521
FXUS02 KWBC 230700
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
300 AM EDT MON OCT 23 2023
VALID 12Z THU OCT 26 2023 - 12Z MON OCT 30 2023
...A HEAVY TO EXCESSIVE RAINFALL THREAT ACROSS PARTS OF THE UPPER
MIDWEST ON THURSDAY...
...HEAVY SNOW INCREASINGLY LIKELY FOR PARTS OF THE NORTHERN PLAINS
ON THURSDAY...
..OVERVIEW
THE MEDIUM RANGE PERIOD BEGINS THURSDAY WITH SHORTWAVE ENERGY
MOVING THROUGH THE CENTRAL U.S. WHICH COULD SUPPORT A HEAVY
RAINFALL THREAT ACROSS PARTS OF THE UPPER MIDWEST ON THURSDAY
ALONG AND AHEAD OF A STRONG COLD FRONT. MEANWHILE, ADDITIONAL
AMPLIFIED ENERGY THROUGH THE NORTHWEST WILL ALLOW FOR AN EARLY
SEASON SNOWSTORM ACROSS PARTS OF THE NORTHERN ROCKIES INTO THE
NORTHERN PLAINS. AMPLIFIED TROUGHING WILL BE RENEWED INTO EARLY
NEXT WEEK ACROSS MUCH OF THE WESTERN U.S. AS THE NEXT SHORTWAVE
DROPS INTO THE PACIFIC NORTHWEST ON FRIDAY. THIS WOULD ALSO ALLOW
FOR A STRONG UPPER RIDGE TO BUILD OVER THE SOUTHEAST QUADRANT OF
THE U.S. THROUGH THE PERIOD.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
AS HAS BEEN THE CASE FOR SEVERAL DAYS, THE GFS CONTINUES TO BE
FAST WITH THE SHORTWAVE THROUGH THE MIDWEST ON THURSDAY AND
SLIGHTLY MORE AMPLIFIED WITH THE INITIAL SYSTEM THROUGH THE WEST.
HOWEVER, COMPARED TO RECENT RUNS, MODELS HAVE COME INTO MUCH
BETTER AGREEMENT ACROSS THE BOARD IN THE EARLY PERIODS AND SO A
GENERAL DETERMINISTIC MODEL BLEND WAS USABLE FOR THE DAY
3-5/THURSDAY-SATURDAY PERIOD FOR TONIGHTS WPC PROGS. MODELS AGREE
THE NEXT SHORTWAVE SHOULD ARRIVE IN THE PACIFIC NORTHWEST AROUND
FRIDAY, WITH SOME HINTS THAT A CLOSED LOW COULD EVENTUALLY FORM
OUT OF THIS. THE GFS IS MOST EXCITED ABOUT THIS EVOLUTION SHOWING
COMPLETE SEPARATION FROM NORTHERN STREAM ENERGY (WHICH SHOULD
SLIDE EAST THROUGH THE NORTHERN TIER) AND BRINGING THE UPPER LOW
MUCH FARTHER SOUTH AND WEST INTO CALIFORNIA/THE SOUTHWEST NEXT
SUNDAY-MONDAY. THE ECMWF AND CMC, WITH SUPPORT FROM THE ENSEMBLE
MEANS, SUGGEST A LITTLE BIT WEAKER SOUTHERN STREAM SYSTEM AND MORE
PHASED TROUGHING OVERALL. THE DAYS 6 AND 7 FORECAST BLEND
INCORPORATED MORE OF THE ENSEMBLE MEANS TO HELP TEMPER THE DETAIL
DIFFERENCES IN THE DETERMINISTIC SOLUTIONS, WITH MINOR
CONTRIBUTIONS STILL FROM THE ECMWF FOR SOME ADDED SYSTEM
DEFINITION. THIS EVOLUTION HAS IMPLICATIONS FOR ANOTHER ROUND OF
HEAVY RAINFALL ACROSS THE CENTRAL PLAINS/MIDWEST REGION LATE
PERIOD, WITH POSSIBLY SNOW ON THE BACKSIDE SO DETAILS WILL NEED TO
BE MONITORED IN THE COMING DAYS.
..WEATHER/HAZARDS HIGHLIGHTS
HIGHLY ANOMALOUS MOISTURE, WITH TROPICAL CONNECTIONS TO WHAT IS
CURRENTLY TROPICAL STORM NORMA, WILL INTERACT WITH A FRONTAL
BOUNDARY THROUGH THE NORTH-CENTRAL U.S TO FUEL A HEAVY TO POSSIBLY
EXCESSIVE RAINFALL THREAT ON THURSDAY ACROSS MUCH OF THE UPPER
MIDWEST/GREAT LAKES. THERE WAS ENOUGH MODEL AGREEMENT TO INTRODUCE
A SLIGHT RISK FROM NORTHEAST IOWA INTO CENTRAL WISCONSIN ON THE
DAY 4/THURSDAY EXCESSIVE RAINFALL OUTLOOK. DESPITE DRY ANTECEDENT
CONDITIONS ACROSS THIS REGION, SLOW MOVING STORMS ALONG THE
FRONTAL BOUNDARY WITH PLENTY OF MOISTURE AND INSTABILITY TO WORK
WITH, COULD POSE A FLASH FLOOD RISK. ON THE NORTH AND WEST OF THIS
SYSTEM, HEAVY SNOW THREATS CONTINUE TO INCREASE ACROSS PARTS OF
THE NORTH-CENTRAL ROCKIES INTO THE NORTHERN PLAINS ON THURSDAY.
THIS WOULD BE THE FIRST ACCUMULATING SNOW EVENT OF THE SEASON FOR
THE LOWER ELEVATIONS OF EASTERN MONTANA/NORTH DAKOTA WHERE SEVERAL
INCHES OF SNOW COULD FALL.
ELSEWHERE, SHOWERS WILL CONTINUE ACROSS PARTS OF THE
SOUTHERN/CENTRAL PLAINS ON THURSDAY ALONG A WEAKENING FRONTAL
BOUNDARY. OUT WEST, ADDITIONAL PRECIPITATION/HIGHER ELEVATION
SNOWS WILL MOVE EASTWARD ACROSS THE REGION THIS COMING WEEKEND. AN
ADDITIONAL HEAVY RAIN THREAT COULD DEVELOP ACROSS PARTS OF THE
CENTRAL PLAINS/MIDDLE MISSISSIPPI VALLEY INTO THE UPPER MIDWEST
EARLY NEXT WEEK, WITH SOME SNOW POTENTIAL FOR THE NORTHERN FRINGE
OF THE PRECIPITATION SHIELD. THIS REMAINS STILL VERY UNCERTAIN BUT
IS WORTH MONITORING.
WELL ABOVE NORMAL TEMPERATURES ACROSS THE CENTRAL U.S. AND THE
MIDWEST WILL SHIFT EAST AND SETTLE THIS WEEKEND ACROSS THE
EAST/SOUTHEAST AS UPPER RIDGING BUILDS OVER THIS REGION.
MEANWHILE, RENEWED AND AMPLIFIED TROUGHING ACROSS THE WEST WILL
CONTINUE A PROLONGED PERIOD OF BELOW NORMAL TEMPERATURES, WITH
DAYTIME HIGHS 15-30 DEGREES BELOW NORMAL TO SPREAD ACROSS MUCH OF
THE INTERIOR WEST AND THE NORTHERN/CENTRAL PLAINS. BY NEXT MONDAY,
MUCH BELOW NORMAL TEMPERATURES COULD SINK AS FAR SOUTH AS THE
SOUTHERN ROCKIES AND NORTHERN TEXAS.
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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