011
FXUS02 KWBC 171914
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
214 PM EST FRI JAN 17 2025
VALID 12Z MON JAN 20 2025 - 12Z FRI JAN 24 2025
...STRONG ARCTIC SURGE WILL MOVE FROM THE CENTRAL U.S. INTO THE
SOUTH/EAST NEXT WEEK...
...CONFIDENCE INCREASING FOR A SOUTHERN TIER WINTER STORM MONDAY-
TUESDAY...
..OVERVIEW
MODELS AND ENSEMBLES CONTINUE TO SHOW A VERY AMPLIFIED MEAN
PATTERN EARLY NEXT WEEK CONSISTING OF A DEEP UPPER TROUGH OVER MUCH
OF THE LOWER 48 AND AN EASTERN PACIFIC RIDGE. CONFIDENCE REMAINS
HIGH IN A SURGE OF ARCTIC AIR PROGRESSING FROM THE CENTRAL U.S. TO
THE EAST EARLY-MID NEXT WEEK DUE TO THIS TROUGH ALOFT AND COLD HIGH
PRESSURE AT THE SURFACE. THIS TROUGH SHOULD LIFT NORTH AND EAST AS
THE WEEK PROGRESSES FOR GRADUALLY MODERATING TEMPERATURES, BUT
TROUGHING IS FORECAST TO RELOAD IN THE CENTRAL U.S. FOR LATER WEEK.
SYSTEMS ON THE SOUTHERN PERIPHERY OF THIS PATTERN WILL CAUSE
PRECIPITATION FROM THE SOUTHERN PLAINS TO SOUTHEAST. THERE IS
GRADUALLY INCREASING CONFIDENCE IN A WINTER STORM ACROSS THE
SOUTHERN TIER, WHICH COULD PRODUCE SNOW/SLEET CLOSE TO THE
WESTERN/CENTRAL GULF COAST ACROSS THE SOUTHEAST AND CAROLINAS, WITH
NOTABLE FREEZING RAIN POSSIBLE FROM THE FLORIDA PANHANDLE JUST
NORTH. THERE IS STILL UNCERTAINTY WITH THE WINTRY PRECIPITATION
AMOUNTS AND AXIS THOUGH. ANOTHER, EVEN MORE UNCERTAIN, ROUND OF
PRECIPITATION IS POSSIBLE ACROSS THE SOUTHERN TIER LATER NEXT WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
BY THE MEDIUM RANGE TIME FRAME THERE IS MORE TYPICAL MODEL SPREAD
COMPARED TO THE PAST COUPLE OF DAYS, WITH DETAIL DIFFERENCES EARLY
ON AND INCREASING SPREAD IN THE MEDIUM TO LARGER SCALE PATTERN AS
THE PERIOD PROGRESSES. EARLY IN THE WEEK, A SHORTWAVE TRACKING
ACROSS THE SOUTHERN TIER SHOWS SOME SPREAD THAT IS MINOR BUT DOES
CREATE SOME SENSIBLE WEATHER DIFFERENCES LIKE AMOUNTS AND TYPE OF
PRECIPITATION. A MULTI-MODEL BLEND FAVORING THE GFS AND ECMWF
SEEMED LIKE THE BEST APPROACH FOR AN INTERMEDIATE FORECAST.
BY MIDWEEK, THE NEXT POTENT SHORTWAVE WILL BE DIGGING INTO THE
NORTHERN ROCKIES OR SO WHILE A POSSIBLE COMPACT CLOSED LOW IN THE
EASTERN PACIFIC MAY OR MAY NOT GET ABSORBED BACK INTO THE MEAN
FLOW. GFS RUNS AND THE GEFS MEAN FROM 00Z AND 06Z MAINTAINED A
BRIEF RIDGE AXIS IN BETWEEN THE INITIAL TROUGH IN THE EAST AND THE
DIGGING ONE IN THE WEST-CENTRAL CONUS. THIS ALLOWS FOR MORE GULF
MOISTURE TO FLOW INTO THE SOUTH FOR MID-LATE WEEK, AND GFS/GEFS
BASED GUIDANCE AND THE NBM WERE AGGRESSIVE IN SHOWING AMPLE
PRECIPITATION THERE. THIS WPC FORECAST DID DECREASE PRECIPITATION
AMOUNTS COMPARED TO THE NBM FOR WEDNESDAY-THURSDAY, BUT NOW THE 12Z
GFS AND GEFS HAVE TRENDED TOWARD MORE ZONAL FLOW AND THUS DRIER.
THIS IS MORE LIKE THE OTHER GUIDANCE, SO EXPECT THE NEXT ISSUANCE
OF NBM AND WPC QPF MAY DECREASE EVEN MORE.
HOWEVER, 00Z/06Z GFS RUNS DID SEEM TO BE A GOOD MIDDLE GROUND WITH
THE TROUGH AXIS MOVING SLOWLY EASTWARD INTO THE CENTRAL U.S.
THURSDAY-FRIDAY AND MATCHED THE ENSEMBLE MEANS BEST COMPARED TO THE
MORE PROGRESSIVE 00Z CMC AND MUCH SLOWER 00Z ECMWF (THE ECMWF WAS
SLOWER THAN MANY OF THE EC-BASED AI/ML MODELS AS WELL). THERE WAS
SOME MINOR MODEL CONVERGENCE IN THE NEWER 12Z RUNS TOWARD A MIDDLE
GROUND SOLUTION ON TROUGH TIMING, BUT STILL SOME NOTABLE
DIFFERENCES. OVERALL THE WPC FORECAST DECREASED THE PROPORTION OF
DETERMINISTIC GUIDANCE AS THE MEDIUM RANGE PERIOD PROGRESSED IN
FAVOR OF THE ENSEMBLE MEANS (60 PERCENT MEANS BY DAY 6 AND 80
PERCENT BY DAY 7) CONSIDERING THE INCREASING SPREAD.
..WEATHER/HAZARDS HIGHLIGHTS
BY MONDAY, A BROAD AREA OF HAZARDOUSLY COLD ARCTIC AIR WILL
ALREADY COVER THE CENTRAL TO EASTERN U.S. WITH DAYTIME HIGHS AT
LEAST 20F BELOW NORMAL FOR MOST. THE COLDEST ANOMALIES ARE LIKELY
TO BE OVER THE HIGH PLAINS AND VICINITY WHERE HIGHS COULD BE 25-35F
BELOW NORMAL. COLDEST TEMPERATURES ON AN ABSOLUTE BASIS THOUGH
SHOULD BE OVER NORTHERN PLAINS AND UPPER MIDWEST WHERE HIGHS WELL
BELOW ZERO AND LOWS IN THE -20S ARE LIKELY EARLY IN THE WEEK. WIND
CHILLS SHOULD BE EVEN COLDER AND MORE DANGEROUS. THE NORTHERN-
CENTRAL ROCKIES/PLAINS SHOULD MODERATE CONSIDERABLY BY TUESDAY-
WEDNESDAY (THOUGH WITH A POTENTIAL FOR GUSTY WINDS) WHILE
ANOMALOUSLY COLD WEATHER MAY PERSIST INTO WEDNESDAY AND POSSIBLY TO
SOME EXTENT THURSDAY ACROSS THE SOUTH AND EAST. THE WEST ON THE
OTHER HAND CAN EXPECT NEAR NORMAL TEMPERATURES GRADUALLY WARMING TO
SLIGHTLY ABOVE NORMAL.
A SHORTWAVE MOVING FROM THE FOUR CORNERS THROUGH THE SOUTHERN TIER
MONDAY-WEDNESDAY WILL PROVIDE SUPPORT FOR PRECIPITATION ACROSS THE
SOUTH AS MOISTURE OVERRUNS A FRONT OR TWO IN THE GULF. GIVEN THE
COLD AIRMASS IN PLACE, THE MAJORITY OF THE PRECIPITATION WILL BE
WINTRY, PERHAPS ALL THE WAY TO THE GULF COAST. SOUTHERN TIER SNOW
POTENTIAL CONTINUES TO SHOW UP IN THE WINTER WEATHER PROBABILITIES
FOR 0.25 INCH LIQUID IN THE FORM OF SNOW, 10-20 PERCENT OVER AN
AREA JUST NORTH OF THE WESTERN GULF COAST FOR THE EARLY MONDAY-
EARLY TUESDAY PERIOD AND 10-50 PERCENT ACROSS A MUCH BROADER SWATH
OF THE SOUTH INTO SOUTHERN MID- ATLANTIC EARLY TUESDAY INTO EARLY
WEDNESDAY. ADDITIONALLY, FREEZING RAIN/ICE REMAINS A CONCERN GIVEN
THE POSSIBILITY OF A WARM NOSE ATOP ARCTIC COLD AIR, WHICH IS MOST
LIKELY IN THE FLORIDA PANHANDLE INTO SOUTHERN GEORGIA AND COASTAL
SOUTH CAROLINA. WPC KEY MESSAGES ARE SET TO BEGIN FOR THIS SOUTH
WINTER STORM THIS AFTERNOON. JUST TO THE SOUTH OF THE WINTER
CONCERNS, RAIN TOTALS ARE INCREASING ACROSS FLORIDA MONDAY AND
ESPECIALLY TUESDAY. THERE MAY BE ENOUGH CONFIDENCE FOR A MARGINAL
RISK IN FUTURE CYCLES FOR TUESDAY'S ERO, BUT AT THIS POINT, THERE
IS STILL UNCERTAINTY IF THIS RAIN WILL CAUSE FLASH FLOODING AS SOME
MODELS ARE MUCH MORE BULLISH THAN OTHERS WITH THE RAIN AMOUNTS. IT
WILL ALSO DEPEND ON RAIN RATES AND THE POTENTIAL FOR REPEATED
ROUNDS OF RAIN OVER THE SAME AREAS.
FARTHER NORTH, THE PATTERN WILL BE FAVORABLE FOR LAKE EFFECT SNOW
ACROSS/DOWNWIND OF THE GREAT LAKES ESPECIALLY MONDAY-TUESDAY, WITH
THE HIGHEST AMOUNTS OFF OF LAKE ONTARIO. BY MID-LATE NEXT WEEK,
PRECIPITATION MAY INCREASE ACROSS THE SOUTH AGAIN INCLUDING SOME
WINTER WEATHER, BUT MODELS HAVE SHOWN CONSIDERABLE VARIATIONS WITH
THAT POTENTIAL, SO WILL CONTINUE TO MONITOR.
THE MEAN UPPER RIDGE IN THE WEST COAST WILL KEEP PRECIPITATION
AMOUNTS LOW AND LIMITED TO THE PACIFIC NORTHWEST. FARTHER INLAND
THE NORTHERN/CENTRAL ROCKIES COULD SEE LIGHT SNOW AT TIMES WITH
UNCERTAIN SNOW SHOWERS ALSO POSSIBLE FARTHER EAST INTO THE HIGH
PLAINS. ALSO OF NOTE, A PATTERN FAVORABLE FOR STRONGER OFFSHORE
WINDS IS POSSIBLE ACROSS SOUTHERN CALIFORNIA AND VICINITY AROUND
MONDAY-TUESDAY WHICH WILL INCREASE FIRE WEATHER CONCERNS. CONTINUE
TO MONITOR STORM PREDICTION CENTER FIRE WEATHER FORECASTS FOR
FURTHER INFORMATION.
TATE/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 (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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