Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 01/10/17


Area Forecast Discussion
National Weather Service La Crosse WI
847 PM CST Mon Jan 9 2017 .UPDATE... Issued at 847 PM CST Mon Jan 9 2017 A very challenging evening forecast. Light precipitation continues to blossom over southeast Minnesota and northeast Iowa where the 10.01Z RAP shows a weak short wave trough moving across with some weak mid level frontogenesis. Further complicating matters, the precipitation is falling out of high cloud bases, on the order of 6 to 8 thousand feet, but is being reported as freezing drizzle or sleet. The forecast has been adjusted to agree with ground truth, but with none of the short range models handling this, lots of uncertainty on how long this mixed precipitation will continue. Looking ahead to later tonight and into Tuesday, the 10.00Z NAM has come in and continued the trend of strengthening the system as it moves across the forecast area. This could have some substantial impacts to the forecast in regards to the precipitation types. By being stronger with the system, the forcing will be stronger and deeper which should allow for more ice to be introduced into the system, especially in the deformation zone on the northwest side of the surface low. Ahead of the surface low, there little to no agreement between the NAM and the RAP this evening. By late tonight, the NAM would suggest little to no ice in the clouds ahead of the surface low over northeast Iowa into southwest Wisconsin south of Interstate 90, which the RAP agrees with. By 12Z though, the NAM has essentially filled this all back in with ice while the RAP continues to show no ice ahead of the surface low. The stronger system may also allow warmer temperatures aloft to get drawn into the southern parts of the area. The NAM would indicate temperatures warm enough for complete melting across northeast Iowa at 12Z and warm enough for partial meting across southwest Wisconsin at 15Z. The RAP is not as warm at 12Z and would have partial melting possible south of Interstate 90 but then by 15Z would have complete melting occurring over northeast Iowa into southwest Wisconsin. The 09.18Z GFS was more in line with the NAM, so would expect the 00Z to trend that way as well. With all these uncertainties, tough to start making too many adjustments to the forecast and may have to wait until the new GFS comes in to have a good feeling on which way to go. One thing that does seem likely, is for the possibility of more snow across southeast Minnesota where is seems more probable that ice will now be in the clouds with temperatures aloft cold enough to primarily keep it all snow. It may be necessary to expand the winter weather advisory into this area to account for this. && .SHORT TERM...(Tonight through Tuesday) Issued at 300 PM CST Mon Jan 9 2017 Snow to a wintry mix is the main forecast concern tonight into Tuesday. Ice in cloud-low level warming playing a big role in pcpn type, and adds some uncertainty to the forecast. 1) This evening: low level warm air advection and favorable isentropic upglide on the 280:295 K sfcs, coupled with a northwest- southeast running frontogenetic band, will continue to fuel the current band of snow across MN and western WI. Time/height x- sections and bufkit soundings favor mostly snow as the pcpn type, although some threat for freezing pcpn across the far south. 2) Overnight: focus for pcpn turns more to a west-east running frontogenetic boundary, which meso models and nam/gfs place right around the I-90 corridor. Persistent dry low/mid layer across the south per bufkit soundings (roughly 700-850 mb) continues, and likely too large to overcome with a seeder-feeder process. Thus, freezing pcpn the higher threat. Temperatures/dew points warming through the night, and likely at or above 32 F by 12z for far northeast IA/southwest WI. That said, road temps are cool and could support ice accumulation. Tough, tough scenario - and will have to be monitored closely. Obvious impacts to the morning commute and school buses if icing is realized. To the far north, temperature profiles and relative humidity still say ice will be in the cloud and it will stay cold, so snow remains the pcpn type. In between (around I-90) it looks more like a mixed bag, with partial to complete melting of any hydrometeors possible, bringing sleet/freezing pcpn into question...along with snow. 3) Tuesday: Upper level shortwave spins across the Northern Plains and then across the local area. Models suggesting a bit stronger compared to some previous runs, and maybe a bit farther south. This trough will work on that west-east running boundary, and also help with lift along its associated cold front (which it pushes into western WI by 18z Tue). Expect some enhancement in the pcpn areas by 18z as this all comes together, favoring the the I-94 corridor and northeast IA/southwest WI. QPF also higher. 4) End result? Snow accumulations from 3 to 5 inches from I-94 north. Winter weather advisory still looks good for Clark/Taylor counties in north-central WI. See some potential for expansion southward a county, but will leave current setup as is. I-90 corridor around an inch (or so) for snow, with some light icing possible. South of I-90, icing the main concern for a few hours, closer to 12z Tue. Challenging forecast here with increasing temps, ice in cloud, and road temps all coming into play. 5)Caveat: 18z GFS/NAM coming in more aggressive with generating qpf along the west-east boundary region Tue morning as the shortwave trough approaching - and lingering it a bit longer. Potential snow/icing amounts may be on the rise if this trend continues. Keep up on latest forecast for adjustments and potential expansion to headlines. .LONG TERM...(Wednesday through Monday) Issued at 300 PM CST Mon Jan 9 2017 GFS/EC/NAM favoring more of a quick moving, zonal flow for the middle/later part of the week. All favor bringing a shortwave across northern parts of the region Wed, sliding a sfc cold front through the area as it does. Band of pcpn would result, mostly as snow. Some ice in cloud/warming concerns in the south though that make mixed pcpn a possibility. Amounts look relatively small at this time, with a few inches of snow possible in the north, less south - but that threat for icing. Something to watch after we get through the tonight/Tue weather system. Quick shot of colder air post the Wed system, but temps already looking to bounce back to the Jan normals by the end of the weekend. && .AVIATION...(For the 00Z TAFS through 00Z Tuesday evening) Issued at 554 PM CST Mon Jan 9 2017 The band of warm air advection light snow has moved by both airports for the most part with just some lingering flurries possible for a while at KLSE. Attention then quickly turns to the next system. The short wave troughs working across the Rockies and onto the West Coast will cause a surface low to form over Nebraska tonight that will then move northeast across the area Tuesday. The 09.18Z NAM has trended stronger with this system which in turns leads to more precipitation than earlier expected. The onset of the next round of precipitation should be late tonight with some questions as to the type for KLSE. Warm air aloft moving north ahead of the surface low will create a warm layer that should lead to partial or complete melting and some sleet or freezing rain at the onset. This then looks to transition over to snow after a couple of hours as the mid levels cool. Precipitation types do not look to be a concern at KRST with just all snow expected, but this could be heavy at times Tuesday morning taking the visibility down to less than a mile. The snow then looks like it should end by late morning or early afternoon. After a short period of VFR conditions this evening, look for MVFR/IFR conditions to move back in ahead of the precipitation with IFR then expected for both airports from late tonight until the precipitation ends. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...Winter Weather Advisory until 3 PM CST Tuesday for WIZ017-029. MN...None. IA...None. && $$ UPDATE...04 SHORT TERM...Rieck LONG TERM....Rieck AVIATION...04
Area Forecast Discussion
National Weather Service Billings MT
813 PM MST Mon Jan 9 2017 .UPDATE... Area of snow is pushing south of Billings as of 8 pm, and our east/southern areas will be favored from now through 08z or so, a trend which recent high res models have caught up to. The Billings area received between a half inch to inch of snow this evening, and this is probably representative of most areas across our west and northeast. Have lowered pops in our NW for the remainder of the night per the drying, including Billings, and have raised pops to likely across our south central and southeast parts over the next 3-6 hours including Sheridan. Precipitation is a result of RRQ divergence associated with southwesterly 90 kt H3 jet, and some mid level frontogenesis associated with Pacific shortwave. Latest surface analysis shows decent pressure rises spreading across south central MT, so would expect the surface boundary which is near Ryegate-Columbus to migrate eastward later tonight. If wind shift to SW-W winds reaches Billings, and it should, we will see temperatures rise a bit overnight. JKL && .SHORT TERM...valid for Tue and Wed... Westerly flow aloft this afternoon promoted mixing at western sites and higher elevation locations but lower valleys remained entrenched in the colder air. Pressure falls over southwest Montana in advance of a Pacific front amplified low level northeasterly winds across portions of south central Montana solidifying the cold air in the Billings area where the highest temperature seen today was 21. Showers moving across southeast Montana currently producing freezing rain and airmass looks poised to make a variety of precipitation types possible this evening. Pacific front poised to move through LVM late this afternoon reaching Billings early this evening before spreading east. This front is producing a line of organized showers near a HLN to BTM line at 21Z and HRRR maintains this line as it moves through the area this evening. Could see rapid warmups as the winds arrive with this line with some freezing rain along and before this line with a transition back to snow behind this line so rapid changing weather is expected this evening. Should not be more than an inch accumulation in any given area but wet sticky flakes could whiten roadways quickly. Behind the front expect expect temperatures to fall a bit overnight but remain well mixed until after daybreak when a switch to northeast winds cause falling temperatures in the afternoon. Shortwave tracks into the area from the northwest while deeper arctic air pushes back into the region. This combination looks to develop an area of more persistent snow across the western half of the forecast area with models showing good dendritic growth zones Tuesday evening west of Billings. Should see accumulations of 2 to 4 inches in the Billings area Tuesday evening into early Wednesday with 4 to 6 inches possible along the I90 corridor west of Billings into the foothills. Eastern areas will see lesser amounts due to less upslope and the cold air getting deep quickly. Below zero temperatures should be expected late Tuesday night. The accumulating snows will persist for the mountains tonight through Tuesday night so the winter storm warning looks good. Temperatures on Wednesday will be 25 to 30 degrees below normal with high temperatures floating around zero. It will be drying through the day though persistent light snow could still be expected in areas where upslope maintains its influence but snow shuts off Wednesday night as airmass becomes drier. borsum .LONG TERM...valid for Thu...Fri...Sat...Sun...Mon... The extended period will start out cold on Thursday morning with widespread subzero temperatures. Though Thursday will be a cool day with single digit high temperatures (aside from the foothills where mid teens are expected) the cooler conditions won`t last as upper level heights build through the weekend. As upper level heights build and westerly downslope flows moves in, the arctic air entrenched over the region should scour out over the weekend as temperatures near 30 move in. The warmer conditions should continue through at least next Tuesday as ensembles suggest a much lower chance of any arctic air intrusions into the region. The big story through most of the extended period will be the winds, which the next section will talk about. By Friday, pressure falls east of divide will help increase the pressure gradients, and accordingly the winds, across regions in Livingston, Nye, Big Timber and nearby foothill locations. For now, it appears the winds will stay near advisory levels but when combined with recent snowfall and below freezing temperatures some blowing and drifting snow is possible. Windy conditions will continue through at least Monday as disturbances embedded in the flow aloft induce periods of pressure falls east of the divide and help maintain the strong pressure gradient across our foothill locations in Livingston, Nye, and Big Timber. Expect travel impacts across these areas until temperatures can climb above freezing. Dobbs && .AVIATION... Band of snow will move southeastward across central and southeast portions of area remainder of this evening producing a couple of hours of IFR/MVFR conditions due to lowered CIGS and reduced visibility. Look for gusty north wind involved as well. Scattered MVFR to mostly VFR will then prevail at most locations behind the frontal band overnight. BT && .PRELIMINARY POINT TEMP/POPS... Tue Wed Thu Fri Sat Sun Mon ----------------------------------------------------------- BIL 010/021 903/005 908/007 002/021 009/028 016/031 019/034 34/S 67/S 41/B 00/N 00/U 00/N 01/N LVM 024/031 003/013 905/018 005/024 009/028 016/034 019/035 44/S 77/S 51/B 00/N 00/N 11/N 11/N HDN 009/021 906/007 914/006 908/019 901/024 009/028 008/031 63/S 76/S 41/B 00/U 00/U 00/B 01/B MLS 001/010 913/004 917/001 914/018 902/022 009/027 012/030 62/S 53/S 21/U 00/U 00/U 00/B 00/U 4BQ 008/023 907/008 911/008 904/020 002/023 006/028 010/031 62/S 53/S 31/B 00/U 00/U 00/U 00/U BHK 001/008 913/001 915/901 916/016 000/022 008/026 012/029 72/S 62/S 11/I 00/U 00/U 00/U 00/B SHR 013/028 904/008 906/010 903/024 001/027 007/031 011/034 62/S 55/S 62/J 00/U 00/U 00/B 02/J && .BYZ WATCHES/WARNINGS/ADVISORIES... MT...Winter Storm Warning in effect until 6 AM MST Thursday FOR ZONE 67. WY...None. && $$ weather.gov/billings
Area Forecast Discussion
National Weather Service Jacksonville FL
846 PM EST Mon Jan 9 2017 .UPDATE... Cold High pressure wedged down the SE U.S. coast into SE GA/NE FL while coastal trof remains offshore with scattered showers over the coastal waters. Evening raob/sounding from JAX shows very shallow cold layer at the surface with southerly winds overtop of this layer and this makes for a complex forecast overnight. The trof over the coastal waters will shift slightly towards the coast but only close enough to generate isolated showers at the immediate coast at the most, with most coastal locations remaining dry. Just inland across NE FL where the warm southerly flow overrides the shallow cold airmass expect some low clouds and patchy fog formation with some Hi-Res models such as the HRRR now forecasting dense fog over inland NE FL and the I-75 corridor, but for now have stayed with the Patchy Fog forecast already in place. Further N across inld SE GA where cold airmass is still slightly deeper still expect a light freeze in some locations with patchy/areas of frost as well. This complex scenario will lead to wide temp ranges by morning with readings in the 30s over inland SE GA/N FL to 40s coastal SE GA/St Johns River Basin to temps rising into the 50s across St Johns/Flagler counties. On Tue...as trof breaks down over the coastal waters and any low clouds/fog over inland areas disperses by mid morning...expect much milder temps by the afternoon with widespread Max temps into the 60s and near 70 across inland NE FL much closer to climo values. Winds becoming SE 5-10 mph by the afternoon. && .AVIATION... Complex forecast tonight as coastal TAF sites will be closer to trof axis with a slight chance of showers at SSI/CRG/SGJ and have generally kept MVFR cigs at SGJ while lower IFR cigs will possible develop at CRG/SSI after 06z. Further inland and JAX/VQQ/GNV expect lower clouds (IFR) and some patchy fog (MVFR/IFR) to develop in the 06z-09z time frame and possibly lower and thicken towards sunrise. Hi-Res models all over the place on this development and confidence is only low-moderate in current TAF set that was issued with the 00z package. Improving conds expected on Tuesday as low clouds break up and lead to BKN clouds in the 3000-4000 ft range by the afternoon. && .MARINE... Small Craft Exercise Caution seas will continue in the 4-6 ft range tonight while N/NE winds around 15 knots on the west side of the trof axis will slowly weaken to around 10 knots towards morning. Variable winds around 10 knots with the trof axis Tue morning will become E/SE in the afternoon while seas continue to slowly subside. Rip Currents: Moderate Risk continues into Tuesday with long period swells slow to subside. && .HYDROLOGY... Minor Flooding expected on the Altamaha River Basin this week along Jeff Davis and Appling counties and River Flood Warnings have been posted. && .PRELIMINARY POINT TEMPS/POPS... AMG 32 66 45 73 / 0 0 0 0 SSI 43 62 50 68 / 10 20 10 10 JAX 40 68 49 72 / 10 10 10 10 SGJ 48 67 53 71 / 20 20 10 10 GNV 40 70 47 74 / 0 0 0 10 OCF 42 71 49 75 / 0 10 10 10 && .JAX WATCHES/WARNINGS/ADVISORIES... FL...None. GA...None. AM...None. && $$ Hess/Kennedy/Nelson
Area Forecast Discussion
National Weather Service North Platte NE
917 PM CST Mon Jan 9 2017 .UPDATE... Issued at 917 PM CST Mon Jan 9 2017 Looking at this evening`s HRRR and NAM12 runs, am beginning to get more concerned about the threat for light freezing precipitation overnight. The latest 00z KLBF RAOB sounding, indicates a very warm layer just off the surface, and this layer is deep. As temperatures drop off into the upper 20s overnight, any precipitation which does develop will freeze at the surface. One thing which may delay its onset however, is the thick veil of mid and high level clouds overnight which will slow down the temperature drop overnight. At this time, based on temperature trends, the greatest threat for freezing precipitation is after 3 am CST and before 9 AM CST. Location of the greatest threat is along and east of a line from Valentine to North Platte. Since this is highly deviant from the previous model solution, confidence in this occurring is only moderate at best right now. That being said, will forgo any headlines right now and see how precipitation trends materialize over the next 2 to 4 hours. && .SHORT TERM...(This evening through Tuesday) Issued at 258 PM CST Mon Jan 9 2017 Upper level shortwave ejects out of the Central Rockies tonight, pushing a strong lee side trough off of the Front Range and through the forecast area. The HRRR has been suggesting some light QPF as the system moves through, however the advection of a dry mid-level airmass off of the mountains will make it difficult for any precipitation to reach the ground. Strong 850mb winds in the wake of the front will help promote some degree of boundary layer mixing overnight and a moderation to temperatures at the surface. The inherited low temperature forecast looked good and made minimal changes. The only notable adjustment would be in the Platte River Valleys of southwest Nebraska where models have shown some decoupling toward the early morning hours. In that situation, light drainage westerly drainage winds down the valley and snow pack would likely lead to cooler lows than surrounding areas. Guidance was too aggressive with temperatures today, which leads to lower confidence in the warmer MEX/MAV output for Tuesday that has much of the area into the upper 40s and low 50s. Although more sunshine is expected tomorrow, 850mb temperatures will only be in the 0C to 5C range. Have elected to remain conservative with the max temperature forecast for now, especially in areas with snow cover where diurnal boundary layer mixing may be limited. .LONG TERM...(Tuesday night through Monday) Issued at 258 PM CST Mon Jan 9 2017 00z Wednesday and beyond. Surface high pressure will build south behind a cold front on Wednesday. The strongest CAA associated with the high will target northern Nebraska where highs in the lower teens are likely Wednesday afternoon. Southwest Nebraska is expected to rise into the lower 30s with the arrival of the front expected mid-morning. The models continue to key on a light qpf signal across our northern zones Wednesday as weak easterly upslope works in conjunction with a disturbance and upper level jet support. The general consensus suggests a few hundreths qpf, which would yield a half inch or so light fluffy snow. A re-enforcing shot of Arctic air arrives on Thursday which will continue the below average trend of temperatures, but the forecast is largely dry. Highs in the teens and 20s are probable with lows in the single digits and low teens. We develop southeast to southerly flow in the lower levels on Friday, which will promote a slight warm-up, but in the upper levels the models diverge some on the handling of the next weather system. The general idea is that west to southwest flow will develop with a shortwave bringing accumulating snow to the central Sandhills Friday. At this point an inch or two snow accumulations are possible. Beyond Friday uncertainty in the forecast amplifies. The Euro camp brings a solid wave just south of the cwa late Saturday and Sunday. This solution accumulates light snow across our southern and southeastern tier. The GFS is largely dry with the system well south of the area. Ensembles support the southern track, but the uncertainty warrants at least a slight chance, will leave the blended builder forecast as is for now. The Arctic airmass will be replaced with a airmass of Pacific origin. Warming temperatures are expected for the weekend and early next week. && .AVIATION...(For the 00Z TAFS through 00Z Tuesday evening) Issued at 628 PM CST Mon Jan 9 2017 Abundant mid and high level clouds will continue to stream into western and north central Nebraska over the next 24 hours. Ceilings will generally range from 10000 to 20000 FT AGL. Some precipitation aloft is possible with the cloudiness, but none is expected to reach the surface. && .HYDROLOGY... Issued at 258 PM CST Mon Jan 9 2017 Frazzle ice continues to impact area streams and rivers. The North Platte River above Lake Mcconaughy has seen fluctuations due to minor ice jamming the past several days, most notably at Lewellen and Lisco. Warmer temperatures will help alleviate some of the ice issues through mid-week, but colder temperatures late week are forecast. Will continue a RVS for both sites until the ice issues are fully resolved. && .LBF WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...Buttler SHORT TERM...Martin LONG TERM...Jacobs AVIATION...Buttler HYDROLOGY...Jacobs
Area Forecast Discussion
National Weather Service Marquette MI
1033 PM EST Mon Jan 9 2017 .UPDATE... Issued at 1033 PM EST MON JAN 9 2017 Upon review of 18z model guidance/21z SREF/00z NAM and hourly RAP runs, opted to expand advy into the western counties for Tue as consensus is for a pretty solid 3-5 inch snowfall, and a good part of that snow will probably fall in a relatively short period. Brief period of w wind lake enhancement will impact that area as well, especially the nw fcst area. That may tack on another couple of inches of snow Tuesday evening. Strong winds gusting to 35+mph for a time will also create considerable blsn on the Keweenaw in the evening. Elsewhere, snowfall overnight will be light and shouldn`t amount to much for most of the area. Lake enhancement off Lake Michigan may provide some assistance, but don`t really expect too much more than 1 to perhaps as much as 3 inches locally. Main event will occur Tue, moslty in the aftn with a good portion of the snow falling in a relatively short period. Right now, it appears much of central Upper MI may end up reaching warning criteria snow amounts. Have nudged snow amounts up some, but will allow next shift to examine all the 00z guidance to determine whether advy headlines need to be upgraded. && .SHORT TERM...(This evening through Tuesday) Issued at 414 PM EST MON JAN 9 2017 The latest water vapor imagery and upper air analysis shows strong Pacific shortwave energy being driven into the northern CA coast by 160-180 kt h25 jet max. Models indicate this strong and energetic upper level jet streak will continue to carry moisture laden air east into the Northern Plains late tonight and Tuesday. As the jet stream interacts with a reinforcing surge of Arctic air from Canada, a low pressure system is forecast to form and rapidly deepen as it moves across the Northern Plains on Tuesday morning and into the Upper Great Lakes late Tuesday. This will bring a couple of waves of snow across Upper Michigan, one tonight with the initial waa ahead of the system and then another perhaps more substantial period of snow on Tuesday as the main shortwave and rapidly deepening sfc low approach the Upper Lakes from the southwest. Model consensus QPF suggests pcpn ranging from .25 inch west to more than .75 inch far scntrl and se with the potential for lake enhancement tonight into maybe Tue morning (h85 temps starting out at -8C to -11c this evening will warm to -5 to -7C by 12z Tuesday) in sse off Lake Mi and the bay of Green Bay into Menominee, Delta and southern Schoolcraft counties. Models still showing differences in track of sfc low with NCEP models (12Z GFS and NAM) generally indicating a track into an IMT to MQT line Tue afternoon while the 12Z ECMWF and Canadian indicate a more eastern track with sfc low across bay of Green Bay and northern Lake Mi. The difference in track of the sfc low will have an impact on determination of location of heavier system snow on Tue. Given that model consensus seems to point toward heavier snow over the se counties, have decided to bump up advisories to winter storm warnings for heavy snow along counties bordering bay of Green Bay/Lake Mi. Expect potential for 6 to 9 inches of snow over these counties for combination of lake enhanced snow tonight and then system snow on Tue. For the rest of the counties from Marquette and Iron eastward have posted winter wx advisories for snow totals generally in the 3 to 6 inches range through the period. Counties farther west should see a general 2 to 4 inches during the event away from best moisture and expected track of sfc low. Southerly winds increasing to 20 to 30 mph on Tuesday could contribute to maybe some blowing snow and thus lower vsbys for warning areas along Lake Mi and the bay of Green Bay. .LONG TERM...(Tuesday night through Monday) Issued at 349 PM EST MON JAN 9 2017 Gusty wnw winds that at least aprch advy criteria and some les/blsn wl impact mainly the favored sn belts near Lk Sup on Tue ngt in the wake of departing shrtwv/lo pres responsible for the wdsprd sn on Tue. There is a great deal more uncertainty in the Wed-Thu fcst as the medium range guidance is inconsistent on the handling/timing of shrtwvs aprchg the wrn Great Lks in the backing flow aloft ahead of a strong shrtwv that is fcst to dig fm scentral Canada into the Upper Great Lks on Thu. Following the passage of this disturbance and its attendant cold fnt, very cold arctic air/well blo normal temps/les wl return for late this week. Trailing hi pres is fcst to linger over the Upr Lks next weekend, resulting in mainly dry wx and slowly moderating temps. In the longer term, a change in the pattern toward a more zonal flow of Pacific air wl likely bring much warmer wx next week. Tue ngt...The arrival of vigorous deep lyr qvector dvgc/subsidence ahead of shrtwv rdg axis trailing the departing shrtwv/lo pres responsible for the pcpn on Tue wl bring an end to any lingering synoptic scale sn. Although h85 temps falling to arnd -15C in the strong w flow behind this lo pres wl be sufficiently cold to generate some les in the sn belts favored by that flow over the wrn cwa to the n of the Porcupine Mtns and near Lk Sup e of Munising, lowering invrn base aob 3k ft agl/warming h85 temps and trend for the llvl flow to become more acyc with aprch of accompanying sfc hi pres rdg axis overngt wl result in a diminishing trend for the sn showers. A more sgnft hazard wl be the strong w winds that wl dvlp under the tight pres gradient in the presence of the caa/ destabilization. Since h925 winds are fcst to reach near 40kts, some of the exposed locations near Lk Sup, especially over the Keweenaw, wl probably see wind gusts at least near advy thresholds along with blowing sn. The gusty winds wl tend to diminish overngt with the aprch of the trailing hi pres rdg axis/ weakening gradient. Wed/Wed ngt...Another arctic branch shrtwv/sfc cold fnt are fcst to track w-e thru the Upr Great Lks on Wed. Although mstr inflow wl be limited, the medium range guidance hints the dpva/deep lyr qvector cnvgc ahead of the shrtwv and band of fgen coincident with the fnt wl cause an axis of nmrs sn showers to accompany the fropa. The 12Z NAM is quite a bit slower than most of the other guidance with the timing of this fnt/pcpn, while the 12Z GFS/Cndn models are faster. Considering there is another shrtwv in the polar branch flow aprchg in the wsw flow alf ahead of yet another shrtwv digging into scentral Canada, do not want to rule out the slower NAM, which has some support fm the 00Z ECMWF. So the fcst wl remain a consensus of the models. Even though h85 temps are fcst to fall to arnd -18C on Wed ngt following the fropa, trend for the llvl flow to turn more acyc with aprch of weak sfc rdg axis/lowering subsidence invrn wl tend to limit the intensity of the les that occurs. Thu/Fri...Next vigorous shrtwv/attendant cold fnt are fcst to swing thru the Upr Lks on Thu. The 12Z GFS/Cndn models fcst some light sn to fall over most of the cwa on Thu mrng well ahead of the fropa as slower shrtwv aprchg fm the sw impacts the area then. The strong cold fropa on Thu aftn is fcst to be mainly dry as the sharper dpva/ deep lyr qvector cnvgc pass to the n. The best chc for accompanying sn showers be over the nrn tier counties with lk moistening and onshore/upslope wnw flow closer to the forcing. As h85 temps tumble toward -25C on Thu ngt following the fropa under wnw h925 winds up to 35-40kts, les and blsn wl return, mainly in the favored sn belts downwind of Lk Sup. Lowering subsidence invrn base to 3-4k ft agl/ near absence of dgz in the arctic air invasion wl tend to limit the les intensity, but the small flakes/gusty winds/blsn wl efficiently reduce vsby. The arrival of the trailing sfc hi pres rdg/more acyc and weakening llvl winds wl bring improvement on Fri even though some light les wl linger as h85 temps remain near -20C. Sat thru Mon...Nearly stnry hi pres rdg under a confluent wnw flow aloft btwn the slowly retreating arctic branch flow in Canada and polar branch dominating the CONUS is fcst to bring mainly dry wx for the weekend. Although daytime temps are likely to slowly moderate as h85 temps recover slowly to near -5C by late Sun, morning lo temps at the interior cold spots may fall blo to perhaps well blo zero depending on whether hi clds on the nrn fringes of polar branch disturbances passing to the s impact the cwa. There is some uncertainty in the fcst for early next week as some of the longer range models show a polar branch disturbance/lo pres tracking farther n into the Great Lks by Mon. && .AVIATION...(For the 00Z TAFS through 00Z Tuesday evening) Issued at 655 PM EST MON JAN 9 2017 An area of -sn will spread across the area this evening, then mostly diminish or end overnight. For KIWD/KCMX/KSAW, this will mean initial VFR conditions will fall to MVFR, then to a period of IFR. While improvement back to MVFR should occur at KIWD/KCMX overnight as -sn diminishes and likely ends, KSAW may remain with IFR conditions under an upslope wind and the potential of -sn lingering. Another round of heavier snow will lift across the area on Tue as a strengthening low pres system tracks ne into the Upper Great Lakes. Expect LIFR conditions to develop at all terminals with the longest duration at KSAW where upslope winds will aid poor conditions. Wind shift to gusty w winds will occur late aftn at KIWD/KCMX and in the evening at KSAW as the low passes. && .MARINE...(For the 4 PM Lake Superior forecast issuance) Issued at 349 PM EST MON JAN 9 2017 S winds will increase up to 30 kts over the e portion of the Lake on Tue ahead of a lo pres system moving toward the Upper Lakes. After this lo passes to the ne late in the day, there will be a wind shift to the w. Then there are likely to be two periods of w-nw gales and probably heavy freezing spray this coming week that impact at least portions of Lake Superior. The first will be on Tue night as the pres gradient tightens between the lo pres exiting to the ne and an incoming hi pres ridge, allowing an influx of arctic air. Opted to issue a gale warning at this time for the entire lake for Tue night. The second significant event will be later on Thu into Fri following the passage of a strong disturbance through Ontario and attendant cold fropa across Lake Superior that introduces another shot over very cold air into the Upper Lakes. && .MQT WATCHES/WARNINGS/ADVISORIES... Upper Michigan... Winter Weather Advisory from 9 AM to 10 PM EST Tuesday for MIZ001>004-084. Winter Weather Advisory until 7 PM EST Tuesday for MIZ006-007- 085. Winter Weather Advisory from 6 AM to 6 PM CST Tuesday for MIZ009. Winter Weather Advisory until 7 PM EST Tuesday for MIZ005. Winter Storm Warning until 7 PM EST Tuesday for MIZ013-014. Winter Weather Advisory until 3 PM CST Tuesday for MIZ010-011. Winter Storm Warning until 6 PM CST Tuesday for MIZ012. Lake Superior... Gale Warning from 7 PM Tuesday to 7 AM EST Wednesday for LSZ264>267. Heavy Freezing Spray Warning from 1 AM to 7 AM EST Wednesday for LSZ243-244-248-249-264>266. Heavy Freezing Spray Warning from 7 PM EST /6 PM CST/ Tuesday to 7 AM EST /6 AM CST/ Wednesday for LSZ162-240>242-263. Gale Warning from 4 PM EST /3 PM CST/ Tuesday to 5 AM EST /4 AM CST/ Wednesday for LSZ162-263. Lake Michigan... None. && $$ UPDATE...Rolfson SHORT TERM...Voss LONG TERM...KC AVIATION...Rolfson MARINE...KC
Area Forecast Discussion
National Weather Service Phoenix AZ
309 PM MST Mon Jan 9 2017 .UPDATE...To Aviation discussion. && .SYNOPSIS... Moist Pacific flow will allow periods of thicker high clouds to stream across the Southwest through the middle of the week, with temperatures hovering in a slightly above average range through mid- week. A stronger storm system will likely affect the region by the latter half of the week with showers and much cooler temperatures. && .DISCUSSION... Tonight through Wednesday... Current 88D radar imagery is now showing the weakening frontal band/line of showers now moving into South-Central AZ at this hour. Rainfall amounts with this system across SE CA and SW AZ have been, as expected, very light, with most locations only seeing trace- couple of hundredths of an inch. Latest HRRR high-res guidance is showing similar amounts being dropped across northern Maricopa and southern Gila Counties this afternoon/evening before the system moves off to the east. Tuesday and Wednesday still look to be dry as flat ridging moves over the region ahead of the next system, under partly to mostly sunny skies. High temperatures will fall slightly with most desert locales dropping into the 60s by Wednesday, and there may be enough moisture working across the coastal mountains to allow a few light showers to develop over portions of far SE California, mainly areas in western Imperial county along with the higher terrain of Joshua Tree NP. Thursday and Friday... There now seems to be greater model consensus on the evolution/details of the next pacific low center that will be affecting our region during this period. The GFS ensemble suite has now come into good agreement with the euro on the track/depth of this low center, moving it southeastward down the CA coast and inland to just south of Yuma on Thursday night and Friday, then eastward into extreme southern NM/west TX on Saturday. Although the coldest/most unstable air associated with the upper low center is forecast to slide just to our south, there appears to be enough moisture/diffluence ahead of this system that, at least scattered shower activity will develop across our cwa during the Thursday night-Friday night timeframe. Although QPF amounts are still expected to be on the light side (1/2 inch or less), locally heavier amounts could still fall in some locations from heavier showers. Temperatures during this period are expected to drop below normal, with lower deserts likely to see highs struggle to rise out of the 50s. However, with 850mb temps forecast to remain mostly above 0C, snowfall likely likely be confined to our highest peaks, with accumulations remaining quite small (mainly aob 2 inches). Have decided to raise POPS a bit more given the increasing model consensus. Saturday and Sunday... A drying and warming trend appears to be on tap for this timeframe as the afomentioned upper low moves off to the east and a drier northwesterly flow develops over the region. && .AVIATION... South-Central Arizona including KPHX, KIWA, and KSDL: Weak frontal band and associated very light showers/virga will continue to track in from the western AZ deserts this afternoon, lowering ceilings down 10-15kft across the Phoenix Metro. West winds 8-12kts will mostly settle into the terminals for the rest of the afternoon/eve, but may take up more erratic and variable headings due to any passing showers. SCT-BKN clouds will linger into the evening, with east winds 6-9kts developing for the terminals by the late evening. Southeast California/Southwest Arizona including KIPL and KBLH: Light surface winds will continue into the afternoon hours with some draw to the west-northwest breeziness. CIGs and light showers/virga will continue to clear to the east with skies remaining SCT-BKN into the evening. Sundowner/evening gustiness from the west is possible into KIPL in the evening, otherwise west-northwest winds to settle in for KIPL and KBLH overnight. Aviation discussion not updated for amended TAFs. && .FIRE WEATHER... Wednesday through Sunday: Rather seasonal and tranquil weather Wednesday and Thursday will give way to much cooler and wetter conditions Friday and Saturday as a developing weather disturbance passes through the districts. Locations in Arizona stand the best chance of receiving wetting rains Friday with much lighter amounts through SE California. Regardless, humidity level will remain quite elevated only falling into a 30 to 50 percent range in the afternoon following excellent overnight recovery. With the passage of this weather system, some gusty winds will be possible through the Colorado River valley though nothing unusual for this time of year. Overall, fire danger will be extremely low throughout the week. && .SPOTTER INFORMATION STATEMENT... Spotter reports will not be needed through the middle of the week. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...None. CA...None. && $$ Visit us on Facebook...Twitter...and at weather.gov/phoenix DISCUSSION...Percha/CB AVIATION...Nolte FIRE WEATHER...MO