Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/26/17

Area Forecast Discussion
National Weather Service Hastings NE
539 PM CST Mon Dec 25 2017 .SHORT TERM...(This evening through Tuesday) Issued at 238 PM CST Mon Dec 25 2017 No huge changes are anticipated to this forecast. Overall issue will be snowfall in mainly the first period from a couple of quick- moving upper level jet streaks. Looks like the HRRR has a pretty good grip on the first round of light snow this afternoon associated with the 150 KT jet streak. Still looks like the expected lull will be realized by this early evening, and then another weaker jet streak will pass through to give us light now/flurries overnight into Tuesday morning. Although there should be a short lull at some points, the separation between the two jet streaks will be minimal, so we will likely have snow on our radar through the night. Trends are for slightly higher amounts of snow, especially west. This looks realistic, considering the cold temperatures and deep dendritic growth zone. We should generally see one to two inches on the Nebraska side, with perhaps some three inch amounts, especially toward our western CWA in Dawson County and areas nearby, as a snow to liquid ratio of over 20 to 1 is expected. The Kansas side should have around an inch or less. I went a tad cooler for highs Tuesday with fresh snow on snow and plenty of sky cover for most of the day, expecting highs near 10 for most of the area. .LONG TERM...(Tuesday night through Monday) Issued at 238 PM CST Mon Dec 25 2017 Pattern is stuck with arctic temperatures and northwest flow aloft and occasional low-amplitude waves or jet streaks giving us a small chance of light snow from time to time during the long term, but mostly staying north/northeast of us. Expect highs mostly in the teens and 20s, perhaps some single digits for the weekend with a reinforcing shot of cold air. && .AVIATION...(For the 00Z KGRI/KEAR TAFS through 00Z Tuesday) Issued at 520 PM CST Mon Dec 25 2017 MVFR CIGS and IFR VSBYS will continue off an on again at both GRI and EAR for the next couple of hours...with VSBYS improving mid- evening as there is expected to be a notable break in light snow. Snow is expected to increase again around midnight...and while there may be some IFR conditions returning...opted to only reintroduce prevailing -SN with MVFR CIGS/VSBYS for the time being. Conditions will then slowly improve around daybreak...with some stratus lingering through the day around 5 KFT and continued northeasterly winds around 10 KTS. && .CLIMATE... Issued at 238 PM CST Mon Dec 25 2017 ..Longest sub-freezing stretch in the Tri Cities in nearly 4 years?.. For the majority of our coverage area, we appear to be in the midst of at least a 10-day stretch of sub-freezing temperatures (it began Saturday Dec. 23 and looks to continue through at least Jan. 1). Specifically at our official Tri Cities airport sites (GRI/HSI/EAR), it`s been almost FOUR YEARS since we`ve seen a longer streak than this: 12 days from Jan. 31-Feb. 1, 2014. The only day between now and Jan. 1 that could come somewhat close to "ruining" our ongoing sub-freezing streak is Thursday (Dec. 28), but at least for now high temperatures in the Tri Cities on Thursday are only projected to reach the mid-20s. && .GID WATCHES/WARNINGS/ADVISORIES... NE...None. KS...None. && $$ SHORT TERM...Heinlein LONG TERM...Heinlein AVIATION...Rossi CLIMATE...Pfannkuch
Area Forecast Discussion...Updated
National Weather Service Saint Louis MO
918 PM CST Mon Dec 25 2017 .UPDATE... Issued at 918 PM CST Mon Dec 25 2017 Water vapor imagery is showing a weak upper level disturbance that is moving quickly across the area. There have been a few reports of snow across western Missouri, but low levels are very dry with this airmass. The RAP is showing some additional mid level forcing moving into the area overnight which will to bring some snow to the area. There a more impressive vort max currently over the central High Plains which will move across the CWA on Tuesday morning. The RAP has been consistent since this afternoon at bringing another round of accumulating snow across the central part of the CWA during the morning and early afternoon hours with the potential for up to around 1". Have upped PoPs and increased snowfall amounts based on these trends. Britt && .SHORT TERM... (Through Late Tuesday Afternoon) Issued at 327 PM CST Mon Dec 25 2017 Conditions continue shape up for some light snow tonight and Tuesday. A vortmax is moving east through Colorado this afternoon, and it will move east-southeast into the Mississippi Valley this evening. This wave is forcing weak cyclogenesis over the Great Plains and turning the flow between 925-850mb around to the south- southwest. The resulting warm advection and low level frontogenesis producing clouds and a lot of light radar returns over Nebraska, Kansas and northern Oklahoma. Some of the precip is reaching the ground as well...mainly over southwest Nebraska. This frontogenetical forcing will move east into our area this evening. Meanwhile, the southeast end of the Arctic High over the northern and central Plains will nose into our forecast area. Temperatures will fall into the teens and single digits which should should tighten the boundary layer temp/dewpoint spread enough for precipitation to reach the surface. Most short range guidance shows at least 2 f-gen bands developing this evening and persisting into the predawn hours of Tuesday. The best chance for accumulating snow will probably be along and south of the I-70 corridor...and some of the latest guidance is hinting a little further north into Audrain and Monroe Counties in central Missouri. QPF is very light...only 0.01-0.02, but S/W ratios should be between 18-23:1 so any snow that falls will be very light, fluffy, and pile up pretty quickly. Think this will generate a dusting up to about an inch for areas where the snow bands linger. Another weak wave will ripple across the Mississippi Valley on Tuesday spreading more low level frontogenesis into our area. However, the f-gen and warm advection associated with this wave does not look as strong as with tongight`s system in most of the guidance. The simulated precip in the HRRR/ESRL HRRR/and NSSL WRF models is also not nearly as robust on Tuesday. There is an exception though...the latest runs of the RAP are stronger than the other NCEP models. F-gen on the RAP is pretty impressive across northern into central Missouri on Tuesday morning with a wide swath of accumulating snow moving into west central Missouri by 14-15Z. This may be partially in response to enhanced upper level divergence and ageostrophic circulations induced by a backbuilding upper level jet. The 18Z NAM and the GFS have some flavor of this forcing as well, but they`re not nearly as robust with the QPF. For now, will keep the light QPF and high chance PoPs with another dusting to possibly an inch in the forecast for Tuesday. Will make sure the evening shift is aware of my concerns for a potentially stronger system and the possibility of needing to increase PoPs/QPF. Carney .LONG TERM... (Tuesday Night through Next Monday) Issued at 327 PM CST Mon Dec 25 2017 The MEAN large scale pattern will change little into early next week with a broad deep longwave trof dominating most of the CONUS to the east of the Rockies. This will result in a continuation of below normal temperatures through the end of 2017. There continue to be differences/variability among the models with: 1) the weak fast-moving low amplitude disturbances/short-waves within the fast cyclonic flow 2) stronger digging short waves, and their impact on the overall depth of the large scale trof and associated timing/intensity of reinforcing cold air surges 3) any chances for snow, although any amounts would be light (Tuesday night - Wednesday) A large 1040+ mb surface high will settle east-southeastward from the northern Plains into the upper/mid MS Valley on Tuesday night. This will bring the coldest air we have seen yet this winter to the region. The evening will begin with extensive clouds remaining from just north of I-70 through southern MO/southern IL. Attendant with these lower clouds will be a chance of flurries through the evening, with the threat shunting southward as the lower clouds clear southward on Tuesday night. Meanwhile the progressively colder air will invade from the north/northwest with temperatures falling below zero across portions of northeast MO and west central IL. Wind chills overnight into early Wednesday morning will be in the -10 to - 15F range, and that will be driven largely by the cold ambient air temperature rather than robust winds. Should the temps be a bit colder or winds a bit stronger a wind chill advisory may be necessary. The surface high will remain dominant as it slowly retreats to the east with the axis extending from the Great Lakes through the western OH Valley by early evening. The very cold air mass along with an increase in clouds during the afternoon will suppress highs with readings averaging 20 degrees or so below normal. (Wednesday night - Thursday night) The region will remain under the influence of western fringes of the retreating surface high on Wednesday night with clouds increasing in advance of the next short wave trof moving through the Plains. The models vary with the strength and depth of this short wave and it moves into the upper/mid MS Valley on Thursday. The GFS is the strongest/deepest model with more southward extent of weak forcing, and suggests potential for some light snow generally across northern MO/west central IL down to around I-70. Alternatively both the NAM an ECMWF are weaker and dry. I would say at this time that confidence is rather low and there are better odds the snow will remain to the north of the CWA, however given the variability in models and recent performance we will have to watch closely. (Friday - Monday) Confidence during this time frame in any one model solution is rather low, especially considering the long range model performance over the last 10 days or so. Both the GFS and ECMWF suggest additional surges of colder air, first late Friday-Saturday and then again Sunday into Monday. The timing and intensity of the colder air varies however, but there is at least a trend showing that the air mass Sunday-Monday may be coldest yet. The GFS also suggests a band of snow may accompany one of the surges and attendant short wave Saturday-Saturday night. We will keep watching these systems closely and hoping for less variability/spread and more consistency. Glass && .AVIATION... (For the 00z TAFs through 00z Tuesday Evening) Issued at 548 PM CST Mon Dec 25 2017 A couple of weak upper level disturbances will move across the area over next 24 hours which will produce some occasional light snow at the terminals. Initial VFR ceilings are expected to fall to MVFR overnight as the atmosphere moistens with falling snow. Visibilities will fall to MVFR or possibly IFR depending on how heavy the snow is in the snow bands. Snowfall will be up to inch or possibly greater depending if the heaviest snow lingers over any one of the terminals. Temperatures are expected to fall into the single digits and teens tonight and remain in the teens tomorrow. SPECIFICS FOR KSTL: While a couple of periods of snow with reduced visibilities are expected after 06Z as weak upper level disturbances move across the area. Initial VFR ceilings will fall to MVFR with the first snowfall and then stay MVFR through most of Tuesday. Visibilities will fall to MVFR or possibly IFR depending on how heavy the snow is in the snow bands. Temperatures are expected to fall into the teens tonight and remain in the teens tomorrow. Britt && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && $$ WFO LSX
Area Forecast Discussion
National Weather Service Memphis TN
849 PM CST Mon Dec 25 2017 .UPDATE... Looking at the latest images out of KPAH radar, a band of light snow or flurries may be occurring from near Malden, Missouri southeastward to near Paris, Tennessee. Clouds have kept temperatures in the lower to mid 30s thus far, but some clearing is expected by sunrise. Temperatures will plummet into the mid 20s once this occurs. Updated earlier to add 20 to 30 pops for light snow showers. No further updates are expected. KRM && .DISCUSSION... /issued 338 PM CST Mon Dec 25 2017/ Cold temperatures and uncertainty with regard to a couple of potential rounds of Wintry weather are the highlights of this forecast update. Current temperatures are in the low to middle 30s across the Midsouth. We briefly saw the sun earlier today...but clouds have returned area wide. As a result...most of the area has likely already reached daily highs. The ECMWF as well as the HRRR still show a weak disturbance moving across East Missouri into Middle TN overnight. WPC seems to favor this solution as well. Will maintain slight chance pops in northern portions of TN, and the Missouri bootheel. Moisture is not particularly will just advertise flurries for now. A very broad trough is currently in place across the entire United States, centered over the Mississippi River. North to Northwest flow across West Canada into the Northern Plains can be traced all the way to the North Pole. If Santa would have made a direct flight into the Central US he would have a great tailwind for the entire flight. This pattern will remain largely unchanged for the upcoming work week into next weekend. However, a series of disturbance moving out of the Northern Plains across the middle Mississippi River valley will result in a couple of rounds of potential Wintry weather. A reinforcing Arctic cold front will move across the Midsouth tomorrow ushering in a bitterly cold Arctic Airmass. Dew points will be in the single digits to teens across much of the region in the wake of this front. Meanwhile along the Gulf coast into South Texas the subtropical jet will become invigorated. A band of rain and or snow showers will likely develop somewhere between the Northern Gulf Coast and North Mississippi. While most of the precipitation is expected to our is difficult to ignore guidance and leave out any mention of wintry weather early Thursday over North Mississippi. Temperatures are expected to warm to near 40 Thursday afternoon, so any lingering precipitation should change back to rain. Another cold front is expected Saturday resulting in bitterly cold temperatures Sunday into early next week. Portions of the Midsouth may struggle to warm above freezing Saturday with widespread temperatures in the teens Sunday and Monday mornings. Uncertainty is high but we could see additional Wintry Weather late Saturday into Sunday. 30 && .AVIATION... VFR conditions with periods of mid and high clouds. Can`t rule out a snowflake in KJBR or KMKL this evening. Expect light ENE winds through Tuesday morning gradually increasing to 8-10 kts as another reinforcing cold front drops south into the region. SJM && && .MEG WATCHES/WARNINGS/ADVISORIES... AR...None. MO...None. MS...None. TN...None. && $$
Area Forecast Discussion
National Weather Service Marquette MI
657 PM EST Mon Dec 25 2017 .SHORT TERM...(This evening through Tuesday) Issued at 401 PM EST MON DEC 25 2017 WV imagery and RAP analysis indicated a broad trough from nrn Ontario and Hudson Bay through much of the nrn CONUS resulting in cyclonic wnw mid/upper level flow through the nrn Great Lakes. At the surface, arctic high pressure from wrn Canada into the plains was bringing very cold air (850 mb temps to -35C upstream of Lake Superior) through the region on wnw winds. Multiple wind parallel LES prevailed into the nw cwa. A dominant band still lingered into the ne cwa but had lifted slowly northward this afternoon. Although the LES was not as heavy over the west, low vsbys with small snowflakes and blsn have lingered with at least moderate accumulations. Otherwise, temperatures remaining in the -8F to 7F range with gusty winds to 20-30 mph has dropped wind chills into the -10 to -30 range. Lake Effect Snow: Very high instability with lake induced CAPE values to around 1k J/Kg will support moderate to occasionally heavy LES where a few stronger bands develop. Otherwise, mainly just light LES will continue but with low vsby. High res models suggest that the strongest low level conv and probability for heaviest LES bands will remain into the far ne CWA, especially the ne portion of Luce. A few heavier bands could also develop to just east of Munising. Additional snow amounts of 5 to 10 inches will be possible east and about 3 to 6 inches west. Predominant 300-310 flow over Lake Superior continues with land breeze and lake induced convergent areas info the far ne cwa and near M-38 and nrn Ontonagon county. Heavy accumulations will be most likely over the northeast where the warning for LES continue. Although some bands may affect M-28, most of the heavier snow will remain to the north. Wind Chills: With temps dropping into the -6F to -18F range and winds remaning around 10 mph, expect wind chill values to drop into the -25 to -35 range over most of the cwa tonight into Tuesday morning where advisory have been posted. The lowest values to near -35 are expected from IWD to IMT. .LONG TERM...(Tuesday night through Monday) Issued at 238 PM EST MON DEC 25 2017 Overall, we`re looking at lingering lake effect snow mainly across west wind snow belts early on, and then these snow showers are expected to push offshore as southerly flow develops ahead of an approaching waves from the west through the end of the week. As this wave tracks across the region, it will bring chances for widespread snow followed by another shot of colder, arctic air and the return of lake effect snow into early next week. Temperatures during this time period will remain 10 to 20 degrees below normal for this time of year, if not a bit colder early on this week. A brief "warm up" into the teens is possible on Friday, otherwise afternoon highs in the single digits and overnight lows for the most part are expected to remain around to below zero, expect across the Keweenaw and near the Great Lakes where temperatures will remain modified a bit. Given the magnitude of the cold air, certainly wind chills below zero are expected through much of the time period. Tuesday night through Friday: Wednesday morning definitely looks to be the coldest day in the extended as overnight lows across the interior west and central plunge into the negative digits. The coldest temperatures are expected near the Wisconsin/Michigan border, where overnight lows should easily drop to around -15, possibly as low as -20 in some locations. Elsewhere temperatures are expected to drop below zero, but lake effect snow/clouds should help moderate temperatures a bit across the west wind snow belts. While the winds won`t be terribly breezy, at those temperatures it won`t take much for wind chill values to drop to around or just below -25. Therefore, it may warrant an expansion of headlines for the tail-end of the bitter cold down the road. Similar conditions are possible on Wednesday night, but with thickening clouds overnight this will likely complicate diurnal cooling trends. Lake effect snow will continue to impact the west to northwest wind snow belts through Wednesday before gradually shifting offshore as flow backs to the south in advance of an approaching system from the west. Quite a bit of uncertainty exists in regards to the strength and speed of this wave ejecting out of the northern plains, but the resulting warm air advection should be sufficient for the production of at least light system snow across the area. Depending on the track of the system, some areas may see some lake enhancement off of Lake Michigan and Lake Superior. However, as the track/speed/strength of this system continue to be fine-tuned, as will the details. Friday night through Monday: This main upper-level trough associated with the above mentioned system continues to dig across the eastern Great Lakes, another reinforcing shot of arctic air will allow for moderate to heavy lake effect snow to kick back in and linger into early next week. Right now, models diverge on what snow belt regions will see the most impacts from this round of lake effect snow, as it will depend highly on the track of the exiting 850mb low and subsequent flow on the backside, so confidence in where higher-end travel impacts may felt later this weekend/early next week are uncertain at this time. && .AVIATION...(For the 00Z TAFS through 00Z Tuesday evening) Issued at 657 PM EST MON DEC 25 2017 Bitterly cold air mass over the Upper Great Lakes will continue to generate widespread lake effect shsn off Lake Superior under w to nw winds. Under these winds, KCMX will be significantly impacted. Due to the very cold air, snowflake size will be small and extremely effective at reducing vis, and winds will easily blow around the snow. As a result, expect LIFR conditions to prevail at KCMX thru this fcst period with vis at or blo airfield landing mins. At KIWD, the southern edge of lake effect shsn streaming off Lake Superior will frequently be just n of the terminal. Conditions will likely fluctuate btwn VFR and MVFR thru the fcst period. However, if winds remain backed sufficiently, VFR will prevail, and conversely if winds veer a bit, conditions will fall to IFR or lower. At KSAW, westerly winds will not be favorable for lake effect snow. Expect VFR conditions thru the fcst period. && .MARINE...(For the 4 PM Lake Superior forecast issuance) Issued at 401 PM EST MON DEC 25 2017 Winds of 25-30 kts will persist over Lake Superior into Tuesday as arctic air sweeps across. Best chance for some gale gusts will be over east half through this evening within vicinity of stronger lake effect snow showers. Winds diminish to 25 kts or less for rest of the week. The arrival of the arctic air mass will also result in periods of heavy freezing spray late tonight into mid week. && .MQT WATCHES/WARNINGS/ADVISORIES... Upper Michigan... Winter Weather Advisory until 1 PM EST Tuesday for MIZ002-004- 084. Winter Storm Warning until 7 PM EST Tuesday for MIZ006-007-085. Winter Weather Advisory until 1 PM EST Tuesday for MIZ001-003. Winter Storm Warning until 7 PM EST this evening for MIZ001-003. Wind Chill Advisory until 1 PM EST /noon CST/ Tuesday for MIZ005- 009>011. Wind Chill Advisory until 1 PM EST /noon CST/ Tuesday for MIZ012>014. Lake Superior... Heavy Freezing Spray Warning until 1 AM EST Wednesday for LSZ249>251-266-267. Heavy Freezing Spray Warning until noon EST /11 AM CST/ Tuesday for LSZ241>245-248-263>265. Heavy Freezing Spray Warning until 7 AM EST /6 AM CST/ Tuesday for LSZ162-240-246-247. Lake Michigan... None. && $$ SHORT TERM...JLB LONG TERM...Ritzman AVIATION...Rolfson MARINE...JLB