533
FXUS02 KWBC 211816
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
216 PM 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
THE NON-GFS GUIDANCE (00Z EC/UKMET/CMC) CONTINUE TO AGREE ON THE
SYNOPTIC EVOLUTION OF THE SOUTHERN STREAM LOW THROUGH DAY 5. THE
OPERATIONAL 00Z EC APPEARS TO BE THE ONLY MODEL TO SUGGEST THAT
REMNANTS OF HURRICANE NORMA WILL PHASE WITH THE UPPER LOW OVER
NORTHERN MEXICO. THE OTHER MODELS HAVE THE ENERGY AND MOISTURE
ASSOCIATED WITH NORMA STREAMING OUT AHEAD OF THE UPPER LOW. THIS
MAY EXPLAIN WHY THE EURO BASED GUIDANCE IS LESS PROGRESSIVE AND
LIGHTER WITH QPF AMOUNTS THAN THE OTHERS. THE 00Z OPERATIONAL
CANADIAN IS THE ONLY MODEL TO KEEP THE UPPER TROUGH OVER NORTHERN
MEXICO BY DAY 6, WHILE THE EC KICKS THE ENERGY OUT OVER THE PLAINS
AND MISSISSIPPI VALLEY.
THE GREATEST UNCERTAINTY DURING THE MEDIUM RANGE LIES OVER THE
NORTHERN TIER, WHERE A TROUGH OR RIDGE MAY DEVELOP. ALL OF THE
CURRENT GUIDANCE AGREES ON AN EMERGING UPPER TROUGH DIVING THROUGH
THE ALASKAN PANHANDLE AND COASTAL BRITISH COLUMBIA EARLY NEXT
WEEK. THIS SYSTEM IS FORECAST TO PRODUCE HEAVY SNOW OVER THE
NORTHERN ROCKIES NEXT WEEK. THE 00Z EC IS MUCH SLOWER THAN THE
OTHER MODELS WITH RESPECT TO THE EVOLUTION OF THIS TROUGH. THE
OPERATIONAL 06Z GFS/GEFS AMPLIFIES IT OVER THE NORTHWEST CONUS BY
DAY 4 WHILE THE REST OF THE GUIDANCE INCLUDING THE ENSEMBLE MEANS
SUGGEST A MUCH MORE MUTED/ZONAL PATTERN EMERGING OVER THE REGION.
THE ENSEMBLE MEANS AREN'T MUCH HELP SINCE THEY THEMSELVES HAVE TO
CONTEND WITH SIGNIFICANT SPREAD. THUS, A MULTI-MODEL BLEND
CONSISTING OF THE NON-GFS OPERATIONAL GUIDANCE WERE FAVORED IN THE
BLEND THROUGH DAY 5 WHEN THE 00Z ECE AND CMCE WERE INTRODUCED. THE
ENSEMBLE MEANS WERE EXCLUSIVELY USED ON DAYS 6 AND 7 TO ACCOUNT
FOR THE VAST DISPERSION IN DETERMINISTIC SOLUTIONS ACROSS THE
LOWER 48.
..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.
KEBEDE/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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