991
FXUS02 KWBC 301959
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
259 PM EST FRI DEC 30 2022
VALID 12Z MON JAN 02 2023 - 12Z FRI JAN 06 2023
...WINTER STORM THREAT FOR THE NORTH-CENTRAL ROCKIES/PLAINS AND
UPPER MIDWEST EARLY NEXT WEEK AS A HEAVY RAIN/SEVERE WEATHER
THREAT REEMERGES FOR THE MID-LOWER MISSISSIPPI VALLEY/MID-SOUTH
THEN SOUTHEAST EARLY THROUGH MIDWEEK...
...MORE ROUNDS OF MODERATE TO HEAVY PRECIPITATION FOR THE WEST
WITH FOCUS ACROSS CALIFORNIA NEXT WEEK...
..OVERVIEW
A DEEPENED LOW PRESSURE SYSTEM FORECAST TO DEVELOP INTO EARLY NEXT
WEEK OVER THE CENTRAL U.S. WILL LIKELY LEAD TO A WINTER WEATHER
EVENT FROM THE NORTH-CENTRAL ROCKIES/PLAINS THROUGH THE UPPER
MIDWEST, WHILE HEAVY RAIN, FLASH FLOODING, AND SEVERE WEATHER
APPEAR LIKELY ACROSS THE SOUTH MONDAY-WEDNESDAY. MEANWHILE THE
WEST SHOULD SEE ADDITIONAL ROUNDS OF MODERATE TO HEAVY
PRECIPITATION NEXT WEEK, WITH HIGHEST AMOUNTS MAINLY ACROSS
CALIFORNIA NEXT WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE MAIN FORECAST CHALLENGES OF THE MEDIUM-RANGE PERIOD INCLUDED
THE EVOLUTION OF AN UPPER-LEVEL TROUGH/CLOSED LOW EJECTING OUT
OVER THE PLAINS FROM THE ROCKIES AND THE SUBSEQUENT EFFECTS ON THE
DEVELOPMENT AND TRACK OF A SURFACE LOW THAT WILL BRING WIDESPREAD
WARM SECTOR RAIN/THUNDERSTORM CHANCES TO THE SOUTHEAST AND MIDWEST
AND SNOW TO THE PLAINS AND UPPER MIDWEST. IN ADDITION, THERE IS
UNCERTAINTY REGARDING THE PROGRESSION OF MORE SUBTLE SHORTWAVES
AND TROUGHING OVER THE WEST COAST WITH A SERIES OF PACIFIC STORM
SYSTEMS THAT WILL KEEP PRECIPITATION CHANCES HIGH ACROSS THE WEST.
IN TERMS OF THE FIRST SYSTEM, THE INITIAL PHASING OF THE
UPPER-LEVEL TROUGH IS GENERALLY CONSISTENT BOTH RUN-TO-RUN OVER
THE INDIVIDUAL DETERMINISTIC AND ENSEMBLE MEAN MODEL GUIDANCE AND
ACROSS THE GUIDANCE OVERALL. MORE DIFFERENCES ARISE IN THE
DEVELOPMENT OF A CLOSED LOW, ASSOCIATED EMBEDDED ENERGY, AND
SUBSEQUENT TRACK NORTHEAST ACROSS THE PLAINS AND INTO THE MIDWEST.
THE PREVIOUS WPC FORECAST DEPICTED THE EVENTUAL EVOLUTION OF A
CLOSED LOW AS DID THE MODEL GUIDANCE, ALBEIT WITH SOMEWHAT
DIFFERENT TIMING/PROGRESSION. THE WPC PRODUCT SUITE BEGAN WITH A
GENERAL DETERMINISTIC MODEL BLEND (00Z ECMWF/CMC/UKMET AND 06Z
GFS) PLUS SOME CONTINUITY FROM THE PRIOR FORECAST TO MAINTAIN THE
BROAD DEPICTION OF THE SYSTEM EVOLUTION WITHOUT EMPHASIZING ANY
MORE SUBTLE AND LESS PREDICTABLE DIFFERENCES FROM THE INDIVIDUAL
GUIDANCE.
IT IS CLEAR BASED ON THE SPREAD OF THE INDIVIDUAL ENSEMBLE MEMBERS
THAT THERE IS GREATER UNCERTAINTY AS TO THE STRENGTH OF THE CLOSED
LOW AS IT EJECTS NORTHEASTWARD OVER THE MIDWEST. FOR EXAMPLE,
THERE IS A RUN-TO-RUN TREND FOR A DEEPER CLOSED LOW IN THE GFS
COMPARED TO THE OTHER GUIDANCE. ADDITIONALLY, MORE SUBTLE DETAILS
BEGIN TO ARISE WITH THE SERIES OF SHORTWAVES AND DEVELOPMENT OF AN
UPPER-LEVEL TROUGH OFF THE WEST COAST LATER IN THE PERIOD. A BLEND
OF THE 00Z ECMWF/CMC AND 06Z GFS AND INTRODUCTION OF THE 00Z
GEFS/ECENS MEANS FOLLOWS CONTINUITY FROM THE PRIOR FORECAST WITH
THE CENTRAL U.S. SYSTEM WHILE ALSO MAINTAINING SUBTLE SHORTWAVES
ALONG THE WEST COAST. THE 00Z UKMET WAS PHASED OUT AS IT WAS AN
OUTLIER WITH RESPECT TO THE PROGRESSION OF THE SHORTWAVE ENERGY IN
THE WEST. WITH RESPECT TO THE CENTRAL U.S. SYSTEM, THE UPDATED
MODEL BLEND WITH A BIT DEEPER CLOSED LOW THAT DEVELOPS EARLIER
RESULTED IN A SURFACE LOW TRACK THAT TRENDED A BIT NORTHWEST OF
THE PRIOR FORECAST, WITH SUBSEQUENT SIMILAR EFFECTS ON THE AXIS OF
HEAVIEST SNOW IN THE PLAINS AND RAIN IN THE MID-SOUTH/LOWER
MISSISSIPPI VALLEY.
THE SMALL-SCALE DETAILS BECOME MORE CUMBERSOME TO RESOLVE DURING
THE MID- TO LATE FORECAST PERIOD WITH BOTH THE EVOLUTION OF THE
CLOSED LOW INTO THE NORTHEAST AND EMBEDDED ENERGY WITHIN THE
LARGER-SCALE TROUGH. THE 00Z EMCWF/CMC DIFFERED FROM THE 00Z/06Z
GFS RUNS AND THE PRIOR WPC FORECAST WITH MAINTAINING A CLOSED LOW,
WHILE THE 00Z UKMET WAS ALSO OUT OF PHASE WITH THE OTHER GUIDANCE
IN NOT INCLUDING RIDGING ALONG THE WEST COAST BETWEEN PASSING
SHORTWAVES. TRENDED INCREASINGLY TOWARDS THE 00Z GEFS/ECENS MEANS
GIVEN INCREASING DIFFERENCES IN THE SMALL-SCALE FEATURES ACROSS
THE DETERMINISTIC GUIDANCE AND CONTINUED GROWING SPREAD AMONGST
THE INDIVIDUAL ENSEMBLE MEMBERS. THE 00Z CMC WAS ALSO REMOVED
LATER INTO THE PERIOD AS THE AFOREMENTIONED DOWNSTREAM TROUGH IN
THE WEST WAS MORE OUT OF PHASE COMPARED TO THE OTHER REMAINING
GUIDANCE. THE LATE-PERIOD BLEND OF THE 00Z GEFS/ECENS MEANS WHILE
MAINTAINING SOME OF THE DETERMINISTIC 00Z ECMWF/06Z GFS GUIDANCE
HELPED TO ACCENTUATE A BIT MORE AMPLIFICATION IN THE PATTERN
BETWEEN THE UPPER-LEVEL TROUGH FORECAST TO MOVE OVER THE EAST
COAST AS WELL AS RIDGING OVER THE PLAINS THAT PRECEDES ENERGY FROM
THE DOWNSTREAM TROUGH OVER THE PACIFIC MOVING OVER THE WEST COAST.
..WEATHER/HAZARD HIGHLIGHTS
UPPER TROUGH EMERGENCE WILL SUPPORT HEAVY SNOW ACROSS THE CENTRAL
ROCKIES THIS WEEKEND INTO MONDAY. SUBSEQUENT SURFACE LOW PRESSURE
CONSOLIDATION ACROSS THE CENTRAL HIGH PLAINS WILL THEN BRING A
SWATH OF SNOW ACROSS THE NORTHERN HALF OF THE PLAINS INTO THE
UPPER MIDWEST, ALONG WITH INCREASINGLY WINDY CONDITIONS AND AN ICY
TRANSITIONAL ZONE. INFLOW EAST OF THE LOW AND LINGERING COLD AIR
MAY ALSO SUPPORT SOME LATER PERIOD SNOW/ICE DOWNSTREAM FROM THE
NORTHERN GREAT LAKES TO A COOLED NORTHEAST. MEANWHILE FARTHER
SOUTH, THE FRONTAL SYSTEM ASSOCIATED WITH THIS LOW AND FAVORABLE
GULF MOISTURE/INSTABILITY AND RIGHT ENTRANCE REGION UPPER JET LIFT
SHOULD PROVIDE A FOCUS FOR ANOTHER EPISODE OF WIDESPREAD HEAVY
RAIN, ALONG WITH A THREAT OF SEVERE WEATHER AS PER SPC, ACROSS
PARTS OF THE LOWER MISSISSIPPI VALLEY/MID-SOUTH THROUGH THE
SOUTHEAST MONDAY-WEDNESDAY. SCATTERED INSTANCES OF FLASH FLOODING
ALSO LOOK POSSIBLE AS THE HEAVY RAIN SPREADS FROM THE LOWER
MISSISSIPPI VALLEY/MID-SOUTH MONDAY DEEPER INTO THE SOUTHEAST
TUESDAY, COVERED BY WPC'S EXPERIMENTAL DAY 4/5 "SLIGHT RISK"
EXCESSIVE RAINFALL OUTLOOKS (EROS). THEREAFTER, A TRAILING FRONTAL
LOW PRESSURE SYSTEM COULD DEVELOP UNDER THE RIGHT ENTRANCE REGION
UPPER JET AND THEN LIFT OVER THE EAST. THIS COULD SPREAD SOME
MODERATE TO HEAVY RAIN UP THE MID-ATLANTIC STATES AND COASTAL NEW
ENGLAND.
ADDITIONAL ROUNDS OF PRECIPITATION ARE ALSO EXPECTED TO CONTINUE
ALONG THE WEST COAST AS THE WEEK PROGRESSES. THERE IS QUITE A BIT
OF UNCERTAINTY WITH THE TIMING OF ADDITIONAL HEAVY PRECIPITATION
EVENTS AT THIS POINT GIVEN THE MORE SUBTLE SHORTWAVE PROGRESSION,
BUT AMOUNTS LOOK TO TREND UPWARD BY WEDNESDAY-THURSDAY ACROSS
CALIFORNIA AS A STRONGER FRONTAL SYSTEM APPROACHES FROM THE
PACIFIC WITH ANOTHER POTENTIAL ATMOSPHERIC RIVER EVENT GIVEN THE
SIGNAL FOR A STRONG FETCH OF MOISTURE WITH THE SYSTEM. MANY AREAS
ARE LIKELY TO BE SENSITIVE TO ADDITIONAL RAINFALL BY THEN GIVEN
THE AMPLE RECENT RAINFALL AND ADDITIONAL RAIN DURING THE SHORT
RANGE PERIOD.
MILDER THAN AVERAGE TEMPERATURES FOR WINTER WILL BE WIDESPREAD
ACROSS THE EASTERN HALF OF THE COUNTRY FOR EARLY NEXT WEEK. LOWS
OF AROUND 15-30F ABOVE AVERAGE AND HIGHS AROUND 10-20F ABOVE
AVERAGE WILL BE COMMON, EVEN REACHING 20-30F ANOMALIES IN THE OHIO
VALLEY/GREAT LAKES TUESDAY AND THE NORTHEAST ON WEDNESDAY. DAILY
RECORDS FOR WARM LOWS COULD BE WIDESPREAD FOR PARTS OF THE CENTRAL
AND EASTERN U.S., WHILE DAILY RECORD HIGHS ARE POSSIBLE AS WELL
ESPECIALLY IN THE OHIO VALLEY. MEANWHILE IN THE WEST, THE OVERALL
WET/SNOWY PATTERN WILL TEND TO KEEP DAYTIME TEMPERATURES AROUND
5-10F BELOW NORMAL. AS THE LARGE-SCALE UPPER TROUGH MOVES THROUGH
THE WESTERN U.S. INTO THE PLAINS, NEAR TO BELOW AVERAGE
TEMPERATURES ARE EXPECTED TO WORK THEIR WAY FROM WEST TO EAST
ACROSS THESE AREAS.
PUTNAM/SCHICHTEL
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
HAZARDS:
- HEAVY RAIN ACROSS PORTIONS OF CALIFORNIA AND THE PACIFIC
NORTHWEST, WED-THU, JAN 4-JAN 5.
- HEAVY RAIN ACROSS PORTIONS OF THE CENTRAL PLAINS, THE LOWER
MISSISSIPPI VALLEY, THE TENNESSEE
VALLEY, THE GREAT LAKES, THE MIDDLE MISSISSIPPI VALLEY, THE
SOUTHERN PLAINS, AND THE OHIO VALLEY,
MON, JAN 2.
- HEAVY RAIN ACROSS PORTIONS OF THE LOWER MISSISSIPPI VALLEY, THE
TENNESSEE VALLEY, THE
MID-ATLANTIC, THE SOUTHERN APPALACHIANS, THE SOUTHEAST, AND THE
OHIO VALLEY, TUE-WED, JAN 3-JAN 4.
- HEAVY SNOW ACROSS PORTIONS OF THE CENTRAL GREAT BASIN,
CALIFORNIA, AND THE SOUTHWEST, WED-THU,
JAN 4-JAN 5.
- HEAVY SNOW ACROSS PORTIONS OF THE CENTRAL ROCKIES, THE CENTRAL
PLAINS, THE UPPER MISSISSIPPI
VALLEY, AND THE NORTHERN PLAINS, MON-TUE, JAN 2-JAN 3.
- SEVERE WEATHER ACROSS PORTIONS OF THE MIDDLE MISSISSIPPI VALLEY,
THE LOWER MISSISSIPPI VALLEY,
THE SOUTHERN PLAINS, THE OHIO VALLEY, AND THE TENNESSEE VALLEY,
MON, JAN 2.
- SEVERE WEATHER ACROSS PORTIONS OF THE SOUTHEAST, THE LOWER
MISSISSIPPI VALLEY, THE SOUTHERN
APPALACHIANS, AND THE TENNESSEE VALLEY, TUE, JAN 3.
- FREEZING RAIN ACROSS PORTIONS OF THE CENTRAL PLAINS, THE MIDDLE
MISSISSIPPI VALLEY, THE UPPER
MISSISSIPPI VALLEY, AND THE NORTHERN PLAINS, MON-TUE, JAN 2-JAN 3.
- HIGH WINDS ACROSS PORTIONS OF CALIFORNIA, THE CENTRAL GREAT
BASIN, THE PACIFIC NORTHWEST, AND THE
SOUTHWEST, WED-THU, JAN 4-JAN 5.
- HIGH WINDS ACROSS PORTIONS OF THE SOUTHERN ROCKIES, THE SOUTHERN
PLAINS, AND THE SOUTHWEST, MON,
JAN 2.
WPC MEDIUM RANGE 500MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,
QUANTITATIVE PRECIPITATION, EXPERIMENTAL EXCESSIVE RAINFALL
OUTLOOK, WINTER WEATHER OUTLOOK PROBABILITIES AND HEAT INDICES ARE
AT:
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
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