277
FXUS02 KWBC 281857
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
257 PM 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 ONE OR MORE EMBEDDED LOWS 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. WELL BEHIND THIS SYSTEM, AN UPPER TROUGH
AND LEADING COLD FRONT PUSHING INTO THE NORTHWEST SHOULD SPREAD
PRECIPITATION SOUTHEASTWARD ACROSS THE REGION BY NEXT WEDNESDAY-
THURSDAY.
..GUIDANCE/PREDICTABILITY ASSESSMENT
LATEST GUIDANCE AGREES IN PRINCIPLE ON MOST ASPECTS OF THE LARGE
SCALE PATTERN EVOLUTION AND DOMINANT SURFACE SYSTEMS, BUT WITH SOME
TYPICAL DETAIL UNCERTAINTIES THAT ARE STILL TO BE RESOLVED.
FOR THE INITIAL WESTERN SYSTEM ULTIMATELY AFFECTING THE
CENTRAL/EASTERN U.S., THE FIRST ISSUE TO ARISE INVOLVES THE LATEST
GFS RUNS DEPICTING A CLOSED UPPER SYSTEM TRACKING NORTHEASTWARD
ACROSS THE PLAINS EARLY NEXT WEEK IN CONTRAST TO MOST OTHER
GUIDANCE SHOWING A MORE OPEN DEPICTION ACROSS THIS REGION. THE
GEFS MEAN IS MORE OPEN BUT BOTH SOLUTIONS LEAD TO A FARTHER
WEST/NORTHWEST TRACK FOR LOW PRESSURE AND EXTENT OF HEAVIEST QPF.
00Z ECMWF-INITIALIZED MACHINE LEARNING MODELS (MLS) SHOW VARIOUS
IDEAS FOR HOW UPPER DYNAMICS MAY EVOLVE DURING THAT TIME BUT STILL
ARE NOT VERY SUPPORTIVE OF THE GFS SPECIFICS.
THE NEXT QUESTION INVOLVES AMPLIFYING CANADIAN/NORTHERN TIER U.S.
ENERGY BY AROUND NEXT TUESDAY-WEDNESDAY. THE BEST CLUSTERING OF
DYNAMICAL MODELS AND MLS SUGGEST THAT THIS NORTHERN STREAM ENERGY
SHOULD YIELD A FAIRLY DEEP UPPER LOW OVER THE CENTRAL-EASTERN GREAT
LAKES BY EARLY WEDNESDAY. THE 00Z CMCENS MEAN WAS A FAST EXTREME.
ON THE OTHER HAND, THE NEW 12Z UKMET/CMC/ECMWF ALL STRAY TO THE
SOUTHWEST OF CONSENSUS FOR THE UPPER LOW AT THAT TIME. TIME WILL
TELL IF THIS IS AN EMERGING TREND. THE MAJORITY SCENARIO WOULD HAVE
THE UPPER LOW AND DEEPENING SURFACE LOW PRESSURE REACH NEW ENGLAND
OR VICINITY BY NEXT THURSDAY, WITH SLOWLY IMPROVED CLUSTERING
YIELDING A DEEPER TREND IN A BLENDED FORECAST AT THE SURFACE AND
ALOFT. GIVEN SOME OF THE TRENDS BY WEDNESDAY, CONFIDENCE THEREAFTER
DECLINES ESPECIALLY WITH THE SURFACE TRACK BECOMING QUITE SENSITIVE
TO UPPER LOW SPECIFICS.
MEANWHILE THERE IS DECENT AGREEMENT FOR THE OVERALL UPPER TROUGH
FORECAST TO MOVE INTO THE NORTHWEST BY MIDWEEK OR SO. SOME GFS RUNS
HAVE LEANED A BIT ON THE DEEP/SHARP SIDE OF THE SPREAD (BUT WITH
SOME SUPPORT FROM THE MLS), WHILE THE 00Z ECMWF SHOWED TWO DISCRETE
SHORTWAVES--EACH FASTER THAN THE SINGLE TROUGH DEPICTED IN THE
GFS/CMC, ENSEMBLE MEANS, AND MLS.
FINALLY, THE LATEST DYANMICAL MODELS AND MEANS ARE STRONGLY
SUPPORT THE IDEA OF LINGERING SOUTHWEST U.S. ENERGY SETTLING INTO
NORTHWESTERN MEXICO AS A TROUGH/UPPER LOW LATER IN THE PERIOD.
INTERESTINGLY, MOST 00Z MLS SUGGEST THIS ENERGY WILL EJECT OUT
MUCH MORE QUICKLY.
GUIDANCE COMPARISONS AMONG 00Z/06Z GUIDANCE FAVORED UPDATING THE
FORECAST WITH AN OPERATIONAL MODEL COMPOSITE, WITH SUFFICIENTLY
MODEST GFS WEIGHT NOT TO HAVE UNDUE INFLUENCE ON THE FORECAST OVER
THE MIDWEST EARLY NEXT WEEK. THE BLEND TRANSITIONED TO A HALF
MODEL/HALF ENSEMBLE MEAN MIX BY DAY 7 THURSDAY, REFLECTING THE
LARGE SCALE GUIDANCE AGREEMENT BUT DECREASING CONFIDENCE IN
DETAILS.
..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 REMAINS IN PLACE IN THE DAY 4 EXCESSIVE RAINFALL OUTLOOK OVER
PORTIONS OF ARIZONA ON SUNDAY WHERE HEAVY RAINFALL MAY OCCUR.
MEANWHILE SNOW IS THE LIKELY PRECIPITATION TYPE IN HIGHER
ELEVATIONS FROM THE MOGOLLON RIM NORTHWARD ACROSS THE INTERMOUNTAIN
WEST TO THE ROCKIES, WITH MODERATE TO HEAVY TOTALS 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 THE DAY 4 ERO DEPICTS A MARGINAL RISK ALONG/NEAR SOUTHERN
COASTAL CALIFORNIA TOO. EXPECT A DRYING TREND OVER MUCH OF THE WEST
MONDAY-TUESDAY. A TRAILING UPPER TROUGH/COLD FRONT MOVING INTO THE
PACIFIC NORTHWEST/NORTHERN ROCKIES SHOULD SPREAD RAIN AND MOUNTAIN
SNOW ACROSS THE REGION LATE TUESDAY ONWARD.
THE INITIAL SOUTHWEST UPPER LOW/TROUGH 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 FROM THE PACIFIC AND GULF WILL LIKELY 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 REMAINS IN PLACE
FROM THE MIDDLE MISSISSIPPI VALLEY INTO THE OHIO VALLEY ON MONDAY
AS A STARTING POINT FOR THE DAY 5 ERO, WITH SOME POTENTIAL FOR
FUTURE POSITION ADJUSTEMENTS AND 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 MAY FOCUS ACROSS THE
TENNESSEE VALLEY INTO THE APPALACHIANS. ALSO THE STORM PREDICTION
CENTER IS MONITORING SEVERE POTENTIAL IN THE WARM SECTOR FROM THE
PLAINS TO JUST WEST OF THE APPALACHIANS EARLY NEXT WEEK.
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.
THROUGH MONDAY, A STRONG FRONT ACROSS MIDDLE LATITUDES EAST OF THE
ROCKIES WILL SEPARATE CHILLY TEMPERATURES ACROSS THE NORTH-CENTRAL
U.S. (HIGHS AT LEAST 10-15F BELOW NORMAL) FROM VERY WARM READINGS
ACROSS THE SOUTHERN HALF OF THE PLAINS AND MISSISSIPPI VALLEY INTO
THE TENNESSEE VALLEY AND SOUTHEAST/SOUTHERN MID-ATLANTIC WITH
UPPER RIDGING HELPING TO ENHANCE THE WARMTH. WARM SECTOR
TEMPERATURES OF 10-20F 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. DEVELOPING LOW
PRESSURE WILL THEN PUSH A TRAILING COLD FRONT EASTWARD, DROPPING
TEMPERATURES IN THE SOUTH-CENTRAL U.S. BY TUESDAY AND FOCUSING THE
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 EARLY NEXT WEEK BEFORE A MODERATING TREND. THE
PACIFIC NORTHWEST COULD SEE A BRIEF PERIOD OF ABOVE AVERAGE
TEMPERATURES EARLY NEXT WEEK.
RAUSCH/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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