIPITATION FRIDAY INTO THE WEEKEND ACROSS THE
NORTH- CENTRAL U.S. AND GREAT LAKES REGION INTO OHIO VALLEY.
PRECIPITATION MAY INCREASE IN COVERAGE AND AMOUNTS BY EARLY NEXT
WEEK. CONFIDENCE REMAINS LOW FOR WHERE PRECIPITATION WILL OCCUR AS
WELL AS THE PRECIPITATION TYPES. SIGNALS ARE INCREASING FOR A QUICK
MOVING LOW PRESSURE ALONG THE NORTHERN PLAINS AND FAR NORTHERN
AREAS OF THE UPPER MIDWEST WHICH MAY BRING A PERIOD OF ACCUMULATING
SNOW.
SOME CHILLY TEMPERATURES MAY LINGER ACROSS THE NORTH-CENTRAL U.S.
THROUGH MUCH OF THE PERIOD, BUT FARTHER SOUTH FROM THE CENTRAL TO
SOUTHERN PLAINS/MISSISSIPPI VALLEY, A NOTABLE WARMING TREND IS
EXPECTED LATE WEEK INTO THE WEEKEND AS UPPER RIDGING BUILDS.
TEMPERATURES OF 10-15 DEGREES ABOVE AVERAGE WILL BECOME WIDESPREAD,
WITH HIGHS IN THE 70S REACHING KANSAS AND MISSOURI WHILE HIGHS
CLIMB INTO THE 90S IF NOT 100F IN FAR SOUTHERN TEXAS. THE ABOVE
NORMAL TEMPERATURES ARE LIKELY TO EXPAND EAST INTO THE
OHIO/TENNESSEE VALLEYS, MID-ATLANTIC, AND SOUTHEAST OVER THE
WEEKEND. MEANWHILE IN THE WEST, NEAR TO ABOVE NORMAL LOWS BUT NEAR
TO BELOW NORMAL HIGHS ARE FORECAST, CONSISTENT WITH THE CLOUDS AND
PRECIPITATION THERE. ONE EXCEPTION MAY BE OVER THE PACIFIC
NORTHWEST WHERE ENOUGH UPPER RIDGING MAY BUILD IN TO PUSH HIGHS A
LITTLE ABOVE NORMAL NEXT WEEKEND.
TATE/TAYLOR
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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