091
FXUS02 KWBC 061859
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
159 PM EST MON JAN 6 2025
VALID 12Z THU JAN 09 2025 - 12Z MON JAN 13 2025
..ARCTIC BLAST PERSISTS FOR THE CENTRAL/EASTERN U.S. THIS WEEK
..OVERVIEW
LINGERING COLD NORTHWESTERLY FLOW WILL STILL SUPPORT GREAT LAKE
EFFECT SNOWS INTO LATER THIS WEEK. MEANWHILE, ORGANIZED
PRECIPITATION WILL RETURN LATER THIS WEEK AS A FRONTAL SYSTEM MOVES
INTO THE WEST AND LOW PRESSURE DEVELOPS OFF THE GULF COAST. THE
FRONTAL SYSTEM IN THE WEST WILL APPROACH THE COAST ON FRIDAY AND
MOVE ACROSS THE REGION THIS WEEKEND WITH WIDESPREAD PRECIPITATION
FROM THE NORTHWEST TO THE NORTHERN AND CENTRAL ROCKIES. THE
DOWNSTREAM GULF SYSTEM IS TRICKER GIVEN UNCERTAIN SOUTHERN STREAM
UPPER TROUGH ENERGY EJECTION FROM THE SOUTHWEST U.S./NORTHERN
MEXICO. THE PATTERN EVENTUALLY DOES SEEM TO SUPPORT THE DEVELOPMENT
OF WIDESPREAD PRECIPITATION FROM THE GULF COAST TO THE SOUTHEAST
LATE THIS WEEK, AND PRECIPITATION MAY SPREAD UP THE EAST COAST AS
IT MOVES OFFSHORE THIS WEEKEND. THERE IS A SIGNIFICANT AMOUNT OF
UNCERTAINTY SURROUNDING THE EVOLUTION OF THE SYSTEM OVER THE GULF
AND ESPECIALLY AS IT MOVES TOWARDS/UP THE EAST COAST AND WESTERN
ATLANTIC, AND THE TIMING AND LOCATION OF THIS SYSTEM WILL BE
IMPORTANT FOR DETERMINING IMPACTS.
..GUIDANCE/PREDICTABILITY ASSESSMENT
GUIDANCE CONTINUES TO STRUGGLE OVERALL WITH THE SPECIFICS
REGARDING THE TIMING, EVOLUTION, AND PHASING OF INDIVIDUAL WAVES
BETWEEN STREAMS DURING THE MEDIUM RANGE PERIOD (THURSDAY JAN 9 -
MONDAY JAN 13). HOWEVER, THE OVERALL PATTERN TENDS TO BE WELL-
REPRESENTED BY THE ENSEMBLE MEANS AND THE ENVELOPE OF THE
INDIVIDUAL DETERMINISTIC GUIDANCE, BEGINNING WITH AN UPPER-LEVEL
TROUGH OVER THE SOUTHWESTERN U.S. THAT EVENTUALLY LIFTS EAST-
NORTHEASTWARD OVER THE SOUTHEAST AND OFF THE EAST COAST THIS
WEEKEND AS INDIVIDUAL UPPER-LEVEL ENERGIES REINFORCE EXPANDING
BROAD-SCALE, POSITIVELY TILTED MEAN UPPER-TROUGHING OVER THE
CENTRAL/WESTERN U.S. BY EARLY NEXT WEEK. A MORE DETAILED REVIEW OF
THE INITIAL PATTERN REVEALS THE MORE COMPLICATED SPECIFICS OF THE
EVOLUTION OF THE SYSTEM THROUGH THE CENTRAL/EASTERN U.S., WITH THE
DETERMINISTIC GUIDANCE SUGGESTING THAT NORTHERN AND SOUTHERN STREAM
ENERGIES OVER THE NORTH-CENTRAL AND SOUTHWESTERN U.S.,
RESPECTIVELY, MAY EVENTUALLY PHASE TOGETHER OVER THE OHIO
VALLEY/SOUTHEAST BEFORE MOVING EASTWARD OFF THE EAST COAST. THE
EVOLUTION OF THIS ENERGY WILL HAVE IMPORTANT RAMIFICATIONS AT THE
SURFACE AS A LOW PRESSURE SYSTEM DEVELOPS IN THE GULF AND THEN
MOVES NORTHEASTWARD ALONG/EAST OF THE EAST COAST, WITH A PATH OF
POTENTIALLY IMPACTFUL WINTER PRECIPITATION FOLLOWING ALONG TO THE
NORTHWEST. WHILE THE PATH AND AREAL COVERAGE OF THIS WINTER
PRECIPITATION ARE HARDER TO PIN DOWN, THE GUIDANCE IS IN GOOD
AGREEMENT ON THE EVOLUTION OF THE SYSTEM INITIALLY AS IT TRACKS
ALONG THE GULF COAST AND LIFTS NORTHEASTWARD TOWARDS THE
SOUTHEASTERN U.S. COAST. THEREAFTER, SPECIFICS ON THE SYSTEM AND
ANY EVENTUAL HAZARDOUS WEATHER BECOME MUCH MORE UNCERTAIN. THE
LATEST 00Z GUIDANCE TRENDS SUGGESTS A LOW THAT WILL REMAIN WELL
OFFSHORE WHICH LOWERS THE CHANCES OF HAZARDOUS WEATHER FURTHER
NORTH ALONG THE EAST COAST THIS WEEKEND. HOWEVER, THE 12Z GFS IN
PARTICULAR WAS MUCH MORE AGGRESSIVE IN DEEPENING A COASTAL LOW
ALONG THE NORTHEASTERN U.S. WHICH WOULD NOT SURPASSINGLY LEAD TO
THE POTENTIAL FOR MUCH MORE SIGNIFICANT PRECIPITATION.
FOLLOWING THE DEPARTURE OF THIS SYSTEM, THE NEXT FEATURE OF
INTEREST WILL BE THE EVOLUTION OF SPLIT STREAM ENERGIES TO THE WEST
OVER THE WESTERN/CENTRAL U.S. AS THESE ENERGIES GENERALLY TEND TO
REINFORCE MEAN, BROAD-SCALE TROUGHING. A NORTHERN STREAM SYSTEM
LOOKS TO PASS ACROSS THE NORTH-CENTRAL U.S., THOUGH FOLLOWING
MULTIPLE FRONTAL PASSAGES INCLUDING THE LATEST EASTERN U.S. SYSTEM
OVER THE WEEKEND, THE MAIN RAMIFICATIONS OF THIS LATTER SYSTEM LOOK
TO BE A REINFORCEMENT OF A COLD, CANADIAN AIRMASS OVER THE COUNTRY
AMIDST GENERALLY DRY CONDITIONS EXCEPT FOR SOME LINGERING SNOWS IN
THE ROCKIES.
GIVEN THE NOTABLE DIFFERENCES WITH REGARDS TO THE SPECIFICS AND
HOW THE OVERALL PATTERN IS WELL-CAPTURED WITH RELATIVE DETAIL IN
THE ENSEMBLE MEANS, OPTED FOR AN UPDATED FORECAST BLEND THAT RELIES
ON THE 06Z GEFS/00Z ECENS MEANS WITH CONTRIBUTIONS EARLY IN THE
PERIOD FROM THE 06Z GFS AND 00Z ECMWF/CMC GUIDANCE WHILE THE
GUIDANCE FALLS WITHIN THE ENVELOPE OF THE ENSEMBLE MEANS. ONE TREND
TO MONITOR IS THAT WITH THE 00Z GUIDANCE THIS FAVORS LIMITED
PRECIPITATION ALONG THE NORTHEASTERN U.S., WHICH WOULD UNDOUBTEDLY
CHANGE IF THE FORECAST WERE TO TREND MORE IN LINE WITH THE 12Z GFS
OVER THE NEXT DAY.
..WEATHER/HAZARDS HIGHLIGHTS
LAKE EFFECT SNOWS WILL PERIODICALLY BE REJUVENATED BY DEEP COLD
SURGES INTO LATER THIS WEEK AS LIGHT TO MODEST PRECIPITATION WILL
FOCUS DOWN THROUGH THE ROCKIES AND NORTH-CENTRAL U.S. WITH SYSTEM
FRONTAL SYSTEM GENESIS. PRECIPITATION CHANCES WILL INCREASE OVER
THE SOUTHERN PLAINS, LOWER MISSISSIPPI VALLEY, AND GULF COAST BY
THURSDAY AS ENERGY FROM AN UPPER-LOW SPREADS NORTHEAST. ANOMALOUS
MOISTURE WILL FOCUS OVER THE WESTERN GULF COAST AS A LOW PRESSURE
SYSTEM STRENGTHENS OVER THE WESTERN GULF, AND HEAVY PRECIPITATION
WILL BE POSSIBLE IN PORTIONS OF TEXAS AND LOUISIANA. WHILE DEEPEST
INSTABILITY AND HEAVIEST RAINS MAY FOCUS OFFSHORE, GUIDANCE SHOWS
AMPLE WESTERN THEN CENTRAL GULF COAST STATE PRECIPITATION
POTENTIAL, SO MARGINAL RISK AREAS HAVE BEEN RETAINED FOR THE DAY
4/THURSDAY AND DAY 5/FRIDAY WPC EXCESSIVE RAINFALL OUTLOOKS TO
ACCOUNT FOR LOCALIZED FLOOD POTENTIAL.
WHILE THE GULF LOW STRENGTHENS, COLD AIR WELL IN PLACE OVER THE
SOUTHERN PLAINS/ARKLATEX WILL SUPPORT POTENTIALLY SIGNIFICANT SNOW
AND MIXED/ICY WINTRY PRECIPITATION INTO THURSDAY, SEE WPC'S KEY
MESSAGES FOR SOUTHERN U.S. WINTER STORM FOR MORE DETAILS.
TEMPERATURES WILL DROP BELOW FREEZING OVERNIGHT FOR MOST OF THE
STATE, AND EVEN PORTIONS OF SOUTH TEXAS COULD BE COLD ENOUGH FOR
SOME ICY PRECIPITATION. MORE UNCERTAIN WINTRY PRECIPITATION MAY
TRANSLATE WITH THE SYSTEM TOWARDS THE TENNESSEE VALLEY AND
CENTRAL/SOUTHERN APPALACHIANS/SOUTHEAST ON FRIDAY.
AS THE GULF SYSTEM PROGRESSES, PRECIPITATION MAY EXPAND
NORTHEASTWARD ACROSS THE EAST FRIDAY INTO SATURDAY. HEAVY
PRECIPITATION POTENTIAL WILL BE STRONGLY DEPENDENT ON THE TIMING
AND PLACEMENT OF THE LOW PRESSURE SYSTEM, WHICH IS HIGHLY UNCERTAIN
AT THIS TIME. IF THE LOW MOVES QUICKLY OFFSHORE AND STRENGTHENS
AWAY FROM THE COAST, THEN IMPACTS WILL BE LIMITED, AND IMPACTS WILL
BE MORE LIKELY WITH A SLOWER LOW THAT STRENGTHENS CLOSER TO THE
U.S. COASTLINE.
THE WEATHER PATTERN WILL FAVOR THE CONTINUATION OF WELL BELOW
NORMAL TEMPERATURES EAST OF THE ROCKIES THROUGH AT LEAST THIS
WEEKEND. TEMPERATURE ANOMALIES OF 10-20 DEGREES BELOW NORMAL ARE
LIKELY FROM THE SOUTHERN/CENTRAL PLAINS AND MID- MISSISSIPPI/OHIO
VALLEYS THROUGH THE APPALACHIANS, ESPECIALLY AS TEMPERATURES REMAIN
QUITE COLD THIS WEEK FOR SNOW COVERED AREAS FROM AN ONGOING MAJOR
LEAD WINTER STORM. THE COMBINATION OF COLDER TEMPERATURES/WIND
CHILLS IS MOST LIKELY TO BE POTENTIALLY DANGEROUS OVER THE SOUTHERN
PLAINS AND FROM THE OHIO VALLEY EASTWARD THROUGH THE MID-
ATLANTIC. MEANWHILE, UPPER RIDGING IN THE WESTERN U.S. WILL OFFER
SLIGHTLY ABOVE NORMAL TEMPERATURES PRIOR TO BREAKDOWN HEADING INTO
THE WEEKEND.
PUTNAM/SCHICHTEL
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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