820
AGUS76 KRSA 201418
HMDRSA
HYDROMETEOROLOGICAL DISCUSSION
NATIONAL WEATHER SERVICE / CALIFORNIA NEVADA RFC / SACRAMENTO CA
720 AM PDT SUN APR 20 2025
...WEAK SYSTEMS IMPACTING FAR NORTHERN AREAS TODAY AND AGAIN
TUE/WED...
...POTENTIAL FOR A LARGER SYSTEM AT THE END OF THE WEEK, LOW
CONFIDENCE...
METEOROLOGICAL CONDITIONS (SUN AM - SAT AM)
A SHORTWAVE APPROACHES THE PACNW THIS MORNING WITH BROADER RIDGING
OVER THE EASTERN PACIFIC STRETCHED UP TO THE GULF OF ALASKA. THE
TROUGH WILL SWING THROUGH THE PACNW THE REST OF TODAY DIGGING SOUTH
INTO NRN CA/NV AS IT PASSES. THIS MAY RESULT IN SOME SHOWERS OVER
FAR NRN CA/NV AND POTENTIALLY A THUNDERSTORM OR TWO AS MODELS SHOW
SOME INSTABILITY. ALSO POTENTIAL FOR SOME SHOWERS OVER THE SIERRA.
GENERAL TROUGHING PATTERN OVERHEAD FOR MONDAY OFF OF A LARGER SYSTEM
IN CANADA. THIS MAY BRING SOME ISOLATED SHOWERS TO THE SIERRA.
ANOTHER SHORTWAVE WILL ROTATE INTO THE PACNW ON TUESDAY DIGGING INTO
NRN CA/NV ON WEDNESDAY. THIS MAY RESULT IN A FEW SHOWERS FOR THOSE
AREAS, BUT NOTHING SIGNIFICANT. BRIEF RIDGING LATER WEDNESDAY AND
INTO THURSDAY BEFORE MODELS HAVE A LARGER SYSTEM APPROACHING FROM
THE GULF OF ALASKA AT THE END OF THE WEEK.
THERE ARE STILL DISAGREEMENTS BETWEEN THE MODELS MAKING FOR
UNCERTAINTY IN ANY RESULTING QPF. THE GFS THURSDAY MORNING AS A
BROAD UPPER LOW OVER THE GULF OF ALASKA WITH TWO EMBEDDED CLOSED
CIRCULATIONS, ONE CLOSER TO ALASKA AND ANOTHER WELL OFFSHORE OF THE
PACNW. THE ECMWF AT THIS TIME HAS THE NORTHERN MOST LOW AND AN
ELONGATED TROUGH. THE GFS ALSO HAS A LARGER SURFACE LOW ENCOMPASSING
MUCH OF THE GULF WHILE THE ONE OUT OF THE ECMWF IS SMALLER AND MUCH
FURTHER NORTH. BOTH MODELS TAKE THESE SYSTEMS IN A SOUTHEASTERLY
DIRECTION INTO FRIDAY, BUT THE GFS HAS A CLOSED VERTICALLY STACKED
LOW WEST OF WA/OR AND A MORE ORGANIZED COLD FRONT FOR FRIDAY WHILE
THE ECMWF IS SHOWING AN UPPER TROUGH AS AN AREA OF SURFACE HIGH
PRESSURE RESIDES WEST OF CA. THIS MAKES FOR SOME DIFFERENCES IN THE
QPF, MAINLY THE GFS SHOWING HIGHER AMOUNTS ALONG THE NORTH COAST AND
OVER THE SIERRA WHILE THE ECMWF HAS MORE WIDESPREAD SHOWERS OVER NV
AS THE TROUGH MOVES THROUGH THE REGION.
THE OFFICIAL FORECAST WAS MAINLY WPC GUIDANCE WITH THE LATEST NBM
BLENDED IN FOR FRIDAY. THROUGH WEDNESDAY GENERALLY EXPECTING A TENTH
OF AN INCH OR LESS ACROSS AREAS OF NRN CA/NV AND THE SIERRA. FOR
THURSDAY/FRIDAY QPF SHOWS 0.10-0.50" ALONG THE NORTH COAST (0.50-1"
SMITH BASIN), AND GENERALLY 0.10" OR LESS INTO SHASTA/NRN/CNTRL
SIERRA.
TEMPERATURES HOVERING AROUND +5 TO +10 DEG F ABOVE SEASONAL NORMALS
INTO MID-WEEK BEFORE COOLING FROM WEST TO EAST THE REST OF THE
PERIOD. MOST OF CA WILL BE BELOW NORMAL FOR FRIDAY UP TO -10 DEG F.
FREEZING LEVELS THURSDAY MORNING 8.5-12 KFT FROM N TO S ACROSS THE
REGION LOWERING TO 5.5-8.5 KFT NORTH OF I-80 BY THE EVENING. LEVELS
WILL CONTINUE TO LOWER FRIDAY SOWN TO 4.5-9 KFT FROM THE NORTH COAST
TO THE SOUTHERN SIERRA. DOWNWARD TREND CONTINUES OVERNIGHT REACHING
4-6.5 KFT NORTH OF I-80 AND 5.5-9.5 KFT FROM I-80 TO THE SOUTHERN
SIERRA EARLY SATURDAY.
QPF GRAPHICS ARE AVAILABLE AT WWW.CNRFC.NOAA.GOV/QPF.PHP
AS
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