Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 03/10/23


Area Forecast Discussion
National Weather Service La Crosse WI
552 PM CST Thu Mar 9 2023 .DISCUSSION...(Tonight through Thursday) Issued at 230 PM CST Thu Mar 9 2023 Key Messages: - Winter storm continues to impact the region tonight, exiting east early Fri morning. A few inches of snow still on tap - Snow chances continue to be highlighted for Sat/Sun with a few inches possible - Quieter start to the new work week * WINTER STORM CONTINUES TONIGHT: a few inches still on tap, highest south of I-94. Exits east early Fri morning. Upper level shortwave trough driving across IA this afternoon/evening, exiting east across the eastern great lakes Friday morning. The sfc low hangs farther south with a trough running north/northwest of the low, sliding across the local forecast area this evening. That boundary could hang around into Fri afternoon. Good low level thermodynamics will provide much of the lift for snow production, with latest RAP showing a lot of upglide along the 280:295 K isentropic surfaces, shifting across north/eastern WI overnight. Not much frontogenetic response across the local forecast area, moreso across southeast WI this evening per latest RAP/NAM. Perky QG convergence in the 700:300 mb layer across the forecast area into the evening while coupled 300 mb jet continues to enhance the overall lift. For additional amounts, SREF and RAP bufkit soundings show DGZs from 100-200 MB thick, fairly isothermal, and through the evening hours. Some hints of instability/convective elements in the soundings for a few hours this evening too. Both would suggest snow ratios above climatology. However, its fairly warm in the near sfc layer - with a wetter nature to the snow - working to hold ratios down. Meanwhile, the lack of much Fgen lowers confidence in enhanced banding and locally higher amounts. Have lowered ratios closer to 10:1 for rest of the afternoon, but ratios should see an uptick this evening with cooler sfc temps and favored lift. Overall though, amounts continue to trend down a bit. Mostly 4 to 7" expected. Localized higher amounts remain possible, although maybe not as high of a threat sans any enhanced bands. For headlines - almost downgraded some of southeast MN/northeast IA to advisories. Per coordination with surrounding offices will hold the warning for now, but if lower amounts continue to realized, maybe do that downgrade sometime this evening. * WEEKEND SNOW: increasingly likelihood, a few inches possible Medium range guidance has been in good agreement with sliding a shortwave trough across the northern plains Sat morning, churning across the upper mississippi river valley Sat aft-Sun. Swath of north-south running low level thermodynamics leads the system across the region, evidenced with upglide along the 280:295K isentropic surfaces. A weak ripple in the upper level flow could precede the main shortwave, coming up from the south and co-located with the low level warming. Some relatively weak north-south running Fgen too. While no tap to southerly moisture currently progged, ample saturation with the shortwave to fuel widespread pcpn. Temperatures locally would favor snow. How much falls? Models have been fairly consistent with suggesting 1- 4" of snow (at 10:1 ratios), the bulk of which falls Sat aft- evening. The DGZ is mostly 50:100 mb per latest GFS/NAM bufkit soundings - not too deep. Some hints in the NAM that we could lose ice in the cloud for a few hours Sat night, although the GFS disagrees. In addition, the models are suggesting there could be a secondary ripple dropping in behind the departing shortwave for Sun/Sun night - running along a northwest hanging sfc front off the exiting low. This could bring another 1-3", although more focused north of I-94 at this time. It could push total amounts into the 3 to 6" range in the north before all is said and done...but over a 36 hour period. Considering the length of time to accumulate these potential totals, the need for a winter weather advisory is probably a 50/50 proposition. However, any small uptick in amounts (either more qpf or higher snow ratios) could push that answer to a "yes". Stay tuned... * START OF WORK WEEK: quiet, milder air returning Shortwave ridging on tap to slide across the region for the start of the new work week. At the sfc, high pressure builds across the region from the northern plains Monday, shifting east Tue night. After a relatively cool start, southerly flow sets up Wed-Thu, pushing milder air northward and bringing temps back to/above normal. && .AVIATION...(For the 00Z TAFS through 00Z Friday evening) Issued at 553 PM CST Thu Mar 9 2023 The back edge of the heavier snow will move out of KRST about 10.02z and KLSE around 10.03z. During this time frame, snow will reduce visibilities to around a half-inch. After these times, expect that the snow rates will dramatically decrease and visibilities will improve. Snow totals by Friday morning will be in the 3 to 5" range. While visibilities will be dramatically improving, ceilings will likely stay IFR/MVFR through this forecast period. && .ARX WATCHES/WARNINGS/ADVISORIES... WI...Winter Storm Warning until 6 AM CST Friday for WIZ032>034- 041>044-053>055-061. Winter Weather Advisory until 6 AM CST Friday for WIZ029. MN...Winter Storm Warning until 6 AM CST Friday for MNZ079-086>088- 094>096. IA...Winter Storm Warning until 3 AM CST Friday for IAZ008-009-018- 019-029. Winter Storm Warning until 6 AM CST Friday for IAZ010-011-030. && $$ DISCUSSION...Rieck AVIATION...Boyne
Area Forecast Discussion
National Weather Service Billings MT
239 PM MST Thu Mar 9 2023 .DISCUSSION... Tonight through Friday... A shortwave that was over Livingston this morning, has pushed as far east as Billings. As it has tracked east, the light snow that was associated with it has decrease and there are only a few weak echos, and not much is reaching the ground. The majority of the the remaining snow this afternoon is located in Fallon County as the main shortwave has moved into the Dakotas. What little snow that remains is light and the Winter Weather Advisory has been cancelled. Overnight, moist flow ahead of another shortwave move that will move in from the Pacific Northwest will start to impact the western mountains. There could There will also be a chance for some fog west of Billings tonight, given the recent moisture and the upslope easterly flow. The HRRR continues to run much warmer for tomorrow than the rest of the of the models. The majority of the ensemble members are running in the 30s for highs. The surface low in associated with the shortwave is much slows, so the colder air can remain in place through the day. The HRRR however continues to push that surface low much faster through the area allowing highs to get into the 50s and approach 60 degrees. Have continued to run under under the NBM to offset the influences of the HRRR solution. As the Pacific front moves through, there will be chances for light snow as far east as Billings. The better chances for accumulations is around the western foothills where an inch or two are possible and the Crazy and Beartooth/Absaroka Mountains where amounts of 6 to 10 inches are still expected. With the front, there will also be some breezy conditions across the area, especially along the western foothills. However, the latest local NBM probabilistic guidance has come down with the chance for strong winds around Livingston with the chance for 50 mph winds only around 70 percent. The chance of Wind Advisory is down under 50 percent. Saturday will still a little breezy, especially from Miles City to Alzada east. However, it should be a little warmer with highs approaching 40s degrees, and should be dry. Reimer Sunday through Thursday... For Sunday cluster analysis is in good agreement the region will be transitioning from the troughing pattern seen on Saturday to a ridging pattern bringing warmer temperatures to the region. Monday and Tuesday the ridge is firmly overhead bringing warm temperatures in the 50s for most areas by Tuesday. By Wednesday there is little agreement in the cluster analysis on the pattern, although all show some kind of troughing returning to the region. This troughing could create some light precipitation Wednesday and lower temperatures. Overall, the long term looks mostly dry with temperatures starting out cool on Sunday with 30s for most before warming into the 50s for areas on Tuesday, then turing a little cooler later in the week. Torgerson && .AVIATION... The next chance of snow for the Beartooth/Absarokas arrives late tonight. More widespread and light snow looks to move into the region around 10Z Friday impacting mostly western areas such as KLVM. Easterly surface winds will prolong the risk of upslope low cloud (i.e. areas of MVFR ceilings) through tonight. There may be a risk of fog as well, especially west of KBIL late tonight. Torgerson && .PRELIMINARY POINT TEMP/POPS... Fri Sat Sun Mon Tue Wed Thu ----------------------------------------------------------- BIL 018/035 022/036 016/032 017/050 036/055 031/048 029/045 12/W 60/N 10/B 00/B 02/R 32/S 22/S LVM 018/039 023/038 017/037 022/049 036/052 029/044 025/041 37/W 80/N 10/B 00/B 14/R 42/S 22/S HDN 013/037 017/034 010/032 010/047 025/056 026/048 024/045 01/B 60/B 00/B 00/B 02/R 42/O 22/S MLS 012/031 019/027 009/024 007/039 023/047 028/043 024/039 01/N 41/N 00/B 00/U 01/B 21/B 11/B 4BQ 013/037 021/030 014/027 009/042 027/052 031/047 027/041 00/E 20/N 00/B 00/U 01/B 21/B 22/S BHK 008/026 017/025 007/020 003/034 021/045 023/038 016/034 01/N 52/J 00/E 00/U 00/B 11/B 11/B SHR 008/041 018/034 009/030 011/044 025/052 024/044 021/038 01/B 40/U 00/B 00/U 01/B 42/O 33/S && .BYZ WATCHES/WARNINGS/ADVISORIES... MT...None. WY...None. && $$ weather.gov/billings
Area Forecast Discussion
National Weather Service Charleston SC
910 PM EST Thu Mar 9 2023 .SYNOPSIS... A cold front will cross the area Friday, followed by high pressure through Saturday night. Developing low pressure will approach the region Sunday then will cross the region Sunday night. This low will pull a strong cold front through the area Monday, then unseasonably chilly high pressure will prevail through mid week. A warming trend is expected later next week. && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/... Current radar and observations trends have dictated a rather substantial increase in pops for the late evening update. KJGX radar shows a band of light to locally moderate rain extending from central Georgia east to just west of the I-95 corridor south of Savannah. The atmosphere under this band has moistened much quicker than expected with surface dewpoints depressions at 10/02z having dropping to 0 degs at KRVJ and 2 deg at KVDI. This has result in measurable rainfall occurring across much of Candler, Tattnal, Evans and Bulloch Counties over the past 1-2 hours where amounts range from 0.01 to as much as 0.14", highest in western Candler County. Steadier rains are still expected to move in from the west overnight as the moisture profiles moisten considerably and a warm frontal feature moves north to near/just north of the I-16 corridor by 10/12z. Forecast lows, temporally defined from 6pm-6am LT, will likely occur this evening to around midnight with patches of light rain aloft/sprinkles inducing at least some degree of diabatic cooling. Temperatures will then hold steady or slowly rise overnight as low-level warm advection intensifies. Influences from diabatic cooling can be seen at KMHP and KRVJ where temperatures dropped quickly with the onset of rainfall. && .SHORT TERM /6 AM FRIDAY MORNING THROUGH SUNDAY/... Friday: All locations will receive measurable rainfall as a cold front presses through the region, although hour by hour details regarding coverage of showers and overall event timing remain somewhat uncertain. Thus, while 12 hour PoPs of 100 percent are appropriate across the region, hourly PoPs may not reflect this degree of certainty. As opposed to a deep layered low pressure, this event will be dominated by a channel of vorticity and moisture transport/pockets of isentropic ascent embedded with a fast quasi- zonal flow. This scenario could initially contribute to a relative lull in shower coverage Friday morning, as depicted by recent HRRR runs, followed by best coverage of showers late morning until mid/late afternoon. in addition, fast/quasi-zonal steering flow could support earlier drying across northern/inland counties, but showers could persist longer, perhaps into early evening. across southern counties as moist plume reorients parallel to the west/northwest to east/southeast steering flow. Also of note, elevated instability and perhaps some degree of surface based instability - especially across southern counties - justifies a mention of thunderstorms. Areas south of I-16 remain within a marginal risk for severe, and high resolution reflectivity progs depict some degree of multicell organization south of the advancing cold front. However, the potential for isolated damaging wind gusts appears limited as model forecasts of shear/instability remain unimpressive for mid-March. All told, most locations should receive 0.25 to 0.50 inch of rain from this event. temperatures should top out in the 60s north and 70s south. Friday night, a few showers could linger south of I-16 early. Otherwise, building high pressure will push cooler/drier air into the the region, and by Saturday morning lows in the 40s will be common most areas. Saturday will start sunny and cool, then high clouds will stream across the region from the west during the afternoon. Temperatures should top out in the 60s most areas except around 70 near the Altamaha River. rain free conditions will continue as late Saturday night/early Sunday low temperatures average in the 40s inland and in the 50s along the coast. Sunday: Another precipitation event will commence, initially dominated by moisture transport/pockets of isentropic ascent embedded within a fast quasi-zonal flow regime and enhanced by overrunning of a retreating wedge of high pressure. A few showers could develop across inland counties Sunday morning, but precipitation coverage should ramp up starting Sunday afternoon, with PoPs increasing to likely across inland counties. A later arrival of showers should allow temperatures to rise to 75-80F across southern counties. On the other hand, across far inland/northern counties, temperatures could remain in the 60s, especially if showers arrive earlier. In between, expect highs 70-75 across a wide swath of the region. Also, some degree of surface based instability could support thunderstorms Sunday afternoon, especially inland. Lake winds: Northwest winds could gust to 25 knots in Lake Moultrie Friday night. Then. in the wake of a strong cold front Monday, winds could gust to 25 knots on the lake through Tuesday. Lake Wind Advisories could be required for these events. && .LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/... Precipitation event which begins Sunday will overspread the region Sunday night. A prominent baroclinic zone could promote surface cyclogenesis, and this surface low could intensify mass/moisture convergence and associated forcing for ascent as it crosses the region. As a result, many locations could pick up another 0.50-1 inch of rain. Further, elevated instability could support at least isolated thunderstorms, which could produce locally greater rainfall. Monday morning should start off with lingering showers, then intensifying low pressure tracking northeast along the coast will drive a strong cold front and sharply drier air into the region. High temperatures in the upper 60s to middle 70s may occur by midday/early afternoon. Dry and unseasonably chilly conditions will then prevail Tuesday and Wednesday. Of greatest concern, freezing temperatures could infiltrate areas away from the coast Tuesday night; frost may remain a secondary concern as north/northwest winds could persist. Also, wind chills could fall into the 20s Tuesday night. As the air mass modifies under high pressure, temperatures should recover back into the 70s late week. && .AVIATION /02Z FRIDAY THROUGH TUESDAY/... KCHS/KJZI: VFR this evening with deteriorating conditions late tonight and especially Friday morning as a warm front moves north through the two terminals. Light rain will spread in from the west overnight with vsbys dropping to MVFR with IFR cigs about 14-15z as the warm front approaches. There could be pockets of lower vsbys at times, but it could be a difficult morning, especially for general aviation. The risk for tstms is non-zero with some elevated instability noted, but the risk looks to low to justify a mention at this time. Rain should end by 20z, but IFR cigs will linger. KSAV: VFR for much of the night with conditions deteriorating after daybreak as a warm front lifts north. An area of widespread rain will likely brush the area by mid-morning with the bulk of the rain remaining north of the terminal. By early afternoon, a band of widespread rain with embedded tstms will push through the terminal 18-21z. There will likely be pockets of heavier rain in convective elements, but widespread MVFR vsby and cigs are likely with occasional periods of IFR, especially in vsbys. A TEMPO group for IFR was introduced to account for this. Tstms were left out of the 00z TAF for the KSAV terminal, but a few rumbles can not be completely ruled out, especially in that 18-21z window. Extended Aviation Outlook: Flight restrictions are likely late Sunday into early Monday associated with showers. After a strong cold front passes, gusty north/northwest winds should develop early next week. && .MARINE... Tonight: High pressure will be in control of the waters, before giving way to a warm front from the west late tonight. Easterly winds will shift out of the SE tonight at speeds less than 15 kt. Seas will average 2 to 4 feet through the night. Mariners can expect showers to spread offshore into the marine community overnight, resulting in a minor reduction in visibilities. Friday through Tuesday: Ahead of an approaching cold front, a tightening SW surface pressure gradient will contribute to elevated winds. We raised a Small Craft Advisory for AMZ350 and AMZ374 as winds should gust to 25 knots was early as Friday morning. After a cold front crosses the region, winds will shift to the NW, and gusts to 25 knots are likely across all marine zones. Winds should diminish and seas should subside for a time saturday into Sunday. Then, ahead of developing/approaching high pressure, south winds could increase Sunday night, and Small Craft Advisory conditions will likely redevelop most/all areas. Of greater concern, a strong cold front will cross the waters Monday. Strong N/NW winds and at least widespread SCA conditions will persist through early next week, and the probability for gale force gusts/hazardous seas will increase as cold air spreads across coastal waters and marine layer mixing intensifies. && .EQUIPMENT... The KCLX WSR-88D will continue to be down for an important upgrade. The radar is expected to return to service by March 20, 2023, assuming no issues are encountered. During the downtime, adjacent radars will be available, including: Columbia, SC (KCAE); Robbins AFB (KJGX); Moody AFB (KVAX); Jacksonville, FL (KJAX); and Wilmington, NC (KLTX). && .CHS WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. MARINE...Small Craft Advisory from 11 AM Friday to 11 AM EST Saturday for AMZ350. Small Craft Advisory from 8 AM Friday to 11 AM EST Saturday for AMZ374. && $$
Area Forecast Discussion
National Weather Service Goodland KS
548 PM MST Thu Mar 9 2023 .SHORT TERM...(This evening through Friday) Issued at 251 PM MST Thu Mar 9 2023 Across the Tri State region this afternoon, skies are a mix from sunny in spots, down to partly sunny as some locales are still seeing remnants cloud cover from this morning as well as from a front moving through the area. Temperatures as of 200 PM MST are ranging widely and are highly dependent on how much cloud cover remains, with upper 30s to low 50s. Winds are mostly northwest and gusting up to 25 to 35 mph a times. For the remainder of the afternoon, region will continue to see a clearing skies going into the evening and overnight hours. Looking for gradient to slacken as well as front and associated low move away from the cwa, giving way to transient surface ridge that will eventually set up east of the cwa going into Friday. Going into Friday, guidance carrying upper level ridging over the Plains, but at the surface, a strong lee-side trough sets up over the Front Range with the aforementioned ridge remaining east of the cwa. The resulting tight southerly gradient will bring windy conditions to the area, along with a continued warmup. Gusts will approach to 30-40 mph mark, especially during the afternoon hours. Despite the expected strong winds, looking for humidity to stay well above criteria for overall fire wx concerns. Latest SPC elevated outlook now well south of the cwa. Increasing cloud cover going into Friday night and carrying much of the upcoming weekend. There will be a couple shortwaves coming through the central Rockies and over the cwa. These will interact with a surface boundary to create some light rain/snow for portions of the area. The aforementioned lee-side trough settles south of the cwa by the end of the weekend, allowing for an eventual shift to easterly flow Saturday, over to northerly on Sunday for most areas. Another windy day is probable for most Saturday as surface low sets up south. The expected easterly fetch will aid in bringing upslope moisture and some weak instability to allow for rain/snow to occur via low cloud deck. Low qpf expected, so little to no snow accum. On Sunday, the second shortwave will focus precip mainly along/west of Highway 27, moving south going into the evening hours as the surface low moves south. For temps, highs on Friday will range from the upper 40s in the northeast, down to the 60F mark in southern and southwest locales. For the upcoming weekend, Saturday will have a range from the upper 40s into the mid 50s and for Sunday, mainly the 40s with warmest areas in the east. Overnight lows will see a range mainly in the 20s, with Friday night seeing the 30s, warmest areas south of the Interstate. .LONG TERM...(Monday through Thursday) Issued at 115 PM MST Thu Mar 9 2023 Upper ridge axis will be moving across the central CONUS to start the period with dry conditions Monday and Tuesday. This will be followed by a slow moving upper trough that moves out of the western CONUS mid week with its axis along the length of the Rockies by Thursday. It will bring a chance for rain and snow mainly Wednesday night and Thursday. Snow amounts are not particularly impressive at this time, and with temperatures remaining above freezing until Thursday night we may be looking at mostly rain. Model QPF is not in very good agreement, other than showing highest amounts in northeast Colorado and lowest amounts in eastern areas from McCook to Hill City. Breezy northwest winds possible on Thursday as well. Temperatures will be slightly below normal on Monday, much above normal Tuesday and Wednesday, then dipping back to slightly below normal on Thursday. && .AVIATION...(For the 00Z TAFS through 00Z Friday evening) Issued at 500 PM MST Thu Mar 9 2023 GLD: Recent runs of the RAP and HRRR suggest that IFR-LIFR stratus (and/or fog) may develop at the GLD terminal late tonight and Friday morning -- beginning ~06-08Z and ending ~13-15Z. Otherwise, VFR conditions will prevail.. with increasing mid/upper level cloud cover (ceilings 12-18 KFT agl) on Friday. Light NE winds will become variable this evening and overnight.. shifting to the SE and increasing to 7-12 knots AOA sunrise Friday morning. Winds will veer to the S and strengthen to 20-30 knots late Friday morning into early Friday afternoon -- as the MSLP/H85 height gradient tightens on the eastern periphery of a developing lee cyclone in Colorado -- decreasing to 15-20 knots mid-late Friday afternoon.. by the end of the TAF period. MCK: Recent runs of the RAP and HRRR suggest that MVFR ceilings/ stratus may briefly develop at the MCK terminal AOA sunrise (12-14Z) Friday morning. Otherwise, VFR conditions will prevail.. with increasing mid/upper level cloud cover (ceilings 12-18 KFT agl) on Friday. Light NE winds will become variable this evening and overnight. Winds will shift to the SE and increase to 7-12 knots AOA sunrise, veering to the SSE-S and strengthening to 15-25 knots Friday afternoon.. as the MSLP/H85 height gradient tightens on the eastern periphery of a developing lee cyclone in Colorado. && .GLD WATCHES/WARNINGS/ADVISORIES... KS...NONE. CO...NONE. NE...NONE. && $$ SHORT TERM...JN LONG TERM...024 AVIATION...Vincent
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
900 PM CST Thu Mar 9 2023 .UPDATE... Issued at 857 PM CST Thu Mar 9 2023 Approaching the mid-evening, areas roughly near and south of I-80 have struggled to transition from rain over to snow with temperatures still hanging onto the upper 30s in spots along the I- 80 corridor. The majority of the metro that has managed to switch over to snow remains too warm to allow accumulation on most roadways. Areas west and northwest of the metro as well as the far northern suburbs are starting to see minor accumulations on roads. Diurnal cooling is sure taking its time with the low cloud cover overhead and we`re certainly not getting any help from continued modest warm advection in the low levels. However, high-res forecast soundings continue to insist upon a good deal of dynamic cooling taking place over the next few hours. While this makes sense with surface wet bulbs sitting closer to freezing, dynamic cooling has been notably lagging behind from what models have been saying thus far this evening. But with the mid-level vort max still approaching from the west, some accelerated cooling may take place as it propagates across the area over the next few hours. This is all to say that we are still anticipating lighter snow coverage to expand southward through the rest of the evening and tonight. RAP mesoanalysis shows the prominent f-gen signature is beginning to make its way off to our east which lines up with where we`re currently seeing the banded precip vs lighter, stratiform precip. That being said, it looks as though the heavier rain and snow will be departing the area over the next hour or two. We still have a good deal of synoptic forcing to work with for the next couple of hours as we remain in the left exit region of a stout mid-level jet max on top of the aforementioned low and mid level vorticity providing ample synoptic ascent for steady precip to persist. There is a bit of a dry slot starting to inch into parts of the western CWA as some drier air begins to infiltrate the mid-levels including through the DGZ. Nonetheless, light precip continues to fall with additional snow showers wrapping around the backside of the low and currently falling over far eastern Iowa. Light precip is still anticipated through most of the night before departing to the northeast through the early morning. A couple of models are resolving one last push of light snow showers in the cold advection regime on the northwestern periphery of the low through mid-morning tomorrow. All in all, still expecting widespread 4 to 6 inches across the northern CWA with a sharp gradient in snow totals likely setting up in the neighborhood of the I-88 corridor. No changes to headlines planned at this time. Doom && .SHORT TERM... Issued at 252 PM CST Thu Mar 9 2023 Through Friday night... No changes are planning to the going headlines. The initial warm air advective surge of precipitation is quickly shifting eastward into northern IL early this afternoon in advance of a quickly approaching vigorous shortwave trough and associated upper level speed max now shifting eastward over the Mid- Missouri Valley. Forced ascent continues to be robust and is largely being driven by rather robust low-to-mid level isentropic upglide (warm air advection) juxtaposed beneath a region of increasingly diffluent upper level flow associated with the exit region of the upper level jet speed max. Given the steep lapse rate environment, heavy precipitation intensities are occurring, with many sites across eastern IA reporting heavy snow with 1/2 to 1/4 mile visibilities and around 1" per hour rates. Expect this activity to steadily translate eastward into northeastern IL and eventually northwestern IN over the next couple hours this afternoon. The main forecast idea with this event has not changed much, though the heavier precipitation is arriving a few hours quicker than originally anticipated. We generally still expect the heaviest snow rates (1" per hour rates) to largely occur north of the I-88/I-290 corridors late this afternoon through mid to late this evening. However, warmer initial temperatures farther to the south over parts of the Chicago metro area and points south and east into northwestern IN will result in the precipitation onsetting as rain for at least a few hours before it begins to mix with snow as far south as the I-80 corridor later this evening. As such, this is likely to result in a sharp snowfall north-to-south snowfall gradient between the I-88 and I-80 corridors. The heavier snow rates are expected to gradually abate from west to east after midnight as the main larger scale forcing peels off to the east. However, lingering mid-level deformation in the vicinity of the 700 mb low track over far northern IL will likely continue to support periods of lighter snow overnight before it ends early Friday morning. Lake effect parameters continue to look rather poor and largely unsupportive of any meaningful lake enhancement to the precipitation overnight. Total snow accumulations of 4 to 7 inches are still favored near the WI state line, with amounts dropping to around an inch across the I-80 corridor. Farther south of I-80, especially south of the Kankakee River Valley, rain will be the primary precipitation type. The weather on Friday is likely to remain cloudy, and some lingering flurries could continue into Friday evening. Otherwise, temperatures during the day will remain in the 30s, with the coolest locations likely to be over the snowpack. Temperatures Friday night are then expected to drop into the 20s as a surface ridge of high pressure builds overhead. KJB && .LONG TERM... Issued at 252 PM CST Thu Mar 9 2023 Saturday through Thursday... Main forecast concerns: * Another round of accumulating snow likely Saturday night-early Sunday * Unseasonably chilly this weekend through Tuesday, especially Monday-Tuesday Surface high pressure will be in control to start Saturday, though with mostly cloudy skies from a mix of lingering stratus east and mid and high clouds moving in from the west. This will be in advance of Saturday evening-overnight`s snow producing system. Temperatures will recover to mid 30s to near 40 I-80 and north, coolest lakeside and far north, and around 40 to lower 40s and locally mid 40s south. A positively tilted mid-level short-wave associated with a brisk southern stream upper jet will eject eastward through Saturday night and become embedded in the trough axis of a stout mid-upper low across the northern Plains. There is variance in the model guidance in handling the progression of the short-wave. In general, the NCEP (GFS and NAM) guidance is slower moving and slower to weaken the wave, with better upper jet support, while the foreign guidance (ECMWF, Canadian, UKMET) is faster to push the wave across and weaken it. The above being said, there`s expected to be sufficient forcing to bring accumulating precip. to the entire area, supporting the NBM`s categorical PoPs. How the short-wave evolves will be more tied to QPF and snow amount distribution, with the NCEP guidance more broad brushed and foreign guidance favoring the western or southwestern half of the CWA. If top-down saturation occurs quickly enough, some light snow and rain may reach into far western and southwestern sections late day Saturday. Most of the precipitation, however, will fall near and after sunset (last CST sunset until November!). Given a cold enough air mass aloft, think the duration of any rain south should be fairly brief. Overall moderate forcing paired with fairly steep lapse rates above the DGZ should generate light to occasionally moderate snowfall rates, barring a much faster weakening of the parent wave. Looking at a typical wet, lower SLR spring snow, and for now, given the model differences, 1-2" accumulations in the grids appear reasonable for now. Expect the typical slushy road and reduced visibility impacts. Some mainly non-accumulating light snow may linger into Sunday morning. Then on Sunday afternoon-night, a vigorous clipper-like low associated with fast southeastward trajectory of the northern Plains upper low may bring snow showers (some robust) as strong cold advection steepens lapse rates. After temperatures top out in the upper 30s to near 40 on Sunday, many locations are unlikely to get out of the low 30s on Monday (30-35F range officially) amidst blustery north-northwest winds. Lake effect snow showers may get going into northwest Indiana, with flurries possible inland, though not mentioned yet. Following chilly conditions under high pressure Monday night- Tuesday evening, should see a warm-up (to what extent is uncertain) during the mid week period and some threat for rain showers. Castro && .AVIATION... For the 00Z TAFs... Aviation Forecast Concerns: * Snow with IFR/LIFR ceiling/vis overnight. Brief period of rain/snow mix at KMDW/KGYY. Snow decreases in intensity after midnight, and lingers into Friday morning before ending. * Breezy east winds become northeast after midnight, then gusty from the north by midday Friday. Evening water vapor imagery shows a compact, vigorous mid-level wave tracking east across IA, which is evident mainly as a south to north oriented trough at the surface. Strongest deep layered ascent with this disturbance will persist through midnight or so, before the mid-level trough axis shifts east of the region. Very dry low level air has taken some time to saturate from the top down, though have finally seen snow or a snow/rain mix develop for the Chicago metro terminals. This should transition over to snow fairly quickly this evening as dynamic/wet-bulb cooling persists. Worst conditions (LIFR/VLIFR) in heavier snow are expected for KRFD, and areas along and north of the IL/WI border, though Chicago metro terminals (KDPA/KORD) will likely also see a period of at least moderate snow and LIFR conditions this evening. Snow should decrease in intensity after midnight, though light snow will likely persist into Friday morning before ending, with IFR cig/vis expected through mid-morning before improvement to MVFR/VFR vis and MVFR cigs is expected. Surface winds will be mainly east-northeasterly overnight, with gusts into the 20-25 kt range possible at times. Winds will turn northeasterly after midnight, and eventually more northerly by late morning Friday. Gusts will likely be limited during the morning in the vicinity of the surface trough, but will become modestly gusty in the 15-20 kt range again by midday. It`s possible winds may waffle between 350-010 degrees or so, though confidence is low in prevailing NW or NE during the day. There may eventually be a trend more toward NE later Friday evening as surface high pressure ridge approaches from the west. Ratzer && .LOT WATCHES/WARNINGS/ADVISORIES... IL...Winter Weather Advisory...ILZ003-ILZ004-ILZ005-ILZ006-ILZ008- ILZ010-ILZ011-ILZ012-ILZ013-ILZ103-ILZ104 until 7 AM Friday. IN...None. LM...Small Craft Advisory...IL nearshore waters until 9 AM Saturday. Small Craft Advisory...LMZ743-LMZ744-LMZ745...10 AM Friday to 3 AM Saturday. && $$ Visit us at weather.gov/chicago Follow us on Facebook, Twitter, and YouTube at: www.facebook.com/NWSChicago www.twitter.com/NWSChicago www.youtube.com/NWSChicago
Area Forecast Discussion
National Weather Service Nashville TN
856 PM CST Thu Mar 9 2023 ...New UPDATE... .UPDATE... Issued at 846 PM CST Thu Mar 9 2023 The latest mesoanalysis shows the weak cold front approaching the Mississippi River with moist, southerly flow ahead of it helping to improve moisture values from 24 hours ago. This evening`s 00Z sounding shows a much more saturated atmosphere with a PWAT of 1.11". Despite this, showers so far today have been unimpressive with any relatively heavier activity to our south. This evening`s update just features freshening up the PoP grids which do stay high overnight as guidance shows shower coverage increasing ahead of the aforementioned cold front. Precipitation tonight is still expected to remain light, below 0.25 inches. Rain should be winding down around sunrise with a quiet Friday on tap for the area. && .SHORT TERM... (This afternoon through Friday Night) Issued at 109 PM CST Thu Mar 9 2023 Intermittent showers continue to push through the area this afternoon with steadier rain to the south. The HRRR shows a weak cold front approaching Middle Tennessee between 7-9pm tonight with a few rain showers possible out ahead of it. The upper levels continue to moisten and mix down to the surface, assisting in lower dewpoint depression and much higher RH values than we saw yesterday. Both GFS and NAM forecast soundings feature an almost totally saturated profile, so rain should make it to the ground with the approaching cold front tonight. Perhaps a few rumbles of thunder for the southernmost counties, but generally will just be rain. QPF values range from a quarter to a tenth of an inch. The line should exit the CWA by early Friday morning. For the remainder of Friday, clouds will clear out during the early afternoon and highs will be in the mid 50s, so not too shabby of a day if you don`t mind the cooler temperatures. Winds will steadily turn out of the north through the day, leading to a cold night Friday with lows sitting right at or a degree below freezing. Clear skies and calm winds could lead to a few areas of patchy frost Friday night. && .LONG TERM... (Saturday through next Thursday) Issued at 109 PM CST Thu Mar 9 2023 We will have a brief respite from the rain during the day Saturday. Temperatures will be in the mid 50s with increasing cloud coverage through the afternoon ahead of the next disturbance. A shortwave will bring another round of light showers to the area by Saturday night. While it`s pushing its way through the area, an upper-level trough that is setting up over the western Great Plains will begin tracking east, supporting a surface low pressure system that will bring yet another round of rain through the area. The rain associated with this system will be more widespread. Current model soundings do not support severe weather, but a few rumbles of thunder will be possible. With the placement of the surface low being almost directly over the state, southern counties will have a better chance of hearing thunder. This front should clear the CWA overnight Sunday into Monday morning. After that, high pressure will begin building in and the weather will stay dry for a few days. QPF values with this system range from 0.75-1.5 inches with the higher values confined to the southern counties. For Monday, clouds will clear out through the day and winds will turn out of the north, ushering in cool, continental air. This cool air is going to stick around for a few days with overnight lows Monday and Tuesday night below freezing areawide. Temperatures will still be cold going into Wednesday morning, but a wind shift out of the south during the day Wednesday should keep temperatures above freezing through the rest of the week. The next chance for rain looks to be late Thursday into Friday. Models do not have a good handle on this system since it`s still a ways out so this is subject to change. && .AVIATION... (00Z TAFS) Issued at 533 PM CST Thu Mar 9 2023 After a slow come down, cigs are finally starting to become MVFR. IFR conditions are expected this evening as more rain moves into the area and the atmosphere becomes more saturated. These should last through daybreak Friday with cigs returning to MVFR by mid- morning, then VFR before sunset Friday. Winds will be relatively light and southerly tonight, then shift to the northeast around sunrise Friday morning as a weak fropa occurs. A few gusts of 15 to 20 kts will be possible post fropa. && .PRELIMINARY POINT TEMPS/POPS... Nashville 44 57 35 57 / 70 0 0 10 Clarksville 41 54 33 55 / 80 0 0 30 Crossville 43 52 30 54 / 90 10 0 0 Columbia 44 57 33 57 / 80 0 0 10 Cookeville 44 52 32 55 / 90 0 0 0 Jamestown 41 50 30 53 / 90 10 0 0 Lawrenceburg 46 57 33 58 / 90 0 0 10 Murfreesboro 44 57 32 58 / 90 0 0 10 Waverly 41 55 33 54 / 80 0 0 30 && .OHX WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE.......Clements SHORT TERM...Baggett LONG TERM....Baggett AVIATION.....Unger