Area Forecast Discussion
Issued by NWS San Francisco Bay Area, CA
Issued by NWS San Francisco Bay Area, CA
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259 FXUS66 KMTR 022248 AFDMTR Area Forecast Discussion National Weather Service San Francisco CA 348 PM PDT Tue Jul 2 2024 ...New SYNOPSIS, SHORT TERM, LONG TERM... .SYNOPSIS... Issued at 158 PM PDT Tue Jul 2 2024 Significant and potentially deadly heat wave begins today lasting into next week. Fire and heat highlights have been extended as confidence in this pattern prolonging increases. Gusty afternoon winds and critically dry fuels will lead to elevated fire weather concerns through the weekend. && .SHORT TERM... (This evening through Wednesday) Issued at 158 PM PDT Tue Jul 2 2024 Current temperatures are running about 10-20 degrees warmer than 24 hours ago as the high pressure builds in. Main changes for today have been extending and adding to our current hazards. I will list out the changes here and talk more about them in the next section since they carry over into the "long term". The Heat Advisory for San Francisco has been extended to include Thursday. The Heat Advisory and Excessive Heat Warning for all other locations originally included have been extended to NEXT Tuesday night. The Red Flag Warnings in the North Bay, Santa Cruz Mtns, and East Bay Hills have been extended to Friday morning. Finally, a Fire Weather Watch was added for interior portions of Monterey and San Bentio Counties, Santa Lucia, and the Southern Salinas Valley for Friday through Sunday. In terms of the forecast from today into Wednesday, there will be no significant change. Some locations may see a degree or two taken off their highs while other will see a degree or two added. Wednesday afternoon, there is a very weak mid-level perturbation that will bring some degree of marine influence to coastal areas and locations around the Bay. While not a significant or even noticeable cool off by any means for most, this may help to limit high temps a bit for San Francisco Wednesday evening going into Thursday. On to the long term to discuss what we expect to happen going forward. && .LONG TERM... (Thursday and beyond) Issued at 158 PM PDT Tue Jul 2 2024 The heat isn`t going anywhere any time soon. Long range guidance and cluster analysis strongly suggest this pattern is here to stay through at least the beginning of next week. Some areas may see a couple of degrees shaved off before the weekend, but it will stay hot. A secondary peak is expected by the weekend into early next week. While it may seem manageable based on looking at a single day of these temps, the length of this event will present an extremely dangerous and potentially historic event. Jogging back in "recent" memory, to find the next most significant heat event in terms of overall scale and longevity, you have to look back to 2006. Sure, some locations have seen higher temps in more recent memory, but this many days in a row may actually be challenging some records based on the current forecast. How long will this actually last? Good question. Taking a look at the ensemble guidance for 850 mb temps...the forecast mean for OAK remains above the 90th percentile and near the maximum moving average through NEXT Friday, July 12. This is especially alarming when compared with a look at how models are handling the overall pattern. In the aforementioned cluster analysis, only 2% of total members support a flattening of the ridge by mid-to-late next week. This strongly suggests that there is high confidence in this pattern and associated heat wave lasting through the forecast period. This aided in the decision to extended the Excessive Heat Warning out for 8 consecutive days, an unprecedented action from our office. It cannot be stressed enough that this is an exceptionally dangerous and lethal situation. It may not seem so if you live near the coast, but an event of this scale, magnitude, and longevity will likely rival anything we`ve seen in the last 18 years for inland areas. Several days of temperatures well above normal and little relief overnight will lead to compounding effects among people and infrastructure, with the possibility of numerous heat related fatalities and rolling black outs. Heat is the number one weather related killer in the United States. By this weekend, it is VERY LIKELY that we add to that statistic if preparations are not taken seriously. && .AVIATION... (18Z TAFS) Issued at 1033 AM PDT Tue Jul 2 2024 Satellite shows clear skies across the region. With the slow moving high pressure system moving closer to our area, expect VFR to prevail through the TAF period for most terminals with the exception of Monterey Bay sites. With the compression of the marine layer, expect some coastal ares to see low ceilings and visibility overnight into the early morning hours. Winds will become breezy this afternoon, with a onshore direction before becoming light and variable tonight. There are some concerns for LLWS for the North Bay overnight but had low confidence to include at this moment. Vicinity of SFO...VFR will prevail through the TAF period. W/NW winds will become breezy this afternoon, with moments of gusty winds up to 25 knots. Winds become light this evening into the morning. Breezy conditions return by tomorrow afternoon. SFO Bridge Approach...Similar to SFO. Monterey Bay Terminals...VFR through the day with IFR/LIFR conditions redeveloping tonight. Confidence is moderate due to lack of agreement on model guidance. Therefore, clearing timing is uncertain and may occur earlier than 15Z. N/NW winds will become breezy this afternoon, but will return to light to moderate overnight. && .MARINE... (Today through Sunday) Issued at 1033 AM PDT Tue Jul 2 2024 Fresh to strong northerly winds continue over the outer coastal waters today, with gale force gusts possible in the northern outer waters through Tuesday night. Winds will diminish and become moderate to fresh by mid- week as surface high pressure strengthens and moves eastward. North to northwest winds prevail through the forecast period but wind direction may become more variable by late week as winds weaken. Elevated significant wave heights between 10-12 feet continue through mid- week before abating by the late week. Portions of the northern outer waters may see peak wave heights between 12-16 feet through mid-week. && .FIRE WEATHER... Issued at 330 PM PDT Mon Jul 1 2024 A Red Flag Warning will be in effect starting at 11pm tonight for some elevated locations in the North Bay Hills, East Bay Hills, Marin and Sonoma Coastal Ranges through late tomorrow evening with the North Bay Hills RFW continuing until 5pm Wednesday. RH values are generally in the teens with gusty north/northeast offshore flow. As the hot and dry pattern persists, fuels continue to dry. ERCs are drying in to the 70-90 percentile range across our region. Combine that with the expected surge of campers over the long holiday weekend and obvious risks of fireworks, putting our area in a combustible situation through next weekend. Fireworks should not be used this year, and campers should be very careful with anything dragging from trailers and securing campfires. && .MTR WATCHES/WARNINGS/ADVISORIES... CA...Coastal Flood Advisory until 11 PM PDT Wednesday for CAZ006-506- 508. Heat Advisory until 7 PM PDT Thursday for CAZ006. Excessive Heat Warning until 11 PM PDT Tuesday for CAZ502>504- 506-510-512>518. Red Flag Warning until 5 AM PDT Friday for CAZ502>504-512-515. Heat Advisory until 11 PM PDT Tuesday for CAZ508-528-529. Fire Weather Watch from Friday morning through Sunday evening for CAZ516>518. PZ...Small Craft Advisory until 3 AM PDT Wednesday for Pt Arena to Pt Reyes 0-10 nm. Gale Warning until 9 AM PDT Wednesday for Pt Arena to Pt Reyes 10-60 NM. Small Craft Advisory until 9 PM PDT this evening for Pigeon Pt to Pt Pinos 10-60 NM. && $$ SHORT TERM...Behringer LONG TERM....Behringer AVIATION...SO MARINE...SO Visit us at www.weather.gov/sanfrancisco Follow us on Facebook, Twitter, and YouTube at: www.facebook.com/nwsbayarea www.twitter.com/nwsbayarea www.youtube.com/nwsbayarea