####018004843#### FXUS66 KMTR 091154 AFDMTR Area Forecast Discussion National Weather Service San Francisco CA 354 AM PST Tue Dec 9 2025 ...New AVIATION, MARINE... .KEY MESSAGES... Updated at 132 AM PST Tue Dec 9 2025 - Tule fog and stratus will clear this afternoon - Quiet weather with warmer temperatures through Friday - Light rain possible next week && .SHORT TERM... Issued at 132 AM PST Tue Dec 9 2025 (Today and tonight) Another round of morning clouds and patchy fog across the Bay Area. The coverage is less than yesterday and these clouds will clear in the afternoon as temperature climbs a few degrees warmer than recent days. The prolonged ridging pattern continues with the amplitude notching up over the next few days. The Eastern Pacific high now extends a ridge across northern California, and there is even a somewhat uncommon cut off high way up at 250 mb directly over the Bay Area. This is the jet stream altitude where the average wind speed this time of year is around 60 knots. We'll be lucky to break 10 knots on the 12Z sounding. This vertically stacked dome of high pressure is leading to widespread subsidence, calm winds, stagnant surface air, and warmer than normal temperatures. && .LONG TERM... Issued at 132 AM PST Tue Dec 9 2025 (Wednesday through Monday) While the ridge has been the main scapegoat for the ongoing Tule Fog, the increasing ridge intensity will compress this cool moist layer closer to the surface and limit it's horizontal spread to the Central Valley and colder interior valleys across the Bay Area. Air quality may also suffer as a result. The 850 mb temperature will climb to around 17C by Wednesday, and park there until Friday. That's around 10C warmer than normal, close to the average for June. Surface temperatures will respond and warm up to 10F above normal, pushing some clear areas of the Bay Area and Central Coast to the mid 70s. This heat will peak on Thursday with noticeable cooling by the weekend. Despite the warm afternoons, the dry atmosphere (PW 0.3- 0.5") and long December nights will still bring morning temperatures into the 40s. The ridge axis will finally move through this weekend, allowing the pattern to become more zonal. This opens the door for some rain next week. While zonal flow doesn't support strong storms or atmospheric rivers, it looks likely that we'll at least end the dry streak sometime next week, possibly as early as Monday. && .AVIATION... (12Z TAFS) Issued at 349 AM PST Tue Dec 9 2025 Higher confidence in clearing out of the fog and stratus today for North Bay terminals. Day-to-day change gradually improving as high pressure builds aloft. Patchy stratus invof SF Bay providing lower confidence there, but based on persistence forecast KOAK likely to remain VFR. Vicinity of SFO...Patch of stratus and fog moving along the peninsula likely to persist through sunrise, clearing to VFR in the few hours following. Lower chance of stratus overnight into Wednesday morning compared to this morning. Medium confidence in cigs holding off until just before sunrise Wednesday. SFO Bridge Approach...Similar to SFO. Monterey Bay Terminals...High confidence in VFR through the TAF period. Light drainage offshore winds overnight with light onshore flow during the afternoons. && .MARINE... (Today through Sunday) Issued at 349 AM PST Tue Dec 9 2025 Northwest winds increase to a strong breeze today into mid week across the outer waters. Gentle breeze persists across the inner coastal waters. A new, long period northwesterly swell is expected by midday Wednesday, lasting into the early weekend. && .BEACHES... Issued at 132 AM PST Tue Dec 9 2025 Long period swell will impact the coast Wednesday - Friday. This energy brings strong rip currents, an increased risk for sneaker waves, and large breaking waves. NW swell around 8 feet with a 15 second period will translate to breaking waves up to 15-20 feet. These conditions may warrant a Beach Hazards Statement, particularly with the warm weather likely luring more people to the Beach. && .MTR WATCHES/WARNINGS/ADVISORIES... CA...Beach Hazards Statement from Wednesday morning through Friday evening for CAZ006-505-509-529-530. PZ...Small Craft Advisory until 9 PM PST this evening for Pt Pinos to Pt Piedras Blancas 0-10 nm. && $$ SHORT TERM...Flynn LONG TERM....Flynn AVIATION...Behringer MARINE...Behringer 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 ####018007680#### FXUS63 KGRR 091156 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 656 AM EST Tue Dec 9 2025 .KEY MESSAGES... - Quick Round of Snow, Freezing Drizzle Possible This Morning - Another Round of Snow and Rain Tonight into Wednesday - Reinforcing short of Arctic Air and Snow Showers Fri-Sun && .DISCUSSION... Issued at 338 AM EST Tue Dec 9 2025 - Quick Round of Snow, Freezing Drizzle Possible This Morning A quick round of snow will move through this morning bringing around an inch of snow for most of the area with 2 to 5 inches north of Grand Haven with the highest amounts north of Muskegon. As snow tapers off freezing drizzle/light rain could develop between 8am- 1pm. This is due to moisture profile flirting with -8C temperatures. One factor that could help is dry air toward the surface with breezy winds. Soundings are not persistent in keeping the low levels saturated, however the NAM is more aggressive. If freezing drizzle/light rain develops it will be along and south of the I-96 corridor and bring with it a light glaze of ice creating slick conditions. - Another Round of Snow and Rain Tonight into Wednesday A brief break in wintry weather is expected this afternoon but it will be short lived as another clipper system swings through the region tonight into Wednesday. This low will be stronger as seen in the 250mb upper level divergence and warming temperatures along with strong warm air advection near the surface with the low level jet. Positive vorticity advection moves in around 10pm along with the better moisture. Precipitation is expected to start out as snow, but strong warm air advection on the south side of the low is expected to transition the snow to rain. We'll need to monitor surface temperatures to see if a brief period of freezing rain will occur. How far north the rain spreads will depend on the overall low track. Additionally the track will also impact snowfall amounts. A slight shift of 50 miles can make a huge difference in this set up. At this time there is higher confidence in snowfall amounts of 4 inches or more along and north of the M-20 corridor with probabilities in the 60 to 90 percent range. Therefore have issued a Winter Weather Advisory from Oceana to Isabella County and northward for tonight into Wednesday afternoon. The 25th to 75th percentile highlight amounts of 3 to 7 inches in this area. If the low tracks further south the advisory may need to be extended southward. Any rain is expected to transition back to snow Wednesday morning with snow showers continuing into the afternoon. Winds will be quite breezy with this system with gusts from the southwest around 30 mph expanding from south to north overnight into Wednesday morning then shifting to the northwest behind the low late Wednesday morning into the afternoon. This will aid in reducing visibilities with the snowfall. The northwest flow off of the lake will also keep some snow shower in the area Wednesday afternoon and night, however moisture is limited so not expected much in the way of additional accumulations. - Reinforcing short of Arctic Air and Snow Showers Fri-Sun The coldest air of the season so far is showing up in some of the ensemble guidance over the weekend as another reinforcing clipper system may impact Michigan by Friday, bringing 850mb temperatures behind it into the -15C to -20C range Saturday and Sunday. This would yield high temperatures mainly in the teens to around 20F away from the lake. Upper low formation around or just north of Lake Superior is a possibility, with some vort maxes pivoting over the region which would help with synoptic lift and lake enhanced snowfall to areas along and west of US 131. This snow will likely be quite powdery and finer grain. Almost all ECE ensemble members show accumulating snow for the lakeshore region this weekend. There are a few interesting takeaways from a global teleconnections standpoint this month. The weak La Nina pattern continues, and the Madden Julian Oscillation just moved out of a strong Phase 7 and decent strength Phase 8, which correlate to colder than normal temperatures across the northern U.S. Additionally, as we ended November and moved into December, a sudden stratospheric warming event occurred which is most easily tracked via a weakening and reversal of winds at 10mb across 60N latitude. The winds did not really reverse as they do during major SSW events, but still this had the effect of weakening the polar vortex and shifting it off the pole. While we haven't gotten the full brunt of the polar vortex here in Michigan, it likely has played some sort of role in modifying the tropospheric weather pattern across our broader region. All this to say is that one of the coldest starts to December on record (top 10 for all climate sites through the first week) is attributable to some of these factors. && .AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/... Issued at 656 AM EST Tue Dec 9 2025 A band of moderate to heavy snow is currently moving toward LAN and JXN. Snowfall rates around 0.5 to 1 inch per hour are expected. This band will shift east of the terminals around 13Z. Light snow will linger along the lakeshore with showers potentially impacting GRR, AZO, and BTL. We'll have to watch for a period of freezing drizzle/light rain between 15-18Z today. Confidence is not high, therefore have it highlighted in the Prob30 group. If any freezing drizzle/light rain develops a light glaze is possible. Ceilings will are expected to lower to IFR this morning and may drop to LIFR Wednesday morning. Snow moves in from the southwest between 00Z to 03Z tonight with a transition to a rain/snow mix to rain along and south of the I-96 corridor into Wednesday morning. There is a concern for freezing rain at the onset of the transition due to the cold ground temperatures. Expect southwest winds to gust to around 25 knots today. A brief lull in the winds is possible after 21Z, but they'll pick back up with our next round of snow/rain this evening with gusts 20 to 30 knots. && .MARINE... Issued at 338 AM EST Tue Dec 9 2025 Gales will taper off after sunrise with Small Craft Advisory conditions continuing through the day. Strong southwest winds then move in tonight into Wednesday bringing another period of gales. Winds will shift to the northwest Wednesday afternoon as the strong low pressure system shifts east. Wave heights during this time are expected to be in the 7 to 12 foot range. Gales subside Wednesday evening with Small Craft Advisory conditions likely through at least Thursday. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...Winter Weather Advisory until 4 PM EST this afternoon for MIZ037- 043. Winter Weather Advisory from 10 PM this evening to 4 PM EST Wednesday for MIZ037>040-043>046. MARINE...Small Craft Advisory until midnight EST tonight for LMZ844>847. Gale Warning from midnight tonight to 7 PM EST Wednesday for LMZ844>847. Small Craft Advisory until 7 AM EST Wednesday for LMZ848. Gale Warning from 7 AM to 7 PM EST Wednesday for LMZ848-849. Gale Warning until 7 AM EST this morning for LMZ849. Small Craft Advisory until 7 AM EST Wednesday for LMZ849. && $$ DISCUSSION...Hoving/RAH AVIATION...RAH MARINE...RAH ####018003640#### FXUS63 KIWX 091159 AFDIWX Area Forecast Discussion National Weather Service Northern Indiana 659 AM EST Tue Dec 9 2025 .KEY MESSAGES... - Light snow diminishing this morning. Snow this evening changing to rain overnight as temps warm. There may be a brief period of freezing rain or sleet at the onset this evening, with potential for slick roads. Little to no snow accumulation expected. - A rain snow mix will change to all snow by Wed afternoon and evening. Lake effect snow persists into Wed night. Snowfall amounts around 1 inch or less expected, with the greatest totals near Lake Michigan. - Turning much colder this weekend with light snow at times. Wind chills mainly zero to -15. Heavy snow is not expected. && .DISCUSSION... Issued at 419 AM EST Tue Dec 9 2025 Challenges this forecast package include the onset and timing of precipitation, types of precipitation including the chance for brief freezing rain producing light icing, and snowfall amounts starting this afternoon after the rain or mixed precipitation changes to all snow. Light snow was spreading into northwest Indiana, but was still west of South Bend as of 345 AM EDT. BUFKIT soundings were showing a fairly dry subcloud layer southwest of Warsaw. Given radar and surface observations, trends, and the latest model data light snow is expected to accumulate less than 1 inch mainly north of the toll road today. The soundings also showed mid levels cooling well before the next round of precipitation beginning later tonight. The cold front should move across the area early Wednesday with a fairly rapid changeover from rain to snow. A brief period of freezing rain is possible. Most of the forecast area should change over to snow by late morning with nearly all areas becoming just snow by mid afternoon Wednesday. Given the long cold pattern since late November and given the cold pavement temperatures, it is likely there will be some slippery spots on rural roads where temperatures have not been warm enough long enough to melt the snow. Thursday is on the threshold of another long and cold period with highs often below 20 degrees and lows in the single digits. Wind chills will often be from -15 to +5 degrees. && .AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/... Issued at 648 AM EST Tue Dec 9 2025 VFR/MVFR conditions to start the period at both terminals, with light snow at KFWA diminishing within the next couple hours. MVFR ceilings (and possibly some BR) build in late morning at KSBN, then possibly into KFWA through this afternoon (less confidence, 14-18z). Winds strengthen out of the S-SW this morning into the afternoon, with gusts to 25 to 30 knots possible at both sites. LLWS early this morning at KSBN before better mixing moves in, then at both sites later tonight. A rain/snow mix develops at KSBN this evening before changing to all rain overnight as temperatures warm. IFR ceilings are likely at KSBN after 23z, with visibility to around 1 1/2SM as rain and snow move in. Slightly later arrival time at KFWA (3-6z time frame), with mainly MVFR ceilings and potential for MVFR/IFR visibilities as rain moves in. && .IWX WATCHES/WARNINGS/ADVISORIES... IN...None. OH...None. MI...None. MARINE...Small Craft Advisory until 10 PM EST this evening for LMZ043- 046. Gale Warning from 10 PM this evening to 7 PM EST Wednesday for LMZ043-046. && $$ DISCUSSION...Skipper AVIATION...MCD ####018007581#### FXUS63 KDVN 091159 AFDDVN Area Forecast Discussion National Weather Service Quad Cities IA IL 559 AM CST Tue Dec 9 2025 ...Updated for 12z Aviation... .KEY MESSAGES... - Freezing rain possible during evening commute today, especially across northwest Illinois and extreme eastern Iowa mainly along/north of Hwy 30. - Vigorous snow showers and the possibility of snow squalls will accompany a strong cold frontal passage overnight/early Wednesday morning. - Windy conditions tonight/Wednesday with peak gusts possibly 45-50+ mph timed for a several hour period after a cold front moves through. - Additional clipper systems will likely result in periods of accumulating snow Thursday through Sunday. - Temperatures will drop for the weekend with wind chills well below zero Friday and Saturday night. && .SHORT TERM /THROUGH WEDNESDAY/... Issued at 341 AM CST Tue Dec 9 2025 Initial clipper system and attendant WAA wing of light snow has moved off to the east early this morning. Lingering low stratus extends across parts of NE Iowa and N Illinois and monitoring for any freezing drizzle potential in continued WAA. However, saturation depth is in question and higher ceilings generally show to where this potential seems very low, but non-zero at this time. Meanwhile, upstream the next clipper system is diving southeast toward the Northern Plains early this morning. This system will deepen as it dives through the Upper Midwest tonight/early Wednesday with ensemble and deterministic guidance in decent agreement on a sub 990 mb surface low tracking from MN through WI. There remains continued uncertainty with how warm temps will get today given the snow cover and cloud cover, particularly across the north. Have continued to follow toward cooler raw models for highs today versus warmer NBM, especially across the northern counties. Thus, have temps only into the lower 30s there, but low to mid 40s far south. WAA wing of precipitation is anticipated to push through the cwa late today through this evening, with soundings generally supportive of limited ice to where the bulk of the precipitation is expected to fall in the form of rain. Surface temps will be critical for freezing rain potential, and with the freezing line anticipated to be in our north this would support areas near/north of Hwy 30 with the best chance for a transient period of freezing rain leading to potential for some slippery travel for the evening commute. Thus, have opted for a Winter Weather Advisory for much of the area north of Hwy 30. Ahead of the clipper this evening we'll see south winds turn more westerly and turn gusty with gusts over 30+ mph and temperatures continuing to warm ahead of an attendant cold front, thus the freezing rain potential looks to be rather fleeting at only a couple hours at any one location across our northern counties. Overnight into Wednesday morning we'll see a strong cold front sweep across the area. Some of the hi-res guidance is supporting the potential for some robust snow showers and possibly snow squalls accompanying the front given some weak surface based instability and saturation coupled with with lapse rates reaching well into the DGZ. Momentum transfer supports potential for some gusty winds possibly over 40-45+ mph leading to sharply reduced visibilities and possibly a quick minor coating of snow. After the front and snow showers sweep through, the signal remains for at least advisory criteria winds through the morning on Wednesday with strong CAA and impressive 50+ kt winds at 850 mb along with a unidirectional profile and steep lapse rate environment. Question is what's the best approach for a headline given the complex nature of the setup between transient short period of impactful snow showers/squalls, and concerns for ground blizzard - mainly with neighbors north/west. In terms of the ground blizzard the feeling is age of recent added snow (3 days) coupled with warming at or above freezing all locations briefly this evening/tonight and also some light rain/freezing rain may work in tandem to limit this potential in our region. Bottom line, since we've still got some time wanted to allow for that to continue to assess and nail down the risk and appropriate headline(s). && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... Issued at 341 AM CST Tue Dec 9 2025 The pattern looks to remain active throughout the period with clipper systems bringing precip chances about every couple of days or so. With that, the deterministic models and ensembles are starting to converge on the next clipper and snow chance arriving by Thursday night. Amounts look to be light with this system. Arctic air will follow by the weekend. There is a signal for a stronger clipper system potentially on Saturday, which combined with colder SLRs in the arctic airmass may result in the potential for several inches of accumulation for parts of the area. Blustery winds will also accompany the arctic air and could result in wind chills potentially nearing -25F at times across our northern counties over the weekend. && .AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/... Issued at 550 AM CST Tue Dec 9 2025 Stratus with lower MVFR to IFR ceilings is lurking just north of the DBQ terminal at the start of the period. To the south some areas of fog and IFR/MVFR visibilities were noted near CID. Between the fog and potential for additional stratus/stratocu development I've opted for an IFR/MVFR period at both sites this morning before going to VFR. Certainly a challenging forecast particularly for DBQ as there's also some potential to remain with degraded conditions all day in low clouds/fog with brief bout of subsidence. Otherwise, predominantly VFR expected today at MLI and BRL. Winds today will be from south/southwest and should turn gusty 15-25 kt by late in the day. This evening, strong elevated warm/moist advection on 50-60+ kt LLJ should foster a transitory wing of light precipitation. Expect this to be rain/sprinkles at MLI and BRL. CID and especially DBQ may be close to freezing for possibly a brief period of light freezing rain before going over to rain as temps further warm this evening. Any icing would be a very light glaze. The freezing rain threat will be determined by how surface temperatures trend, and so this potential will continue to be refined in later forecasts. After 06z through 12z, a strong cold front will sweep through the area. Ahead of this front, LLWS will be a threat with westerly winds around 50-55 kts near 2kft agl, while surface winds will be gusty from S/SW at 15-25+ kts. Scattered snow showers will also accompany the cold front along with increased surface wind gusts from W/NW at 30-40+ kts. This may lead to brief periods of signficant visibility reduction. For now this potential has been handled with PROB30 mention late in the period. && .DVN WATCHES/WARNINGS/ADVISORIES... IA...Winter Weather Advisory from 6 PM this evening to midnight CST tonight for IAZ040>042-051>054. IL...Winter Weather Advisory from 6 PM this evening to midnight CST tonight for ILZ001-002-007. MO...None. && $$ SHORT TERM...05 LONG TERM...05 AVIATION...05