599
FXUS02 KWBC 250659
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
259 AM EDT MON MAR 25 2024
VALID 12Z THU MAR 28 2024 - 12Z MON APR 01 2024
...POSSIBLY HEAVY RAIN COULD CONTINUE ACROSS THE EASTERN SEABOARD
INTO THURSDAY...
...ROUNDS OF HEAVY RAIN AND SNOW POSSIBLE ACROSS MUCH OF THE WEST
THROUGH THE PERIOD...
..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
RECENT MODEL GUIDANCE IS IN RELATIVELY GOOD AGREEMENT ON THE LARGE
SCALE. MODELS SHOW TROUGHING INITIALLY ACROSS THE EAST-CENTRAL
U.S. THURSDAY PIVOTING EAST AND TAKING ON A NEGATIVE TILT BEFORE
SOUTHERN STREAM ENERGY LIKELY CLOSES OFF AN UPPER LOW NEAR NEW
ENGLAND/CANADIAN MARITIMES/WESTERN ATLANTIC BY THE WEEKEND.
HOWEVER, SMALL DIFFERENCES IN THE TROUGH CREATE SOMEWHAT DRAMATIC
DIFFERENCES IN THE SENSIBLE WEATHER SUCH AS QPF. ON THURSDAY-FRIDAY
THE 12Z CMC AND UKMET SHOWED MUCH MORE QPF INLAND COMPARED TO THE
ECMWF AND GFS RUNS THAT SHOWED THE HEAVIEST PRECIPITATION AXIS
OFFSHORE OF THE MID-ATLANTIC AND NORTHEAST. THE NBM AND ECMWF/GFS
SEEMED LIKE A BETTER FIT AND FORTUNATELY THE NEWER 00Z CMC AND
UKMET CAME IN MORE LIKE THEM. RAINFALL AMOUNTS DID INCREASE
WESTWARD SOMEWHAT COMPARED TO THE PREVIOUS FORECAST, SO HOPEFULLY A
GOOD MIDDLE GROUND BETWEEN THE EXTREME WESTERN AND EASTERN
SOLUTIONS. AT TIMES OVER THE PAST COUPLE OF DAYS, ECMWF RUNS HAVE
BEEN QUITE SLOW WITH THE ATLANTIC LOW TRACK. THE 12Z RUN LOOKED IN
GOOD ALIGNMENT WITH THE OTHER DETERMINISTIC MODELS AND THE
AI/MACHINE LEARNING MODELS, BUT THE NEWER 00Z ECMWF IS ON THE SLOW
SIDE AGAIN.
FOR THE WEST, THERE ARE SOME UNCERTAINTIES REMAINING THURSDAY-
FRIDAY, AS ADDITIONAL ENERGY ROUNDS THE BASE OF AN ALREADY
ESTABLISHED UPPER LOW IN THE EASTERN PACIFIC. MODELS VARY IN TERMS
OF HOW/WHEN THE UPPER FEATURES COMBINE ALONG WITH THE SURFACE LOWS.
BUT AT LEAST GUIDANCE AGREES THAT BY THE WEEKEND, THE ENERGIES ARE
WITHIN A DEEP CLOSED UPPER LOW OFFSHORE OF CALIFORNIA THAT SLOWLY
TRACKS EAST. THERE IS SOME MINOR MODEL SPREAD REGARDING THE TIMING
OF THE LOW/TROUGH, BUT CERTAINLY WITHIN TYPICAL LEVELS FOR THE LATE
MEDIUM RANGE PERIOD.
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
A PAIRED JET STRUCTURE (RIGHT ENTRANCE AND LEFT EXIT REGIONS) AND
DEVELOPING SURFACE LOW PRESSURE IN THE WESTERN ATLANTIC WILL
SUPPORT POTENTIALLY HEAVY RAIN ACROSS PARTS OF THE EAST COAST ON
THURSDAY, THOUGH RELATIVE LACK OF INSTABILITY COULD BE A LIMITING
FACTOR. MODELS HAVE VARIED ON HOW MUCH RAIN WILL FALL ONSHORE
RATHER THAN OFFSHORE, BUT SEEM TO BE CONVERGING SOMEWHAT ON A HEAVY
RAINFALL AXIS. THURSDAY'S MARGINAL RISK IN THE EXCESSIVE RAINFALL
OUTLOOK REMAINS SIMILAR TO THE PREVIOUS ISSUANCE, STRETCHING
FARTHEST INLAND OVER NORTH CAROLINA BUT MORE LIMITED TO THE COASTAL
AREAS INTO THE MID-ATLANTIC AND NORTHEAST. BY FRIDAY, MOST
PRECIPITATION SHOULD BE PIVOTING AWAY FROM SHORE, WITH THE POSSIBLE
EXCEPTION OF DOWNEAST MAINE. THERE MAY BE SOME SNOW IN HIGHER
ELEVATIONS OF THE NORTHEAST FARTHER INLAND DEPENDING ON HOW FAR
WEST THE PRECIPITATION SHIELD STRETCHES. BRISK WINDS MAY ALSO OCCUR
IN NEW ENGLAND ON THE BACKSIDE OF THE LOW LATE WEEK.
ROUNDS OF PRECIPITATION ARE LIKELY ACROSS THE WEST LATE WEEK INTO
EARLY NEXT WEEK. MORE SPECIFICALLY, ON THURSDAY SOME MODERATE RAIN
AMOUNTS ARE LIKELY FOR COASTAL AND LOWER ELEVATION AREAS OF THE
PACIFIC NORTHWEST INTO NORTHERN CALIFORNIA, WHILE POSSIBLY HEAVY
SNOW IS FORECAST FOR THE CASCADES/SIERRA NEVADA AND TOWARD THE
NORTHERN ROCKIES AND WIND RIVER RANGE AS PRECIPITATION TRACKS
FARTHER EAST INTO THE INTERMOUNTAIN WEST. THEN MODEL TRENDS HAVE
CONTINUED TO INDICATE THAT CALIFORNIA SHOULD SEE INCREASING HEAVY
PRECIPITATION BY FRIDAY INTO THE WEEKEND BASED ON WHERE AN EASTERN
PACIFIC UPPER LOW/TROUGH SETS UP AND DIRECTS A POSSIBLE ATMOSPHERIC
RIVER INTO THE STATE. THIS SOUTHERN SHIFT WOULD ALSO BRING
PRECIPITATION INTO THE CENTRAL GREAT BASIN AND SOUTHWEST FOR THE
WEEKEND. 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, BUT NORTHERN TIER SNOW AND
FREEZING RAIN CANNOT BE RULED OUT.
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
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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