Area Forecast Discussion
FXUS66 KMTR [Monterey CA] 310601 AFDMTR ∨
FXUS66 KMTR 310601 AFDMTR [HEAD]
National Weather Service San Francisco Bay Area 11:01pm PDT Thu Oct 30 2014 ∨
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA 1101 PM PDT THU OCT 30 2014 [HEAD]
Synopsis. A cold front will spread rain across the entire region late tonight into Friday. Showers and possible thunderstorms are forecast from late Friday afternoon through Friday night. Scattered showers will continue into Saturday. Dry weather will return by Sunday and continue through much of next week as high pressure rebuilds. ∨
.SYNOPSIS...A COLD FRONT WILL SPREAD RAIN ACROSS THE ENTIRE REGION LATE TONIGHT INTO FRIDAY. SHOWERS AND POSSIBLE THUNDERSTORMS ARE FORECAST FROM LATE FRIDAY AFTERNOON THROUGH FRIDAY NIGHT. SCATTERED SHOWERS WILL CONTINUE INTO SATURDAY. DRY WEATHER WILL RETURN BY SUNDAY AND CONTINUE THROUGH MUCH OF NEXT WEEK AS HIGH PRESSURE REBUILDS. [DISC]
Discussion. As of 8:45pm PDT Thursday… incoming Pacific weather system continues to look promising on satellite with a cold upper trough digging SE offshore. Precipitable water values as high as 1.2 inches are feeding in from the SW along the cold-frontal rain band which is approaching the Northern California coast this evening. Models have lately been trending wetter with this system and that seems like a good bet given relatively strong dynamics and a good moisture source. Another model trend has been to focus the heavier precipitation across the southern portion of our forecast area. ∨
.DISCUSSION...AS OF 8:45 PM PDT THURSDAY...INCOMING PACIFIC WEATHER SYSTEM CONTINUES TO LOOK PROMISING ON SATELLITE WITH A COLD UPPER TROUGH DIGGING SE OFFSHORE. PRECIPITABLE WATER VALUES AS HIGH AS 1.2 INCHES ARE FEEDING IN FROM THE SW ALONG THE COLD- FRONTAL RAIN BAND WHICH IS APPROACHING THE NORTHERN CA COAST THIS EVENING. MODELS HAVE LATELY BEEN TRENDING WETTER WITH THIS SYSTEM AND THAT SEEMS LIKE A GOOD BET GIVEN RELATIVELY STRONG DYNAMICS AND A GOOD MOISTURE SOURCE. ANOTHER MODEL TREND HAS BEEN TO FOCUS THE HEAVIER PRECIP ACROSS THE SOUTHERN PORTION OF OUR FORECAST AREA. [DISC]
Timing of precipitation onset remains consistent. Rain will likely begin in the North Bay late tonight and spread into San Francisco by around sunrise. Looks like much of the SF Bay Area will have a wet morning commute… particularly the North Bay… San Francisco Peninsula and East Bay. Rain probably won't reach the South Bay until late morning and then the Monterey Bay Area around midday or early afternoon. The southeastward progression of the frontal rain band is expected to slow considerably around early afternoon as a 130 knot [150 mph] upper jet digs into the base of the upper trough offshore. Also… the NAM [North American Meso (formerly Eta) model] forecasts a wave to develop along the front just west of Monterey Bay late Friday morning… which will slow the front down and enhance low level convergence and precipitation intensity. For these reasons it looks like the largest rainfall totals will be over areas from the Santa Cruz Mountains southward. In fact… the 00Z [5pm PDT] NAM [North American Meso (formerly Eta) model] forecasts over 2 inches of rain in the Santa Cruz Mountains vs. Only about a tenth in the interior of Sonoma County. Other models show a more uniform QPF [Quantitative Precipitation Forecast] distribution… but all of the models agree that heavier amounts will be across the south. ∨
TIMING OF PRECIP ONSET REMAINS CONSISTENT. RAIN WILL LIKELY BEGIN IN THE NORTH BAY LATE TONIGHT AND SPREAD INTO SAN FRANCISCO BY AROUND SUNRISE. LOOKS LIKE MUCH OF THE SF BAY AREA WILL HAVE A WET MORNING COMMUTE...PARTICULARLY THE NORTH BAY...SAN FRANCISCO PENINSULA AND EAST BAY. RAIN PROBABLY WON`T REACH THE SOUTH BAY UNTIL LATE MORNING AND THEN THE MONTEREY BAY AREA AROUND MIDDAY OR EARLY AFTERNOON. THE SOUTHEASTWARD PROGRESSION OF THE FRONTAL RAIN BAND IS EXPECTED TO SLOW CONSIDERABLY AROUND EARLY AFTERNOON AS A 130 KNOT UPPER JET DIGS INTO THE BASE OF THE UPPER TROUGH OFFSHORE. ALSO...THE NAM FORECASTS A WAVE TO DEVELOP ALONG THE FRONT JUST WEST OF MONTEREY BAY LATE FRIDAY MORNING....WHICH WILL SLOW THE FRONT DOWN AND ENHANCE LOW LEVEL CONVERGENCE AND PRECIP INTENSITY. FOR THESE REASONS IT LOOKS LIKE THE LARGEST RAINFALL TOTALS WILL BE OVER AREAS FROM THE SANTA CRUZ MOUNTAINS SOUTHWARD. IN FACT...THE 00Z NAM FORECASTS OVER 2 INCHES OF RAIN IN THE SANTA CRUZ MOUNTAINS VS. ONLY ABOUT A TENTH IN THE INTERIOR OF SONOMA COUNTY. OTHER MODELS SHOW A MORE UNIFORM QPF DISTRIBUTION...BUT ALL OF THE MODELS AGREE THAT HEAVIER AMOUNTS WILL BE ACROSS THE SOUTH. [DISC]
Precipitation will begin to taper off in the North Bay by midday… across the rest of the SF Bay Area by mid afternoon… but not until mid evening from Monterey Bay south. ∨
PRECIP WILL BEGIN TO TAPER OFF IN THE NORTH BAY BY MIDDAY...ACROSS THE REST OF THE SF BAY AREA BY MID AFTERNOON...BUT NOT UNTIL MID EVENING FROM MONTEREY BAY SOUTH. [DISC]
The airmass will become increasing unstable during the late afternoon and evening hours of Friday as cold advection occurs behind the front. Isolated thunderstorms are possible from late afternoon Friday through Friday night. Best chances will be over the ocean and across the southern half of the CWA [County Warning Area; see the LWP home page (link at bottom of page) for a CWA map]. ∨
THE AIRMASS WILL BECOME INCREASING UNSTABLE DURING THE LATE AFTERNOON AND EVENING HOURS OF FRIDAY AS COLD ADVECTION OCCURS BEHIND THE FRONT. ISOLATED THUNDERSTORMS ARE POSSIBLE FROM LATE AFTERNOON FRIDAY THROUGH FRIDAY NIGHT. BEST CHANCES WILL BE OVER THE OCEAN AND ACROSS THE SOUTHERN HALF OF THE CWA. [DISC]
Shower activity is expected to gradually diminish Friday night… but then become more widespread by late Saturday morning as a shortwave drops in on the backside of the departing longwave trough. Showers will then taper off Saturday evening and end by late Saturday night as the upper trough shifts well to our east. ∨
SHOWER ACTIVITY IS EXPECTED TO GRADUALLY DIMINISH FRIDAY NIGHT...BUT THEN BECOME MORE WIDESPREAD BY LATE SATURDAY MORNING AS A SHORTWAVE DROPS IN ON THE BACKSIDE OF THE DEPARTING LONGWAVE TROUGH. SHOWERS WILL THEN TAPER OFF SATURDAY EVENING AND END BY LATE SATURDAY NIGHT AS THE UPPER TROUGH SHIFTS WELL TO OUR EAST. [DISC]
Rain totals across the north will mostly range from a quarter to a half inch. Farther south rain totals are generally expected to range from a half inch to an inch… except from one to two inches in the Santa Cruz and Santa Lucia Mountain ranges. ∨
RAIN TOTALS ACROSS THE NORTH WILL MOSTLY RANGE FROM A QUARTER TO A HALF INCH. FARTHER SOUTH RAIN TOTALS ARE GENERALLY EXPECTED TO RANGE FROM A HALF INCH TO AN INCH...EXCEPT FROM ONE TO TWO INCHES IN THE SANTA CRUZ AND SANTA LUCIA MOUNTAIN RANGES. [DISC]
This system is not expected to produce strong winds. Local wind gusts of up to about 25 mph are possible… but probably not much higher. ∨
THIS SYSTEM IS NOT EXPECTED TO PRODUCE STRONG WINDS. LOCAL WIND GUSTS OF UP TO ABOUT 25 MPH ARE POSSIBLE...BUT PROBABLY NOT MUCH HIGHER. [DISC]
Temperatures will be much cooler over the weekend… with highs mainly in the 60s… as much as 20° cooler than what we've seen lately. ∨
TEMPERATURES WILL BE MUCH COOLER OVER THE WEEKEND...WITH HIGHS MAINLY IN THE 60S...AS MUCH AS 20 DEGREES COOLER THAN WHAT WE`VE SEEN LATELY. [DISC]
Dry weather is expected from Sunday through most of next week as an upper level ridge builds over California. Temperatures will gradually warm to levels above seasonal norms by midweek. A weak system may bring rain to the northern portion of our area late in the week. ∨
DRY WEATHER IS EXPECTED FROM SUNDAY THROUGH MOST OF NEXT WEEK AS AN UPPER LEVEL RIDGE BUILDS OVER CA. TEMPERATURES WILL GRADUALLY WARM TO LEVELS ABOVE SEASONAL NORMS BY MIDWEEK. A WEAK SYSTEM MAY BRING RAIN TO THE NORTHERN PORTION OF OUR AREA LATE IN THE WEEK. [DISC]
Aviation. As of 11:01pm PDT Thursday… for 06Z [11pm PDT] TAFs [Terminal Aerodrome Forecasts]. Doppler radar is beginning to pick up some returns off the coast as the front gradually moves our way. KSTS [Santa Rosa CA] began reporting light rain over the terminal this hour… however Doppler radar is not picking up these showers just yet as the showers pass just under the radar beam. As the front moves closer to the coast showers will begin to spread across the region from north to south and winds will turn south to southeasterly. Mainly MVFR [Marginal Visual Flight Rules] ceilings expected with the exception of KSTS [Santa Rosa CA] that will see IFR [Instrument Flight Rules] ceilings through much of the period. Rain is forecast to begin over the North Bay around 12Z [5am PDT] tonight then is expected to spread southward early Friday morning. Bay Area should anticipate rain to begin around 14Z [7am PDT] with Monterey area terminals holding out till around 18Z [11am PDT]. Wet runways and south plan expected for the morning rush Friday. ∨
.AVIATION...AS OF 11:01 PM PDT THURSDAY...FOR 06Z TAFS. DOPPLER RADAR IS BEGINNING TO PICK UP SOME RETURNS OFF THE COAST AS THE FRONT GRADUALLY MOVES OUR WAY. KSTS BEGAN REPORTING LIGHT RAIN OVER THE TERMINAL THIS HOUR...HOWEVER DOPPLER RADAR IS NOT PICKING UP THESE SHOWERS JUST YET AS THE SHOWERS PASS JUST UNDER THE RADAR BEAM. AS THE FRONT MOVES CLOSER TO THE COAST SHOWERS WILL BEGIN TO SPREAD ACROSS THE REGION FROM NORTH TO SOUTH AND WINDS WILL TURN SOUTH TO SOUTHEASTERLY. MAINLY MVFR CIGS EXPECTED WITH THE EXCEPTION OF KSTS THAT WILL SEE IFR CIGS THROUGH MUCH OF THE PERIOD. RAIN IS FORECAST TO BEGIN OVER THE NORTH BAY AROUND 12Z TONIGHT THEN IS EXPECTED TO SPREAD SOUTHWARD EARLY FRIDAY MORNING. BAY AREA SHOULD ANTICIPATE RAIN TO BEGIN AROUND 14Z WITH MONTEREY AREA TERMINALS HOLDING OUT TILL AROUND 18Z. WET RUNWAYS AND SOUTH PLAN EXPECTED FOR THE MORNING RUSH FRIDAY. [AVIA]
Vicinity of KSFO [San Francisco CA]… MVFR [Marginal Visual Flight Rules] ceilings expected tonight as the front approaches. Southeast winds will develop overnight with light rain likely by 14Z [7am PDT] Friday. Would expect to start the day with southeast winds and wet runways. Periods of moderate to heavy downpours possible around 21Z [2pm PDT]. Wind shift to the SW also anticipated around 21Z [2pm PDT]. ∨
VICINITY OF KSFO...MVFR CIGS EXPECTED TONIGHT AS THE FRONT APPROACHES. SOUTHEAST WINDS WILL DEVELOP OVERNIGHT WITH LIGHT RAIN LIKELY BY 14Z FRIDAY. WOULD EXPECT TO START THE DAY WITH SOUTHEAST WINDS AND WET RUNWAYS. PERIODS OF MODERATE TO HEAVY DOWNPOURS POSSIBLE AROUND 21Z. WIND SHIFT TO THE SW ALSO ANTICIPATED AROUND 21Z. [AVI2]
KSFO [San Francisco CA] bridge approach… similar to KSFO [San Francisco CA]. ∨
KSFO BRIDGE APPROACH...SIMILAR TO KSFO. [AVI2]
Monterey Bay Area terminals… MVFR [Marginal Visual Flight Rules] ceilings expected tonight as the front approaches. Southeast winds will develop overnight with light rain likely by 18Z [11am PDT] Friday. Periods of moderate to heavy downpours possible around 02Z [7pm PDT]. Wind shift to the SW anticipated in the afternoon. ∨
MONTEREY BAY AREA TERMINALS...MVFR CIGS EXPECTED TONIGHT AS THE FRONT APPROACHES. SOUTHEAST WINDS WILL DEVELOP OVERNIGHT WITH LIGHT RAIN LIKELY BY 18Z FRIDAY. PERIODS OF MODERATE TO HEAVY DOWNPOURS POSSIBLE AROUND 02Z. WIND SHIFT TO THE SW ANTICIPATED IN THE AFTERNOON. [AVI2]
Marine. As of 8:58pm PDT Thursday… light wind and seas are expected through late tonight. Winds will gradually increase early Friday morning as a strong cold front approaches the northern waters. Winds will briefly increase ahead and just behind the frontal passage as rain moves from north to south through the waters on Friday along with a slight chance of thunderstorms. Behind the front lighter NW winds are forecast Friday evening. On Saturday stronger NW winds and building seas to around 10 feet will develop creating some hazardous seas for the start of crab season. ∨
.MARINE...AS OF 8:58 PM PDT THURSDAY...LIGHT WIND AND SEAS ARE EXPECTED THROUGH LATE TONIGHT. WINDS WILL GRADUALLY INCREASE EARLY FRIDAY MORNING AS A STRONG COLD FRONT APPROACHES THE NORTHERN WATERS. WINDS WILL BRIEFLY INCREASE AHEAD AND JUST BEHIND THE FRONTAL PASSAGE AS RAIN MOVES FROM NORTH TO SOUTH THROUGH THE WATERS ON FRIDAY ALONG WITH A SLIGHT CHANCE OF THUNDERSTORMS. BEHIND THE FRONT LIGHTER NW WINDS ARE FORECAST FRIDAY EVENING. ON SATURDAY STRONGER NW WINDS AND BUILDING SEAS TO AROUND 10 FEET WILL DEVELOP CREATING SOME HAZARDOUS SEAS FOR THE START OF CRAB SEASON. [AVIA]
.MTR WATCHES/WARNINGS/ADVISORIES... .TNGT...SCA...PIGEON PT TO PT PINOS 0-10 NM FROM 6 AM SCA...PT ARENA TO PT REYES 0-10 NM FROM 3 AM SCA...PT ARENA TO PT REYES 10-60 NM FROM 3 AM SCA...PT REYES TO PIGEON PT 10-60 NM FROM 3 AM SCA...PT PINOS TO PT PIEDRAS BLANCAS 0-10 NM FROM 6 AM SCA...PT REYES TO PIGEON PT 0-10 NM FROM 6 AM [WARN]
Public Forecast: Dykema; Aviation/Marine: CW ∨
PUBLIC FORECAST: DYKEMA AVIATION/MARINE: CW [CRED]
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2:51am PDT Oct 31 2014
Overnight. A 40% chance of rain. Cloudy, with a low around 56°. SSW wind around 15 mph, with gusts as high as 18 mph.
Friday. Showers, with thunderstorms also possible after 11am. High near 60°. South wind 6 to 16 mph becoming NNW in the morning. Winds could gust as high as 21 mph. Chance of precipitation is 100%.
Friday Night. Showers likely and possibly a thunderstorm. Some of the storms could produce small hail. Cloudy, with a low around 52°. WNW wind 5 to 14 mph. Chance of precipitation is 70%.
Saturday. A 30% chance of showers. Partly sunny, with a high near 59°. WNW wind 8 to 13 mph increasing to 16 to 21 mph in the afternoon. Winds could gust as high as 26 mph.
Saturday Night. Partly cloudy, with a low around 51°. NNW wind 10 to 15 mph, with gusts as high as 18 mph.
Sunday. Sunny, with a high near 61°.
Sunday Night. Mostly clear, with a low around 53°.
Monday. Mostly sunny, with a high near 63°.
Monday Night. Partly cloudy, with a low around 52°.
Tuesday. Mostly sunny, with a high near 64°.
Tuesday Night. Partly cloudy, with a low around 54°.
Wednesday. Mostly sunny, with a high near 69°.
Wednesday Night. Partly cloudy, with a low around 56°.
Thursday. Mostly sunny, with a high near 69°.