Area Forecast Discussion
FXUS66 KMTR [Monterey CA] 262343 AFDMTR ∨
FXUS66 KMTR 262343 AFDMTR [HEAD]
National Weather Service San Francisco Bay Area 3:43pm PST Wed Nov 26 2014 ∨
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA 343 PM PST WED NOV 26 2014 [HEAD]
Substantial rainfall event slated for Friday through at least Wednesday. ∨
...SUBSTANTIAL RAINFALL EVENT SLATED FOR FRIDAY THROUGH AT LEAST WEDNESDAY... [DISC]
Hydro concerns likely by next Tuesday. ∨
...HYDRO CONCERNS LIKELY BY NEXT TUESDAY... [DISC]
Synopsis. High pressure will bring dry weather with seasonable temperatures through tomorrow. Rain will return for Friday into Saturday and continue into next work week. Another round of rain will then move across our area around Tuesday and continue into Wednesday or Thursday. ∨
.SYNOPSIS...HIGH PRESSURE WILL BRING DRY WEATHER WITH SEASONABLE TEMPERATURES THROUGH TOMORROW. RAIN WILL RETURN FOR FRIDAY INTO SATURDAY AND CONTINUE INTO NEXT WORK WEEK. ANOTHER ROUND OF RAIN WILL THEN MOVE ACROSS OUR AREA AROUND TUESDAY AND CONTINUE INTO WEDNESDAY OR THURSDAY. [DISC]
Discussion. As of 3:00pm PST Wednesday… mostly sunny conditions across our area today with very comfortable temperatures — generally in the 60s. Tonight should be a near repeat of last night with patchy fog over the North Bay along with cool temps for almost all spots. Thanksgiving Day should be a near repeat of today. ∨
.DISCUSSION...AS OF 3:00 PM PST WEDNESDAY...MOSTLY SUNNY CONDITIONS ACROSS OUR AREA TODAY WITH VERY COMFORTABLE TEMPERATURES -- GENERALLY IN THE 60S. TONIGHT SHOULD BE A NEAR REPEAT OF LAST NIGHT WITH PATCHY FOG OVER THE NORTH BAY ALONG WITH COOL TEMPS FOR ALMOST ALL SPOTS. THANKSGIVING DAY SHOULD BE A NEAR REPEAT OF TODAY. [DISC]
On Friday conditions will change as a strong (983 mb surface low/538 dm [decameters] heights at 500 mb) Pacific storm system 1200 miles to the NW of SF 650 miles continues to approach our area while an associated cold front 650 miles to the west nears our CWA [County Warning Area; see the LWP home page (link at bottom of page) for a CWA map]. This will represent the switch to active weather and the return of rain. Model solutions are in good agreement and bring the start of the rain to the North Bay Friday evening… down to the SF Bay Metro Friday night and down to the Monterey Bay region on Saturday. This initial push is associated with a moist plume of PW [precipitable water] values up to 1.25" that will take a direct aim on our CWA [County Warning Area; see the LWP home page (link at bottom of page) for a CWA map]. On the flip side, isentropic [vertical motion associated with thermal advection] values are not impressive (10–20 kt [12–23 mph]) and PVA [Positive Vorticity Advection] only looks marginal at best. Favorable instability for convection will be limited to the northern waters plus the coastal North Bay. In those spots some small hail is possible. ∨
ON FRIDAY CONDITIONS WILL CHANGE AS A STRONG (983 MB SURFACE LOW/538 DM HEIGHTS AT 500 MB) PACIFIC STORM SYSTEM 1200 MILES TO THE NW OF SF 650 MILES CONTINUES TO APPROACH OUR AREA WHILE AN ASSOCIATED COLD FRONT 650 MILES TO THE WEST NEARS OUR CWA. THIS WILL REPRESENT THE SWITCH TO ACTIVE WEATHER AND THE RETURN OF RAIN. MODEL SOLUTIONS ARE IN GOOD AGREEMENT AND BRING THE START OF THE RAIN TO THE NORTH BAY FRIDAY EVENING...DOWN TO THE SF BAY METRO FRIDAY NIGHT...AND DOWN TO THE MONTEREY BAY REGION ON SATURDAY. THIS INITIAL PUSH IS ASSOCIATED WITH A MOIST PLUME OF PW VALUES UP TO 1.25" THAT WILL TAKE A DIRECT AIM ON OUR CWA. ON THE FLIP SIDE, ISENTROPIC VALUES ARE NOT IMPRESSIVE (10-20 KT) AND PVA ONLY LOOKS MARGINAL AT BEST. FAVORABLE INSTABILITY FOR CONVECTION WILL BE LIMITED TO THE NORTHERN WATERS PLUS THE COASTAL NORTH BAY. IN THOSE SPOTS SOME SMALL HAIL IS POSSIBLE. [DISC]
Immediately following the passage of the front, another slug of moisture will move in from the SW and bring more rain to our area late Saturday into Sunday. This one will have similar PW [precipitable water] values with better PVA [Positive Vorticity Advection] plus isentropic [vertical motion associated with thermal advection] flow, so amounts could be greater with the second impulse compared to the first. Southerly winds will also pick up with speeds of 15–25 mph and local gusts to 40 mph possible. Higher values can be anticipated in the hills and coastal spots that have a southwestern exposure. Rain will taper off by late Sunday. ∨
IMMEDIATELY FOLLOWING THE PASSAGE OF THE FRONT, ANOTHER SLUG OF MOISTURE WILL MOVE IN FROM THE SW AND BRING MORE RAIN TO OUR AREA LATE SATURDAY INTO SUNDAY. THIS ONE WILL HAVE SIMILAR PW VALUES WITH BETTER PVA PLUS ISENTROPIC FLOW, SO AMOUNTS COULD BE GREATER WITH THE SECOND IMPULSE COMPARED TO THE FIRST. SOUTHERLY WINDS WILL ALSO PICK UP WITH SPEEDS OF 15 TO 25 MPH AND LOCAL GUSTS TO 40 MPH POSSIBLE. HIGHER VALUES CAN BE ANTICIPATED IN THE HILLS AND COASTAL SPOTS THAT HAVE A SOUTHWESTERN EXPOSURE. RAIN WILL TAPER OFF BY LATE SUNDAY. [DISC]
By the time we get to Monday morning, rainfall totals are expected to be up to 3" for higher elevations with generally 1/2"-1.5" for most valley and urban spots. Worth noting that some of the latest guidance that has just come in has backed off a bit on values. Newest CNRFC [California Nevada River Forecast Center] numbers are also a bit of a departure from the past few values. For now, will hold off dropping our precipitation numbers until at least one more series of models comes across. ∨
BY THE TIME WE GET TO MONDAY MORNING, RAINFALL TOTALS ARE EXPECTED TO BE UP TO 3" FOR HIGHER ELEVATIONS WITH GENERALLY 1/2"-1.5" FOR MOST VALLEY AND URBAN SPOTS. WORTH NOTING THAT SOME OF THE LATEST GUIDANCE THAT HAS JUST COME IN HAS BACKED OFF A BIT ON VALUES. NEWEST CNRFC NUMBERS ARE ALSO A BIT OF A DEPARTURE FROM THE PAST FEW VALUES. FOR NOW, WILL HOLD OFF DROPPING OUR PRECIP NUMBERS UNTIL AT LEAST ONE MORE SERIES OF MODELS COMES ACROSS. [DISC]
After a fairly dry Monday, the models bring the third and likely most substantial amount of rain to our area either late Monday or Tuesday. This will be due to both the surface and upper level low moving overhead. Due to some disagreement with the track of the low, the start and end times for the rain remains a difficult call. Decision was made to go with a compromise between the faster GFS [Global Forecast System: global spectral model used primarily for aviation weather forecasts; provides guidance out to 384 hours at 00, 06, 12 and 18UTC.] and the slower ECMWF [European Center for Medium-Range Weather Forecasts model]. There is also disagreement with where the best PW [precipitable water] values will be aimed. ECMWF [European Center for Medium-Range Weather Forecasts model] which tracks a bit slower and more to the south has the rain focused south of SF while the GFS [Global Forecast System: global spectral model used primarily for aviation weather forecasts; provides guidance out to 384 hours at 00, 06, 12 and 18UTC.] shows a widespread event with the highest rainfall totals over the North Bay. In addition, the models disagree in regard to wind concerns with the GFS [Global Forecast System: global spectral model used primarily for aviation weather forecasts; provides guidance out to 384 hours at 00, 06, 12 and 18UTC.] solutions much windier. Depending on which one verifies, rain will end either Wednesday or Thursday. ∨
AFTER A FAIRLY DRY MONDAY, THE MODELS BRING THE THIRD AND LIKELY MOST SUBSTANTIAL AMOUNT OF RAIN TO OUR AREA EITHER LATE MONDAY OR TUESDAY. THIS WILL BE DUE TO BOTH THE SURFACE AND UPPER LEVEL LOW MOVING OVERHEAD. DUE TO SOME DISAGREEMENT WITH THE TRACK OF THE LOW, THE START AND END TIMES FOR THE RAIN REMAINS A DIFFICULT CALL. DECISION WAS MADE TO GO WITH A COMPROMISE BETWEEN THE FASTER GFS AND THE SLOWER ECMWF. THERE IS ALSO DISAGREEMENT WITH WHERE THE BEST PW VALUES WILL BE AIMED. ECMWF WHICH TRACKS A BIT SLOWER AND MORE TO THE SOUTH HAS THE RAIN FOCUSED SOUTH OF SF WHILE THE GFS SHOWS A WIDESPREAD EVENT WITH THE HIGHEST RAINFALL TOTALS OVER THE NORTH BAY. IN ADDITION, THE MODELS DISAGREE IN REGARD TO WIND CONCERNS WITH THE GFS SOLUTIONS MUCH WINDIER. DEPENDING ON WHICH ONE VERIFIES, RAIN WILL END EITHER WEDNESDAY OR THURSDAY. [DISC]
Additional rainfall amounts for the system next week should be as great — if not greater — than what we will see this weekend. Urban spots should see another 1/2"-1.5" with higher elevation locations in the 3–6" range. If things line up just right, some of the local spots in the hills could end up with 7 day rainfall totals of nearly a foot! ∨
ADDITIONAL RAINFALL AMOUNTS FOR THE SYSTEM NEXT WEEK SHOULD BE AS GREAT -- IF NOT GREATER -- THAN WHAT WE WILL SEE THIS WEEKEND. URBAN SPOTS SHOULD SEE ANOTHER 1/2"-1.5" WITH HIGHER ELEVATION LOCATIONS IN THE 3-6" RANGE. IF THINGS LINE UP JUST RIGHT, SOME OF THE LOCAL SPOTS IN THE HILLS COULD END UP WITH 7 DAY RAINFALL TOTALS OF NEARLY A FOOT! [DISC]
High pressure is forecast to build back to our area for the second half of next week allowing for a return to dry conditions. ∨
HIGH PRESSURE IS FORECAST TO BUILD BACK TO OUR AREA FOR THE SECOND HALF OF NEXT WEEK ALLOWING FOR A RETURN TO DRY CONDITIONS. [DISC]
Aviation. As of 3:40pm PST Wednesday… VFR [Visual Flight Rules] conditions with light winds through the forecast period. High cloud continue to stream in over the North Bay this evening. These insulating clouds will work against fog development… however can't quite rule out fog at KSTS [Santa Rosa CA]… but may do so at the 06Z [10pm PST] TAFs [Terminal Aerodrome Forecasts]. ∨
.AVIATION...AS OF 3:40 PM PST WEDNESDAY...VFR CONDITIONS WITH LIGHT WINDS THROUGH THE FORECAST PERIOD. HIGH CLOUD CONTINUE TO STREAM IN OVER THE NORTH BAY THIS EVENING. THESE INSULATING CLOUDS WILL WORK AGAINST FOG DEVELOPMENT... HOWEVER CANT QUITE RULE OUT FG AT KSTS... BUT MAY DO SO AT THE 06Z TAFS. [AVIA]
Vicinity of KSFO [San Francisco CA]… VFR [Visual Flight Rules]. ∨
VICINITY OF KSFO...VFR. [AVI2]
KSFO [San Francisco CA] bridge approach… similar to KSFO [San Francisco CA]. ∨
KSFO BRIDGE APPROACH...SIMILAR TO KSFO. [AVI2]
Monterey Bay Area terminals… VFR [Visual Flight Rules]. ∨
MONTEREY BAY AREA TERMINALS...VFR. [AVI2]
Marine. As of 03:33pm PST Wednesday… southerly winds will prevail north of Pigeon Point [Pescadero CA] and northerly winds will prevail south of Pigeon Point [Pescadero CA] through Friday. Southerly flow will develop over all of the coastal waters this weekend as a storm system begins to impact the region. Unsettled weather is expected Friday into early next week with periods of rain and gusty winds. The sea state will likely deteriorate rapidly early next week as the strongest storm moves through. ∨
.MARINE...AS OF 03:33 PM PST WEDNESDAY...SOUTHERLY WINDS WILL PREVAIL NORTH OF PIGEON POINT AND NORTHERLY WINDS WILL PREVAIL SOUTH OF PIGEON POINT THROUGH FRIDAY. SOUTHERLY FLOW WILL DEVELOP OVER ALL OF THE COASTAL WATERS THIS WEEKEND AS A STORM SYSTEM BEGINS TO IMPACT THE REGION. UNSETTLED WEATHER IS EXPECTED FRIDAY INTO EARLY NEXT WEEK WITH PERIODS OF RAIN AND GUSTY WINDS. THE SEA STATE WILL LIKELY DETERIORATE RAPIDLY EARLY NEXT WEEK AS THE STRONGEST STORM MOVES THROUGH. [AVIA]
.MTR WATCHES/WARNINGS/ADVISORIES... .TNGT...NONE. [WARN]
Public Forecast: Bell; Aviation: MM/DRP; Marine: MM ∨
PUBLIC FORECAST: BELL AVIATION: MM/DRP MARINE: MM [CRED]
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3:06pm PST Nov 26 2014
Tonight. Mostly clear, with a low around 53°. Calm wind.
Thanksgiving Day. Sunny, with a high near 64°. Light and variable wind.
Thursday Night. Partly cloudy, with a low around 49°. South wind 6 to 9 mph.
Friday. Mostly sunny, with a high near 57°. South wind around 10 mph.
Friday Night. Rain, mainly after 4am. Low around 51°. SSE wind 13 to 16 mph, with gusts as high as 21 mph. Chance of precipitation is 80%.
Saturday. Rain. High near 59°. Chance of precipitation is 80%.
Saturday Night. Rain. Low around 52°. Chance of precipitation is 90%.
Sunday. Rain likely. Cloudy, with a high near 60°.
Sunday Night. Rain likely. Cloudy, with a low around 52°. Breezy.
Monday. A chance of rain. Cloudy, with a high near 59°. Breezy.
Monday Night. A chance of rain. Mostly cloudy, with a low around 51°. Breezy.
Tuesday. Rain likely. Mostly cloudy, with a high near 59°. Breezy.
Tuesday Night. A chance of rain. Mostly cloudy, with a low around 50°.
Wednesday. A chance of showers. Mostly cloudy, with a high near 60°.