945
FXUS02 KWBC 260616
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
215 AM EDT THU OCT 26 2023
VALID 12Z SUN OCT 29 2023 - 12Z THU NOV 02 2023
..ARCTIC SURGE THROUGH THE CENTRAL U.S INTO NEXT WEEK.
..OVERVIEW
UPPER TROUGHING LOOKS TO BE SLIDING THROUGH THE WEST AS THE PERIOD
BEGINS ON SUNDAY, WITH SHORTWAVES WORKING TO MAINTAIN AND RENEW
THE TROUGHING AS IT MOVES THROUGH THE MIDWEST AND EVENTUALLY INTO
THE EAST NEXT WEEK. THIS ALLOWS FOR A MUCH BELOW NORMAL AIRMASS TO
SPILL INTO THE CENTRAL U.S., INCLUDING AS FAR SOUTH AS TEXAS AND
THE GULF COAST, SLIDING EAST WITH TIME. HEAVY RAIN LOOKS TO BE A
THREAT SUNDAY ALONG A FRONTAL BOUNDARY THROUGH THE SOUTH-CENTRAL
PLAINS AND MIDWEST, BUT CONDITIONS SHOULD DRY OUT THEREAFTER AS
SURFACE HIGH PRESSURE ENVELOPES MUCH OF THE NATION. UPPER RIDGING
SHOULD BUILD OVER THE WEST AGAIN BY NEXT MIDWEEK AS THE NEXT
TROUGH WORKS INTO THE EAST PACIFIC/WEST COAST.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
THE MAIN FORECAST ISSUES DURING THE MEDIUM RANGE ARE WITH STRENGTH
AND TIMING OF A SHORTWAVE FROM THE NORTHERN PLAINS TO THE
NORTHEAST TUESDAY-THURSDAY. THE ECMWF HAS CONSISTENTLY BEEN MUCH
MORE AMPLIFIED WITH THIS THAN THE REST OF THE GUIDANCE, WITH
YESTERDAYS 12Z RUN EVEN SHOWING A CLOSED LOW OVER THE UPPER
MIDWEST/OHIO VALLEY. THROUGH YESTERDAYS 12Z/18Z MODEL RUNS, THE
GFS BARELY SHOWS THIS FEATURE AT ALL/IS MUCH WEAKER AND THE CMC
WAS A NICE MIDDLE GROUND BUT MUCH FASTER. HOWEVER, THE NEW 00Z
GUIDANCE FOR TONIGHT FROM THE GFS AND CMC HAS TRENDED
STRONGER/MORE AMPLIFIED, THOUGH STILL NOT AS STRONG AS THE ECMWF.
OTHERWISE, MODELS SHOW GOOD AGREEMENT FOR AN INITIAL SHORTWAVE
THROUGH THE NORTHERN TIER ON SUNDAY-MONDAY AND UPPER RIDGING
BUILDING BACK IN OVER THE WEST. THERE ARE SOME GREATER DIFFERENCES
WITH THE NEXT TROUGH TOWARDS THE WEST COAST LATE IN THE PERIOD.
THE WPC FORECAST FOR TONIGHT USED A BLEND OF THE LATEST
OPERATIONAL GUIDANCE DAYS 3-5. TRENDED MORE TOWARDS THE ENSEMBLE
MEANS (WITH MINOR CONTRIBUTIONS FROM THE DETERMINISTIC SOLUTIONS)
FOR THE LATTER HALF OF THE PERIOD WHICH SEEMED TO PROVIDE A NICE
MIDDLE GROUND FOR THE SHORTWAVE DIFFERENCES THROUGH GREAT
LAKES/NORTHEAST AND MAINTAINED ACCEPTABLE CONTINUITY WITH THE
PREVIOUS WPC FORECAST.
..WEATHER/HAZARDS HIGHLIGHTS
INSTABILITY AND ANOMALOUS MOISTURE ALONG A SLOW MOVING FRONT INTO
SUNDAY WILL CONTINUE TO PROVIDE FOCUS FOR HEAVY RAINFALL FROM
PARTS OF THE SOUTH-CENTRAL PLAINS INTO THE MIDWEST/OHIO VALLEY
WITH POTENTIAL FOR REPEAT/TRAINING OF STORMS. SOME LINGERING
UNCERTAINTY ON EXACTLY WHERE THE HEAVIEST TOTALS SET UP, AND DRY
ANTECEDENT CONDITIONS COULD LIMIT A WIDESPREAD FLASH FLOOD THREAT,
BUT LATEST MODEL QPF AMOUNTS COMBINED WITH THE POTENTIAL FOR
ADDITIONAL RAINS OVER THE NEXT FEW DAYS LEADING INTO THE MEDIUM
RANGE FORECAST PERIOD DO SEEM TO STILL SUPPORT A SLIGHT RISK AREA
ON THE DAY 4/SUNDAY ERO ACROSS THE MID-MISSISSIPPI VALLEY, WITH A
MARGINAL RISK EXTENDING NORTHEAST AND SOUTHWESTWARD ALONG THE SPAN
OF THE FRONTAL BOUNDARY. SOME POTENTIAL FOR LINGERING SNOW ACROSS
THE CENTRAL ROCKIES AND ADJACENT HIGH PLAINS ON SUNDAY ON THE
NORTH SIDE OF THE PRECIPITATION SHIELD, WITH TRANSITION ZONE
FREEZING RAIN/SLEET JUST SOUTH OF THIS AREA. BEYOND THAT INTO NEXT
WEEK, MUCH OF THE COUNTRY SHOULD BE MAINLY DRY AS HIGH PRESSURE
DOMINATES THE CONUS. THERE SHOULD BE MODEST LAKE EFFECT RAIN/SNOW
SHOWERS DOWNWIND OF THE GREAT LAKES. OF NOTE IS ALSO AN UNCERTAIN
LIFTING OF A LOW UP FROM THE CARIBBEAN TO THE SOUTHWESTERN
ATLANTIC IN SOME GUIDANCE IN ADVANCE OF A MAIN COLD FRONT THAT IS
NOW BEING MONITORED BY NHC. MEANWHILE, THE APPROACH OF AN
AMPLIFIED EASTERN PACIFIC UPPER TROUGH/HEIGHT FALLS AND SURFACE
SYSTEM ENERGIES DOES OVERALL FAVOR A MODERATELY WETTER PATTERN IN
ABOUT A WEEK FOR THE NORTHWEST.
MUCH BELOW NORMAL TEMPERATURES ACROSS THE WEST INTO THE
NORTHERN/CENTRAL PLAINS WILL CONTINUE TO EXPAND SOUTH AND EAST ON
SUNDAY BRINGING THE FIRST REAL COLD SNAP OF THE SEASON TO MANY
ACROSS THE CENTRAL U.S., INCLUDING AS FAR SOUTH AS THE SOUTHERN
PLAINS/TEXAS AND COINCIDING WITH OUTDOOR HALLOWEEN FESTIVITIES
NEXT TUESDAY. DAYTIME HIGHS 20-30 DEGREES BELOW NORMAL ARE LIKELY
WITH A FEW DAILY RECORDS POSSIBLE WITHIN THIS COLD AIR MASS.
MEANWHILE, WELL ABOVE NORMAL TEMPERATURES WILL CONTINUE SUNDAY AND
MONDAY FOR THE SOUTHEAST/EAST UNDERNEATH A RETREATING UPPER RIDGE.
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. THE CHILLY CENTRAL U.S. AIRMASS SHOULD PUSH EASTWARD
WITH TIME NEXT WEEK (WITH SOME MODERATION) WITH MUCH OF THE
COUNTRY EAST OF THE ROCKIES BELOW NORMAL NEXT TUESDAY-THURSDAY.
AFTER MONDAY, TEMPERATURES ACROSS THE WEST SHOULD BE WITHIN A FEW
DEGREES OF NORMAL.
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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