A storm system is expected to bring strong winds, widespread heavy rainfall, and flooding concerns to the Hawaiian Islands through the weekend. Strong to severe thunderstorms are forecast from the Southern Plains to the Mid-Missouri Valley Thursday afternoon and evening. Large hail and strong winds are the primary threats. Read More >
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698 FXUS66 KMTR 090701 AFDMTR Area Forecast Discussion National Weather Service San Francisco CA 1201 AM PDT Thu Apr 9 2026 ...New SHORT TERM, LONG TERM... .KEY MESSAGES... Updated at 1159 PM PDT Wed Apr 8 2026 - Unsettled weather Thursday through the weekend - Thunderstorms are possible today through Sunday with the best chances Friday and Saturday && .SHORT TERM... Issued at 1159 PM PDT Wed Apr 8 2026 (Tonight through Friday night) A surface low near 38 N, -133 W in the Eastern Pacific Ocean will be the talk of the short term. Our area narrowly escaped thunderstorms Wednesday as steeper lapse rates just to our north and east yielded greater instability. We did have enough lift and moisture however to record measurable precipitation. With the over performance that occurred Wednesday, I would expect more of the same Thursday as the low slowly treks eastward. The best chances for thunderstorms on Thursday will be in the North Bay, Interior East Bay, and Eastern Santa Clara County - the same areas that were narrowly missed today. Rain showers on Thursday will be more efficient as the low-levels have become saturated; in fact, the April 9th 00Z sounding observed a PWAT value of 1.04" which is the second highest for the date and time behind 1.08" from 2016. The greatest chances for thunderstorms will be Friday as the low enters our waters and continues its journey inland. The exact location and timing will make all the difference as the center of the low will offer an area of convergence. Since it is associated with an upper-level cutoff low, the independence from the jet stream unfortunately makes the precision side of the forecast very difficult. Nonetheless, the best chances are across the Interior Bay Area. Thunderstorm hazards on Thursday and Friday include: lightning, locally heavy rainfall, erratic/gusty winds, and small hail. Aside from thunderstorms, southwesterly winds carrying moist, warm air from the tropics will increase ahead of the cold front with pre-frontal rain showers expected in the warm sector. The slow movement and training effect of the rain bands may lead to localized flooding if a heavier rain shower/thunderstorm were to develop, especially in poor drainage and/or urban areas. && .LONG TERM... Issued at 1159 PM PDT Wed Apr 8 2026 (Friday night through next Wednesday) An upper-level low in the Gulf of Alaska will dig down the West Coast Saturday, absorbing the first low as it does so. This second system is much more dynamic which will yield two noticeable differences: widespread rainfall instead of just rain showers and thunderstorms capable of rotating. The three thunderstorm ingredients of lift, instability, and moisture will be similar if not better than the first low. A surface low and its attendant cold front will be the primary lifting mechanism, cold air filtering in aloft (850 mb temperatures near freezing) will steepen lapse rates and increase instability as a result, and PWAT values will remain near the 90th percentile ahead of the cold front. The shear profiles will be very different between the vertically stacked first low and the progressive second low. The vertically stacked low will have low shear while the progressive low will have sufficient low-level shear to support rotation within thunderstorms. All of this to say, widespread rainfall with lingering thunderstorm chances are expected over the weekend with the best chances on Saturday. Moisture will be a limiting factor behind the cold front, but if the coldest conditions overlap with ample moisture, snow is possible in the mountain peaks Sunday morning with snow levels around 4,000 feet. Rainfall totals between Thursday and Sunday continue to trend higher with totals on the order of 0.50"-1.50" with up to 3.00" in the coastal ranges. Commercial and recreational fisherpeople are encouraged to use extreme caution now through the weekend with the unsettled weather moving in. Thunderstorms over the waters will be capable of producing: lightning, locally heavy rainfall, gale force gusts, small hail, and waterspouts. In the cold front`s wake we will be left with, you guessed it, cold air! Cold starts to the day can be expected as skies clear and dry air filters in. The warming and drying trend kicks off Monday and lasts at least until Wednesday as surface high pressure builds into the West Coast. && .AVIATION... (06Z TAFS) Issued at 1001 PM PDT Wed Apr 8 2026 IFR stratus has developed at the coast and will expand inland through the night, as moderate onshore winds become light through Thursday morning. Timing of stratus impacts is low to moderate confidence as the pace of expansion has been slower than the model output has depicted. Stratus will lift and retreat to the coastal regions through the course of Thursday morning, with mid- to high level clouds across the region as a system approaches, causing southwest winds across the region on Thursday afternoon. Some isolated showers are possible in the coastal region and North Bay valleys, but most terminals should not see rain until Friday past the end of the TAF period. Also beyond the TAF period, expect scattered thunderstorms to develop late Friday morning and continue through the day. Vicinity of SFO... Moderate northwest winds will diminish overnight with IFR stratus developing in the next few hours and lasting through late Thursday morning. Exact stratus formation time is uncertain owing to poor model depictions of the present situation. Ceilings will lift late Thursday morning into the early afternoon, with moderate winds resuming from a southwesterly direction in advance of a system that will bring MVFR-IFR ceilings and some isolated showers to the region on Thursday evening into Friday morning, but with most of the rain expected to arrive after the end of the TAF period. Also beyond the TAF period, expect scattered thunderstorms to develop late Friday morning and continue through the day. SFO Bridge Approach... Similar to SFO. Monterey Bay Terminals... It appears that large-scale southwest flow is already impacting the stratus pattern at the terminals with the stratus deck deflected to the north of MRY and SNS as of the latest satellite imagery. Expecting this deck to inch its way southward as light winds continue at the terminals, but timing of impacts is uncertain as models are not capturing this situation well. Stratus will scatter out through the course of Thursday morning, leaving a layer of mid- to high level clouds with moderate onshore winds through the afternoon. Some isolated showers could arrive Thursday evening but most impacts, including scattered thunderstorms, should arrive beyond the TAF period on Friday. && .MARINE... (Tonight through next Tuesday) Issued at 1001 PM PDT Wed Apr 8 2026 Gentle to moderate northwest winds across the coastal waters are shifting to the south and southwest tonight as a low pressure system approaches the coast. This system will result in showers and a chance of thunderstorms Thursday through Sunday, with SW winds increasing to a strong breeze on Saturday. As high pressure builds behind the system, fresh northwest winds will develop Sunday through Monday. && .MTR WATCHES/WARNINGS/ADVISORIES... CA...None. PZ...None. && $$ SHORT TERM...Sarment LONG TERM....Sarment AVIATION...DialH MARINE...DialH Visit us at www.weather.gov/sanfrancisco Follow us on Facebook, X, and YouTube at: www.facebook.com/nwsbayarea x.com/nwsbayarea www.youtube.com/nwsbayarea |
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