669
FXUS02 KWBC 170659
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
258 AM EDT MON OCT 17 2022
VALID 12Z THU OCT 20 2022 - 12Z MON OCT 24 2022
..OVERVIEW
ONE MORE DAY OF AMPLIFIED UPPER TROUGHING IS FORECAST FOR THE
EASTERN U.S. AS THE MEDIUM RANGE PERIOD BEGINS ON THURSDAY,
CAUSING COOLER THAN NORMAL TEMPERATURES IN THE EAST AND WARM
TEMPERATURES UNDERNEATH RIDGING IN THE WEST, WITH DRY CONDITIONS
FOR MOST AREAS. THEN A PRONOUNCED PATTERN CHANGE IS EXPECTED FOR
LATE WEEK AS A TROUGH IN THE WEST DEVELOPS AND PERSISTS INTO EARLY
NEXT WEEK WITH SOME MOVEMENT EASTWARD. THE ENERGY ALOFT AND A
SURFACE FRONTAL SYSTEM OR TWO WILL LEAD TO INCREASING
PRECIPITATION CHANCES ACROSS THE WEST WITH HIGHER ELEVATION SNOW,
WHILE TEMPERATURES COOL THERE AS WARMER THAN AVERAGE TEMPERATURES
SHIFT TOWARD THE CENTRAL U.S. INTO THE NORTHEAST.
..MODEL AND PREDICTABILITY ASSESSMENT
MODEL AGREEMENT REMAINS QUITE GOOD AT THE BEGINNING OF THE PERIOD
FOR EASTERN TROUGHING EXTENDING FROM A SOUTHEASTERN CANADA UPPER
LOW, RIDGING ACROSS THE WEST, AND A SOUTHERN STREAM UPPER LOW
OFFSHORE CALIFORNIA. THERE ARE ONLY MINOR DIFFERENCES WITH
EMBEDDED SHORTWAVES AND ASIDE FROM ANY INFLUENCE ON LAKE EFFECT
PRECIPITATION, IMPACTS ON SENSIBLE WEATHER SHOULD BE MINIMAL GIVEN
THE OTHERWISE DRY PATTERN. BY DAY 4/FRIDAY MODELS SHOW THE BULK OF
THE EASTERN TROUGHING IS LIKELY TO RETREAT NORTHEASTWARD, BUT WITH
SOME ENERGY LINGERING IN THE SOUTHERN STREAM THAT IS MORE
UNCERTAIN. ECMWF RUNS HAVE BEEN PERSISTENT WITH SHOWING A CLOSED
UPPER LOW FORMING BY SATURDAY, THOUGH WITH SOME POSITION
OSCILLATIONS, AS HAVE SOME EC ENSEMBLE MEMBERS, WHILE OTHER
GUIDANCE HAS BEEN WEAKER. THE WEAK AND FAIRLY SMALL SCALE NATURE
OF THIS ENERGY LEADS TO LOW PREDICTABILITY IN THE MEDIUM RANGE
TIME FRAME, SO THE WPC FORECAST CONTINUES TO TAKE A CONSERVATIVE
APPROACH WITH SOME WEAK TROUGHING AND ITS RELATION TO A WAVY FRONT
IN THE WESTERN ATLANTIC, NOT AS STRONG AS THE ECMWF.
MEANWHILE IN THE WEST, ENERGY BEGINS TO SUPPRESS THE INITIAL
WESTERN RIDGE BY FRIDAY BUT ADDITIONAL, STRONGER ENERGY IS
FORECAST TO DIG INTO THE NORTHWEST BY SATURDAY TO DEEPEN
TROUGHING. MODEL GUIDANCE IS AGREEABLE ABOUT THIS, BUT THE MORE
UNCERTAIN FACTOR IS WITH THE POSSIBILITY OF PHASING THE TROUGH
WITH THE SOUTHERN STREAM LOW. THROUGH THE 12/18Z MODEL CYCLE, GFS
RUNS SHOWED MORE PHASING OF THE FEATURES COMPARED TO THE ECMWF AND
CMC THAT MAINTAIN SEPARATION, WHILE ENSEMBLE MEMBERS SHOW
CONSIDERABLE VARIABILITY. BY SUNDAY AND MONDAY THIS LEADS TO ONE
TROUGH TREKKING MORE SLOWLY ACROSS THE WEST-CENTRAL U.S. IN THE
GFS, WHILE THE EC/CMC HAVE THE NORTHERN STREAM TROUGH TRACKING
ACROSS THE NORTH-CENTRAL U.S. FASTER WHILE THE SOUTHERN STREAM LOW
LINGERS NEAR BAJA CALIFORNIA. THE 00Z GFS REMAINS MORE PHASED
WHILE THE 00Z ECMWF STICKS WITH STREAM SEPARATION, AND THE 00Z CMC
SWITCHES TO MORE PHASING. THESE UNCERTAINTIES IN THE UPPER LEVELS
WILL AFFECT THE FRONTAL POSITION AND THE TIMING OF RAIN BEGINNING
IN THE CENTRAL U.S., SO THE FORECAST IS LIKELY TO BE REFINED WITH
TIME. ANOTHER ROUND OF ENERGY MAY APPROACH THE WEST BY MONDAY BUT
WITH CONSIDERABLE VARIABILITY. THE ECWMF INCLUDING THE 00Z RUN IS
ON THE STRONGER SIDE OF THE GUIDANCE WITH THIS ENERGY.
THE WPC FORECAST FOR FRONTS/PRESSURES WAS BASED ON A BLEND OF THE
DETERMINISTIC 12Z/18Z MODELS TO RESOLVE LINGERING DETAIL QUESTIONS
DURING THE FIRST PART OF THE PERIOD, AND THEN INCORPORATED GEFS
AND EC ENSEMBLE MEANS FOR THE LATTER PART OF THE PERIOD AND
QUICKLY INCREASED THEIR PROPORTIONS AS OPERATIONAL MODELS DIVERGED
WITH VARIOUS DETAILS. THIS APPROACH MAINTAINED GOOD CONTINUITY
WITH THE PREVIOUS FORECAST ASIDE FROM TYPICAL NUDGES REFLECTING
LATEST TRENDS.
..SENSIBLE WEATHER AND POTENTIAL HAZARDS
THE CONTIGUOUS U.S. SHOULD OVERALL BE RATHER DRY ON THURSDAY, WITH
THE EXCEPTION OF LINGERING LIGHT LAKE EFFECT RAIN/SNOW DUE TO
UPPER LEVEL ENERGY AND THE WESTERLY FLOW ACROSS THE RELATIVELY
WARM GREAT LAKES COMPARED TO THE COLD AIR TEMPERATURES. SOUTH
FLORIDA MAY SEE A FEW RAIN SHOWERS AS WELL. BY LATE IN THE WEEK
THROUGH NEXT WEEKEND, THE UPPER TROUGH ARRIVAL/AMPLIFICATION
ACROSS THE WEST AND AN ASSOCIATED SURFACE FRONT PUSHING ACROSS THE
REGION SHOULD PRODUCE A NOTABLE INCREASE IN PRECIPITATION COVERAGE
AND INTENSITY. THE BEST FOCUS WILL BE OVER FAVORED WINDWARD
TERRAIN OVER THE PACIFIC NORTHWEST ON FRIDAY AND THEN EXTENDING
SOUTHEASTWARD INTO THE NORTHERN/CENTRAL ROCKIES AND WASATCH OVER
THE WEEKEND, WITH HIGHER ELEVATION SNOW AND LOWER ELEVATION RAIN.
CONFIDENCE IN A MEANINGFUL PRECIPITATION EVENT IS BECOMING FAIRLY
GOOD, BUT EXACT AMOUNTS OF RAIN/SNOW AND TIMING WILL STILL NEED TO
BE REFINED WITH TIME. PRECIPITATION MAY ALSO BE POSSIBLE ACROSS
THE SOUTHWEST FRIDAY AND ESPECIALLY SATURDAY DEPENDING ON THE
TRACK OF THE SOUTHERN STREAM LOW AND ITS EVENTUAL POSSIBLE
PHASING. BY EARLY NEXT WEEK, RAIN CHANCES MAY INCREASE FOR THE
CENTRAL U.S. AS GULF MOISTURE STREAMS IN AHEAD OF A COLD FRONT.
MEANWHILE SOME RAIN MAY BE POSSIBLE ALONG OR NEAR THE EAST COAST
THIS WEEKEND INTO MONDAY, BUT WITH LOW CONFIDENCE ON HOW MUCH RAIN
COULD FALL ONSHORE.
THE AMPLIFIED WESTERN RIDGE IN PLACE FOR THE EARLY PART OF THE
PERIOD WILL CAUSE WARMER THAN AVERAGE TEMPERATURES ACROSS THE
NORTHWEST IN PARTICULAR, WITH HIGHS COMMONLY 10-20F ABOVE AVERAGE,
POTENTIALLY LEADING TO SOME DAILY RECORD HIGHS THROUGH THURSDAY.
CONVERSELY, THE ANOMALOUS UPPER LOW/TROUGH IN THE EAST SHOULD
PRODUCE RATHER COLD TEMPERATURES MORE COMMON TO NOVEMBER AND
DECEMBER FROM THE PLAINS EASTWARD FOR THURSDAY. BELOW NORMAL
TEMPERATURES BY 10-20F WILL BE WIDESPREAD AND TRANSLATE INTO LOWS
IN THE 30S SPREADING SOUTH POSSIBLY ALL THE WAY TO THE GULF COAST
(MOBILE, ALABAMA FOR EXAMPLE), WHICH COULD SET LOW TEMPERATURE
RECORDS ACROSS THE SOUTHEAST. AS THE UPPER LEVEL PATTERN RELAXES
AROUND FRIDAY AND THEN TRANSITIONS TO A WESTERN TROUGH/EASTERN
RIDGE PATTERN, ABOVE NORMAL TEMPERATURES SHOULD GET PUSHED INTO
THE CENTRAL U.S., WITH THE NORTH-CENTRAL PLAINS SEEING HIGHS OF
10-20F ABOVE AVERAGE. TEMPERATURES ARE ALSO EXPECTED TO GRADUALLY
WARM IN THE MIDWEST TO NORTHEAST EARLY NEXT WEEK. MEANWHILE BELOW
AVERAGE TEMPERATURES PARTICULARLY FOR HIGHS ARE LIKELY ACROSS THE
WEST GIVEN THE TROUGH ALOFT.
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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