086
FXUS02 KWBC 210649
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
248 AM EDT SAT OCT 21 2023
VALID 12Z TUE OCT 24 2023 - 12Z SAT OCT 28 2023
...A HEAVY TO POSSIBLY EXCESSIVE RAINFALL THREAT INCREASINGLY
LIKELY FOR PARTS OF THE SOUTHERN AND CENTRAL U.S. EARLY TO MID
NEXT WEEK...
..OVERVIEW
THE MEDIUM RANGE PERIOD BEGINS TUESDAY WITH AN UPPER LOW DIVING
THROUGH THE SOUTHWEST INTO NORTHERN MEXICO WHICH MAY LINGER FOR A
DAY OR TWO BEFORE WEAKENING AND LIFTING THROUGH THE CENTRAL U.S.
MID TO LATER NEXT WEEK. ADDITIONAL ENERGY LOOKS TO MOVE INTO THE
NORTHWEST AROUND MID-WEEK, BUT MODEL GUIDANCE CONTINUES TO SHOW
CONSIDERABLE UNCERTAINTY IN THE TRACK AND STRENGTH OF THIS ENERGY
AND POTENTIAL INTERACTIONS WITH THE UPPER LOW OVER THE SOUTHWEST.
REGARDLESS, IT SEEMS LIKELY REMNANT ENERGY/MOISTURE FROM WHAT IS
CURRENTLY HURRICANE NORMA COULD STREAM NORTHWARD TO SPREAD
POTENTIALLY HEAVY RAINFALL INTO PARTS OF THE SOUTHERN AND CENTRAL
U.S., WHILE ON THE BACKSIDE, SNOW CHANCES INCREASE IN THE NORTHERN
ROCKIES AND PERHAPS EVEN INTO PARTS OF THE NORTHERN PLAINS LATE
NEXT WEEK.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
AS EARLY AS DAY 4/WEDNESDAY, THE GUIDANCE SHOWS CONSIDERABLE
UNCERTAINTY REGARDING BOTH THE UPPER LOW OVER THE
SOUTHWEST/NORTHERN MEXICO AND ENERGY NEAR/INTO THE NORTHWEST. THE
GFS REMAINS THE QUICKEST AND MOST AMPLIFIED TO BRING A COMPACT
CLOSED LOW THROUGH THE NORTHWEST ON WEDNESDAY-THURSDAY WHICH ACTS
TO KICK THE SOUTHWEST UPPER LOW THROUGH THE SOUTHERN PLAINS MUCH
EARLIER THAN THE REST OF THE GUIDANCE, EVENTUALLY SPINNING UP A
NICE LOOKING CYCLONE OVER THE NORTH-CENTRAL U.S. LATER IN THE
WEEK. THE BETTER CONSENSUS AND LATEST MODEL TRENDS HOWEVER SUGGEST
MUCH WEAKER ENERGY MANIFESTING OVER BRITISH COLUMBIA, EVENTUALLY
BRINGING SOME SORT OF SHORTWAVE/TROUGHING THROUGH THE NORTHWEST
BUT NOT UNTIL FRIDAY, WHICH CAUSES THE SOUTHWEST UPPER LOW TO
LINGER A COUPLE OF DAYS BEFORE BEING LIFTED THROUGH THE
SOUTH-CENTRAL U.S.. EVENTUALLY BY DAY 7/SATURDAY, MODELS SORT OF
CONVERGE ON BROAD TROUGHING ACROSS THE WEST/NORTH WITH BLOCKY
RIDGING OVER THE EAST. ENSEMBLE GUIDANCE ALSO SHOWS SIGNIFICANT
SPREAD IN THE DETAILS OF THESE SYSTEMS LEAVING THIS A VERY LOW
CONFIDENCE FORECAST. A LOOK AT THE NEW 00Z RUNS (AVAILABLE AFTER
FORECAST GENERATION TIME) GENERALLY MAINTAINS STATUS-QUO WITH NO
MAJOR SHIFTS IN INDIVIDUAL PIECES OF GUIDANCE.
THE FORECAST BLEND FOR TONIGHT DID USE A FULLY DETERMINISTIC BLEND
DAYS 3 AND 4, BUT MORE HEAVILY WEIGHTED TOWARDS THE ECMWF. AFTER
THIS, THE GFS WAS REPLACED WITH THE ENSEMBLE MEAN GUIDANCE WHICH
MADE UP THE MAJORITY OF THE BLEND BY DAYS 6 AND 7. THIS MAINTAINS
GOOD CONTINUITY WITH THE PREVIOUS WPC FORECAST AS WELL WHICH SEEMS
PRUDENT AT THIS TIME GIVEN THE UNCERTAINTY AND RUN TO RUN
VARIABILITY IN THE GUIDANCE.
..WEATHER/HAZARDS HIGHLIGHTS
FAVORABLE MOISTURE FROM THE REMNANTS OF NORMA SHOULD BEGIN
SPREADING IN EARNEST INTO THE SOUTHWEST/SOUTHERN PLAINS BY TUESDAY
AHEAD OF THE UPPER LOW PARKED OVER THE SOUTHWEST/NORTHERN MEXICO,
INTERACTING WITH A FRONTAL BOUNDARY THROUGH THE SOUTHERN PLAINS.
MODELS ARE BEGINNING TO CONVERGE ON AN INCREASING THREAT FOR HEAVY
RAINFALL AND DESPITE DRY ANTECEDENT CONDITIONS, COULD POSE A FLASH
FLOOD THREAT GIVEN THE TROPICAL MOISTURE CONNECTION AND POTENTIAL
FOR TRAINING ALONG THE THE FRONT. GIVEN THIS, OPTED TO INTRODUCE A
SLIGHT RISK TO THE DAY 4/TUESDAY EXCESSIVE RAINFALL OUTLOOK ACROSS
PARTS OF NORTH TEXAS INTO WEST-CENTRAL OKLAHOMA. MODEST RAINFALL
MAY ALSO SPREAD NORTHWARD INTO THE CENTRAL PLAINS/MIDWEST AHEAD OF
A STRONGER COLD FRONT THROUGH THE REGION AND THERE IS A MARGINAL
RISK ACROSS THIS REGION ON THE ERO TO COVER THIS POTENTIAL.
RAINFALL SHOULD LINGER ACROSS THE SOUTHWEST/SOUTHERN
PLAINS/MID-MISSISSIPPI VALLEY INTO WEDNESDAY AS WELL, WITH SOME
HEAVY RAINFALL POTENTIAL, BUT UNCERTAINTY IN AMOUNTS AND LOCATION
OF THE HIGHEST AMOUNTS IS TOO UNCERTAIN FOR ANYTHING MORE THAN A
MARGINAL ON THE DAY 5 ERO AT THIS TIME. RAINFALL MAY TREND LIGHTER
AND SLIGHTLY EASTWARD LATER IN THE WEEK AS THE UPPER LOW BEGINS TO
WEAKEN ACROSS THE SOUTH-CENTRAL U.S.. OUT WEST, PROBABILITIES FOR
MEANINGFUL SNOW AT HIGHER ELEVATIONS OF THE NORTHERN ROCKIES
SHOULD START INCREASING BY EARLY IN THE WEEK, WITH SOME POTENTIAL
FOR GENERALLY LIGHT BUT ACCUMULATING SNOWFALL EVEN EXTENDING INTO
PARTS OF THE NORTHERN PLAINS LATER IN THE WEEK, BUT HIGHLY
DEPENDENT ON THE CURRENTLY VERY UNCERTAIN UPPER LEVEL AND SURFACE
PATTERN EVOLUTION.
WELL ABOVE NORMAL TEMPERATURES WILL SPREAD FROM THE MIDWEST INTO
THE EAST TUESDAY-THURSDAY WITH THE GREATEST ANOMALIES (15-20
DEGREES ABOVE NORMAL) LIKELY TUESDAY ACROSS PARTS OF THE MIDWEST.
IN THE NORTHEAST, MORNING LOW TEMPERATURES ON TUESDAY MAY BE COLD
ENOUGH TO SUPPORT A FROST/FREEZE THREAT, BUT SHOULD MODERATE
THEREAFTER AS UPPER RIDGING BUILDS INTO THE REGION. TEMPERATURES
WILL TREND COOLER WEDNESDAY AND BEYOND FOR THE NORTHERN
ROCKIES/PLAINS WHERE DAYTIME HIGHS COULD BE 10-20 DEGREES BELOW
NORMAL BEHIND THE COLD FRONT.
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
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page