352
FXUS02 KWBC 150709
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
309 AM EDT TUE OCT 15 2024
VALID 12Z FRI OCT 18 2024 - 12Z TUE OCT 22 2024
..OVERVIEW
DEEP UPPER TROUGHING WITH A DEVELOPING CLOSED LOW IN THE INTERIOR
WEST WILL LEAD TO A COOL AND WET PATTERN THERE, INCLUDING HIGHER
ELEVATION SNOW AND FROST/FREEZE CONCERNS IN SOME OF THE VALLEYS.
HEAVY RAIN CHANCES COULD INCREASE IN THE SOUTHERN/CENTRAL PLAINS BY
THE WEEKEND. UPPER RIDGING AHEAD OF THIS TROUGH/LOW WILL PROMOTE
WARMER THAN AVERAGE TEMPERATURES IN THE NORTHERN/CENTRAL PLAINS TO
MIDWEST AS IT MEANDERS. THE RIDGE SHOULD GRADUALLY WARM THE EAST AS
WELL AND PROMOTE DRY CONDITIONS FOR THE MOST PART, EXCEPT FOR
SOUTH FLORIDA. ADDITIONAL ROUNDS OF PRECIPITATION MAY COME INTO THE
PACIFIC NORTHWEST LATE WEEK INTO THE WEEKEND.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODEL GUIDANCE IS REASONABLY AGREEABLE REGARDING THE LARGE SCALE
PATTERN DURING MUCH OF THE PERIOD. MODELS AGREE AN UPPER TROUGH
DIGGING INTO THE GREAT BASIN FRIDAY WILL SPLIT OFF A CLOSED UPPER
LOW INTO THE SOUTHERN STREAM ATOP THE SOUTHWEST BY THE WEEKEND.
THERE IS MODEST SPREAD AMONG DETERMINISTIC MODELS/ENSEMBLE
MEMBERS/AI MODELS WITH THE TIMING AND PLACEMENT OF THIS UPPER LOW,
WITH SPREAD INCREASING BY EARLY NEXT WEEK AS IT EJECTS NORTHEAST
AND MAY JOIN BACK UP WITH THE MEAN FLOW BY TUESDAY. CMC RUNS HAVE
BEEN ON THE SLOWER SIDE OF THE GUIDANCE ENVELOPE THOUGH
INTERESTINGLY THE 12Z CMC ENSEMBLE MEAN WAS FASTER THAN OTHER
MEANS. PREFERRED THE 12Z GEFS MEAN OVER THE 18Z GEFS MEAN AS IT
MATCHED BETTER WITH THE 12Z EC MEAN (12Z MEANS BOTH SLOWER). BUT
OVERALL THE MODEL SPREAD FOR THIS FEATURE IS WELL WITHIN TYPICAL
RANGES FOR A CLOSED UPPER LOW LIKE THIS IN THE MIDDLE TO LATE
MEDIUM RANGE PERIOD.
UPPER RIDGING IS AGREEABLE AHEAD OF THIS TROUGH/LOW BUILDING FROM
THE EAST-CENTRAL U.S. FRIDAY TOWARD THE EASTERN SEABOARD SATURDAY
DISPLACING INITIAL TROUGHING, BUT MORE UNCERTAIN SHORTWAVES COULD
DISRUPT THIS RIDGING IN THE EAST BY SUNDAY. A RIDGE IS FORECAST TO
REBUILD ATOP THE MISSISSIPPI VALLEY AND VICINITY INSTEAD BY SUNDAY,
DOWNSTREAM OF THE SOUTHWEST UPPER LOW, PUSHING EAST INTO THE
WORKWEEK AS THE UPPER LOW DOES TOO.
ENERGY IS LIKELY TO DIVE SOUTHWARD THROUGH THE EASTERN PACIFIC
EARLY NEXT WEEK AND PERHAPS FORM A CLOSED LOW OFFSHORE. THIS LEADS
TO SOME NOTABLE UNCERTAINTIES IN THE FLOW PATTERN REACHING THE WEST
WITHOUT MUCH AGREEMENT IN THE DETAILS YET.
THE WPC FORECAST WAS BASED ON A BLEND OF THE DETERMINISTIC MODELS
EARLY IN THE PERIOD, WITH SOME ENSEMBLE MEANS INTRODUCED BY DAY 5
AND INCREASING TO ABOUT HALF BY DAY 7 FOR THE MASS FIELDS GIVEN THE
INCREASING SPREAD.
..WEATHER/HAZARDS HIGHLIGHTS
THE UPPER LOW CLOSING OFF ACROSS THE SOUTHWEST LATE WEEK INTO THE
WEEKEND WILL PUSH PRECIPITATION INTO THE FOUR CORNERS STATES,
ROCKIES, AND HIGH PLAINS. EXPECT ENHANCED PRECIPITATION TOTALS IN
TERRAIN WITH HIGHER ELEVATION SNOW, WHICH WILL BE THE FIRST SNOW OF
THE SEASON IN SOME LOCATIONS GIVEN THE WARM FALL IN THE WEST THUS
FAR. SOME PRECIPITATION COULD CONTINUE ACROSS THE CENTRAL/SOUTHERN
ROCKIES INTO THE WEEKEND. BY LATER FRIDAY INTO THE WEEKEND, GULF
MOISTURE MAY STREAM IN JUST AHEAD OF THE UPPER LOW FOR INCREASING
RAIN CHANCES IN THE CENTRAL/SOUTHERN HIGH PLAINS. WHILE FORECAST
DETAILS VARY, MODELS HAVE BEEN FAIRLY PERSISTENT IN SHOWING SOME
MODERATE TO HEAVY RAIN POTENTIAL FOCUSED IN NORTHEASTERN NEW MEXICO
AND NEARBY, WITH SOME MODEST INSTABILITY. THE DAY 5/SATURDAY ERO
PROPOSES A MARGINAL RISK THERE AND HEAVY RAIN WOULD BE MOST
CONCERNING ATOP SENSITIVE BURN SCAR AREAS. THE CURRENT FORECAST
INDICATES THAT THE SOUTH-CENTRAL PLAINS SHOULD CONTINUE TO BE A
FOCUS FOR ENHANCED PRECIPITATION ON SUNDAY BEFORE FINALLY MOVING
EASTWARD MONDAY. ADDITIONALLY, MORE ROUNDS OF PRECIPITATION ARE
LIKELY FOR THE PACIFIC NORTHWEST INTO THE WEEKEND WITH ADDITIONAL
IMPULSES COMING THROUGH.
MEANWHILE, THE EASTERN U.S. IS FORECAST TO BE GENERALLY DRY LATE
WEEK INTO EARLY NEXT WEEK, WITH THE EXCEPTION OF PARTS OF THE
FLORIDA PENINSULA. THERE, RETURN FLOW OF MOISTURE NEAR A MEANDERING
FRONT COULD INCREASE RAIN AND THUNDERSTORM CHANCES ESPECIALLY FOR
SOUTH FLORIDA BY FRIDAY AND INTO THE WEEKEND. THERE COULD BE A
NONZERO CHANCE FOR FLASH FLOODING WITH THIS ACTIVITY ESPECIALLY IF
HEAVY RAIN RATES OCCUR IN THE SENSITIVE URBAN AREAS. HOWEVER, AS
MODELS CONTINUE TO VARY WITH HOW MUCH RAIN MAY FALL ONSHORE VERSUS
OFFSHORE, NO AREAS ARE CURRENTLY DELINEATED IN THE DAYS 4-5/FRIDAY-
SATURDAY EROS AWAITING HOPEFULLY BETTER MODEL AGREEMENT.
AN UPPER RIDGE ALIGNED OVER THE EAST-CENTRAL U.S. FRIDAY WILL
PROMOTE ABOVE NORMAL TEMPERATURES IN ITS VICINITY. THE BIGGEST
ANOMALIES OF PLUS 10-20 DEGREES ARE FORECAST ACROSS THE MIDWEST.
MEANWHILE ANOTHER ROUND OF CHILLY MORNING LOWS MAY CAUSE
FROST/FREEZE CONCERNS FOR THE INTERIOR NORTHEAST AND APPALACHIANS.
GRADUAL MODERATION/WARMING IS LIKELY TO CONTINUE THERE INTO THE
WEEKEND WHEN UPPER RIDGING COMES OVERHEAD, ALLOWING FOR
TEMPERATURES AROUND 5-10 DEGREES ABOVE NORMAL IN THE NORTHEASTERN
TIER. THEN THE RIDGE REBUILDING OVER THE CENTRAL U.S. EARLY NEXT
WEEK WILL LEAD TO WARMER THAN AVERAGE TEMPERATURES IN THE NORTHERN
PLAINS TO UPPER MIDWEST ONCE AGAIN. ON THE OTHER HAND, THE UPPER
TROUGH AND FRONTAL SURGES IN THE WEST WILL CAUSE BELOW NORMAL
TEMPERATURES TO SPREAD ACROSS THE GREAT BASIN/INTERMOUNTAIN WEST
AND SOUTHWEST ON FRIDAY WITH SLOW MODERATION INTO THE WEEKEND.
THESE COLDER TEMPERATURES MAY ALSO LEAD TO ADDITIONAL FROST/FREEZE
CONCERNS FOR ANY STILL SUSCEPTIBLE GROWING AREAS/VALLEY LOCATIONS.
TATE
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 (QPF), EXCESSIVE RAINFALL
OUTLOOK (ERO), WINTER WEATHER OUTLOOK (WWO) PROBABILITIES, HEAT
INDICES, AND KEY MESSAGES CAN BE ACCESSED FROM:
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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