821
FXUS02 KWBC 040622
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
221 AM EDT TUE OCT 04 2022
VALID 12Z FRI OCT 07 2022 - 12Z TUE OCT 11 2022
..OVERVIEW
A FAIRLY AMPLIFIED UPPER PATTERN WILL BE IN PLACE WHEN THE MEDIUM
RANGE PERIOD STARTS FRIDAY WITH LARGE SCALE TROUGHING ACROSS THE
EAST, AND A BLOCKY RIDGE OVER THE WEST COAST AND EAST PACIFIC.
THIS TROUGH OVER THE EAST WILL PUSH A COLD FRONT OFF THE EAST
COAST WITH EXPANSIVE HIGH PRESSURE IN ITS WAKE SPREADING FROM THE
NORTH-CENTRAL U.S. ON FRIDAY INTO THE MIDWEST/EAST THIS COMING
WEEKEND AND BRINGING A PERIOD OF CONSIDERABLY COOLER TEMPERATURES.
BEHIND THIS EASTERN TROUGH, ANOTHER SHORTWAVE/POSSIBLE CLOSED LOW
WILL SKIRT THROUGH THE NORTHERN TIER STATES LIKELY ASSOCIATED WITH
SOME ADDITIONAL SHOWERS. A WEEK UPPER LEVEL LOW OVER THE SOUTHWEST
U.S. WILL KEEP MONSOONAL MOISTURE PLENTY DURING THE PERIOD ACROSS
THE FOUR CORNERS REGION AS WELL. BY NEXT MONDAY-TUESDAY, MODELS
SHOW ANOTHER AMPLIFIED FEATURE DROPPING INTO THE NORTHERN HIGH
PLAINS FROM WESTERN CANADA.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
THE LATEST MODELS AND ENSEMBLES MAINTAIN FAIRLY GOOD AGREEMENT ON
THE OVERALL PATTERN, PARTICULARLY THE FIRST HALF OF THE PERIOD.
EMBEDDED DETAILS REMAIN SOMEWHAT UNCERTAIN THOUGH, AS THERE ARE
SOME TIMING DIFFERENCES WITH THE EASTERN U.S. TROUGH AS IT SHIFTS
THROUGH THE GREAT LAKES/NORTHEAST. THERE IS ALSO GOOD AGREEMENT
OUT WEST REGARDING THE RIDGE WHICH SHOULD SLOWLY RETROGRADE INTO
THE EASTERN PACIFIC AS A WEEK UPPER LOW NEAR ARIZONA/NEW MEXICO
SETTLES INTO THE NORTHERN GULF OF CALIFORNIA BEFORE EVENTUALLY
OPENING UP BY SUNDAY OR MONDAY. FOR THE FIRST HALF OF THE PERIOD,
A GENERAL MODEL BLEND BETWEEN THE GFS, ECMWF, AND CMC WORKED WELL.
THE LAST FEW CYCLES OF GUIDANCE HAVE TRENDED STRONGER WITH A
COMPACT SHORTWAVE (WITH SOME RUNS SUGGESTING AN EMBEDDED CLOSED
LOW) DROPPING INTO THE FAR NORTHERN STATES AROUND DAY 5/SUNDAY.
THE ECMWF HAS CONSISTENTLY BEEN STRONGEST WITH THIS, MAINTAINING A
SMALL CLOSED LOW FEATURE ALL THE WAY INTO TUESDAY JUST TO THE
NORTH OF LAKE SUPERIOR. THE GFS IS WEAKER AND A BIT QUICKER, BUT
STILL FAIRLY COMPARABLE TO THE ECMWF. THE CMC ON THE OTHER HAND
WANTS TO DROP THE LOW DUE SOUTH AND WITH IT LINGERING OVER THE
NORTHERN HIGH PLAINS REGION INTO THE MIDDLE OF NEXT WEEK. THIS
LIKELY IS A RESULT OF A MUCH STRONGER/BLOCKIER RIDGE OVER THE
WESTERN U.S. WHICH KEEPS THE NEXT BATCH OF ENERGY FROM THE GULF OF
ALASKA LATE PERIOD MUCH WEAKER AND STAYING WELL NORTH INTO CANADA.
BOTH THE GFS AND ECMWF HAVE SUPPORT FROM THE ENSEMBLES THAT THIS
ALASKAN TROUGHING WILL DROP INTO SOUTHWEST CANADA AND EVENTUALLY
THE NORTHERN ROCKIES/HIGH PLAINS, WHICH WOULD ACT TO PUSH THE
FIRST SHORTWAVE OUT TO THE NORTHEAST MUCH QUICKER. BASED ON THIS
ASSESSMENT, THE BLEND FOR THE LATTER HALF OF THE PERIOD TRENDED
MORE TOWARDS THE ENSEMBLE MEANS TO HELP MITIGATE SOME OF THE
DETAIL UNCERTAINTIES, BUT STILL KEPT A MODEST AMOUNT OF THE
DETERMINISTIC GFS AND ECMWF. GIVEN THE UNCERTAINTY IN TIMING AND
AMPLITUDE OF BOTH SYSTEMS OF NOTE, THE PATTERN DEPICTED BY THE
ENSEMBLE MEANS GETS UNDERSTANDABLY FLAT, SO IT SEEMED NECESSARY TO
INCLUDE DETERMINISTIC SOLUTIONS TO TRY AND MAINTAIN SOME LEVEL OF
WEAK AMPLITUDE WITH FEATURES.
FOR THE QPF, THE NATIONAL BLEND OF MODELS ONCE AGAIN SEEMED MUCH
TOO LIGHT AND NOT BROAD ENOUGH WITH ITS QPF FOOTPRINT, ESPECIALLY
ACROSS THE SOUTHWEST. QPF FROM THE NBM WAS ESSENTIALLY
NON-EXISTENT SO SOME CONSIDERABLE AMOUNTS OF THE GFS AND ECMWF
WERE NEEDED TO ADD SOME QPF ACROSS THE NORTHERN PLAINS/UPPER
MIDWEST ASSOCIATED WITH THE COMPACT SHORTWAVE THROUGH THE REGION
LATE WEEKEND AND EARLY NEXT WEEK.
..WEATHER/HAZARDS HIGHLIGHTS
THE COMBINATION OF PERSISTENT MONSOONAL MOISTURE AND AN UPPER LOW
SETTLING OVER THE NORTHERN GULF OF CALIFORNIA WILL PRODUCE DIURNAL
SHOWERS AND THUNDERSTORMS OVER PARTS OF THE SOUTHWEST/SOUTHERN
ROCKIES, WITH LOCALLY HEAVY RAINFALL POSSIBLE IN SOME SPOTS.
INTENSITY AND COVERAGE MAY VARY FROM DAY TO DAY, WITH SOME EAST
AND WEST EXPANSION OF RAINFALL POSSIBLE BY EARLY NEXT WEEK AS THE
UPPER LOW OPENS UP. TO THE NORTH, THE FIRST COLD FRONT SHIFTING
ACROSS THE MIDWEST AND GREAT LAKES MAY BRING SOME LIGHT RAIN
MAINLY AROUND THURSDAY, AND THEN LAKE ENHANCED SHOWERS IN THE
WESTERLY FLOW BEHIND THE FRONT FRIDAY AND PERHAPS SATURDAY. BEHIND
THIS FRONT, MUCH BELOW NORMAL TEMPERATURES WILL SHIFT FROM THE
NORTHERN PLAINS INTO THE MIDWEST AND EAST. DAYTIME HIGHS IN SOME
LOCATIONS COULD BE 15 TO 20 DEGREES BELOW AVERAGE (MAINLY
THURSDAY-SATURDAY) WHILE OVERNIGHT TEMPERATURES ARE FORECAST TO
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 PARTICULARLY FRIDAY MORNING. THE
NEXT COLD FRONT INTO THE NORTHERN TIER THIS WEEKEND LIKELY BRINGS
SOME SHOWERS WITH IT, BUT STILL CONSIDERABLE UNCERTAINTY IN
COVERAGE AND AMOUNTS. OUT WEST, TEMPERATURES WILL BE WARM INTO
EARLY NEXT WEEK UNDERNEATH A BLOCKY UPPER RIDGE, WITH DAYTIME
HIGHS OVER THE NORTHWEST 10 TO 15 DEGREES OR SO ABOVE NORMAL.
DESPITE THE ANOMALIES, THE RESULTING TEMPERATURES PEAKING IN THE
70S AND 80S (90S FOR PARTS OF CALIFORNIA) ARE UNLIKELY TO CREATE
ANY HEAT RELATED HAZARDS. WESTERN U.S. TEMPERATURES MAY TREND BACK
CLOSER TO NORMAL BY TUESDAY NEXT WEEK AS THE RIDGE RETROGRADES
INTO THE EASTERN PACIFIC.
SANTORELLI
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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