####018007115#### FXUS65 KRIW 092003 AFDRIW Area Forecast Discussion National Weather Service Riverton WY 103 PM MST Tue Dec 9 2025 .KEY MESSAGES... - Moderate snowfall will continue across the northwest and northern WY higher elevations today and through Wednesday night, with periods of lighter precipitation and periods of heavier snowfall. Total snow accumulation through Thursday will reach 2 to 3 feet in some locations in the northwest mountains. Warmer valley temperatures will inhibit most snowfall accumulations. Winter Storm Warnings and Advisories continue through late Wednesday afternoon. - Strong and gusty winds continue across much of the state today, with High Wind Warnings in effect for much of southern and central Wyoming. Wind gusts over 50 mph are also occurring in the higher elevations of the western and northwest WY mountains. - Temperatures remain 10 to 20 degrees above normal through Thursday in the foothills and lower elevations, with some cooler air moving into northern WY Friday and Saturday. && .UPDATE... Issued at 102 PM MST Tue Dec 9 2025 The very energetic west-northwest moist flow pattern continues over Wyoming this afternoon into Wednesday. A weak shortwave trough in the flow is currently moving from central Montana into northern WY enhancing snow/rain more over northwest and northern WY this afternoon as higher surface pressure follows the trough southward. Gusty north-northwest winds are expected across northern WY through about 8 PM. With precipitation continuing over the higher terrain, snow/rain should also push into the northeast Bighorn Basin and Johnson County from about 3-6 PM. Have opted to not issue a winter weather advisory or high wind warning for northern Johnson County given the short duration of the snowfall and winds in the 20-30 mph range with gusts 35-40 mph. This trough will push the mid-level moist WNW flow southward back to mid-western WY overnight to bring light to moderate snow back to the western WY mountains while it decreases over the northern WY mountains. Another embedded shortwave trough in this pattern then approaches after midnight tonight, increasing precipitation over northwest WY, which will continue over the winter storm warning area through mid- to late-afternoon Wednesday. This trough will also increase mid- level flow to 40-50 knots, which will increase winds over the area again on Wednesday (after somewhat of a lull overnight). Conditions appear to be increasing for strong downslope winds along the Absarokas and Wind Rivers Thursday morning as well in advance of some colder air pushing into northern WY Friday and Saturday. Have increased the winds in the forecast over the higher terrain of the western mountains per feedback from higher elevation observation sites and the avalanche center. QPF and snow forecast are still consistent with previous forecasts. && .DISCUSSION... Issued at 145 AM MST Tue Dec 9 2025 The next passing shortwave energy is beginning to impact the NW higher elevations this morning, and the overall flow the next several days continues to be favorable for continued snow accumulation. Between orographic lifting and the passing wave, accumulations of 2 to 3 feet are becoming more likely for the Tetons and Absarokas, with 6 to 12 inches for remaining higher mountain ranges and the greater YNP region. Current variety of winter warnings and advisories are well positioned, so no adjustments needed at this time. In a usual winter, temperatures would be cold enough to help get some of this precip into the lower valleys, but not this year. Temperatures today will be in the 40s for the western valleys, and in the low 50s for the lower elevations east of the Divide, so snowfall will be locked into the mountains for the remainder of the week. The core of the low-level jet streak will be passing by just to the north today, and with temperatures in the 50s, a large chunk of this wind energy will mix to the sfc during the afternoon. With H7 winds at 70kts as they pass by, peak sfc wind gusts of 50 to 60 mph are likely for southern WY stretching NE into the Casper vicinity. The only question is winds across northern Johnson County late this afternoon as the cold front barrels through. While winds sfc and aloft are aligned, models are not really bringing winds up until the system gets a little farther east. Will monitor this if High Wind Warnings are needed there. Beyond this, the H5 ridge along the Rockies doesn't move much through the weekend, deflecting weather systems to the north and east, and keeping the unusually warm temperatures in place. && .AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/... Issued at 1034 AM MST Tue Dec 9 2025 VFR conditions across nearly all terminals through the period with the one exception being KJAC where a weather system will bring periods of rain/snow. Rain/snow showers will periodically move through KJAC for the start of the period. MVFR to possibly IFR conditions may be possible at times especially with any heavier showers. Precipitation will be possible at KJAC through the overnight with temperatures likely at or slightly above freezing leading to a mix of rain/snow or all rain. Showers should gradually dissipate by the late morning hours on Wednesday. The other terminals that may see an isolated brief shower or two are KCOD, KPNA, KCPR, and KWRL. Most of these terminals have low chances, less than 30% for a shower with possibly better chances at KCOD Wednesday morning. The other main concern will be strong gusty winds of 35 to 45 knots at KCOD, KCPR, and KRKS. These winds are expected to persist for another 2 or 3 hours after the start of the period before weakening. Winds will return to these terminals once again Wednesday morning with 30 to 40 knots possible through the end of the period. All other terminals are not forecast to see as strong of winds but gusty conditions will still be possible at times. Widespread gusts of 25 to 35 knots are possible at or shortly after the start of the period with these winds weakening after sunset with breezy conditions lingering. Mountain obscuration will likely persist through all of the TAF period with some improvement possible near the end of the period. Please see the Aviation Weather Center and/or CWSU ZDV and ZLC for the latest information on smoke, icing, and turbulence forecasts. && .RIW WATCHES/WARNINGS/ADVISORIES... Winter Storm Warning until 5 PM MST Wednesday for WYZ001-002- 012. Winter Weather Advisory until 5 PM MST Wednesday for WYZ008- 014-015-024. High Wind Warning until 2 PM MST this afternoon for WYZ016. High Wind Warning until 5 AM MST Thursday for WYZ019-020-022- 027>030. && $$ UPDATE...McDonald DISCUSSION...Straub AVIATION...Dziewaltowski ####018009917#### FXUS63 KLOT 092003 AFDLOT Area Forecast Discussion National Weather Service Chicago/Romeoville, IL 203 PM CST Tue Dec 9 2025 .KEY MESSAGES... - A brief period of freezing rain may result in a glaze of ice on untreated surfaces this evening, impacting part of the PM commute (~5-9 PM CST), mainly northwest of a Rochelle to Waukegan line (30% chance). - Strong southwest winds are expected late this evening before becoming northwest on Wednesday (gusts to 35-40 mph). - The potential for hazardous travel conditions is increasing for the Wed AM commute due to a period of wind-whipped snow. - More fast-moving clipper systems will likely result in some additional periods of accumulating snow in or near our area late this week into the weekend. - Temperatures will turn colder for the latter half of the week and especially this coming weekend, when dangerously cold wind chills may also be observed at times. && .DISCUSSION... Issued at 203 PM CST Tue Dec 9 2025 Through Wednesday: Two primary concerns are the potential for freezing rain early this evening across the far north and then a period of moderate snow or snow squalls Wednesday morning. Some sunshine earlier today and warmer air on southwesterly winds allowed temps to warm into the mid 30s for the southern two thirds of the cwa or so. Low clouds limited sunshine across the far north where temps are near or slightly below freezing. With dewpoints slowly rising into the upper 20s/lower 30s, temps may only fall a few degrees with sunset before rising again during the evening. The challenging part is how much temps may drop before or during the precip arrival across the far northern cwa, which may result in a short duration of freezing rain on lesser traveled pavement. The current forecast has just a chance of freezing rain mainly from a Dixon to McHenry line. Have only tweaked this by maintaining chance pops for freezing rain, but shifted slightly south, mainly from a Rochelle to Waukegan line, though overall confidence is low. There may also be some snow that mixes with the rain, or freezing rain, this evening, mainly across the far northern cwa. With the short duration of any possible freezing rain, will continue with an SPS to highlight the potential. The precipitation will become all rain by mid evening and then is expected to taper off after midnight with at least a few hours overnight with little to no precipitation falling. Southwest winds will continue to diminish through sunset, then will steadily increase this evening with gusts into the 30-40 mph range and then shift westerly overnight. While it will remain windy, the strongest winds appear to have shifted mainly southwest of the cwa and not planning any wind advisories at this time. Much of the 12z guidance shifted from showing mainly snow squalls Wednesday morning, to now showing a band of snow along the front that moves across the area. The results may be the same, a short period of wind blown moderate snow with low visibility and minor snow accumulations during or toward the end of the morning rush hour. There is also the potential for some lake enhancement across far northeast IL. Initially, temps may be around freezing and marginal for accumulation, but it appears temps will drop at least into the lower 30s with the snow and perhaps upper 20s as the cold front moves through and if the snow is indeed moderate, then some minor snow accumulation, less than one inch, is possible. Lake effect snow may continue into Wednesday afternoon across Porter County in northwest IN and there may be some lingering snow showers and flurries across the rest of the area. cms Wednesday Night through Tuesday: An active belt of strong northwesterly upper-level flow will persist in tandem with an associated lower-level baroclinic zone oriented from the northern Plains southeastward across the lower Great Lakes through later this weekend. Accordingly, the parade of of clipper-type systems dropping southeastward across our general region will continue into the weekend, with each one coming with good chances (50%+) of accumulating snowfall in our very near our area. There are currently two distinct periods of potential accumulating snow we are watching for at least portions of the area Thursday through the weekend. The first, looks to come with a clipper Thursday night into at least early Friday, with the second coming with another clipper on Saturday. Each clipper is likely to lay down a ~150 mile wide swath of accumulating snow, with an even narrower corridor of more substantial accumulations (perhaps in excess of 4"), from the Upper Midwest into the lower Great lakes region. The main question that remains, is which areas will be favored for some of the more substantial amounts and rates. Ultimately, this will be tied to the exact placement of the lower- level baroclinic zone where the strongest mesoscale frontogenetic response can be expected to enhance snow rates. Currently, ensemble guidance is favoring areas southwest of the Chicago metro area for some of these potential higher snow rates from the first clipper (Thursday night into early Friday), with generally lighter amounts in the Chicago area. With that being said we will have to watch this as there still continues to be some spread. For the Saturday clipper, there continues to be a a signal in the guidance that the swath of better accumulations could be a bit farther to the north, potentially impacting more of northern IL and northwestern IN. In addition, the Saturday system in particular may feature notably higher than climo (~12:1) snow ratios. Nevertheless, while some uncertainty persists we will need to keep an eye on these two periods for potential impacts to travel from accumulating snowfall in, or very near, the area. Aside from the snow potential, the other weather concern this weekend continues to be the very cold conditions as another arctic airmass engulfs much of the Midwest and Great Lakes region. The ensemble signal for this remains strong, and current indications continue to generally support upper single digit to teens high temperatures and overnight lows at or below zero in most locations for the weekend. Most concerning is the potential for a period of blustery northwesterly winds to accompany this deep cold over the weekend and produce subzero wind chills, potentially as low as -15 to -25 below early Sunday morning. KJB && .AVIATION /18Z TAFS THROUGH 00Z THURSDAY/... Issued at 1138 AM CST Tue Dec 9 2025 Key Messages: - Strong and increasingly gusty winds expected tonight into Wednesday, initially from a southwesterly to westerly direction, then turning northwesterly early Wednesday morning. - A period of rain expected this evening. - About a 1 to 3 hour period of wind-whipped snow showers and associated low VSBY's expected early Wednesday morning. A potent clipper system will race east-southeastward across southern WI tonight into early Wednesday morning. This approaching system will foster increasingly gusty winds (25-30kt) from the west-southwest tonight, followed by a period of 30-35 kt west-northwesterly gusts with a cold frontal passage Wednesday morning. Northwesterly winds are then expected to remain gusty into the afternoon, but magnitudes will ease through the day. A majority of the precipitation with this system is anticipated to remain north of the the area. With that being said, a period of rain is still expected for a few hours this evening before waning overnight. Still cannot rule out a very brief (<1 hour) wintry mix with the rain onset this early this evening, but the chances and duration of any wintry mix are expected to remain short enough to exclude the mention from the main terminals. Finally, a second period of precipitation is expected with this system early Wednesday morning (roughly 11 to 15Z timeframe) as the cold front and colder airmass surges back southward into the area. Precipitation type with this batch of precipitation is expected to be snow, with some minor accumulations possible. In combination with the strong gusty northwest winds, wind- whipped snow showers may support a short (1-2 hour) period of sub 1 mile VSBYs early Wednesday morning. Conditions should then gradually improve mid to late morning as the snow shifts out of the area, though some MVFR CIGs look to persist into the afternoon. KJB && .MARINE... Issued at 210 PM CST Tue Dec 9 2025 A gale warning remains in effect from late this evening through Wednesday afternoon. Strong low pressure will move across southern WI this evening and cross south/central Lake Michigan early Wednesday morning. Southwest gales are expected to develop by late this evening, turning westerly overnight then shift to the north by mid morning Wednesday. The highest speeds, likely in the 40kt range with perhaps a few higher gusts, are expected when the winds shift northerly mid morning Wednesday. Speeds will gradually diminish Wednesday afternoon with gales expected to end by early Wednesday evening. cms && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...Gale Warning from 9 PM this evening to 3 PM CST Wednesday for Winthrop Harbor IL to Gary IN. Gale Warning from 9 PM this evening to 6 PM CST Wednesday for Gary to Burns Harbor IN-Burns Harbor to Michigan City IN. && $$ Visit us at weather.gov/chicago ####018002809#### FXUS65 KFGZ 092004 AFDFGZ Area Forecast Discussion National Weather Service Flagstaff AZ 104 PM MST Tue Dec 9 2025 .SYNOPSIS...Expect warm days, chilly night and dry weather to continue well into next week. && .DISCUSSION...A dry northwest flow will remain entrenched across the southwest United States into Saturday. Later on Saturday through Monday a weak embedded weather disturbance will deliver slightly cooler temperatures and variable high clouds, but that is about it. Dry northwest flow will return for the remainder of next week. This afternoon through Saturday...A mild and dry air mass with origins from over the central Pacific will result in unseasonably warm daytime temperatures ranging from 10 to 20 degrees above average. The dry air mass and mainly clear skies associated with this pattern will result in strong radiational nocturnal cooling with seasonably chilly overnight lows. Winds will primarily remain light and variable at 5 to 10 mph through the period. The exception, local drainage breezes of 10 to 20 mph south of the Mogollon Rim due to the strong nocturnal cooling. From Saturday into early next week...A weak and dry low pressure system will result in slightly cooler daytime temperatures. Otherwise, look for high clouds from Saturday afternoon into Sunday associated with the core of this weak system. Light winds will continue, southwest to west on Saturday and Sunday shifting to more northwesterly on Sunday and Monday. It appears our dry northwest flow pattern strengthens again later next week. && .AVIATION...Wednesday and Thursday...Dry and warm conditions will continue with high temperatures reaching 10-20 degrees above average. Light and variable daytime winds around 5 to 15 mph each day. Minimum RH values between 20-35% each afternoon. Friday through Sunday...Dry and warm conditions will continue this weekend with high temperatures remaining 10-20 degrees above average. Light and variable daytime winds around 5 to 15 mph each day. Minimum RH values between 20-35% each afternoon. && .FIRE WEATHER...Today and Wednesday...Dry and warm conditions will continue. Light and variable daytime winds around 5 to 15 mph each day. Minimum RH values between 15-35% each afternoon. Thursday through Saturday...Dry and warm conditions will continue through the end of the week. Light and variable daytime winds around 5 to 15 mph each day. Minimum RH values between 20-40% each afternoon. && .FGZ WATCHES/WARNINGS/ADVISORIES...None. && $$ PUBLIC...McCollum AVIATION...Bernhart FIRE WEATHER...Bernhart For Northern Arizona weather information visit weather.gov/flagstaff