188
FXUS02 KWBC 270713
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
212 AM EST TUE DEC 27 2022
VALID 12Z FRI DEC 30 2022 - 12Z TUE JAN 03 2023
...MULTIPLE ROUNDS OF PRECIPITATION ARE LIKELY IN THE WEST WITH
LOWER ELEVATION HEAVY RAIN/FLOODING AND HIGHER ELEVATION HEAVY
SNOW...
...HEAVY RAINFALL AND FLOODING ARE POSSIBLE ACROSS THE GULF COAST
STATES LATE THIS WEEK WITH A HEAVY RAIN THREAT REEMERGING OVER THE
LOWER MISSISSIPPI VALLEY IN EARLY 2023...
..OVERVIEW
THE MEDIUM RANGE PERIOD BEGINS FRIDAY WITH UPPER TROUGHING ACROSS
THE CENTRAL U.S. THAT SHOULD LIFT OVER THE WEEKEND. AHEAD OF THIS
TROUGH AND FRONTAL SYSTEMS AT THE SURFACE, GULF MOISTURE WILL
STREAM INTO THE EASTERN THIRD OF THE U.S. THROUGH LATE WEEK
CAUSING POTENTIALLY HEAVY RAINFALL AND POSSIBLE FLOODING WITH A
FOCUS ACROSS THE GULF COAST STATES. NOTABLY WARMER THAN AVERAGE
TEMPERATURES WILL ENSURE THAT MOST OF THIS PRECIPITATION FALLS AS
RAIN EVEN IN MUCH OF THE NORTHERN TIER. MEANWHILE IN THE WEST,
CONSIDERABLE MOISTURE INFLUX FROM A LONG FETCH OF PACIFIC MOISTURE
WILL LEAD TO ADDITIONAL PRECIPITATION LATE WEEK, WITH FLOODING
CONCERNS IN LOWER ELEVATIONS OF CALIFORNIA IN PARTICULAR AND HEAVY
SNOW ACROSS MUCH OF THE HIGHER ELEVATIONS. BY THE START OF 2023
EARLY NEXT WEEK, A SURFACE LOW PRESSURE SYSTEM COULD CONSOLIDATE
AROUND AS THE CENTRAL HIGH PLAINS IN RESPONSE TO ANOTHER UPPER
TROUGH, AND LIFT NORTHEAST ACROSS THE CENTRAL U.S. TO MIDWEST FOR
INCREASING CHANCES OF SNOW/WINTRY WEATHER ON THE BACKSIDE AND
ANOTHER ROUND OF POSSIBLY HEAVY RAIN CENTERED OVER THE LOWER
MISSISSIPPI VALLEY REGION AROUND MONDAY.
..GUIDANCE/PREDICTABILITY ASSESSMENT
RECENT MODEL CYCLES HAVE KEPT WITH THE PATTERN OF RELATIVELY GOOD
AGREEMENT WITH THE LARGE SCALE PATTERN OF CENTRAL U.S. TROUGHING
WITH UPPER RIDGING AHEAD OF IT IN THE EASTERN U.S. LATE WEEK
LIFTING BY EARLY NEXT WEEK, WHILE ANOTHER TROUGH DIGS INTO THE
WESTERN U.S. SUNDAY AND TRAVERSES EASTWARD. BUT THERE ARE STILL
SOME DIFFERENCES IN THE DETAILS LIKE EXACT SHORTWAVE/LOW
PRESSURE/FRONTAL PLACEMENTS. A FAIRLY TYPICAL MODEL BLEND WAS THUS
EMPLOYED FOR THE WPC FORECAST, FAVORING A MULTI-MODEL BLEND OF THE
DETERMINISTIC GUIDANCE EARLY ON AND A TRANSITION TO AROUND HALF
DETERMINISTIC MODELS/HALF GEFS AND EC ENSEMBLE MEANS BY THE END OF
THE PERIOD. THIS SERVED TO MINIMIZE THE DETAIL DIFFERENCES AND
PROVIDE A MIDDLE GROUND FORECAST. THE MAIN OUTLIER SEEN WAS THE
12Z CMC THAT SHOWED A SLOWER TRACK WITH THE SECOND TROUGH MOVING
ACROSS THE WESTERN HALF OF THE U.S. AND EXHIBITING A CLOSED LOW
WITHIN THE TROUGH. THE NEWER 00Z CMC SEEMS TO HAVE COME INTO
BETTER ALIGNMENT IN TIMING WITH THE REST OF THE GUIDANCE.
..WEATHER/HAZARD HIGHLIGHTS
A SERIES OF PACIFIC FRONTS/SYSTEMS SHOULD CONTINUE TO SUSTAIN A
MULTI-DAY HEAVY PRECIPITATION EVENT ACROSS THE WESTERN U.S. WHILE
THE STRONGEST ATMOSPHERIC RIVER EXPECTED IS NOW FULLY WITHIN THE
SHORT RANGE PERIOD, ADDITIONAL ROUNDS OF HEAVY RAINFALL ALONG
COASTAL AREAS MAY CAUSE FLOODING PROBLEMS IN AREAS THAT WILL BE
HYDROLOGICALLY SENSITIVE BY THAT TIME. SLIGHT RISK AREAS ARE SHOWN
IN BOTH THE DAYS 4 AND 5 EXPERIMENTAL EXCESSIVE RAINFALL OUTLOOKS
ACROSS COASTAL CALIFORNIA AND ALONG THE FOOTHILLS OF THE SIERRA
NEVADA DUE TO BOUTS OF HEAVY RAIN MOVING IN DURING THOSE DAYS.
ONCE THE RAIN GETS INTO SOUTHERN CALIFORNIA SATURDAY, BURN SCARS
ACROSS THAT REGION WILL BE PARTICULARLY VULNERABLE TO FLOODING.
ADDITIONALLY, SIGNIFICANT SNOW AMOUNTS ARE LIKELY IN HIGHER
ELEVATIONS OF THE WEST THROUGH THE LATTER PART OF THE WEEK AND
INTO THE WEEKEND. EXACT TIMING AND PLACEMENT DETAILS OF THE
HEAVIEST PRECIPITATION STILL SHOW SOME DIFFERENCES, SO CONTINUE TO
MONITOR FORECASTS FOR SPECIFICS AS THE DETAILS COME INTO BETTER
FOCUS OVER COMING DAYS. HOWEVER, THERE IS A GENERAL TREND OF
PRECIPITATION LIGHTENING IN NORTHERN AREAS BY THE WEEKEND WHILE
THE BETTER FOCUS FOR PRECIPITATION BECOMES ACROSS CALIFORNIA
THROUGH THE CENTRAL/SOUTHERN GREAT BASIN AND THE SOUTHWEST. AFTER
THAT BRIEF BREAK, ANOTHER ROUND OF PRECIPITATION IS FORECAST FOR
THE WEST COAST STATES BY MONDAY.
EAST OF THE ROCKIES, DEVELOPING MOISTURE INFLOW FROM THE GULF OF
MEXICO INTO THE MISSISSIPPI VALLEY AND VICINITY AHEAD OF ONE OR
MORE PLAINS LOW PRESSURE/FRONTAL SYSTEMS AND SUPPORTING UPPER
TROUGH WILL LEAD TO INCREASING COVERAGE AND INTENSITY OF
PRECIPITATION, MOST OF IT RAIN. WITHIN THIS EXPANDING MOISTURE
SHIELD, RAINFALL COULD BECOME HEAVY WITH HIGHEST RAINFALL TOTALS
CURRENTLY EXPECTED THURSDAY ACROSS THE CENTRAL GULF COAST REGION,
WHERE A SLIGHT RISK OF EXCESSIVE RAINFALL IS IN PLACE FOR THESE
AREAS AS INSTABILITY COULD PRODUCE HIGH RAINFALL RATES THAT MAY
CAUSE FLOODING/FLASH FLOODING. NORTH OF THERE, PROGRESSION OF A
POTENTIAL PLAINS INTO GREAT LAKES SYSTEM NEXT WEEKEND SHOULD
SPREAD MOISTURE THROUGH THE REST OF THE EAST AS MOISTURE STREAMS
NORTHWARD, BUT WITH MAXIMUM RAINFALL TOTALS LOWER. MOST
PRECIPITATION SHOULD STAY RAIN BUT WITH SOME CHANCE OF MINOR SNOW
ACCUMULATIONS IN THE UPPER MIDWEST AND THE HIGHEST PEAKS OF THE
INTERIOR NORTHEAST. BETTER BUT STILL UNCERTAIN CHANCES FOR SNOW
MAY BE ACROSS THE CENTRAL HIGH PLAINS BY SUNDAY AND SPREADING INTO
THE NORTH-CENTRAL U.S. MONDAY AS ANOTHER UPPER TROUGH PROVIDES
COLDER AIR THERE, AND THERE ARE INCREASING PROBABILITIES FOR A LOW
PRESSURE SYSTEM TO CONSOLIDATE AND LIFT TOWARD THE MIDWEST.
FARTHER SOUTH THE COLD FRONT ASSOCIATED WITH THIS LOW COULD
PROVIDE A FOCUS FOR ANOTHER BOUT OF HEAVY RAIN ACROSS PARTS OF THE
MISSISSIPPI VALLEY BY MONDAY-TUESDAY.
AFTER THE RECENT COLD SPELL, THE TEMPERATURE PATTERN IN THE MEDIUM
RANGE PERIOD WILL SIGNIFICANTLY CHANGE ACROSS MUCH OF THE NATION.
WARMER THAN AVERAGE TEMPERATURES WILL BE WIDESPREAD ACROSS THE
EASTERN HALF OF THE COUNTRY LATE THIS WEEK INTO EARLY NEXT WEEK,
WITH LOWS AROUND 15-25F ABOVE AVERAGE AND HIGHS AROUND 10-20F
ABOVE AVERAGE. DAILY RECORDS FOR WARM LOWS MAY BE WIDESPREAD AS
THE WARMEST AIR REACHES THE EAST, WHILE A FEW ISOLATED DAILY
RECORD HIGHS CANNOT BE RULED OUT. THOUGH MEANWHILE IN THE WEST,
THE WET/SNOWY PATTERN WILL TEND TO KEEP DAYTIME TEMPERATURES
AROUND 5-10F BELOW NORMAL. LOWS SHOULD GENERALLY BE A BIT ABOVE
AVERAGE UNTIL EARLY NEXT WEEK AS THE SECOND LARGE-SCALE UPPER
TROUGH MOVES THROUGH, BRINGING LOWS WITHIN A FEW DEGREES OF NORMAL.
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, EXPERIMENTAL EXCESSIVE RAINFALL
OUTLOOK, WINTER WEATHER OUTLOOK PROBABILITIES AND HEAT INDICES 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
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