Area Forecast Discussion
Issued by NWS San Francisco Bay Area, CA
Issued by NWS San Francisco Bay Area, CA
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651 FXUS66 KMTR 031113 AFDMTR Area Forecast Discussion National Weather Service San Francisco CA 413 AM PDT Mon Jun 3 2024 ...New SHORT TERM, LONG TERM, MARINE... .SYNOPSIS... Issued at 1254 PM PDT Sun Jun 2 2024 Cooler temperatures hang on through today with breezy daytime winds and marine layer stratus overnight. Tuesday sees a dramatic warmup with a Heat Advisory in effect for the inland areas through Thursday. Temperatures will moderate towards the latter part of the week. && .SHORT TERM... (Today and tonight) Issued at 413 AM PDT Mon Jun 3 2024 Milder morning temperatures are occuring courtesy of a mix of low clouds and incoming higher level clouds from the northwest, higher dewpoint temperatures (measure of water vapor), areas of mixing surface winds and the lower level temperature inversion (all slowing nocturnal radiative cooling). Dewpoint temperatures are mainly in the lower to mid 50s across the forecast area, in contact with 50F-54F sea surface temperatures helping to form coastal fog and drizzle. Higher water vapor also extends into the vertical, precipitable water (pw) on last evening`s Oakland upper air sounding was 1.19" which is near the long term max moving average in early June. The GFS has been forecasting the pw to peak near 1.40" by late this morning, not far from a couple daily maximums ~ 1.50"-1.55" on the period of record (since 1948) in early to mid June. With 500 mb heights mainly at or slightly greater than 580 decameters (about typical for June) there isn`t enough broad based cooling e.g. positive vorticity to largely precipitate out the increased water vapor at our latitude (like it certainly could in winter season), rather like Sunday morning on the coastline, the higher levels of water vapor may still produce either patchy coastal drizzle or very light rain, add in a surface based cool front forecast to arrive later today and this too may help further produce light measurable precipitation, best chances on the coastline. A fair amount of clouds are rolling in, the best chance of sunny breaks today will be inland and during the afternoon. Daytime highs will be about the same today compared to Sunday except cooler farther inland, i.e. due to increasing cloud cover and post frontal cool air advection later today. Some coastal stratus is likely to roll back in this evening, lower level winds also shifting to north to northeasterly direction starting late tonight. && .LONG TERM... (Tuesday through Sunday) Issued at 413 AM PDT Mon Jun 3 2024 Model forecasts are consistently showing a steepening ACV-SFO pressure gradient, increasing 925 mb and 850 mb temperatures and steadily climbing 500 mb heights Tuesday, all indicating higher pressure moving in and warmer to hotter temperatures soon to develop over the forecast area. Lower to mid level tropospheric temperatures will increase under compressional warming, readings nearing the max moving average for early June, 500 mb heights (peaking near 590 decameters) will be between the 90th percentile and the max moving average in early June. As we have been advertising, it`ll turn warm to hot fairly quickly especially inland. A heat advisory remains in effect Tuesday-Thursday. The marine layer will become compressed, likely to 1000 feet or less, preventing inland areas from receiving afternoon & evening sea breeze relief. Midweek timeframe by midday Wednesday is when the apex of 500 mb heights will pass east of our forecast area, the center of the high continuing to shift eastward reaching NM/TX late week before becoming approximately stationary; a strong zonal jet stream across the Pacific and western CONUS likely helping to at least initially move the ridge well inland at a quickened pace. Have mentioned in a previous discussion current coastal sea surface temperatures are in good shape, running 1F to 2F below June normals and the PDO is in negative phase. This will help restore a sea breeze, question is how quickly later on this week, plus pw values are forecast to remain above normal even during mid to late week which will eventually help restore coastal stratus & fog. To add, more recent meso-scale and global model output have scaled back the potential for a coastally trapped southerly wind reversal here in our forecast area mid to late week. It still may happen, can`t completely rule it out, but from a numerical weather prediction aspect it currently looks less favorable. Rather a reinforcement of surface high pressure over the coastal and offshore waters may bring in cooler air, re-establishing an onshore SFO-SAC pressure gradient while the ACV-SFO pressure gradient (northerly winds) will have already decreased by late week. Helpful life saving information/tips from previous discussion: Moderate HeatRisk is expected for the inland North Bay, the East and South Bays, and the inland Central Coast through Thursday, meaning that there`s a moderate risk of heat-related illnesses for sensitive populations (children, the elderly, pregnant women, those with certain medical conditions, or anyone working outside without cooling or hydration). In addition, we`re also starting to see major HeatRisk in some areas of the North Bay valleys and far eastern Contra Costa county on Tuesday, corresponding to a major risk of heat-related illnesses to anyone without effective cooling, adequate hydration, or both. Here are some heat safety tips: * Stay hydrated and drink plenty of fluids. * Wear lightweight, light-colored clothing. * Reduce time spent outdoors or stay in the shade. * Never leave people or pets unattended in vehicles. * Use sunscreen if going to the coast or the pool. && .AVIATION... (06Z TAFS) Issued at 1150 PM PDT Sun Jun 2 2024 Coastal stratus will continue to push inland through much of the night, bringing low IFR CIGs for many terminals. Models do suggest CIGs even dipping into LIFR territory, though confidence on this is only moderate for the SF Bay region. However, with an approaching ridge, this could lead to compression, thereby lowering CIGs, so it is not entirely out of the question that CIGs could go LIFR. Therefore, have decided to include LIFR CIGs in select TAF sites for now, though this will be something to keep an eye on through the night. Into the afternoon tomorrow, moderate westerly winds return, though gusts will likely be isolated to coastal terminals, reaching about 20-25 knots. Clearing to VFR is expected to be late for most, occuring in the afternoon as winds begin to increase. Vicinity of SFO...Currently IFR. Moderate confidence in becoming LIFR into the later overnight hours. High clouds will also be present through the morning. Late clearing of stratus is expected in the afternoon time, VFR but with SCT low clouds as winds increase and gust to around 30 knots out of the west. Clouds are anticipated to continue to dissipate through the end of the TAF period leading to widespread VFR. SFO Bridge Approach...Similar to SFO. Monterey Bay Terminals...IFR conditions persist through much of the night, becoming LIFR in the early morning of Monday. Stratus will begin to lift again near sunrise, eventually becoming MVFR in the late afternoon. Not expecting clearing to VFR tomorrow, so have left CIGs in the TAF. Westerly winds breezy in the afternoon tomorrow, then easing into the late night. && .MARINE... (Tonight through next Friday) Issued at 254 AM PDT Mon Jun 3 2024 Moderate to fresh NW winds persist through the midweek, but increase to become strong towards Wednesday with gale force gusts possible in the northern waters. Moderate wave heights will persist before rough seas build towards the mid-week with significant wave heights of 10-12 feet expected. && .CLIMATE... Issued at 127 AM PDT Sat Jun 1 2024 Record high temperatures at the long term climate stations for June 4th and 5th: Station June 4th June 5th Santa Rosa 98 in 1949 102 in 1926 Kentfield 101 in 1981 102 in 1926 Napa 102 in 1981 105 in 1903 Richmond 90 in 1955 86 in 1983 Livermore 105 in 1960 104 in 1926 San Francisco 92 in 1949 95 in 1883 SFO Airport 92 in 1955, 1949 89 in 1972 Redwood City 100 in 1981 97 in 2002, 1972 Half Moon Bay 71 in 1955 74 in 1958 Oakland downtown 96 in 1981 87 in 2002 San Jose 98 in 1904 100 in 1926 Salinas Airport 92 in 1949 87 in 1949 King City 102 in 1981, 1957 105 in 1926 && .MTR WATCHES/WARNINGS/ADVISORIES... CA...Heat Advisory from 8 AM Tuesday to midnight PDT Thursday night for CAZ503-504-506-510-515. Heat Advisory from 8 AM Wednesday to midnight PDT Thursday night for CAZ513-514-518. PZ...Small Craft Advisory from 3 PM this afternoon to 9 PM PDT this evening for Mry Bay. Small Craft Advisory until 3 AM PDT early this morning for Pigeon Pt to Pt Pinos 10-60 NM-Pt Arena to Pt Reyes 0-10 nm- Pt Arena to Pt Reyes 10-60 NM-Pt Reyes to Pigeon Pt 0-10 nm. Small Craft Advisory from 3 PM this afternoon to 3 PM PDT Tuesday for Pigeon Pt to Pt Pinos 10-60 NM-Pt Arena to Pt Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60 NM. Small Craft Advisory from 3 PM this afternoon to 3 AM PDT Tuesday for Pigeon Pt to Pt Pinos 0-10 nm-Pt Reyes to Pigeon Pt 0-10 nm. Small Craft Advisory from 9 AM to 3 PM PDT Tuesday for Pigeon Pt to Pt Pinos 0-10 nm-Pt Reyes to Pigeon Pt 0-10 nm. Small Craft Advisory until 3 PM PDT Tuesday for Pt Pinos to Pt Piedras Blancas 0-10 nm. && $$ SHORT TERM...Canepa LONG TERM....Canepa AVIATION...AC MARINE...AC 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