131
FXUS02 KWBC 191901
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
200 PM EST TUE DEC 19 2023
VALID 12Z FRI DEC 22 2023 - 12Z TUE DEC 26 2023
...HEAVY RAIN THREAT FOR ARIZONA FRIDAY EMERGES OVER THE
SOUTH-CENTRAL U.S. THROUGH THE HOLIDAYS...
...HEAVY SNOW THREAT FROM THE GREAT BASIN/ROCKIES TO THE
NORTH-CENTRAL PLAINS THIS WEEKEND INTO CHRISTMAS...
..OVERVIEW
A CLOSED UPPER TROUGH/LOW WILL DIG SOUTHEASTWARD OFF CALIFORNIA
BEFORE WORKING INLAND THROUGH BAJA TO THE SOUTHWEST BY SATURDAY.
THIS WILL BRING PERIODS OF LEADING/WRAPPING ENHANCED MOISTURE AND
PRECIPITATION INTO THE SOUTHWEST. THE EJECTION OF THE DYNAMIC
SYSTEM WILL SPAWN DOWNSTREAM SOUTH-CENTRAL PLAINS HOLIDAY
CYCLOGENESIS/FRONTOGENESIS. RETURN MOISTURE AND INSTABILITY WILL
FUEL AN EMERGING AREA OF ENHANCED RAINS AND CONVECTION WITH BROAD
FOCUS OVER THE SOUTH-CENTRAL U.S. STATES. MEANWHILE, A THREAT OF
HEAVY SNOW IS EXPECTED TO DEVELOP ON THE BACKSIDE OF THE SYSTEM
FROM THE GREAT BASIN/ROCKIES INTO SATURDAY TO THE NORTH-CENTRAL
PLAINS IN TIME FOR CHRISTMAS EVE AND CHRISTMAS.
..GUIDANCE/PREDICTABILITY ASSESSMENT
THE CURRENT 00/06Z GUIDANCE DOES A DECENT JOB OF RESOLVING THE
EVOLUTION OF THE UPPER TROUGH AS IT PROPAGATES THROUGH THE WEST
THROUGH DAY 4. THE BULK OF THE UNCERTAINTY BEGINS ON DAY 5 WHEN NO
TWO DETERMINISTIC MODELS' 500 HEIGHTS RESEMBLE THE OTHER. THERE'S
LITTLE TO NO RUN-TO-RUN CONSISTENCY IN THE EC AND GFS GUIDANCE AS
WELL. THIS IS REFLECTED IN THE CURRENT QPF AND DAYS 4/5 EROS. THIS
DETERMINISTIC DISPERSION SPILLS INTO DAYS 6 AND 7 WHICH IS WHY THE
BLEND LEANS HEAVILY INTO THE ENSEMBLE MEANS BEGINNING DAY 6. THE
CURRENT BLEND CONSISTS OF A GENERAL MODEL BLEND CONSISTING OF THE
00Z EC/CMC/UKMET AND 06Z GFS ON DAYS 3-5 WITH LESS WEIGHTING
TOWARD THE 06Z GFS ON DAY 4 DUE TO A SLIGHT OVER AMPLIFICATION OF
THE WESTERN TROUGH COMPARED TO THE REST OF THE GUIDANCE. THE 00Z
GFS WAS USED ON DAY 6 BECAUSE IT CLUSTERED WELL WITH THE ENSEMBLE
MEAN GUIDANCE.
..WEATHER/HAZARDS HIGHLIGHTS
ORGANIZED RAINS AND TERRAIN/MOUNTAIN SNOWS ARE SET TO WORK INLAND
INTO THE SOUTHWEST AND THE SOUTH-CENTRAL GREAT BASIN/ROCKIES
HEADING INTO THE WEEKEND WITH CLOSED SYSTEM APPROACH AND PASSAGE.
A WPC EXCESSIVE RAINFALL OUTLOOK (ERO) MARGINAL RISK AREA REMAINS
IN PLACE FROM THE CALIFORNIA DESERTS TO ARIZONA FOR DAY 4/FRIDAY
ON THE WARMER/RAINY SIDE OF THE SYSTEM. AGAIN CONSIDERED A SLIGHT
RISK FOR PARTS OF ARIZONA GIVEN THE PRECIPITABLE WATER ANOMALIES
LOOK TO BE WELL OVER THE 90TH IF NOT 95TH PERCENTILE FOR THIS TIME
OF YEAR AND THE AMPLE DIVERGENCE ALOFT WITH THE UPPER LOW, BUT
WITH SOMEWHAT DRY ANTECEDENT CONDITIONS AND A SEEMINGLY LACK OF
NOTABLE INSTABILITY. THEN, SYSTEM/ENERGY DOWNSTREAM PROPAGATION IS
SLATED TO GENERATE AN EMERGING WET PATTERN WITH POTENTIAL FOR SOME
STRONG CONVECTION FOR THE HOLIDAY WEEKEND FROM THE SOUTH-CENTRAL
PLAINS INTO THE LOWER MISSISSIPPI VALLEY AND CENTRAL GULF COAST
STATES TO MONITOR WITH SYSTEM GENESIS GIVEN RETURN MOISTURE INFLOW
SIGNAL IN GUIDANCE AND UPPER SUPPORT. THE NORTHWARD EXPANSION OF
THE BROAD PRECIPITATION SHIELD WITH FRONTAL WAVE PROPAGATION IS
LIKELY TO SPREAD MODERATE PRECIPITATION AMOUNTS UP THOUGH THE
PLAINS/MISSISSIPPI VALLEY/MIDWEST, WITH A MORE BLOCKY EASTERN U.S.
SURFACE RIDGE HOLDING DOWNSTREAM. THIS COULD INCLUDE SOME NORTHERN
TIER WINTRY PRECIPITATION TO INCLUDE A THREAT FOR MEANINGFUL SNOW
FOR THE NORTH-CENTRAL HIGH PLAINS.
TEMPERATURES SHOULD TREND QUITE WARM ACROSS THE CENTRAL U.S.,
ESPECIALLY INTO THE NORTHERN PLAINS AND UPPER MIDWEST NEXT
WEEKEND. DAYTIME HIGHS COULD BE 20 TO 25 DEGREES ABOVE NORMAL IN
THIS REGION, WHILE LOWS OF 25-35 DEGREES ABOVE AVERAGE ARE
EXPECTED. A FEW RECORD HIGHS ARE FORECAST WHILE RECORD WARM
MINIMUM TEMPERATURES MAY BE WIDESPREAD. ELSEWHERE, DAYTIME HIGH
ANOMALIES RETURN BACK TO NORMAL ACROSS THE EAST AS UPPER RIDGING
BUILDS AND UPPER TROUGHING INTO THE WEST SHOULD RESULT IN A
COOLING TREND LATER THIS WEEK AND ESPECIALLY BY THE WEEKEND.
KEBEDE/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, 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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