789
FXUS02 KWBC 171852
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
152 PM EST WED JAN 17 2024
VALID 12Z SAT JAN 20 2024 - 12Z WED JAN 24 2024
...ANOTHER ARCTIC AIRMASS PUSHES INTO THE CENTRAL U.S. THIS
WEEKEND, BUT NOT AS EXTREME AS THE FIRST ONE...
...MULTIPLE ROUNDS OF POTENTIALLY HEAVY PRECIPITATION WILL AFFECT
THE WEST...
...HEAVY RAIN POTENTIAL INCREASES ACROSS THE SOUTH-CENTRAL U.S.
NEXT WEEK...
..OVERVIEW
THE BROAD AND DEEP UPPER TROUGHING THAT HAS DOMINATED THE PATTERN
OVER THE LOWER 48 THIS WEEK SHOULD FINALLY GET SHUNTED EAST THIS
WEEKEND AS AN UPPER RIDGE AXIS MOVES FROM THE INTERMOUNTAIN WEST
SATURDAY INTO THE CENTRAL U.S. SUNDAY AND TOWARD THE EAST EARLY
NEXT WEEK. NORTHWESTERLY FLOW AHEAD OF THE RIDGE WILL BRING IN
ANOTHER ARCTIC SURFACE HIGH, PRODUCING MUCH BELOW NORMAL
TEMPERATURES ACROSS THE CENTRAL AND EASTERN U.S. THIS WEEKEND.
WHILE TEMPERATURES ARE FORECAST TO BE GENERALLY BE 15-30F BELOW
AVERAGE, THIS SECOND ROUND OF COLD TEMPERATURES SHOULD BE LESS
EXTREME THAN THE RECENT COLD WAVE AT MOST LOCATIONS. MEANWHILE,
UPPER TROUGHING WITH MULTIPLE EMBEDDED SHORTWAVES WILL BE ATOP THE
WESTERN HALF OF THE U.S., LEADING TO MULTIPLE ROUNDS OF
PRECIPITATION IN THE WEST THIS WEEKEND INTO NEXT WEEK.
ADDITIONALLY, FOR THE EARLY PART OF NEXT WEEK, RETURN FLOW FROM
THE GULF OF MEXICO COULD LEAD TO HEAVY RAIN ACROSS THE
SOUTH-CENTRAL U.S., WITH SOME WINTRY WEATHER POSSIBLE ON THE
NORTHERN SIDE OF THE PRECIPITATION SHIELD AROUND THE GREAT LAKES
EVEN AS TEMPERATURES WARM.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODEL AGREEMENT ON THE UPPER LEVEL PATTERN IS PRETTY GOOD THIS
AFTERNOON. THE UPPER TROUGH IN THE EAST WILL SHIFT INTO THE
ATLANTIC WHILE A RIDGE FOLLOWS IN ITS WAKE. MEAN TROUGHING WILL
PERSIST OVER THE WEST COAST WITH SEVERAL EMBEDDED SHORTWAVES
MOVING ONSHORE TROUGHOUT THE PERIOD. THERE ARE SOME DIFFERENCES IN
THE HANDLING OF UPSTREAM ENERGY IN THE PACIFIC/GULF OF ALASKA THAT
WILL HAVE SOME AFFECT ON THE TIMING AND POSITION OF THESE
SHORTWAVES, BUT THESE DIFFERENCES FALL WITHIN TYPICAL SPREAD
EXPECTED IN THE MEDIUM RANGE PERIOD. BY TUESDAY-WEDNESDAY, ENERGY
MAY CONSOLIDATE TO DEVELOP AN UPPER LOW IN THE SOUTHWEST, POSSIBLY
SPLITTING AWAY FROM THE TROUGH INTO THE SOUTHERN STREAM. THIS WILL
CONTINUE TO BE MONITORED AS THE DETAILS ARE STILL NEBULOUS.
GIVEN GOOD GENERAL AGREEMENT OF THE MODEL GUIDANCE, THE WPC
FORECAST BEGAN WITH A MULTI-MODEL DETERMINISTIC BLEND AND WAS ABLE
TO MAINTAIN A BLEND OF PRIMARILY DETERMINISTIC RUNS THROUGHOUT THE
WHOLE PERIOD. THE GFS WAS FAVORED SLIGHTLY MORE IN THE BLEND EARLY
IN THE PERIOD BECAUSE IT HAS SHOWN HIGHER RUN TO RUN CONSISTENCY.
SOME GEFS AND EC ENSEMBLE MEANS WERE INCORPORATED THROUGH THE
LATTER HALF OF THE PERIOD TO SMOOTH OUT MODEL DIFFERENCES BUT
MAINTAIN SOME STRENGTH IN INDIVIDUAL SYSTEMS.
..WEATHER/HAZARDS HIGHLIGHTS
THE WEST COAST STATES CAN EXPECT ROUNDS OF PRECIPITATION THIS
WEEKEND INTO EARLY NEXT WEEK. HEAVY RAIN MAY CAUSE LOCALIZED
FLOODING ISSUES FOR LOWER ELEVATION PORTIONS OF NORTHERN
CALIFORNIA ON SATURDAY, SO A MARGINAL RISK IS IN PLACE IN THE
EXCESSIVE RAINFALL OUTLOOK. SUNDAY LOOKS TO BE A BIGGER DAY FOR
HEAVY RAINFALL WITH A POTENT SHORTWAVE PROVIDING UPPER LEVEL
DYNAMICAL SUPPORT, PERIODS OF HIGH RAIN RATES (POSSIBLY REACHING
WELL OVER HALF AN INCH PER HOUR), AND SOME INSTABILITY SNEAKING
ONSHORE. ADDITIONALLY, A WET PERIOD LATE THIS WEEK COULD PRIME
SOILS AHEAD OF THIS EVENT. THUS A SLIGHT RISK IS IN PLACE IN THE
ERO FOR SUNDAY-SUNDAY NIGHT FOR PORTIONS OF NORTHERN CALIFORNIA.
THE SLIGHT AREA WAS EXPANDED A BIT SOUTHWARDS THIS AFTERNOON TO
ACCOUNT FOR A SOUTHWARD TREND IN MODEL GUIDANCE. MODELS VARY ON
HOW MUCH PRECIPITATION REACHES SOUTHERN CALIFORNIA--THE
GFS/GEFSMEAN/UKMET KEEP PRECIPITATION FARTHER NORTH WHILE THE
ECMWF/CMC RUNS HAVE PLENTY FARTHER SOUTH. PART OF COASTAL SOUTHERN
CALIFORNIA IS IN A MARGINAL RISK DUE TO THE RELATIVELY LOWER
PROBABILITIES GIVEN THE MODEL DISAGREEMENTS. THE PACIFIC NORTHWEST
WILL ALSO SEE PERIODIC PRECIPITATION, AND PARTS OF THE INTERIOR
NORTHWEST COULD HAVE SOME POSSIBLY PERSISTENT FREEZING RAIN THIS
WEEKEND. THE SIERRA NEVADA WILL LIKELY RECEIVE HEAVY SNOW WITH THE
PRECIPITATION ACTIVITY THIS WEEKEND INTO EARLY NEXT WEEK. SOME
SNOW IS ALSO LIKELY FARTHER INTO THE INTERMOUNTAIN WEST.
INCREASING MOISTURE AHEAD OF THE WESTERN U.S. TROUGHING WILL START
TO SPREAD RAIN INTO THE SOUTHERN PLAINS ON SUNDAY. HEAVY RAIN MAY
START OVER SOUTH TEXAS LATE SUNDAY NIGHT, SO A MARGINAL RISK AREA
HAS BEEN ADDED FOR THIS AREA ON THE DAY 5 EXCESSIVE RAINFALL
OUTLOOK. RAIN TOTALS ARE FORECAST TO QUICKLY RAMP UP ON MONDAY AND
TUESDAY FOR PARTS OF THE SOUTHERN PLAINS INTO THE LOWER
MISSISSIPPI VALLEY, AND THESE HEAVY TOTALS COULD PRODUCE FLASH
FLOODING CONCERNS, THOUGH BEYOND THE EXCESSIVE RAINFALL OUTLOOK
PERIOD. THE PRECIPITATION SHIELD WILL GRADUALLY SPREAD
NORTHEASTWARD ON MONDAY AND TUESDAY AND COULD CAUSE SOME WINTRY
WEATHER ON ITS NORTHERN SIDE. THE GREAT LAKES VICINITY IS MOST
LIKELY TO SEE WINTRY WEATHER OUT OF THIS PRECIPITATION, BUT
FREEZING RAIN OR MIXED PRECIPITATION CANNOT BE RULED OUT FARTHER
SOUTH, BUT WITH LOW CONFIDENCE IN THE DETAILS. ELSEWHERE, THE EAST
WILL GENERALLY BE DRY THROUGH THE PERIOD AFTER SOME LINGERING LAKE
EFFECT SNOW INTO SATURDAY.
ARCTIC HIGH PRESSURE WILL PROVIDE A REINFORCING SURGE OF COLD AIR
THAT SHOULD BE WELL INTO THE CENTRAL AND EASTERN U.S. BY SATURDAY.
TEMPERATURES 15-30 DEGREES BELOW NORMAL WILL BE WIDESPREAD ON
SATURDAY, AND THE HIGHEST POTENTIAL FOR HAZARDOUS COLD AND
DANGEROUS WIND CHILLS WILL BE ACROSS THE NORTH-CENTRAL PLAINS INTO
PARTS OF THE UPPER MIDWEST. LOCALIZED ANOMALIES MORE THAN 30F
BELOW NORMAL ARE POSSIBLE RIGHT UNDERNEATH THE HIGH IN THE
NORTH-CENTRAL PLAINS/MISSISSIPPI VALLEY, WITH LOW TEMPERATURES
NEAR OR BELOW -20F POSSIBLY SETTING RECORDS. WINDS WILL AT LEAST
BE WEAK RIGHT IN THE VICINITY OF THE HIGH TO LIMIT WIND CHILLS.
OVERALL THIS COLD EPISODE WILL STILL BE NOTABLE EVEN IF NOT QUITE
AS EXTREME AS THE CURRENT/RECENT COLD EVENT FOR MOST AREAS.
TEMPERATURES SHOULD STILL BE CHILLY ON SUNDAY BUT STARTING TO
MODERATE TOWARD NORMAL. THEN TEMPERATURES LOOK TO CONTINUE TO WARM
MONDAY-WEDNESDAY AS THE SURFACE HIGH SHIFTS INTO THE ATLANTIC AND
THE UPPER RIDGE ALLOWS FOR MORE SOUTHERLY FLOW. BY MIDWEEK, THE
EASTERN HALF OF THE COUNTRY SHOULD SEE ABOVE NORMAL TEMPERATURES,
AROUND 15-30F ABOVE AVERAGE FOR LOWS AND 10-20F ABOVE FOR HIGHS.
FROM THE ROCKIES WESTWARD, NEAR NORMAL TEMPERATURES FOR HIGHS AND
LOW TEMPERATURES AROUND 10-15F ABOVE NORMAL ARE EXPECTED.
DOLAN/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, 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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