Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 11/29/18

Area Forecast Discussion
National Weather Service Denver/Boulder CO
842 PM MST Wed Nov 28 2018 .UPDATE... Issued at 814 PM MST Wed Nov 28 2018 Generally just minor adjustments to the ongoing forecast planned at this time. A strong zonal flow aloft will be over the state tonight, with Pacific moisture bringing light to moderate snowfall to the north central mountains of CO, primarily the west/southwest facing slopes of zones 31 and 33 with 3 to 6 inches overnight. A mix of rain and snow showers may also occur along the northern border along and east of the Cheyenne Ridge late tonight into Thursday morning. Only adjustment may involve dragging the pops a little further south into Weld, Logan, Morgan and Washington counties. There is also the potential of low stratus possibly pushing south into the Denver area Thursday morning, from around 5 to 9 am. As a result, I may increase the cloud cover some as well. && .SHORT TERM...(This evening through Thursday) Issued at 217 PM MST Wed Nov 28 2018 Radar and satellite imagery show moisture moving into Colorado from Utah in westerly flow. Tonight a winter system will effect the mountains bringing up to 6 inches to locations such as Rabbit Ears Pass with much less elsewhere. Near the Wyoming border the NAM and HRRR indicate a strip of moisture moving onto the extreme northern plains overnight. This could be the result of additional lift provided by the left exit region of an upper level jet. Cloudy conditions are expected tonight with a partial clearing by late afternoon Thursday. Thursday a Pacific low will move onshore and begin it`s trek east toward Colorado in persistent westerly upper level flow. There will be a brief lull in snow intensity Thursday afternoon before increasing again. See below for further details. .LONG TERM...(Thursday night through Wednesday) Issued at 320 PM MST Wed Nov 28 2018 Models have southwesterly flow aloft in place Thursday night ahead of an upper trough that is supposed to move into and across Colorado Friday from 12Z through 03Z Friday evening. There is upper ridging and weak zonal flow aloft overnight and Saturday. Southwesterly flow aloft is progged Saturday night. The QG Omega fields have moderately strong upward vertical velocity for the CWA late Thursday night and much of Friday across the CWA with the upper trough. The energy is stronger now than it was on yesterday`s 12Z model runs. Low level drainage winds should prevail Thursday night. On Friday, weak north and easterly winds are progged. Downsloping northwesterlies are in place Friday night into Saturday morning. North and northeasterly winds are progged much of Saturday and Saturday night. For moisture, it is pretty deep, especially in the mountains Thursday night and much of Friday. Moisture decreases a bit on Saturday, but increases again Saturday night into the later periods. The QPF fields keep limited amounts of measurable precipitation over the mountains all 5 periods. There is a tad out on the plains Friday afternoon into Saturday morning. The highest snowfall amounts for the high mountains appear to be late Thursday night into Friday morning. Amounts still are not significant but models are trending to higher values. No highlights for now. For temperatures, Friday`s highs look to be 3-7 C cooler than Thursday`s. Saturday`s highs are 1-3 C cooler than Friday`s. For the later days, Sunday through Wednesday, the medium range models show a mean upper trough over 2/3rds of the U.S., including Colorado Sunday and Monday. There is northwesterly flow aloft on Tuesday and upper ridging moving in by later Wednesday. There is a cold airmass in place and some moisture Sunday and Monday. It starts drying out on Tuesday, warming up a bit too. && .AVIATION...(For the 06Z TAFS through 06Z Thursday night) Issued at 814 PM MST Wed Nov 28 2018 Although VFR conditions should prevail into Thursday evening, there is the potential for a brief period of low stratus impacting the KBJC and KDEN terminals from around 10z-16z Thursday morning. Overall confidence is low to medium but I did include a sct cloud deck around 800 ft agl in the terminal forecast at that time. A west/northwest wind shift associated with weak frontal boundary will likely precede the stratus. If it does develop it should be quite shallow and dissipate by late Thursday morning. Surface winds will be southerly 11-16 kts this evening then a weaker west/northwest shift toward 12z Thursday morning, followed by a light easterly component Thursday afternoon. && .BOU WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...Cooper SHORT TERM...Sullivan LONG TERM...RJK AVIATION...Cooper
Area Forecast Discussion
National Weather Service Grand Forks ND
952 PM CST Wed Nov 28 2018 .UPDATE... Issued at 952 PM CST Wed Nov 28 2018 Radar returns continue to move eastward across the northern forecast area. The echos seem showery and more rain like in nature, and dual pol data has some rain as precip type from Mayville/Finely up towards Tolna and Larimore. However, the dual pol data has more snow indication on CC as it moves east towards GFK, and the airport and base have reported light snow. The last ground truth for freezing rain was down in Jamestown a bit ago, although a few spots are reporting mist. None of the high resolution models are handling the system very well, although the HRRR does have some redevelopment on the backside of the system that is mostly snow. Will extend the mention of freezing rain or drizzle mixing with snow further east, but will not expand the advisory at this point as impacts will be pretty isolated. && .SHORT TERM...(This evening through Thursday) Issued at 310 PM CST Wed Nov 28 2018 Regional radar loop shows a couple of circulations, one moving into the northern Red River Valley and another over central North Dakota. Looking at webcams, the snow itself seems to be pretty minimal. Although there are echoes over northwest Minnesota, it appears that very little snow has fallen there yet. The most snow has fallen over northeast North Dakota, where Langdon has estimated 2 inches and Grand Forks is also nearing an inch or so. Got a report from Fargo of about half an inch. This is just enough snow to cause slippery spots. However, the bigger problem is the potential for any lingering freezing precipitation. Reports from earlier today were mainly within the winter weather advisory area. The North Dakota DOT road condition website shows ice or compacted snow from Cando to Devils Lake to Valley City. Looking ahead into tonight, still expect some light snow across northwest Minnesota. Accumulations should still be in the 1 to 2 inch range. Have some uncertainty with what happens with the echoes on radar over central North Dakota. Think there may be some bright banding out there, but it could still produce a little freezing precipitation over portions of eastern North Dakota this evening. Do not plan to change the advisory area, but the next shift may be able to cancel it a little early. Otherwise, some light snow may linger into Thursday across the Lake of the Woods region. .LONG TERM...(Thursday night through Wednesday) Issued at 310 PM CST Wed Nov 28 2018 00Z Fri - 00Z Sun...Split flow to develop across North America with southern stream over the southern states and northern stream along the International border. Upper level ridge over the Pacific Northwest will move over the Dakotas by 00Z Sun and build. Upper low over CA will move into the Central Plains by the end of the period. A storm system is expected to occur in states to the south. The GFS has been trending north while the ECMWF has trended south over the last couple model runs. Storm system to the south is expected to brush the far southern zones and may continue to shift south with later forecasts. Sun - Wed...Long wave pattern amplifies through the period. Long wave trough over northern Canada will deepen over central Canada and into the Northern plains. Split flow is forecast with northern stream over central Canada and Northern Plains and the southern stream over the southern states. The GFS and the ECMWF were in reasonable agreement through 108 hours. Thereafter the GFS is fast in the southern stream and the ECMWF is fast in the northern stream. Next chance for snow would be Tue. && .AVIATION...(For the 00Z TAFS through 00Z Thursday evening) Issued at 654 PM CST Wed Nov 28 2018 Ceilings are mostly MVFR, with snow on and off across much of the northern forecast area. Snow is mostly in the 2-5SM range although could not rule out some 1SM at KTVF and KBJI later tonight as the main precip moves east. Some lowering to IFR ceilings later on this evening. Precip will taper off from west to east, ending at all but KBJI by 06Z. KBJI snow will taper off towards morning although cannot rule out a few lingering flurries past that. The clouds will hang on a bit longer, with IFR to MVFR ceilings continuing for much of the day. KDVL could see some improvement by the end of the period. Winds will shift around from the southeast at around 15 kts to the northwest at around 10 kts by tomorrow afternoon. && .FGF WATCHES/WARNINGS/ADVISORIES... ND...Winter Weather Advisory until midnight CST tonight for NDZ014- 024-028-038. MN...None. && $$ UPDATE...JR SHORT TERM...Godon LONG TERM...JH AVIATION...JR
Area Forecast Discussion
National Weather Service Louisville KY
927 PM EST Wed Nov 28 2018 .Forecast Update... Issued at 927 PM EST Wed Nov 28 2018 ...Brief Wintry Mix Possible Thursday Morning... No major changes/updates planned to the forecast this evening, although do have some minor tweaks to mention. A challenging forecast is setting up for the overnight period through mid morning on Thursday. Temperatures are currently running in the upper 20s and low 30s over most of the area, with a few spots in our far east in the mid 20s. These temps should mostly stay put for the evening into the overnight as variable upper clouds and a light SE surface flow combat limited radiational cooling. However, as we move toward the pre-dawn hours expect temps to begin to slowly rise as southerly winds increase in response to a weak low level jet spreading overhead. Light precipitation is expected to begin during this time as 1000-700 mb moisture pools and isentropic lift commences. Given a shallow cold airmass below freezing, and a +5 C warm nose overunning the region we are likely to see some pockets of freezing rain/drizzle starting around 5 AM EST over southern Indiana and west central KY. I suppose a very brief period of sleet could occur at precipitation onset before the warm nose gets established, but it would be of no consequence. Starting time around the Louisville metro would be 6 or 7 AM EST, and between 8 and 9 AM EST in the Bluegrass region. Temps should quickly rise above freezing after precipitation onset, however there will be a brief window a quick glaze of ice. As the day shift discussion mentioned, there may also be a lag in surface recovery behind the air temps as we have been cold for a brief stretch. At this point, think the most likely area for some light glazing of ice would be across southern Indiana and far north central KY before and around sunrise. This are will see precipitation onset first and seems to have an hour or two longer residence time in the freezing rain zone before temps recover. As far as the rest of central Kentucky goes, there is a less confidence/certainty in the timing of precipitation onset versus temp recovery. In addition, precipitation onset may not occur until after sunrise which may hurt the potential for brief ice accumulation. On the other hand, the Bluegrass is seeing the coldest temps right now ranging in the 25 to 30 degree range. Pretty tricky setup indeed! Should see some recovery toward dawn, but the rain may be falling into a slightly deeper cold layer in that region. Will have to see how they progress toward dawn. Only other tweak to the SPS will be to add Ohio, Butler, Grayson given early onset. Road temps appear to be ranging in the mid to upper 30s at this hour, and are only slowly falling. Given the low confidence in timing/road temps, the short window for frozen precipitation potential, and the minimal/spotty nature if it occurs at all cannot justify anything more than a Special Weather Statement at this time. Will continue to go with this messaging and graphics highlighting best timing/areas for minor impacts. && .Short Term...(This evening through Thursday) Issued at 329 PM EST Wed Nov 28 2018 ...BRIEF PERIOD OF WINTRY WEATHER POSSIBLE THURSDAY MORNING... ...THURSDAY MORNING COMMUTE COULD BE IMPACTED... ...Rest of This Afternoon and Evening... Afternoon satellite and observations show partly to mostly cloudy skies across southern Indiana and central Kentucky this afternoon. The thin cirrus is allowing some sunshine through. Temperatures had risen into the lower 30s across southern IN and most of northern KY. Southern KY has seen temps warm into the middle 30s. Warmest readings were out in the far western part of the state, with very cold readings in the southeastern KY higher elevations. In the near term, quiet and dry weather is expected this afternoon and evening. We`ll continue to see plenty of mid-high level cloudiness stream into the region. Temperatures will likely top out in the next hour or so and then fall back into the upper 20s this evening. The presence of the mid-high level cloud deck is likely to keep us from completely radiating out during the evening hours. ...Tonight and Early Thursday Morning... Overnight, mid-level cloudiness will continue to increase as we remain in a strong southwest flow aloft. Ceilings are expected to lower throughout the night and into the early morning hours. Aloft, a weak mid-level perturbation will push in from the west. This feature, combined with good isentropic upglide should lead to saturation late tonight. Precipitation is expected break out toward dawn and is expected to be generally light in nature. Now the complicated part... ########################## Thermal Structure ########################## Model proximity soundings show a classic warm nose aloft type sounding. Low-level jet axis will likely push a strong warm nose (near 5C) up over the top of a pre-existing cold airmass. This cold airmass is not overly mature as its less than 60 hours old and not sufficiently deep. Nonetheless, surface temperatures are likely to be below freezing early in the overnight period with a slow upward trend in temperatures toward morning. The majority of the guidance has temperatures right around the freezing mark by sunrise Thursday. Temperatures are then forecast to warm above freezing during the mid- morning hours. ########################### Precipitation Production ########################### Precipitation production and start time are another critical forecast concern. Quite a bit of the model guidance (Euro, GFS, ARW- WRF, GEM, HRRR, and HRRR ensembles) remain steadfast in keeping precipitation production at a minimum overnight and delaying it until mid-morning. On the other hand, the NMM based NAM12 and NAM3km remain more robust in generating light precipitation in the pre-dawn hours around the Thu AM commute time. Given the anticipated thermal profiles, this could be a mix of very light rain and/or light freezing drizzle that may last 1-3 hours depending on how strong the low-level warm air advection evolves. ############################ Surface Skin Temperature ############################ Surface skin temperatures are probably the most critical part of the forecast. We`ve have been monitoring pavement temperatures outside the office this afternoon. With filtered sunshine and surface temps of 33-34, our pavement readings have jumped back up to around 39-40 degrees on bare concrete and around 44-46 on the black top. In shaded areas with relatively little solar insolation, temps remained in the upper 20s to the lower 30s. We`ll probably see pavement temps cool a bit with the loss of sun this evening and into the overnight period and even with temps warming slightly overnight, there is likely to be a lag in the skin temps compared to the air temperatures. ############################# Forecast/Impacts ############################# Taking all of the above into consideration, this remains a low confidence forecast as of this writing. I`m generally concerned about the precipitation production and whether or not we`ll saturate completely. The lack of QPF support from the majority of the models is concerning, but we do have to take the biases of the NAM-NMM into account. After coordinating with surrounding offices, we did came to the conclusion, based on the latest data, that confidence was not high enough to warrant an advisory based on the model signal. However, and I cannot stress enough, that this is a non-zero threat for a short, but possibly impactful light glazing event toward dawn. The area at most threat would generally be in areas along and north of the I-64 corridor where the low-level cold air could remain in place through much of the night. If precipitation does start falling toward dawn, and in the middle of the AM rush, we could easily see pockets of freezing rain/drizzle in parts of the area, especially where pavement temperatures lag behind surface air readings. For now we will highlight our messaging of impacts in social media, and in the HWO and a strongly worded Special Weather Statement product. The evening and overnight shifts will continue to examine the 28/18Z and 29/00Z datasets and make appropriate adjustments to the forecasts as required. In the meantime, residents of southern Indiana and most of north- central Kentucky should keep abreast of the latest forecasts this evening and be prepared for hazardous travel Thursday morning. .Long Term...(Thursday night through Wednesday) Issued at 200 PM EST Wed Nov 28 2018 A mild but unsettled pattern will set up for the end of the week, starting with a warm front lifting through the Ohio Valley Thursday night. Rain will be fairly widespread, but mostly light through the day on Friday. By Friday night ridging starts to amplify ahead of a deep and negatively tilted trof that digs into the Plains. The increasing low/mid-level southerly flow will feed copious amounts of moisture into the Ohio Valley, supporting QPF that will approach 1 inch by 12Z Sat along and west of I-65. Low-level jetting will support isolated thunder, which will mainly be limited to south-central Kentucky Friday night, but will spread across the entire CWA on Sat. SVR threat on Saturday is non-zero but highly conditional. Instability will be a serious limiting factor, but we could at least become marginally unstable across part of the area just ahead of the front. Shear could be quite favorable, but is still dependent on the low not tracking too far to our north and west. A lot of questions to be sorted out, so will just keep it a broad and generic mention of potential strong storms for now. The first half of next week will trend back to below-normal temps, but other than that forecast confidence is low as models struggle to come into agreement with each other, or from run to run. Will stick with consensus for now, which keeps us somewhat cold and unsettled. && .Aviation...(00Z TAF Issuance) Updated at 639 PM EST Wed Nov 28 2018 Conditions will start out VFR this evening with a light SE surface wind and Bkn-Ovc mid clouds streaming overhead. As we head into the pre-dawn hours, low level moisture will overrun a warm front stationed over the region. This will lead to a period of light rain and drizzle, along with ceilings close to the VFR/MVFR threshold. Temperatures may be right around freezing at this time, so a brief window of -fzra or -fzdz is possible. Temperatures should quickly warm above freezing with sunrise, so p-type will be plain rain from there on. However, ceilings will lower into the MVFR and likely fuel- alternate ranges by late morning to midday. Lower visibilities in showery rain and fog will be possible Thursday evening, along with IFR ceilings. Also mentioned some LLWS at SDF/BWG early this morning as a strong low level inversion couples with a veering 30 knot low level jet to create very good directional shear. Speed isn`t all that great, but the directional shear has enough magnitude to warrant LLWS mention. && .LMK WATCHES/WARNINGS/ADVISORIES... IN...None. KY...None. && $$ Update...BJS Short Term...MJ Long Term....RAS Aviation...BJS