####018003604#### FXUS63 KDLH 162035 AFDDLH Area Forecast Discussion National Weather Service Duluth MN 335 PM CDT Fri May 16 2025 .KEY MESSAGES... - Rain showers continue tonight and Saturday with minimal accumulations. - Turning much cooler this weekend with highs in the 40s and 50s. - Frost and a potential freeze possible Sunday night into Monday. && .DISCUSSION... Issued at 335 PM CDT Fri May 16 2025 Vertically stacked low pressure was located over western Minnesota this afternoon. Areas of light showers were rotating around the low across the Northland. The low will slowly meander across eastern Minnesota and northern Wisconsin overnight, ending up across Upper Michigan by Saturday morning. With a northwest flow regime on the backside of the low, light showers will persist Saturday into Saturday night as the low continues to move further east. Cooler air will also arrive with the northwest flow bringing highs in the 40s and 50s for Saturday and Sunday. This will be around 10 to 20 degrees below normal for mid-May. High pressure builds in on Sunday with east to northeasterly winds across the region. The coolest highs Sunday will be near Lake Superior as a result. Global models keep some shower activity over the region Sunday, but this is hard to believe given the building high and drier air pushing in. Overnight lows Saturday night and Sunday night will fall into the 30s with some upper 20s possible Sunday night as well. This will lead to widespread areas of frost across the Northland each night with a freeze possible Sunday night across parts of northeastern Minnesota. Much of next week looks dry with upper ridging in place. A system will move across the Central Plains into Mid-Mississippi Valley Monday into Tuesday, but the high pressure in place overhead looks to keep the effects of this system to our south. There may be some shower activity late week into the weekend in spots, but global models are telling different stories keeping overall confidence low. Temperatures will slowly warm back into the 60s over the course of the week, but persistent easterly flow off the lake will keep temperatures cooler near the lake. && .AVIATION /18Z TAFS THROUGH 18Z SATURDAY/... Issued at 1227 PM CDT Fri May 16 2025 MVFR to IFR conditions are expected to persist, steadily decreasing through the evening and overnight. There is about a 10 percent chance that some LIFR conditions could sneak in at times overnight. Gusty southerly winds should calm into this evening and then become northwesterly into Saturday morning, again starting to gust up to 20 knots or more. && .MARINE /FOR NEAR SHORE WATERS OF WESTERN LAKE SUPERIOR/... Issued at 335 PM CDT Fri May 16 2025 No marine concerns are expected over the next 48 hours. Light showers will persist for tonight into Saturday night. Winds tonight into tomorrow will be northwesterly at 5 to 15 knots before becoming easterly Saturday night and Sunday. Winds of 5 to 15 knots will be seen on Sunday with gusts to 20 knots at the head of the lake. A period of stronger easterly winds is expected for next week starting on Monday which may lead to conditions hazardous to small craft. For the open water discussion, refer to the NWS Marquette Area Forecast Discussion at weather.gov/mqt. && .DLH WATCHES/WARNINGS/ADVISORIES... MN...None. WI...None. MARINE...None. && $$ DISCUSSION...BJH AVIATION...Levens MARINE...BJH ####018008367#### FXUS65 KRIW 162036 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 236 PM MDT Fri May 16 2025 .KEY MESSAGES... - A 20% chance of showers and 10% chance of isolated thunderstorms persists across northern WY through the afternoon, diminishing quickly after sunset. - 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 /18Z TAFS THROUGH 18Z SATURDAY/... Issued at 1144 AM MDT Fri May 16 2025 VFR flight conditions are expected this TAF period at all terminals. There is a low chance (30%) of showers at KCOD, KJAC, and northwest Wyoming this afternoon and early evening. There is less than a 20% chance for showers at KBPI, KPNA, and KRIW through 02Z Saturday. A few rumbles of thunder cannot be ruled out, however this probability is low. Conditions are expected to remain VFR but a brief period of MVFR flight conditions in a heavier shower is not out of question. Shower and thunderstorm chances increase again late in the TAF period (after 16Z) on Saturday at KRKS and this is communicated as a PROB30 group. Otherwise, expect gusty winds around 20kts at all west of the Divide terminals and KCPR this afternoon and early evening. 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...Gerhardt ####018005282#### FXUS66 KMTR 162039 AFDMTR Area Forecast Discussion National Weather Service San Francisco CA 139 PM PDT Fri May 16 2025 ...New SYNOPSIS, SHORT TERM, LONG TERM... .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. && .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... (18Z TAFS) Issued at 1055 AM PDT Fri May 16 2025 It's VFR except for a lingering patch of stratus over the Monterey Bay. VFR prevailing today with VFR extending into the evening, otherwise increasing coastal stratus and patchy fog /IFR-MVFR/ tonight and Saturday morning with patchy light coastal drizzle possible. Gusty northwest winds aloft resulting in low level wind shear over KSTS Airport 12z-17z Saturday morning. Vicinity of SFO...VFR. Light northeast wind until early afternoon then shifting to westerly and increasing with gusts near 30 knots during the afternoon and evening. Gusty westerly wind tonight and Saturday. SFO Bridge Approach...Similar to SFO. Monterey Bay Terminals...MVFR-VFR improving to VFR by early afternoon under diurnal surface warming and mixing winds. MVFR due to coastal stratus developing tonight, a few patches of light drizzle are possible as well. MVFR Saturday morning. Onshore winds 5 to 15 knots, strongest during the afternoon and early evening. && .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-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. Small Craft Advisory until 3 PM PDT Saturday for Pigeon Pt to Pt Pinos 0-10 nm-Pt Pinos to Pt Piedras Blancas 0-10 nm. Gale Warning until 3 AM PDT Saturday for Pigeon Pt to Pt Pinos 10-60 NM. && $$ SHORT TERM...RGass LONG TERM....RGass AVIATION...Canepa MARINE...Canepa 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