849
FXUS02 KWBC 042036
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
435 PM EDT TUE OCT 04 2022
VALID 12Z FRI OCT 07 2022 - 12Z TUE OCT 11 2022
..OVERVIEW
A STRONG MEAN RIDGE, INITIALLY NEAR THE WEST COAST ON FRIDAY AND
LIKELY RETROGRADING OFFSHORE THEREAFTER, WILL ANCHOR A FAIRLY
AMPLIFIED UPPER PATTERN DURING THE PERIOD AND SUPPORT VERY WARM
TEMPERATURES OVER THE WEST INTO AT LEAST MONDAY. MEANWHILE A
DOWNSTREAM UPPER TROUGH ALONG WITH TRAILING PLAINS INTO EASTERN
U.S. HIGH PRESSURE WILL BRING A PERIOD OF WELL BELOW NORMAL
TEMPERATURES THROUGH EARLY MONDAY. GUIDANCE HAS BEEN WAFFLING
WITH DETAILS OF A POSSIBLE SHORTWAVE/SURFACE SYSTEM THAT MAY DROP
INTO THE NORTHERN TIER AROUND SUNDAY AND THEN WITH A LARGER SCALE
TROUGH EXPECTED TO REACH THE CANADA AND THE NORTHWESTERN U.S.
DURING THE FIRST HALF OF NEXT WEEK. A WEAK UPPER LOW MAY OPEN
UP/EJECT FROM ITS POSITION OVER FAR NORTHWESTERN MEXICO AFTER
SUNDAY BUT COULD BE REPLACED BY OTHER WEAK ENERGY DESCENDING OVER
THE WEST, KEEPING A MODEST MEAN TROUGH OVER THE SOUTHWEST.
OVERALL THIS PATTERN WILL SUPPORT FAIRLY LOW COVERAGE/INTENSITY OF
PRECIPITATION OVER THE LOWER 48. THE BEST DEFINED RAINFALL FOCUS
WILL BE OVER THE FOUR CORNERS STATES AND VICINITY WITH THE
COMBINATION OF THE PERSISTENT UPPER TROUGH/LOW NEAR THE WESTERN
MEXICO BORDER AND MONSOONAL MOISTURE IN PLACE. OTHER AREAS OF
RAINFALL WILL BE POSSIBLE OVER THE GREAT LAKES/NORTHEAST EARLY IN
THE PERIOD AND THE FLORIDA PENINSULA. UNCERTAIN DETAILS OF THE
NORTHERN/CENTRAL U.S. FRONT SUNDAY ONWARD AS WELL AS HOW MUCH
TROUGHING REACHES THE NORTHWEST WILL DETERMINE CORRESPONDING
PRECIPITATION OVER THOSE AREAS DURING THE FIRST HALF OF NEXT WEEK.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
WITHIN THE EASTERN MEAN TROUGH, THERE IS STILL SOME SPREAD AND
VARIABILITY FOR THE LEADING SHORTWAVE ENERGY/SURFACE SYSTEM
CROSSING SOUTHEASTERN CANADA AND NEW ENGLAND LATE THIS WEEK.
RELATIVE TIMING HAS SWITCHED FROM 24-36 HOURS AGO, WITH THE 00Z
ECMWF NOW A BIT ON THE SLOWER SIDE WITH OTHER SOLUTIONS FASTER TO
VARYING DEGREES. THE 00Z UKMET WAS CLOSE TO THE GFS/CMC BUT THE
NEW 12Z RUN HAS STRAYED FASTER THAN THE OTHERS. AN INTERMEDIATE
FORECAST APPEARS BEST FOR THIS SYSTEM. TRAILING SHORTWAVE
DIFFERENCES HAVE LESS IMPACT ASIDE FROM PERHAPS HOW MUCH OF A
SURFACE TROUGH COULD BRUSH THE GREAT LAKES/NORTHEAST.
THE ECMWF HAS BEEN MOST CONSISTENT WITH THE SHORTWAVE AND SURFACE
LOW/FRONT REACHING THE NORTHERN TIER BY SUNDAY. THE 00Z UKMET WAS
SIMILAR TO THE 00Z ECMWF. REMAINING MODELS HAVE HAD VARYING
IDEAS, INCLUDING SPLITTING THE ORIGINAL GULF OF ALASKA ENERGY (00Z
GFS) OR DEPICTING A SLOWER CLOSED LOW/TROUGH (00Z CMC/06Z GFS).
THE NEW 12Z UKMET TRENDED A LITTLE SLOWER AND DEEPER/MORE CLOSED
BUT THE GFS/CMC ARE NOW A BETTER FIT WITH THE OVERALL CLUSTER.
PREFERENCE SIDES WITH A BLENDED/CONTINUITY APPROACH.
SPREAD AN RUN-TO-RUN VARIABILITY BECOME SIGNIFICANT FOR THE TROUGH
EXPECTED TO BEING AMPLIFYING INTO CANADA AND THE
NORTHWESTERN/NORTHERN U.S. EARLY NEXT WEEK. ECMWF/ECMWF RUNS HAVE
TENDED TO SHOW MORE TROUGHING INTO THE NORTHWEST, WITH MULTI-RUN
CONTINUITY OF THE ECMWF OVERALL SHOWING A TREND TOWARD MORE
TROUGHING INTO THE NORTHWEST. THE 12Z GFS AND 00Z CMC ARE ON THE
OTHER EXTREME, WITH A FARTHER EAST PACIFIC RIDGE/DOWNSTREAM TROUGH
CONFIGURATION. THE 06Z GFS WAS CLOSER TO THE LATEST GEFS/CMCENS
RUNS THAT ARE JUST A LITTLE EAST OF THE ECMWF MEAN. MULTI-DAY D+8
MEANS SHOW SOME DIFFERENCES IN THE POSITION OF THE EXPECTED CORE
OF POSITIVE HEIGHT ANOMALIES OVER THE NORTHEASTERN PACIFIC/GULF OF
ALASKA BUT TELECONNECTIONS RELATIVE TO THIS ANOMALY CENTER
GENERALLY SUPPORT SOME DEGREE OF TROUGH ELONGATION INTO THE WEST
NEAR AND SOON AFTER THE END OF THE MEDIUM RANGE PERIOD. THIS
WOULD AT LEAST RECOMMEND LEANING AWAY FROM THE 00Z/12Z GFS AND 00Z
CMC.
GUIDANCE PREFERENCES ULTIMATELY LED TO USING A 00Z/06Z MODEL
COMPOSITE EARLY IN THE PERIOD, FOLLOWED BY TRENDING THE FORECAST
TO EVEN PROPORTIONS OF THE 06Z GFS/00Z ECMWF, THEIR ENSEMBLE
MEANS, AND WPC CONTINUITY. FOR THE QPF, THE NATIONAL BLEND OF
MODELS ONCE AGAIN SEEMED TOO CONFINED WITH ITS COVERAGE,
ESPECIALLY ACROSS THE SOUTHWEST AND FOR EARLY-PERIOD LAKE
EFFECT/TERRAIN ENHANCED ACTIVITY IN THE NORTHEAST. THE NBM ALSO
APPEARED SOMEWHAT UNDERDONE WITH RAINFALL OVER THE CENTRAL U.S.
EARLY NEXT WEEK WITH THE EMERGENCE OF SOME SOUTHWEST MONSOONAL
MOISTURE AND POSSIBLE FRONTAL APPROACH, THOUGH WITH LOW CONFIDENCE
IN THE MAGNITUDE.
..WEATHER/HAZARDS HIGHLIGHTS
THE COMBINATION OF PERSISTENT MONSOONAL MOISTURE AND AN UPPER LOW
OVER THE NORTHERN GULF OF CALIFORNIA WILL PRODUCE DIURNAL SHOWERS
AND THUNDERSTORMS OVER PARTS OF THE SOUTHWEST/SOUTHERN ROCKIES
THROUGH THE WEEKEND, WITH LOCALLY HEAVY RAINFALL POSSIBLE IN SOME
SPOTS. INTENSITY AND COVERAGE MAY VARY FROM DAY TO DAY. THE UPPER
LOW SHOULD OPEN UP AFTER SUNDAY BUT MAY BE REPLACED BY ADDITIONAL
WEAK ENERGY. THIS EVOLUTION MAY HELP TO SPREAD SOME OF THE
MOISTURE EASTWARD INTO THE PLAINS WHERE IT COULD INTERACT WITH A
FRONT, WHILE LEADING TO A SOMEWHAT LIGHTER AND MORE SCATTERED
TREND FOR RAINFALL OVER THE SOUTHWEST. THE SYSTEM ANCHORING THE
PLAINS FRONT COULD ALSO BRING LIGHT RAIN INTO THE MIDWEST/GREAT
LAKES BUT WITH LOW CONFIDENCE IN SPECIFICS AT THIS TIME. UPPER
TROUGHING AND A COLD FRONT REACHING THE NORTHWEST/NORTHERN ROCKIES
BY NEXT TUESDAY COULD BRING SOME RAIN AND PERHAPS EVEN HIGH
ELEVATION SNOW INTO REGION, AGAIN WITH FAIRLY LOW CONFIDENCE FOR
NOW. IN THE EAST, LAKE EFFECT/TERRAIN ENHANCED PRECIPITATION
SHOULD TAPER OFF AFTER FRIDAY. LIGHT TO LOCALLY MODERATE RAINFALL
WILL LIKELY SPREAD NORTHWARD OVER THE FLORIDA PENINSULA AS
EASTERLY LOW LEVEL FLOW STRENGTHENS BEHIND A FRONT THAT ULTIMATELY
REPLACES AN INITIAL FRONT STALLED NEAR THE KEYS.
MUCH OF THE WEST WILL SEE ABOVE NORMAL TEMPERATURES AT LEAST
THROUGH MONDAY, WITH HIGHS 10-15F OR SO ABOVE NORMAL MOST LIKELY
OVER THE NORTHWEST. EVEN WITH THESE ANOMALIES, THE RESULTING
TEMPERATURES PEAKING IN THE 70S AND 80S (90S FOR PARTS OF
CALIFORNIA) ARE UNLIKELY TO CREATE ANY MORE THAN ISOLATED/MODERATE
HEAT RELATED ISSUES. EXPECT A COOLING TREND BY TUESDAY. ON THE
OTHER HAND, AN AREA OF WELL BELOW NORMAL TEMPERATURES WILL EXTEND
FROM THE NORTHERN TWO-THIRDS OF THE PLAINS INTO THE EAST LATE THIS
WEEK INTO EARLY MONDAY. SOME AREAS MAY SEE HIGHS 15-20F BELOW
NORMAL FRIDAY-SATURDAY. MORNING LOWS MAY BE A LITTLE LESS EXTREME
BUT SHOULD STILL DROP INTO THE 30S FOR MANY LOCATIONS FROM THE
NORTHERN HALF OF THE PLAINS INTO THE CENTRAL APPALACHIANS, AND
EVEN 20S FOR NORTH DAKOTA AND NORTHERN MINNESOTA ON FRIDAY MORNING.
RAUSCH/SANTORELLI
HAZARDS:
- HIGH WINDS ACROSS PORTIONS OF THE GREAT LAKES, FRI, OCT 7.
- MUCH BELOW NORMAL TEMPERATURES ACROSS PORTIONS OF THE CENTRAL
PLAINS, THE NORTHEAST, THE CENTRAL APPALACHIANS, THE NORTHERN
PLAINS, THE TENNESSEE VALLEY, THE MIDDLE MISSISSIPPI VALLEY, THE
MID-ATLANTIC, THE SOUTHERN APPALACHIANS, THE UPPER MISSISSIPPI
VALLEY, THE SOUTHEAST, THE GREAT LAKES, AND THE OHIO VALLEY,
FRI-SUN, OCT 7-OCT 9.
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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