Area Forecast Discussion
FXUS66 KMTR [Monterey CA] 270609 AFDMTR ∨
FXUS66 KMTR 270609 AFDMTR [HEAD]
National Weather Service San Francisco Bay Area 11:09pm PDT Wed Oct 26 2016 ∨
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA 1109 PM PDT WED OCT 26 2016 [HEAD]
Synopsis. Rain will move into the area Thursday morning then increases in coverage and intensity late Thursday afternoon through early Friday morning with periods of heavy rain likely, especially for the coastal hills in Monterey County. Showers will taper Friday afternoon. Unsettled weather expected to continue Saturday before another front arrives from the northwest with rain likely late Saturday night and Sunday. Halloween afternoon and evening looks mostly dry with another system possible by late Monday into Tuesday. ∨
.SYNOPSIS...RAIN WILL MOVE INTO THE AREA THURSDAY MORNING THEN INCREASES IN COVERAGE AND INTENSITY LATE THURSDAY AFTERNOON THROUGH EARLY FRIDAY MORNING WITH PERIODS OF HEAVY RAIN LIKELY, ESPECIALLY FOR THE COASTAL HILLS IN MONTEREY COUNTY. SHOWERS WILL TAPER FRIDAY AFTERNOON. UNSETTLED WEATHER EXPECTED TO CONTINUE SATURDAY BEFORE ANOTHER FRONT ARRIVES FROM THE NORTHWEST WITH RAIN LIKELY LATE SATURDAY NIGHT AND SUNDAY. HALLOWEEN AFTERNOON AND EVENING LOOKS MOSTLY DRY WITH ANOTHER SYSTEM POSSIBLE BY LATE MONDAY INTO TUESDAY. [DISC]
Discussion. As of 9:05pm PDT Wednesday… temperatures topped out in the 60s along the coast, 70s inland and low to mid 80s in the warmest inland valleys today under mostly sunny skies. A significant change in the weather is expected tomorrow as the next in a series of storms take aim at the region. ∨
.DISCUSSION...AS OF 9:05 PM PDT WEDNESDAY...TEMPERATURES TOPPED OUT IN THE 60S ALONG THE COAST, 70S INLAND AND LOW TO MID 80S IN THE WARMEST INLAND VALLEYS TODAY UNDER MOSTLY SUNNY SKIES. A SIGNIFICANT CHANGE IN THE WEATHER IS EXPECTED TOMORROW AS THE NEXT IN A SERIES OF STORMS TAKE AIM AT THE REGION. [DISC]
Latest model runs indicate rain will begin as early at Thursday morning becoming widespread across the forecast area through the day. Doppler radar is already picking up return well off the coast at this hour with all indications pointing to an early morning start to the rain over the North Bay Thursday. Moisture associated with hurricane seymore spinning about 775 miles west southwest of the southern tip of Baja Mexico will become in entrained in the southerly flow of the frontal boundary moving toward the Central Coast. Precipitable water values of over 1.5" are forecast to move in over Monterey County Thursday afternoon and evening. Periods of heavy rainfall are anticipated Thursday night into Friday as an upper level closed low pulsates around the longwave trough collides with the plume of moisture as it moves onshore over the Big Sur coast. These enhanced dynamics will translate into rainfall totals of 2–4 inches over the Santa Lucia Range. Along with increased rainfall rates this shortwave will bring an increased chance of thunderstorms over the area south of Big Sur. A Flash Flood Watch remains in effect for the soberanes and the chimney fire burn scar. ∨
LATEST MODEL RUNS INDICATE RAIN WILL BEGIN AS EARLY AT THURSDAY MORNING BECOMING WIDESPREAD ACROSS THE FORECAST AREA THROUGH THE DAY. DOPPLER RADAR IS ALREADY PICKING UP RETURN WELL OFF THE COAST AT THIS HOUR WITH ALL INDICATIONS POINTING TO AN EARLY MORNING START TO THE RAIN OVER THE NORTH BAY THURSDAY. MOISTURE ASSOCIATED WITH HURRICANE SEYMORE SPINNING ABOUT 775 MILES WEST SOUTHWEST OF THE SOUTHERN TIP OF BAJA MEXICO WILL BECOME IN ENTRAINED IN THE SOUTHERLY FLOW OF THE FRONTAL BOUNDARY MOVING TOWARD THE CENTRAL COAST. PRECIPITABLE WATER VALUES OF OVER 1.5" ARE FORECAST TO MOVE IN OVER MONTEREY COUNTY THURSDAY AFTERNOON AND EVENING. PERIODS OF HEAVY RAINFALL ARE ANTICIPATED THURSDAY NIGHT INTO FRIDAY AS AN UPPER LEVEL CLOSED LOW PULSATES AROUND THE LONGWAVE TROUGH COLLIDES WITH THE PLUME OF MOISTURE AS IT MOVES ONSHORE OVER THE BIG SUR COAST. THESE ENHANCED DYNAMICS WILL TRANSLATE INTO RAINFALL TOTALS OF 2 TO 4 INCHES OVER THE SANTA LUCIA RANGE. ALONG WITH INCREASED RAINFALL RATES THIS SHORTWAVE WILL BRING AN INCREASED CHANCE OF THUNDERSTORMS OVER THE AREA SOUTH OF BIG SUR. A FLASH FLOOD WATCH REMAINS IN EFFECT FOR THE SOBERANES AND THE CHIMNEY FIRE BURN SCAR. [DISC]
From previous discussion. Rainfall totals have been adjusted upward from the overnight package for most spots especially for Monterey County. Totals by Friday afternoon will likely range from 1/2" to 1" for many urban spots to more than 4" for the Santa Lucia Range. Thankfully winds will not be as much of an issue compared to previous events. ∨
FROM PREVIOUS DISCUSSION...RAINFALL TOTALS HAVE BEEN ADJUSTED UPWARD FROM THE OVERNIGHT PACKAGE FOR MOST SPOTS ESPECIALLY FOR MONTEREY COUNTY. TOTALS BY FRIDAY AFTERNOON WILL LIKELY RANGE FROM 1/2" TO 1" FOR MANY URBAN SPOTS TO MORE THAN 4" FOR THE SANTA LUCIA RANGE. THANKFULLY WINDS WILL NOT BE AS MUCH OF AN ISSUE COMPARED TO PREVIOUS EVENTS. [DISC]
Rain will switch to showers with a few forecast to be around into Saturday. By Saturday an upper level low and surface low will move toward the Northern California coast directly from the west. Unlike the first system, the location of the low will bring higher rainfall amounts to the North Bay with 1–2" likely in parts of the North Bay mountains. Rainfall will be less for the remainder of our region with another 1/3–2/3" around SF Bay with small amounts for inland spots to the south. Santa Cruz Mountains could pick up another inch. Rainfall will generally end late on Sunday with just a few showers forecast for Monday. ∨
RAIN WILL SWITCH TO SHOWERS WITH A FEW FORECAST TO BE AROUND INTO SATURDAY. BY SATURDAY AN UPPER LEVEL LOW AND SURFACE LOW WILL MOVE TOWARD THE NORCAL COAST DIRECTLY FROM THE WEST. UNLIKE THE FIRST SYSTEM, THE LOCATION OF THE LOW WILL BRING HIGHER RAINFALL AMOUNTS TO THE NORTH BAY WITH 1-2" LIKELY IN PARTS OF THE NORTH BAY MOUNTAINS. RAINFALL WILL BE LESS FOR THE REMAINDER OF OUR REGION WITH ANOTHER 1/3 TO 2/3" AROUND SF BAY WITH SMALL AMOUNTS FOR INLAND SPOTS TO THE SOUTH. SANTA CRUZ MOUNTAINS COULD PICK UP ANOTHER INCH. RAINFALL WILL GENERALLY END LATE ON SUNDAY WITH JUST A FEW SHOWERS FORECAST FOR MONDAY. [DISC]
In many cases, we will be fortunate with the first two systems and both of them will focus the bulk of rainfall on different parts of our CWA [County Warning Area; see the LWP home page (link at bottom of page) for a CWA map]. That should mitigate some of the flooding potential. ∨
IN MANY CASES, WE WILL BE FORTUNATE WITH THE FIRST TWO SYSTEMS AND BOTH OF THEM WILL FOCUS THE BULK OF RAINFALL ON DIFFERENT PARTS OF OUR CWA. THAT SHOULD MITIGATE SOME OF THE FLOODING POTENTIAL. [DISC]
For those with Halloween plans, Monday should stay mostly dry for the afternoon and evening before a third system quickly moves through Monday night into Tuesday. This feature will be moving in from the NW with the center of the low expected to go over Monterey County or San Luis Obispo County. Due to the speed of the system plus PW [precipitable water] values not exceeding 0.95" through the period rainfall amounts should be less than the first two systems. ∨
FOR THOSE WITH HALLOWEEN PLANS, MONDAY SHOULD STAY MOSTLY DRY FOR THE AFTERNOON AND EVENING BEFORE A THIRD SYSTEM QUICKLY MOVES THROUGH MONDAY NIGHT INTO TUESDAY. THIS FEATURE WILL BE MOVING IN FROM THE NW WITH THE CENTER OF THE LOW EXPECTED TO GO OVER MONTEREY COUNTY OR SAN LUIS OBISPO COUNTY. DUE TO THE SPEED OF THE SYSTEM PLUS PW VALUES NOT EXCEEDING 0.95" THROUGH THE PERIOD RAINFALL AMOUNTS SHOULD BE LESS THAN THE FIRST TWO SYSTEMS. [DISC]
Model solutions then diverge for the second half of next week with some brining in a fourth system while the others indicate dry weather. CPC [Climate Prediction Center] 8–14 day outlook does favor wetter than normal conditions, so active weather remains in the cards at least through November 9th. ∨
MODEL SOLUTIONS THEN DIVERGE FOR THE SECOND HALF OF NEXT WEEK WITH SOME BRINING IN A FOURTH SYSTEM WHILE THE OTHERS INDICATE DRY WEATHER. CPC 8 TO 14 DAY OUTLOOK DOES FAVOR WETTER THAN NORMAL CONDITIONS, SO ACTIVE WEATHER REMAINS IN THE CARDS AT LEAST THROUGH NOVEMBER 9TH. [DISC]
Aviation. As of 11:09pm PDT Wednesday… light winds. The rest of the forecast is low-moderate confidence regarding timing of ceilings, visibilities and rain. An upper low located well to the W-SW of the Bay Area may slow in forward motion Thursday and possibly Friday due to the relative proximity of rapidly decaying Hurricane Seymour and its subsidence located far outside of the cyclone. Area of weak upward motion arrives Bay Area tonight causing periodic light rain late tonight/Thursday. Then rain with low pressure area located to our southwest returns later Thursday into Friday. Model guidance is going mostly with MVFR [Marginal Visual Flight Rules] ceilings except forecasting IFR [Instrument Flight Rules] at KSTS [Santa Rosa CA] for instance. 06Z [11pm PDT] KSTS [Santa Rosa CA] TAF [Terminal Aerodrome Forecast] MVFR [Marginal Visual Flight Rules] borderline IFR [Instrument Flight Rules] Thursday. Best chances for MVFR [Marginal Visual Flight Rules]/VFR [Visual Flight Rules] conditions will be over southern 2/3 of the forecast area tonight and Thursday. Ceilings lowering Thursday night and Friday with wet weather. ∨
.AVIATION...AS OF 11:09 PM PDT WEDNESDAY...LIGHT WINDS. THE REST OF THE FORECAST IS LOW-MODERATE CONFIDENCE REGARDING TIMING OF CIGS, VSBYS AND RAIN. AN UPPER LOW LOCATED WELL TO THE W-SW OF THE BAY AREA MAY SLOW IN FORWARD MOTION THURSDAY AND POSSIBLY FRIDAY DUE TO THE RELATIVE PROXIMITY OF RAPIDLY DECAYING HURRICANE SEYMOUR AND ITS SUBSIDENCE LOCATED FAR OUTSIDE OF THE CYCLONE. AREA OF WEAK UPWARD MOTION ARRIVES BAY AREA TONIGHT CAUSING PERIODIC LIGHT RAIN LATE TONIGHT/THURSDAY. THEN RAIN WITH LOW PRESSURE AREA LOCATED TO OUR SOUTHWEST RETURNS LATER THURSDAY INTO FRIDAY. MODEL GUIDANCE IS GOING MOSTLY WITH MVFR CIGS EXCEPT FORECASTING IFR AT KSTS FOR INSTANCE. 06Z KSTS TAF MVFR BORDERLINE IFR THURSDAY. BEST CHANCES FOR MVFR/VFR CONDITIONS WILL BE OVER SOUTHERN 2/3 OF THE FORECAST AREA TONIGHT AND THURSDAY. CIGS LOWERING THURSDAY NIGHT AND FRIDAY WITH WET WEATHER. [AVIA]
Vicinity of KSFO [San Francisco CA]… VFR [Visual Flight Rules] with light winds. Period of light rain Thursday tapering off to VCSH [Rain Showers in the Vicinity] in the afternoon. Light to occasionally moderate rain returns Thursday evening into Friday. ∨
VICINITY OF KSFO...VFR WITH LIGHT WINDS. PERIOD OF LIGHT RAIN THURSDAY TAPERING OFF TO VCSH IN THE AFTERNOON. LIGHT TO OCCASIONALLY MODERATE RAIN RETURNS THURSDAY EVENING INTO FRIDAY. [AVI2]
SFO [San Francisco CA] bridge approach… similar to KSFO [San Francisco CA]. ∨
SFO BRIDGE APPROACH...SIMILAR TO KSFO. [AVI2]
Monterey Bay terminals… VFR [Visual Flight Rules] with light winds. VCSH [Rain Showers in the Vicinity] Thursday afternoon with light-moderate rain Thursday evening into Friday. ∨
MONTEREY BAY TERMINALS...VFR WITH LIGHT WINDS. VCSH THURSDAY AFTERNOON WITH LIGHT-MODERATE RAIN THURSDAY EVENING INTO FRIDAY. [AVI2]
Marine. As of 10:49pm PDT Wednesday… periodic light rain by Thursday morning followed by a break. Low pressure area 900 miles southwest of the Bay Area tonight will be 300 miles southwest of the Bay Area Thursday evening. Hurricane Seymour rapidly weakens in the sub-tropics Thursday and Friday and its forward motion will slow and turn north then northeastward. Amplification in the eastern Pacific pattern combined with large scale subsidence outside of the diminishing hurricane may slow the arrival of the aforementioned low… rain returns late Thursday into Friday. Moderate northwest swell will gradually subside through the work week before a larger northwest swell train arrives early into the weekend. ∨
.MARINE...AS OF 10:49 PM PDT WEDNESDAY...PERIODIC LIGHT RAIN BY THURSDAY MORNING FOLLOWED BY A BREAK. LOW PRESSURE AREA 900 MILES SOUTHWEST OF THE BAY AREA TONIGHT WILL BE 300 MILES SOUTHWEST OF THE BAY AREA THURSDAY EVENING. HURRICANE SEYMOUR RAPIDLY WEAKENS IN THE SUB-TROPICS THURSDAY AND FRIDAY AND ITS FORWARD MOTION WILL SLOW AND TURN NORTH THEN NORTHEASTWARD. AMPLIFICATION IN THE EASTERN PACIFIC PATTERN COMBINED WITH LARGE SCALE SUBSIDENCE OUTSIDE OF THE DIMINISHING HURRICANE MAY SLOW THE ARRIVAL OF THE AFOREMENTIONED LOW...RAIN RETURNS LATE THURSDAY INTO FRIDAY. MODERATE NORTHWEST SWELL WILL GRADUALLY SUBSIDE THROUGH THE WORK WEEK BEFORE A LARGER NORTHWEST SWELL TRAIN ARRIVES EARLY INTO THE WEEKEND. [AVIA]
.MTR WATCHES/WARNINGS/ADVISORIES... .TNGT...NONE. [WARN]
Public Forecast: CW; Aviation/Marine: Canepa ∨
PUBLIC FORECAST: CW AVIATION/MARINE: CANEPA [CRED]
VISIT US AT WWW.WEATHER.GOV/SANFRANCISCO [LINK]
FOLLOW US ON FACEBOOK AND TWITTER AT: WWW.FACEBOOK.COM/NWSBAYAREA WWW.TWITTER.COM/NWSBAYAREA [DISC]
27 Oct 2:55am PDT
Overnight A 40% chance of rain. Mostly cloudy, with a low around 54°. SSE wind around 8 mph. New precipitation amounts of less than a tenth of an inch possible.
Thursday Rain. High near 62°. SE wind 7 to 14 mph. Chance of precipitation is 80%. New precipitation amounts between a quarter and half of an inch possible.
Thursday Night Rain. Low around 56°. SSE wind 5 to 8 mph becoming calm after midnight. Chance of precipitation is 90%. New precipitation amounts between a half and three quarters of an inch possible.
Friday A 50% chance of showers. Cloudy, with a high near 62°. South wind 6 to 13 mph. New precipitation amounts between a tenth and quarter of an inch possible.
Friday Night A 30% chance of rain. Mostly cloudy, with a low around 55°. SSW wind 8 to 13 mph. New precipitation amounts of less than a tenth of an inch possible.
Saturday A 40% chance of rain. Mostly cloudy, with a high near 62°. New precipitation amounts of less than a tenth of an inch possible.
Saturday Night Rain likely. Mostly cloudy, with a low around 54°. Chance of precipitation is 60%.
Sunday Rain likely. Mostly cloudy, with a high near 61°. Breezy.
Sunday Night A chance of rain. Mostly cloudy, with a low around 53°.
Monday A slight chance of rain. Mostly sunny, with a high near 61°.
Monday Night A chance of rain. Mostly cloudy, with a low around 52°.
Tuesday A chance of rain. Mostly cloudy, with a high near 62°.
Tuesday Night A slight chance of rain. Mostly cloudy, with a low around 52°.
Wednesday A slight chance of rain. Partly sunny, with a high near 63°.
A 40 percent chance of rain. Mostly cloudy, with a low around 54. South southeast wind around 8 mph. New precipitation amounts of less than a tenth of an inch possible.
Rain. High near 62. Southeast wind 7 to 14 mph. Chance of precipitation is 80%. New precipitation amounts between a quarter and half of an inch possible.
Rain. Low around 56. South southeast wind 5 to 8 mph becoming calm after midnight. Chance of precipitation is 90%. New precipitation amounts between a half and three quarters of an inch possible.
A 50 percent chance of showers. Cloudy, with a high near 62. South wind 6 to 13 mph. New precipitation amounts between a tenth and quarter of an inch possible.
A 30 percent chance of rain. Mostly cloudy, with a low around 55. South southwest wind 8 to 13 mph. New precipitation amounts of less than a tenth of an inch possible.
A 40 percent chance of rain. Mostly cloudy, with a high near 62. New precipitation amounts of less than a tenth of an inch possible.
Rain likely. Mostly cloudy, with a low around 54. Chance of precipitation is 60%.
Rain likely. Mostly cloudy, with a high near 61. Breezy.
A chance of rain. Mostly cloudy, with a low around 53.
A slight chance of rain. Mostly sunny, with a high near 61.
A chance of rain. Mostly cloudy, with a low around 52.
A chance of rain. Mostly cloudy, with a high near 62.
A slight chance of rain. Mostly cloudy, with a low around 52.
A slight chance of rain. Partly sunny, with a high near 63.