395
FXUS02 KWBC 251900
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
200 PM EST WED JAN 25 2023
VALID 12Z SAT JAN 28 2023 - 12Z WED FEB 01 2023
***COLDEST WEATHER SO FAR THIS MONTH EXPECTED ACROSS THE DAKOTAS
AND THE UPPER MIDWEST STARTING THIS WEEKEND***
..SYNOPTIC OVERVIEW
GUIDANCE AGREES ON A LARGE SCALE PATTERN FEATURING A POSITIVELY
TILTED MEAN TROUGH OVER THE LOWER 48, BETWEEN AN AMPLIFIED EASTERN
PACIFIC INTO ALASKA UPPER RIDGE AND ANOTHER UPPER RIDGE EXPECTED
TO MEANDER OVER THE BAHAMAS AND CUBA. THIS PATTERN WILL SUPPORT
PERSISTENTLY COLD TEMPERATURES FROM THE NORTHERN/CENTRAL ROCKIES
INTO THE UPPER MIDWEST, WHILE THE WEST WILL TREND COLDER (WITH A
PERIOD OF TERRAIN-ENHANCED PRECIPITATION) AS A SHORTWAVE DROPPING
INTO THE WESTERN SIDE OF THE MEAN TROUGH PUSHES A COLD FRONT
SOUTHWARD THROUGH THE REGION. THE BAHAMAS/CUBA UPPER RIDGE WILL
TEND TO KEEP THE SOUTHEAST ON THE WARMER SIDE OF NORMAL,
ESPECIALLY AFTER THE WEEKEND. EXPECT THE SOUTHEASTERN QUADRANT OF
THE COUNTRY TO SEE THE HIGHEST RAINFALL TOTALS DURING THE PERIOD
AS SHORTWAVE ENERGY INTERACTS WITH GULF MOISTURE AND ONE OR MORE
SURFACE FRONTS BECOMING PARALLEL TO THE WEST-SOUTHWESTERLY MEAN
FLOW ALOFT EAST OF THE ROCKIES.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE PRIMARY FORECAST ISSUE INVOLVES THE VIGOROUS SHORTWAVE
DROPPING SOUTHWARD ALONG AND NEAR THE WEST COAST DURING THE
PERIOD, WITH VARYING IDEAS FOR TIMING AND AMPLITUDE. IN THE
00Z/06Z GUIDANCE THE UKMET LEANED TO THE SLOWER/WESTWARD AMPLIFIED
SIDE TOWARD THE END OF ITS RUN ON MONDAY WHILE GFS RUNS LEANED TO
THE MORE AMPLIFIED SIDE (WHILE ALSO CARRYING A MORE PERSISTENT
UPPER LOW) BY DAYS 5-7 MONDAY-WEDNESDAY. OTHER MODELS HAVE BEEN
SHOWING POTENTIAL FOR AN UPPER LOW BUT ONE THAT WOULD BE MORE
TRANSIENT AND WITH A FARTHER NORTHEAST TRACK, IF IT FORMS AT ALL.
LATEST GEFS/ECENS/CMCENS MEANS LEAN MUCH MORE TOWARD THE 00Z
ECMWF/CMC AND NEW 12Z ECMWF/CMC. THE GFS IS ACCEPTABLE AS PART OF
A BLEND THOUGH. WHILE THE OVERALL CLUSTERING OF GUIDANCE IS
BETTER THAN AVERAGE FOR A DAYS 6-7 FORECAST AT THE MOMENT, GFS
RUNS OVER THE PAST COUPLE DAYS HAVE BEEN HIGHLY VARIABLE WITH HOW
PROGRESSIVE THIS WESTERN SHORTWAVE WILL BE AND EVEN THE ECMWF WAS
A LOT FASTER A COUPLE DAYS AGO AFTER STABILIZING UPON THE CURRENT
SCENARIO STARTING WITH THE 00Z/24 RUN. THE MODEL VARIABILITY AND
FULL ENSEMBLE SPREAD OFFER THE POTENTIAL FOR SOME ASPECTS OF THE
FORECAST TO GO ASTRAY AGAIN FOR A TIME IN THE NEAR FUTURE. THERE
ARE ALSO UNCERTAINTIES WITH HOW NORTHERN STREAM FLOW COULD
INFLUENCE EASTERN U.S. SURFACE WAVINESS TOWARD NEXT WEDNESDAY.
ONE OTHER NOTE IS THAT THE 00Z GFS RAISED AN ADDED QUESTION MARK,
REGARDING EVOLUTION OF THE ALASKA UPPER RIDGE AND NEARBY SHORTWAVE
ENERGY LATE IN THE PERIOD. THAT RUN BECOME MORE CLOSED WITH THE
ALASKA RIDGE AND ULTIMATELY ALLOWED MORE PACIFIC FLOW TO REACH THE
NORTHWEST U.S. BY MIDWEEK. THUS FAR THE 00Z GFS SCENARIO IS VERY
MUCH IN THE MINORITY IN THAT REGARD.
THE UPDATED FORECAST MAINTAINED THE GENERAL APPROACH OF AN
OPERATIONAL MODEL COMPOSITE EARLY (00Z ECMWF, 06Z GFS, 00Z CMC,
00Z UKMET FROM MORE TO LESS WEIGHT) AND THEN A TREND TO A
MODEL/ENSEMBLE MEAN MIX. THIS YIELDED GOOD CONTINUITY FOR THE
OVERALL PATTERN ALBEIT WITH SOME TYPICAL RUN-TO-RUN ADJUSTMENTS
FOR THE CORRESPONDING SURFACE REFLECTION.
..WEATHER/HAZARD HIGHLIGHTS
BEHIND A COLD FRONT ANCHORED BY A DEPARTING EASTERN CANADA SURFACE
LOW, STRONG HIGH PRESSURE BUILDING INTO AREAS FROM THE
NORTH-CENTRAL U.S. INTO NORTHERN ROCKIES WILL BRING MUCH BELOW
NORMAL TEMPERATURES FROM THE WEEKEND THROUGH AT LEAST THE FIRST
HALF OF NEXT WEEK. THERE MAY BE ONE OR MORE DAYS WITH HIGHS AS
MUCH AS 30-40F BELOW NORMAL FROM THE CENTRAL HIGH PLAINS INTO
MONTANA, WITH SUNDAY-MONDAY EXPECTED TO BE THE COLDEST DAYS. THIS
WOULD BE THE COLDEST WEATHER SINCE CHRISTMAS FOR THIS REGION, WITH
LOCATIONS FROM EASTERN MONTANA TO NORTHERN MINNESOTA LIKELY
REMAINING BELOW ZERO FOR HIGHS SATURDAY OR SUNDAY THROUGH MONDAY.
SOME OF THIS COLD WEATHER SHOULD ALSO REACH INTO THE
NORTHWEST/NORTHERN INTERMOUNTAIN WEST WITH SOME LOCATIONS 15-25F
BELOW NORMAL BY LATE WEEKEND INTO THE NEXT WORK WEEK. SOUTHERN
PARTS OF THE WEST WILL TREND COLDER AS WELL, WITH DECENT COVERAGE
OF HIGHS 10-20F BELOW NORMAL BY MONDAY-WEDNESDAY. UPPER TROUGH
PASSAGE COMBINED WITH LOW LEVEL UPSLOPE FLOW WILL PRODUCE MODERATE
TO LOCALLY HEAVY TERRAIN ENHANCED SNOWS ACROSS NORTH-CENTRAL PARTS
OF THE INTERMOUNTAIN WEST/NORTHERN ROCKIES/WESTERN HIGH PLAINS
SATURDAY AND SUNDAY. WHILE SOME UNCERTAINTY REMAINS WITH THE
EVOLUTION OF THE UPPER-LEVEL PATTERN OVER THE WESTERN U.S., RAIN
AND MOUNTAIN SNOW PROSPECTS SHOULD GENERALLY INCREASE WITH TIME IN
CALIFORNIA AND THE SOUTHWEST AS THE PACIFIC COLD FRONT DROPS
SOUTHWARD, WITH AT LEAST SOME HIGHER ELEVATION/INTERIOR SNOWFALL
AND RAIN FOR THE SOUTHERN CALIFORNIA COAST AND DESERT SOUTHWEST.
THERE MAY BE SOME LOCALIZED TERRAIN ENHANCEMENT BUT THIS EVENT
SHOULD HAVE A LOT LESS MOISTURE TO WORK WITH THAN MANY RECENT
PRECIPITATION EPISODES.
WEAK SHORTWAVE ENERGY INITIALLY EJECTING FROM THE SOUTHWESTERN
U.S. WILL LIKELY SUPPORT ONE OR MORE SURFACE WAVES FROM THE
SOUTHERN PLAINS/GULF COAST INTO THE EAST DURING THE WEEKEND INTO
EARLY NEXT WEEK. GULF MOISTURE RETURN MAY SUPPORT A CORRIDOR OF
MODERATE TO HEAVY RAINFALL OVER PORTIONS OF THE CENTRAL GULF COAST
STATES AND VICINITY SATURDAY AND SUNDAY, WITH MORE MODEST RAINS
SPREADING NORTHWARD OVER THE EAST-CENTRAL U.S. INTO/AHEAD OF A
WAVY FRONT. THE DAY 5 (12Z SUNDAY-12Z MONDAY) EXCESSIVE RAINFALL
OUTLOOK MAINTAINS A SLIGHT RISK AREA FROM SOUTHERN LOUISIANA TO
THE FAR WESTERN FLORIDA PANHANDLE, WHERE MULTIPLE ROUNDS OF HEAVY
RAINFALL WILL BE POSSIBLE. SOMEWHAT LESSER PROBABILITIES OF HEAVY
RAINFALL EXIST OVER A LARGER PORTION OF THE SOUTHEAST. ANOTHER
WAVE NEAR THE CENTRAL GULF COAST WILL INCREASE RAIN CHANCES AGAIN
LATER IN THE PERIOD BY TUESDAY OR WEDNESDAY, WITH POTENTIAL
SENSITIVITY FOR AREAS WHERE THE TWO EPISODES OF RAINFALL COULD
OVERLAP. MEANWHILE WINTER WEATHER WILL BE POSSIBLE FARTHER NORTH,
WITH LOCATIONS FROM THE MIDWEST INTO NEW ENGLAND GENERALLY IN THE
MOST FAVORED AXIS FOR SNOWFALL. SUFFICIENT PERSISTENCE OF COLD
AIR BY LATE IN THE PERIOD COULD INCREASE THE POSSIBILITY FOR A
TRANSITION ZONE OF FREEZING RAIN/SLEET BETWEEN THE RAIN AND SNOW
AREAS BUT ANY SPECIFICS HAVE LOW CONFIDENCE AT THIS TIME.
RAUSCH/HAMRICK
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, 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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