####018006462#### FXUS66 KMTR 170356 AAA AFDMTR Area Forecast Discussion...UPDATED National Weather Service San Francisco CA 856 PM PDT Fri May 16 2025 ...New UPDATE... .SYNOPSIS... Issued at 137 PM PDT Fri May 16 2025 Breezy to windy conditions and cooler temperatures on tap for the weekend as a potent system enters the Great Basin. A warming and drying trend is expected through the upcoming week as high pressure builds into the Pacific Northwest and northern California. && .UPDATE... Issued at 855 PM PDT Fri May 16 2025 The short term forecast is in good shape with no tweaks needed. We continue to monitor the potential for increased winds this weekend. At present time, the fiercest winds are anticipated over the open waters of the Pacific Ocean, however, some of the higher terrain regions such as the North and East Bay Mountains and Hills, as well as the higher terrain of the Diablo and Santa Lucia Ranges may see gusts exceed 45 mph (around a 60-70% chance). At this time, the coverage of gusts above 45 mph appears too small to warrant any sort of wind products. There's an elevated risk for grass fires with the increased winds and afternoon humidity falling down below 30% in some locations. With most areas (though not all) still benefiting from winter rains. Given the marginal nature of wind/fire weather concerns, we'll simply advertise these hazards via messaging (AFD, text products, IDSS, and graphics/social media). Be sure to avoid activities that could spark a grass fire and obey any local fire restrictions. && .SHORT TERM... (This evening through Saturday) Issued at 137 PM PDT Fri May 16 2025 Mostly clear sky conditions have returned to the region this afternoon. Afternoon temperatures will be within a few degrees (-5 to +5) of seasonal averages. However, passing high clouds continue over the region. Low clouds are likely to return tonight and into Saturday morning, and push further inland, as we have abundant low level moisture. Coastal drizzle will also be possible Saturday morning as the marine layer deepens overnight. Low clouds spreading further inland, the deepening of the marine layer, and an approaching trough of low pressure will result in a slight cool down for Saturday afternoon. Maximum forecast high temperatures will range from the mid 50's to mid 60's on northwest facing coastal locations to upper 60's to mid 70's across the interior. Northwesterly winds are expected by Saturday afternoon with gusts 25-35 mph in lower elevations across the region with stronger gusts up to 45 mph in the higher elevations and just along the North Bay coast. && .LONG TERM... (Saturday night through next Thursday) Issued at 137 PM PDT Fri May 16 2025 Winds ease slightly Saturday night into Sunday morning, with the exception of the higher elevations. Breezy and gusty winds will persist on Sunday afternoon with similar values mentioned above, maybe a tad bit stronger. The aforementioned upper level trough will dig into the Great Basin through Sunday before ejecting further to the east. This will result in northerly, potentially offshore winds in the higher elevations and typically windy gaps and passes of Napa, Contra Costa, Alameda, and Santa Clara counties Sunday night into Monday. This will lead to elevated fire weather conditions as humidity values will be in the 40-50% range Sunday night and as low as 15% on Monday afternoon (again in the higher elevations). High pressure will begin to build into the Pacific Northwest and northern California in wake of the exiting trough with the warmest day currently anticipated to be Wednesday. Temperatures Wednesday afternoon look to be 5-15 degrees above seasonal averages with mid 60's to mid 70's for coastal areas, mid 70's to lower 80s across the bayshore, and mid 80's to lower 90's across the interior. More of a zonal flow is expected by late next week with the likely return of a shallow marine layer and more seasonal temperatures. && .AVIATION... (00Z TAFS) Issued at 423 PM PDT Fri May 16 2025 VFR is expected to persist through much of the evening, until coastal stratus and patchy fog produce /IFR- MVFR/ cigs, primarily after midnight. Gusty northwest winds aloft will result in periods of low level wind shear at KSTS Airport 12z-17z Saturday morning. Vicinity of SFO...VFR is expected to persist through much of the evening with /IFR- MVFR/ cigs set to settle in after midnight. Gusty westerly winds will produce wind gusts at or exceeding 35 knots at times this evening, with an Airport Weather Warning in place until 9 PM tonight. Similarly gusty winds are expected to develop Saturday afternoon and evening. SFO Bridge Approach...Similar to SFO. Monterey Bay Terminals...MVFR due to coastal stratus developing tonight, a few patches of light drizzle are possible as well. Cigs may break at times until late in the overnight, when MVFR cigs are expected to persist through the day and evening hours with the development of steady onshore winds from 10 to 20 knots, strongest from Saturday afternoon into the evening hours. && .MARINE... (Today through Wednesday) Issued at 1045 AM PDT Fri May 16 2025 Gusty to strong northwest winds will continue over the coastal waters today through the weekend, including much of early to mid next week. Hazardous marine conditions with rough to very rough seas will continue through Tuesday night. && .MTR WATCHES/WARNINGS/ADVISORIES... CA...None. PZ...Small Craft Advisory until 3 PM PDT Saturday for Mry Bay-Pigeon Pt to Pt Pinos 0-10 nm-Pt Pinos to Pt Piedras Blancas 0-10 nm-SF Bay N of Bay Bridge. Gale Warning until 3 PM PDT Saturday for Pt Arena to Pt Reyes 0- 10 nm-Pt Arena to Pt Reyes 10-60 NM-Pt Reyes to Pigeon Pt 0- 10 nm. Gale Warning until 3 AM PDT Saturday for Pigeon Pt to Pt Pinos 10-60 NM. && $$ UPDATE...Bain SHORT TERM...RGass LONG TERM....RGass AVIATION...JM MARINE...Canepa 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 ####018007180#### FXUS63 KDTX 170357 AFDDTX Area Forecast Discussion National Weather Service Detroit/Pontiac MI 1157 PM EDT Fri May 16 2025 .KEY MESSAGES... - Clusters of thunderstorms move through SE Michigan from midnight to 2 AM. A few storms could produce small hail and gusty wind but with diminishing potential for severe intensity. - Windy and cooler this weekend with westerly gusts of 30 to 40 mph Saturday. && .AVIATION... Well-mixed and gusty SW surface wind has spread into Lower Mi in warm sector fashion ahead of low pressure occluding into the northern Great Lakes. The associated cold front sweeps remaining thunderstorm potential into Ontario by the 06Z forecast issuance leaving a few hours of VFR in the system dry slot during the late night. This precedes MVFR ceiling as it expands eastward from the Midwest where coverage is widespread around the SW flank of the surface low center. Gusty wind also becomes a weather highlight late tonight and especially as daytime instability builds by late morning through the afternoon. West gusts well in into the 30 knot range are expected which also helps ceiling break into low end VFR late in the day and Saturday evening. For DTW/D21 Convection... Thunderstorms move east of the DTW terminal area from 06Z onward late tonight. THRESHOLD PROBABILITIES... * Low for ceiling 5000 feet or less late tonight the high in the morning through Saturday evening. && .PREV DISCUSSION... Issued at 943 PM EDT Fri May 16 2025 UPDATE... Ongoing storms from central Lower Mi into southern Lake Mi continue moving eastward while new development is likely out ahead and farther east into SE Mi late this evening. Expanding convection is boosted by height falls and DCVA on the leading edge of the 500 mb low which then feed off MUCAPE holding in the 1000-1500 J/kg range and effective bulk shear in the 30-50 kt range. This has already been supportive of the large hail producing supercell exiting Isabella county at forecast issuance. Hourly mesoanalysis and RAP projections maintain favorable 700-500 mb lapse rate near 8 C/km as the moisture axis sweeps through Lower Mi ahead of the cold front. This is combined with the 00Z DTX sounding that shows both the lapse rate and dry air centered around 700 mb along with a dry inverted-V profile below cloud base. Bottom line here is that we continue to expect strong to severe storms, with large hail as the primary hazard and damaging wind also possible, in SE Mi until the cold front sweeps activity into Ontario around 2 AM. PREV DISCUSSION... Issued at 344 PM EDT Fri May 16 2025 DISCUSSION... Southeast Michigan holding position late this afternoon immediately downstream of a closed mid level pivoting across Wisconsin. A warm but drier profile now entrenched, with a brief window of deeper stability in residence now evident by a simply a limited coverage of diurnal cu. Dry and stable conditions to hold through at least 00z, with attention tonight shifting to a mid level perturbation shearing out ahead of the main height fall center. Noted increase in forced ascent attendant to this feature set to sweep across the local area 01z-07z. Renewed boundary layer moistening will commence at the same time, offering at least a weakly unstable low level environment. Mixed signal yet across the model solution space on possible degree of destabilization, with variability noted in dewpoint recovery by as much as 8-10 degrees. This will impact both prospective coverage and vigor of any convective development within this window. Assuming the upward vertical motion field can overcome residual capping issues, then potential exists for cells to attain greater updraft depth given very steep mid level lapse rates. Background wind field more than sufficient to offer organization to any vigorous updrafts. This conditional setup carries enough potential should greater instability materialize to warrant an upgrade in the Day 1 SPC outlook to a slight risk for southern portions of the area, highlighting a damaging wind gust and hail threat. A secondary window exists for sub-severe convective development with the actual cold frontal passage late tonight. Mid level low offers greater influence on conditions to start the weekend, with the circulation center passing thru northern lower MI during the daylight hours Saturday. Cold front exits to the east Saturday morning, with ensuing cold air advection battling daytime heating throughout the day. Minimal thermal recovery expected off morning lows. Temperatures parked in the upper 50s to lower 60s. Notably breezy conditions as mixing capitalizes on a firm west- southwest gradient. Gusts in excess of 30 mph Saturday afternoon. Moist cyclonic flow engaging daytime heating will maintain a chance of showers. Seasonably cool conditions persist Sunday under deeper layer northwest flow. Aside from a broad, thicker diurnal stratocu field, generally benign weather conditions to finish the weekend as general subsidence takes control. Cooler and drier profile maintains residence Monday as low level northeast flow governs conditions under building high pressure from the north. A high amplitude, slowly evolving large scale pattern emerges for the midweek period. Southeast Michigan likely holds position between the high to the north and organizing low pressure to the west. Potentially unsettled conditions at times this period, depending the pace and trajectory of the closed low. Maintenance of east flow with prospective cloud/shower potential on the rise will keep temperatures on the cooler side of average through the rest of the week. MARINE... Low pressure tracks over Lake Superior this evening sweeping a respectable cold front late this evening. A broken line of showers and storms likely develops in advance with isolated embedded strong to severe thunderstorms possible. Moderate west-southwest winds follow Saturday with the strongest winds (20-30kts) expected over the southern half of the region where the gradient is strongest. Small craft advisories have been issued for all nearshore waters daytime Saturday as a result. Low fully departs Sunday shifting winds to the northwest. Gusts peak near 20kts during the day before weakening overnight as weak high pressure slides overhead. && .DTX WATCHES/WARNINGS/ADVISORIES... MI...None. Lake Huron...Small Craft Advisory from 8 AM to 10 PM EDT Saturday for LHZ421-422- 441>443. Lake St Clair...Small Craft Advisory from 8 AM to 10 PM EDT Saturday for LCZ460. Michigan waters of Lake Erie...Small Craft Advisory from 8 AM to 10 PM EDT Saturday for LEZ444. && $$ AVIATION.....BT UPDATE.......BT DISCUSSION...MR MARINE.......KDK You can obtain your latest National Weather Service forecasts online at www.weather.gov/detroit. ####018008688#### FXUS65 KRIW 170358 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 958 PM MDT Fri May 16 2025 .KEY MESSAGES... - Isolated showers linger mostly across northern WY this evening, gradually dissipating by the early morning hours Saturday. - A better chance of showers and storms Saturday (30 to 50%), with strong storms possible over southwestern Wyoming. - Turning much cooler Sunday and Monday with rain and mountain snow across much of the area. && .UPDATE... Issued at 235 PM MDT Fri May 16 2025 The forecast remains on track for the next 24 to 48 hours. The HRRR, along with several other CAMs have been tracking well with weak convection developing this afternoon. Convection has already begun to develop along the Cody Foothills, but as expected is very weak, generally just virga. By 1600-1900L there will be slightly better instability, though still <100 J/kg SB CAPE. Thus, during that time frame, there could be an isolated stronger storm with gusty winds to 30 to 40 mph and up to pea size hail being the primary threats. Best chances for these stronger storms (10 to 20%) will be along the Cody Foothills and eastern Bighorn Basin, as well as Yellowstone NP. Any lingering convection will taper off and end quickly after sunset and things should remain fairly quiet overnight. Saturday morning, models remain on track with timing showers and thunderstorms pushing into southwest WY then spreading east through the day. Isolated stronger storms will be possible (30% to 40% chance) across southwest WY, with gusty winds being the main threat but small hail could also be a concern. SPC continues with a marginal risk for Severe for that area as well, which aligns well with local thoughts and model guidance. && .DISCUSSION... Issued at 317 AM MDT Fri May 16 2025 Active weather will continue as we head through the next several days. We do have signs summer is coming though. The first sign is the predawn light when I go out to prepare the weather balloon for launch. This is around 4:45 am. Another sign is twilight still in the sky when I drive to work around 9:45 pm for my favorite shift, the midnight shift. (Yes, I am one of those weird people who prefers working at night). It will not feel like summer the next several days though, and some locations will feel like winter at times, especially early next week. Today looks like one of the least active days of the next several. Shortwave ridging will move across Wyoming and bring a lull in the persistent showers and storms. There will be a weak trailing shortwave that could being some showers this afternoon and evening, but these would be restricted to northern Wyoming and most of the population centers should stay mainly dry. Temperatures will also be somewhat warmer, but still only around 5 degrees below normal for most. And the shortwave will bring gusty wind to Johnson County for another day, but there should not be 60 mph gusts like yesterday. Ensemble guidance only gives a 1 in 3 chance of gusts past 40 mph for most at this time. Things start getting more active on Saturday, as an upper level low moves onshore in the Pacific Northwest and increases moisture across the area once again. Saturday should start dry for most, but coverage of showers and thunderstorms will increase as the low approaches. And things may get a little interesting. There will be decent upper level divergence across the area, and some morning sunshine may destabilize the atmosphere somewhat. Lifted indices will be negative and CAPE values will increase to 500 J/kg at times across southwestern Wyoming. The Storm Prediction Center has put this portion of Wyoming under a Marginal risk, with the main threat being strong wind gusts. The most numerous storms will be across western Wyoming. In areas east of the Divide, southwesterly flow will raise some high temperatures to around 70 degrees. It is also likely to keep most areas dry most of the time, with the average chance of a shower or thunderstorm around 1 out of 4 in this area. The aforementioned upper level low will then dive southeastward through the weekend and into Monday, with lee cyclogenesis likely occurring Sunday night into Monday in eastern Colorado and lifting into the Plains, with another upper level low developing over the western states. As a result showers will become more numerous across the area on Sunday, with another chance of afternoon thunderstorms, this time with thunder mainly east of the Divide where the best instability will be. And this will be the day we may make a transition back into winter for some locations. As flow turns northerly behind the low, much colder air will move in. Some model guidance drops 700 millibar temperatures as low as minus 5C across western Wyoming Sunday night, and this could lead to snow levels falling as low as 6000 to 6500 feet, possibly bring a coating of snow to the western valleys. The colder air then spreads east of the Divide Sunday night and especially Monday. And this is where the bulk of the precipitation will be that day. The air won't be quite as cold here, with 700 millibar temperatures generally bottoming out at around minus 7C, which would put snow levels around 5000 feet. And, given the position of the low and north-northeasterly flow, the Bighorns would be the most impacted area. Some probabilities for over 6 inches of snow include around 3 out of 4 in the higher elevations of the Bighorns and Wind River Range, with about a 3 out of 5 chance in the Tetons and Absarokas through Monday night. Chances of a foot are generally only 1 out of 2 at the very highest elevations so if highlights are needed it would likely be Advisories. This also looks to be a wet storm, with most locations east of the Divide and the northern mountains having at least a 1 out of 2 chance of a half an inch or more of QPF and favored north- northeast upslope locations like Buffalo, Thermopolis and Lander having a 1 in 2 chance of an inch of QPF or more. As for flooding, areas northeast of a Casper to Cody line have a marginal risk of excessive rainfall on Sunday and areas along and east of Interstate 25 have one for Monday. The rain will fall over a fairly long period though. In addition, with the colder air moving in, rain on snow is not likely as the higher elevations would see mainly snow. We will watch it though. Monday will be the coldest day of the week, with many locations having highs in the 40s. We should begin to dry out as the low moves away on Tuesday, although some lingering moisture will keep a few showers around, especially in eastern Wyoming. Flat ridging should then hold for the rest of the period, bringing more seasonal temperatures. Another shortwave may bring some showers and storms by midweek, but timing is all over the place this far out. && .AVIATION /06Z TAFS THROUGH 06Z SUNDAY/... Issued at 957 PM MDT Fri May 16 2025 An isolated rain shower remains possible overnight mainly around KCOD and KJAC, but the chance is only up to 15%. Wind will remain light tonight and increase Saturday morning. Scattered rain showers and thunderstorms will develop Saturday afternoon. Initially storms will develop across southwest Wyoming and move northeast through the area Saturday afternoon into Saturday evening. Gusty wind will occur with showers and storms Saturday afternoon. Wind gusts as high as 60 mph are possible (20%) across southwest Wyoming Saturday afternoon. Terminals where this wind is possible are KRKS, KBPI, and KPNA. All terminals where the chance of rain/thunderstorms is around 30% have PROB30 groups and this includes KBPI/KPNA/KJAC/KCPR/KCOD/KRKS. Conditions will mainly remain low VFR Saturday afternoon/evening as the showers and storms move through, but brief reductions to MVFR are not out of the question with the strongest cells. Mountain obscuration will occur at times from Saturday afternoon through Saturday evening, becoming more widespread across western mountains Saturday night. Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for the latest information on icing and turbulence forecasts. && .RIW WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...Hensley DISCUSSION...Hattings AVIATION...Rowe