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FXUS66 KMTR [Monterey CA] 211341 AFDMTR 

FXUS66 KMTR 211341
AFDMTR [HEAD]

National Weather Service San Francisco Bay Area 5:41am PST Sat Jan 21 2017 

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA
541 AM PST SAT JAN 21 2017 [HEAD]

Synopsis. Lingering showers will persist over the region today with another potent storm system arriving late tonight into Sunday. This system will result in widespread heavy rainfall and strong to very strong winds that will likely result in downed trees and isolated power outages. Flooding of small creeks and urban areas is also likely. In wake of the frontal passage Sunday morning, lingering showers will be possible through Tuesday before drying conditions return later in the week. 

.SYNOPSIS...LINGERING SHOWERS WILL PERSIST OVER THE REGION TODAY
WITH ANOTHER POTENT STORM SYSTEM ARRIVING LATE TONIGHT INTO
SUNDAY. THIS SYSTEM WILL RESULT IN WIDESPREAD HEAVY RAINFALL AND
STRONG TO VERY STRONG WINDS THAT WILL LIKELY RESULT IN DOWNED
TREES AND ISOLATED POWER OUTAGES. FLOODING OF SMALL CREEKS AND
URBAN AREAS IS ALSO LIKELY. IN WAKE OF THE FRONTAL PASSAGE SUNDAY
MORNING, LINGERING SHOWERS WILL BE POSSIBLE THROUGH TUESDAY BEFORE
DRYING CONDITIONS RETURN LATER IN THE WEEK. [DISC]

Discussion. As of 04:17am PST Saturday… an unstable post-frontal environment remains in place over the region early this morning with isolated to scattered showers pushing inland. These showers will persist through the early morning and are forecast to taper off in coverage briefly early this afternoon. Rain will then being to spread back into the region late this afternoon and into the evening hours ahead of our next storm system. 

.DISCUSSION...AS OF 04:17 AM PST SATURDAY...AN UNSTABLE POST-
FRONTAL ENVIRONMENT REMAINS IN PLACE OVER THE REGION EARLY THIS
MORNING WITH ISOLATED TO SCATTERED SHOWERS PUSHING INLAND. THESE
SHOWERS WILL PERSIST THROUGH THE EARLY MORNING AND ARE FORECAST TO
TAPER OFF IN COVERAGE BRIEFLY EARLY THIS AFTERNOON. RAIN WILL THEN
BEING TO SPREAD BACK INTO THE REGION LATE THIS AFTERNOON AND INTO
THE EVENING HOURS AHEAD OF OUR NEXT STORM SYSTEM. [DISC]

As the main mid/upper level low drops southward out of the Gulf of Alaska and rotates toward the Pacific Northwest coast, a strong frontal boundary will push into Northern California late tonight and through the Central Coast Sunday morning. The latest forecast models also show deepening surface low pressure and 925 mb winds ahead of the cold front reaching into the 50–60 kt [58–69 mph] range. This will likely result in strong to very strong winds with gusts in the 60–70 mph range along the coast and in the higher elevations. As a result, a High Wind Warning is now in effect for those areas while inland valley locations are under a Wind Advisory from late tonight into Sunday morning. The strongest winds will impact locations just ahead of and along the frontal passage. Widespread downed trees and sporadic power outages will be likely as soils remain saturated from abundant rainfall over the past few weeks. 

AS THE MAIN MID/UPPER LEVEL LOW DROPS SOUTHWARD OUT OF THE GULF OF
ALASKA AND ROTATES TOWARD THE PACIFIC NORTHWEST COAST, A STRONG
FRONTAL BOUNDARY WILL PUSH INTO NORTHERN CALIFORNIA LATE TONIGHT AND
THROUGH THE CENTRAL COAST SUNDAY MORNING. THE LATEST FORECAST MODELS
ALSO SHOW DEEPENING SURFACE LOW PRESSURE AND 925 MB WINDS AHEAD OF
THE COLD FRONT REACHING INTO THE 50-60 KT RANGE. THIS WILL LIKELY
RESULT IN STRONG TO VERY STRONG WINDS WITH GUSTS IN THE 60-70 MPH
RANGE ALONG THE COAST AND IN THE HIGHER ELEVATIONS. AS A RESULT, A
HIGH WIND WARNING IS NOW IN EFFECT FOR THOSE AREAS WHILE INLAND
VALLEY LOCATIONS ARE UNDER A WIND ADVISORY FROM LATE TONIGHT INTO
SUNDAY MORNING. THE STRONGEST WINDS WILL IMPACT LOCATIONS JUST AHEAD
OF AND ALONG THE FRONTAL PASSAGE.  WIDESPREAD DOWNED TREES AND
SPORADIC POWER OUTAGES WILL BE LIKELY AS SOILS REMAIN SATURATED
FROM ABUNDANT RAINFALL OVER THE PAST FEW WEEKS. [DISC]

Rain will increase in coverage and intensity late tonight and into the overnight hours as PWAT [precipitable water] values of 1.00–1.25" advect inland along and ahead of the frontal boundary. In addition, the strong southerly winds mentioned above will help enhance rainfall rates along the south/southwest facing slopes. These areas will likely see the greatest rainfall accumulations from this system where 2.00" to 5.00" are likely with isolated amounts upwards of 6.00" possible, especially from the Santa Cruz Mountains and along the coastal ranges of Monterey County. Urban areas can expect to pick up another 0.75" to 1.50" totals with locally higher amounts in the North Bay and along the coast. (note: the strong southerly flow may initially limit rainfall amounts in portions of the region such as the Santa Clara Valley, Salinas Valley and even portions of the Monterey Peninsula due to rain shadow effect/downsloping.) this additional rainfall and potential locally heavy rainfall at times will result in an increased threat for flash flooding, flooding of area streams and urban areas. Thus, a Flash Flood Watch remains in effect through Sunday afternoon. 

RAIN WILL INCREASE IN COVERAGE AND INTENSITY LATE TONIGHT AND INTO
THE OVERNIGHT HOURS AS PWAT VALUES OF 1.00-1.25" ADVECT INLAND ALONG
AND AHEAD OF THE FRONTAL BOUNDARY. IN ADDITION, THE STRONG SOUTHERLY
WINDS MENTIONED ABOVE WILL HELP ENHANCE RAINFALL RATES ALONG THE
SOUTH/SOUTHWEST FACING SLOPES. THESE AREAS WILL LIKELY SEE THE
GREATEST RAINFALL ACCUMULATIONS FROM THIS SYSTEM WHERE 2.00" TO 5.00"
ARE LIKELY WITH ISOLATED AMOUNTS UPWARDS OF 6.00" POSSIBLE,
ESPECIALLY FROM THE SANTA CRUZ MOUNTAINS AND ALONG THE COASTAL
RANGES OF MONTEREY COUNTY. URBAN AREAS CAN EXPECT TO PICK UP ANOTHER
0.75" TO 1.50" TOTALS WITH LOCALLY HIGHER AMOUNTS IN THE NORTH BAY
AND ALONG THE COAST. (NOTE: THE STRONG SOUTHERLY FLOW MAY INITIALLY
LIMIT RAINFALL AMOUNTS IN PORTIONS OF THE REGION SUCH AS THE SANTA
CLARA VALLEY, SALINAS VALLEY AND EVEN PORTIONS OF THE MONTEREY
PENINSULA DUE TO RAIN SHADOW EFFECT/DOWNSLOPING.) THIS ADDITIONAL
RAINFALL AND POTENTIAL LOCALLY HEAVY RAINFALL AT TIMES WILL RESULT
IN AN INCREASED THREAT FOR FLASH FLOODING, FLOODING OF AREA STREAMS
AND URBAN AREAS. THUS, A FLASH FLOOD WATCH REMAINS IN EFFECT THROUGH
SUNDAY AFTERNOON. [DISC]

In wake of the frontal passage, winds will diminish after sunrise Sunday morning with showers likely to persist region-wide. Conditions will also become more unstable Sunday afternoon and evening which would result in the potential for embedded thunderstorms. Latest thinking is that showers will persist over the region into Monday night if not early Tuesday morning as a mid/upper level low slides southward down the West Coast through the unstable environment. 

IN WAKE OF THE FRONTAL PASSAGE, WINDS WILL DIMINISH AFTER SUNRISE
SUNDAY MORNING WITH SHOWERS LIKELY TO PERSIST REGION-WIDE.
CONDITIONS WILL ALSO BECOME MORE UNSTABLE SUNDAY AFTERNOON AND
EVENING WHICH WOULD RESULT IN THE POTENTIAL FOR EMBEDDED
THUNDERSTORMS. LATEST THINKING IS THAT SHOWERS WILL PERSIST OVER
THE REGION INTO MONDAY NIGHT IF NOT EARLY TUESDAY MORNING AS A
MID/UPPER LEVEL LOW SLIDES SOUTHWARD DOWN THE WEST COAST THROUGH THE
UNSTABLE ENVIRONMENT. [DISC]

By Tuesday afternoon, the broad mid/upper level trough shifts inland while a ridge of high pressure builds over the eastern Pacific. This will finally allow for dry conditions to return to the region from Tuesday through the extended forecast period. It is worth noting that the ECMWF [European Center for Medium-Range Weather Forecasts model] and CMC [Canadian Meteorological Centre] have hinted at another weak system moving into the Pacific Northwest coast Wednesday into Thursday, yet the ridge should keep this mostly dry system to our north. Thus, dry weather and seasonable temperatures are forecast from mid/late week and likely into next week. 

BY TUESDAY AFTERNOON, THE BROAD MID/UPPER LEVEL TROUGH SHIFTS INLAND
WHILE A RIDGE OF HIGH PRESSURE BUILDS OVER THE EASTERN PACIFIC. THIS
WILL FINALLY ALLOW FOR DRY CONDITIONS TO RETURN TO THE REGION FROM
TUESDAY THROUGH THE EXTENDED FORECAST PERIOD. IT IS WORTH NOTING
THAT THE ECMWF AND CMC HAVE HINTED AT ANOTHER WEAK SYSTEM MOVING
INTO THE PACIFIC NORTHWEST COAST WEDNESDAY INTO THURSDAY, YET THE
RIDGE SHOULD KEEP THIS MOSTLY DRY SYSTEM TO OUR NORTH. THUS, DRY
WEATHER AND SEASONABLE TEMPERATURES ARE FORECAST FROM MID/LATE WEEK
AND LIKELY INTO NEXT WEEK. [DISC]

Aviation. As of 5:30am PST Saturday… scattered showers today then a rapid transition back over to steady stratiform widespread rain much later today, heavy rain tonight/Sunday morning. VFR [Visual Flight Rules]/MVFR [Marginal Visual Flight Rules] today, MVFR [Marginal Visual Flight Rules] tonight into Sunday morning with localized visibilities down to IFR [Instrument Flight Rules] in heavy rain. Pre-cold frontal winds will quickly strengthen this evening and overnight, added low-level wind shear to all 12Z [4am PST] TAFs [Terminal Aerodrome Forecasts] due to forecast frontal strengthening and lower level wind shear. Convective parameters will likely be offset somewhat in the pre-frontal environment, however, it'll become much more unstable in post-frontal environment Sunday and Sunday night; model forecasts indicate high amounts of atmospheric instability. 

.AVIATION...AS OF 5:30 AM PST SATURDAY...SCATTERED SHOWERS TODAY
THEN A RAPID TRANSITION BACK OVER TO STEADY STRATIFORM WIDESPREAD
RAIN MUCH LATER TODAY, HEAVY RAIN TONIGHT/SUNDAY MORNING. VFR/MVFR
TODAY, MVFR TONIGHT INTO SUNDAY MORNING WITH LOCALIZED VISIBILITIES
DOWN TO IFR IN HEAVY RAIN. PRE-COLD FRONTAL WINDS WILL QUICKLY
STRENGTHEN THIS EVENING AND OVERNIGHT, ADDED LLWS TO ALL 12Z TAFS
DUE TO FORECAST FRONTAL STRENGTHENING AND LOWER LEVEL WIND SHEAR.
CONVECTIVE PARAMETERS WILL LIKELY BE OFFSET SOMEWHAT IN THE PRE-
FRONTAL ENVIRONMENT, HOWEVER, IT`LL BECOME MUCH MORE UNSTABLE IN
POST-FRONTAL ENVIRONMENT SUNDAY AND SUNDAY NIGHT; MODEL FORECASTS
INDICATE HIGH AMOUNTS OF ATMOSPHERIC INSTABILITY. [AVIA]

Vicinity of KSFO [San Francisco CA]VFR [Visual Flight Rules]/MVFR [Marginal Visual Flight Rules] and off/on showers today then steady rain later today. Conditions deteriorate quickly this evening and overnight as a strong cold front reaches the Bay Area by early Sunday morning. Low-level wind shear in 12Z [4am PST] TAF [Terminal Aerodrome Forecast] for strong lower level wind shear prior to the arrival of the cold front early Sunday morning. Showers and thunderstorms Sunday afternoon and night. 

VICINITY OF KSFO....VFR/MVFR AND OFF/ON SHOWERS TODAY THEN STEADY RAIN
LATER TODAY. CONDITIONS DETERIORATE QUICKLY THIS EVENING AND OVERNIGHT
AS A STRONG COLD FRONT REACHES THE BAY AREA BY EARLY SUNDAY MORNING.
LLWS IN 12Z TAF FOR STRONG LOWER LEVEL WIND SHEAR PRIOR TO THE ARRIVAL
OF THE COLD FRONT EARLY SUNDAY MORNING. SHOWERS AND THUNDERSTORMS
SUNDAY AFTERNOON AND NIGHT. [AVI2]

SFO [San Francisco CA] bridge approach… similar to SFO [San Francisco CA]

SFO BRIDGE APPROACH...SIMILAR TO SFO. [AVI2]

Monterey Bay terminals… VFR [Visual Flight Rules]/MVFR [Marginal Visual Flight Rules] and off/on showers today then steady rain later today. Conditions deteriorate quickly this evening and overnight as a strong cold front reaches the north Central Coast by early Sunday morning. Low-level wind shear added to 12Z [4am PST] TAFs [Terminal Aerodrome Forecasts] for strong lower level wind shear prior to the arrival of the cold front. Heavy showers and thunderstorms Sunday afternoon and night. 

MONTEREY BAY TERMINALS...VFR/MVFR AND OFF/ON SHOWERS TODAY THEN
STEADY RAIN LATER TODAY. CONDITIONS DETERIORATE QUICKLY THIS EVENING
AND OVERNIGHT AS A STRONG COLD FRONT REACHES THE NORTH CENTRAL COAST
BY EARLY SUNDAY MORNING. LLWS ADDED TO 12Z TAFS FOR STRONG LOWER
LEVEL WIND SHEAR PRIOR TO THE ARRIVAL OF THE COLD FRONT. HEAVY SHOWERS
AND THUNDERSTORMS SUNDAY AFTERNOON AND NIGHT. [AVI2]

Marine. As of 4:57am PST Saturday… scattered showers today will transition to a steady moderate to heavy rain beginning this evening as a fast moving cold front approaches from the west. Prior to the arrival of this cold front expect storm force winds tonight over much of the coastal waters with occasional storm force gusts also possible from San Pablo Bay to the Delta very late tonight and Sunday morning. Showers and thunderstorms are expected Sunday into Monday. Very large and dangerous westerly swell will persist through Sunday morning. 

.MARINE...AS OF 4:57 AM PST SATURDAY...SCATTERED SHOWERS TODAY
WILL TRANSITION TO A STEADY MODERATE TO HEAVY RAIN BEGINNING THIS
EVENING AS A FAST MOVING COLD FRONT APPROACHES FROM THE WEST.
PRIOR TO THE ARRIVAL OF THIS COLD FRONT EXPECT STORM FORCE WINDS
TONIGHT OVER MUCH OF THE COASTAL WATERS WITH OCCASIONAL STORM
FORCE GUSTS ALSO POSSIBLE FROM SAN PABLO BAY TO THE DELTA VERY
LATE TONIGHT AND SUNDAY MORNING. SHOWERS AND THUNDERSTORMS ARE
EXPECTED SUNDAY INTO MONDAY. VERY LARGE AND DANGEROUS WESTERLY
SWELL WILL PERSIST THROUGH SUNDAY MORNING. [AVIA]

MTR Watches/Warnings/Advisories

  • Today: High Surf Warning…entire coastline from Sonoma to Monterey County Small Craft Advisory…Monterey Bay until 3pm Small Craft AdvisoryPt Arena [Mendocino CA] to Pt Reyes [San Francisco CA] 0–10 nm [11 miles] until 3pm Small Craft AdvisoryPt Reyes [San Francisco CA] to Pigeon Pt [Pescadero CA] 0–10 nm [11 miles] until 3pm Small Craft AdvisoryPigeon Pt [Pescadero CA] to Pt Pinos [Monterey CA] 0–10 nm [11 miles] until 3pm Small Craft AdvisoryPt Pinos [Monterey CA] to Pt Piedras Blancas [San Simeon CA] 0–10 nm [11 miles] until 3pm Small Craft AdvisoryPt Arena [Mendocino CA] to Pigeon Pt [Pescadero CA] 10–60 nm [69 miles] until 3pm Small Craft AdvisoryPigeon Pt [Pescadero CA] to Pt Piedras Blancas [San Simeon CA] 10–60 nm [69 miles] until 3pm GLWPigeon Pt [Pescadero CA] to Pt Pinos [Monterey CA] 0–10 nm [11 miles] from 3pm GLWPt Arena [Mendocino CA] to Pt Reyes [San Francisco CA] 0–10 nm [11 miles] from 3pm GLWPt Arena [Mendocino CA] to Pigeon Pt [Pescadero CA] 10–60 nm [69 miles] from 3pm GLWPigeon Pt [Pescadero CA] to Pt Piedras Blancas [San Simeon CA] 10–60 nm [69 miles] from 3pm Small Craft Advisory…rough bar advisory for SF bar Small Craft Advisory…SF Bay until 10am 
.MTR WATCHES/WARNINGS/ADVISORIES...
.TDAY...HIGH SURF WARNING...ENTIRE COASTLINE FROM SONOMA TO
MONTEREY COUNTY
SCA...MRY BAY UNTIL 3 PM
SCA...PT ARENA TO PT REYES 0-10 NM UNTIL 3 PM
SCA...PT REYES TO PIGEON PT 0-10 NM UNTIL 3 PM
SCA...PIGEON PT TO PT PINOS 0-10 NM UNTIL 3 PM
SCA...PT PINOS TO PT PIEDRAS BLANCAS 0-10 NM UNTIL 3 PM
SCA...PT ARENA TO PIGEON PT 10-60 NM UNTIL 3 PM
SCA...PIGEON PT TO PT PIEDRAS BLANCAS 10-60 NM UNTIL 3 PM
GLW...PIGEON PT TO PT PINOS 0-10 NM FROM 3 PM
GLW...PT ARENA TO PT REYES 0-10 NM FROM 3 PM
GLW...PT ARENA TO PIGEON PT 10-60 NM FROM 3 PM
GLW...PIGEON PT TO PT PIEDRAS BLANCAS 10-60 NM FROM 3 PM
SCA...ROUGH BAR ADVISORY FOR SF BAR
SCA...SF BAY UNTIL 10 AM [WARN]

Public Forecast: Rgass; Aviation: Canepa; Marine: Canepa 

PUBLIC FORECAST: RGASS
AVIATION: CANEPA
MARINE: CANEPA [CRED]
VISIT US AT WWW.WEATHER.GOV/SANFRANCISCO [LINK]

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Point Forecast

Montara CA

21 Jan 6:55am PST

Today A chance of showers, mainly before 10am, then rain likely after 4pm. Mostly cloudy, with a high near 58°. Breezy, with a west wind 17 to 22 mph decreasing to 10 to 15 mph in the afternoon. Winds could gust as high as 28 mph. Chance of precipitation is 60%. New precipitation amounts between a tenth and quarter of an inch possible.
Tonight Rain. The rain could be heavy at times. Low around 49°. Windy, with a SSE wind 25 to 35 mph increasing to 36 to 46 mph after midnight. Winds could gust as high as 55 mph. Chance of precipitation is 100%. New precipitation amounts between three quarters and one inch possible.
Sunday Rain before 10am, then showers after 10am. High near 59°. Windy, with a south wind 28 to 38 mph decreasing to 11 to 21 mph in the morning. Winds could gust as high as 47 mph. Chance of precipitation is 90%. New precipitation amounts between a quarter and half of an inch possible.
Sunday Night Showers likely and possibly a thunderstorm. Cloudy, with a low around 44°. WSW wind around 16 mph, with gusts as high as 21 mph. Chance of precipitation is 70%. New rainfall amounts between a quarter and half of an inch possible.
Monday Showers likely and possibly a thunderstorm before 10am, then a chance of showers. Cloudy, with a high near 55°. WSW wind around 11 mph. Chance of precipitation is 60%. New precipitation amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.
Monday Night Showers likely. Mostly cloudy, with a low around 45°. Chance of precipitation is 70%. New precipitation amounts between a tenth and quarter of an inch possible.
Tuesday A 30% chance of showers. Partly sunny, with a high near 57°.
Tuesday Night Mostly clear, with a low around 43°.
Wednesday Mostly sunny, with a high near 56°.
Wednesday Night Mostly clear, with a low around 44°.
Thursday Sunny, with a high near 57°.
Thursday Night Mostly clear, with a low around 45°.
Friday Sunny, with a high near 56°.
Today
A chance of showers, mainly before 10am, then rain likely after 4pm. Mostly cloudy, with a high near 58. Breezy, with a west wind 17 to 22 mph decreasing to 10 to 15 mph in the afternoon. Winds could gust as high as 28 mph. Chance of precipitation is 60%. New precipitation amounts between a tenth and quarter of an inch possible.
Tonight
Rain. The rain could be heavy at times. Low around 49. Windy, with a south southeast wind 25 to 35 mph increasing to 36 to 46 mph after midnight. Winds could gust as high as 55 mph. Chance of precipitation is 100%. New precipitation amounts between three quarters and one inch possible.
Sunday
Rain before 10am, then showers after 10am. High near 59. Windy, with a south wind 28 to 38 mph decreasing to 11 to 21 mph in the morning. Winds could gust as high as 47 mph. Chance of precipitation is 90%. New precipitation amounts between a quarter and half of an inch possible.
Sunday Night
Showers likely and possibly a thunderstorm. Cloudy, with a low around 44. West southwest wind around 16 mph, with gusts as high as 21 mph. Chance of precipitation is 70%. New rainfall amounts between a quarter and half of an inch possible.
Monday
Showers likely and possibly a thunderstorm before 10am, then a chance of showers. Cloudy, with a high near 55. West southwest wind around 11 mph. Chance of precipitation is 60%. New precipitation amounts between a tenth and quarter of an inch, except higher amounts possible in thunderstorms.
Monday Night
Showers likely. Mostly cloudy, with a low around 45. Chance of precipitation is 70%. New precipitation amounts between a tenth and quarter of an inch possible.
Tuesday
A 30 percent chance of showers. Partly sunny, with a high near 57.
Tuesday Night
Mostly clear, with a low around 43.
Wednesday
Mostly sunny, with a high near 56.
Wednesday Night
Mostly clear, with a low around 44.
Thursday
Sunny, with a high near 57.
Thursday Night
Mostly clear, with a low around 45.
Friday
Sunny, with a high near 56.

This page is generated dynamically from the National Weather Service's NWS point forecast and Area Forecast Discussion, reformatted for readability. NWS glossary; about point forecasts. For more information, visit the Lobitos Weather Project home page. Comments and corrections are welcome: