Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 02/08/20

Area Forecast Discussion
National Weather Service Denver/Boulder CO
303 PM MST Fri Feb 7 2020 .SHORT TERM...(This evening through Saturday) Issued at 300 PM MST Fri Feb 7 2020 A jet streak in the NNW flow aloft continues to sustain heavy snow and strong winds in the mountains, as well as bands of snow along the urban corridor and out to the adjacent plains. In particular, a long sustained narrow snow band from Grand County stretching southeast across Jefferson and Douglas counties...which continues all the way down into Texas, has produced over a foot of snow in our forecast area today. Models haven`t performed so well with this event, typical of jet induced banded snow, so just need to look at the big picture. With the speed max currently laying across the Front Range Mountains and slowly drifting southeast, should see bands continuing late this afternoon into the early evening. This can be seen with cloud tops cooling and snow bands already reforming over the mountains and spreading southeast over the urban corridor. While confidence remains low in the models, several show the long sustained band moving slightly north and east, with additional bands pushing across the metro areas through early this evening. Therefore, will continue the advisories out for the plains and foothills, with snow expected to decrease and diminish in the late evening. The southern foothills Advisory will likely be able to be cancelled by later this evening. RAP is showing a second speed max pushing in that may sustain some light snow over the plains through midnight, but will have to keep watch on the model trends. The heavy snow, strong winds and blowing snow will continue to bring terrible travel conditions to the high country through the rest of the evening with another 3 to 6 inches by midnight. Rates and winds will be decreasing after this, but will likely still see another 1 to 4 inches. Flow will turn more westerly for Saturday with a lee surface trough forming. Brief upper ridging across the area will bring clearing skies, and warm advection combined with downsloping winds into the surface lee trough will bring much warmer temperatures compared to today. Light snow may still occur over the far northern mountains in the morning, before snow will increase in the afternoon ahead of the next system dropping down along the Northern Rockies. The jet ahead of this system and the digging surface trough will increase winds across the mountains again and down into the foothills and possibly the western suburbs. Blowing snow will likely become an issue again even with little snow, if any, falling yet. .LONG TERM...(Saturday night through Friday) Issued at 300 PM MST Fri Feb 7 2020 Next storm system is quick on the heels of this one, already dropping southeast off the coast of British Columbia. This system will continue to move southeast into the Northern Rockies on Saturday. QG fields show most of this energy splitting as it moves into the Central Rockies by Saturday night. However, we`ll still have the support of the right rear entrance region of an upper level speed max stretching across Colorado. This lift, along with increasing mid level moisture and modest orographic lift, will be enough to get another round of snow going in the high country Saturday night. We expect periods of mainly light snow to then continue through Sunday and Sunday night under the nearly persistent right entrance region of the upper jet. Despite the weakening orographic component during this time frame, given the jet`s proximity, can`t rule out a few heavier embedded bands. On the plains, we`ll see a cold front move across late Saturday evening, with shallow upslope developing along the Front Range. That upslope gradually deepens through Sunday, so we`ll also see snow develop across the foothills and nearby adjacent plains and I-25 Corridor. Right now, initial accumulation projections Saturday night through Sunday night would be 4-10 inches in the mountains, and 1-5 inches along the Front Range. By Monday, we`re looking at another piece of energy dropping southward across the Northern Rockies and Northern High Plains. This will probably push a weak reinforcing cold front across northeast Colorado, and keep at least a chance of light snow in the forecast. Temperatures will stay well below normal, with highs struggling to reach freezing. Tuesday should feature dry conditions with a gradual warming trend, but then we expect another weak trough late Wednesday or Thursday with cooler temperatures and a chance of light snow. Friday should be in between systems, but another storm system will likely impact the area by next weekend. && .AVIATION...(For the 00Z TAFS through 00Z Saturday evening) Issued at 300 PM MST Fri Feb 7 2020 Snow is expected to once again spread across the urban corridor later this afternoon and into the evening. In general, the snowfall rates be lighter compared to this morning, but MVFR ceilings and visibilities will likely return to prevail through this afternoon, with brief IFR associated with the bands of snow. Additional accumulations will likely be in the 1-2 inch range this afternoon into the evening, but it would be higher if a heavier snow band develops right over the airport. Southerly winds will become drainage this evening, increasing out of the west Saturday mid morning as downsloping winds push east from the foothills. Gusts up to 25 kts will occur near the foothills and western suburbs. A cold front will likely push through Saturday evening. && .BOU WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory until midnight MST tonight for COZ030- 032-035-036-038>041-043-045-046. Winter Storm Warning until midnight MST tonight for COZ031-033- 034. && $$ SHORT TERM...Kriederman LONG TERM...Barjenbruch AVIATION...Kriederman
Area Forecast Discussion
National Weather Service Des Moines IA
548 PM CST Fri Feb 7 2020 .DISCUSSION.../Tonight through Friday/ Issued at 309 PM CST Fri Feb 7 2020 .Overview...Lingering light snow or flurries, mainly over southeast into central Iowa, will come to an end late this afternoon or early this evening. Focus then is on the significant winter storm that will largely be focused over northern Iowa and southern Minnesota Saturday night into Sunday. Trends for the mid-week system are beginning to favor perhaps a drier conditions, though there still remains some uncertainty. .Details...Early afternoon GOES-East clean IR imagery shows the longwave trough still over the central and eastern US with the axis now into the Ohio and Tennessee River Valleys. Shortwave trough embedded in this longwave trough is beginning to move out of the state to the southeast with light snow winding down over all but the southeastern part of the forecast area. Forecast soundings from the HRRR and RAP show low level saturation lingering with weak lift within this saturation indicating some final flurries before all the snow ends. This low level saturation seems to correspond fairly well with the stratus as viewed in the Day Cloud Phase Distinction and Day Snow Fog RGBs and also with surface observations that have -SN reported underneath these clouds. Therefore, have added flurries on the northwest side of the more persistent snow that will taper off later this afternoon or evening. Surface high pressure will build into the region tonight and move out on Saturday as the flow in the mid-levels splits off into a northern stream shortwave and the other piece forming a closed low over the southwestern US. The northern stream shortwave with an associated surface low pressure will advance towards the state Saturday night with a majority of models (12z GFS/12z GEFS/12z EC/12z CMC) having the low passing through northern if not central Iowa. The one outlier is the 12z NAM that has the low passing along the Iowa/Minnesota border. As the low approaches the state, low level thermal lift will increase and there will be strong QG convergence moving in overhead as well. Initially, cross sections do show dry air in the low levels around 00z over northern Iowa, but that will erode away between 3z and 6z. As saturation does occur, a strong frontogenetical band, which will be maximized in the 850-700mb layer, will move over northern Iowa and southern Minnesota. Cross sections show strong lift in the dendritic growth zone over northern Iowa starting around 6z (snow onset roughly) lingering to around 12z. If the NAM`s surface low track verifies, this strong lift may be very focused over southern Minnesota. At this time range, there appears to be high confidence in strong lift within the dendritic growth zone for enhanced snow rates of 1"/hour over northern Iowa and/or southern Minnesota. This is supported by this morning`s 12z HREF probability of 1"/hr snow rates with isolated 2"/hr rates over southern Minnesota. This area of enhanced snow rates and therefore snow totals will be further refined as the event enters the forecast window of the high resolution guidance (e.g. HRRR, RAP) in the upcoming forecast cycles. Writing about snow totals, the track of the low will be a key piece and that is why it was mentioned earlier. While warmer air will be drawn into the state in the low levels, this will allow for some of the snow from Saturday night to changeover to rain during the day Sunday. Further, a dry slot will move in over southern and central Iowa on Sunday, though how far north will depend on the exact low track. The dry slot will either 1) end ice introduction resulting in a change from snow to freezing drizzle or rain to drizzle where it is warm enough or 2) end precipitation all together. Either one of these scenarios will serve to bring a sharp cut off to the higher snow totals, which will likely be over northern Iowa. As the low passes, winds will become from the northwest and turn gusty. How gusty will again depend on low track with BUFKIT NAM profiles suggesting wind gusts to around 35 mph while the BUFKIT GFS profiles are not as strong. All the precipitation will come to an end by Sunday evening as large scale subsidence and drying enter the area. High pressure will pass through the region early next week followed by a shortwave trough and associated moisture-starved, cold front diving southward. The aforementioned closed low over the southwestern US will begin to move eastward toward the central and southern Plains early next week. There is still some disagreement on how high pressure will move over the northern Plains, but there has been a trend in the deterministic models of pushing the precipitation farther south. && .AVIATION.../For the 00Z TAFS through 00Z Saturday evening/ Issued at 548 PM CST Fri Feb 7 2020 Lower cigs continue to hold on; especially northeast sites at KMCW, KDSM, and KOTM where MVFR conditions continue for now. Elsewhere, MVFR giving way to some VFR pockets with gradual transition to VFR from KFOD northwestward. Have slowed departure of lower cigs due to a band swinging southeast overnight. Will monitor trends through 06z, but generally more improvement expected between 06-12z most sites. /rev && .DMX WATCHES/WARNINGS/ADVISORIES... Winter Storm Watch from late Saturday night through Sunday afternoon for IAZ004>007-016-017. && $$ DISCUSSION...Ansorge AVIATION...REV
National Weather Service Wilmington OH
932 PM EST Fri Feb 7 2020 .SYNOPSIS... Surface high pressure will bring a brief period of dry weather later this afternoon into this evening. Another, quick moving low pressure system will offer a chance for light snow late tonight into Saturday. An active weather pattern looks to continue this weekend into next week with several chances for precipitation. && .NEAR TERM /THROUGH SATURDAY/... Spotty snow showers developed this afternoon in the deep-layer WNW flow, and a few of these remain across the area this evening, though with very isolated coverage. Outside of these snow showers, skies have remained generally clear, allowing temperatures to drop off a little quicker than previously anticipated. Min temps have been reduced by a few degrees, particularly in the northern and eastern sections of the forecast area. A shortwave and associated surface trough are now moving eastward through Illinois, soon to enter Indiana. As flow turns briefly southwesterly ahead of the wave, a small 850mb theta-e ridge will also be present as a result, with an area of snow developing on the northeastern periphery of the theta-e ridge. While the overall forecast thinking has not changed, the overall forcing and thermodynamic environments are somewhat marginal, and the method of forcing will not support a lengthy period of accumulating snow -- likely only a few hours at any given point on the map. While there will be saturation within the dendritic growth zone, temperatures will cool through the layer, meaning that the DGZ will not be particularly deep. Overall snowfall forecast numbers on this forecast update are slightly lower than with the previous forecast, but not enough to really change the expected impacts, and thus the advisory will remain as placed. Previous discussion > Still a few patches of flurries this afternoon across the south and east as influence from the low pressure slowly fades. Beneath the dominant upper level trough, a weak 700-850 mb ridge moves in from the west tonight, resulting in partly to mostly clouds skies and initially dry conditions. Temperatures currently range from 30-33 degrees this afternoon with perhaps a degree of warming before temperatures begin to decrease. Expect temperatures to drop into the mid to upper 20s with favorable radiational cooling, especially across the northwest. Late tonight, a respectable shortwave currently located over the upper Mississippi Valley propagates eastward into the Ohio Valley, promoting another round of light snow across the area. Majority of the snow falls during the day on Saturday, but it enters the area from the west late tonight. Winter weather advisories have been issued for portions of SW Ohio, SE Indiana, and N Kentucky starting late tonight. Guidance suggest the best lift arrives in the tri-state area a few hours before sunrise. Forecast soundings from the RAP show a favorable thermodynamic profile with modest lift in the DGZ between 6-8AM. This should result in robust dendrites (-10 to -20C) that will accumulate quickly over a short period of time. For this particular event however, the length of time limits overall accumulations to 1-2 inches. Regarding the winter weather advisory issuance...Similar to Friday`s events, the timing of greatest snow rates and deteriorating road conditions occur around sunrise leading to hazardous travel. While the overall traffic flow should be lower, those who do have to travel during the morning should expect hazardous travel conditions. For this forecast package, the advisory focused on the area that will experience the snow during the optimum time frame (4am-9am) and also contains a lower criteria (2" for advisory) due to the surrounding terrain. Some areas outside the advised area (further north and east)are forecast to see 1-2 inches but were not included in the advisory due to higher tolerance and a less optimum time frame (9am-1pm). Adjustments to the advisory are possible overnight as the situation evolves. && .SHORT TERM /SATURDAY NIGHT/... Saturday morning, snow is still expected to be ongoing across the forecast area as the trough continues to move east. Through mid-morning and early afternoon, lift gradually weakens and snow rates decrease. Along with the decreasing snow rates, solar radiation and warming temperatures help to limit overall impacts for eastern/northern locations. With warming temperatures, can`t rule out a period of rain-snow mix/rain to across the south as precipitation moves east and out of the area. Could still see light accumulations into the afternoon, especially across the north, before the trough dissipates during the evening hours as another weak ridge builds into the Ohio Valley. Temperatures Saturday night drop into the mid 20s area wide. && .LONG TERM /SUNDAY THROUGH FRIDAY/... Precipitation will develop on Sunday afternoon and evening ahead of an approaching front. There could be some rain-snow mix or just snow in northern counties at onset, but beyond then expect this to be a rain event. The rain will push across the forecast area Sunday night and move off to the southeast on Monday as a cold front moves through the area. High pressure will build in Monday night through Tuesday night. There remains considerable uncertainty from Wednesday into Thursday night. GFS continues to have a stronger northern stream which keeps any southern stream system and its associated precipitation south of the forecast area. However, there is enough spread within the GEFS members to still suggest at least a chance of precipitation into the area. ECMWF and it ensemble have trended further south with time although it solutions are still further north than the GFS. There are also timing uncertainty with when the southern stream energy ejects out of the southwest. Thus will rely heavily on ensemble means, using a blend of the GEFS and ECMWF ensemble. This suggests that there is still a good chance of precipitation Wednesday night into Thursday. Expect rain in southern counties with a rain-snow mix or perhaps even all snow further north as uncertainties in solutions also impact thermal profiles and thus precipitation type. There is general agreement that high pressure will be building in by Friday with slightly below normal temperatures. && .AVIATION /02Z SATURDAY THROUGH WEDNESDAY/... The main concern for this set of TAFs is the snow moving into the area late overnight into tomorrow morning. While generally VFR conditions are expected going into the overnight hours, snow will overspread the TAF sites from southwest to northeast. This snow will bring several hours of MVFR visibilities and MVFR to IFR ceilings, and it is likely that most of the TAF sites will also experience an hour or two of IFR visibilities as a result of the snow. Once the snow comes to an end, some persisting MVFR visibilities and low-end MVFR ceilings may continue for a while, and a few snow showers could still impact the Dayton and Columbus TAF sites through early to mid afternoon. Ceilings will gradually improve late in the day, with VFR conditions expected some time after 00Z. OUTLOOK...MVFR conditions are possible again on Sunday night into Monday with rain. MVFR ceilings may continue into Tuesday morning. && .ILN WATCHES/WARNINGS/ADVISORIES... OH...Winter Weather Advisory from 3 AM to 10 AM EST Saturday for OHZ070>072-077>080. KY...Winter Weather Advisory from 3 AM to 10 AM EST Saturday for KYZ089>097. IN...Winter Weather Advisory from 3 AM to 10 AM EST Saturday for INZ066-073>075-080. && $$ SYNOPSIS...AR NEAR TERM...Hatzos/McGinnis SHORT TERM...McGinnis LONG TERM... AVIATION...Hatzos
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
533 PM CST Fri Feb 7 2020 .SHORT TERM... 236 PM CST Through Saturday... A light snow dusting tonight, mainly along/south of I-80 with some flurries north, is the item of interest in the short term. Lake effect snow had dissipated across northwest Indiana as surface ridging scoots into the area. Aloft in the mid levels, a low amplitude positively tilted trough is angled across Iowa this afternoon and will gradually move across the forecast area tonight. This short wave trough is emphasized some by a vorticity maximum (vort max) near the Iowa/Missouri border that will move slightly south of east before turning more due east tonight. It is near this vort max where differential vorticity advection and a pocket of isentropic lift will bring periods of light snow. For our CWA, that`s mainly along/south of a line from Streator IL to Rensselaer IN. A small area of one half to on the high end one inch may fall in that far southern part of the CWA helped by the lift collocated with the dendritic growth zone (-12C to -18C). North of there, forcing is much more transient and weaker along with the fact the low level air is significantly dry (2 pm T/Td spreads are 25 to 35 degrees F). This should result in mainly just transient flurries and likely no accumulation. Any light snow from this system should end early Saturday morning. Upstream conditions in Iowa and Minnesota would point toward broken stratocumulus clouds likely during Saturday, although they may be thin with some holes at times in mainly northeast Illinois. These clouds will reside in the vertical thermal profile near -10C per RAP and NAM soundings, with some slight cold advection induced low-level instability. That could bring some flurries. Highs on Saturday with the clouds look to be around 5 degrees cooler than today. MTF && .LONG TERM... 238 PM CST Sunday through Friday... The Madden Julian Oscillation (MJO) is expected to become active in phase 6 (Western Pacific) through next week. Teleconnections related to an active MJO in this phase tends to favor a negative PNA-type pattern (Upper Trough in the west, ridding in the east) across the CONUS. For this reason, the weather pattern across the central CONUS is likely to remain active, but with temperatures near seasonal averages in our area. The first weather system of note is hybrid clipper type system talked about in the previous discussion. This system is expected to track eastward from the northern Plains to the western Great lakes region late Saturday through early Sunday evening. A lower level southerly wind response is likely to occur in advance of it across much of the Mid-Mississippi Valley and lower Great Lakes into early Sunday. This will in turn set up a large region of isentropic upglide (warm air advection) over the region into Sunday, thus setting the stage for a period of precipitation into our area for Sunday. The current track of the associated surface low suggests that the band of heaviest snowfall of 6"+ will occur across parts of southern MN and northern IA, eastward into adjacent areas of WI Saturday night into early Sunday. However, farther southeast into our area lighter total snow amounts are expected. It appears that the snow could begin to onset across northern IL by early Saturday morning, possibly just prior to daybreak in parts of north central IL. This initial period of snow early Saturday morning could even fall at a moderate to heavy clip as it appears a transient band of fairly strong lower-mid level frontogenesis will shift across the area beneath a corridor of steepen mid-level lapse rates. As a result, a quick inch or two of accumulation will be possible for some during the morning hours, especially for areas north of I-80. During the afternoon a drier mid-level air mass will try to shift over the area. Once this arrives we will see an end to the accumulating snow sometime into the afternoon on Sunday, with only some light drizzle possible into Sunday evening. Surface temperatures are expected to warm to near, or even a degree or two above freezing during the afternoon Sunday, so any lingering precipitation should be in the form of drizzle into early Sunday evening. Total snow amounts continue to look the highest over far northern parts of IL, especially near the WI state line, where around 2 to 3 inches look possible. Amounts should tapper off with southward extent over the area. Following this quick moving weather disturbance, it is looking like we will see a couple of quiet weather days across the area Monday and Tuesday of next week as surface high pressure dominates. Temperatures both days looks to be in the low to mid 30s. By midweek forecast guidance is not in very good agreement with the evolution of another storm system expected to develop over the southwest. Some of the 12z guidance suggests this storm system will largely remain south of the area as a colder airmass builds southward over our area under another area of high pressure. However, there remains some guidance and ensembles supporting some local impacts from this storm system. Given the high uncertainty during this period, I did not stray from the general blended guidance, which gives some low chance POPs for the area. KJB && .AVIATION... For the 00Z TAFs... Aviation forecast concerns: -Chance of flurries/very light snow overnight, and a few flurries Saturday afternoon. No significant impacts expected to terminals. -MVFR ceiling potential Saturday. Weak area of surface low pressure was analyzed over eastern IA late this afternoon, in association with a weather disturbance which will track east-southeast through central IL/IN through Saturday morning. Regional radar mosaic depicts a resulting area of light precipitation, mainly light snow, across parts of eastern IA and western IL, which is expected to track largely south of the terminals. Farther north, weaker forcing and a somewhat moisture starved thermodynamic profile is expected to produce several thinner cloud layers tonight and early Saturday, with the potential mainly for just a few no-impact flurries later tonight. Little/no accumulation is anticipated for the metro terminals, with a light dusting at best, with better potential for some minor accumulations south of the Interstate 80 corridor. Mainly VFR conditions are expected, though some high-end MVFR ceilings are possible after midnight. Modest west winds will diminish quickly this evening as weak high pressure and the approaching weak surface trough result in a weak and baggy surface pressure gradient. Winds will turn westerly near 10 kts Saturday behind the departing system. Forecast soundings would maintain support for an MVFR stratocu deck 2500-3000 ft to linger Saturday. With the top of the cloud layer colder than -10C, a few flakes may be produced, though just flurries with no impact to visibility and no accumulation. Ratzer && .LOT WATCHES/WARNINGS/ADVISORIES... IL...None. IN...None. LM...None. && $$ Visit us at Follow us on Facebook, Twitter, and YouTube at: