834
FXUS02 KWBC 232058
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
457 PM 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 WILL BEGIN THURSDAY WITH SHORTWAVE ENERGY
LIFTING NORTHEASTWARD THROUGH THE CENTRAL U.S., WHICH COULD
CONTRIBUTE TO A HEAVY RAINFALL THREAT ACROSS PARTS OF THE UPPER
MIDWEST ALONG AND AHEAD OF A STRONG COLD FRONT. A SEPARATE
SHORTWAVE EJECTING FROM THE NORTHWEST U.S. WILL PRODUCE AN EARLY
SEASON SNOWSTORM ACROSS PARTS OF THE NORTHERN ROCKIES INTO
NORTHERN PLAINS ON THURSDAY AS WELL, AND HELP TO DEVELOP A WAVE
ALONG THE UPPER MIDWEST FRONT. UPSTREAM ENERGY DROPPING DOWN THE
EAST SIDE OF STRONG NORTHEAST PACIFIC/ALASKA RIDGING WILL FURTHER
AMPLIFY THE MEAN TROUGH ALOFT OVER THE WEST BY THE WEEKEND INTO
EARLY NEXT WEEK. AT THE SAME TIME A STRONG UPPER RIDGE SHOULD
PERSIST OVER THE SOUTHEAST QUADRANT OF THE U.S. AND GULF OF MEXICO
THROUGH THE PERIOD. THIS PATTERN SHOULD SUPPORT A MULTI-DAY PERIOD
OF ENHANCED RAINFALL OVER PARTS OF THE CENTRAL U.S., WITH A
PRONOUNCED CONTRAST BETWEEN UNSEASONABLY COLD CONDITIONS OVER THE
WEST PLUS GRADUALLY INCREASING COVERAGE OVER THE PLAINS AND VERY
WARM WEATHER FARTHER EASTWARD.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
THE UPDATED FORECAST BASED ON 00Z/06Z GUIDANCE MAINTAINED THE
APPROACH OF BLENDING THE LATEST OPERATIONAL RUNS EARLY IN THE
PERIOD AND MIXED IN SOME OF THE GEFS/ECENS MEANS LATER ON TO
ACCOUNT FOR DECREASING CONFIDENCE IN EXACT DETAILS WITHIN AN
OVERALL AGREEABLE LARGE SCALE PATTERN. AT THE START OF THE PERIOD
EARLY THURSDAY, THE GFS CONTINUES TO BE A BIT SLOWER AND MORE
CLOSED WITH THE SHORTWAVE CROSSING THE NORTHWEST. THEN THE GFS
BECOMES A LITTLE WEAKER AND MORE SUPPRESSED WITH THE ASSOCIATED
SURFACE WAVE THAT DEVELOPS OVER THE UPPER MIDWEST AND THEN TRACKS
INTO EASTERN CANADA. BY THE LATTER HALF OF THE PERIOD THE PRIMARY
ISSUES INVOLVE HOW CLOSED THE ENERGY DIGGING INTO THE WEST MAY
BECOME AND EXACT PROGRESSION OF NORTHERN STREAM FLOW--I.E., HOW
MUCH PHASING EXISTS BETWEEN THE TWO STREAMS. ALTHOUGH NOT A
PERFECT MATCH, A MORE CLOSED WESTERN LOW (PER LATEST GFS/CMC RUNS)
GENERALLY GOES ALONG WITH A SLIGHTLY MORE PROGRESSIVE NORTHERN
STREAM AND FASTER SURFACE FRONT PROGRESSION OVER THE NORTHEAST
U.S. LATER IN THE PERIOD. THUS FAR GUIDANCE HAS BEEN SPLIT WITH NO
CLEAR MAJORITY/TREND BECOMING EVIDENT YET. THE UPDATED BLEND KEPT
THE FORECAST CLOSE TO CONTINUITY, REFLECTING AN INTERMEDIATE
SOLUTION WITH SOME HINT OF SEPARATION ALOFT OVER THE WEST BUT NOT
QUITE A CLOSED LOW ALONG WITH SOMEWHAT SLOWER NORTHEAST FRONTAL
PROGRESSION THAN THE GFS/GEFS/CMC. THE NEW 12Z ECMWF HAS ADJUSTED
A LITTLE TOWARD THE MIDDLE OF THE PRIOR SPREAD SO THE ENVELOPE
SEEMS TO BE NARROWING SOME.
..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 AREA FROM NORTHEAST IOWA INTO CENTRAL WISCONSIN ON
THE DAY 4/THURSDAY EXCESSIVE RAINFALL OUTLOOK, WITH LATEST
GUIDANCE REASONABLY SUPPORTIVE OF MAINTAINING THIS OUTLOOK AREA
WITHOUT CHANGE FOR NOW. THERE HAS BEEN A LITTLE MORE VARIABILITY
ON WHERE THE AXIS OF HEAVY RAINFALL MAY CROSS NORTHERN MICHIGAN
(MOSTLY IN THE U.P.) SO THIS WILL BE ONE LOCATION OF ONGOING
EVALUATION WITH REGARD TO SLIGHT VERSUS MARGINAL RISK. 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
SIDE 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. BY THE
FRIDAY-FRIDAY NIGHT TIME FRAME COVERED IN THE DAY 5 ERO, GUIDANCE
IS SHOWING DECENT INSTABILITY AND INCREASINGLY ANOMALOUS MOISTURE
AHEAD OF THE WAVY FRONT SLOWLY ADVANCING OVER THE SOUTHERN PLAINS,
WITH SOME SIGNAL FOR LOCALIZED ENHANCED TOTALS (12Z UKMET BEING
HEAVIEST SO FAR). THE BEST POTENTIAL FOR SOME FAIRLY INTENSE RAIN
RATES SHOULD BE OFFSET JUST TO THE EAST OF HIGHEST TOTALS IN PRIOR
DAYS BUT THE PATTERN AND INGREDIENTS SEEM TO FAVOR INTRODUCTION OF
A MARGINAL RISK AREA FROM CENTRAL TEXAS INTO NORTHWESTERN ARKANSAS
AND FAR SOUTHWESTERN MISSOURI.
ELSEWHERE, SHOWERS WILL CONTINUE ACROSS PARTS OF THE
SOUTHERN/CENTRAL PLAINS ON THURSDAY ALONG A WEAKENING FRONTAL
BOUNDARY BEFORE THE STRONGER FRONT APPROACHES ON FRIDAY. BEYOND
FRIDAY, THIS STRONG FRONT SHOULD CONTINUE TO SERVE AS A FOCUS FOR
SIGNIFICANT RAINFALL OVER PARTS OF THE EASTERN HALF OF THE PLAINS
INTO AT LEAST THE MISSISSIPPI VALLEY. IT WILL TAKE SOME ADDITIONAL
TIME TO DETERMINE HOW MUCH OVERLAP MAY OCCUR (YIELDING THE HIGHEST
TOTALS) OVER THE MULTIPLE DAYS OF THIS LONGER TERM EVENT. LIGHTER
RAIN SHOULD EXTEND INTO THE GREAT LAKES/NORTHEAST FROM THE WEEKEND
INTO EARLY NEXT WEEK. OUT WEST, ADDITIONAL PRECIPITATION/HIGHER
ELEVATION SNOWS WILL MOVE EASTWARD ACROSS THE REGION THIS COMING
WEEKEND FOLLOWED BY A DRIER TREND AS THE MOISTURE CONTRIBUTES TO
THE ENHANCED RAINFALL AREA FARTHER EAST. POTENTIAL EXISTS FOR SOME
SNOW IN THE NORTHERN FRINGE OF THE PRECIPITATION SHIELD ACROSS THE
NORTHERN TIER. SPECIFICS REMAIN VERY UNCERTAIN BUT REQUIRE
MONITORING.
RENEWED AND AMPLIFIED TROUGHING ACROSS THE WEST WILL CONTINUE A
PROLONGED PERIOD OF BELOW NORMAL TEMPERATURES, WITH DAYTIME HIGHS
15-30 DEGREES BELOW NORMAL (LOCALLY COLDER OVER MONTANA LATE THIS
WEEK) 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
NORTHWESTERN TEXAS. A FEW DAILY RECORDS ARE POSSIBLE WITHIN THIS
COLD AIR MASS. MEANWHILE, 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. EXPECT A BROAD AREA OF HIGHS 10-20 DEGREES ABOVE
NORMAL WITH SOME MORNING LOWS 20-25 DEGREES ABOVE NORMAL. DAILY
RECORDS ARE POSSIBLE, WITH RECORD WARM LOWS LIKELY TO BE MORE
NUMEROUS THAN RECORD HIGHS.
RAUSCH/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
HAZARDS:
- HEAVY RAIN ACROSS PORTIONS OF THE CENTRAL/SOUTHERN PLAINS AND
THE MIDDLE/LOWER MISSISSIPPI
VALLEY, SAT, OCT 28.
- HEAVY RAIN ACROSS PORTIONS OF THE MIDDLE/LOWER MISSISSIPPI
VALLEY, AND THE SOUTHERN PLAINS, FRI,
OCT 27.
- HEAVY RAIN ACROSS PORTIONS OF THE GREAT LAKES AND THE UPPER
MISSISSIPPI VALLEY, THU, OCT 26.
- HEAVY SNOW ACROSS PORTIONS OF THE NORTHERN PLAINS, THU, OCT 26.
- FROST/FREEZE ACROSS PORTIONS OF THE CENTRAL/SOUTHERN PLAINS AND
THE UPPER/MIDDLE MISSISSIPPI
VALLEY, SUN-MON, OCT 29-OCT 30.
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
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page