899
FXUS02 KWBC 221910
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
310 PM EDT SUN OCT 22 2023
VALID 12Z WED OCT 25 2023 - 12Z SUN OCT 29 2023
...A HEAVY TO EXCESSIVE RAINFALL THREAT CONTINUING INTO WEDNESDAY
FOR PARTS OF THE SOUTHERN AND CENTRAL U.S....
..OVERVIEW
THE MEDIUM RANGE PERIOD BEGINS WEDNESDAY WITH AN UPPER LOW NEAR
THE SOUTHWEST/NORTHERN MEXICO WHICH SHOULD WEAKEN AND LIFT
NORTHEASTWARD LATE IN THE WEEK IN RESPONSE TO ENERGY DROPPING
THROUGH THE NORTHWEST, WHICH GUIDANCE CONTINUES TO SHOW
SIGNIFICANT UNCERTAINTY ON, PARTICULARLY AS IT REACHES THE
PLAINS/ROCKIES THURSDAY-FRIDAY. REGARDLESS, REMNANT ENERGY FROM
WHAT IS CURRENTLY TROPICAL STORM NORMA LOOKS TO INTERACT WITH GULF
OF MEXICO MOISTURE AND THE SOUTHWEST UPPER LOW TO SPREAD HEAVY TO
EXCESSIVE RAINFALL ACROSS PARTS OF THE SOUTHERN AND CENTRAL
PLAINS. TO THE NORTH, ACCUMULATING SNOWS ARE LIKELY IN THE
NORTHERN ROCKIES ON WEDNESDAY, WITH PARTS OF THE HIGH PLAINS/NORTH
DAKOTA POSSIBLY SEEING THEIR FIRST ACCUMULATING SNOW EVENT OF THE
SEASON TOO BY THURSDAY. ANOTHER SHORTWAVE IS FORECAST TO DROP INTO
THE NORTHWEST NEXT FRIDAY, WITH MEAN AMPLIFIED TROUGHING LIKELY
ACROSS THE WEST NEXT WEEKEND, AS A SOMEWHAT BLOCKY RIDGE SETS UP
OVER THE SOUTHEAST.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
THE LATEST RUN OF MODEL GUIDANCE CONTINUES TO DEPICT THE GFS
FASTER IN EJECTING AN UPPER LOW/SOUTHWEST ENERGY ALONG WITH A MUCH
MORE AMPLIFIED/FASTER SHORTWAVE ENERGY THROUGH THE WEST ON
WEDNESDAY. THIS SOLUTION FAVORS THE DEVELOPMENT OF A ROBUST
SURFACE LOW PRESSURE SYSTEM OVER THE CENTRAL PLAINS THAT TRACKS A
SNOWSTORM ACROSS THE NORTHERN ROCKIES AND NORTHERN PLAINS. THERE
WAS BETTER CLUSTERING WITH THE ECWMF, CMC, UKMET AND THE ENSEMBLE
MEANS WHEN COMPARED TO THE GFS AND GIVEN CONTINUITY UTILIZED A
COMBINATION OF THESE SOLUTIONS, MAINTAINED A SIMILAR APPROACH FOR
THIS FORECAST.
THIS CONTINUES TO BE A LOW CONFIDENCE FORECAST AND LIKELY WILL
TAKE UNTIL THE SHORT RANGE PERIOD TO FULLY RESOLVE DETAILS.
INCREASED UNCERTAINTY REMAINS IN REGARDS TO THE NEXT SHORTWAVE
ACROSS THE NORTHWEST. THE ECMWF AND CMC PERSIST IN SHOWING A
CLOSED LOW IN THE REGION, WHILE THE GFS IS MUCH WEAKER/MORE OPEN
(LIKELY IN RESPONSE TO THE STRONGER SYSTEM DOWNSTREAM). BOTH THE
ECMWF AND CMC ARE SHOWING A DECENT SURFACE LOW ACROSS THE NORTHERN
U.S. NEXT WEEKEND WHILE THE GFS AND ENSEMBLE MEANS ARE LESS
ENTHUSIASTIC.
THE WPC FORECAST USED A ECMWF BASED BLEND FOR DAYS 3-5, WITH
SMALLER AMOUNTS OF THE DETERMINISTIC MODELS. TRENDED QUICKLY
TOWARDS A VAST MAJORITY ENSEMBLE MEAN BASED FOR DAYS 6 AND 7 GIVEN
THE GREAT UNCERTAINTY. SOME MINOR ECMWF WAS CONTINUED THROUGH DAY
7 THOUGH JUST FOR SOME ADDED SYSTEM DEFINITION.
..WEATHER/HAZARDS HIGHLIGHTS
REMNANT MOISTURE FROM WHAT IS CURRENTLY TROPICAL STORM NORMA ALONG
WITH HIGHLY ANOMALOUS MOISTURE INTERACTING WITH A STATIONARY
FRONTAL BOUNDARY WILL LEAD TO ANOTHER WET PERIOD ACROSS THE
SOUTHERN PLAINS, INCREASING THE RISK FOR HEAVY TO EXCESSIVE
RAINFALL. THE INHERITED DAY 4 SLIGHT RISK AREA WAS EXPANDED
WEST/NORTH ACROSS TEXAS, OKLAHOMA AND INTO SOUTH KANSAS AND
EASTWARD ACROSS CENTRAL TEXAS. THE MARGINAL RISK AREA ALSO WAS
EXPANDED WESTWARD ACROSS PARTS OF WEST TEXAS AND THE TEXAS
PANHANDLE. A HEAVY RAINFALL IS POSSIBLE FARTHER NORTH ALONG
ANOTHER COLD FRONT MOVING THROUGH THE NORTH-CENTRAL U.S., BUT WITH
MORE UNCERTAINTY ON AMOUNTS/LOCATION AND IS COVERED BY THE
NORTHERN EXTEND OF THE MARGINAL RISK AREA. ON DAY 5/THURSDAY,
RAINFALL SHOULD TREND LIGHTER ACROSS THE SOUTHERN PLAINS BUT MAY
CONTINUE ACROSS THE UPPER MIDWEST/GREAT LAKES REGION. THE MARGINAL
RISK FOR DAY 5 WAS MAINTAINED ALONG WITH AN EXTENSION ALONG THE
SOUTH/SOUTHWEST BOUNDS INTO WESTERN MISSOURI/EASTERN KANSAS.
MEANWHILE, MEANINGFUL SNOW APPEARS LIKELY ACROSS THE NORTHERN
ROCKIES ON WEDNESDAY, WITH INCREASING POTENTIAL FOR ACCUMULATING
SNOWS EVEN INTENDING INTO THE LOWER ELEVATIONS AND THE NORTHERN
PLAINS. TOTAL ACCUMULATIONS AND EXACT LOCATION OF THE HIGHEST
AMOUNTS REMAIN UNCERTAIN AS IT WILL BE HIGHLY DEPENDENT ON THE
EVENTUAL UPPER LEVEL AND SURFACE PATTERN EVOLUTION. ON
WEDNESDAY/THURSDAY, PRECIPITATION IS LIKELY ACROSS THE NORTHWEST
AS THE NEXT SHORTWAVE MOVES TOWARDS THE REGION, AND THIS MOISTURE
SHOULD SPREAD EAST WITH TIME. ADDITIONAL ROUNDS OF AT LEAST
LOCALLY HEAVY RAINS ARE POSSIBLE ACROSS THE CENTRAL U.S. AGAIN BY
NEXT WEEKEND WITH SNOW POTENTIAL WELL NORTH STILL VERY UNCERTAIN
BUT WORTH WATCHING.
WELL ABOVE NORMAL TEMPERATURES WILL SPREAD FROM THE
MIDWEST/SOUTHERN U.S. INTO THE EAST WEDNESDAY-FRIDAY AND BEYOND
UNDERNEATH A BUILDING RIDGE. MEANWHILE, TROUGHING ACROSS THE WEST
WILL CONTINUE A PROLONGED PERIOD OF BELOW NORMAL TEMPERATURES,
WITH THE GREATEST DAYTIME HIGH ANOMALIES (20-30 DEGREES BELOW
NORMAL) EXPANDING FROM THE NORTHERN ROCKIES INTO THE NORTHERN
PLAINS BY NEXT WEEKEND.
CAMPBELL/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 FORECAST, EXCESSIVE RAINFALL OUTLOOK,
WINTER WEATHER OUTLOOK PROBABILITIES, HEAT INDICES AND KEY
MESSAGES 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
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=OVW
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