964
FXUS02 KWBC 220729 AAC
PMDEPD
EXTENDED FORECAST DISCUSSION...UPDATED
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
329 AM EDT FRI MAR 22 2024
VALID 12Z MON MAR 25 2024 - 12Z FRI MAR 29 2024
...HEAVY SNOW LIKELY TO CONTINUE INTO MONDAY FOR PARTS OF THE
NORTH-CENTRAL PLAINS AND UPPER MIDWEST...
...HEAVY RAIN THREAT ACROSS THE LOWER MISSISSIPPI VALLEY TO
SOUTHEAST EARLY TO MIDWEEK...
..OVERVIEW
A STRONG LOW PRESSURE SYSTEM IS FORECAST TO INTENSIFY AND TRACK
ACROSS THE CENTRAL PLAINS TO THE UPPER MIDWEST MONDAY-TUESDAY,
BRINGING HEAVY SNOW TO THE NORTH-CENTRAL U.S. TO THE LOW'S NORTH
AND WEST. STRONG WINDS AND VERY COLD TEMPERATURES ARE ALSO
FORECAST. ON THE WARM SIDE OF THE SYSTEM, HEAVY RAIN ASSOCIATED
WITH STRONG THUNDERSTORMS AHEAD OF A RELATIVELY POTENT COLD FRONT
WILL LIKELY LEAD TO FLOODING ISSUES ACROSS THE LOWER MISSISSIPPI
VALLEY AND SOUTHEAST MONDAY-TUESDAY, WITH SOME UNCERTAINTY BEYOND
THAT IN HOW MUCH RAIN MAY FALL FOR THE EAST COAST. MEANWHILE, A LOW
PRESSURE SYSTEM FROM THE PACIFIC IS FORECAST TO MOVE INTO THE
NORTHWESTERN U.S., BRINGING RAIN AND MOUNTAIN SNOW TO THE REGION.
..GUIDANCE/PREDICTABILITY ASSESSMENT
12/18Z MODEL GUIDANCE WAS REASONABLY CONSISTENT WITH THE SURFACE
LOW POSITION IN THE NORTH-CENTRAL U.S. MONDAY-TUESDAY, WITH GOOD
AGREEMENT ACROSS MODEL SUITES AND RUN-TO-RUN CONSISTENCY. THE
INCOMING 00Z SUITE ACTUALLY SHOWS A LITTLE MORE SPREAD WITH THE
TIMING OF THE LOW, WITH THE GFS TRENDING FASTER WHILE THE ECMWF
TRENDED SLOWER. FORTUNATELY THE 12/18Z AVERAGE POSITION WAS IN
BETWEEN. THERE IS HIGH CONFIDENCE IN THE IMPACTFUL WINTER STORM
OCCURRING, THOUGH WITH TYPICAL UNCERTAINTY IN MESOSCALE BANDING OF
PLACEMENT OF HEAVIEST AMOUNTS AS WELL AS THE TIMING. BY WEDNESDAY,
SPREAD INCREASES WITH THE LOW PLACEMENT. THE 12Z/18Z GFS RUNS WERE
AGGRESSIVE IN SHOWING A LOW ALONG THE FRONT DOWN IN THE LOWER
MISSISSIPPI VALLEY THAT ZOOMS NORTH TOWARD THE UPPER GREAT LAKES
AND INTERACTS WITH THE MAIN LOW. A SECONDARY LOW THAT POTENT SEEMS
LESS LIKELY AND FORTUNATELY THE 00Z GFS HAS BACKED OFF, WITH STILL
SOME VARIATIONS BY WEDNESDAY AMONG GUIDANCE IN THE LOW BUT WITHIN
TYPICAL SPREAD.
FARTHER SOUTH, THERE REMAINS NOTABLE MODEL SPREAD REGARDING THE
HEAVY RAIN AREA IN THE SOUTH-CENTRAL TO SOUTHEASTERN U.S., WITH THE
GFS/GEFS KEEPING THE HEAVIEST RAINFALL FARTHER NORTH THAN THE
ECMWF CLUSTER BY TUESDAY. THIS IS PROBABLY PARTLY DUE TO THAT
SECONDARY FRONTAL LOW THAT THE GFS WAS SHOWING. AT LEAST THERE IS
SOME OVERLAP IN THE HEAVY RAINFALL POTENTIAL TO INDICATE A SLIGHT
RISK. THE DIFFERENCES ALOFT AND AT THE SURFACE AND WITH RAINFALL
PLACEMENT ONLY GROW FROM MID- TO LATE WEEK. THE 12Z ECMWF IS SLOW
WITH MOVING SOUTHERN STREAM ENERGY DEVELOPING INTO A CLOSED LOW
OVER THE SOUTHEAST COMPARED TO OTHER GUIDANCE AND EVEN THE EC-BASED
AI/ML MODELS. THE EC ENSEMBLE MEAN WAS SLOWER TOO BUT NOT TO THE
SAME EXTENT OF SHOWING A SLOW CLOSED LOW. THUS FAVORED A GFS/GEFS
MEAN/EC MEAN BLEND FOR THE EAST BY DAYS 6-7. THE 00Z GFS HAS SLOWED
A BIT WHILE THE 00Z ECMWF IS FASTER, SO HOPEFULLY THERE WILL BE
SOME CONTINUED MODEL CONVERGENCE THERE.
IN THE WEST, THE FIRST MODEL THAT LOOKS TO DIVERGE FROM CONSENSUS
WAS THE 12Z CMC BY WEDNESDAY, WHICH SHOWED UPPER AND SURFACE LOWS
MUCH FARTHER WEST IN THE EASTERN PACIFIC THAN OTHER GUIDANCE. THEN
THE GFS ENDED UP BRINGING THE POTENT ENERGY QUICKLY EAST INTO THE
INTERMOUNTAIN WEST THURSDAY-FRIDAY. THE ECMWF SEEMED LIKE A GOOD
MIDDLE GROUND IN TRACKING THE TROUGH EASTWARD AND GENERALLY MATCHED
WELL WITH THE AI/ML MODELS. WITH THIS AND CONSIDERING THE GFS'S
FAST BIAS, FAVORED THE EC MORE.
THE WPC FORECAST USED A BLEND OF THE DETERMINISTIC GUIDANCE EARLY
IN THE FORECAST PERIOD. GIVEN THE AFOREMENTIONED ISSUES WITH THE
ECMWF IN THE EAST, THE GFS IN THE WEST, AND THE CMC EVERYWHERE,
GRADUALLY INCREASED THE PROPORTION OF GEFS/EC ENSEMBLE MEANS TO THE
ENTIRE BLEND BY DAY 7.
..WEATHER/HAZARDS HIGHLIGHTS
THE DEEP SURFACE LOW TRACKING FROM THE CENTRAL PLAINS TO UPPER
MIDWEST WILL BE THE DRIVER (ALONG WITH UPPER-LEVEL SUPPORT) FOR
MULTI-HAZARD IMPACTFUL WEATHER FOR EARLY-MID NEXT WEEK. A
WIDESPREAD LATE SEASON WINTER STORM SHOULD BE ONGOING MONDAY WITH
HEAVY SNOW ACCUMULATION (8+") LIKELY FROM NORTHEASTERN NEBRASKA
INTO EASTERN PARTS OF THE DAKOTAS, MUCH OF MINNESOTA, AND FAR
NORTHWESTERN WISCONSIN, AS THIS REGION WILL BE ON THE COLDER SIDE
OF THE LOW WITH A DEFORMATION ZONE DEVELOPING. HIGH WINDS DUE TO
THE DEEP SURFACE LOW COULD LEAD TO BLIZZARD CONDITIONS IN SOME
AREAS. TIMING/TRACK UNCERTAINTY MAY CHANGE THE EVENTUAL LOCATION
OF THE IMPACTFUL WINTER WEATHER, BUT THE RISK FOR DISRUPTIONS TO
DAILY LIFE AND HAZARDOUS TRAVEL IS LIKELY. HIGH WINDS ARE ALSO
POSSIBLE SOUTHWARD ACROSS THE PLAINS ON MONDAY BEHIND THE COLD
FRONT, THOUGH WITH DRIER WEATHER.
FARTHER SOUTH AHEAD OF THE COLD FRONT, AMPLE MOISTURE STREAMING IN
AND A STRONG JET ALOFT WILL SUPPORT HEAVY RAIN AND POTENTIALLY
SEVERE THUNDERSTORMS FOR THE LOWER MISSISSIPPI VALLEY MONDAY,
SHIFTING INTO THE SOUTHEAST ON TUESDAY. SLIGHT RISKS ARE IN PLACE
IN THE DAY 4-5 EXCESSIVE RAINFALL OUTLOOKS DUE TO THE POTENTIAL OF
A LIKELY SQUALL LINE CAUSING RAIN RATES OF 2+" PER HOUR. THE AREAL
COVERAGE OF HEAVY QPF IS SOMEWHAT LESS ON TUESDAY COMPARED TO
MONDAY, BUT STILL HAVE A SLIGHT RISK CONSIDERING THAT THE
ECMWF/GFS ARE AGREEABLE IN INDICATING THE SQUALL LINE LASTING INTO
THE EARLY PART OF THE DAY ON TUESDAY INTO MS/AL. BY MIDWEEK, THE
STORMY WEATHER THEN REACHES THE FLORIDA PANHANDLE NORTH INTO THE
CAROLINAS UP THE EASTERN SEABOARD, BUT WITH CONSIDERABLE SPREAD IN
RAINFALL AMOUNTS BY WEDNESDAY-THURSDAY DUE TO THE MODEL
DIFFERENCES.
SOME LINGERING MODERATE SNOW IS POSSIBLE ACROSS PARTS OF THE
SOUTH-CENTRAL ROCKIES ON MONDAY, WITH LIGHT AMOUNTS ELSEWHERE
ACROSS THE INTERMOUNTAIN WEST. THE PACIFIC NORTHWEST COULD SEE SOME
MODERATE LOWER ELEVATION RAIN AND HIGHER ELEVATION SNOW AMOUNTS
MONDAY, WITH INCREASING TOTALS BY TUESDAY-WEDNESDAY AND EXPANDING
INTO CALIFORNIA AS TROUGHING AND LOW PRESSURE APPROACH. SOME
MODERATE TO HEAVY PRECIPITATION SHOULD EXPAND INTO THE
INTERMOUNTAIN WEST MIDWEEK, AND WILL CONTINUE TO MONITOR THE
POTENTIAL FOR FURTHER EXPANSION OF THE PRECIPITATION POSSIBLY IN
THE FORM OF SNOW TO AFFECT THE NORTH-CENTRAL PLAINS ONCE AGAIN BY
THURSDAY.
MUCH COLDER THAN AVERAGE TEMPERATURES (MORE COMPARABLE TO JANUARY)
ARE LIKELY FOR THE NORTHERN AND CENTRAL HIGH PLAINS IN THE WAKE OF
THE STRONG COLD FRONT. HIGHS WILL ONLY BE IN THE 20S AND 30S FOR
THESE AREAS ON MONDAY, BUT A MODERATING TREND WILL COMMENCE GOING
INTO THE MIDDLE OF THE WEEK, EVEN THOUGH MONTANA AND NORTH DAKOTA
WILL STILL REMAIN CHILLY BY LATE MARCH STANDARDS. THE WEST SHOULD
SEE GENERALLY COOLER THAN AVERAGE HIGHS AND NEAR AVERAGE LOWS NEXT
WEEK, WHILE THE EAST CAN EXPECT BOUTS OF ABOVE AND BELOW NORMAL
TEMPERATURES AVERAGING OUT TO NEAR NORMAL.
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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