280
FXUS66 KSTO 171201
AFDSTO
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SACRAMENTO CA
401 AM PST SUN NOV 17 2024
SYNOPSIS
A QUICK MOVING SYSTEM TRAVERSES INTERIOR NORCAL LATE TODAY INTO
MONDAY BRINGING LIGHT RAIN AND MOUNTAIN SNOW AND BREEZY SOUTHERLY
VALLEY WINDS, LOCALLY GUSTY WEST MOUNTAIN WINDS. COLD OVERNIGHT/MORNING
TEMPERATURES ARE EXPECTED INTO EARLY THIS WEEK, COLDEST ON
TUESDAY WITH WIDESPREAD FROST. WET WEATHER IS EXPECTED MID TO
LATE WEEK, PARTICULARLY NORTH OF INTERSTATE 80, WITH MORE
WIDESPREAD PRECIPITATION POTENTIAL BY NEXT WEEKEND.
DISCUSSION
HIGH PRESSURE RIDGING IS OVER THE AREA, WITH A SHORTWAVE TROUGH TO
THE NORTH APPROACHING. WINDS THIS MORNING ARE MUCH LIGHTER THAN
THIS TIME YESTERDAY, WHEN THERE WERE SOME BREEZY NORTHERLY WINDS.
THOSE WINDS KEPT TEMPERATURES RELATIVELY WARM, WHILE THE LIGHT
WINDS TO CALM CONDITIONS HAVE ALLOWED TEMPERATURES TO DROP INTO
THE MID TO UPPER 30S IN PORTIONS OF THE SOUTHER SACRAMENTO AND
NORTHERN SAN JOAQUIN VALLEYS, AS WELL AS THE DELTA. HIGH CLOUDS
ARE SPREADING AHEAD OF THE TROUGH AND SHOULD LIMIT FURTHER COOLING
THIS MORNING. SOME PATCHY FROST IS ALSO POSSIBLE IN LOWER,
SHELTERED AREAS.
HIGH TEMPERATURES THIS AFTERNOON ARE EXPECTED TO BE SIMILAR TO
WHAT WERE SEEN ON SATURDAY. THE DIGGING SHORTWAVE WILL RESULT IN
BREEZY SOUTH WINDS OVER THE VALLEY, WITH TO GUSTY WEST WINDS
OVER THE SIERRA THIS AFTERNOON THROUGH EARLY MONDAY MORNING.
THIS QUICK MOVING WAVE IS EXPECTED TO BRING SOME LIGHT
PRECIPITATION TO THE AREA THIS AFTERNOON INTO MONDAY MORNING,
THOUGH THE VALLEY LOOKS TO BE MOSTLY SHADOWED, WITH JUST A FEW
HUNDREDTHS OF AN INCH OF RAIN EXPECTED, MAINLY OVER THE NORTHERN
SACRAMENTO VALLEY. CURRENT PROBABILITIES OF PRECIPITATION
EXCEEDING 0.25" FOR THE MOUNTAINS ARE AROUND 40% TO 60%. PROBABILITIES
OF SNOWFALL EXCEEDING 4" SIT AROUND 50% TO 75% FOR ELEVATIONS
ABOVE 6500 FEET. THIS COULD BRING SOME WINTER DRIVING IMPACTS,
INCLUDING POSSIBLE DELAYS AND CHAIN CONTROLS, WITH THE HEAVIEST
SNOW MIDNIGHT TONIGHT TO 4 AM PDT MONDAY. LINGERING LIGHT MOUNTAIN
SHOWERS ARE EXPECTED INTO MONDAY AFTERNOON INTO EARLY EVENING,
WITH DRY WEATHER RETURNING FOR THE REST OF THE AREA.
BREEZY NORTHERLY WINDS ARE ANTICIPATED IN THE WAKE OF THIS SYSTEM
THOUGH, WHICH WILL WORK TO BRING COOLER TEMPERATURES TO THE
REGION, ESPECIALLY INTO TUESDAY MORNING. AS WINDS LESSEN INTO THE
OVERNIGHT PERIOD AND SKIES CLEAR AS THE SYSTEM DEPARTS TO THE
EAST, APPRECIABLE RADIATIONAL COOLING CONDITIONS ARE LOOKING
LIKELY. RESULTANT PROBABILITIES OF TUESDAY MORNING LOW
TEMPERATURES LESS THAN 36 F CONTINUE TO BE AROUND 40% TO 80% FOR
MOST VALLEY AND FOOTHILLS LOCATIONS. THERE IS THE POTENTIAL FOR
AREAS TO POSSIBLY WIDESPREAD FROST DEVELOPMENT, IF IDEAL
RADIATIONAL COOLING IS REALIZED. CONSIDER COVERING OR BRINGING IN
SENSITIVE VEGETATION, AS WELL AS OUTDOOR PETS.
EXTENDED DISCUSSION (THURSDAY THROUGH SUNDAY)
A STRONGER GULF OF ALASKA TROUGH LOOKS TO DIG SOUTHWESTWARD OVER
THE EASTERN PACIFIC OCEAN AS RIDGING BUILDS OVER THE ROCKY
MOUNTAINS. RESENT ENSEMBLES HAVE SHOWN A REMARKABLY DEEP,
ANOMALOUSLY DEEP CLOSED LOW DEVELOPING OFF THE PACIFIC
NORTHWEST/BRITISH COLUMBIA. AN IMPRESSIVE MOISTURE STREAM IS
EXPECTED TO DEVELOP, AIMED INTO NORTHWESTERN CALIFORNIA. THERE IS
ALSO A STRONG EXTREME FORECAST INDEX (EFI) SIGNATURE FOR SNOW FOR
WESTERN SHASTA COUNTY AND AREAS TO THE NORTH AND WEST. CURRENT
PROBABILITIES OF SNOWFALL EXCEEDING 4" FROM WEDNESDAY THROUGH
FRIDAY FOR INTERSTATE 5 ARE CURRENTLY 45%, WHILE NEAR 100% FOR THE
MOUNTAINS TO THE NORTH AND WEST, WHERE THERE IS A 40 TO 80%
CHANCE OF SNOW GREATER THAN 12". SNOW LEVELS ARE THE LIMITING
FACTOR FOR IMPACTS TO INTERSTATE 5, WITH THE NBM CURRENTLY AROUND
3000-3500 FEET EARLY WEDNESDAY. THE SOUTHERN CASCADES AND FAR
NORTHERN SIERRA COULD SEE WINTER IMPACTS, WITH A 40-70% CHANCE OF
6" OF SNOW, WHILE AREAS AROUND INTERSTATE 80 SOUTH HAVE JUST A
10-15% CHANCE.
CURRENT PROBABILITIES OF RAINFALL EXCEEDING 1" FROM WEDNESDAY
THROUGH FRIDAY ARE AROUND 40% TO 85% FOR NORTH OF INTERSTATE 80,
WITH 40% TO 60% PROBABILITIES OF EXCEEDING 0.25" OF PRECIPITATION
FROM INTERSTATE 80 SOUTHWARD. TEMPERATURES ARE EXPECTED TO TREND
CLOSER TO SEASONAL NORMALS THROUGH THE END OF THE WEEK. THERE IS
ALSO INCREASING CONFIDENCE IN ANOTHER SYSTEM MOVING ONSHORE NEXT
WEEKEND, BRINGING MORE WIDESPREAD PRECIPITATION IMPACTS.
AVIATION
VFR CONDITIONS ACROSS INTERIOR NORTHERN CALIFORNIA OVER THE NEXT
24 HRS. BREEZY SOUTH WINDS INCREASE AFTER 21Z SUNDAY WITH GUSTS UP
TO 20 MPH UNTIL 06Z MONDAY BEFORE WINDS DECREASE AND TURN
NORTHERLY, LINGERING ACROSS THE DELTA AND NOR. SAN JOAQUIN AREAS
THROUGH MONDAY 18Z.
STO WATCHES/WARNINGS/ADVISORIES
NONE.
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