Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/25/16

Area Forecast Discussion
National Weather Service Billings MT
828 PM MST Sat Dec 24 2016 .UPDATE... Bands of snow beginning to fill in north of a warm front near the MT/WY state line. Best band of snow currently extends from Bighorn County east through Baker. Upsloping north/northeast winds are beginning to set in across the foothills and central Plains and will continue through the night. Should see significant increase in snow coverage as deepening upper-low pushes further east after midnight. Winds have been higher than forecast this evening in the Baker area with gusts around 40 mph over the last few hours, therefore adjusted wind speeds up to match the obs for the remainder of the overnight period. Travel conditions will begin to deteriorate across most of the region by early Sunday as snow ratios increase to 15:1 and accumulations pile up. Walsh && .SHORT TERM...valid for Sun and Mon... Upper level trof over the western US with strongest pocket of energy moving through the base of the trough over Arizona and beginning its journey northeastward. This allows a strong upper level low to quickly spin up over eastern Colorado on Sunday and quickly moving to South Dakota by Sunday afternoon. Diffluent flow and isentropic lift over the northern Rockies has been producing widespread snow in the western half of the state and radar is showing increasing coverage over the mountains. Airmass is quickly moistening over the region due to easterly flow and expect snow to become more widespread early this evening. Bufkit shows favorable dendritic growth regions forming from Billings westward towards midnight so expect accumulating snow to start late this evening. HRRR has transitioned strongly during the past 5 hours to producing much more precipitation over a wider portion of the region so confidence in the snowfall forecasts has increased this afternoon. Expected timing remains the same with snow holding off for most of the night for eastern areas and then becoming heavier Christmas morning. Really rapid pressure falls midday Sunday will cause winds to accelerate during the afternoon causing blowing and drifting to begin. Winter storm warning looks good for those areas and just watching to see if places like Rosebud County or Big Horn county realize higher than expected snowfall amounts. Conditions quickly ramp down Christmas night as the upper low move quickly into northern Minnesota. Snow ends across the region from west to east and winds will taper off with coldest temperatures expected Monday morning so may wind chills persisting to 20 below zero or lower over southeast Montana Monday morning. Otherwise it dries quickly and leeside trough forms allowing for gap flow winds to develop Monday night but brining moderating temperatures. borsum .LONG TERM...valid for Tue...Wed...Thu...Fri...Sat... Pacific jet moves over the region on Tuesday, helping to set-up lee-troughing and associated winds in the gap areas. This flow should also generate snow showers over the mountains. Could get a few snow showers in the lower elevations Tuesday night as a weak shortwave trough axis crosses the region. Snow showers could continue on Wednesday in the mountains...but elsewhere dry weather expected in the downslope flow. Could get a stray snow shower in the plains on Wednesday due to instability as advertised on the ECMWF, but given flow, fairly dry air, and that GFS does not have as much instability, kept PoPs low. Upper anticyclonic flow builds in for Thursday and Friday, bringing tranquil weather to much of the area (aside from wind in the gap areas). Northern areas could get a few snow showers on Friday as some weak energy moves through the west/northwest flow aloft. Next best chance of snow arrives Friday night as pronounced shortwave trough propagates southeastward across Montana. Could produce a widespread light snow then. Shortwave ridging should bring dry weather to the area next Saturday. Windy conditions are expected for Billings and west through much of the extended, with the strongest winds in the gap areas west of Billings. Highest winds at this time expected on Tuesday. Temperatures should be near or just below seasonal normals through the extended. RMS/Borsum && .AVIATION... Conditions will deteriorate through the night. All terminals will fall to MVFR and lower overnight. KBIL was already in IFR with moist upslope flow and this will hold through the night. A storm system to the south will spread snow into the area overnight with snow overspreading the entire area by Christmas morning. Conditions will lower to LIFR as snow intensifies, especially from KBIL eastward. Eastern terminals will likely have VLIFR conditions by Christmas afternoon with heavy snow and strong northwest winds dramatically reducing visibility. Northwest winds will gust over 30kts at KMLS and KBHK by Christmas afternoon. TWH && .PRELIMINARY POINT TEMP/POPS... Sun Mon Tue Wed Thu Fri Sat ----------------------------------------------------------- BIL 009/016 006/024 014/033 024/033 016/029 016/034 017/028 89/S 41/U 01/N 31/N 11/N 10/N 42/S LVM 010/015 008/026 016/032 022/030 017/031 020/036 017/030 88/S 31/N 02/J 42/J 21/N 12/J 43/S HDN 008/015 901/024 005/035 020/034 009/028 008/034 013/028 69/S 51/B 01/E 21/B 11/U 10/B 32/S MLS 010/016 000/018 007/033 021/032 013/028 010/031 012/023 6+/S 82/S 01/B 21/B 11/U 12/J 42/S 4BQ 010/019 003/022 008/034 019/033 014/029 011/032 012/025 5+/S 92/S 01/B 11/N 11/U 00/B 43/S BHK 010/021 000/015 005/031 020/030 013/025 011/029 009/021 6+/S +2/S 00/B 01/N 11/U 12/J 32/S SHR 009/014 003/024 008/035 018/031 009/029 012/035 012/026 38/S 41/U 01/B 21/B 11/U 10/B 33/S && .BYZ WATCHES/WARNINGS/ADVISORIES... MT...Winter Weather Advisory in effect until 6 PM MST Sunday FOR ZONES 28-34-39>42-56-63>66. Winter Weather Advisory in effect until midnight MST Sunday night FOR ZONES 29>31-35-38-57-58. Winter Storm Warning in effect from 6 AM Sunday to 6 AM MST Monday FOR ZONES 32-33-36-37. WY...Winter Weather Advisory in effect until midnight MST Sunday night FOR ZONES 98-99. && $$
Area Forecast Discussion...CORRECTED
National Weather Service Austin/San Antonio TX
627 PM CST Sat Dec 24 2016 .AVIATION...Corrected to include the number 2 in from of KFT /00Z TAFS/ MVFR cigs are already occurring at all area terminals (KAUS could have a short- break of VFR within the 00Z hr). IFR cigs and vbsys are expected first across KDRT (03Z) as dewpoint depression is only few degrees from the actual temperature as of 00Z. Along the I-35 sites, IFR conditions are forecast to happen within the 04Z to 08Z Sunday time frame. Most models suggest for LIFR conditions to begin at KDRT around 09Z with NAM solution showing around 03Z. For the I-35 sites, models show LIFR around day-break. Holding off for now on this as all models show a strong southerly flow overnight into Sunday morning thanks to a low level jet of 25 to 40 knots in the first 2 KFT. Also, both NAM and GFS area forecast soundings are in good agreement with the statement above. If any of the area sites to have a chance to go LIFR late tonight is KSSF as winds are forecast to be in the 6 to 10 knots range. That said, will be monitoring closely hourly obs and adjusting area tafs as needed. HiRes reflectivity products show drizzle/very light rain around midnight through Sunday morning mainly across the I-35 airports. && .PREV DISCUSSION... /ISSUED 245 PM CST Sat Dec 24 2016/ SHORT TERM (Tonight through Sunday Night)... The continued pattern of abundant moisture flux into the region will continue through the short term period. The deep troughing over the western CONUS will push eastward over the next 24 hours and leave the region in a southwest flow regime while it takes a negative tilt turning north. Meanwhile a very strong 850 mb LLJ strengthens out of the due south to over 50 kts by tomorrow morning. While the low level wind field and moisture flux are strong, very strong capping and a lack of moisture above 850 mb, as indicated by proximity soundings on the RAP at KDRT, should prevent much in the way of any QPF generation beyond some sporadic showers and drizzle overnight. Winds should become gusty overnight out west as well as the pressure gradient intensifies on the Plateau. A frontal passage from the west will begin to enter the western zones tomorrow afternoon and provide the best opportunity for more more significant rain, however as noted previously, the lack of a deep moisture tap and ideal upper level support staying well to the north and northeast, it looks like the best rain potential will stay to the north as well. The front is expected to stall and not quite reach our portion of the I-35 corridor. Which will leave the western zones mostly cloud free but keeping the eastern half still under mostly cloudy skies. Still expecting highs tomorrow to be well above average, especially south and east of the stalled boundary. LONG TERM (Monday through Saturday)... The aforementioned stalled boundary will the focus for PoPs over the next several days. After this weekend`s system moves northeast and out of the area, the LLJ should decrease in intensity but still be feeding moisture out of the due south. Convergence along this stationary front should produce showers and possibly a few rumbles of thunder Monday and into Tuesday morning. This feature lingers through much of the week but as low level convergence wanes each day, the low level moisture tap for showers should also decrease. The next significant front will be on the horizon for late week with about a 12 hour difference in timing between the 12Z ECMWF and GFS. While much of the week 60s and 70s will be the story, the front does look similar in strength in both models as both ECE and MEX guidance show about a 20 degree difference in high temperature either Thursday or Friday, depending on the timing of the front. && .PRELIMINARY POINT TEMPS/POPS... Austin Camp Mabry 66 76 64 72 58 / 30 30 30 50 30 Austin Bergstrom Intl Airport 66 76 64 72 58 / 20 30 30 50 30 New Braunfels Muni Airport 65 75 65 74 59 / 30 30 30 50 30 Burnet Muni Airport 63 72 60 67 54 / 30 30 30 40 30 Del Rio Intl Airport 63 74 57 69 58 / 30 30 10 20 30 Georgetown Muni Airport 65 74 62 69 56 / 30 30 30 40 30 Hondo Muni Airport 65 77 64 74 61 / 30 30 20 40 30 San Marcos Muni Airport 65 76 65 74 59 / 20 30 30 50 30 La Grange - Fayette Regional 66 78 67 76 62 / 20 20 40 50 30 San Antonio Intl Airport 66 75 65 74 61 / 30 30 30 50 30 Stinson Muni Airport 66 76 66 75 62 / 30 30 20 50 30 && .EWX WATCHES/WARNINGS/ADVISORIES... None. && $$ Mesoscale/Aviation...17 Synoptic/Grids...09 Public Service/Data Collection...30
Area Forecast Discussion
National Weather Service Green Bay WI
955 PM CST Sat Dec 24 2016 Updated aviation portion for 06Z TAF issuance .UPDATE... Issued at 907 PM CST Sat Dec 24 2016 Received report of some dense fog in east-central Wisconsin where skies cleared earlier. Added mention of that to the forecast for the rest of the evening, but with clouds now overhead would expect that to gradually diminish. Have seen enough support for FZDZ potential late tonight and early Sunday to warrant some adjustments to the forecast. Models continue to show light QPF in central/east-central Wisconsin, shifting into the northeast with time. This is supported by increasing areas of weak returns near the KARX and KMPX radars. In addition, cold frontal boundary settling into the area will provide the focus for added low-level lift once flow begins to strengthen from the southeast later tonight. Will pull the start time of the FZRA advisory back to 09Z, since the time most favored for FZDZ is around daybreak. Will also expand the advisory into east-central Wisconsin. Will leave lakeshore areas out of advisory for now with the expectation increasing SE winds will bring enough warming inland to reduce the amount of freezing that occurs, though this will need to be watched closely give current temperatures. Made some tweaks to start times of the remaining headlines to match things up. See coding below or upcoming WSW for details. Updated product suite will be out within 1/2 hour or so. UPDATE Issued at 659 PM CST Sat Dec 24 2016 Two weather concerns this evening. The first is the rapid drop in temperatures at locations in east-central Wisconsin where skies were mostly clear. KGRB ASOS down to 21F. The concern is this will cause water lingering on roads, sidewalks, and parking lots to quickly freeze into glare ice. Highlighted the situation with an SPS, and will be following up with Social Media posts. The second issue is the potential for FZDZ later tonight. The depth of the moisture looks marginal at first (08Z-10Z), but should become sufficient as we approach daybreak. Lift may also be enhanced as SE winds begin to lift over cold front currently dropping south across the area. Will review a little more of the 00Z guidance suite before making a final decision, but will probably update the forecast to hit FZDZ potential late tonight and early Sunday a little harder. && .SHORT TERM...Tonight and Sunday Issued at 241 PM CST Sat Dec 24 2016 A strong storm across the central plains tonight will move slowly into Canada on Monday. This system is expected to bring a variety of precipitation types. For tonight, all models show light precipitation amounts after midnight across central into northeast Wisconsin, in response to 850mb warm advection and weak 700mb lift. This seems reasonable and hard to argue the gfs/wrf/ECMWF and the HRRR models indicating light precipitation breaking out. Tried to move up start time to the freezing rain/winter weather advisories, but offices to the west wanted to keep the 15z start time. There is a possibility the start time will need to be moved up. Mid level moisture continues to be lacking through noon on Christmas Day. Thus expect drizzle or freezing drizzle during the morning hours. A perusal of the Metro Road forecast would suggest that road temperatures should climb above freezing by mid-morning, and near Wausau/Wisconsin Rapids line to Marinette around mid-day. Model differences continue across the north in how quick the cold air will retreat, thus went with a winter weather advisory over the far north for a mix. Mid level moisture and steadier/heavier precipitation during the afternoon on Christmas. Even locations that will see rain could also experience some sleet as a cold pocket at 925mb (-5C) was noted on the bufkit soundings. Based on cloud cover, went slightly warmer for lows tonight and a took a compromise between the warmer met and colder mav guidance for highs on Christmas Day. Highs on Christmas Day will be about 10 degrees above normal. .LONG TERM...Sunday Night Through Saturday Issued at 241 PM CST Sat Dec 24 2016 Deep cyclone tracking from the Central plains to the Northern Great Lakes region Sunday into Monday will provide an active weather pattern. Primary issue into Sunday night or early Monday morning will be precipitation type. Warm air lifting over the initially cold boundary layer will provide a wintry mix into Sunday night. Latest progs suggests the boundary layer warms enough over central and east central Wisconsin to turn to rain by Sunday evening. But the mix potential lasts longer over north central and far northeast Wisconsin Sunday night. A wide range of scenarios play out Sunday evening with the brunt of the water equivalent arriving during that time while surface temperatures will start out near or below freezing. Will start out with a Winter Weather Advisory due to the mix. ZR to R the likely trend but sleet possible as well. Some concern that the Winter Weather Advisory may need to be upgraded but there is lack of cold air training into the area at this time. Winds are mainly from the east in the evening. Winds will be on the increase Sunday night and especially into Monday in the wake of the front. Possibly wind headlines will be issued later this weekend. High pressure building into the area Monday night will subside winds while temperatures continue to fall. Overall quieter weather for the remainder of the week with lake effect snow showers far north for a few days. Next chance for light snow appears around Wednesday night or Thursday and then toward Saturday. && .AVIATION...for 06Z TAF Issuance Issued at 954 PM CST Sat Dec 24 2016 Generally poor flight conditions are expected for the next 24 hours. The breaks in the clouds over east-central Wisconsin have filled in, and ceilings are expected to edge downward the rest of the night and into Sunday. FZDZ is likely across the area late tonight and early tomorrow morning. A more significant area of precipitation (mixed in the northwest part of the area and mainly liquid in the southeast) is likely to overspread the area tomorrow afternoon. && .GRB WATCHES/WARNINGS/ADVISORIES... Freezing Rain Advisory from 3 AM to 9 AM CST Sunday FOR WIZ038- 039-045-048-049. Freezing Rain Advisory from 3 AM to 2 PM CST Sunday FOR WIZ020- 030-031-035>037-074. Winter Weather Advisory from 9 AM Sunday to 2 AM CST Monday FOR WIZ005-010>012-018-019. Winter Weather Advisory from 6 AM Sunday to 2 AM CST Monday FOR WIZ013-021-073. && $$ UPDATE.........Skowronski SHORT TERM.....Eckberg LONG TERM......TDH AVIATION.......Skowronski
Area Forecast Discussion
National Weather Service Greenville-Spartanburg SC
1017 PM EST Sat Dec 24 2016 .SYNOPSIS... A weak cold front will stall over the area this evening. On Sunday, a wedge will develop over the Carolinas with strong high pressure centered well to our north. A more substantial front will cross the area on Tuesday, with yet another cold front expected to move through the southeast on Thursday. && .NEAR TERM /THROUGH SUNDAY/... As of 10 PM EST Saturday...most of the precip activity continues to move across eastern TN, brushing the NC mtns. Will maintain a chance of precipitation along the TN border, tapering off to slight chance across the mtns, while most of the area east of the Blue Ridge remains dry for the next few hours. The interim model guidance suggested including a small chance across the northern Tier of zones during the early morning hours, so that was added. Fortunately, temps will remain mild through the overnight hours. The cold front was analyzed well to the north at 00Z, so it might not make meaningful progress until closer to daybreak. Once the front crosses the area east of the mtns, a cold air damming wedge will set up. For Christmas Day, 850mb flow will shift back to southwest with another slug of moisture and isentropic lift, which should lead to another round of low clouds during the day. However, even with the northeasterly winds and the strengthening damming, temperatures will soar again, possibly even warmer than what we`re seeing this afternoon, and a good 10 degrees above average. With upslope flow beginning across the escarpment, also could see the beginning of some light precipitation late in the period. All in all a fairly uneventful but unseasonably warm Christmas Day. && .SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/... As of 230 PM EST Saturday...An amplified upper ridge will begin to gradually flatten thru the Short Term, as a series of short waves track thru the Great Lakes. At the surface, a strong high will migrate from the central Quebec to east of the Canadian Maritimes by late Monday. The high will initially supply some cooler and drier air into the area from the north, but will need precip to lock in cooler temps by Monday afternoon. Guidance generally agrees that as the high shifts east, return flow out of the Atlantic will moisten profiles up to about 850 mb by daybreak Monday. The moisture along with increasing isentropic lift and SELY upslope should result in a cloudy and somewhat wedgy day. I will continue to mention a chance for light rain and drizzle, especially along the eastern escarpment and adjacent foothills. Temps will start out well above normal Monday morning, then only rise a few degrees under the wedge. Monday night thru Tuesday...Low-level flow will veer from SE to SW and lose most of the upslope and upglide. So there may be a lull in rain/drizzle Monday evening, but cloudy conditions will continue. Then a cold front will lay over the area from the NW on Tuesday, bringing a chance for showers, primarily in the NC mountains. Temps will remain elevated overnight ahead of the front, then the wedge is expected to erode and allow temps to warm about 15 degrees above normal on Tuesday, despite a fair amount of cloud cover. PoPs will range from likely along the TN line to slight chance southeast of I-85. && .LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/... As of 200 PM Sat: Transient high pressure crosses the area in the wake of the front Tuesday night. Global models diverge from there, as they differ in the placement of a broad upper trough and sfc low near the US-Canada border. The 24/00z EC shows the system developing further west, and the stalled front also being reactivated over the lower Mississippi Valley. This evolution would bring precip back to our area late Wed into Thu; it is shown in some fashion on perhaps half of the NAEFS members, and is reflected in the WPC medium range fcst. The 24/12z GFS is further east with the northern low and instead develops the frontal wave over the Gulf Stream, keeping us dry. Regardless of how the frontal wave develops, temps are expected to remain above normal Wed-Thu, permitting us to advertise an all- liquid forecast for that portion of the period. A cold front however is expected to push through Thursday. Expect brisk winds across the area following the fropa, with gusts possibly approaching advisory criteria in the higher elevations of the mtns. NW flow precip (some of which is expected to be snow) returns to the mountains Thu night lasting into Fri. A second sprawling high moves across the Southeast to end the week. This will keep temps a few degrees below normal Fri- Sat. && .AVIATION /03Z SUNDAY THROUGH THURSDAY/... At KCLT and elsewhere...VFR through the evening hours, or at least through the time when operations taper off late tonight. Light rain may move across the mtns and nrn Foothills through mid evening...but this should not cause any restrictions. However, it will help to bring the ceiling down from mid-levels into the lower end of VFR, around 050 or so. Wind will be S to SW for the evening, but high pressure well to the north will push a boundary south across the fcst area later tonight. Wind will most likely go light/variable during the early morning hours, eventually returning from the NE as the sfc high exerts its influence. The first problem looks like the extent and amount of fog late tonight and Sunday morning. Have taken a compromise of the pessimistic LAMP guidance and optimistic RAP guidance, which develops the visibility to MVFR after 05Z-06Z. After that, the other question is the amount of low clouds and how high the ceiling forms. The LAMP guidance looks way too pessimistic with its widespread IFR over the Piedmont. Prefer to keep the current fcst going which features an MVFR ceiling developing from midday to mid-afternoon. Outlook: Moisture will linger atop the region on Christmas day with continuing restrictions possible. Another front and associated moisture will approach from the west early next week. Confidence Table... 03-09Z 09-15Z 15-21Z 21-00Z KCLT High 100% High 87% Low 52% High 85% KGSP High 100% High 100% High 80% High 94% KAVL High 100% High 85% Med 71% High 100% KHKY High 94% Med 78% Med 63% Med 66% KGMU High 100% High 100% High 83% High 94% KAND High 100% High 100% High 80% High 86% The percentage reflects the number of guidance members agreeing with the scheduled TAF issuance flight rule category. Complete hourly experimental aviation forecast consistency tables and ensemble forecasts are available at the following link: && .GSP WATCHES/WARNINGS/ADVISORIES... GA...None. NC...None. SC...None. && $$ SYNOPSIS...JPT NEAR TERM...PM/TDP SHORT TERM...ARK LONG TERM...Wimberley AVIATION...PM
Area Forecast Discussion...UPDATED
National Weather Service Huntsville AL
818 PM CST Sat Dec 24 2016 .NEAR TERM...(Tonight) Issued at 818 PM CST Sat Dec 24 2016 An update for this Christmas Eve. A weak frontal boundary remained draped from south of Memphis and Nashville to the far western corner of western Virginia. Scattered showers continued along this boundary across most of Tennessee, with more numerous showers just to the west across the Mid South; central/eastern Arkansas, northern Mississippi and far western Tennessee. Simple trajectories of this activity and short term model output; HRRR, RAP new NAM keep this precipitation north of the forecast area. Given how close it the southern edge is, opted to keep some mention in our northern areas this evening, but will decrease rain chances a bit faster than our earlier issuance. Only minor tweaks were made to night time low temperatures. With a potential of less clouds (or more higher altitude variety), residual lower level moisture and light winds; a risk for fog development still looms for the late night. Soundings from the NAM (12 and 00Z) and the RAP still show fog in the late night. The fog could become locally dense, especially in/near bodies of water, valleys and wind sheltered locations. Given that only the Meridianville site has experienced brief visibility reductions, and temperature/dewpoint separations are more than 3 degrees at most sites, will hold off on a Dense Fog Advisory Non-Precip-Warning at this time. We wish all a very Merry Christmas from the National Weather Service! .SHORT TERM...(Christmas Day through Monday) Issued at 239 PM CST Sat Dec 24 2016 This building anomalously strong ridge will continue during Christmas Day making the way for what could be record breaking daytime highs! Any remaining fog from overnight should begin to dissipate during the morning hours but due to the low sun angle this fog may actually take longer to dissipate. The daytime highs will soar close to 80 degrees especially with the broken cloud cover, and the antecedent warm airmass. The all time record highs for December for Huntsville and Muscle Shoals are 81F and 78F, respectively. The main reason for the stronger ridge is an upstream deepening trough over the Intermountain West and a downstream deepening trough over the western Atlantic. Definitely a stark contrast from last year`s record breaking rainfall/flooding on Christmas Day! Some radiational cooling will take place on Sunday night, but cloud cover will increase as the previously mentioned deepening trough moves rapidly over the Intermountain West and Central Plains. Due to the strength of the prevailing ridge, a shortwave trough within the parent trough will move north acquiring a negative tilt over the Central Plains. The deepening low and resulting kinematics/thermodynamics from this system should create a severe weather scenario over the Central Plains. Meanwhile, a surface cold front accompanying this trough will gradually move east/southeast over the Southern Plains on Sunday arriving over the Lower MS River Valley by Monday morning. There may be some pre-frontal isentropic lift for light showers late on Monday morning/afternoon before the front arrives late on Monday night, but the models are continuing to show a drier solution. As a result, have reduced POPs/WX for that time period. .LONG TERM...(Monday night through Friday) Issued at 239 PM CST Sat Dec 24 2016 Moderate southwest flow aloft will be in place across our region at the beginning of the extended forecast period, with a strong subtropical ridge centered across the northwestern Bahamas. However, as a progressive northern stream trough shifts enewd across southern Ontario/Quebec, the subtropical ridge will begin to weaken and retrograde across the Gulf of Mexico placing the forecast area beneath an unamplified zonal flow regime. With models suggesting that the strongest mid-level ascent associated with northern stream trough will bypass the region to the north, the associated surface cold front should be the primary forcing mechanism for a line of convection that will impact the region Tuesday morning. With the exception of the GEM, guidance continues to delay the southward advancement of the front, with it now expected to enter the far northwestern zones around 12Z and exit the southeastern zones between 18-21Z. Forecast soundings still indicate sufficiently steep lapse rates aloft and elevated CAPE to include a slight chance of thunderstorms, but with the wswly low-level jet expected to only reach 25-30 knots the primary threats with any storms will be lightning and brief winds gusts of 30-35 mph. A cooler/highly modified Canadian airmass will be advected into the region in the wake of the front, and we have indicated morning highs temps -- with values steady or slowly falling through the afternoon. By Tuesday night/Wednesday, attention will focus on a slightly colder mid-level trough forecast to be spreading esewd across the northern Rockies. Upstream 500-mb height falls associated with this feature will force the cold front to stall to our south Tuesday night before lifting northward as a warm front late Wednesday morning, with scattered showers possible as this occurs. Although there are significant differences in forward speed of the northern stream trough (which will have an impact on the quality of deep- layer moisture return), most guidance suggests that a shallow layer of modified Gulf moisture will be in place in advance of the deepening mid-level trough and a sharpening cold front. This front is progged to sweep eastward into the MS valley Wednesday afternoon and across our region late Wednesday night/early Thursday morning. Weighing the impacts of the shallow layer of moisture against strength of low- level convergence along the intensifying front argues that a narrow line of fast-moving, low-topped showers is the most likely scenario for this event. Colder/drier air will rush into the region later Thursday morning, although based on properties of the airmass temperatures will certainly not be as cold as they could be this time of year. A period of strong northwest flow aloft is expected from Thursday night into Friday, as the broader longwave trough amplifies and shifts slowly eastward across the eastern CONUS. The next system of interest will be a southern stream vort max, which will eject across the southern Rockies/Plains early next weekend as the remnants of a cutoff low west of Baja at the beginning of the extended period. A rapid increase in mid-high cloud cover is expected by Saturday morning as warm/moist advection regime begins atop lingering cold air at the surface. Precipitation should begin to overspread the region from west-to east Saturday afternoon, and may begin as sleet if forecast soundings are correct in their depiction of the wet bulb temp profile. && .AVIATION...(For the 00Z TAFS through 00Z Sunday evening) Issued at 546 PM CST Sat Dec 24 2016 A frontal boundary should remain north of the region into the overnight. Showers moving along this boundary should also remain north of the area. Thus with lower rain chances, clouds should decrease somewhat tonight. The more clear skies, light winds and plenty of lower level moisture could set the stage for the formation of fog, with visibilities falling below one mile at times. Even lower VIS mins cannot be ruled out; will address that in the next TAF. Light SE winds this evening and in the late night should increase to around 10kt during Christmas Day, along with very warm temperatures - rising into the mid 70s to near 80. Daytime heating and mixing should dissipate fog shortly after sunrise Sunday morning. && .HUN WATCHES/WARNINGS/ADVISORIES... AL...NONE. TN...NONE. && $$ NEAR TERM...RSB SHORT TERM...SL.77 LONG TERM...70/DD AVIATION...RSB For more information please visit our website at
Area Forecast Discussion...UPDATED
National Weather Service Jacksonville FL
924 PM EST Sat Dec 24 2016 .UPDATE... FOG IS RAPIDLY FORMING ACROSS NORTH FLORIDA AND SOUTHEAST GEORGIA. BASED ON SEVERAL STATIONS GOING DOWN TO 1/2 MILE AND BELOW ALONG WITH SOUNDING AND MODEL GUIDANCE INDICATING THE FOG WILL BECOME WIDESPREAD OVERNIGHT HAVE DECIDED TO PULL THE TRIGGER ON A DENSE FOG ADVISORY FOR PORTIONS OF THE AREA. WITH PEOPLE TRAVELING FOR THE HOLIDAY FELT IT WAS MORE PRUDENT TO BE PROACTIVE WITH THE ADVISORY THAN TO WAIT UNTIL CLOSER TO MIDNIGHT. && .AVIATION...Another round of low CIGs and dense fog expected to develop inland...with fog likely not as widespread along coast. Although HRRR is backing off on dense fog forecast...other model guidance supporting dense fog. Conditions seem favorable for fog to develop during the 03-05z...with areas of dense fog 05z thru dawn. Have shown this trend in latest TAFs. Expect fog and very low CIGs to gradually diminish 13-15z...but guidance suggests some MVFR CIGs could spread inland over ne FL from the east and affect FL TAF sites. Have included a BKN025-030 late morning and afternoon at all sites except KSSI which may be north of the clouds...and KGNV where clouds may be more scattered in nature. && .MARINE...a few very light showers or light rain offshore from Ponte Vedra Beach southward this evening. With the surface ridge being reinforced tomorrow the onshore flow of 10 knots will increase to 15 knots with seas still 3-6 ft. We should hold on to Small Craft Exercise Caution for the offshore portion due to seas through Monday. Rip Currents: Moderate Risk of Rip Currents continues in the onshore flow and lingering long period swells. && .PRELIMINARY POINT TEMPS/POPS... AMG 52 76 58 73 / 0 0 10 10 SSI 57 70 61 69 / 0 0 10 30 JAX 55 76 63 75 / 0 10 10 20 SGJ 61 75 65 75 / 10 20 20 20 GNV 58 80 63 80 / 0 10 10 20 OCF 61 81 64 81 / 0 20 10 20 && .JAX WATCHES/WARNINGS/ADVISORIES... FL...Dense Fog Advisory until 9 AM EST Sunday for Baker-Bradford-Clay- Coastal Duval-Coastal Nassau-Columbia-Hamilton-Inland Duval- Inland Nassau-St. Johns-Suwannee-Union. GA...Dense Fog Advisory until 9 AM EST Sunday for Appling-Atkinson- Bacon-Brantley-Charlton-Clinch-Coastal Camden-Coastal Glynn- Coffee-Echols-Inland Camden-Inland Glynn-Jeff Davis-Pierce- Ware-Wayne. AM...None. && $$ Sandrik
Area Forecast Discussion
National Weather Service North Platte NE
641 PM CST Sat Dec 24 2016 .SHORT TERM...(This evening through Sunday) Issued at 331 PM CST Sat Dec 24 2016 The trend of the system continues to be west which indicates lesser snow impacts for the cwa on Christmas. That being said, freezing rain and/or drizzle and fog will be a concern tonight for much of the forecast area. In addition, our far northwest will still see measurable snow that will be buffeted by strong winds during the afternoon hours on Christmas. The lesser snow is a problem for our current Winter storm warning, if one only considers criteria. The models continue to be at odds with the lower tropospheric thermal profiles. A degree or two would make a huge difference in how much snow is actually realized. That being said, the NAM was deemed too cool, thus the ever important temperature forecast was trended toward the warmer MAV guidance with a bit of BC data thrown in to account for the snow field across northwest Nebraska. This warmed our temperatures slightly /1-2F/. Because of this, snow amounts across the Warning area were lowered noticeably. As the forecast sits now, only the Pine Ridge of far northwest Sheridan county comes close to reaching Winter Storm Warning snow criteria. We considered this, but will keep the WSW going from 09z tonight to 06z Monday for both zones. Notice the start time was upped for the Warning as bufkit soundings across nw Nebraska reveal sub-zero deep saturation in the low levels but no saturation in the DGZ overnight tonight. Ice accumulations may not be all that heavy, but accumulate to at least a few hundreths of an inch. The WSW was also retained for the wind and snow threat that comes later in the day. The latest projections show height rises of 5mb per hour at times across nw Nebraska with the latest momentum xfer reaching 40kts by mid afternoon. Any snow that has fallen or is falling would create near white out conditions across northwest Nebraska. The freezing drizzle and/or freezing rain threat with the potential of a late afternoon change over to snow prompted us to include eastern Cherry and Keya Paha counties in a Winter Weather Advisory. The advisory will parallel the start and end time of the Winter Storm Warning. The precipitation initially is a product of deep upglide on the 285- 300k surfaces with the WCB pumping anomalously deep warm moisture into the region. As the system matures and closes a low over northeast Colorado/Nebraska Panhandle a TROWAL signature sets up and becomes the primary focus of qpf for northwest Nebraska especially as the WCB and upglide focuses east toward the mid-Missouri Valley. The TROWAL will shift northeast with the precipitation ending from southwest to north through the afternoon. Note that we fully expect freezing ptypes tonight, with a change over to rain or thunder during the day on Christmas, then a changeover to snow as the cool air is pulled into the system. South of the winter weather headlines we fully anticipate some hazards whether from dense fog or drizzle/freezing drizzle. The latest projections continue to indicate rapid saturation below the DGZ. Temperatures should be coldest before midnight tonight, but remain below 0C for a few hours thereafter when the drizzle begins. Soundings over north central Nebraska indicate moderate freezing drizzle or even some freezing rain. The warm sector is anomalously strong and we feel that temperatures will warm rather quickly as the modified Gulf moisture races north across the cwa, thus light ice accumulations, but this will be watched with the possibility of a short-fused headline. With that, a dense fog advisory may be needed and rather than issue one now, we felt it was best to hold off and see if the thermal profiles are slow to warm, if so then a freezing precip headline would be required. As for the convective threat, the steady fetch of moisture will create some instability in the lowest levels /sub 3km/ of the troposphere. CAPE is weak, generally less than 100 j/kg, but shear is through the roof. 0-1 km shear late morning and early afternoon at KBBW approaches 40kts with SRH values of greater than 500. Luckily cool sfc temperatures and the relatively stable BL should keep any convection at bay or elevated. We will keep a mention of isolated thunder going for the elevated threat. The best chances of thunderstorms will be east of a KIML to KANW line Christmas morning and early afternoon, however a few rumbles of thunder are not out of the question across northwest Nebraska. A dry slot will provide for the clearing from southwest to north on Christmas. Winds though will become strong. As the forecast sits, wind gusts in excess of 30 mph will buffet the entire cwa, with gusts to 40 mph possible by late afternoon .LONG TERM...(Sunday night through Saturday) Issued at 331 PM CST Sat Dec 24 2016 Sunday night through Saturday...the model consensus has sped up the speed of the powerhouse storm lifting through Wrn Nebraska and the Nrn Plains Sunday and Monday. It is now forecast to move at 35 mph which is very fast. WPC suggested not using the NAM because it only depends the sfc low to around 992mb which the ECM and GFS deepen to around 982mb. The GFS is also slower than the ECM and NAM. The GFS forecast wind speeds 20 mph stronger than NAM Sunday night and 10 mph stronger than the ECM. This is the result of different mixing processes in these models. The GFS is known to mix deeply and the NAM does not. There is an excellent opportunity for high winds as the cold front moves through Sunday night. The very fast storm motion and nocturnal timing favor sporadic high winds versus a prolonged event which would occur with a slower storm motion. The NAM and GFS`s 70-75kt winds at h800-h700mb would support a high wind event if mixing reaches those levels. The NAM limits mixing to around 875mb while the GFS mixes to 850mb. All models show the corridor of strongest winds in different locations. The 12z and 18z NAM showed them briefly across Swrn Neb Sunday aftn which redevelop across Sheridan and Cherry Counties Sunday night. The GFS also suggests high winds Sunday night across Cherry and Sheridan County while the ECM suggested the Central Sandhills Sunday night. Later forecasts will address this feature more closely and for this forecast we ramp up wind speeds to 35 to near 40 mph across Nrn Neb with gusts of 55 mph. Lesser speeds are expected across Swrn Neb. A blend of the GFS and NAM produce high winds across Sheridan and Cherry Counties but this is at 06z Sunday night which may not verify. Just to note the HRRR experimental is available to 22z Sunday and it shows a belt of high winds swinging through the Wrn Panhandle. If this trend continues then a high wind warning would likely be needed. Snow should end across Sheridan and Wrn Cherry Counties Sunday evening. The latest model blend suggested around an inch accumulation which is a bit heavier than the previous forecast. The very fast motion of this storm does not favor significant wrap around except around the Black Hills but this is not shown to occur...too dry. A blend of guidance plus bias correction produces lows in the single digits Monday morning. With wind speeds still elevated...wind chill reading fall to the single digits above and below zero. Temperatures moderate Tuesday and Wednesday. A strong Pacific cold front moves through Thursday cooling highs a few degrees. A stronger more arctic cold front is expected Saturday which could produce some snow showers across Sheridan and Wrn Cherry Counties as a result of convergence around the Black Hills. Otherwise the forecast is dry. && .AVIATION...(For the 00Z TAFS through 00Z Sunday evening) Issued at 630 PM CST Sat Dec 24 2016 A complex weather situation over the next 24 hours. The main concerns are freezing precipitation potential, thunderstorm chances, winds, and flight categories in the TAF period. Below normal confidence continues with respect to precipitation type forecast as differences in thermal profiles continue to be present in the lower troposphere. Latest satellite imagery shows stratus/fog currently present across eastern NEB with clear skies elsewhere. Latest surface plot confirms a mix of visibilities being reported between IFR and LIFR across eastern NEB with ceilings largely LIFR. Stratus/fog continues to advance westward. Stratus/fog is expected to enter the eastern part of the local forecast area between 9 and 10 PM CST based on trends and hi-res guidance. Fog/stratus is expected to advance westward before midnight east of US-83. Elsewhere, VFR conditions should prevail along and west of US-83, after that time fog/stratus will advance across the remainder of western NEB. Overnight, a mix of freezing precipitation, either light freezing rain or freezing drizzle, will be possible. However, warm air will begin to be ushered into south central NEB and spread northward early Sunday causing a change from freezing precipitation to drizzle or just rain. Timing continues to be a challenge and will need to be refined, however, current thinking is threat will diminish slowly south to north by early-mid morning. A changeover to snow is then anticipated across northwest NEB as the system develops and the surface low moves into western NEB wherein snow accumulations are expected. Elsewhere outside of northwest NEB, rain is expected with the potential for isolated thunderstorms in the afternoon. VCTS has been included at this time at the KLBF terminal but no thunderstorms are expected at KVTN. Precipitation across the remainder of the eastern NEB Panhandle and portions of western NEB can then expect a changeover to snow mid-late afternoon. Strong winds are expected to develop tomorrow afternoon as the surface low moves into northern nebraska wherein gusts exceeding 30-40 kts are likely. Confidence in winds is higher than precipitation type presently. && .LBF WATCHES/WARNINGS/ADVISORIES... Winter Storm Warning from 3 AM CST /2 AM MST/ Sunday to 6 AM CST /5 AM MST/ Monday for NEZ004-094. Winter Weather Advisory from 3 AM CST /2 AM MST/ Sunday to 6 AM CST /5 AM MST/ Monday for NEZ005-006. && $$ SHORT TERM...Jacobs LONG TERM...CDC AVIATION...ET
Area Forecast Discussion
National Weather Service Memphis TN
922 PM CST Sat Dec 24 2016 .UPDATE... At 9 PM CST... Light showers are still ongoing, now primarily just west of the Mississippi River, and along a frontal boundary that extends from near Memphis northeast to middle Tennessee. This feature will gradually move north as a warm front tonight, with dense fog becoming an issue across the northern third of the FA, prompting the earlier issuance of a Dense Fog Advisory. Current temperatures across north Mississippi are still in the low 60s, and have such bumped up lows tonight by a couple of degrees. Also slightly adjusted Christmas Day highs upward. Otherwise, no other updates are necessary at this time. ZDM && .PREV DISCUSSION... /issued 246 PM CST Sat Dec 24 2016/ DISCUSSION... Active/unsettled pattern will continue across the Mid-South through much of the next week. The best chances for precipitation will be tonight, Monday afternoon through Tuesday afternoon, and possibly mid-week. Colder air will move in late in the week, before another system approaches next weekend. Tonight-Sunday...surface front over the CWA will slowly lift north tonight as large storm system develops over the western U.S. Associated precip band should become more scattered into the evening and lift north as well. Will keep chance POPs going overnight, especially over northern portions of the CWA. May see areas of fog along and just north of the frontal boundary so will include in the forecast and HWO, and increasing moisture may lead to patchy fog south of boundary as well. Mild/warm conditions are expected Sunday with breezy southeast/southerly surface flow. Sunday Night-Tuesday...large storm system will lift northeast through the central/northern plains. While the vast bulk of lift/dynamics will remain northwest of our CWA, the trailing front will move slowly through the area. Expect warm advection showers, possibly some thunder depending on the instability, Sunday night/early Monday. Showers/thunder moving into the northwest CWA in earnest Monday afternoon, and exiting the southeast CWA Tuesday afternoon. Wednesday-Saturday...disagreement exists between GFS/ECMWF on mid-week system, with ECMWF farther south and wetter while GFS takes system more across the upper Midwest/Great Lakes. Will keep modest POPs in due to uncertainty but confidence in precip is not high. This system will tap colder air and bring a stronger front through on Thursday. Temps will cool but only to near seasonal normals. Surface ridge will hold on through Friday keeping cooler temps in the CWA. Ridge should move east, and southerly flow (and POPs) will return to CWA by next weekend as the next system approaches. GW && .AVIATION... 00Z TAFs 23Z surface analysis showed a stationary front oriented along an MEM-MKL line. LIFR CIGs prevailed near the front, which will remain nearly stationary through the evening. Shortly after 06Z, the front will lift north as warm front, bringing VLIFR potential to JBR toward daybreak, while conditions should improve slightly at MEM and MKL. TUP a little more problematic. Both NAM Bufr and RUC forecast soundings show a potential for late evening IFR, pending the clearing out of midlevel CIGS. Deepening mixing will occur Sunday, as low level pressure gradient tightens with the approach of a deep midlevel trof over the plains. Expect improvement to VFR by midday to early afternoon for most Midsouth terminals. PWB && .MEG WATCHES/WARNINGS/ADVISORIES... AR...Dense Fog Advisory until 9 AM CST Sunday for Clay-Craighead- Greene-Lawrence-Mississippi-Poinsett-Randolph. MO...Dense Fog Advisory until 9 AM CST Sunday for Dunklin-Pemiscot. MS...None. TN...Dense Fog Advisory until 9 AM CST Sunday for Benton TN-Carroll- Crockett-Decatur-Dyer-Gibson-Haywood-Henderson-Henry-Lake- Lauderdale-Madison-Obion-Tipton-Weakley. && $$
Area Forecast Discussion
National Weather Service Twin Cities/Chanhassen MN
803 PM CST Sat Dec 24 2016 .SHORT TERM...(This evening through Sunday) Issued at 404 PM CST Sat Dec 24 2016 Model solutions remained on track today with driving a deepening low pressure system over eastern CO Sunday morning to far northern MN by Monday morning. The only real change seen over the past several runs is a little bit of a slowing trend on the heavier precipitation moving northeast across our FA on Sunday. This is about a three hour difference. This is actually good as it should allow surface temperatures to rise some before the heavier precipitation moves in and should keep the icing down in the Twin Cities. More about this later. But first, we have to deal with dense fog overnight across south central into west central MN. There was some improvement today around Albert Lea but further west and south the fog has held. The HRRR visibility grids have had a good handle on this and suggest it will be until late this evening before it pushes west of our area. Hence, we extended the dense fog advisory once more for the the southwest FA until 06z tonight. As the evening progress, the depth of the low level moisture will increase along with increasing southeast wind. Mid/upper level ridging over the area will move away allowing for minor ripples in the southwest flow to spread northeast. The forcing is rather subtle but we should start seeing light freezing drizzle break out during the overnight hours and continue Sunday morning. Because of the continued model slowing, the deep forcing and heavier QPF really doesn`t push into southwest MN until late in the morning, reach central MN and the Twin in the early afternoon and then west central WI during the late afternoon. The main concern is how fast temperatures rise above freezing. The GEFS plume data remains solid on forecasting sites around the FA rising a few degrees above freezing during the afternoon with temperatures continuing to climb into the lower and middle 40s during the evening. After all the work in the gridded data base was completed, we still ended up with around a quarter inch of ice accumulation in central MN where the ice storm warning is in effect. Ice accumulation to the west and south of the Twin Cities ranged from 0.10 to 0.15 inches, which seems plausible since it will be coldest there when the precipitation moves in during the morning. From the Twin Cities on north and east the ice accumulation ended up being less than a tenth of an inch. Therefore the advisory and warning headlines locations and times remain unchanged. We did note today that backward trajectory forecasts for the Twin Cities valid during the day on Sunday show the air is coming from around SE WI and across Lake Michigan in SW lower MI. This is an area where low level temperatures are well above freezing and this should bode well on our temperatures rising as the day progresses. So, after the first batch of precipitation moves through in the late morning and early afternoon, there will be a little bit of a lull. Then, the CAMS continue to show a broken line of showers and thunderstorms developing ahead of the dry line/cold front across southwest MN during the late afternoon and then pushing northeast across the Twin Cities...southeast MN and west central WI during the evening. Certainly quite the day ahead tomorrow with ice in the morning and possible thunderstorms in the afternoon and evening. We are still seeing PW values around 1 inch working across our FA late tomorrow afternoon and evening. Hence, some of that rain may be briefly heavy when the showers move through. This PW values is outside the GEFS climate return interval...6 standard deviations above normal. This is also above any December MPX UA PW measured from 1948 to present. Again, this testifies to the abnormal day ahead weatherwise on Christmas! .LONG TERM...(Sunday night through Saturday) Issued at 404 PM CST Sat Dec 24 2016 From Sunday night onward the only real items of concern are in the Sunday night and Monday periods, with pretty benign conditions for the remainder of the period. On the large scale, we`ll see fairly zonal westerly flow for most of the period once Sunday`s system gets out of our hair. There is a weak short wave trough expected to move through around midweek, then another short wave trough dropping in from the north at the end of the period as the heart of the cold air to our north tries to get a bit closer. For Sunday night, we`ll see temperatures rising during the evening hours, with readings likely getting above 40 over portions of the south and east before the cold front moves through. A few thunderstorms, still cannot be ruled out, mainly south of I-94 and east of I-35 during the early evening hours. Given the strength of the flow aloft, these could bring some good gusts down to the surface, so yet another thing to watch. In terms of precip-types, most of the area should be just rain by Sunday evening, with best chances of precipitation over the north and east after 9 PM or so. The cold front will sweep east overnight into Monday morning, with any lingering precipitation changing back into snow, although most looks to be north of us by late Sunday night and Monday. Although forecast soundings this morning are not as bullish with winds behind the front late Sunday night and Monday morning, it still looks like 40-50 kt will be present in the mixed layer, particularly across the west and southwest. So, later shifts may need to consider a wind advisory for a good portion of the area overnight Sunday night into Monday. However, given the uncertainty and inconsistency in the solutions, wind warning criteria could still be met for some locations out west for a period of time depending on how well the isallobaric and gradient components work together with mixing. The next chance for precipitation, in the form of light snow, will come on Wednesday as the aforementioned short wave trough moves through, although the forcing with that looks to be mainly north of us. The other short wave trough on Saturday looks like it should bring a slightly better chance of some snow to the area, although nothing too significant given lack of decent moisture return ahead of it. It does look, however, to bring a good short of cold air for the second part of the weekend. Temperature-wise, readings look to be near or slightly above normal for the week. && .AVIATION...(For the 00Z TAFS through 00Z Sunday evening) Issued at 743 PM CST Sat Dec 24 2016 Freezing drizzle and low ceilings will be the biggest concern late tonight at the TAF sites. IFR conditions are expected. The main band of moderate rain/sleet moves in late in the morning in western MN and tracks east across the rest of the TAF sites in eastern MN and western WI during the afternoon. The winds will start gusting near 30kts around when the heavier precipiation arrives. KMSP... The biggest concern over the next 6-12 hours is the potential for freezing drizzle early in the morning with temperatures around 32 degrees. We think the temperatures will rise above freezing by late morning with IFR conditions mist/drizzle continuing until the heavier rain/sleet arrives in the afternoon. Sleet will likely only mix in with the rain for a couple hours before going completely over to rain. It`s entirely possible the airport remains between 32-34 for the rest of the night and the drizzle doesn`t really freeze on contact. /OUTLOOK FOR KMSP/ Mon...MVFR and windy. Wind W at 25G35kt. Tue...VFR. Wind WSW at 5-10kt. && .MPX WATCHES/WARNINGS/ADVISORIES... WI...Freezing Rain Advisory from 9 AM to 3 PM CST Sunday for WIZ014>016-023>028. MN...Freezing Rain Advisory from 6 AM to 3 PM CST Sunday for MNZ054>058-064>067-073>076-082>085-091>093. Ice Storm Warning from 9 AM to 6 PM CST Sunday for MNZ041>043- 047>049. Freezing Rain Advisory from 9 AM to 3 PM CST Sunday for MNZ044- 045-050>053-059>063-068>070-077-078. Dense Fog Advisory until midnight CST tonight for MNZ073-074-082- 083-091-092. && $$ SHORT TERM...RAH LONG TERM... AVIATION...CLF
Area Forecast Discussion
National Weather Service Phoenix AZ
801 PM MST Sat Dec 24 2016 .SYNOPSIS... A strong weather system will clear most of the region tonight, but not before dropping a few more valley rain showers and mountain snow. Locally windy conditions and much cooler temperatures will also be common across the area. Conditions will dry by Sunday with temperatures hovering below average through Monday. Slightly above normal temperatures will return Tuesday and continue through much of the week. && .DISCUSSION... Vigorous main part of strong trough has passed through the Phoenix metro area with a strong push of cold air behind it. Some remnant lines of showers remain along northern Maricopa County, extreme southwest Maricopa County, and across the higher terrain of southern Gila County and northeast Pinal County. Temperatures have been on the decline as cold air is pushed in from the north. Most of the CWA is in the 40s now with the exception being the low 50s in southwest Arizona and southern Imperial County and the 30s up in Gila County. Rainfall amounts have ranged from 0.10" in southeast California, 0.15" to 0.50" in the Phoenix area, to nearly 1" in northeast Maricopa County. For the remainder of the evening we can expect a few more pockets of showers through the middle of the night. Most notably the HRRR is indicating one band to form in southwest Maricopa County around 06Z and move through the Phoenix area through 09Z. So, will keep a chance of showers for the area. That should be the last significant chance for precip from this system as moisture levels will drop, yielding fair weather for Christmas Day for the lower deserts. Moisture and a chance for rain and snow showers will linger for the higher terrain of southern Gila County through 12Z tonight. By morning the cloud cover should be minimal. Temperatures Sunday will be well below normals and some spots will drop into the mid to upper 30s for Sunday night with the weaker wind flow and lack of cloud cover allowing for more radiational cooling. Fog will also be possible in a few outlying valley locations Monday morning. The period from Monday through Wednesday should be quiet with zonal wind flow and weak ridging helping to inch temperatures up above normal levels. By late Thursday into Friday we will see the next weather system affecting the region with cooler temperatures, chance for rain, and breezy conditions. The ECMWF develops that system into a cutoff low over central Arizona whereas the GFS shows more of a trough affecting northern Arizona more. So, this could give us one more chance to add to the year`s total rainfall amounts. .PREVIOUS DISCUSSION... A deep PV anomaly swinging through the Los Angeles basin was beginning to translate into SE CA with a classic satellite appearance of cold cloud tops and distinct upper divergent signature. Within the region of greatest CAA aloft and closest to the basal jet core, mountain waves and synoptically forced strong winds will impact parts of Imperial County through this evening. The wind advisory in this area still looks appropriate. Meanwhile, a sfc front has surged through western Arizona during the late morning/early afternoon hours and 30-40kt H8 LLJ winds have finally been tapped in the warm sector ahead of this boundary. Despite recent rainfall, these wind gusts has been sufficient to pick up dust from barren fields and transport marginally dense blowing dust downstream into the eastern parts of the Phoenix metro. However, the rapidly advancing sfc front and line of showers will essentially eliminate any further dust threat and the blowing dust advisory was allowed to expire at 2 pm MST. Otherwise, ML/MUCapes were quickly waning, though strong frontogentical and vorticity forced ascent could still support a brief isolated embedded thunderstorm into the late afternoon. Heading into the evening, travel concerns over higher terrain locations will be most paramount. Local KIWA radar dual polarization data showed melting layers west of the Phoenix metro plummeting from around 6000 feet to 3500 feet rapidly behind the frontal boundary, and this trend will continue eastward into Gila county. Although the intensity of the precipitation will drop off rather dramatically behind the front, deep layer southwesterly flow will remain favorable for orographic lift across much of Gila County. Although the thermal profiles and SLR`s will change quite variably across the area, preliminary QPF will support accumulations of 3 to 6 inches above 5000 feet before moisture is scoured from the -15C dendritic layer later Sunday morning. At slightly lower elevations, precipitation will change over to snow later in the night down to a 3000-3500 feet level; and a dusting to an inch of snow is possible in and around the Globe area through late Sunday morning. While some light snow/flurries will linger across the eastern portions of southern Gila County and the White Mountains, across the lower deserts a drier more subsident pattern will develop late tonight as the aforementioned trough becomes more negatively tilted and lifts into the northern Plains (creating blizzard conditions there). Despite the decrease in clouds, temperatures will languish roughly 10 to 15 degrees below average Sunday afternoon. The forecast high temperature in Phoenix of 55 degrees would be the coolest day since February 2nd. Latest operational GFS and ECMWF have come into somewhat better agreement for next week. Both models depict another Pacific trough cutting off, but remaining well west of the Baja Peninsula through much of the weak. Further eastward a weak ridge will build across the Desert Southwest, resulting in height rises and a return to slightly above normal temperatures through much of the week. The aforementioned cutoff will likely migrate eastward late in the week. However, there is still considerable uncertainty with regard to how much moisture will be transported into the region. Latest model consensus yields PoPs between 10 and 20 percent Friday/Saturday, though this system bears watching. && .AVIATION... South-Central Arizona including KPHX, KIWA, and KSDL: Somewhat reduced ceilings, some lingering showers, and occasional wind gusts will be the major aviation weather concerns into the early evening hours. The ceilings look to hang around the 5K foot mark, but may lift a little higher overnight. The lowest ceilings will bank against the mountains north and east of KPHX as most of the shower activity should be well east of Phoenix by 01Z. The wind gusts will settle down through the late afternoon/early evening but winds look to stay westerly at 10 kts through the overnight. Otherwise, there should be few, if any, aviation weather concerns by tomorrow late morning as all the shower activity will be gone and ceilings lift above 10k feet. Southeast California/Southwest Arizona including KIPL and KBLH: The major aviation weather concern through tonight will be strong westerly gusts 30 to 40 mph with speeds decreasing by midnight. Otherwise, only a few passing clouds will impact SE CA terminal sites. Aviation discussion not updated for amended TAFs. && .FIRE WEATHER... Monday through Friday: Modest drying conditions and warming temperatures are expected into the middle of next week as highs reach to slightly above normal starting Tuesday. Minimum humidities decrease through Tuesday, but overall remain somewhat high through the week, mostly between 25 and 35 percent for the deserts. A potential weather system for late in the week may bring a return of precipitation and increasing humidities. Winds will overall be light, but some breeziness down the Lower Colorado River is likely on most days. && .SPOTTER INFORMATION STATEMENT... Spotter activation is not expected this week. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...Winter Weather Advisory until 8 AM MST Sunday for AZZ024. CA...None. && $$ Visit us on Facebook...Twitter...and at DISCUSSION...Waters/MO AVIATION...Deemer FIRE WEATHER...Kuhlman
Area Forecast Discussion For Western SD and Northeastern WY
National Weather Service Rapid City SD
904 PM MST Sat Dec 24 2016 .UPDATE... Issued at 845 PM MST Sat Dec 24 2016 Current surface map shows low deepening across southern Wyoming/northern Colorado. Water vapor imagery has strong wave across northern Arizona. Latest NAM/HRRR/RAP/GFS runs coming in this evening indicate some uncertainty to current forecast, especially transition zone from heavy snow to freezing rain/sleet/rain. Appears latest runs have shifted a bit further west, with RAP showing potential for freezing rain as far west as Rapid City. This would mean lower snowfall totals along eastern edge of blizzard warning, but increased impact from freezing rain and high winds. Strong inversion setting up across the area tonight with northeast-east boundary layer flow due to 1040mb high centered over Manitoba. Eastern extent of freezing rain will be determined by how warm surface temperatures can get under this strong inversion. Some elevated CAPE across far western South Dakota in the morning/early afternoon could result in some thundersnow with intense snowfall rates. One other note about the blizzard warning. Even though the blizzard warning starts in the morning, widespread blizzard conditions not expected until early afternoon. However, heavy snowfall and/or freezing rain before the winds increase will cause significant travel problems. Minor adjustments to forecast at this time. && .SHORT TERM...(This Evening Through Sunday Night) Issued at 157 PM MST Sat Dec 24 2016 Upper level analysis has deep trof digging into the western CONUS with strong shortwave just lifting out of the base of the trof across Arizona and Utah. Across the Northern Plains, cirrus is beginning to invade Northeast WY and western SD. Low stratus deck has pushed into northwest SD. At the surface, arctic cold front has dropped south through much of the area. Winds have shifted to the east and northeast generally north of I-90. Mild temperatures and southerly winds are holding out across far southern SD and much of Northeast WY. Developing storm system to the west will bring a wide variety of weather to the region late tonight through early Monday. Model runs have not changed much, so only minor adjustments made to the forecast for most areas. Warnings and advisories have now been issued for all areas, with Tripp County added to the Winter Weather Advisory in south central SD for some light ice accumulations Sunday morning. For tonight...Strong upper level storm system crosses the Rockies. Ahead of the storm, low stratus clouds will continue to back into the Black Hills area behind the arctic front this evening. Forecast soundings show potential for at least some patchy areas of fog and freezing drizzle tonight across the SD plains and foothills of the Black Hills. Areas of light snow could develop late tonight, especially over Northeast WY and northwestern SD. Sunday...Snow will develop in earnest Sunday morning across northeast WY and much of western SD as low pressure wraps up over northeast CO and moves rapidly northeastward. Strong energy wrapping around the low will allow more intense precipitation to develop by mid to late morning, with snow moderate to heavy at times through the afternoon. There will at least be a narrow band of mixed pcpn and freezing rain over portions of west central into southwest SD in the morning and early afternoon before colder air wraps in. Temps will warm above freezing across south central SD during the morning as the low tracks to the west of that area, with mostly rain into the afternoon and a thunderstorm or two not out of the question. Still, ground temperatures will remain at or just below freezing during the morning hours, so some light ice accumulation will be possible across far south central SD. Surface temperatures should warm by mid day with icing threat diminishing by afternoon. Precipitation will taper off generally from south to north across the CWA Sunday night. Winds will begin to increase late Sunday morning, with strong northwest winds developing by mid to late afternoon in most areas as the low moves quickly east and north of the area. Significant blowing and drifting of snow is expected over the blizzard warning area, with travel becoming very difficult or impossible. The strong winds will continue through much of Sunday night before gradually decreasing Monday morning. Snowfall amounts across a good portion of northeast WY and western SD will be in the 4 to 7 inch range, with amounts up to 10 inches or more possible over portions of northwest SD, especially in the Lemmon and Dupree areas. Snowfall will be more limited toward south central SD, but strong winds Sunday night will cause vsby issues with any snow that falls. .LONG TERM...(Monday Through Saturday) Issued at 157 PM MST Sat Dec 24 2016 Snow will move from northwestern SD by Mon morning as storm moves into northern MN. Gusty winds will continue with momentum transfer of more than 30kt into early afternoon, with widespread blowing snow diminishing through the day. Temperatures will begin to warm Tues as lee trof forms over eastern MT and surface high builds over Great Basin. Next upper trof crosses the northern Plains Wed will be mainly dry for the forecast area, but will bring cooler temperatures with cyclonic NW flow. Another system deepens over the northern Rockies toward the end of the week, with precipitation spreading across the area. && .AVIATION...(For the 00Z TAFS Through 00Z Sunday Evening) Issued At 411 PM MST Sat Dec 24 2016 IFR/LIFR ceilings and fog will continue to move slowly south across western South Dakota this evening, and will cover much of the area late by late tonight. The lowest ceiling and visibility will be around the Black Hills. Some -FZDZ is also possible overnight. Snow will move into the area early Sunday morning, with heavy snow across northeast Wyoming and far western South Dakota into Sunday afternoon. The transition from snow to freezing rain and rain will setup across south central South Dakota on Sunday. Northwest winds will increase through the day, with very strong winds across western south Dakota Sunday afternoon. This will result in widespread LIFR visibilty in blizzard conditions. && .UNR WATCHES/WARNINGS/ADVISORIES... SD...Winter Storm Warning from 6 AM Sunday to noon MST Monday for SDZ024-028. Winter Storm Warning from 6 AM Sunday to 5 AM MST Monday for SDZ027-029-041-044. Winter Weather Advisory from 6 AM Sunday to 6 AM CST Monday for SDZ046-047-049. Blizzard Warning from 6 AM Sunday to noon MST Monday for SDZ001- 002-012>014-025-026-030>032-042-043-072>074. WY...Winter Storm Warning from 6 AM Sunday to noon MST Monday for WYZ057. Winter Storm Warning from 6 AM Sunday to 5 AM MST Monday for WYZ054-056-058. Blizzard Warning from 6 AM Sunday to noon MST Monday for WYZ071. Winter Weather Advisory from 6 AM Sunday to midnight MST Sunday night for WYZ055. && $$ Update...7 SHORT TERM...15 LONG TERM...55 AVIATION...7