Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 10/22/20

Area Forecast Discussion
National Weather Service Bismarck ND
1034 PM CDT Wed Oct 21 2020 .UPDATE... Issued at 1033 PM CDT Wed Oct 21 2020 Current radar imagery shows a narrow west-to-east band of reflectivity intensifying across southern Grant, Sioux, southern Emmons, and McIntosh Counties. While there may still be some drier air underneath these echoes, analysis suggests it is not as dry as what was sampled by the 00Z Bismarck sounding farther to the north, and some snow is likely reaching the ground. Therefore, the start time of the Winter Storm Warning was moved up from 1 AM CDT to now. The Winter Weather Advisory for Grant County has also been moved up to start now. All other headlines remain the same. UPDATE Issued at 927 PM CDT Wed Oct 21 2020 The two biggest concerns for this forecast update are a low to mid level layer of dry air entrenched over central North Dakota and an eastward-moving intense band of heavy snow currently over northeast Montana. The 00Z observed sounding from Bismarck shows a layer of very dry air from 850 to 700 mb. This dry layer is being well simulated by the 18Z NAM and GFS, but poorly by the most recent iterations of the RAP and HRRR. While total saturation of the column may not be completely necessary for snow to commence at any given location, the observed sounding suggests it will take longer for snow to reach the surface than what is being depicted by model reflectivity and QPF fields. NAM and GFS 850 mb RH fields were heavily relied on to delay the north and eastward progression of the start time of snow over central North Dakota, which is the most notable change to the forecast for this update. There was also a slight reduction in total snow amounts along the Missouri River Valley from Bismarck to Lake Sakakawea, but only by a few tenths of an inch at most. A strong mid level shortwave is producing an intense band of snow over northeast Montana, with estimated snow rates as high as 2 inches per hour. Deterministic guidance with different model cores and physics packages strongly suggest that this wave will deamplify as it approaches the North Dakota border, with rapidly dissolving frontogenesis expected by 06Z. However, the NAM and to some extent the GFS continue to show strong lift within the dendritic-growth zone over Williams County later tonight accompanied by pockets of negative EPV, suggesting heavier snow may be possible. Feel that the best course of action at this time is to not add Williams County to the advisory and continue to closely monitor observed trends for the next 1-3 hours. Aside from these discussed challenges, the rest of the forecast appears to be trending well. Snow is falling along and southwest of line from Beach to Hettinger, but has not quite reached Dickinson as of this writing. A chance of freezing drizzle mixing in with the snow along the Highway 12 corridor continues for a few more hours. But most, if not all impacts will be caused by snow. UPDATE Issued at 605 PM CDT Wed Oct 21 2020 The biggest change for this update was to introduce chances for freezing drizzle mixing with snow along the Highway 12 corridor through the evening, along with areas of fog. Surface observations at Hettinger and Baker, MT have routinely been reporting visibility at or below 2 miles this afternoon with -SN and BR. Area webcams suggest that the visibility restrictions are more due to the fog/mist/drizzle than the falling snow. The presence of liquid hydrometeors is also supported by the HRRR and RAP, whose soundings at Bowman show a saturated layer from 0.5 to 1.5 km AGL with temperatures greater than -10 C and strong upward vertical motion. The start time for the Winter Weather Advisory in these areas is 6 PM MDT, a little less than hour ahead of this update. Despite the ongoing snowfall and freezing drizzle potential, we are still okay with this start time given ground temperatures are likely still above freezing, and fog being the more dominant visibility restriction. && .SHORT TERM...(This evening through Thursday) Issued at 1243 PM CDT Wed Oct 21 2020 A winter storm will impact the northern Plains tonight through Thursday evening. The southward trend in model runs continues today with the greatest snowfall potential across south central and southeast ND. As confidence grows in amounts and location, we have decided to issue a Winter Weather Advisory for the I-94 corridor and southwest ND and a Winter Storm Warning for locations south of I-94 across south central ND. Ahead of the upcoming system, broad but weak low-level warm air advection is producing some light snow across southwest ND. This area of snow should produce an inch or less. Tonight, a trough is expected to deepen over the Rockies and progress east towards the northern Plains. As this trough enters the northern Plains mid to upper-level ascent will increase. A 700mb frontogenesis band will strengthen with the arrival of the upper-level jet streak. The 12 UTC model suite is consistent in keeping the best frontogenetical forcing near the southern North Dakota border through Thursday morning. This is well supported by ensemble guidance as the 12Z EC/GFS/CMC mean ensemble probabilities keep the highest QPF axis along the southern border. The southern tier of counties (mainly east of the Missouri River) look likely to see the greatest snowfall totals with probability of exceeding 6 inches in the 40 to 70 percent range (highest probs across the southern portions of the counties). Guidance has continued to push the brunt of the forcing (and QPF) over to the South Dakota side. North of I-94 to Highway 2 between one and four inches of snow may fall. North of Highway 2 an inch or less is expected. .LONG TERM...(Thursday night through Wednesday) Issued at 1243 PM CDT Wed Oct 21 2020 Potentially record breaking cold temperatures are forecast this weekend into early next week. Another system may bring accumulating snow this weekend as well. Snow tapers off Thursday evening as high pressure settles in behind the trough. A seasonably cold 850mb air mass is expected to accompany the cold surface high with NAEFS guidance showing both 850mb temperatures and MSLP near climatological minimum and maximum respectively Friday into early next week. Forecast lows drop into the teens and single digits with daily highs consistently below freezing. Some locations across southwest ND may even see below zero temperatures early next week. Another round of snow will be possible Saturday as the next trough crosses the region. The latest global model runs show a very similar setup to tonight/tomorrow`s system coming through Saturday night into Sunday. While differences exist between deterministic models in north-south placement, ensemble probabilities increased with NBM producing higher end PoPs across the south during this period. && .AVIATION...(For the 00Z TAFS through 00Z Thursday evening) Issued at 1033 PM CDT Wed Oct 21 2020 Snow accompanied by MVFR to IFR ceilings and visibility will spread across western and southern North Dakota this evening and tonight, lasting through Thursday afternoon. KMOT is expected to remain outside of the heaviest snow, but could still see MVFR ceilings through the forecast period, and MVFR visibility reductions due to light snow on Thursday. Winds will gradually turn from east to north through the forecast period, increasing to around 15 kts on Thursday. && .BIS WATCHES/WARNINGS/ADVISORIES... Winter Weather Advisory until 7 PM CDT /6 PM MDT/ Thursday for NDZ019-020-034>037. Winter Weather Advisory until 7 PM CDT /6 PM MDT/ Thursday for NDZ017-018-031>033-040>044. Winter Storm Warning until 7 PM CDT /6 PM MDT/ Thursday for NDZ045>048-050-051. && $$ UPDATE...Hollan SHORT TERM...AJ LONG TERM...AJ AVIATION...Hollan
National Weather Service Hastings NE
646 PM CDT Wed Oct 21 2020 ...AVIATION UPDATE... .DISCUSSION...(This evening through Wednesday) Issued at 326 PM CDT Wed Oct 21 2020 The biggest issue within the next 24 hours will be the potential for fog tonight. The combination of a warm front approaching from the south, increasing dew points, and upslope flow indicate that we are primed for this. The HRRR, SREF, and RAP all indicate some level of potential for dense fog across either the entire CWA(HRRR)or at least a narrow band of the CWA near and just north of the warm front. Increasing concern for the need for a dense fog advisory tonight into Thursday morning. Isentropic lift is expected ahead of the approaching upper wave. The signal for drizzle by tonight into Thursday is strong as well. Turbulent mixing increases near the base of our lowering ceilings as low-level saturation increases, making drizzle almost certain for at least a part of our CWA tonight and into Thursday morning. HREF ensembles point toward much of any elevated instability to the south/southeast of the CWA tonight, and I am pulling thunder out of the forecast. HREF ensembles do indicate we may be close at some point Thursday morning, but it is not looking too favorable. The awaited upper level trough will move into the Rockies for Thursday, which will give us southwest flow aloft before the cold front slams through. Models are pointing toward a more saturated low- level on Thursday, reducing our chance of much sunshine, and I would conclude that temperatures on the lower side of guidance will prudent, although there is a chance of a big bust for highs as the potential for a large temperature gradient is high given the timing of the cold front on Thursday. The timing of the cold front on Thursday is indeed a bit of a head scratcher, but the overall anomalously cold set of days coming with the cold air that the front is introducing is certain. Other than the cold air for several days, the biggest feature to focus on is the winter system this weekend. Models are still clearly taking this well north of our area with the best synoptic lift remaining in the northern Plains, but we are not completely out of the woods as far as snow accumulation as mid-level lift is potentially strong Sunday night in the 700-500 mb layer and the GFS paints the possibility of a few inches nearby. Another minor snow is possible in the Monday afternoon-Tuesday time frame depending on what model we look at, but this is far out, and relatively benign- looking for snow amounts at this time. && .AVIATION...(For the 00Z KGRI/KEAR TAFS through 00Z Friday) Issued at 634 PM CDT Wed Oct 21 2020 Main concerns are low vis and low cigs overnight due to fog and low stratus ahead of a warm front that is pushing northward from KS. Visibilities have already begun to drop with increasing drizzle and mist and IFR cigs which are quickly descending to LIFR at around 400ft. A few light showers are expected around day break tomorrow along with the formation of dense fog with visibility expected to drop to around 1/4 mile or possibly less at times. Conditions will begin to improve later in the morning and in the afternoon with cigs lifting to MVFR, but winds at the sfc will pick up behind a passing cold front and could bring gusts to around 35kts. && .GID WATCHES/WARNINGS/ADVISORIES... NE...Freeze Watch from late Thursday night through Friday morning for NEZ048-049-061>064-072>077-082>087. Dense Fog Advisory from 10 PM this evening to 10 AM CDT Thursday for NEZ039>041-046>049-060>064-072>077-082>087. KS...Freeze Watch from late Thursday night through Friday morning for KSZ005>007-017>019. Dense Fog Advisory from 10 PM this evening to 10 AM CDT Thursday for KSZ005>007-017>019. && $$ DISCUSSION...Heinlein AVIATION...Shawkey
Area Forecast Discussion
National Weather Service Goodland KS
553 PM MDT Wed Oct 21 2020 .SHORT TERM...(This evening through Saturday) Issued at 215 PM MDT Wed Oct 21 2020 Low clouds continue to slowly erode west to east this afternoon, however as the sun sets and temperatures start to cool they will begin to retreat westward. In addition, models strongly suggesting fog will accompany the low clouds, and already see some lower visibilities just east of the area. Will follow the HRRR closely and have dense fog advisory starting this evening for areas east of the Colorado border, through Thursday morning. It is possible areas not in the current advisory may be added later, but confidence in western/southern extent of the fog not quite as high. Some drizzle also possible. Low temperatures will be in the upper 30s to middle 40s, so no freezing precipitation expected. Cold front will sweep through the area Thursday morning and scour out the low clouds and fog. Timing has the front through the entire area by 16-18z. Lowered high temperatures a bit more based on that timing. As for wind and dust, confidence has dropped compared to yesterday. Winds will primarily be driven by pressure rises behind the front rather than deep mixing, and with a strong cap around 700mb do not see anything in that surface layer higher than about 30-35kts. Rather than remove mention of blowing dust completely, which is tempting, changed wording to patchy. Winds will diminish by early evening. High temperatures will range from around 50 in northern areas to lower 60s in southern areas. Freeze watch continues for Thursday night/Friday morning with low temperatures ranging from the upper teens in northeast Colorado to the upper 20s in Norton/Graham counties. Will be under zonal flow aloft on Friday with no real weather impacts expected. Skies will be partly sunny at best with cirrus moving off the Rockies. It will be much colder with high temperatures in the upper 30s to lower 40s. Low temperatures Friday night will drop into the lower to middle 20s. Will see temperatures briefly warm on Saturday ahead of the next system. High temperatures will range from the upper 40s in eastern areas to the lower 60s in northeast Colorado with breezy southeast winds and increasing clouds. As shortwave trough approaches from the northern Rockies, there will be a chance for rain and snow after midnight, mainly north of Interstate 70. Little to no accumulation expected through Saturday night. Low temperatures will be in the teens and 20s. .LONG TERM...(Sunday through Wednesday) Issued at 214 PM MDT Wed Oct 21 2020 Southwest flow prevails at the start of the long term period on the east side of an upper trough. The trough deepens as it digs into the Rockies on Sunday, and colder air filters into the High Plains. Currently, the forecast calls for this disturbance to generate chances for light snow through Sunday night and continuing through Monday night as the trough slowly pushes east. Then, dry weather returns Tuesday into Wednesday. Light snow accumulations will be possible. However, there is some disagreement among guidance, particularly with the timing and placement of this system. There are major differences on how the trough evolves/when it closes off to a low over the desert southwest. These factors will need to be resolved in the coming days to get a clearer picture of the forecast. Right now, forecast confidence is low as a result. Much colder temperatures are expected during this timeframe. On Sunday, highs range from the mid 20s in the northwest to mid 30s in the southeast. This is followed by the mid 20s to near 30 degrees from west to east on Monday. A warming trend is anticipated on Tuesday (upper 30s/low 40s) and Wednesday (upper 40s/low 50s). Low temperatures drop into the single digits and teens Sunday and Monday nights, then "warm" up to the upper teens/low 20s Tuesday night. && .AVIATION...(For the 00Z TAFS through 00Z Thursday evening) Issued at 531 PM MDT Wed Oct 21 2020 MCK will transition from MVFR to IFR by 04Z due to decreases in visibility and ceilings with fog with a potential for dense fog and LIFR to VLIFR between 10-15Z. Conditions begin to improve after 15Z as winds turn to the north and become gusty following the passage of a cold front after 15Z with a return to VFR conditions by 22Z. As winds increase through the day, gusts to 35kts after 22Z may produce areas of blowing dust. GLD will will transition quickly from VFR to LIFR with low ceilings and visibility with fog moving into the region after 06Z. Conditions begin to improve as fog diminishes and ceilings raise between 13-16Z as winds turn to the north and become gusty following the passage of a cold front. MVFR conditions are expected after 16Z with a return to VFR by 21Z. Winds will increase through the day with areas of blowing dust possible after 21Z with gusts to 35kts. && .GLD WATCHES/WARNINGS/ADVISORIES... KS...Freeze Watch from late Thursday night through Friday morning for KSZ001>004-013>016-027>029-041-042. Dense Fog Advisory from 9 PM MDT /10 PM CDT/ this evening to 10 AM MDT /11 AM CDT/ Thursday for KSZ001>004-013>016-027>029. CO...NONE. NE...Freeze Watch from late Thursday night through Friday morning for NEZ079>081. Dense Fog Advisory from 9 PM MDT /10 PM CDT/ this evening to 10 AM MDT /11 AM CDT/ Thursday for NEZ079>081. && $$ SHORT TERM...024 LONG TERM...JBH AVIATION...LOCKHART
Area Forecast Discussion...Updated
National Weather Service Saint Louis MO
941 PM CDT Wed Oct 21 2020 .UPDATE... Issued at 936 PM CDT Wed Oct 21 2020 Dense fog has developed across western and central MO and is expected to expand into northeastern MO and west-central IL over the next few hours; therefore, prompting a dense fog advisory. Fog should begin lifting and dissipating from south to north during early Thursday morning with northward advancement of a warm front. Pfahler && .SHORT TERM... (Through Late Thursday Night) Issued at 255 PM CDT Wed Oct 21 2020 Latest surface analysis shows that warm front extended across southern Missouri into far southern Illinois. Low clouds and areas of fog has persisted much of the day across the CWA along with east to northeast winds keeping temperatures down. Scattered showers and isolated thunderstorms have developed north of the front in a band of moisture convergence on the nose of a broad low level jet. This activity will continue to move north across northeast Missouri and west central Illinois as the latest runs of the RAP continue to show this forcing slowing moving north late this afternoon into this evening. Then mainly dry weather is expected late tonight through tomorrow as latest runs of the HREF as well as GFS/NAM show the front moving north of the area. Southwesterly winds will set up warm air advection over the area and GFS soundings are showing mixing up into 800-850mb layer. This supports keeping highs in the low-mid 80s under a mostly sunny sky. A upper trough will move into the Central Plains by Thursday night. This will increase ascent across Missouri and Illinois from west to east during the night. An attendant cold front will enter northwest Missouri on Thursday evening and move halfway through the CWA by early Friday morning. Will continue high chance/likely PoPs for showers/isolated thunderstorms on Thursday night. Britt .LONG TERM... (Friday through Next Wednesday) Issued at 240 PM CDT Wed Oct 21 2020 EPS and GEFS means remain consistent in bringing a low amplitude trough across Missouri and Illinois before it quickly shears out in the confluent flow over the Ohio Valley. The attendant cold front is still on track to move through the region during the day on Friday, so will keep the chance of showers and thunderstorms with its passage. The upper flow will then transitions to the west-southwest through early next week with another weak trough moving across the area on Sunday. This will bring another cold front and another chance of showers and thunder across the region on Sunday. Ascent over the area will increase as another trough drop out of Canada and deepens over the Plains. Will keep a chance of precipitation going Monday into Tuesday. Temperatures will cool down behind the front on Friday and below normal temperatures are expected Saturday as cool easterly flow sets up over the area. There will be some moderation on Sunday with warm air advection ahead of the front, but then there will be a another cool down behind Sunday`s front. Guidance plumes continue to show a a wide range between the 25th and 75th percentile in both the NBM and EPS members given the large contrast in the air mass over the central CONUS over the weekend into early next week, so will not deviate from the NBM guidance. Britt && .AVIATION... (For the 00z TAFs through 00z Thursday Evening) Issued at 722 PM CDT Wed Oct 21 2020 IFR stratus and fog is anticipated at all terminals overnight, with LIFR at KCOU and KUIN. Fog could become dense at both KCOU and KUIN Conditions should improve to MVFR across all terminals as a warm front moves north later tonight/early Thursday morning likely lifting most fog and stratus as winds turn to the south and increase. Marginal low-level wind shear of 35 to 40 kt is expected by early Thursday morning at KCOU and KUIN, but will weaken after sunrise as surface winds increase. VFR cumulus could develop by Thursday afternoon along with gusty southerly winds. Pfahler && .CLIMATE... Issued at 256 PM CDT Sun Oct 18 2020 Thursday October 22, 2020 High Temperature Records St. Louis 86 (1947) Columbia 88 (1899) Quincy 85 (1963) && .LSX WATCHES/WARNINGS/ADVISORIES... MO...Dense Fog Advisory until 7 AM CDT Thursday for Audrain MO-Boone MO-Callaway MO-Knox MO-Lewis MO-Marion MO-Monroe MO- Montgomery MO-Pike MO-Ralls MO-Shelby MO. IL...Dense Fog Advisory until 7 AM CDT Thursday for Adams IL-Brown IL- Pike IL. && $$ WFO LSX
Area Forecast Discussion
National Weather Service Lubbock TX
634 PM CDT Wed Oct 21 2020 .AVIATION... Moist low level southerly flow will continue overnight. Flow also will be stronger including development of a low level jet that will lead to a period of Low Level Wind Shear (LLWS) across the terminals late tonight and early Thursday. Solutions indicate the best likelihood for a low stratus layer late tonight will be to our south, over the lower Pecos Valley extending into the Big Country. Uncertainty how far west this layer may reach, with latest HRRR suggesting a low cloud MVFR layer may reach as near as about 30 miles south of KLBB by 13Z Thursday. We have added a FEW020 to the KLBB forecast between 13Z and 16Z Thursday until this can be shaken out further. VFR otherwise should dominate along with gusty south to southwest breezes Thursday. RMcQueen && .PREV DISCUSSION... /issued 225 PM CDT Wed Oct 21 2020/ SHORT TERM... Tonight weak southwesterly flow aloft will continue with southerly flow at the surface. This pattern will keep overnight temperatures on the warmer side and a steady stream of low level moisture coming into the region. Near day break a lee-side surface low will stall over SE CO shifting the surface flow to the southwest promoting one last day of dry, breezy and warm conditions. High temperatures will push into the upper 80s area wide. These conditions will also lead to the potential for elevated fire weather concerns near the Texas/New Mexico state line. LONG TERM... Early part of the long term period will see a cold front move quickly through the forecast area early Friday with high temperatures a good 30 degrees cooler than on Thursday. Temperatures will quickly rebound mostly into the 70s on Saturday as zonal aloft induces a lee surface trough and a quick return to south to southwest winds across the forecast area. Buckling of the upper flow over the CONUS late weekend into early work week with a trough being carved out over the intermountain West just downstream from a ridge over the eastern Pacific will allow cold air to spill southward into the forecast area during the Sunday with strong cold advection Sunday night. Models are struggling today with the handling of the main piece of short wave energy that will carve out this longer wave trough with both closing off into a low but with the GFS much more progressive than the ECMWF. As a result potential exits for a range of possibilities from a brief window of post-frontal precipitation as the low moves across the region with a quick transition from rain to snow to a longer window of precipitation (Sunday night into Tuesday night) as a slow-moving closed low over the desert southwest then opens up and ejects to the north of the region with the potential for more rain and freezing rain and less snow. Very few model or ensemble solutions are showing anything more than light precipitation amounts at this time. Given this range of solutions confidence is high in cold temperatures Sunday night through Tuesday night but low relative to precipitation chances, and more importantly, precipitation type. Have inserted more freezing rain into the forecast, but generally in tandem with a snow and/or rain mention, mostly as a result of the uncertainties at this time. FIRE WEATHER... Thursday the combination of ERCs in the 50th to 74th percentile, above normal temperatures, and 20 ft winds southwest at around 10-15 mph will create elevated fire weather conditions across the NM/TX state line and the southwestern Texas Panhandle. Conditions will remain below Red Flag warning criteria, but a Rangeland Fire Danger statement may be needed as conditions materialize. && .LUB WATCHES/WARNINGS/ADVISORIES... None. && $$ 99/99/05
Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
912 PM CDT Wed Oct 21 2020 .UPDATE... Issued at 911 PM CDT Wed Oct 21 2020 Trends from the HRRR/RAP are shedding some uncertainty into the going winter storm forecast. Both of these models have nudged the central MN snow band north a tad, keeping the heaviest snow north of AXN. They have also bumped QPF totals down a bit, with WAA precip farther southeast likely impacting quality of moisture available up there. However, haven`t changed the snow forecast much, as when looking at the GEFS plumes from 18z, it absolutely slams AXN over toward Mille Lacs, with snow totals off a 10:1 snow ratio ranging from 5-12 inches (RAP/HRRR fall below that range). Other bit of uncertainty the HRRR/RAP brings in is with where the zone of mixed precip ends up residing. Both have this zone ending up pretty close to Mankato up through the Twin Cities, east of our current advisory. That`s the bad news, the good news is the predominate p-type they produce with this mix is sleet, not freezing rain. Was on the fence about sweeping Watonwan, Blue Earth, Brown, and Nicollet counties into the advisory, where more freezing rain is depicted by the HRRR, but decided to wait and see if we actually see surface temps drop below freezing before the precip arrives. && .SHORT TERM...(This evening through Thursday night) Issued at 326 PM CDT Wed Oct 21 2020 There are two key messages for the weather forecast over the next several days. 1) Late tonight into Thursday a large storm system will bring a band of moderate to heavy snow across central/northern Minnesota. There will also be an area of a wintry mix south of the heavy snow band. Right now the most likely area to see a wintry mix is central Minnesota into northern Wisconsin. Meanwhile mainly rain is expected across southern Minnesota into west central Wisconsin. 2) On Saturday night through Sunday, one more system will bring wintry weather across the region. As of now, the heaviest precipitation should fall along and south of I-90. Before digging into the details of the upcoming storms, we need to address the current weather. An area of light snow and drizzle was ongoing across the southern part of the forecast area. SPC Mesoanalysis showed a weak area of 700mb FGEN, and this was enough to produce clouds and light precipitation. This light precipitation should weaken as the FGEN signal wanes overnight and becomes more focused to the northwest in the eastern Dakotas. As a result, expect precipitation to develop across the eastern Dakotas into west central Minnesota. This precipitation will be mainly snow, and should see a few locations pick up over 8 inches near the SD/MN/ND border, with lesser amounts extending east/northeast. This puts a few counties across the northwest forecast area above 6 inches of snow, so have transitioned them into a Winter Storm Warning. Meanwhile, another area of precipitation will lift up from the south early on Thursday. Initially this should be all rain as it crosses I- 90, but as it lifts northward, it will interact with a cooler thermal profile and there should be an area of a wintry mix between the heavy snow to the northwest, and the rain to the south. Freezing rain is possible during the onset of precipitation, but it should transition to rain as surface temperatures warm throughout the day on Thursday. Areas in western Minnesota should make the transition slower, so have a Winter Weather Advisory for those locations. .LONG TERM...(Friday through Wednesday) Issued at 326 PM CDT Wed Oct 21 2020 As mentioned above, cold air will linger across the region and another system will act on this temperature gradient and produce an area of precipitation across the Upper Midwest late Saturday into Sunday. There is still uncertainty with this system, but as of now it appears that thermal profiles should be cold enough for mostly snow, and the highest amounts should be along the I-90 corridor and south. The low level thermal gradient is a nice set up, but the positive tilt of the upper level wave doesn`t really let this system get its act together. We`ll see how it evolves over the next few days. It certainly looks like most locations will pick up some snow over the weekend. This will be followed by seasonably cold temperatures, with lows in the teens for Sunday night, and the single digits for Monday night. && .AVIATION...(For the 00Z TAFS through 00Z Thursday evening) Issued at 658 PM CDT Wed Oct 21 2020 No significant changes to going TAFs, with these 00z TAFs slightly favoring a slower timing from the RAP for precip onset. Main areas of uncertainty are with p-type at RWF/STC, where they`ll be on the threshold for seeing all modes of wintry precip, including fzra. Latest runs of the RAP/HRRR are creating some uncertainty for AXN as well, as both models have nudged the central MN band of snow a bit north, with this nudge being enough to push the heaviest snow north of AXN. This potential not really portrayed in the 00z TAF though. For MKT/MSP/RNH/EAU, it looks like precip initially comes in as a -RAPL mix, before quickly transitioning to all rain. However, surface temperatures are expected to remain in the 34 to 37 range, so temperatures staying any cooler than currently forecast would result in much more wintry precip (most likely fzra/pl) than currently indicated. Only field that has much of a TS threat looks to be EAU in the afternoon. KMSP...Did remove TS mention and also shortened the wintry mix window, though temperatures won`t need to come in much cooler than currently forecast to push much more of the precip into the frza/pl category. /OUTLOOK FOR KMSP/ FRI...VFR. Chc MVFR cigs. Wind NW 10-20kts. SAT...VFR. Wind N 5 kts. SUN...IFR or lower and SN likely. Wind NNE 5-10 kts. && .MPX WATCHES/WARNINGS/ADVISORIES... MN...Winter Weather Advisory from 4 AM to 10 PM CDT Thursday for Benton-Chippewa-Kanabec-Kandiyohi-Lac Qui Parle-Meeker- Mille Lacs-Pope-Redwood-Renville-Stearns-Swift-Yellow Medicine. Winter Storm Warning from 4 AM to 10 PM CDT Thursday for Douglas- Morrison-Stevens-Todd. WI...None. && $$ UPDATE...MPG SHORT TERM...JRB LONG TERM...JRB AVIATION...MPG
Area Forecast Discussion
National Weather Service Marquette MI
705 PM EDT Wed Oct 21 2020 .SHORT TERM...(This evening through Thursday) Issued at 506 PM EDT WED OCT 21 2020 Water vapor imagery and RAP analysis show a mid-level trof dominating Canada from coast to coast with the trof anchored by a mid-level low centered just n of Hudson Bay. The southern extent of this trof leaves broad troffing across the northern tier of the Lower 48. Within this broad cyclonic flow, shortwave that generated the rain/snow across the fcst area last night is currently in the vcnty of James Bay. Upstream, the next shortwave of interest is dropping along the BC coast into the Pacific NW. This wave will impact the weather here Thu into Thu night. Closer to home, in the wake last night`s wave, clouds have been slow to clear out today. Some spotty light pcpn has been noted on the Keweenaw under a brisk westerly low-level flow and under 850mb temps that have fallen to around -6C. These w winds have been gusting to around 30mph at KCMX. Sfc high pres ridge currently extending from the Dakotas to the Lower Ohio Valley will shift ne tonight, reaching Upper MI late tonight/Thu morning. So, it will be a quiet night. Under chilly westerly flow in advance of the high, 850mb temps around -6C, at least this evening, will be marginally cold enough to support some light lake effect pcpn across the Keweenaw. Moisture does not extend to the -10C isotherm, so ptype would likely be sprinkles or -shra if anything does occur. Mid/high clouds area already spreading into the area, so even where lower clouds have cleared out or will clear out during the evening, not expecting any notable period of radiational cooling tonight. Mins should range from the mid 20s to the mid 30s. On Thu, attn turns to the aforementioned shortwave currently over the Pacific NW. This wave will move se into the northern Rockies tonight and then shift out across the northern Plains on Thu. Fcst is full of challenges, making for low confidence in what the outcome will be on Thu. Backing winds ahead of the wave will spread a decent push of isentropic ascent into the area on Thu. Mixing ratios in the 700-750mb layer of at least 4g/kg will support the potential of 4in/6hr snowfall rates where pcpn is all snow. There are indications, especially in the GFS, of -EPV situated above the sloping FGEN, which supports the potential of banded heavier pcpn as well. As for ptype, models over the last day or so have been trending s and colder, bringing a more wintry scenario into the picture. While the GFS offers a more solid snow event over the nw third, a significant one at that as it is high qpf outlier, the NAM is more aggressive in surging a well elevated warm nose above 0C n into the area, roughly in the 7-9kft layer. Deep subfreezing layer blo would indicate sleet depending on whether the snowflakes completely melt or not in the warm layer. Better chc of that occurring would be later in the aftn from Iron/Dickison counties northeastward. Given much uncertainty in the thermal profiles and the pcpn amounts due to model spread, fcst leans away from the extremes. Best chc of reaching advy level snow during the day on Thu (2-4in for low SLR snow) should be across Gogebic/Ontonagon counties e to western Marquette County and Iron County. If the GFS verifies, those amounts will be way underdone with the Keweenaw getting in on hvy snow as well. Ptype should be predominantly rain from roughly Marquette-Iron Mtn e. Some instability well aloft may lead to a few rumbles of thunder s central and e later in the day. .LONG TERM...(Thursday night through Wednesday) Issued at 446 PM EDT WED OCT 21 2020 Thursday evening the complex and messy winter storm will be continuing over the entire U.P. With models continuing to trend colder last night and today, and come more in line with the GFS (which has had the colder and snowier solution all along). Regardless of choice of model, still looks like a period of impressive forcing in the 00z-06z time window. NAM shows strong fgen throughout the column, maximized in the 800-700 mb layer, as well as -EPV in the 700-600 mb layer. NAM cross sections further illustrate CSI in the mid levels with geostrophic momentum surfaces crossing theta-e* surfaces, and even a few spots of elevated CAPE (where the vertical derivative of theta-e* goes negative). All of this points to a band of heavy precip setting up over the area, or rather, probably two bands: one over the western half of the U.P. and one over the south-central and east. Went bullish with QPF during this period given the impressive forcing. Still uncertain what the exact ptype will be, and given such heavy rates in a relatively short window, the ptype is crucial. Therefore, have to stress that certainty is low, even less than 36 hours out. Think the most likely outcome is predominantly snow north of a line from the Hurons to about Watersmeet, and then a 50/50 mix of sleet and snow south of that line and north of a line from about Munising to southern Dickinson County. have hoisted a Winter Weather Advisory for the west and central, in two segments: one for mainly snow and one for a mix of snow and sleet. Late Thursday night (after 06z) as the synoptic theta-e advection forcing for ascent pulls out and CAA wraps in, there will be a transition to lake-enhanced upslope precip. Model soundings show a lack of cloud ice as the cyclone develops further and the mid-level dryslot develops overhead. This means there will probably be a mix of snow and drizzle in the upslope/north wind lake-effect regions. Surface temps during this period should stay above freezing for the most part, so not expecting much if any FZDZ though can`t completely rule some out over the highest elevations of the interior west. This could continue through late morning Friday until temps aloft cool enough to reintroduce cloud ice, at which point precip will transition to pure lake-effect rain/snow showers with additional snow amounts around an inch possible in the N to NW wind LES belts of the west half (it`ll be too warm for much if any snow in the eastern half LES belts). Friday night and Saturday look quiet expect for some lingering light lake-effect snow showers Friday night in the NW wind LES belts as high pressure builds in to the southwest. The next chance for more widespread precip comes Sunday into Monday as a frontal wave passes by to our south across Lower Michigan. The EC continues to be more robust with its QPF, but even that`s only around 0.1-0.2". Other models are drier. Thus, while rain and snow showers are likely across the area, significant accumulations are not expected. One possible exception to that would be Sunday night into Monday morning. During this time period, the GFS and EC both indicated an inverted trough extending northward from the frontal wave into Lake Superior. This trough could serve as the focus for enhanced convergence and generate a more significant LES band given sufficient lake-based instability (850 mb temps around -7 to -10 C) and deep moisture/high inversion heights. Definitely something to watch there. By the middle of next week the models and their ensembles are split on whether a warm front brings a brief respite to our period of below normal temps, or a reinforcing shot of cold air prolongs below normal temps and lake-effect chances. Stay tuned. && .AVIATION...(For the 00Z TAFS through 00Z Thursday evening) Issued at 704 PM EDT WED OCT 21 2020 As somewhat drier air moves into the area, expect MVFR conditions at KIWD to improve to VFR over the next few hrs. KCMX and KSAW will stay VFR overnight. As the next low pressure begins to take shape over the central Plains, winds swing around to the ne and pcpn spreads ne toward Upper MI, expect cigs to fall back to MVFR at KIWD/KSAW at all sites Thu morning. Near the end of the fcst period, -snra should developwith cigs dropping to IFR. && .MARINE...(For the 4 PM Lake Superior forecast issuance) Issued at 522 PM EDT WED OCT 21 2020 Relatively tight pres gradient btwn low pres trof to the ne of Lake Superior and high pres ridge from the Dakotas to the Lower Ohio Valley is currently supporting a few westerly gale gusts over central and eastern Lake Superior. As the high pres ridge lifts ne tonight, reaching Lake Superior late tonight/Thu morning, winds will diminish to under 20kt. On Thu, as the ridge continues shifting ne and low pres develops across the central Plains, ne winds will increase. Could be a few gale force gusts down toward the Apostles and Duluth late in the aftn. NE winds to 30kt and possibly some gale gusts to 35kt will then be the rule across most of Lake Superior Thu night. As the low lifts across Lower MI Thu night and toward Quebec on Fri, winds will back n to nw. While there may be some gale force gusts over the e half of the lake on Fri, winds will diminish to under 20kt over the w by late aftn. With high pres ridge building across the Upper Lakes on Sat, expect winds under 20kt. These lighter winds will linger thru Sun. && .MQT WATCHES/WARNINGS/ADVISORIES... Upper Michigan... Winter Weather Advisory from 2 PM EDT /1 PM CDT/ Thursday to 8 AM EDT /7 AM CDT/ Friday for MIZ005-006-010-011. Winter Weather Advisory from noon EDT /11 AM CDT/ Thursday to 8 AM EDT /7 AM CDT/ Friday for MIZ002>004-009-084. Lake Superior... Gale Warning until 8 PM EDT this evening for LSZ242>244. Lake Michigan... None. && $$ SHORT TERM...Rolfson LONG TERM...RJC AVIATION...07 MARINE...Rolfson
Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
815 PM MDT Wed Oct 21 2020 .UPDATE... Issued at 809 PM MDT Wed Oct 21 2020 FGEN zone continues to develop this evening with snow/sleet expanding across NW SD. ZL/FG has diminished some, where more persistent light snow has developed. However, as the main area of forcing shifts NE expect ZL/FG to redevelop later tonight, esp along the eastern/northern Black Hills foothills and adjacent plains. Given adjusted snow amounts and light icing potential, have expanded the adv a row of zones south in SD. && .DISCUSSION...(This Evening Through Wednesday) Issued at 236 PM MDT Wed Oct 21 2020 A broad upper-level trough covers the northern CONUS. At the surface, high pressure sits over eastern SD, and with low pressure over southeastern WY, winds across our CWA are southeasterly. Moisture advecting in along the area of 650-750 mb frontogenesis that stretches across SD continues to produce a band of snow over northern/central SD, gradually shifting northward. Temperatures this afternoon range from the 30s across the north to the 40s in the south. For northern SD, not much of a break in precipitation is expected between systems tonight. As this first band of frontogenesis dissipates, a stronger system will approach from the northwest. Upper low currently over Alberta/Saskatchewan will dig a shortwave trough with strong positive vorticity advection through the northern Rockies tonight into Thursday morning. The 700 mb low is progged to slide from eastern MT into northern SD during this time, with cold air filtering in behind. As isentropic lift develops along the baroclinic zone/band of 700-650 mb frontogenesis, precipitation will develop across mainly the northern CWA, especially along the ND/SD border. Wet-bulb zero heights indicate mainly snow as the precipitation type, although the southern edge of precip may be a mix, including freezing rain, especially across south central SD. The greatest lift within the dendritic growth zone will be across northern, especially northeastern, SD. Northerly winds behind the cold front will be breezy, strongest across northeastern WY where pressure rises will be 3-4 mb/3 hrs. This may contribute to some upslope-enhanced snow over the northern Black Hills Thursday, with snow lingering there after snow on the plains begins to diminish with synoptic forcing. NAM and HRRR Froude Numbers reach 1-2 in the afternoon. Breezy winds may also produce a little blowing snow. Snow will gradually end late Thursday. Beneath cloudy skies and a colder airmass, highs will be in and around the 30s. Snow amounts are expected to remain within advisory criteria across the CWA, although the northern Black Hills may approach 6 inches in the higher elevations. A convergence zone near the southern Hills could result in a local minor maximum there of a couple inches; generally, however, places south of I-90 will receive less than an inch. Some light icing could be possible south of I-90 with freezing rain. A brief reprieve is expected Friday, before another Canadian low pressure system pushes into the region. Weather will be dry, but temperatures will remain chilly, with highs in the mid 20s to mid 30s. Friday night, the Canadian low will dive into western MT. Southeasterly surface winds will become breezy ahead of the incoming low early Saturday morning. As the 700 mb low shifts into western SD early Saturday morning, models show precipitation beginning across northwestern/central SD by 12Z, along the area of Q-vector convergence and isentropic lift. Positive vorticity advection and enhanced upper divergence will contribute to enhanced snow development across the region, gradually shifting southeastward with the low. Snow will end Sunday. Models have continued to keep the higher amounts across the north. Current forecast places at least advisory criteria snow across the area, with more than 6 inches possible across the northern tier...again, generally north of I-90. Very cold air will sink into the region behind this system. NAEFS shows 850 mb temps 2-3 standard deviations below normal Sunday into Monday. Highs both days will be in the 20s, with lows both nights in the single digits. However, breezy winds will make daytime temperatures feel like they`re in the single digits above and below zero. Beyond this, the GFS/ECMWF are hinting at a period of warmer, drier weather. && .AVIATION...(For the 00Z TAFS Through 00Z Thursday Evening) Issued At 540 PM MDT Wed Oct 21 2020 Widespread MVFR/IFR (local LIFR INVOF the Black Hills) conds will continue into Thurs morning along with periods of drizzle/freezing drizzle. Snow will develop over the NW and slowly shift south tonight as a cold front moves southeast through the area. Conds should improve some Thurs afternoon, esp in the lee of the Black Hills where NW downslope winds will develop. Gusty NW winds can be expected behind the cold front, esp in NE WY Thur morning. && .UNR WATCHES/WARNINGS/ADVISORIES... SD...Winter Weather Advisory until 6 PM MDT Thursday for SDZ001-002- 012>014-024-025-032-072-073. WY...Winter Weather Advisory until 6 PM MDT Thursday for WYZ054-056- 057-071. && $$ Update...JC DISCUSSION...Pojorlie AVIATION...JC