680
FXUS02 KWBC 280659
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
259 AM EDT THU MAR 28 2024
VALID 12Z SUN MAR 31 2024 - 12Z THU APR 04 2024
...A LOW PRESSURE/FRONTAL SYSTEM WILL SPREAD POTENTIALLY HEAVY
RAIN AND MOUNTAIN/NORTHERN TIER SNOW TO MUCH OF THE COUNTRY NEXT
WEEK...
..OVERVIEW
UPPER TROUGHING WITH AN EMBEDDED UPPER LOW WILL MOVE ACROSS
CALIFORNIA AND THE FOUR CORNERS STATES EARLY NEXT WEEK. THIS
FEATURE AND ITS SURFACE LOW PRESSURE SYSTEM WILL DIRECT MOISTURE
INTO CALIFORNIA AND THE SOUTHWEST/GREAT BASIN INTO THE ROCKIES ON
SUNDAY AND PRODUCE HEAVY RAIN AND HIGHER ELEVATION SNOW. THESE
UPPER/SURFACE FEATURES WILL INTERACT WITH NORTHERN STREAM TROUGHING
IN THE NORTH-CENTRAL TO NORTHEASTERN U.S. TO CONSOLIDATE A SURFACE
LOW THAT SHOULD MOVE FROM THE CENTRAL PLAINS TO THE NORTHEAST
DURING THE WORKWEEK. EXPANSIVE PRECIPITATION COVERAGE IS LIKELY
WITH THIS SYSTEM, WITH SNOW AND FREEZING RAIN POSSIBLE ON ITS NORTH
SIDE, AND HEAVY RAIN IN THE WARM SECTOR AS MOISTURE POOLS ALONG
THE SURFACE LOW'S FRONTS.
..GUIDANCE/PREDICTABILITY ASSESSMENT
RECENT MODEL GUIDANCE CONTINUES TO BE IN FAIRLY GOOD AGREEMENT
THROUGH THE EARLY PART OF NEXT WEEK WITH THE OVERALL PATTERN
CONSISTING OF AN UPPER LOW MOVING INTO THE SOUTHWESTERN U.S. AND A
BROAD RIDGE AHEAD OF IT ACROSS MUCH OF THE CENTRAL AND EASTERN U.S.
WHILE NORTHERN STREAM SHORTWAVES TRACK THROUGH THE FAR NORTHERN
TIER. A MULTI-MODEL BLEND OF THE DETERMINISTIC MODELS WORKED WELL
FOR THE FIRST PART OF THE MEDIUM RANGE PERIOD.
THROUGH THE WORKWEEK, MORE MODEL DIFFERENCES ARISE AS THE WEST LOW
MOVES EASTWARD AND ENERGY COMBINES/INTERACTS WITH A NORTHERN
SYSTEM DROPPING INTO THE GREAT LAKES. THE DETAILS OF POSSIBLE
PHASING OF THESE SYSTEMS ARE VERY UNCERTAIN, WITH CONSIDERABLE
VARIATIONS IN THE OPERATIONAL AND AI/MACHINE LEARNING MODELS.
GENERALLY THE MODEL LEAN SEEMS TO BE TOWARD PHASING BY TUESDAY OR
WEDNESDAY RATHER THAN THE SOUTHERN STREAM LOW AND THE NORTHERN
STREAM TROUGH REMAINING SEPARATE. EVEN AMONG THE MORE PHASED
SOLUTIONS, SOME ENERGY MAY BE LEFT BEHIND IN NORTHERN MEXICO OR SO
THOUGH. THE 12Z GFS AND ECMWF WERE REASONABLY AGREEABLE IN SHOWING
DEVELOPMENT OF A CLOSED UPPER LOW ATOP THE NORTHEAST LATE
WEDNESDAY-EARLY THURSDAY WHILE A TONGUE OF ENERGY/TROUGHING
STRETCHES SOUTHWEST. HOWEVER, THE 18Z GFS SEEMS TO DIG MORE
VORTICITY FROM THE NORTHERN STREAM SOUTHWARD, COMBINING WITH
SOUTHERN STREAM ENERGY TO PRODUCE A CLOSED LOW EARLIER AND FARTHER
SOUTHWEST OF THE 12Z GUIDANCE, WHICH NATURALLY ALSO AFFECTS THE
SURFACE LOW POSITION. THIS 18Z GFS RUN SEEMED LIKE AN OUTLIER. THE
00Z MODEL SUITE FORTUNATELY SHOWS SOMEWHAT LESS SPREAD IN THE
DEVELOPING CLOSED LOW POSITION.
UPSTREAM, SOME TROUGHING COMING INTO THE PACIFIC NORTHWEST BY
MIDWEEK HAS SOME MODEL SPREAD AS WELL. THE 00Z ECMWF CAME IN QUITE
A BIT FASTER THAN ITS PREVIOUS RUN.
BY THE MID TO LATE MEDIUM RANGE PERIOD, USED INCREASING AMOUNTS OF
THE GEFS AND EC ENSEMBLE MEANS IN THE BLEND TO 60 PERCENT BY DAY 7
GIVEN THE INCREASING MODEL SPREAD. FOR QPF, MADE A NOTABLE CHANGE
TO THE NBM TO BRING DOWN PRECIPITATION AMOUNTS ACROSS THE MIDWEST
TO GREAT LAKES AROUND MONDAY. THE NBM/BIAS-CORRECTED MODEL BLEND
SEEMED TO BE HEAVILY INFLUENCED BY THE 18Z GEFS MEAN THAT HAD
HEAVIER PRECIPITATION FARTHER NORTH THERE, WHILE EVEN INDIVIDUAL
GFS RUNS AS WELL AS OTHER MODEL SUITES HAVE QPF FOCUSED FARTHER
SOUTH.
..WEATHER/HAZARDS HIGHLIGHTS
A POTENT STORM SYSTEM WILL MOVE WEST TO EAST NEXT WEEK AND LEAD TO
WIDESPREAD PRECIPITATION ACROSS MUCH OF THE COUNTRY. ON SUNDAY, A
WEAK ATMOSPHERIC RIVER SHOULD BE PUSHING INTO ARIZONA. A MARGINAL
RISK IS IN PLACE IN THE EXCESSIVE RAINFALL OUTLOOK FOR MUCH OF
ARIZONA ON SUNDAY WHERE HEAVY RAINFALL MAY OCCUR, BUT FROM THE
MOGOLLON RIM NORTHWARD ACROSS THE INTERMOUNTAIN WEST TO ROCKIES,
SNOW IS THE LIKELY PRECIPITATION TYPE IN HIGHER ELEVATIONS.
MODERATE TO HEAVY SNOW TOTALS ARE POSSIBLE. ADDITIONALLY, THOUGH
THE ATMOSPHERIC RIVER WILL HAVE PASSED BEYOND SOUTHERN CALIFORNIA
BY SUNDAY, CONVECTIVE RAINFALL COULD OCCUR THERE AS STEEPER LAPSE
RATES COME IN WITH THE UPPER LOW OVERHEAD. THESE SHOWERS MAY HAVE
SOME HIGHER RAIN RATES THAT COULD CAUSE SOME ISOLATED FLOODING
CONCERNS ESPECIALLY AFTER A WET COUPLE OF DAYS, SO A MARGINAL RISK
IS DELINEATED IN SOUTHERN CALIFORNIA TOO. A DRYING TREND IS
EXPECTED IN THE WEST MONDAY-TUESDAY, EXCEPT FOR THE PACIFIC
NORTHWEST THAT WILL SEE INCREASING SUPPORT FOR PRECIPITATION BY
TUESDAY AND BEYOND.
THE UPPER LOW WILL CONTINUE SHIFTING INLAND THROUGH EARLY NEXT
WEEK, AND WITH CONSOLIDATING SURFACE LOW PRESSURE IN THE CENTRAL
PLAINS, A PERIOD OF GUSTY WINDS IS POSSIBLE ACROSS MUCH OF NEW
MEXICO AND SOUTHWEST TEXAS. FARTHER EAST, MOISTURE LIKELY FROM THE
PACIFIC AND GULF WILL COMBINE AND PRODUCE RAIN AND THUNDERSTORMS
ESPECIALLY NEAR FRONTAL BOUNDARIES. THE OHIO VALLEY WILL BE ONE
AREA OF FOCUS FOR POTENTIALLY HEAVY RAINFALL. SOME RAIN IS LIKELY
THERE ON SUNDAY BUT AMOUNTS ARE FORECAST TO INCREASE BY MONDAY. A
MARGINAL RISK IS IN PLACE FROM THE MIDDLE MISSISSIPPI VALLEY INTO
THE OHIO VALLEY ON MONDAY AS A STARTING POINT FOR THE DAY 5 ERO,
WITH CERTAINLY SOME POTENTIAL FOR FUTURE UPGRADES. MOISTURE AND
INSTABILITY ARE ANOMALOUSLY HIGH FOR THIS TIME OF YEAR, AND SHOWERS
AND STORMS COULD TRAIN ALONG THE WEST TO EAST ORIENTED WARM FRONT
NEARBY. BY TUESDAY THE COLD FRONT AND LOW SHOULD CONTINUE TO PUSH
EAST AND THE HEAVIEST RAINFALL AT THAT POINT IS FORECAST TO FOCUS
IN THE TENNESSEE VALLEY INTO THE APPALACHIANS.
ON THE NORTHERN SIDE OF THE STORM SYSTEM, SNOW AND FREEZING RAIN
ARE POTENTIAL THREATS FROM THE NORTH-CENTRAL PLAINS ON SUNDAY,
STRETCHING INTO THE UPPER MIDWEST AND GREAT LAKES REGION MONDAY AND
HIGHER ELEVATIONS OF THE NORTHEAST BY TUESDAY-WEDNESDAY. HOWEVER,
THERE IS STILL CONSIDERABLE UNCERTAINTY IN THE PLACEMENT AND
AMOUNTS OF SNOW AND ICE, SO CONTINUE TO MONITOR FORECASTS. THE
INTERIOR NORTHEAST MAY SEE THE HEAVIEST SNOW AMOUNTS OVERALL
BECAUSE OF THE DURATION OF THE POTENTIAL SNOW EVENT THERE COMPARED
TO THE NORTH-CENTRAL U.S./MIDWEST/GREAT LAKES.
CHILLY TEMPERATURES LINGER ACROSS THE NORTH-CENTRAL U.S. THROUGH
MONDAY, BUT ACROSS THE SOUTHERN HALF OF THE PLAINS AND MISSISSIPPI
VALLEY INTO THE TENNESSEE VALLEY AND SOUTHEAST/SOUTHERN MID-
ATLANTIC, NOTABLE WARMTH IS EXPECTED INTO SUNDAY AS UPPER RIDGING
BUILDS. TEMPERATURES OF 10-20 DEGREES ABOVE AVERAGE WILL BECOME
WIDESPREAD, WITH HIGHS WELL INTO THE 70S REACHING KANSAS TO
VIRGINIA WHILE HIGHS CLIMB INTO THE 90S TO EVEN 100F IN SOUTHERN
TEXAS. A COLD FRONT IS FORECAST TO DROP TEMPERATURES IN THE SOUTH-
CENTRAL U.S. BY TUESDAY, FOCUSING THIS WARMTH IN THE SOUTHEAST
BEFORE THE FRONT PUSHES THROUGH THERE TOO BY MIDWEEK. MEANWHILE IN
THE SOUTHWEST, COOLER THAN AVERAGE TEMPERATURES PARTICULARLY IN
TERMS OF HIGHS ARE LIKELY UNDERNEATH THE UPPER LOW. THE PACIFIC
NORTHWEST COULD SEE ABOVE AVERAGE TEMPERATURES FOR A PERIOD EARLY
NEXT WEEK THOUGH.
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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