703
FXUS02 KWBC 121854
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
254 PM EDT FRI APR 12 2024
VALID 12Z MON APR 15 2024 - 12Z FRI APR 19 2024
...DEEPENING PLAINS SURFACE LOW LIKELY TO BRING SEVERE AND HEAVY
RAINFALL THREATS AHEAD OF IT AND STRONG WINDS AND NOTABLE SNOW
BEHIND...
..OVERVIEW
A CLOSED LOW OVER THE SOUTHWEST U.S. TO START THE PERIOD MONDAY
WILL PROGRESS EASTWARD AND SUPPORT A DEEPENING LOW PRESSURE SYSTEM
OVER THE PLAINS BY TUESDAY. VARIOUS HAZARDS ARE LIKELY WITH THIS
STORM SYSTEM, INCLUDING SEVERE WEATHER AND BANDS OF HEAVY RAINFALL
ON THE WARM SIDE ALONG WITH A BROAD AREA OF GUSTY WINDS. BEHIND
THIS STORM, ANOTHER UPPER TROUGH DIGGING DOWN FROM BRITISH COLUMBIA
INTO THE NORTHWEST U.S. EARLY NEXT WEEK SHOULD ULTIMATELY EVOLVE
INTO A BROADER POSITIVELY TILTED MEAN TROUGH FROM SOUTH-CENTRAL
CANADA THROUGH THE WEST. EXPECT THIS TROUGH TO BRING COLDER
TEMPERATURES AND MULTIPLE DAYS OF SNOW POTENTIAL ESPECIALLY TO THE
NORTHERN HALF OF THE ROCKIES/HIGH PLAINS. MEANWHILE UPPER RIDGING
OVER THE MISSISSIPPI VALLEY ON MONDAY WILL SHIFT EASTWARD AND
SETTLE NEAR THE EAST COAST TUESDAY-THURSDAY, LEADING TO A
CORRESPONDING SHIFT FOR ABOVE NORMAL TEMPERATURES.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODEL GUIDANCE REMAINS REASONABLY AGREEABLE REGARDING THE UPPER
LOW MOVING FROM THE WESTERN TO CENTRAL U.S. TO THE MIDWEST MONDAY-
WEDNESDAY, AS WELL AS THE ASSOCIATED STRONG CYCLOGENESIS AT THE
SURFACE. MORE MODEL DIFFERENCES ARISE UPSTREAM WITH THE UPPER
TROUGH/POSSIBLE CLOSED LOW DROPPING INTO THE NORTHWEST BY TUESDAY
AND EAST AS THE WEEK PROGRESSES. BY WEDNESDAY 00Z CMC AND ECMWF
RUNS INDICATED THIS FEATURE EASTWARD CLOSER TO THE FIRST LOW, NOT
AMPLIFIED AS SOUTH INTO THE NORTHWEST AS GFS RUNS. EC AND GEFS
ENSEMBLE MEMBERS GENERALLY FIT THEIR DETERMINISTIC COUNTERPARTS.
HOWEVER, THE ECMWF-BASED AI MODELS WERE MORE LIKE THE GFS/GEFS THAN
THE OPERATIONAL ECMWF SUITE AND THIS PROVIDED SOME EVIDENCE TO
LEAN MORE TOWARD THE GFS/GEFS DIRECTION. THESE DIFFERENCES MAKE THE
QPF SOMEWHAT UNCERTAIN. THE GEFS/GFS SUITE PROVIDES MORE FORCING
FOR SNOW IN MONTANA AND THE VICINITY. ALSO, THIS FORECAST TRENDED
TOWARD A SLOWER MOVEMENT OF QPF WITH A SOUTHWARD DISPLACEMENT IN
THE MIDWEST/GREAT LAKES/OHIO VALLEY COMPARED TO THE PREVIOUS
FORECAST. NOW IN THE NEWER 12Z RUNS, THE GFS DOES NOT DIG AS FAR
SOUTH AS ITS PREVIOUS RUN TUESDAY-WEDNESDAY, BUT THE ECMWF IS EVEN
FARTHER NORTH AND BY THE LATTER PART OF THE WEEK HAS A NEGATIVELY
TILTED TROUGH/LOW AS IT EVOLVES DIFFERENTLY. THERE ARE ALSO
DIFFERENCES UPSTREAM WITH WHETHER UPPER RIDGING COMES INTO THE
NORTHWEST OR STAYS OUT IN THE EASTERN PACIFIC DEPENDING ON HOW MUCH
ENERGY LINGERS. OVERALL, THERE IS STILL AMPLE SPREAD WITH THE
DETAILS OF THE PATTERN. THUS THE WPC FORECAST USED A MULTI-MODEL
DETERMINISTIC BLEND EARLY ON BUT REDUCED THE DETERMINISTIC
COMPONENTS (PARTICULARLY THE ECMWF AND CMC) IN FAVOR OF THE GEFS
AND EC ENSEMBLE MEANS, WITH THE MEANS OVER HALF THE BLEND BY DAYS
6-7 GIVEN THE MODEL DIFFERENCES.
..WEATHER/HAZARDS HIGHLIGHTS
PRECIPITATION WILL BE INCREASING IN COVERAGE ACROSS THE
ROCKIES/CENTRAL U.S. WITH MULTIPLE WEATHER HAZARDS AS THE UPPER LOW
HELPS TO DEEPEN A PLAINS SURFACE LOW MONDAY-TUESDAY. THE STORM
PREDICTION CENTER IS ALREADY HIGHLIGHTING AREAS OF SEVERE POTENTIAL
FOR THE PLAINS ON MONDAY AND FOR THE LOWER TO MID- MISSISSIPPI
VALLEY TO WESTERN OHIO VALLEY ON TUESDAY GIVEN THE ABUNDANT
INSTABILITY AND MOISTURE PRESENT WITH THIS SYSTEM. THESE
INGREDIENTS COULD ALSO PRODUCE HEAVY RAINFALL WITH INTENSE RATES
CAPABLE OF FLASH FLOODING OVER PARTS OF THE PLAINS AND THE MIDWEST.
GUIDANCE CONTINUES TO SHOW A FAIR AMOUNT OF SCATTER WITH THE
DETAILS, AND SOME AREAS HAVE DRY ANTECEDENT CONDITIONS THAT COULD
LIMIT THE POTENTIAL, BUT THE OVERALL THREAT REMAINS SUFFICIENT TO
SHOW VERY BROAD MARGINAL RISK AREAS ON BOTH THE DAYS 4 AND 5
(MONDAY-TUESDAY NIGHT) EXCESSIVE RAINFALL OUTLOOKS. THESE STRETCH
FROM THE SOUTH-CENTRAL PLAINS/MISSISSIPPI VALLEY WHERE POTENTIALLY
SEVERE CONVECTION COULD PRODUCE HEAVY RAINFALL RATES, TO FARTHER
NORTH ACROSS THE NORTHERN HALF OF THE PLAINS INTO THE UPPER MIDWEST
WHERE CONVECTION PIVOTING CLOSER TO THE LOW CENTER COULD MOVE MORE
SLOWLY FOR POSSIBLY A LONGER DURATION OF HEAVY RAIN. AN EMBEDDED
SLIGHT RISK COULD BE ADDED IF AND WHEN MODELS NARROW IN ON A FOCUS
FOR HEAVY RAINFALL, ESPECIALLY ACROSS PARTS OF THE UPPER MIDWEST ON
TUESDAY, BUT FOR NOW THERE IS STILL TOO MUCH SPREAD TO BE
CONFIDENT IN THE PLACEMENT. BEHIND THE LOW, THE STORM SHOULD
PRODUCE A BROAD AREA OF GUSTY WINDS. THESE WINDS WILL PARTICULARLY
FOCUS OVER THE SOUTHERN/CENTRAL HIGH PLAINS MONDAY ALONG WITH
WILDFIRE CONCERNS, AND STRETCH INTO THE NORTH-CENTRAL HIGH PLAINS
TUESDAY.
THE NEXT UPPER TROUGH DIGGING INTO THE WESTERN U.S. AND EVENTUALLY
EXTENDING INTO THE NORTHERN PLAINS EARLY-MID WEEK, ALONG WITH
ANOTHER FRONTAL BOUNDARY, SHOULD TEND TO FOCUS PRECIPITATION OVER
THE NORTHERN HALF OR SO OF THE ROCKIES AND HIGH PLAINS FOR A FEW
DAYS. THUS MEANINGFUL SNOW WILL BE POSSIBLE OVER AT LEAST THE
HIGHER ELEVATIONS, AND SOME SNOW MAY EXTEND INTO THE HIGH PLAINS BY
MIDWEEK AS COLDER AIR REACHES THE REGION. BLOWING SNOW IS ALSO A
CONCERN THAT MAY CAUSE IMPACTS. FARTHER SOUTH, BY AROUND THURSDAY
OR SO, THE SURFACE FRONT AHEAD OF THIS TROUGH MAY BECOME PARALLEL
TO THE UPPER LOW OVER THE SOUTH-CENTRAL TO EAST-CENTRAL U.S. THE
COMBINATION OF DECELERATING PROGRESSION AND SOME GULF INFLOW MAY
LEAD TO INCREASING RAINFALL NEAR THE FRONT AROUND THAT TIME.
PLAINS/MISSISSIPPI VALLEY UPPER RIDGING WILL SUPPORT WELL ABOVE
NORMAL TEMPERATURES ACROSS THE CENTRAL U.S. INTO MONDAY WITH SOME
NORTHERN/CENTRAL AREAS SEEING HIGHS AND LOWS 20-25F ABOVE NORMAL.
THEREAFTER, THE PATTERN EVOLUTION WILL LEAD TO A BROAD AREA OF
ABOVE NORMAL TEMPERATURES OVER THE EASTERN HALF OF THE COUNTRY INTO
THE SOUTHERN PLAINS, WITH ADVANCING FRONTAL SYSTEMS SLOWLY
TRIMMING THE WESTERN SIDE OF THE WARMTH. EXPECT HIGHS IN THE
EASTERN U.S. TO BE UP TO 10-15F OR SO ABOVE NORMAL WITH ANOMALIES
FOR MORNING LOWS TENDING TO BE SEVERAL DEGREES HIGHER. THE
SOUTHWESTERN U.S. WILL SEE BELOW NORMAL HIGHS THROUGH MONDAY WITH
THE UPPER LOW CROSSING THE REGION. THEN THE UPPER TROUGH DIGGING
INTO THE WEST AND THEN INCLUDING THE NORTHERN PLAINS WILL LIKELY
START TO BRING BELOW NORMAL HIGHS INTO THE NORTHWEST EARLY NEXT
WEEK, FOLLOWED BY READINGS 10-20F BELOW AVERAGE OVER THE NORTHERN
ROCKIES/HIGH PLAINS BY NEXT WEDNESDAY-FRIDAY. LESS EXTREME COOL
ANOMALIES MAY EXTEND FARTHER SOUTHWESTWARD.
TATE/SANTORELLI
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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