####018007051#### FXUS66 KMTR 272021 AFDMTR Area Forecast Discussion National Weather Service San Francisco CA 121 PM PDT Wed Mar 27 2024 ...New SYNOPSIS, SHORT TERM... .SYNOPSIS... Issued at 120 PM PDT Wed Mar 27 2024 Unsettled conditions will prevail through the upcoming weekend. Thunderstorms are most likely in the Friday afternoon through Saturday timeframe in the post frontal environment. Then, warmer and drier conditions are expected next week. && .SHORT TERM... (This evening through Thursday) Issued at 120 PM PDT Wed Mar 27 2024 Light rain is currently falling over the North Bay and will spread southward overnight as a weak frontal boundary moves through the region. Rainfall amounts are expected to be light amounting to 0.50- 1.00" in the coastal ranges, 0.25-0.50" in the low lands and coastal areas, with <0.25" in the rain shadowed valleys through Thursday morning. Overnight lows will generally be in the low-to-mid 40s and near 50 degrees closer to the coastline. Thursday will feature cool and mostly dry conditions, but cannot rule out lingering post frontal rain showers especially over the northern half of the region. && .LONG TERM... (Thursday night through Tuesday) Issued at 319 AM PDT Wed Mar 27 2024 After a brief pause in rain into Thursday evening, another quicker-moving cold front and low pressure move into the upper level trough pattern. The momentum of this next system will pull the trough farther south and placing the trough axis into the Bay Area. What does this mean? Increased moisture arriving into the Bay Area and Central Coast compared to today's system, and a cool- looking momentum transfer on the forecast maps. The overnight forecast update took some time looking at this second system, and there still is a fair amount of variability possible. The current trend pushes the focus of this system's main rain band farther south, increasing rain amounts along Big Sur, and reducing them for the North Bay. Thunderstorm and shower chances behind the rain band still look fairly evenly spread across the Bay Area and Central Coast Friday night through Saturday evening, peaking around 25% during that time frame. Rainfall totals from Thursday night through early Sunday morning look to range from: -0.5" to 1" for most areas -1" to 1.25" for coastal low lands and interior North Bay -1.25" to 2" for higher elevations along the coast - and above 2" for the highest peaks along the coast with some isolated areas on the Big Sur Coast reaching above 3" Winds will be stronger with this next system, but the variability makes it difficult to pin down which spots will be most affected, but breezy to gusty conditions should be expected Friday afternoon and into that night. This will be something worth checking back in on within the next few forecast updates. Beyond these back-to-back systems, dry weather returns as an upper level ridge snaps into place over the California Coast into the next work week. This will push any oncoming rain systems North and into the Washington and Oregon coasts. && .AVIATION... (18Z TAFS) Issued at 1108 AM PDT Wed Mar 27 2024 Increased precipitation coverage and decreased CIG/visibilities will occur as a weak cold front approaches the Bay Area and Central Coast. Moderately gusty southerly to southwesterly winds will continue through mid tomorrow morning. For the North Bay, radar indicates that scattered showers have arrived near STS and APC. For airports south of STS and APC, precipitation chances will start to increase moving into the late morning to afternoon hours. Showers will move into OAK and SFO between 20-22Z, between 22-23Z for LVK and SJC, and between 00-03Z for MRY and SNS. MVFR CIGS are expected to prevail through most of the TAF period with VFR CIGS returning for most stations by mid to late tomorrow morning. Vicinity of SFO...Mid level overcast cloud cover is starting to move over the SF peninsula with low level overcast skies expected by 21Z. Moderately gusty S to SW winds will start to pick up heading into the afternoon with gusts up to 25 knots possible. Rain cover will increase between 21-23Z with some reductions in visibility possible if a stronger storm moves directly over the airport. This system has slowed down slightly so will continue to monitor to see if timing of rain starting needs to be pushed back. Looking ahead to the end of the TAF period, as the system moves away from the Bay Area VFR CIGS will return and W to SW winds will weaken. SFO Bridge Approach...Similar to SFO. Monterey Bay Terminals...Some early morning low level cloud cover has moved out of SNS with clear skies expected through the late morning. Heading into the afternoon, MVFR CIGS will return by 00-03Z as a cold front reaches the Central Coast and brings widespread light rain. Moderate S to SW winds will prevail with light, variable winds and VFR CIGS returning towards the end of the TAF period. Model guidance has shown this system slowing down with some models suggesting a later rain arrival time between 03-05Z. && .MARINE... (Today through Monday) Issued at 1108 AM PDT Wed Mar 27 2024 Moderate winds gradually turning S to SW through Wednesday as a weak cold front, producing scattered light to moderate showers, moves through the coastal zones. A second, stronger low pressure system will reach the coastal waters Friday, bringing moderate precipitation, gusty southerly winds, and allow for wave heights to build. This second system will create widespread conditions that are hazardous to small crafts. Long period northwesterly swell will continue to abate through the waters through the end of the month. && .MTR WATCHES/WARNINGS/ADVISORIES... CA...None. PZ...Small Craft Advisory until 9 PM PDT this evening for Pt Arena to Pt Reyes 0-10 nm-SF Bay N of Bay Bridge. Small Craft Advisory until 3 AM PDT Thursday for Mry Bay. Small Craft Advisory from 3 AM Thursday to 3 AM PDT Friday for Pt Arena to Pt Reyes 0-10 nm-Pt Arena to Pt Reyes 10-60 NM. Small Craft Advisory from 3 PM Thursday to 3 AM PDT Friday for Pigeon Pt to Pt Pinos 0-10 nm-Pt Pinos to Pt Piedras Blancas 0-10 nm-Pt Reyes to Pigeon Pt 0-10 nm. Small Craft Advisory until 9 PM PDT this evening for Pt Arena to Pt Reyes 10-60 NM. Small Craft Advisory from 9 AM Thursday to 3 AM PDT Friday for Pigeon Pt to Pt Pinos 10-60 NM. && $$ SHORT TERM...RGass LONG TERM....Murdock AVIATION...Kennedy MARINE...Kennedy 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 ####018004492#### FXUS66 KSTO 272022 AFDSTO Area Forecast Discussion National Weather Service Sacramento CA 122 PM PDT Wed Mar 27 2024 .Synopsis... The first of two weather systems is moving through today into Thursday, bringing periods of mountain snow, rain, breezy winds, and isolated thunderstorms. The second storm is expected Friday into Saturday, bringing similar impacts. Drier weather by the end of the weekend continuing into early next week. && .Discussion... Current GOES-West satellite imagery shows a band of moisture draped across much of the far western US. Both radars, KBBX and KDAX, have been flipped over into precipitation mode as showers and mountain snow spread inland across interior northern California this afternoon. Periods of moderate to heavy mountain snow,breezy winds, rain and isolated thunderstorms are in the forecast for the rest of the week and into the weekend. Moderate to heavy mountain snow will move in this afternoon and continue into Thursday morning. High resolution guidance shows snow rates of up to 1 to 3 inches per hour over this timeframe. The Winter Storm Warning remains in effect for portions of the northern Sierra Nevada and western Plumas County/Lassen area through Thursday morning. Snowfall will become more showery on Thursday, and then a secondary wave will bring more moderate snow Friday into Saturday. The National Blend of Models (NBM) has a 25-55% probability of 12 inches of snow above 5500 ft today into Thursday, and a 25-45% probability of the same amount from Friday into Saturday. Periods of mountain travel delays, chain controls and snow covered roads can be expected over the next few days. Be sure to check road conditions from Caltrans and the weather forecast before traveling into the mountains. Periods of showers and light rain will bring slick road conditions at times over the next few days as well. The NBM suggests a 35-95% probability of 0.50" in the Valley and foothills through Thursday night (best chances in the northern Sacramento Valley and foothills), with a 55-95% probability of the same amount from Friday through Saturday night. Expect locally heavier amounts where any thunderstorms develop. The NBM projects a 10-25% probability of thunderstorm development today, Thursday and Saturday, with the most likely timeframe being in the afternoon and evening hours. Small hail, lightning, brief heavy rain and gusty winds are possible with any thunderstorms that develop. Gusty southerly winds are in the forecast through this evening, mainly in the northern and central Sacramento Valley, adjacent foothills, and Sierra Nevada where the NBM has a 50-90% probability of wind gusts of 40 mph or greater. Strongest winds are expected through this evening, however lingering breezy conditions will continue through the week and into Saturday. //KH && .EXTENDED DISCUSSION (Sunday THROUGH Wednesday)... Lingering light showers are anticipated on Sunday, mainly over the Sierra foothills and mountains with little to no impacts. Upper ridging builds into the PacNW early next week with offshore flow over interior NorCal. Therefore, expect drier and warmer conditions across the region early to mid week. Locally gusty north to east wind may develop Monday and Tuesday, mainly along the west side of the Sacramento Valley, foothills and northern Sierra Nevada. The NBM is currently showing a 30-80% probability of northerly to easterly wind gusts of at least 25 mph, with probabilities of wind gusts greater than 40 mph less than 10-20%. Above normal temperatures are expected, with Valley highs in the 70s, 60s and low 70s over the foothills, and 40s to mid 60s over the mountains. && .AVIATION... In Central Valley, areas MVFR/IFR developing through the afternoon. Areas of south surface wind up to 20 kts with local gusts up to 30 kts. In foothills and mountains, widespread MVFR/IFR with local LIFR over the next 24 hours. Snow levels 5500-6500 today, lowering to 3500-4000 feet by Thursday morning. Areas south to southwest sfc wind 15-25 kts with local gusts up to 40 kts or more over higher terrain. && .STO WATCHES/WARNINGS/ADVISORIES... Winter Storm Warning until 11 AM PDT Thursday for West Slope Northern Sierra Nevada-Western Plumas County/Lassen Park. && $$ ####018008840#### FXUS61 KBOX 272023 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 423 PM EDT Wed Mar 27 2024 .SYNOPSIS... A frontal wave will bring more widespread rain to the region from late today through Thursday, and possibly lingering into early Friday. This additional rainfall may lead to renewed flooding concerns. Rain coming to an end Friday may finish as a quick burst of low impact snow. Sunny, but windy, Friday and Saturday with a chance for a few showers Sunday night. Mix of clouds and sun on Sunday and Monday with near to above normal temperatures. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/... Clouds had dissipated across quite a bit of central southern New England, but more clouds are waiting just off to the west. Steep inversion remained in place, along with the humidity below it. Thus, clouds should be quick to return past sunset and temperatures drop. Widespread rainfall still expected to overspread southern New England between 10 PM and 2 AM. Could be a little earlier along and west of the CT River. Thinking rainfall tonight will be on the lighter side, generally one half inch or less. && .SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/... Key Messages... * Widespread rain likely * Axis of heaviest rain remains uncertain Latest guidance suite still has some issues with the axis of the heaviest rainfall Thursday into Thursday day. Now looking like there may be two axes of heavier rainfall. One would be over the ocean towards the outer Cape and east of Nantucket, so not much of a concern. The other looks to be right where we would not want it, eastern CT, northwest RI, and portions of eastern MA. Since this area already had several inches of rain for this past weekend, will be issuing a Flood Watch for portions of southern New England. Right now, thinking that 1-2 inch rainfall amounts would be most likely. However, ensembles do suggest a 30-50% probability for more than 2 inches of rainfall across RI and portions of southeast MA. Should that amount of rainfall occur, it is possible that more significant river flooding would result. Will need to closely monitor this potential over the next 24-36 hours. Not much wind for this rain event. So the focus is all on the rainfall and potential flooding. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... Highlights * Rain comes to an end Friday morning and may briefly transition to snow as low pressure departs into the Gulf of Maine * Blustery conditions Friday into Saturday will lead to sunnier conditions to start the weekend * Unsettled conditions mid week next week garner our next significant precip chance Friday and Saturday... Inverted trough/low pressure gradually swings to our east/northeast Friday allowing precipitation to come to an end by around lunchtime. It's possible that there is a brief period of snow wrapping around cyclonic flow as 850mb temps drop to as cold as -6 behind the departing low. Given warm antecedent conditions and a very saturated ground, thinking that some of the Hi-Resolution solutions, like the HRRR and NAM12 are much to aggressive with their 10:1 snow accumulation forecasts of 3-6"+, and even with their positive snow depth change estimates of up to 2-3" of snow across parts of eastern MA, but would not be shocked to see a few 10ths of an inch of snow accumulate across the high terrain before precip ends around mid day. Blustery conditions will develop late Friday and will maintain overnight Saturday through mid day as pressure gradient remains quite tight on the back side of the low. Additionally, a 925mb jet of 40-50kt will mix to the surface, yielding gusts in the 30-35kt range, with gusts to 40kt possible across the highest terrain of the Berkshires. Will note the NBM guidance was quite high compared to other models, which has been the case in estimating wind gusts as of late, so, blended in the NBM1 10th percentile guidance to keep gusts below wind advisory criteria. It's not out of the question that we see the strongest axis of the LLJ shifts a bit west would allow more widespread 40kt gust to develop, thus, not completely ruling out the potential need for a wind advisory for the period. The column dries pretty rapidly thanks to brisk NW flow, yielding sunny skies the second half of Friday through the first half of the weekend; a welcome sight for southern New Englanders after a mostly cloudy week. May see some spotty rain showers overnight Saturday as a weak shortwave tracks across northern New England. Sunday and Monday... Winds subside to around 20kt by Sunday as gradient slackens and more zonal mid level flow develops. Should see a mix of clouds and sun on Sunday and Monday as PWATs surge to near a half an inch, with moisture concentrated between the top of the boundary layer and 700mb. Mid level ridging building from the west lat Sunday into Monday will bring above normal temps back to southern New England, with temps approaching the mid 50s by Monday afternoon! Mid Next Week... Unsettled weather returns mid next week as low pressure digs from southern Ontario before emerging off the southern New England coast sometime between late Tuesday and Thursday. At this time, there remains significant uncertainty in the timing of this system, but we would be remiss to not at least mention the possibility of some mixed precipitation, especially across the high terrain, as cold air infiltrates the region on north/northeast flow. && .AVIATION /21Z WEDNESDAY THROUGH MONDAY/... Forecast Confidence Levels: Low - less than 30 percent. Moderate - 30 to 60 percent. High- greater than 60 percent. Through 00Z...high confidence on trends, lower on exact timing and details. Mainly VFR, with areas MVFR towards the Cape and islands. Tonight...high confidence. MVFR/VFR at 00z, lowering to IFR/MVFR as showers overspread the region tonight. LIFR possible across the hilly terrain of CT and MA. Light SSE winds. Thursday and Thursday night...high confidence. Widespread IFR/LIFR in rain, heavy at times possibly across eastern CT into RI and eastern MA. Light/variable wind becoming NNE. KBOS TAF...High confidence in trends, some uncertainty in exact timing of details. KBDL TAF...High confidence in trends, some uncertainty in exact timing of details. Outlook /Friday through Monday/... Friday: Mainly VFR, with local MVFR possible. Windy with gusts up to 30 kt. Chance RA. Friday Night through Saturday: VFR. Windy with gusts up to 35 kt. Saturday Night: VFR. Windy with local gusts up to 30 kt. Slight chance RA. Sunday through Sunday Night: VFR. Breezy. Monday: VFR. Slight chance RA. && .MARINE... Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. * NNE winds finally shift to the SSE Wed afternoon * Heavy rain possible late tonight into Thursday Night Weak high pressure remains over the waters into tomorrow. Showers become widespread, limiting vsby. Low pressure intensifies at it moves offshore Thursday into Thursday night. Rain, heavy at times, limits vsby. Outlook /Friday through Monday/... Friday: Strong winds with gusts up to 30 kt. Rough seas up to 10 ft. Chance of rain. Friday Night: Strong winds with gusts up to 35 kt. Rough seas up to 10 ft. Slight chance of rain. Saturday: Strong winds with gusts up to 35 kt. Areas of rough seas. Saturday Night: Low risk for Small Craft Advisory winds with gusts up to 30 kt. Seas up to 5 ft. Slight chance of rain. Sunday through Sunday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Monday: Winds less than 25 kt. Seas locally approaching 5 ft. Slight chance of rain. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...Flood Watch from 2 AM EDT Thursday through late Thursday night for CTZ004. MA...Flood Watch from 2 AM EDT Thursday through late Thursday night for MAZ004>007-012>024-026. RI...Flood Watch from 2 AM EDT Thursday through late Thursday night for RIZ001>007. MARINE...Small Craft Advisory until 8 AM EDT Friday for ANZ250. Small Craft Advisory until 8 AM EDT Thursday for ANZ251. Small Craft Advisory until 8 PM EDT Thursday for ANZ254>256. && $$ SYNOPSIS...Belk/KS NEAR TERM...Belk SHORT TERM...Belk LONG TERM...RM AVIATION...Belk/KS MARINE...Belk/KS