599
AGUS76 KRSA 240423
HMDRSA
HYDROMETEOROLOGICAL DISCUSSION
NATIONAL WEATHER SERVICE / CALIFORNIA NEVADA RFC / SACRAMENTO CA
825 PM PST TUE DEC 23 2025
..WIDESPREAD MDT/HVY PRECIP SPREADS ACROSS THE AREA ON WEDNESDAY
..BEST TOTALS OVER TRANSVERSE RANGES NEXT 24 HOURS
..ANOTHER ROUND OF PRECIP CHRISTMAS DAY INTO FRIDAY
METEOROLOGICAL CONDITIONS (SHORT TERM: TUE PM - THU AM)
A DEEPENING SFC LOW OFF THE WEST COAST DOWN TO ABOUT 993-MB IS
CONTINUING TO MOVE TO THE NORTH-NORTHEAST AND WILL MOVE FROM ITS
CURRENTLY LOCATION WEST OF THE SF BAY AREA TO NEAR THE CA/OR BORDER
TOMORROW MORNING WHEN IT WILL BOTTOM OUT AROUND 989-MB. THIS WILL
GENERATE INCREASING SOUTH TO SOUTHEAST LOW-LEVEL FLOW...VEERING TO A
SOUTH TO SOUTHWEST DIRECTION ALOFT. THIS IS ALL AHEAD OF A BROAD
DEEP UPR TROF OVER EASTERN PACIFIC WITH ITS AXIS PRIMARILY SITUATED
ALONG 135W. AHEAD OF THIS FEATURE...THE SOUTHERLY FLOW WILL DRAW
TROPICAL MOISTURE FROM THE LOWER LATITUDES...EVENTUALLY INTERSECTING
THE SOUTHERN CA COAST OVERNIGHT BETWEEN SANTA BARBARA AND VENTURA
COUNTIES...SIGNALING THE BEGINNING OF THIS INITIAL HEAVY PRECIP
EVENT THAT WILL LAST THROUGH CHRISTMAS EVE. LOOK FOR THE MOISTURE
PLUME TO THEN SLOWLY SHIFT TO THE SOUTHEAST AND CLEAR THE CA/MX
BORDER BY THE EVENING HOURS. PW VALUES WITHIN THIS PLUME ARE QUITE
IMPRESSIVE...PEAKING JUST OVER 1.50-INCHES. ALONG WITH SOUTHERLY
FLOW AT 850-MB PEAKING AROUND 50-KT...LOOK FOR IDEAL OROGRAPHIC
ENHANCEMENT OVER THE TRANSVERSE RANGES BETWEEN POINT CONCEPTION AND
SOUTHWEST SAN BERNARDINO COUNTY. PRECIP TOTALS FROM NOW THROUGH
CHRISTMAS EVE WILL BE IN THE RANGE OF 5.00- TO 10.00-INCHES WITH
SOME LOCALIZED HIGHER AMOUNTS NEAR 12.50-INCHES.
ALSO...WITH FLOW ALOFT VEERING MORE TO THE SOUTHWEST FOR OROGRAPHIC
ENHANCEMENT AND GOOD MOISTURE TRANSPORT INLAND TOWARD THE
SIERRA...WIDESPREAD MODERATE TO HEAVY PRECIP WILL FALL ALONG THE
WEST SLOPE WITH THE BEST TOTALS OVER THE CENTRAL/SOUTHERN PORTION OF
THE RANGE WITH 3.00- TO 5.00-INCHES...LOCAL TO 6.00-INCHES FALLING
THROUGH CHRISTMAS EVE.
ANOTHER AREA OF INTEREST WILL BE THE NORTHERN CA COASTAL MOUNTAINS
AND WESTERN PORTION OF THE SHASTA LAKE DRAINAGE...WHERE THE LOW-LEVEL
SOUTH TO SOUTHEAST FLOW WILL GENERATE UPSLOPE AND CONVERGENT
CONDITIONS. AMOUNTS WERE INCREASED IN THIS AREA AND NOW RANGE FROM
1.00- TO 3.00-INCHES WITH SOME LOCALIZED TOTALS ABOVE SHASTA DAM IN
THE RANGE OF 3.00- TO 5.00-INCHES.
FOR THE PERIODS AFTER THIS FIRST EVENT...ANOTHER SHOT OF PRECIP WILL
ROLL ACROSS THE REGION ON CHRISTMAS DAY INTO FRIDAY AS THE UPR TROF
STARTS TO PUSH EASTWARD ACROSS THE REGION WITH ANOTHER AREA OF LOW
PRESSURE MOVING FROM SOUTHWEST TO NORTHEAST TOWARD THE CA/OR BORDER
REGION. ALTHOUGH THERE WILL NOT BE AS MUCH MOISTURE TO WORK WITH FOR
THIS ROUND OF PRECIP...LOOK FOR WIDESPREAD MODERATE TO LOCALLY HEAVY
AMOUNTS WITH THE BEST FALLING ON THE WEST SLOPE OF THE SIERRA AND
THE SHASTA LAKE DRAINAGE WITH ANOTHER 2.50- TO 5.00-INCHES (LOCAL TO
6.00-INCHES OVER THE FEATHER RIVER BASIN). ALONG COASTAL AREAS
BETWEEN THE CA/OR BORDER AND THE LA BASIN...LOOK FOR AMOUNTS TO
GENERALLY RANGE FROM 1.00- TO 3.00-INCHES.
FREEZING LEVELS RIGHT NOW RANGE FROM 7500-FEET FAR NORTHWEST CA TO
NEAR OR OVER 10000-FEET FOR SOUTHERN AND EASTERN AREAS. THESE WILL
FALL AS THE UPR TROF APPROACHES AND BOTTOMING OUT FROM 4500-FEET
NORTHWEST TO 7500-FEET SOUTHEAST BY SATURDAY MORNING.
QPF GRAPHICS ARE AVAILABLE AT WWW.CNRFC.NOAA.GOV/QPF.PHP
DRK
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