904
FXUS02 KWBC 202000
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
359 PM EDT FRI OCT 20 2023
VALID 12Z MON OCT 23 2023 - 12Z FRI OCT 27 2023
...MODERATE TO HEAVY RAINFALL INCREASINGLY LIKELY FOR PARTS OF THE
SOUTHERN AND CENTRAL U.S. EARLY TO MID NEXT WEEK...
..OVERVIEW
THE MEDIUM RANGE PERIOD BEGINS MONDAY WITH TROUGHING EXITING THE
EAST COAST TO BE REPLACED BY A DEVELOPING UPPER RIDGE LASTING MUCH
OF THE WEEK. OUT WEST, AN UPPER LOW IS LIKELY TO DIVE INTO THE
SOUTHWEST/NORTHERN MEXICO BEFORE WEAKENING AND LIFTING INTO THE
SOUTHERN U.S. 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 ANY 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. AHEAD OF A STRONG COLD FRONT, 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 LATEST GUIDANCE GENERALLY AGREE THAT A CUTOFF LOW WILL DIVE
INTO THE SOUTHWEST U.S./NORTHWESTERN MEXICO AND INFLUENCE SENSIBLE
WEATHER IMPACTS OVER THE SOUTHERN/CENTRAL PLAINS NEXT WEEK.
HOWEVER, THE AREAS OF UNCERTAINTY REMAIN AROUND WHETHER THIS UPPER
LOW WILL STALL OUT OR NOT AND TO WHAT EXTENT HURRICANE NORMA WILL
PHASE WITH OR INFLUENCE IT. THE 00Z EC/CMC/UKMET WERE WELL
CLUSTERED ON THE SLOWER SIDE OF THE TROUGH'S PROPAGATION, WHEREAS
THE LAST SEVERAL RUNS OF THE GFS HAVE NOT ONLY BEEN INCONSISTENT
WITH ONE ANOTHER BUT ALSO WEAKER AND MUCH MORE PROGRESSIVE WITH
THE TROUGH. THE GFS IS ESPECIALLY FASTER WITH THE TROUGH AFTER DAY
5 WHEN IT KICKS IT OUT INTO THE MISSISSIPPI VALLEY WHILE THE OTHER
GUIDANCE KEEPS IT SLOWLY MOVING THROUGH THE SOUTHERN PLAINS.
MEANWHILE, A NORTHERN STREAM TROUGH SET TO ENTER THE NORTHWEST
EARLY THIS WEEK CONTINUES TO CARRY A SUBSTANTIAL AMOUNT OF
UNCERTAINTY WITH IT, PARTICULARLY AFTER DAY 4. THE 06Z GEFS AND
00Z CMCE TEND TO BE FASTER THAN THE 00Z ECE WITH RESPECT TO THIS
TROUGH, BUT EACH ENSEMBLE SUITE STILL DEVELOPS A LOT OF SPREAD
THROUGHOUT THE EVOLUTION OF THIS SYSTEM. RUN-TO-RUN, THE
OPERATIONAL GFS APPEARS TO BE MORE CONSISTENT THAN THE EC, WITH
SEVERAL ECE MEMBERS DEVELOPING A RIDGE OVER THE PAC NW. THIS
SOLUTION APPEARS TO CLUSTER WELL WITH SOME CANADIAN MEMBERS AS
WELL. STILL THOUGH, A SOLUTION FEATURING A TROUGH OF SOME SORT IS
FAVORED OVER THE NORTHWEST AS THIS WILL LIKELY PRODUCE HEAVY SNOW
OVER THE NORTHERN ROCKIES.
..WEATHER/HAZARDS HIGHLIGHTS
THE BETTER CONSENSUS SUGGESTS MONDAY SHOULD BE RELATIVELY QUIET
ACROSS THE COUNTRY, THOUGH RECENT RUNS OF THE GFS HAVE BEEN RATHER
PERSISTENT IN DEPICTING THE ONSET OF LOCALLY HEAVY RAINFALL OVER
THE SOUTHERN PLAINS AS EARLY AS MONDAY, SO THIS IS SOMETHING TO
WATCH. STILL, GIVEN THE UNCERTAINTY, OPTED TO KEEP THE DAY 4
EXCESSIVE RAINFALL OUTLOOK BLANK, BUT A RISK AREA MAY NEED TO BE
INTRODUCED IN FUTURE UPDATES IF OTHER PIECES OF GUIDANCE TREND
FASTER LIKE THE GFS. BY TUESDAY, FAVORABLE MOISTURE AND
INSTABILITY FROM NORMA REMNANTS SHOULD BEGIN SPREADING IN EARNEST
INTO THE SOUTHERN PLAINS, WITH AT LEAST LOCALLY HEAVY RAINFALL
LIKELY, POSSIBLY SPREADING INTO PARTS OF THE MIDWEST ALONG THE
STRONG FRONTAL BOUNDARY. A BROAD MARGINAL RISK FOR EXCESSIVE
RAINFALL WAS INTRODUCED ON THE DAY 5/TUESDAY ERO, STRETCHING FROM
EASTERN NEW MEXICO NORTHWARD INTO THE UPPER MIDWEST. IT IS
POSSIBLE AN EMBEDDED SLIGHT RISK MAY BE NEEDED SOMEWHERE, BUT AT
LEAST THE SOUTHERN HALF OF THIS REGION HAS BEEN VERY DRY LATELY
AND THERE IS STILL A CONSIDERABLE AMOUNT OF UNCERTAINTY ON TIMING
AND RAINFALL AMOUNTS. RAINFALL MAY LINGER OR SPREAD VERY SLOWLY
EASTWARD LATER NEXT WEEK, BUT SHOULD TREND LIGHTER AS THE BETTER
MOISTURE WEAKENS AND THE UPPER LOW OPENS UP AND MOVES EAST. OUT
WEST, PROBABILITIES FOR MEANINGFUL SNOW AT HIGHER ELEVATIONS OF
THE NORTHERN ROCKIES SHOULD START INCREASING BY MONDAY/TUESDAY,
WITH SOME POTENTIAL FOR GENERALLY LIGHTER SNOWFALL AMOUNTS EVEN
EXTENDING INTO PARTS OF THE NORTHERN PLAINS LATER IN THE WEEK, BUT
HIGHLY DEPENDENT ON THE CURRENTLY VERY UNCERTAIN UPPER LEVEL
PATTERN EVOLUTION.
WELL ABOVE NORMAL TEMPERATURES WILL SPREAD FROM THE PLAINS INTO
THE MIDWEST/NORTHEAST MONDAY-WEDNESDAY WITH THE GREATEST ANOMALIES
(15-20 DEGREES ABOVE NORMAL) LIKELY MONDAY ACROSS THE CENTRAL
PLAINS. TO THE EAST, MORNING LOW TEMPERATURES ON MONDAY MAY BE
COLD ENOUGH FROM THE GREAT LAKES INTO THE APPALACHIANS TO SUPPORT
A GENERALLY FROST THREAT FOR MANY, BUT SHOULD MODERATE THEREAFTER
AS UPPER RIDGING BUILDS INTO THE REGION. TEMPERATURES WILL TREND
COOLER WEDNESDAY AND BEYOND FOR MUCH OF THE WEST, BUT ESPECIALLY
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
HAZARDS:
- HEAVY RAIN ACROSS PORTIONS OF THE CENTRAL PLAINS, THE MIDDLE
MISSISSIPPI VALLEY, THE LOWER MISSISSIPPI VALLEY, THE SOUTHERN
PLAINS, AND THE UPPER MISSISSIPPI VALLEY, TUE-THU, OCT 24-OCT 26.
- HEAVY SNOW ACROSS PORTIONS OF THE NORTHERN PLAINS AND THE
NORTHERN ROCKIES, TUE-WED, OCT 24-OCT 25.
- FROST/FREEZE ACROSS PORTIONS OF THE NORTHEAST, THE CENTRAL
APPALACHIANS, THE TENNESSEE VALLEY, THE MID-ATLANTIC, THE SOUTHERN
APPALACHIANS, THE SOUTHEAST, THE GREAT LAKES, AND THE OHIO VALLEY,
MON-TUE, OCT 23-OCT 24.
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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