535
FXUS02 KWBC 172113
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
512 PM EDT MON OCT 17 2022
VALID 12Z THU OCT 20 2022 - 12Z MON OCT 24 2022
..OVERVIEW
A MAJOR SHIFT IN THE UPPER-LEVEL PATTERN IS EXPECTED TO OCCUR
ACROSS THE U.S. DURING THE MEDIUM RANGE PERIOD. A MUCH AMPLIFIED
UPPER LOW/TROUGH ANCHORED OVER THE EASTERN U.S. IS FORECAST TO
RETREAT BY LATE THIS WEEK AS AN ANOMALOUS RIDGE OVER THE WEST IS
FORECAST TO BE REPLACED BY MAJOR TROUGHING ARRIVING FROM THE
NORTHEASTERN PACIFIC BY THE WEEKEND. THIS WILL LIKELY RESULT IN A
RATHER AMPLIFIED TROUGH TO EXIT THE ROCKIES INTO THE PLAINS BY
EARLY NEXT WEEK. MEANWHILE, THE PRESENCE OF AN UPPER LOW WEST OF
BAJA CALIFORNIA WILL INTRODUCE UNCERTAINTY INTO THE FORECAST FOR
THE SOUTHWEST EARLY NEXT WEEK. A SMALLER SCALE UPPER LOW AND ITS
INTERACTION WITH AN OFFSHORE FRONT WILL ALSO INTRODUCE UNCERTAINTY
TO THE FORECAST ALONG THE EAST COAST FROM THE WEEKEND TO EARLY
NEXT WEEK.
..MODEL AND PREDICTABILITY ASSESSMENT
DETERMINISTIC MODEL SOLUTIONS ARE IN GOOD AGREEMENT AS THE
MEDIUM-RANGE PERIOD BEGINS ON THURSDAY. TIMING AGREEMENT REMAINS
GOOD THROUGH LATE WEEK REGARDING THE AMPLIFIED UPPER LOW/TROUGH
LIFTING OUT OF THE EASTERN U.S. BY THE WEEKEND, MODELS HAVE
GENERALLY TRENDED TOWARD A MORE AMPLIFIED TROUGH TO DIG FASTER
ACROSS THE NORTHEASTERN PACIFIC TOWARD THE PACIFIC NORTHWEST.
MEANWHILE, MODELS CONTINUE TO SHOW POOR AGREEMENT ON THE EVOLUTION
OF AN UPPER LOW SITUATED WELL OFF BAJA CALIFORNIA AND THE DEGREE
OF INTERACTION WITH THE INCOMING MAJOR TROUGHING ACROSS THE
WESTERN U.S. THE 00Z CMC IS FASTEST IN TERMS OF THE WESTERN U.S.
TROUGH LIFTING THE BAJA UPPER LOW INTO NORTHWESTERN MEXICO BY LATE
IN THE WEEKEND. THE ECMWF AND GFS BOTH KEEP THE BAJA UPPER LOW
FARTHER OFFSHORE. BY EARLY NEXT WEEK, INCREASING SOUTHERLY FLOW
IS FORECAST FOR THE PLAINS, WITH GFS AND CMC INTRODUCING HEAVIER
RAINS ACROSS SOUTHERN TEXAS. ON THE OTHER HAND, THE ECMWF KEEPS
THE SOUTHERN PLAINS DRY. THE ECMWF IS ALSO MOST ENTHUSIASTIC IN
DEVELOPING AN UPPER LOW NEAR COASTAL SOUTHEASTERN U.S. THIS
WEEKEND INTO EARLY NEXT WEEK, WHILE THE GFS IS FASTER AND WEAKER
BRINGING THIS FEATURE UP AND JUST OFF THE EAST COAST. THE CMC IS
SOMEWHERE IN BETWEEN THESE TWO EXTREMES.
THE WPC FORECAST FOR FRONTS/PRESSURES WAS BASED ON A BLEND OF THE
00Z EC/EC MEAN, 00Z CMC/CMC MEAN, AND THE 06Z GFS/GEFS,
TRANSITIONING TO MOSTLY A BLEND OF THE ENSEMBLE MEANS BY DAY 7.
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 AN
ANOMALOUSLY COLD UPPER LOW SITUATED OVER THE RELATIVELY WARM GREAT
LAKES WATERS. SOUTH FLORIDA MAY SEE A FEW RAIN SHOWERS AHEAD OF A
STRONG COLD FRONT APPROACHING FROM THE NORTH. 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. THE ECMWF HAS THE FASTEST ARRIVAL TIME OF
THE PRECIPITATION OVER THE PACIFIC NORTHWEST ON FRIDAY.
PRECIPITATION MAY ALSO BE POSSIBLE ACROSS THE SOUTHWEST FRIDAY AND
ESPECIALLY SATURDAY DEPENDING ON THE TIMING AND TRACK OF THE
SOUTHERN STREAM LOW AND ITS EVENTUAL POSSIBLE PHASING. BY EARLY
NEXT WEEK, RAIN CHANCES SHOULD GENERALLY INCREASE ACROSS THE
PLAINS AND INTO THE UPPER MIDWEST AHEAD OF THE UPPER TROUGH AND A
DEVELOPING LOW PRESSURE SYSTEM WITH AREAS OF ENHANCED RAINFALL
POSSIBLE BUT THE SPECIFICS ARE NOT YET CLEAR AT THIS TIME.
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 EXTEND WARM SPELL ACROSS THE NORTHWEST INTO THURSDAY
WITH HIGH TEMPERATURES CHALLENGING SOME DAILY RECORD RECORDS.
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 AMPLIFYING TROUGH BARRELS
INTO THE PACIFIC NORTHWEST AND REPLACE THE STAGNANT UPPER RIDGE,
THE WARM SPELL ACROSS THE WEST WILL ABRUPTLY ENDS THIS WEEKEND
FOLLOWED BY WIDESPREAD BELOW NORMAL TEMPERATURES BY EARLY NEXT
WEEK. TEMPERATURES ARE ALSO EXPECTED TO GRADUALLY WARM FROM THE
PLAINS TO THE MISSISSIPPI VALLEY AND THEN EXPAND INTO THE
NORTHEAST EARLY NEXT WEEK WITH EXPANSIVE HEIGHT RISES AHEAD OF THE
UPPER TROUGH.
KONG/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
HAZARDS:
- HEAVY PRECIPITATION ACROSS PORTIONS OF THE PACIFIC NORTHWEST AND
THE NORTHERN GREAT BASIN, FRI,
OCT 21 AND SUN, OCT23.
- FLOODING OCCURRING OR IMMINENT ACROSS PORTIONS OF THE SOUTHEAST.
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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