822
FXUS02 KWBC 220656
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
255 AM 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 GFS BASED SOLUTIONS (INCLUDING ENSEMBLES) HAVE BEEN PERSISTENT
THE PAST FEW DAYS IN SHOWING A MUCH QUICKER EJECTION OF SOUTHWEST
U.S. ENERGY/UPPER LOW AND MUCH MORE AMPLIFIED/FASTER SHORTWAVE
ENERGY THROUGH THE WEST ON WEDNESDAY. THIS EVENTUALLY SPINS UP A
RATHER STRONG SURFACE LOW PRESSURE SYSTEM ACROSS THE CENTRAL U.S.
RESULTING IN A DECENT SNOWSTORM FOR THE NORTHERN ROCKIES/PLAINS.
WPC FORECASTS HAVE SIDED MORE WITH THE BETTER CONSENSUS OF A
SLOWER/WEAKER EVOLUTION CLOSEST TO THE ECMWF, CMC, AND UKMET AND
THERE IS NO REASON TO GO AGAINST CONTINUITY AT THIS POINT, BUT IT
IS INTERESTING HOW CONSISTENT GFS SOLUTIONS HAVE BEEN. THIS
CONTINUES TO BE A LOW CONFIDENCE FORECAST AND LIKELY WILL TAKE
UNTIL THE SHORT RANGE PERIOD TO FULLY RESOLVE DETAILS.
THERE IS ALSO A LOT OF UNCERTAINTY LATER IN THE WEEK WITH THE NEXT
SHORTWAVE MOVING INTO THE NORTHWEST. THE ECMWF AND CMC BOTH SHOW A
CLOSED LOW INTO 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
ANOTHER DAY OF HEAVY RAINS ARE LIKELY WEDNESDAY ASSOCIATED WITH
NORMA REMNANTS AND HIGHLY ANOMALOUS MOISTURE INTERACTING WITH A
STATIONARY BOUNDARY ACROSS THE SOUTHERN PLAINS. GIVEN THE SET UP,
AND HEAVY RAINFALL LIKELY ON TUESDAY AS WELL, A SIZABLE SLIGHT
RISK WAS ADDED TO THE NEW DAY 4/WEDNESDAY EXCESSIVE RAINFALL
OUTLOOK SPANNING ACROSS CENTRAL TEXAS INTO OKLAHOMA. HEAVY
RAINFALL IS POSSIBLE FARTHER NORTH ALONG ANOTHER COLD FRONT MOVING
THROUGH THE NORTH-CENTRAL U.S., BUT WITH MORE UNCERTAINTY ON
AMOUNTS/LOCATION. A MARGINAL RISK WAS MAINTAINED INTO THE UPPER
MIDWEST FOR DAY 4. ON DAY 5/THURSDAY, RAINFALL SHOULD TREND
LIGHTER ACROSS THE SOUTHERN PLAINS BUT MAY CONTINUE ACROSS THE
UPPER MIDWEST/GREAT LAKES REGION, SO A MARGINAL RISK WAS INCLUDED
ON TONIGHTS DAY 5 ERO.
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. EXACT AMOUNTS AND RESULTING IMPACTS ARE STILL VERY
UNCERTAIN AND 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.
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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