956
FXUS02 KWBC 190649
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
248 AM EDT WED OCT 19 2022
VALID 12Z SAT OCT 22 2022 - 12Z WED OCT 26 2022
..OVERVIEW
A SIGNIFICANT PATTERN CHANGE REMAINS LIKELY FOR THE MEDIUM RANGE
PERIOD COMPARED TO THE WEST UPPER RIDGE/EAST UPPER TROUGH PATTERN
IN THE SHORT RANGE. UPPER TROUGHING WILL STRENGTHEN IN THE WEST
THIS WEEKEND AND PROGRESS TOWARD THE CENTRAL U.S. INTO NEXT WEEK.
THIS DEEP TROUGH AND A COUPLE OF COLD FRONTS WILL LEAD TO AREAS OF
LOWER ELEVATION RAIN/HIGHER ELEVATION SNOW AS WELL AS COOLER
TEMPERATURES OVER THE WEST, AND WILL EVENTUALLY SPREAD INCREASING
RAIN CHANCES TO THE PLAINS/MISSISSIPPI VALLEY NEXT WEEK. AHEAD OF
THE TROUGH AND FRONT, WARMER THAN AVERAGE TEMPERATURES ARE
FORECAST TO SHIFT FROM THE CENTRAL U.S. INTO THE NORTHEAST, WITH
MAINLY DRY CONDITIONS IN THE EAST ASIDE FROM SOME POSSIBLE RAIN
ALONG THE EAST COAST DEPENDENT ON THE POSITIONING OF A WAVY
OFFSHORE FRONT AND UPPER-LEVEL ENERGY.
..MODEL AND PREDICTABILITY ASSESSMENT
WHILE MODEL GUIDANCE IS AGREEABLE THAT TROUGHING WILL AMPLIFY IN
THE WEST THIS WEEKEND, PREDICTABILITY AND CONFIDENCE QUICKLY
DECREASE EARLY NEXT WEEK AS MODELS DIVERGE. MUCH OF THE MODEL
SPREAD ARISES FROM DIFFERENCES IN THE POTENTIAL PHASING OF THE
TROUGH FORMING IN THE NORTHERN STREAM AND A SOUTHERN STREAM UPPER
LOW OFFSHORE OF CALIFORNIA AND MEXICO. THIS HAS BEEN AN AREA OF
CONSIDERABLE DISAGREEMENT OVER THE LAST FEW DAYS IN OPERATIONAL
GUIDANCE AND ENSEMBLE MEMBERS. THE ECMWF RUNS HAVE BEEN MOSTLY
CONSISTENT WITH LEAVING THESE TWO FEATURES IN THEIR SEPARATE
STREAMS THROUGH AT LEAST MONDAY, LEADING TO A FASTER NORTHERN
STREAM TROUGH/FORMING UPPER LOW WHILE THE SOUTHERN STREAM LOW
SPINS IN THE EASTERN PACIFIC BEFORE EVENTUALLY COMING INTO THE
SOUTHWEST. MEANWHILE GFS RUNS HAD GENERALLY BEEN ON THE MORE
PHASED SIDE, CREATING ONE TROUGH THAT STEADILY PROGRESSES EAST
WITH IN-BETWEEN TIMING...UNTIL THE 18Z GFS RUN THAT WAS PRETTY
SIMILAR TO THE 12Z ECMWF. THE CMC AND UKMET BOTH PHASE THE
ENERGIES PRETTY QUICKLY TO CREATE A DEEP GREAT BASIN/FOUR CORNERS
LOW SUNDAY-MONDAY. MODELS WITH MORE STREAM SEPARATION LIKE THE
ECMWF AND 18Z GFS INDICATE A FASTER NORTHERN STREAM COLD FRONT OF
COURSE, AND KEEP PRECIPITATION IN THE NORTH-CENTRAL U.S. EARLY
NEXT WEEK, LESS SO IN THE SOUTH-CENTRAL U.S. LIKE OTHER GUIDANCE
AND THE ENSEMBLE MEANS. ENSEMBLE MEMBERS REMAIN QUITE VARIABLE,
WHICH DOES NOT LEAD TO GOOD CONFIDENCE IN ANY PARTICULAR SOLUTION.
THE 00Z MODEL GUIDANCE INCLUDING THE ECMWF CAME IN MORE ON THE
PHASED SIDE, THOUGH ONCE AGAIN NOT AS AGGRESSIVE WITH THE PHASING
AS THE UKMET AND CMC.
MEANWHILE, AT LEAST MODEL CLUSTERING HAS IMPROVED SOMEWHAT WITH
MID-UPPER ENERGY MOVING NORTHWARD NEAR THE EAST COAST THIS WEEKEND
INTO MONDAY WITH PERHAPS A WEAK SURFACE LOW, FOR SOME RAIN CHANCES
ESPECIALLY ALONG THE COAST BUT POTENTIALLY SPREADING MORE INLAND
INTO THE NORTHEAST AROUND SUNDAY-MONDAY. THERE ARE STILL SOME
DETAIL DIFFERENCES WITH THIS RELATIVELY SMALL-SCALE FEATURE
THOUGH. AND MODELS HAVE SHOWN SOME WAFFLING ON TIMING OF POSSIBLY
A COUPLE OF ROUNDS OF ADDITIONAL ENERGY COMING INTO THE WEST
BEHIND THE INITIAL DEVELOPING TROUGH. GFS RUNS/GEFS ENSEMBLE
MEMBERS HAVE SHOWN MORE RIDGING ACROSS THE WEST IN BETWEEN THE
TROUGHING FEATURES THAN THE BULK OF THE EC GUIDANCE SUITE FOR
TUESDAY-WEDNESDAY.
THUS THE WPC FORECAST COULD USE A MULTI-MODEL DETERMINISTIC BLEND
FOR THE BEGINNING OF THE FORECAST TIMEFRAME, BUT THE INCREASING
MODEL DIFFERENCES LED TO INCREASING USAGE OF THE ENSEMBLE MEANS
THROUGH THE PERIOD. THIS FORECAST ATTEMPTED TO GIVE A NOD TOWARD
THE MORE SEPARATED STREAM SOLUTIONS BUT NOT AS AGGRESSIVELY AS THE
12Z ECMWF/18Z GFS, WHICH WAS LIKELY GOOD GIVEN THE SOMEWHAT MORE
PHASED 00Z RUNS. RELATIVELY LARGE CHANGES TO MANY FORECAST
VARIABLES INCLUDING THE QPF MAY BE NECESSARY OVER THE NEXT FEW
DAYS GIVEN THE CURRENT LOW PREDICTABILITY EXTENDING EVEN INTO DAYS
4-5.
..SENSIBLE WEATHER AND POTENTIAL HAZARDS
PRECIPITATION IS LIKELY ACROSS THE MUCH OF THE WEST BY SATURDAY AS
THE UPPER TROUGH AMPLIFIES AND THE FIRST SURFACE COLD FRONT MOVES
THROUGH, FOR ONE OF THE FIRST MAJOR COOL SEASON-TYPE PRECIPITATION
EVENTS SINCE MUCH EARLIER THIS YEAR. PRECIPITATION WILL BE
ENHANCED ACROSS FAVORED WINDWARD TERRAIN OF THE CASCADES, ROCKIES,
AND WASATCH OVER THE WEEKEND, WITH HIGHER ELEVATION SNOW AND LOWER
ELEVATION RAIN. CONFIDENCE IN A MEANINGFUL PRECIPITATION EVENT
REMAINS FAIRLY GOOD, BUT EXACT AMOUNTS OF RAIN/SNOW AND TIMING
WILL STILL NEED TO BE REFINED WITH TIME. ANOTHER COUPLE OF ROUNDS
OF PRECIPITATION COULD CONTINUE/REFORM EARLY NEXT WEEK IN THE
NORTHWEST BUT WITH EVEN MORE UNCERTAINTY. PRECIPITATION MAY ALSO
BE POSSIBLE ACROSS THE SOUTHWEST FOR THE WEEKEND BUT WILL BE
DEPENDENT ON THE TIMING AND TRACK OF THE SOUTHERN STREAM LOW AND
ITS EVENTUAL POSSIBLE PHASING. BY EARLY NEXT WEEK, PRECIPITATION
CHANCES SHOULD GENERALLY INCREASE ACROSS THE PLAINS AND INTO THE
MISSISSIPPI VALLEY AHEAD OF THE UPPER TROUGH AND A DEVELOPING LOW
PRESSURE SYSTEM. AREAS OF ENHANCED TO POSSIBLY HEAVY RAINFALL ARE
LIKELY, WHILE THERE MAY BE SOME SNOW ON THE BACKSIDE OF THE
SURFACE LOW INTO THE NORTHERN HIGH PLAINS, BUT THE SPECIFICS OF
BOTH ARE NOT YET CLEAR AT THIS TIME. MEANWHILE, SOME RAIN MAY BE
POSSIBLE ALONG OR NEAR THE EAST COAST THIS WEEKEND INTO MONDAY
ASSOCIATED WITH A FRONTAL BOUNDARY AND POSSIBLE LOW PRESSURE
SYSTEM, BUT WITH LOW CONFIDENCE ON HOW MUCH RAIN COULD FALL
ONSHORE VERSUS REMAINING OFFSHORE.
TEMPERATURES ARE LIKELY TO BE WARMER THAN AVERAGE ACROSS THE
CENTRAL U.S. FOR THE WEEKEND AHEAD OF THE DEVELOPING WESTERN UPPER
TROUGH. HIGHS AND LOWS OF 10-20F ABOVE NORMAL, WITH SOME SPOTS
HIGHER, WILL BE WIDESPREAD ACROSS THE PLAINS TO UPPER MIDWEST.
MEANWHILE, AN AREA OF BELOW NORMAL TEMPERATURES WILL EXPAND FROM
THE WEST COAST STATES INTO THE GREAT BASIN AND ROCKIES THIS
WEEKEND, WITH LOWS AROUND 5-15F BELOW AVERAGE AND HIGHS 10-20F
BELOW AVERAGE. TEMPERATURES SHOULD COOL TO NEAR NORMAL AND EVEN
BELOW NORMAL FOR THE NORTH-CENTRAL U.S. NEXT WEEK AS THE UPPER
TROUGH AND COLD FRONT(S) MOVE THROUGH. THIS WILL PUSH WARMER THAN
AVERAGE TEMPERATURES INTO THE NORTHEASTERN U.S. BY
MONDAY-WEDNESDAY.
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, 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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