969
FXUS02 KWBC 051858
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
158 PM EST THU DEC 5 2024
VALID 12Z SUN DEC 8 2024 - 12Z THU DEC 12 2024
***HEAVY RAIN FOR THE CENTRAL GULF COAST EARLY NEXT WEEK***
19Z UPDATE: OVERALL, THE 12Z MODEL GUIDANCE SUITE HAS CONSOLIDATED
MORE COMPARED TO YESTERDAY WITH THE AMPLIFYING UPPER LEVEL PATTERN
ACROSS THE CONTINENTAL U.S. AND THE DEEP UPPER TROUGH SITUATED OVER
THE NORTH-CENTRAL STATES. THE GFS IS INITIALLY FASTER WITH A LEAD
SHORTWAVE CROSSING THE OHIO VALLEY ON MONDAY, WHEREAS THE AI
GUIDANCE AND NON-NCEP GUIDANCE SUGGEST A SLOWER SOLUTION, BUT
MATCHES UP WELL ELSEWHERE. LOOKING AHEAD TO WEDNESDAY, THE ECMWF
BECOMES STRONGER IN BRINGING A REINFORCING TROUGH ACROSS THE UPPER
MIDWEST AND THEN ACROSS THE OHIO VALLEY BY THURSDAY. IT IS ALSO
STRONGER WITH THE NEXT OFFSHORE TROUGH APPROACHING THE PACIFIC
NORTHWEST. THE ENSEMBLE MEANS WERE GRADUALLY INCREASED TO ABOUT
40-50% BY NEXT THURSDAY AS MESOSCALE UNCERTAINTY INCREASES. THE
PREVIOUS DISCUSSION IS APPENDED BELOW. /HAMRICK
-------------------
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE WPC MEDIUM RANGE PRODUCT SUITE VALID FOR SUNDAY AND MONDAY WAS
PRIMARILY DERIVED FROM A COMPOSITE OF BEST CLUSTERED GUIDANCE OF
THE 18 UTC GFS AND 12 UTC ECMWF/UKMET. THESE HAVE GOOD ENSEMBLE
SUPPORT AND CONTINUITY IN AN ACTIVE PATTERN WITH ABOVE NORMAL
OVERALL PREDICTABILITY DESPITE LINGERING EMBEDDED SHORTWAVE TIMING
ISSUES MITIGATED BY THE BLENDING PROCESS. PIVOTED AT LONGER TIME
FRAMES TO THE MOST COMPATIBLE SOLUTIONS OF THE 18 UTC GEFS MEAN AND
12 UTC ECMWF/ECMWF ENSEMBLE MEAN TO MAINTAIN BEST CONTINUITY AS
FORECAST SPREAD GROWS TO AVERAGE LEVELS. THE 01 UTC NATIONAL BLEND
OF MODELS AND LATEST GUIDANCE FROM THE 00 UTC GUIDANCE CYCLE MAINLY
SEEMS IN LINE WITH THE FORECAST PLAN.
..WEATHER/HAZARDS HIGHLIGHTS
IT REMAINS WELL HERALDED IN GUIDANCE THAT EMERGING MOIST RETURN
FLOW FROM THE GULF OF MEXICO AS AMBIENT HIGH PRESSURE OVER THE
SOUTH RETREATS TO THE EAST WILL SUPPORT INCREASING COVERAGE OF
ENHANCED TO HEAVY SHOWERS AND THUNDERSTORMS FROM THE WEST-CENTRAL
GULF COAST STATES TO THE SOUTHERN APPALACHIANS AND PARTS OF THE
SOUTHEAST THIS WEEKEND THROUGH EARLY-MID NEXT WEEK. IN TERMS OF THE
WPC EXCESSIVE RAINFALL OUTLOOK, THE DAY 4/SUNDAY SLIGHT RISK AREA
HAS BEEN ADJUSTED SLIGHTLY TO THE EAST BY APPROXIMATELY A ROW OF
COUNTIES/PARISHES TO ACCOUNT FOR NEW TRENDS IN THE 12Z GUIDANCE
OVER THE ARKLAMISS REGION. THE DAY 5/MONDAY SLIGHT RISK HAS BEEN
TRIMMED SOME TO THE SOUTH WITH MOST OF THE HEAVIEST CONVECTIVE
RAINFALL LIKELY CONFINED CLOSER TO THE GULF COAST. THIS REGION WILL
BE IN A FAVORED RIGHT ENTRANCE REGION OF THE UPPER JET PATTERN TO
SUPPORT MULTIPLE ROUNDS OF CONVECTION, AS STRONG MOISTURE FLUX FROM
THE GULF CONTINUES AHEAD OF AN APPROACHING COLD FRONT. THERE MAY
ALSO BE SOME SEVERE WEATHER THAT DEVELOPS IN THE WARM SECTOR OF
THIS LOW PRESSURE SYSTEM, AND THIS IS BEING MONITORED BY THE STORM
PREDICTION CENTER.
LATER IN THE FORECAST PERIOD, THE MODERATE TO HEAVY RAIN AND
CONVECTIVE FOCUS IS EXPECTED TO ENCOMPASS MORE OF THE SOUTHEAST
AND UP ACROSS THE EAST COAST WITH SYSTEM TRANSLATION THROUGH THE
MIDDLE OF NEXT WEEK. COLDER AIR ON THE NORTHERN PERIPHERY OF THIS
BROAD SYSTEM AND ADDITIONAL NORTHERN STREAM ENERGIES WILL LIKELY
HERALD THE RETURN TO LAKE EFFECT SNOW BY WEDNESDAY AND INTO
THURSDAY WITH STRONG COLD AIR ADVECTION ACROSS THE GREAT LAKES.
UPSTREAM, MODERATELY HEAVY TERRAIN ENHANCED PRECIPITATION IS
EXPECTED TO DEVELOP THIS WEEKEND OVER THE PACIFIC NORTHWEST WITH
ENERGETIC UPPER TROUGH PASSAGE AND LONG LEAD MOISTURE FEED.
TERRAIN ENHANCED SNOWS WILL THEN SPREAD INCREASINGLY INLAND ACROSS
THE NORTHWEST TO THE NORTH-CENTRAL ROCKIES AND EVENTUALLY SPREAD
LIGHTER WINTER PRECIPITATION OVER THE NORTHERN PLAINS/UPPER MIDWEST WITH
COLD FRONTAL PASSAGE OVER/OUT FROM THE WEST INTO EARLY-MID NEXT
WEEK. EXPECT A WARMING TREND AHEAD OF THE FRONT OUT FROM THE WEST
THIS WEEKEND/EARLY NEXT WEEK PRIOR TO COLD FRONTAL AND SECONDARY
SEASONAL SURGES ACROSS MOST OF THE CENTRAL TO EASTERN U.S.
SCHICHTEL/HAMRICK
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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