Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/13/16

Area Forecast Discussion
National Weather Service Columbia SC
935 PM EST Mon Dec 12 2016 .SYNOPSIS... A cold front will become nearly stationary across Georgia and coastal South Carolina tonight. The front will move back north as a warm front Tuesday. Rain chances will increase Tuesday into Wednesday as weak low pressure moves through the area along the front. A cooler and drier air mass will return late in the week. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/... A weak cold front has pushed through the area this evening. However, ample low-level moisture has caused areas of dense fog to develop across portions of the eastern Midlands with visibilities less than a quarter mile at times. Therefore, a Dense Fog Advisory has been issued through Tuesday morning. Additionally, isentropic lift and a surface wave developing along the front will cause showers to move into the area overnight, with moderate rain possible by morning. The latest HRRR guidance starts bringing rain into the Augusta area just after midnight. Rain will then spread northeastward through Tuesday morning. Overnight lows tonight will range from the lower 40s north to the lower 50s south. && .SHORT TERM /6 AM TUESDAY MORNING THROUGH WEDNESDAY/... The chances for rain lingers Tuesday into Wednesday. Isentropic lift continues over the area Tuesday as a frontal boundary to our south lifts northward. A wave of low pressure is forecast to develop along the front over the deep south and move northeast. Lift will also be aided by weak short wave troughs in fast flow aloft. Highest pops and qpf will be across the southern Midlands and CSRA near strongest frontal convergence. Have indicated pops ranging from likely across the north Midlands to categorical across the south for Tuesday. The chance for rain will diminish Wednesday as the front moves off the coast and winds become downslope. A dry and cold area of high pressure is forecast to spread into the southeastern states from the Midwest Wednesday night into Friday. && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... Cold high pressure ridging into area from the north Friday night into Saturday. Both the GFS and ECMWF show weak isentropic lift. Should see increasing clouds Friday night into Saturday given lift and a cold front approaching from the west. Temperatures Friday night are forecast to cool into the upper 20s north to mid 30s south. Though the GFS indicated light wintry precip moving into the Piedmont, the ECMWF and Canadian models hold precip west of our forecast area in the Upstate. Will keep the Midlands and CSRA dry...although cannot completely rule out spotty freezing drizzle. Temperatures will warm 50s and 60s Saturday as the flow turns southerly ahead of an approaching cold front. The cold front will cross the area Sunday night into Monday...bringing another chance for showers. Unseasonably warm temperatures ahead of the front on Sunday will moderate to seasonal normal for Monday. && .AVIATION /03Z TUESDAY THROUGH SATURDAY/... Expect a return to IFR conditions tonight. A cold front will stall just south of the terminals tonight. Moisture convergence along the front and nocturnal cooling will help support lowering ceilings and visibilities tonight. The NAM and GFS MOS indicated IFR conditions developing with the GFS faster with the timing. Many SREF members indicated the GFS may to too fast. We followed an average of the guidance. The models depicted isentropic lift developing and expect rain will overspread the area. The ARW and HRRR displayed rain spreading into the area from southwest to northeast around 12z. The IFR conditions should continue through the rest of the TAF period. EXTENDED AVIATION OUTLOOK...Widespread IFR conditions will likely occur through Wednesday associated with a stalled frontal boundary in the region. && .CAE WATCHES/WARNINGS/ADVISORIES... GA...None. SC...Dense Fog Advisory until 10 AM EST Tuesday for SCZ015-016-022- 029-031-036>038. && $$
Area Forecast Discussion
National Weather Service Fort Worth TX
613 PM CST Mon Dec 12 2016 .AVIATION... A very challenging weather scenario continues across North Central Texas early this evening, with a large area of stratus at flight levels 015-020 basically bisecting the DFW Metroplex. This region of cloudiness has edged slightly westward through the late afternoon hours, with ceilings now present from near a DAL-ADS- LNC line eastward. With a low level easterly wind component expected to continue for a few hours, these ceilings should begin to impact DAL, DFW and GKY through 02z, and persist until 06z. At this point, we believe FTW and AFW will stay VFR, though some scattered stratus may reach these airports as well. It gets even trickier by 06z and afterwards, as the latest RAP guidance suggests that winds in the lowest 2-3kft will veer to a southwesterly direction and pick up a bit. If this indeed happens, any additional westward movement of the stratus will be retarded, and ceilings at DFW, GKY and DAL should go scattered. Am going with this scenario, given its persistence from earlier runs in the day. While winds a couple of thousand feet above the surface will pick up overnight, they will be decoupled from very light and variable conditions near the surface. Dewpoints over the eastern half of the Metroplex - and on east into NE Texas - are from 5 to 10 degrees higher than those in the west, and humidities should approach saturation as skies clear out and temps drop later tonight. Believe we`ll see at least patchy fog after 06z, and have kept some MVFR reductions in visibility at all TAF sites. Would not be surprised to see IFR conditions, however, if clearing occurs earlier and surface moisture is able to work farther westward across the Metroplex overnight. The forecast for Waco is not drastically different from that of FTW/GKY. Low clouds should remain east of the airport, but increasing moisture from the east overnight should yield MVFR fog conditions after 06z. A pronounced frontal passage should occur across the DFW Tracon area in the 14-16z timeframe Tuesday, with winds veering to a northerly direction at speeds of 08-14kts. Right now, we`re not showing any post-frontal ceilings with this front, but wouldn`t be surprised to see a brief period of scattered-broken conditions for at least a couple of hours between 14z-17z. Just not confident enough at this point to include a ceiling reduction based on the guidance I`m seeing so far. Bradshaw && .PREV DISCUSSION... /ISSUED 400 PM CST Mon Dec 12 2016/ After a very warm day yesterday temperatures have returned to more seasonal levels under mostly sunny skies and light winds. The only exception is the far eastern counties where skies have been cloudy most of the day thanks to persistent moisture in the 1000-800mb layer. Light east winds above the surface in the Arklatex region will help push some of this lower cloud cover back to the east through this evening before more robust southwest winds aloft take over. Tonight`s temperature forecast is a little tricky with the cloud cover and increasing potential for fog later tonight. As the boundary layer cools this evening...light surface winds and drier air aloft may promote widespread fog development. It`s a little unclear how dense the fog could be given that stronger winds above the moist surface layer may tend to disrupt for now will just mention patchy fog. Temperatures should fall into the upper 30s across our northwest with 40s elsewhere. On Tuesday...the large upper low over central Canada will continue to slowly drift southeast. This should allow another weak cold front to slide through the southern Plains tomorrow. This front won`t be considerably colder although north winds 10-15 mph may make it feel cooler by tomorrow afternoon. A reinforcing shot of cooler air arrives on Wednesday with highs falling back into the upper 40s near the Red River to mid 50s south of I-20. On Wednesday night...persistent northeast surface winds around a 1036mb high in the Plains will allow some colder air to filter down into west-central Texas. This means that our northwest counties may fall to below freezing by Thursday morning. In addition...flow above the surface will begin to strengthen pulling moisture northward over the cooler air. At this time...the moisture return does not appear at robust as it did yesterday and think that more in the way of low clouds appears possible for Thursday morning. Nonetheless...will keep a 20 PoP for drizzle or light rain Thursday morning into the midday hours for areas mainly west of I-35. At this time it appears that surface temperatures will warm above freezing before any precipitation actually occurs so no significant impacts are expected. The southerly winds noted aloft on Thursday will strengthen significantly on Friday ahead of a strong shortwave that moves into the western U.S. Friday is expected to be breezy and warm across all of North Texas with highs in the low to mid 70s west of I-35. Areas east of I-35 may stay in the 60s with more cloud cover and low rain chances by afternoon. The rapid warmup on Friday is in response to strong surface cyclogenesis across the Plains ahead of the main upper trough. This surface low will race off to the northeast on Saturday and allow an arctic cold front to blast through North Texas. The exact timing of the front is still a little uncertain but it appears that it will move through during the afternoon hours. This means that many areas may warm up considerably ahead of the front...possibly into the mid 70s before temperatures tumble into the 30s after dark. Gusty north winds will make it feel much colder. The best upper forcing will initially be well removed from North Texas so rain/storm chances will be low through the day. Showers and thunderstorms along the cold front to the northeast of the region may tend to unzip along the front itself into our area late in the day. Will have some 20 PoPs across the eastern counties to account for this. By Saturday night as cold air settles into the region the base of the 500mb trough will approach the region spreading the strongest forcing for ascent across North Texas after midnight. This also occurs as a band of mid level frontogenesis develops across our northwest counties into southeast Oklahoma. While this pattern isn`t overly favorable for wintry precipitation as moisture is generally in the process of getting scoured out...the forcing will be quite strong so any available moisture could quickly get turned into precipitation. Thermal profiles will, however, be favorable for wintry precipitation...either in the form of sleet or snow. At this time...given the uncertainty in moisture availability and general timing of the front...will leave any mention of precipitation out of the current forecast behind the cold front...although it does bear watching over the next several days. Sunday and Sunday night should be quite cold with highs in the 30s and 40s and lows in the upper teens and 20s. Dunn && .PRELIMINARY POINT TEMPS/POPS... Dallas-Ft. Worth 44 59 40 54 38 / 0 0 0 0 5 Waco 42 64 42 58 39 / 0 0 0 5 5 Paris 44 56 40 50 33 / 5 0 0 0 5 Denton 40 56 34 51 32 / 0 0 0 0 5 McKinney 42 56 39 50 35 / 0 0 0 0 5 Dallas 45 60 43 54 38 / 0 0 0 0 5 Terrell 45 58 43 53 37 / 0 0 0 0 5 Corsicana 47 64 46 58 41 / 5 0 0 0 5 Temple 46 66 43 59 39 / 0 0 0 5 10 Mineral Wells 40 57 34 53 35 / 0 0 0 0 5 && .FWD WATCHES/WARNINGS/ADVISORIES... None. && $$
Area Forecast Discussion
National Weather Service Hastings NE
543 PM CST Mon Dec 12 2016 .UPDATE... Issued at 512 PM CST Mon Dec 12 2016 Updated the forecast this evening to more sharply lower temperatures behind the arctic front moving through the CWA. Latest observations are in the single digits as close as Ainsworth already. I also sharply increased wind gusts directly behind the front, and then substantially back off of gusts roughly 50 to 100 miles behind the front, as is occurring currently, as gusts to 31 kts are recorded in Broken Bow, but Ainsworth is already down to 16 kts. The HRRR seems to be doing a decent job with short-term temperature trends and winds, so I relied more heavily on the HRRR than other solutions. && .SHORT TERM...(This evening through Tuesday) Issued at 230 PM CST Mon Dec 12 2016 A strong cold front is expected to track rapidly south across the local area this afternoon through tonight...resulting in a significant drop in temperatures and shifting winds. These breezy northerly winds combined with a drop in temperatures of 40+ degrees from this afternoons highs, will make for unpleasant conditions for those out and about late tonight. Otherwise...moisture associated with this front is very limited...and other than saturation in the mid levels...the remainder of the atmosphere is likely to remain unsaturated overnight. As a will be very difficult to squeeze out any measurable precipitation with this front...but could potentially see a few flurries as a strong jet streak rides across the center of the local area overnight providing a bit of forcing. While the odds of flurries is still is not maintained a slight chance for the most favored areas overnight. For Tuesday...expect surface high pressure to settle in across the local area behind this evenings front. While the lighter winds will be welcome...the airmass will be significantly cooler...and expect highs in the mid 20s at best across the majority of the local area. Evidence of this colder airmass can be seen in observations just to our Ord is currently sitting at 50 degrees (as of 230 PM) just ahead of the front...with Valentine at 13 degrees on the backside of this front. .LONG TERM...(Tuesday night through Monday) Issued at 230 PM CST Mon Dec 12 2016 The story of the extended periods continues to be the cold temperatures forecast to persist through the majority of the week and into next weekend...with some small chances for snow across the local area still possible at times beginning across our north on Thursday...and continuing off and on across portions of the local area through Saturday afternoon. In the upper levels of the atmosphere...expect progressive west northwestelry flow to continue across the center of the country through at least Thursday...when a strong area of low pressure moves onshore across the west coast. As this low digs south across California and eventually into the desert southwest on Friday...expect weak ridging to be realized locally, resulting in the warmest day of the extended periods on Friday...albeit very near normal for mid-December. This warm-up will be a short term tease, however, as the next cold front blasts across the region late Friday...bringing in a potentially dangerously cold airmass over the upcoming weekend. With temperatures expected to dive 10+ degrees below normal Saturday morning...along with breezy northerly winds...expect wind chill values during the morning hours to be in the -10 to -20 degree range across much of the local area. Due to these expected near or even critical values...opted to include a mention in the HWO for those who need to venture outdoors early Saturday morning. While the initial cold blast is expected overnight Friday into Saturday morning...continued cold air advection into the daytime hours on Saturday will likely make it difficult for some areas to climb out of the single digits by afternoon. While blended guidance captures some of this very cold is definitely on the conservative side compared to some of the individual operational models...which are another 5-7 degrees cooler than what we currently have in the forecast. Either way...the coldest airmass of the season will likely invade the local area over the upcoming weekend...with some small chances for snow along with near or critically cold wind chills both Saturday and Sunday mornings. && .AVIATION...(For the 00Z KGRI/KEAR TAFS through 00Z Tuesday evening) Issued at 540 PM CST Mon Dec 12 2016 The main issue will be wind gusts directly behind an arctic cold front moving south this evening. VFR conditions are forecast, but we do have a shot at some flurries in the area, especially southwest of the terminals, and KEAR was just close enough to include some VCSH in the forecast tonight. && .GID WATCHES/WARNINGS/ADVISORIES... NE...None. KS...None. && $$ UPDATE...Heinlein SHORT TERM...Rossi LONG TERM...Rossi AVIATION...Heinlein
Area Forecast Discussion
National Weather Service Lincoln IL
905 PM CST Mon Dec 12 2016 .UPDATE... Issued at 855 PM CST Mon Dec 12 2016 Arctic cold front making steady progress across central Iowa this evening and will sweep across our area tomorrow morning. Meanwhile, to the southwest, a weak shortwave was seen on the water vapor loop over western Oklahoma and that feature was tracking east as well. Mid clouds continue to increase ahead of the southern shortwave with most of the short term models and the latest 00z NAM indicating some light precipitation breaking out ahead of the wave after midnight over extreme southwest Illinois and then tracking east-northeast across south- central through southeast Illinois during the morning hours. RAP forecast soundings over southeast Illinois continue to depict a fairly significant warm layer just below 850 mb during the early morning hours suggesting the potential for some light freezing rain as the precipitation develops. However, models continue to show a very dry air mass also in place below 850 mb, so it may take some time to saturate the column before we can get any precip to reach the ground. With the very dry low levels, at least initially, evaporative cooling will cool the layer between 850 and 950 mb sufficiently enough for any spotty freezing rain, if it occurs at all, to quickly change over to light snow. We currently have low chance POPs down in the southeast for late tonight through Tuesday morning, with scattered areas of light snow or flurries possible along the Arctic front to the north by late tonight as well. Any accumulation of snow over south central through southeast Illinois should be an inch or less the way it looks now. Will wait to see how the 00z GFS handles the southern stream wave and precip types across our south for tomorrow before making any significant changes. For now, have made some minor tweaks to the evening temperature trends, otherwise, the current forecast looks reasonable with no ZFP update needed at this time. && .SHORT TERM...(This evening through Tuesday) ISSUED AT 305 PM CST Mon Dec 12 2016 Weak high pressure of 1022 mb was over central MO/IL this afternoon had decreased the stratocumulus clouds over eastern IL. Though mid/high clouds were quickly streaming ENE into central and southwest IL by mid afternoon. Temperatures at mid afternoon ranged from mid 20s nw of the IL river, to the mid 30s near highway 50 in southeast IL. An arctic cold front over central MN into northern Nebraska, will track southeast to near the IL river by 12Z/Tue and will race southeast of IL by 18Z Tue. Some moisture is advected into central IL overnight and Tue morning ahead of arctic front and have increased/expanded light snow chances during that time. Best chances of light snow appear to be Tue morning southeast of I-55 but snow accumulations appear to be less than a half inch with a bit higher amounts east over central IN. Lows overnight range from 15F by Galesburg to upper 20s southeast of I-70. Morning highs Tue range from upper teens nw of IL river, to mid to upper 30s from I-70 southeast. Brisk nw winds to cause temps to slip behind the arctic front on Tue with temps at 5 pm Tue ranging from 12F at Galesburg to 32F at Lawrenceville. Wind chills will get down to zero to 5 above over northern CWA on Tue. .LONG TERM...(Tuesday night through Monday) ISSUED AT 305 PM CST Mon Dec 12 2016 Cold arctic air will be in place across the northern Plains, Midwest, and northeastern U.S. through midweek as a deep 500 mb low over southeastern Canada drives the air mass into the region. A second surge of arctic air looks to arrive Wednesday afternoon following a shortwave feature rotating around the upper low. Model consensus brings 850 mb temperatures to around -20 C along I- 74. Temperatures Tuesday night ranging from 8 in Galesburg to 18 in Lawrenceville will only rise as high as 19 to 29 Wednesday before plummeting to 3 to 13 degrees Wednesday night. West to northwest winds 10 to 15 mph Wednesday and Wednesday night will bring the coldest wind chill temperatures associated with the event reaching below zero across central and SE Illinois, as low as -15 north of I- 74. Although winds look to subside Thursday afternoon as surface high pressure crosses the area, highs only in the teens will remain quite cold. The storm system Friday into Saturday continues to have minor although significant track uncertainties with ECMWF continuing its low pressure center track up the Ohio Valley and the Canadian/GFS trending farther south closer to that track. Have brought mention of freezing rain/sleet into areas along/east of I-57 for Friday night as that area/time period looks to have the highest probabilities of mixed precipitation...but kept weather type to rain/snow elsewhere. Otherwise...brought rain or rain/snow mix up to near I-72 by Saturday...then changing back to snow for Saturday night as the wedge of warm air aloft slides off to the east and the cold front pushes across the area. Saturday night and Sunday, cold Canadian air will surge back into the area with highs in the teens and 20s, lows in the teens and single digits returning. && .AVIATION...(For the 00Z TAFS through 00Z Tuesday evening) Issued at 510 PM CST Mon Dec 12 2016 VFR conditions are expected through the evening hours with a weather system expected to move across the area during the early morning hours Tuesday. That system may bring some light snow to parts of the area after 07z, especially from DEC to CMI. Forecast soundings show enough moisture in the column for a period of light snow and possibly some MVFR cigs at both of those sites into the morning hours. Further west and north, we are still looking at mainly VFR cigs as an Arctic cold front sweeps across the area during the morning. There may be a period of MVFR cigs along the cold front Tuesday morning, but confidence at this point is too low to include in this TAF issuance. Surface winds tonight will be out of a light southerly direction and then shift into the northwest and increase on Tuesday morning to between 12 and 17 kts with a few gusts up to 22 kts possible during the afternoon. && .ILX WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...Smith SHORT TERM...07 LONG TERM...37 AVIATION...Smith
National Weather Service Jackson KY
1005 PM EST Mon Dec 12 2016 .UPDATE... Issued at 1005 PM EST MON DEC 12 2016 00z NAM has come in and supports a quick shot for some light snow or flurries across northern Kentucky around daybreak. This activity continues to look like it should be north of I-64, and may actually just clip our far northern counties in our forecast area. Either way looks like a 1 to 3 hour window for some flurries. A dusting of snow may be possible with temperatures already back into the low 30s in that area. Better snow potential will reside much farther north where a band of snow could across southern Indiana and southern Ohio. Elsewhere, dry conditions will persist through Tuesday morning. Models show moisture and lift return around midday working in from Tennessee and across southeast Kentucky through the afternoon and early evening hours. Pretty good model agreement, so have increased pops a bit across the far southeast. Should be a tight gradient back to the northwest, where mainly just some sprinkles are anticipated. All the afternoon activity should come in the form of rain with temperatures in the 40s. Could be a brief mix above 3kft if temperatures cannot rebound fast enough with the precipitation moving in. UPDATE Issued at 656 PM EST MON DEC 12 2016 No significant changes to the forecast this evening. Updated to merge current temperatures in with the ongoing forecast. HRRR/RAP continue to show a band of light precipitation forming across northern Kentucky after 10z or 5 am tonight. HRRR has been very consistent from run to run, so may need to look at speeding up precipitation chances and if this is the case, could get a light coating of snow across the north with temperatures sitting in the lower 30s and no warm air aloft. At this time, still looks like a non-measurable liquid event, but certainly could pick up a tenth or two of snow on elevated surfaces. The main question is how far south this band extends and does it clip the I-64 corridor. We will continue to monitor trends this evening and may do another update a bit later to adjust pops if models continue to stay consistent. && .SHORT TERM...(This evening through Tuesday night) Issued at 420 PM EST MON DEC 12 2016 20z sfc analysis shows low pressure moving off to the east while high pressure is building into the western parts of the Ohio Valley. The rain exited the area this morning trailing the cold front with a few pockets of sprinkles and drizzle left behind - but those have cleared off now. Cigs came up off the deck as the day wore on and are now running in the 2 to 3k foot range. Even some patches of sunshine broke out through during the afternoon. However, CAA on northwest winds of 5 to 10 mph - with occasional gusts to 15 mph - kept readings from budging much as they are currently in the mid 40s most places - but they made it back up to the low 50s in the far east thanks to them seeing a bit more sunshine. Dewpoints, meanwhile, have dropped into the mid and upper 30s northwest to the low and mid 40s southeast. The models are in fairly good agreement aloft with the key features through the short term portion of the forecast. They all depict the strengthening and very deep vortex over north central Canada leading to height falls deep down into the United States. For Kentucky, this means more energy moving through the fast flow but not much in the way of sfc features to drive the wx. As such, the forecast is suffering from lower confidence due primarily to the fast and subtle features moving through the longwave trough over the region that vary just enough among the models through 12z Wednesday. Accordingly, have gone with a blended solution with a strong lean toward the HRRR, CONSShort, and NAM12 for the bulk of this part of the forecast. Sensible weather will feature high pressure moving quickly east tonight as fast mid level flow scoots the wx across the region. This will allow for low pressure and some return moisture to seep back into the area towards dawn Tuesday - limiting the cooling overnight, but also the temp rise during the day. As such, the weak sfc features will bring with it enough moisture to squeeze out some light showers or flurries/sprinkles through the day. The best chances for any flurries or a stray snow shower will be generally across the northern portion of the CWA, but that is also the location of the lowest PoPs for the forecast, too. So, rain showers are anticipated across the south as the sfc wave will pass through the Cumberland Valley with appropriately higher PoPs and better shot at seeing more than a trace of QPF. Speedy systems continue into Tuesday night with high pressure pushing the lower east of Kentucky again and bringing in colder air, possibly changing any lingering light pcpn to snow showers and flurries as this weak low departs. No accumulations of snow will occur through the short term, though, owing to very low QPF and warm grounds. Used the CONSShort and ShortBlend for the grids through the short term with only some slight temperature adjustments. Did also adjust the PoPs to introduce a bit more uncertainty into the light pcpn chances on Tuesday than the blend implied. .LONG TERM...(Wednesday through Monday) Issued at 420 PM EST MON DEC 12 2016 High pressure will nose in to start the period and ahead of this will be a strong cold front. We do see NW flow pattern on the backside of this will lead to upslope flurries by Wednesday night into Thursday morning given decent support in the sounding data. This will usher in the coldest air of the season with 850mb around -12C to -20C across the region. That said high temperatures on Thursday will struggle to make it out of the teens in the Bluegrass and most only climbing into the 20s. This will set the stage for a very cold night Thursday night as high pressure crest across portions of the region. Overall looks like the coldest temperatures will be across the Bluegrass, Big Sandy, and far east potions of the region where temperatures are expected to drop into single digits in spots. We do begin to see WAA kick in by Friday, as the surface high kicks east and 850mb temp tick up. Even so temperatures will struggle to make it above freezing for areas north and east of Lake Cumberland region. The more convoluted portion of the forecast begin late Friday into the weekend. The models have started to trend toward the same timing with latest runs. The first complication will be the precip onset Friday night given the ascendant cold air and temps struggling to get above freezing Friday afternoon. The issue here is strong WAA will lead to a low level warm layer and thus chance for freezing rain on the onset based on the latest forecast soundings. Confidence has increased enough to introduce this idea to the forecast grids given we have seen this in several runs now. Did opt to begin the mention in the HWO as wintry mix for now given we are talking day 5 still. The good thing is the window seems quite short given the 70 plus knot 850mb jet that screams across the region by Saturday morning. This will bring definite to likely chances rain through the day on Saturday into Saturday night. Given the strong jet energy associated with this system we could very well see around a inch to an inch and a half of rain for many. The exit this system will have the possibility of bringing another mix/snow/flurries on the back side. Then we see high pressure build east across the Ohio Valley for the rest of the period. && .AVIATION...(For the 00Z TAFS through 00Z Tuesday evening) ISSUED AT 656 PM EST MON DEC 12 2016 Some MVFR cigs continue to plague southeast Kentucky and model soundings support some moisture remaining in a thin layer through about the evening hours. With this in mind, will carry MVFR cigs at Jackson, London, and Big Sandy through the evening, before returning to VFR. We may see a return to VFR a bit sooner, but confidence is weak on when this cloud cover will finally erode for good. GFS LAMP guidance keeps it around through at least 03z or 04z. VFR conditions will likely be seen through the remainder of the period, although some low clouds could creep into northern Kentucky tomorrow morning and could reach as far south as Morehead. Right now, this is a very low probability. Otherwise, some low cigs may enter the picture again across southeast Kentucky late tomorrow as a weak wave pushes some shower activity northward into this area. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...KAS SHORT TERM...GREIF LONG TERM...DJ AVIATION...KAS
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
956 PM CST Mon Dec 12 2016 .UPDATE... 956 PM CST Evening Update.. Several adjustments to overnight and early Tuesday morning portions of the forecast made this evening. Most notable are some changes in timing/axis of light snow later tonight, with a slightly slower arrival and a track a little further south into the I-88 corridor through sunrise Tuesday. Given this have also lingered light snow early Tuesday morning across northwest IN and east central IL a little longer than previous. Also, based on obs trends have lowered temps across snow pack this evening, with temps rising a bit overnight as clouds and weak south- southwest wind develops in advance of approaching front. 00Z upper air analysis depicts a large upper trough across much of Canada and the northern Plains. Several little speed maxima noted within quick west-northwesterly flow within the southern periphery of the big trough, with a couple of very small amplitude short-wave features evident in vapor/IR imagery propagating through the mid-Missouri toward our region. Looking at some of the recent high-res guidance (HRRR/RAP/4km WRF) suggests that isentropic upglide around the 290 K theta surface works to saturate mid-levels across the area overnight, though condensation pressure deficits appear to struggle to get below 10 mb. Combined with dry low levels noted in DVN 00Z sounding below about 600 mb suggest saturation/precip development may struggle. Hourly high- res guidance has caught on to this, slowing development of precip per simulated reflectivity depictions. Trend in HRRR/RAP runs and supported by the 00Z 12/4km WRFs is the development of an axis of light precip (snow) more along the I-88 corridor from the Quad Cities into the Chicago area during the post-midnight hours. QPF amounts are pretty minimal (generally trace to a few hundredths) which seems appropriate given saturation issues. Did rework the hourly pops and qpf axes based on these model solutions, which effectively lowers the inch amounts previously expected closer to the IL/WI border. May be tough to even get an inch, but could happen somewhere along aforementioned band especially closer to Chicago and the south/southeast side toward morning. As indicated above, temps crashed (1 above at Rochelle at 7 pm) over fresh snow pack and under clear skies. Have adjusted mins lower in areas west of Chicago based on these obs, though temps already rising a bit as mid/high clouds begin to spread in from the west and light south wind develops. Also added a mention of patchy through the rest of the evening southwest/south of Chicago where temp/dew point spreads have decreased and fog has been observed. Fog should dissipate with arrival of cloud cover after midnight. Digital/text forecasts updated and available. Ratzer && .SHORT TERM... 154 PM CST Through Tuesday... Forecast focus is on a brief quick hitting snow overnight tonight for some areas, then on the initial stages of our very cold temperatures/wind chills that will take up residence across our region this week and only get colder. Several weak lobes of energy will rotate east around the base of the very cold upper low across central Canada, the source of our very cold airmass. The first of these will come through overnight. Forecast soundings indicate fairly steep lapse rates aloft and very good lift right in the prime dendritic growth zone in the warm advective wing ahead of this wave. Hi- res guidance including the RAP/HRRR/Several HopWRF members and NAM all depict QPF with this wave, beginning late this evening across north central Illinois, then spreading east after midnight across the remainder of the area. Cobb output indicates 14-18:1 ratios with this dry snowfall, and while QPF is not high, NAM QPF output for ORD of only 0.07 lays down a quick inch of snow. The RAP even shows over 0.1 inches of QPF across the WI border that could quickly put down and inch or so. The focus of guidance is I-88 north, though it is possible for some lighter snows farther south. Fortunately for Tuesday morning commuters this looks to fall largely overnight and would not be a lot of snow given how fast the wave will be, but could certainly be a nuisance to start the day in some areas with cold ground easily allowing snow to stick and could catch early commuters. All that said, feel like for many areas moisture will be lacking where this shouldn`t be too big of a deal. Monday morning we had a little cold surge behind our weekend snow, and behind this, we get round two as slightly colder air filters southeast, with more significant cold coming in the the next few days. It will feel very cold with another stiff NW wind in the morning as the pressure gradient will again tighten between the high in the plains and this weaker surface feature. Temperatures will hold in the teens for most locations with 20s far south and east. In spite of some clearing, temperatures will warm very little and will likely fall with the cold advection in place. Area wide wind chills will be from the single digits below zero in north central IL to single digits above SE, reaching negative double digits in some locations by sunset. KMD && .LONG TERM... 315 PM CST Tuesday night through Monday... An active and cold pattern more representative of mid-winter will continue through at least the next 7-10 days. An impressive and deep lobe of polar air will extend into central Canada and the Great Lakes/Midwest regions Tuesday night through Thursday. The 500mb heights are forecast by the GFS/EC to be around 475dm and temperatures at that level near -50C. Those are at record lows for this time of year per reanalysis over a large part of Ontario and the northern Great Lakes. Needless to say, the pattern will favor stout cold advection followed by near-record cold for mid-December (see Climate AFD below for more on that aspect). Tuesday night will see temperatures to near zero across much of north central Illinois by mid evening already. Some high clouds and increasing winds overnight may cause temperatures to slowly inch upward. But that`s of little significance, as the true arctic front will advance through Wednesday, with 850mb temperatures dropping from around -12C to -22C in about 9 hours. This will likely result in afternoon surface temperatures dropping back into the single digits. Sometimes with such a front there is brief shallow but robust snow showers, and cannot rule out guidance is missing that potential, but as of right now it looks like a dry passage. Winds will increase to 10 to 20 mph with even higher gusts during Wednesday afternoon into the evening. Combined with falling temperatures it looks like at least northern parts of the area would drop into Wind Chill Advisory criteria (<= -20F) into Thursday morning. With the west-northwest winds at 10 to 15 mph through Thursday, the cold advection over the snow pack here and upstream will keep temperatures from rebounding hardly at all. Have readings forecast in the single digits across the snow- covered portion of the CWA. Broad arctic high pressure of 1035 mb is forecast to migrate quickly southeast across the Missouri River Valley as a strong northwest jet keeps the pattern moving. Thursday evening has some signs that it could see temperatures drop fast to several degrees below zero even by 8-9 pm before a slight rebound overnight as clouds move in. Too far away yet to tell when clouds will move in and how quickly and low the wind will drop. Attention then turns to a large system favored over the middle of the country during Friday into Saturday. One part of the upper wave driving this is presently off the British Columbia shore and is still a couple days from moving onshore the Pacific northwest, but another driving force is a polar-origin wave dropping out of Canada. How those phase/interact and how they strengthen/undulate what should already be an impressive baroclinic zone across the Plains and south of our CWA, is just too far away to say for certain. The signal though in guidance and their ensembles for a widespread modest to high QPF event across the Midwest has been shown for numerous runs over several days now. Of note for precipitation type, the cold air mass for midweek and the snow cover helping to lock it to not modify, will be difficult to moderate ahead of the low...that is if the low ends up this far north. There has been a southward trend in the ECMWF over the past 24 hours and would not be surprised to see other guidance like the GFS trend slightly further south in time given the significant cold forecast to push south midweek. This is key because on recent runs of the GFS there would be freezing rain concerns over the snow pack, including as far north as our northern CWA. Have leaned more toward the EC, though do now have at least a mention of freezing rain in the southeast third of the forecast area. Again though, uncertainty factors are high given the guidance spread and a likely robust thermal gradient aloft and one possibly near or just north of the the snow cover edge. The potential for an accumulating snow, possibly significant, would be the higher threat with a south system track. Have likely snow mentioned for several periods in our north for Friday and Saturday, but the speed of the system too remains highly uncertain, so it may be less duration. Temperatures then look to take another dive behind this system. Depending on the track/orientation, lake effect snow could be a concern into northwest Indiana for the rest of the weekend. Plenty to keep our eyes on later this week. MTF && .CLIMATE... 300 PM CST The high temperatures for Thursday, December 15 are forecast to remain in the single digits across the area. For Rockford, the current forecast is for a record cold high, as the current record is 9 degrees set in 1932. The record for Chicago is not forecast to be broke, as it is a very cold -2 in 1901. For Rockford, the last time a high below 10 degrees occurred on or before December 15th was December 10, 2009 (only time since 2000). For Chicago, it has not occurred since December 11, 1995. Record daily low temperatures are presently not forecast. MTF && .AVIATION... For the 00Z TAFs... 527 pm...A weak upper wave currently over southwest IA will move east/northeast across northern IL overnight. Currently only mid clouds with this feature but most guidance saturate the low levels as this moves across the area overnight with light snow developing over the area. Confidence is medium that light snow will develop but still some uncertainty regarding how low the vis will drop as well as where the snow will track. Its possible that snow may be confined to a small area that may track north of mdw/gyy. Other than some minor timing big changes to the going forecast and will monitor trends this evening for possible changes with the 03z updates. This wave should be east of the area by sunrise Tuesday morning. Southwesterly winds may shift more southerly this evening before turning back west/southwest overnight...with speeds generally less than 10kts. Winds will shift to the northwest Tuesday morning with speeds increasing to 10-15kts and gusts to 20kts. cms && .MARINE... 327 PM CST West winds will continue across the lake tonight and become slightly northwest by Wednesday and increase in speed. This will support Small Craft Advisory conditions across the northwest Indiana shore. An arctic cold front will advance southeast across the lake late Tuesday night into early Wednesday, supporting northwest gales. These presently look to peak around 40 kt though cannot rule out some higher gusts. These gales look to persist through early Thursday. The first freezing spray concern of the season looks to develop as the colder air accompanies the gales. Another gale event is possible during the weekend as a strong low pressure tracks northeast across the mid-section of the country. MTF && .LOT WATCHES/WARNINGS/ADVISORIES... IL...NONE. IN...NONE. LM...Small Craft Advisory...LMZ744-LMZ745...10 AM Tuesday TO 3 AM Wednesday. Gale Watch...LMZ777-LMZ779...3 AM Wednesday TO NOON Thursday. && $$ VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE) FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT: WWW.FACEBOOK.COM/NWSCHICAGO WWW.TWITTER.COM/NWSCHICAGO WWW.YOUTUBE.COM/NWSCHICAGO
Area Forecast Discussion
National Weather Service Omaha/Valley NE
920 PM CST Mon Dec 12 2016 .UPDATE... Issued at 920 PM CST Mon Dec 12 2016 Updated grids and products a few times this evening, as cold air continued to pour into the area. Front was almost through all of the forecast area as of 9 pm. There has been a surge of stronger winds behind the front for a few hours, then these drop off. Lowered low temperatures tonight, mainly northern parts of the area. Did not go quite as cold as the HRRR or RAP models are suggesting, but trended toward those. && .SHORT TERM...(Tonight through Thursday) Issued at 304 PM CST Mon Dec 12 2016 A few mid-level clouds are not doing much to dispel the milder day across the area, but the surface cold front already is impinging. Subjective 12Z upper-air analysis indicates fast and mainly zonal flow continuing across the US, with a 100-140kt upper-level jet extending across the CONUS from OR/CA through NE/KS/IA and over to New England. Two centers of falling 500mb heights were noted, one centered in MB and the other in MI. An 850mb ridge was noted from central NE/central KS into OK/TX. A pool of much colder 850mb temperatures was noted in the Prairie Provinces. A surface low at 20Z was centered in northeast NM, with an elongated trough axis/cold front from northeast KS through central to northeast NE into southwest MN. With the cold front, a sharp thermal gradient was noted, with temperatures falling 20-30 degrees over the width of about 50 miles. Main forecast concern in the short term is the coming temperature plunge, along with small potential for intermittent flurries. Temperatures will plunge quickly tonight, offset only slightly by potential for midlevel clouds and breezy winds. Wind chills will reach 0F to -10F along and north of I-80. Have removed flurries for tonight, as better mid-level moisture and lift both remain further west in central to southwest NE. For Tuesday through Wednesday night, forecast is pretty similar, with lows in the single digits to teens and highs in the upper teens to mid-20s. Weak ripples along the baroclinic zone near NE/IA could be enough to spark flurries, but limited moisture and weak/transient forcing should keep any of these non-measurable. On Thursday, an upper-level trough should move from off the Pacific coast and into the Pacific Northwest. Ahead of the digging trough, another weak shortwave trough and a band of mid-level warm air advection may be enough to allow flurries or light snow to develop in a swath across SD into northeast NE, sliding northeastward through the day. Low-level moisture remains limited, and think any precipitation would be very light, but have maintained the model blend POPs for now. .LONG TERM...(Thursday night through Monday) Issued at 304 PM CST Mon Dec 12 2016 Much of Thursday night and Friday morning should remain precip-free (or with drizzle/flurries) as warm air advection continues ahead of a digging western US trough. Models remain in pretty good agreement and consistency regarding the system (with some devil in the details), with chances for snow increasing on Friday afternoon as a surface low slides from northeast CO into KS. Warm sector looks to be warm enough ahead of the surface inverted trough to allow potential for a rain/snow mix or all rain in some part of the southern CWA, if precipitation does develop there. The swath of precipitation (likely snow) from SD/MN into northern NE/northwest IA should develop on the cold side of the system and persist into Friday night. Models have occasionally picked up on an interesting trend of weakening the wraparound/cold-belt precipitation on Friday night/Saturday morning, then developing a second mesoscale band somewhere along the mid-level cold front (KS-MO-southern NE-southern IA, in current runs) that persists Saturday. While the feature is mesoscale in nature and almost certain to dance in and out of the progs and around the geography, it is certainly a feature to continue to watch over the next few days as this system evolves. Being in the day 5-6 time frame, it is too early to get bent around the pole regarding snowfall amounts, the rain/snow line, and other details. For now, it is enough to say that there is a potential for mixed precipitation or snow on Friday and snow on Saturday. Behind the front and its associated precipitation, strong cold air advection will continue on Saturday and Saturday night. Have pushed temperatures on Sunday morning below the national blend, following raw model guidance. Particularly in any areas where snow pack exists, subzero temperatures are pretty confident. Any breath of surface wind should send wind chills into critical thresholds, but with the surface high sliding in or near the area, at least the winds should be on the low side. Cold weather will continue on Sunday, but models are now tilting warmer for Monday instead of hanging on to the true cold. Moderation also likely will depend on where snow pack exists, but at least the pattern now does not look quite as cold as it did a few days ago. && .AVIATION...(For the 00Z TAFS through 00Z Tuesday evening) Issued at 550 PM CST Mon Dec 12 2016 VFR conditions are expected through the TAF cycle. A cold front will continue to drop southeast through the TAF sites this evening with northwest gusts to around 20 kts behind the boundary. && .OAX WATCHES/WARNINGS/ADVISORIES... NE...None. IA...None. && $$ UPDATE...Miller SHORT TERM...Mayes LONG TERM...Mayes AVIATION...Kern
Area Forecast Discussion
National Weather Service Seattle WA
255 PM PST Mon Dec 12 2016 .SYNOPSIS...Showers will decrease and mostly end tonight as cold and drier air spreads south across Western Washington. Dry cold weather will prevail Tuesday and Wednesday. A chance of snow will return Wednesday night and Thursday as a weather system passes to the south. Temperatures will remain cold Friday and Saturday, then moderate early next week. && .SHORT TERM...Colder air will seep south tonight and Tuesday but precipitation will mostly come to end before temperatures are cold enough for snow showers. The HRRR shows a focused precip band over SeaTac sagging south over the next few hours then fizzling. Current radar seems to be backing this idea. Heavier precipitation in this band might be enough to drag snow levels down to the surface but it is probably just too warm that far south for any snow accumulations through this evening. Tuesday will be dry with decreasing clouds. Highs will be mostly in the 30s. Low will be mostly in the 20s. Wednesday will also be dry and chilly. A weather system moving onshore to the south will spread moisture into the forecast area Wednesday night. It will be cold enough that any precipitation that develops will fall as snow. Accumulating snow is most likely over the far south interior with rapidly decreasing chances farther north. Details are hard to pin down this far out of course but models do seem to be coming into better agreement with this scenario. Thursday will be another chilly day with a few lingering snow showers. Schneider .LONG TERM...Friday looks dry and cold. A reinforcing shot of Fraser outflow is expected as a surface high builds south into southern British Columbia. This could actually be the coldest day of the week. Dry northerly flow aloft will continue Saturday for another chilly day. A Pacific frontal system will reach the area Sunday. Temperatures should be moderating but some cold air will probably linger for a rain/snow mix before temperatures warm for just rain in the lowlands. Another pacific frontal system will reach the area Monday. Schneider && .AVIATION...Somewhat moist westerly flow aloft will continue over W WA through tonight. A weak upper level shortwave ridge will move over W WA this evening then dissipate late tonight. A 1037 MB surface ridge over the B.C. interior will gradually shift winds to a northeasterly offshore direction through this evening. Colder and drier air from the Fraser river valley will spread over W WA overnight. A convergence zone has formed over S Puget sound near KSEA and will probably dissipate by 03Z. The air mass over W WA will remain moist tonight through much of Tuesday. Drier low level air spreading across the north interior should produce mainly VFR conditions. Upslope flow near KCLM could produce local MVFR or IFR conditions. From Puget Sound across the SW interior MVFR conditions should predominate. KSEA...The moist air mass over the area will allow MVFR conditions to predominate at KSEA tonight through Tuesday morning, with IFR CIGS possible at times. Some lifting and clearing is possible Tuesday afternoon. A convergence zone has formed in the vicinity of KSEA at 22Z but should dissipate by 03Z. Temperatures are in the lower 40s so snow is unlikely. Other than the convergence zone it does not look like there will be any precipitation producer around KSEA through tonight, so it doesn`t look like snow will develop. Surface winds will be northerly 3-8 KT through 04Z then shift easterly. Kam && .MARINE...A 1037 MB surface ridge over interior B.C. will gradually weaken through this week. A surface trough will remain along the WA coast. This will maintain NE offshore flow through this week. NE outflow through the Fraser river valley has been gradually weakening this afternoon which will allow all areas except for the waters north of the San Juan Islands to fall below the SCA threshold. SCA winds are expected to continue north of the San Juan islands through Tuesday morning. A frontal system approaching from the SW will induce pressure falls just offshore on Wednesday and Wednesday night allowing easterly winds to rise back to SCA levels over the coastal waters and parts of the inland waters. Kam && .HYDROLOGY...River flooding is not expected for the next 7 days. && .SEW WATCHES/WARNINGS/ADVISORIES... WA...None. PZ...Small Craft Advisory until 10 AM PST Tuesday for Northern Inland Waters Including The San Juan Islands. && $$ You can see an illustrated version of this discussion at