Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/19/17

Area Forecast Discussion...Updated
National Weather Service Billings MT
850 PM MST Mon Dec 18 2017 .UPDATE... Winds have been slowly decreasing from Livingston to Nye to Big Timber. Have not had warning criteria for quite a while at Livingston, and winds were now safely below advisory criteria. Cold front was pushing south through the forecast area this evening, and winds should continue to decrease. Will cancel the wind highlights. Band of light rain/snow was stretching from around Harlowton to near Ashland, and has been slowly sinking south with the front. Models have not done a very good job at all with the band, as they have it placed way too far north. Latest RAP and GFS have finally caught up with it, and linger this band in the current position through the early overnight hours, then lift it north. Have raised PoPs to account for this. Precipitation has been on the light side within this band, but as the cold air sinks in, could actually see some light accumulations with it, especially over along the northern tier of zones. Have raised snow amounts a bit. TWH && .SHORT TERM...valid for Tue and Wed... Strong winds continue along the western foothills this afternoon with recent gusts to 60 mph being observed at Livingston and Nye. Winds will gradually decrease through the evening as a cold front drops into the area, but will remain somewhat breezy near Livingston and Nye overnight. Have extended the High Wind Warning for the Livingston area and Beartooth foothills through 9pm. The aforementioned cold front will drop south into the area this evening bringing increasing chances for rain/snow, transitioning over to all snow tonight as colder air works into the area. Best chances for precipitation will be over the SW mountains, as well as for areas generally north of a Harlowton to Roundup to Miles City line. A few inches of snow can be expected on south and west facing slopes in the Beartooth/Absaroka mountains overnight, with an inch or less of snow for northern areas, as the best forcing and precipitation chances are across northern Montana. Weak shortwave ridging tries to build into the area on Tuesday with snow showers continuing over the southwest mountains and far northern areas. Surface pressure gradients tighten once again Tuesday evening/night with strong winds possible for the Upper Yellowstone and Upper Stillwater valleys. Will need to monitor for any potential wind highlites. Heading into Wednesday, the next disturbance arrives in the form of a deepening trough and associated upper low. An associated cold front is expected to dive south during the day ushering in colder temperatures along with increasing snow chances. Depending on how quickly we cool across the area, roads may experience some melting snow initially, before freezing and accumulating with snow. Models are somewhat out of phase with the timing of the front, however, there is general agreement on much of the area seeing an inch or two of snow, with better chances for accumulating snow over the foothills and mountains. Will hopefully have a better feel on snow accumulations over the next day or so as models come into better agreement. Winds will increase Wednesday evening and night as a surface low departs the area, bringing the potential for blowing and drifting snow. High temperatures will range from the 30s and 40s for Tuesday and Wednesday. Wednesday`s highs will likely be reached early in the day with temperatures falling throughout the afternoon. Lows in the 20s can be expected tonight and Tuesday night, with temperatures down into the single digits Wednesday night. STP .LONG TERM...valid for Thu...Fri...Sat...Sun...Mon... Did not need to make any large changes to the going extended forecast. Both the GEFS and ECMWF ensembles showed increasing spread with the pattern during the period. Noted that on Monday, the GEFS plumes had temperature spreads around 60 degrees for the forecast area. The deterministic 12Z models were not that different from their previous runs and were actually fairly similar with their forecasts through much of the period. There were some differences in temperature details beginning on Sunday. Still had high confidence in much colder than normal temperatures for most of the period with a good chance of snow Friday into Saturday. Trough moves out of the area on Thursday with snow ending over SE MT by afternoon with little accumulation. Temperatures will reach the teens and 20s. The next system dives SE into the area Thu. night and Friday, ushering in much colder air and snow with the cold front. Chances for snow will spread SE across the area Thu. night and continue across the region on Friday. The best chances for snow will be over the NE and N upslope areas, where at least several inches of snow are expected. Highs will reach only the teens. Chances for snow will decrease through Saturday as the upper trough swings SE of the area. Expect highs in the single digits to teens on Saturday. Windy conditions will create areas of blowing snow Fri. through Saturday. Decent pressure gradient will create windy conditions Sat. night from Harlowton to Big Timber to Livingston. Northerly flow will be over the region on Sunday with drier conditions. Blended guidance kept highs in the single digits to teens. Kept forecast mostly dry through Monday, although ECMWF brought more energy down in the N flow with some QPF. Surface gradient again supported windy conditions in the W Sunday night and Monday. Arthur && .AVIATION... Southwest winds will remain gusty tonight near KLVM and K6S0, but gusts should be near or below 45 kt. Rain and snow showers are expected over areas of southern MT overnight into Tuesday. MVFR CIGS are possible overnight over SE MT. IFR CIGS are expected at BIL overnight into Tuesday and are possible at SHR late tonight into Tuesday morning due to upslope flow in those areas. Mountains will be obscured tonight into Tuesday. RMS && .PRELIMINARY POINT TEMP/POPS... Tue Wed Thu Fri Sat Sun Mon ----------------------------------------------------------- BIL 029/039 029/034 008/025 016/019 005/014 003/017 004/017 62/S 17/S 62/S 34/S 32/S 21/N 11/N LVM 037/045 033/035 010/025 018/018 003/012 002/015 004/020 32/O 16/O 51/U 45/S 32/S 21/N 11/N HDN 026/043 027/037 006/025 015/019 007/016 003/017 001/018 62/S 16/S 72/S 35/S 33/S 32/S 11/B MLS 026/036 023/033 007/021 013/019 006/014 001/014 901/015 62/S 26/S 62/S 23/S 22/S 21/B 11/B 4BQ 026/042 026/041 008/023 011/020 004/015 001/016 901/015 61/E 12/O 73/S 13/S 32/S 31/B 11/B BHK 022/034 021/031 003/017 009/015 002/011 903/009 904/012 41/E 34/S 72/S 23/S 32/S 21/B 11/B SHR 024/043 026/045 009/024 009/020 003/014 000/017 902/019 21/B 13/R 83/S 24/S 32/S 22/S 11/B && .BYZ WATCHES/WARNINGS/ADVISORIES... MT...None. WY...None. && $$
Area Forecast Discussion...UPDATED
National Weather Service Corpus Christi TX
950 PM CST Mon Dec 18 2017 .DISCUSSION... Cleaned up the hourly grids based on latest trends. Main issue remains the fog, especially over inland parts of the area. Vsbys towards the coast have improved a bit, but HRRR does suggest they could lower again this evening/overnight. So for now, the dense fog advisory will remain in effect, but will need to monitor things over the next several hours. && .PREVIOUS DISCUSSION... /Issued 626 PM CST Mon Dec 18 2017/ DISCUSSION... Visibilities crashed quickly across the area within the last hour or so, prompting many changes to the forecast. Numerous observing stations are reporting vsbys less than a mile with a handful at one quarter of a mile or less. As a result, a dense fog advisory was issued for much of the area, and will likely need to expand into Webb/LaSalle counties at some point. In addition, the marine dense fog advisory is also in effect now with many locations along the water at a mile or less. Both headlines will run concurrently through 15z. Complicating factor will be how rain chances evolve. One area should continue to push northeast out of the area within the next hour or two. Another round of showers may move out of Mexico later tonight and impact locations across western parts of the area. This could result in vsbys bouncing around a bit, but overall trends should still support dense fog. Will continue to monitor. Please see 18z aviation section below. AVIATION... IFR/LIFR conditions developed quickly this evening as very low stratus and dense fog blanket much of the area. These conditions should persist for much of the night into Tuesday morning. Rain will be possible at times, but was only confident enough to include VCSH remarks in the forecast. Southerly winds will pick up mid to late morning on Tuesday, which will help vsbys gradually improve. Some gusts between 20 and 25 knots will be possible in the afternoon at ALI/CRP/VCT with lighter winds expected at LRD. Despite the fog mixing out by late morning, low clouds should hang on into the afternoon hours and remain in the IFR/MVFR range. PREVIOUS DISCUSSION... /Issued 350 PM CST Mon Dec 18 2017/ SHORT TERM (Tonight through Tuesday night)... Mixture of stratiform/convective precipitation over the CWA today likely associated with the upper jet streak and isentropic lift/low condensation pressure deficits (300K at least), and the isolated/scattered shower/thunderstorm activity over the MSA linked to the coastal trough. Confident that the upper disturbance/500-mb low will enter TX overnight, with associated synoptic scale lift over the CWA after 12z Tuesday. Expect the coastal trough to move onshore and over the ERN CWA early Tuesday in response to the foregoing upper disturbance. The combination of surface/upper forcing and sufficient moisture will contribute to scattered convection/areas of rainfall Tuesday. With respect to thunderstorms, surface-based activity should be restricted to the ERN CWA near the surface trough Tuesday afternoon. Elevated thunderstorms may occur over the WRN CWA. Drier conditions expected from west to east Tuesday night as the upper system moves east. MARINE (Tonight through Tuesday night)... NAM/GFS/RAP deterministic consistent with the development of onshore flow developing overnight over all of the MSA along with increasing moisture advection. NAM deterministic predicts surface dew points to exceed SST values (per 17 December 2017 1800 UTC SPoRT SST Composite and current select SST values at Port Aransas/Port Lavaca/Baffin Bay) after 06z Tuesday. Issued a dense fog advisory for the bays and nearshore waters for the 06-15z Tuesday period. LONG TERM (Wednesday through Monday)... The sun should finally make an appearance across the area on Wednesday as moisture decreases behind a boundary that pushes through Tuesday night. High temperatures warm into the mid and upper 70s for Wednesday and a bit further Thursday, into the upper 70s and lower 80s. And that`s where the simple part of the forecast ends. Upper level trough will dig into the western US late week, and will bring active weather back to the region. Details of the forecast remain unclear as wild swings continue to occur from run to run, especially with the outlook from Sunday onward. What we do expect at this time... A warm front lifts northward on Thursday bringing an increase in moisture and possibly some showers as early as Thursday afternoon in the east. Marine fog would also become a concern with very warm moist air flowing over the cool nearshore waters and bays. A cold front then follows on Friday bringing a substantial drop in temps, though timing is not clear yet as to whether we have a chance to warm in the morning before the front or not. Behind the front temperatures drop back to the 50s or lower 60s for highs Saturday and lows in the 40s. Will also see a chance for rain Friday, especially in the east where better moisture pooling is. Another stronger front looks to move through at some point between Sunday morning and Tuesday morning with more of an arctic. airmass. Obviously this makes for a tricky holiday forecast. Models have trended a bit earlier with this front, closer to the Sunday time frame, but still too much variation to put much stock into the timing. At this point, going to go with a cool day on Christmas, with just a slight chance of rain in the east. Stay tuned for updates! && .PRELIMINARY POINT TEMPS/POPS... Corpus Christi 63 76 57 75 58 / 40 30 20 10 10 Victoria 62 76 54 73 54 / 50 60 40 10 10 Laredo 59 70 52 75 58 / 40 20 10 0 0 Alice 61 76 55 78 57 / 40 30 10 10 10 Rockport 64 72 59 71 60 / 40 30 30 10 10 Cotulla 57 70 48 76 54 / 50 50 10 0 0 Kingsville 62 78 56 78 58 / 30 20 20 10 10 Navy Corpus 65 73 61 72 62 / 30 20 30 10 10 && .CRP WATCHES/WARNINGS/ADVISORIES... TX...Dense Fog Advisory until 9 AM CST Tuesday For the following zones: Aransas...Bee...Calhoun...Duval...Goliad...Jim Wells...Kleberg...Live Oak...McMullen...Nueces...Refugio... San Patricio...Victoria. GM...Dense Fog Advisory until 9 AM CST Tuesday For the following zones: Bays and Waterways from Baffin Bay to Port Aransas... Bays and Waterways from Port Aransas to Port O`Connor... Coastal waters from Baffin Bay to Port Aransas out 20 NM... Coastal waters from Port Aransas to Matagorda Ship Channel out 20 NM. && $$ TB/78...SHORT TERM
Area Forecast Discussion
National Weather Service Austin/San Antonio TX
620 PM CST Mon Dec 18 2017 .UPDATE... /DENSE FOG ADVISORY ISSUED/ With decreasing precipitation rates forecast by the recent runs of the HRRR for the rest of tonight, the likelihood of an extended period for possible dense fog could continue through the early morning hours. The advisory is now expanded to cover all counties along and SE of an Eagle Pass to Bandera to Burnet line. Only other minor change was to remove thunder from the evening grids for areas generally along/north of I-10. && .AVIATION... /00Z TAFS/ VLIFR CIGs/VSBYs will become more widespread this evening into the overnight. Have these conditions at KAUS, KSAT, KSSF through midday on Tuesday. However, as RA becomes more widespread with ISOLD TSRA late tonight into morning, CIGs/VSBYs may improve slightly and have this mentioned in PROB30s for TSRA from 19/14Z-20Z. Out west at KDRT, CIGs/VSBYs will lower to LIFR, possibly VLIFR overnight as -RA develops there. As drier air filters into our area in wake of the upper level trough mentioned below moves across, RA/TSRA will move off to the east with CIGs/VSBYs becoming VFR, at KDRT early in the afternoon and KAUS, KSAT, KSSF late afternoon into early evening. VRBL winds of 5 KTs will prevail tonight into Tuesday, then become westerly 5 to 10 KTs during the afternoon into evening. && .PREV DISCUSSION... /ISSUED 243 PM CST Mon Dec 18 2017/ SHORT TERM (Tonight through Tuesday Night)... Light winds at the surface and a stout inversion up to 850 mb has kept moisture trapped in the boundary layer all day today with foggy conditions still being reported. With little change expected for the rest of the afternoon and tonight, the fog should remain in place and expand in coverage again through the overnight hours. Temperatures have been kept in check a bit because of this with current values in the middle to upper 50s. A large upper trough axis near the AZ/NM border continues to slowly push east and as it does so widespread forcing for ascent will overspread the region mainly after 06z and will provide a widespread coverage of showers and isolated thunderstorm activity for the eastern two-thirds of the CWA. In the mean-time, ascent in the southwest flow aloft is leading to light rain across the southeastern third of the CWA and points to the southeast this afternoon. The overnight showers and storms will continue to move to the northeast in the morning hours before the bulk of the activity moves out of the CWA around mid-day. Later in the afternoon, the Pacific front associated with the upper low will be moving through the area. This will provide surface focus for convection which will allow for the redevelopment of some shower and thunderstorm activity tomorrow afternoon. There will be continued upper support as the main forcing from the upper low arrives to Texas. The trough will be in the process of transitioning from a positive tilt to becoming negatively tilted which will help increase upward motions. However, the best lift will be in North Texas as the center of the low is progged to move through the Red River Valley. With the aforementioned conditions this should be sufficient enough for some scattered showers and storms are a broken line of convection along the frontal boundary as it moves from west to east tomorrow afternoon. The convective storm environment shows CAPE values around 1000 J/kg and 0-6 km shear values in excess of 60 knots. With this setup, can`t rule out a strong to marginally severe storm across our eastern counties, but the instability looks to to be the limiting factor. In addition, a mid-level dry slot may also help limit convective updrafts. All activity will be east of the region by the evening hours tomorrow. Highs tomorrow will be in the 70s in the southeastern CWA where some heating will occur in the warm-sector ahead of the front and lows Tuesday night will bottom out in the 40s and lower 50s. LONG TERM (Wednesday through Monday)... Wednesday and Thursday will likely be the warmest days of the week behind the Pacific front with highs in the 70s. There could be some warm air advection showers across the Coastal Plains in the afternoon Thursday and will mention a 20 PoP there. On Friday, another large trough axis will push through the Central Conus and another stronger front will arrive to the area Friday morning. A slight chance to chance of showers are expected with the higher PoPs across the eastern counties. Highs Friday will likely be right before the front arrives with temperatures dropping into the 40s and 50s behind it. The pattern will remain progressive and not expecting any precip beyond Friday evening with this system. The ECMWF shows return flow by Saturday ahead of the next reinforcing shot of colder air but the GFS keeps weak north flow in place. Regardless, temperatures on Saturday will likely top out in the 50s. The stronger front arrives Sunday morning and will bring with it a brief chance of showers and a strong bite of cold air. Highs on Christmas Eve will likely struggle to get out of the 40s for most of the area and highs on Christmas Day will likely be in the 30s and lower 40s. Christmas morning will feel like it as well with lows possibly in the 20s and 30s. Have your coats ready this Christmas season. && .PRELIMINARY POINT TEMPS/POPS... Austin Camp Mabry 56 69 49 75 51 / 80 100 30 0 0 Austin Bergstrom Intl Airport 56 70 48 74 49 / 80 100 30 0 0 New Braunfels Muni Airport 56 70 48 75 50 / 80 90 20 0 0 Burnet Muni Airport 55 63 45 72 49 / 60 100 20 0 0 Del Rio Intl Airport 52 69 44 75 49 / 50 30 0 0 0 Georgetown Muni Airport 55 67 48 72 50 / 70 100 30 0 0 Hondo Muni Airport 55 68 44 76 48 / 70 70 10 0 0 San Marcos Muni Airport 56 70 48 74 49 / 80 90 20 0 0 La Grange - Fayette Regional 60 71 52 73 51 / 70 90 70 0 0 San Antonio Intl Airport 57 69 49 75 52 / 80 80 10 0 0 Stinson Muni Airport 57 70 48 75 51 / 80 80 10 0 0 && .EWX WATCHES/WARNINGS/ADVISORIES... Dense Fog Advisory until midnight CST tonight for the following counties: Bastrop...Bexar...Blanco...Burnet...Caldwell...Comal... Guadalupe...Hays...Kendall...Lee...Travis...Williamson. && $$ Mesoscale/Aviation...04 Synoptic/Grids...Oaks Public Service/Data Collection...YB
Area Forecast Discussion
National Weather Service Grand Rapids MI
946 PM EST Mon Dec 18 2017 LATEST UPDATE... Update .SYNOPSIS... Issued at 311 PM EST Mon Dec 18 2017 The mixed precipitation affecting the area earlier will push out of the area by this evening. A good deal of cloud cover will remain, but we will see a gradual clearing of the clouds through Tuesday afternoon. Temperatures will stay mild through Tuesday as many see lows tonight above freezing, and highs on Tuesday well into the 40s. A system well north of the area could clip areas north of I-96 Wednesday night into Thursday. A more significant system is likely to affect the area with multiple precipitation types from Thursday night through Saturday. Much colder air will then filter in over the area over the Christmas weekend. && .UPDATE... Issued at 946 PM EST Mon Dec 18 2017 The overall forecast is on track however it seems the clouds, especially the lower clouds have moved out and due to drier air forecast to come in at low to mid levels. This is shown nicely by time sections in BUFKIT of the GFS, RAP and HRRR models as well as the HRRR layered cloud forecast image in AWIPS and GFE Aviation. It can be seen looking at the IR image loops too. So our forecast now calls for partial clearing overnight. There is enough wind in the boundary layer tonight to keep the air mixed so I do not think less clouds will allow the temperatures to drop significantly more than were in our previous forecast. && .SHORT TERM...(This evening through Wednesday night) Issued at 311 PM EST Mon Dec 18 2017 Fairly quiet weather by December standards expected for the short term. We will be timing out pcpn/cloud cover at the beginning, and then timing in some light snow chances for Wed night. Nothing looks significant through Wed night. The last of the rain in the area extends from near South Haven to Lansing as of 1930z. This is likely at the tail end of the upper wave that is almost through the area. All of the pcpn is occurring where the sfc temps and atmosphere are warm enough for rain. Low clouds shroud the remainder of the area. Some clearing breaks are trying to work their way in from Srn Lake Michigan. The high dew points over the snowpack will resist the clearing initially. The strengthening winds tonight are expected to blow the low clouds out eventually, leaving mainly mid clouds into Tue morning. Models are in good agreement that the area should clear out for Tue afternoon, minus some high clouds. Good mixing with sunshine, and warmer air moving in from the SW should help temps well into the 40s on Tue. Temps will cool down Tue night and Wed as a dry back door cold front drops down Tue evening. Our next chance for precipitation will come Wed night across the nrn half of the area in the form of some light snow. The aforementioned front from Tue night will try to push NE as the system emerges from the Rockies. Mid level fgen/moisture return will develop at the leading edge of the warmer air aloft. This will be overcoming an initially dry atmosphere, so amounts will be limited Wed night. .LONG TERM...(Thursday through Monday) Issued at 311 PM EST Mon Dec 18 2017 The main challenge deals with the potential impacts from the storm system that tracks through the region Thursday through Friday. Models are coming into agreement in showing a band of snow impacting northern parts of my cwa. The latest GFS shows more than 6 inches...while the High Res Euro keeps the values under 3 inches. An elevated warm layer shows up as well...and that increases the risk for a period of freezing rain. Either way some impacts look possible in that will increase POPs...mention some accumulations and add a risk for a period of freezing rain mainly north of a Hart to Big Rapids to Mount Pleasant line. We also added the potential into the Hazardous Weather Outlook. The arctic air starts to flow in behind this departing storm Saturday and into early next week. There are some indications that a wave of low pressure will form along the frontal zone off to the east. This may support a period of snow around Sunday if the wave does develop. Good confidence on the arrival a very cold airmass early next week as the persistent northwest flow continues. Will keep the mention of snow showers going and feature well below normal temperatures. && .AVIATION...(For the 00Z TAFS through 00Z Tuesday evening) Issued at 540 PM EST Mon Dec 18 2017 Like last night, the low clouds that prevail now are expected to break up this evening and all taf sites should have several hours of VFR cigs. Also like last night later in the evening the low clouds come back as the atmosphere cools off as it typically does at night causing the boundary layer to saturate (hence low clouds form). I am thinking around 06z for this to happen. Also unlike last night we have a warm front trying to come through tonight. Once that does come through skies will really clear. That should be in the 09z time frame. There is to much wind for much fog tonight so that should not really be an issue. I have put low level wind shear in all of the overnight TAFS as by 03z we have 40-45 knots at 1000 ft AGL creating around 20 knots of shear that will be around most of the rest of the night. Tuesday we will be between the warm front and the cold front. This will result in mostly clear skies with a west wind from 10 to 20 knots. The cold front comes through around 06z on Wednesday that will bring some lower clouds into the picture then. && .MARINE... Issued at 311 PM EST Mon Dec 18 2017 We will be extending the Small Craft Advisory out through Wednesday afternoon due to the persistent winds and waves expected through then. Winds will come up this afternoon in the wake of the wave moving through. This gradient will last into Wed before relaxing a bit. We can not rule out gales occurring, especially up north. The likely scenario is that we max out advisory conditions. && .HYDROLOGY... Issued at 311 PM EST Mon Dec 18 2017 The Looking Glass River at Eagle has shown consistent improvement in the last couple of days. It is now within banks and the advisory has been dropped. There no remaining advisories in Southwest Lower. Ice continues to be observed on multiple rivers. Gauges at sites such as Whitehall (WHTM4) and Portland (PORM4) are still reflecting some erratic behavior due to the affects of the ice. Coordination with Ionia County officials did verify that the Portland site is elevated near bankfull in locations where land is lower, but largely not affecting anything otherwise. The White River at Whitehall remains within banks with the gauge periodically sending in erroneous reports above flood stage. We will continue to monitor each of the locations through the week. Forecast precipitation amounts for the upcoming week have not changed much. Milder air, snowmelt and rain/snow later in the week could lead to additional rises. This may actually be beneficial by giving a bigger push to lose ice, clearing some of it downstream through the end of the week. Flooding is not expected at this time, but rivers will continue to be monitored for ice jam potential. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. LM...Small Craft Advisory until 4 PM EST Wednesday for LMZ844>849. && $$ UPDATE...WDM SYNOPSIS...NJJ SHORT TERM...NJJ LONG TERM...MJS AVIATION...WDM HYDROLOGY...JAM MARINE...NJJ
Area Forecast Discussion
National Weather Service Huntsville AL
914 PM CST Mon Dec 18 2017 .NEAR TERM...(Tonight) Issued at 914 PM CST Mon Dec 18 2017 After a cloudy and foggy start earlier today, the sun actually broke through, helping to warm temperatures across the Tennessee Valley into the upper 50s and lower 60s - notably warmer than it has been in the recent past, and "normal" highs of around 52 degrees this time of year. 9 PM temperatures have cooled into the mid 40s to around 50. The above noted clear skies (still mostly clear over the Tennessee Valley east of the I-65 corridor) have allowed for radiational cooling and the formation of fog. The older GOES-13 low cloud/fog view nicely indicated the areas of fog especially in and near river valleys; as well as newly commissioned GOES-16 (now GOES-East) night-time microphysics view. Dense fog has already affected parts or NE Alabama and Southern Middle Tennessee, with surface visibilities at or below 1/4 of a mile. The temperatures/dewpoint spread at the Huntsville Int`l and Decatur airports was staying near zero, and reports of ground fog have been received in and near the larger cities. Given the fog affecting the eastern half of the area, went ahead with a Dense Fog Advisory for the forecast areas through 9 AM Wed AM. The movement of higher altitude cirrus over the western areas may slow down fog development there, but still think some could occur, before lower clouds arrive towards dawn Wed AM. New output from the NAM, as well as the HRRR and RAP held off on precipitation affecting the forecast area till after 6 AM, so did likewise in recent grid updates. .SHORT TERM...(Tuesday through Thursday) Issued at 253 PM CST Mon Dec 18 2017 Attention will quickly turn to another upper-level shortwave and its associated heavy rainfall and thunderstorm potential from midday Tuesday through Wednesday afternoon. Most locations will remain dry through the morning as cloud cover begins to increase with the advancing front. The aforementioned boundary will slowly creep northward into the Tennessee Valley by 18z and continue to lift NE through the afternoon. The associated lift from this weak frontal boundary will help to generate a clusters of numerous showers and possibly a few isolated to scattered thunderstorms, thanks to some weak instability. This front will also help to advect richer Gulf moisture into the area as PWATs climb to 1.5 inches or so by 00z Wednesday. Total QPF forecast for Tuesday is expected to be 1/2 to 3/4 of an inch, with heavier rains to come Tuesday Night into Wednesday. As alluded to, chances for precipitation will continue to increase through the evening hours and overnight period. An mid-level shortwave will become negatively tilted as it tracks into the Mid South late Tuesday evening. In response, a strong 70 kt LLJ will ramp up from Central Mississippi into Northern Alabama late Tuesday night into Wednesday morning. Most of the Tennessee Valley will be placed in a favorable location for lift, the front entrance region of the jet. The combination of deep moisture and strong synoptic and mesoscale lift will result in numerous to widespread heavy showers late Tuesday Night through Wednesday morning, before a cold front sweeps through by midday/early afternoon. Current model projections show roughly 2 to 3 inches of rain, mainly occurring between 18z Tuesday and 18z Wednesday, with the highest totals occurring over NW Alabama. While we have been fairly dry of late, this much rainfall could lead to some runoff and localized areal flooding issues in the usual flood prone areas. This certainly warrants a mention in the HWO and at this point, a need for a Hydrologic Outlook to address flooding concerns for this event and another potential system late this week. In addition to the flood threat, there will be some limited elevated instability to generate some scattered to isolated thunderstorms, especially Wednesday morning as the LLJ maxes out over Northern Alabama. Given that the "better" instability does not develop until later in day when the best lift has exited the area, think the primary mode will be rain showers or at the very least subsevere thunderstorms. However, due to the magnitude of this LLJ and a warm front nearby, cannot totally rule out a strong storm developing Wednesday morning (with gusty winds being the main threat), and have maintained a mention of this in the HWO. The cold front will pass through the area Wednesday afternoon, bringing in some drier air and an end to precipitation by the evening. The end result will be a dry night and then day on Thursday, with the best shot for sunshine we`ve seen in almost a week. Mild temperatures will continue as highs in the 60s and lows in the 50s can be expected for most of this period. .LONG TERM...(Wednesday night through Sunday) Issued at 253 PM CST Mon Dec 18 2017 The extended portion of the forecast begins Friday with an area of low pressure having developed across portions of MO and the Ern Great Plains. This feature is in response to a deepening H5 trof across much of the Central CONUS/Intermountain W, with a cold front stretching W/SW into Central/Southern portions of TX. Let me preface much of the extended forecast with these two words: it depends. There has been very little run-to-run model continuity over the past few days, and recently some models that were favoring warm/wet solutions have now flip-flopped to cold/dry (and vice versa). So, I say "it depends" depending on which model you favor for what time period as to what the forecast could potentially end up being. As of this forecast package, I`m leaning towards warmer/wetter through the weekend (and perhaps Christmas - maybe), with a more cold/dry turn for the time period after that. Then again, all of this could flip-flop again by this time tomorrow, so stay tuned for forecast updates over the next few days, as I`m sure there will be plenty of them between now and the Christmas holiday! The extended forecast can be broken up into 3 sections: Rain, Severe Wx (low risk), and Uncertainty. More details below: RAIN: While much of Thursday will be dry for much of the area, increasing Srly winds ahead of the approaching upper trof will allow for decent isentropic lift to occur, and likely for showers to develop/blossom by daybreak Friday morning. This will be the first `round` of rainfall, of sorts, to affect the region, with the brunt of the precipitation arriving/developing later in the day closer to the later afternoon/early evening hours. A few disturbances will ride up/over the front oriented SW to NE across the Southeast, which will set the stage for several rounds of moderate to heavy rainfall through midday Saturday. Storm-total rainfall amounts upwards of 3.5- 4" are possible across NW portions of the area, dwindling down to around 1.5-2" for SErn portions of the area. This in and of itself is a lot of rainfall, but following so quickly on the rainfall from earlier in the week, I`m thinking that we`ll have at least a few issues from either areal flooding, river flooding, or more likely, both. We`ll see how much rainfall occurs with the midweek system to give a better idea on exactly what we can expect with these kinds of rainfall totals to end the week. Please refer to the Hydrologic Outlook for more general information about the flooding possibilities for this time period, and as always, if a warning is issued for your location later in the week or over the weekend. SEVERE WX (low risk): Aside from all the talk about the heavy rainfall that we`re expecting, there`s also the potential (albeit a low risk at this point in time) for some strong to severe storms on Friday as the cold front pushes across the area, depending on your model of choice. For example, the GFS has a high in the low 70s Friday, whereas the ECMWF is 10 degrees cooler in the lower 60s. You`re going to have different values of instability with those sfc based temps. As with other systems that have moved across the region earlier this Fall, we`ve seen little in the way of instability, and a lot in the way of shear. This system isn`t too different with its parameters, but this time, there is a little sfc based instability that may be realized, which may pose a wind threat more than anything. With the model flip-flopping of recent days, I don`t feel comfortable believing a model output 100% to include the "T-word" at the moment, but right now, it`s on the lower end of likelihood of occurring. 850mb winds will increase to 50kts during the aftn, with 925mb winds around 40-45kts. This should translate to a windy day outside of any tstorm activity, with sustained winds around 15-20mph (with higher gusts likely). As the cold front approaches the area later in the day Friday, wind gusts up to 60mph may occur along the line of showers and storms along the front. IF we were to see something rotate, there`d be a brief window around 00Z Saturday for this to happen, when the best shear intersects with the little instability that we have in place. That said, there MAY be a chance for something Friday morning with the first round of showers blossoming across the area. If the warm front isn`t well N of the area, anything that crosses over that boundary may enhance what little rotation is there. So, I`m not saying that we`ll have 2 rounds of tornadoes, but there is a tiny possibility that something may try to rotate at 2 points during the day. As of this model run. Which may change tomorrow. Stay tuned for more on that. UNCERTAINTY: As if that`s not enough, there is a lot of uncertainty in the forecast from Christmas Day onward across the Tennessee Valley. The big question is how much of the Arctic air bottled up to the NW of the CWFA will make it here, and how much moisture will linger over us as well. If you believe the latest run of the GFS, we`ll have snow in our higher elevations on Christmas night. The ECMWF isn`t much different, but the big problem with QPF spit out by the models compared to sounding analysis shows big differences between the two. Whereas the models try to produce light snow for us, the soundings are really dry in the lower and mid levels, so even IF something was to develop and fall, it`d evaporate before it hit the ground. This all relates back to the big uncertainty that exists in this portion of the forecast right now. The upper levels that far out in the extended look to have W/SW flow aloft, and you`re just not going to get crazy cold without something plunging this far S (and sticking around more than a day). Long story short, I didn`t make many changes to Christmas and beyond thanks to all the model flip-flopping, but it looks as if we`ll at least get a couple of chances to have cooler than normal weather next week. && .AVIATION...(For the 00Z TAFS through 00Z Tuesday evening) Issued at 547 PM CST Mon Dec 18 2017 Good flying weather this early evening, will deteriorate in the late evening and overnight, as patchy fog forms across the region. Some of this fog could become locally dense, with visibilities falling below 1/2 of a mile at times. Did not take this pessimistic view in the TAF this issuance, but do have MVFR VIS and CIGS in the 1000-2000ft AGL developing after midnight. A storm system forming over the NW Gulf will move to the ENE, and bring more lower clouds and good shower chances after daybreak Wed. CIG/VIS values in the MVFR range should be reduced to IFR by the early afternoon. LIFR CIG/VIS reductions are possible in the mid/late afternoon. An isolated to scattered t-storm cannot be totally ruled out Wed afternoon too, but did not include given high uncertainty on convection. && .HUN WATCHES/WARNINGS/ADVISORIES... AL...Dense Fog Advisory until 9 AM CST Tuesday for ALZ001>010-016. TN...Dense Fog Advisory until 9 AM CST Tuesday for TNZ076-096-097. && $$ NEAR TERM...RSB SHORT TERM...AMP.24 LONG TERM...12 AVIATION...RSB For more information please visit our website at
Area Forecast Discussion
National Weather Service Wilmington NC
939 PM EST Mon Dec 18 2017 .SYNOPSIS... Warm and increasingly moist air ahead of an area of low pressure will result in widespread wet weather late Tuesday night into Wednesday night with rain and perhaps a brief rumble of thunder. A brief cool down will occur Thursday, followed by a return to unseasonable warmth with the risk for showers during the weekend and perhaps on Christmas day itself. && .NEAR TERM /THROUGH TUESDAY/... As of 945 PM Monday...00Z soundings from MHX and GSO confirm what models were showing with the depth of boundary layer moisture being nearly ideal for fog tonight. In fact we`re already seeing substantial drops in visibility from Florence and Marion to Wilmington as fog is already beginning to develop. In Florence visibility recovered back to 10 miles as soon as the winds increased to 4 knots. Gauging how strong surface winds will be overnight will be critical to determining how widespread and how dense fog may become. Latest GFS LAMP guidance indicates fog not becoming that big a deal overnight due to winds and steadily falling dewpoints. It`s worth noting that LAMP guidance is already badly too low with its current-hour dewpoints, so I`m not going trust it. Among the better initialized guidance, the HRRR shows very little fog while the RAP and NAM show substantial fog developing in the Cape Fear region overnight. A good nocturnal inversion is already developing from Florence, Marion and Conway northward despite 15-20 kt of wind at the 1000 foot height. Given this observation, I`ll keep "areas" of fog in the forecast tonight and highlight the Cape Fear region for special concern as this is where boundary layer moisture should remain richest. Other changes to the forecast were generally minor. Discussion from 300 PM follows... A weak frontal boundary draped across SC into coastal NC will continue to support weak lift advecting some sprinkles and clouds across the area. A mid to upper level ridge extending up from S Florida and broad trough to the north will maintain a basically zonal or westerly flow aloft. Some energy in the mid to upper levels will ride across the area later today, at which time the models show a slight increase in lift and potential for light pcp through the early eve hours. Otherwise, SW to W return flow at the sfc and westerly flow aloft pushed temps into the mid 60s to near 70 most places this afternoon and it will remain mild into this eve. There is also some potential for sea fog to develop and brush the coast primarily early on as winds along the coast have backed to the S to SW and increased slightly into early this evening before the winds veer to a more westerly direction which should help keep it away from the coast overnight. Any sprinkles will dissipate into late eve and there will be a decent amount of clearing overnight. Mild and damp weather will continue though, with overnight lows in the mid 40s to lower 50s and dewpoint temps close to that. This shallow moisture will lead to areas of fog developing across the area. Moisture profiles actually show the greatest potential for sea fog across coastal locations heading into early this eve with fog inland developing later, around 08Z. The deep westerly flow aloft should mix down and break up the fog leaving increasing sunshine through Tues aftn and temps reaching into the 70s. && .SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY NIGHT/... As of 300 PM Monday...Moisture will be streaming into the area Tuesday night in deep layer westerly flow. Low level winds will be largely parallel to isotherms at first limiting ascent. This changes rapidly Wednesday morning however as a flat wave of low pressure approaches from the west. Despite a fairly meager backing in the warm sector the winds strengthen on the north side of the baroclinic zone resulting in significant frontogenesis. Moderate rain should break out west to east and include most of the area. The bulk of the rain may fall north of our CWA and far southern zones will be hard- pressed to get meaningful rain amounts given the current anticipated storm track, but models have been uncertain of this and thus so is QPF. Have also left thunder out of the forecast not only based upon forecast model soundings but with the support of SPC SWODY3. The specter of convection though does further erode QPF confidence. Dry air then sweeps in from the north Wednesday night as the wedge asserts itself behind the departing low. && .LONG TERM /THURSDAY THROUGH MONDAY/... As of 300 PM Monday...In the wake of a cold front, high pressure will build south and wedge into the area Thu and Thu night, briefly knocking temps down to values more typical for late December. In fact Thu may be the only day in which temps are below normal this forecast period as clouds get trapped beneath a subsidence inversion. A weak coastal trough is expected to develop offshore Thu night and Fri with the wedge breaking down and high pressure shifting offshore Fri. A deep trough in the middle of the nation is expected to be reinforced, remaining upstream of the eastern Carolinas through Christmas day. This will bring a return to a strong and deep SW flow. Thu and Fri should be dry. A rather weak surface cold front to the west is expected to drift into the area during the weekend and will likely get hung up in close proximity given the prevailing flow. As a consequence, the holiday weekend is looking unsettled and unseasonably warm. The risk for showers will be on the increase Fri night. Will carry chance POPs for the weekend and Mon, but higher POPs could be in store for at least portions of the area with later forecasts. High temps will be in the 50s Thu and 60s for the remainder of the period. Highs may reach 70 over the weekend. The coolest night will be Thu night, mainly 40s although a few inland spots could dip into the upper 30s. Lows will be mainly in the 50s for the weekend. The unseasonable warmth may eventually result in the development of sea fog. Dewpoint recovery coupled with a favorable wind direction will make sea fog development most probable this weekend. && .AVIATION /02Z TUESDAY THROUGH SATURDAY/... As of 23Z...A weak stationary boundary continues to sit to our south with some of the moisture overriding it resulting in some light showers across the region with no impact on aviation. Main concern for the overnight period will be models indicating some low stratus clouds and fog with IFR/LIFR across the terminals after 08z. Could see some sea fog near the coast but w winds should keep the sea fog from moving across KMYR and KCRE. Conditions improve after 13z all terminals with VFR conditions through 20/00z. Extended Outlook... Unsettled weather Tuesday night through Thursday morning as a near stationary front moves in and out of the region. Possible showers Saturday. && .MARINE... NEAR TERM /THROUGH TUESDAY/... As of 715 PM Monday...6-7 PM buoy observations near Cape Fear showed seas about half a foot higher than predicted, mainly due to a pulse of stronger westerly winds over the past few hours with gusts 20-25 knots out at the Frying Pan Shoals buoy. These winds should diminish over the next few hours with directions remaining westerly. Radar shows only a few very light showers or sprinkles south of Cape Fear, which should dissipate entirely before midnight. Dewpoints remain quite high for this time of year and we`ll continue to monitor for the potential of sea fog developing. Discussion from 300 PM follows... Quiet marine conditions although there may be some sea fog in the mix. A light SW return flow will veer to the west through tonight around 10 kts. Sea fog may develop late this afternoon in a moist and warm SW flow with dewpoint temps up around 60 and water temps in the 50s. Overall seas will be 1-2 feet with perhaps a few three footers into tonight as winds pick up slightly. SHORT TERM /TUESDAY NIGHT THROUGH WEDNESDAY NIGHT/... As of 300 PM Monday...West to southwesterly flow in place Tuesday night with high pressure centered over Bahamas and Florida. A wave of low pressure will approach from the west along a sagging frontal boundary and this will tighten the gradient and lead to considerable backing of the flow Wednesday. Late in the day the boundary will sag across most of the NC zones turning winds all the way to the NE briefly before turning back to E. This all hinges upon the yet uncertain position of the front and so it subject to change. AS the frontal wave moves offshore Wednesday evening a wedge of high pressure will quickly move in and lead to a gusty NE flow that could allow advisory-worthy seas to affect the outer portions of NC waters. LONG TERM /THURSDAY THROUGH SATURDAY/... As of 300 PM Monday...In the wake of a cold front, high pressure will briefly build south Thu and Thu night. A coastal trough is expected to develop offshore Thu night into Fri. A deep trough across the middle of the nation will be reinforced with the flow across our waters shifting from NE Thu and Thu night to E and SE Fri and finally to S and SW Fri night and Sat ahead of a rather weak front. Small Craft Advisory conditions may linger into Thu and this is when the strongest winds are expected this period. Wind speeds will subside late Thu through most of Fri and then increase to around 15 kt Fri night and Sat. The highest seas Thu will be in the 4 to 6 ft range. Seas will subside to 3 ft Thu night and 2 ft Fri before building to 4 to 5 ft by Sat. && .ILM WATCHES/WARNINGS/ADVISORIES... SC...None. NC...None. MARINE...None. && $$ SYNOPSIS...RJD NEAR TERM...TRA/RGZ SHORT TERM...MBB LONG TERM...RJD AVIATION...MAC MARINE...
Area Forecast Discussion
National Weather Service Lincoln IL
907 PM CST Mon Dec 18 2017 .UPDATE... Issued at 905 PM CST Mon Dec 18 2017 High pressure centered to the southeast of Illinois, across the SE states will maintain a general influence over the weather in central Illinois tonight. Some low clouds and fog are expected to surge northward into southern and southeast Illinois later tonight, on southwest winds/return flow behind the high pressure. Most of counties should escape any coverage from the low clouds/fog, except for towards Lawrenceville based on the latest HRRR model. The sky grids have that scenario handled ok, but we did not introduce fog yet due to 2 other high res models keeping fog clear of our SE counties. Will continue to monitor trends with those weather elements. Low temps tonight will be kept warmer with steady SW winds and warm advection flows. Lows should be in the upper 30s. On Tuesday, an surface trough approaching from the northwest will pass across Illinois, with minimal impact expected. Mainly mid and high clouds are forecast for our forecast area. Prevailing sunshine should help temps climb well above normal, into the low 50s north of Peoria, to the upper 50s south of I-70. Winds will shift to the NW during the afternoon, after the surface trough passes. && .SHORT TERM...(This evening through Tuesday) ISSUED AT 301 PM CST Mon Dec 18 2017 Skies will continue to clear late this afternoon and skies should be mostly clear through the night and into tomorrow. Could be some scattered clouds around but not enough to hold temps down. Temps overnight should remain above freezing tonight and then with southwesterly winds tomorrow, plenty of WAA and sunshine to allow temps to climb above 50 across the entire CWA. .LONG TERM...(Tuesday night through Monday) ISSUED AT 301 PM CST Mon Dec 18 2017 A weather system is forecast to move across the southern Mississippi valley mid week but looks like the precip should remain south of the CWA through the period. This will bring in some clouds and slightly cooler temps, through still above normal for middle of Dec. As this moves east, southerly winds will return with lots of WAA continuing ahead of the next weather system. The next weather system will bring clouds and precip into the northwest parts of the CWA beginning Thursday evening. The precip should remain across the far northern portions of central IL Thur night. Models then disagree on speed of this system and the secondary system moving through Fri and Fri night. GFS is quickest and Canadian is slowest. So prefer the middle ECMWF solution that has the low pressure area of the system moving into Mich by Fri evening. Precip is expected with this system with the highest pops being in the eastern and southeastern part of the CWA Friday afternoon and evening. P-type will be a mainly rain on Friday, with a rain/snow mix in the northwest early. By afternoon, it will be warm enough everywhere that all precip will be liquid. As the front goes by, colder air is supposed to move into the area. With the slower ECMWF solution, the rain will change to a mix of rain and snow, to just all snow Friday night. Temps will be warm ahead of the system and then get colder after the front moves through. The timing of this colder air will determine when the change over to snow occurs, which could be around the time the precip is ending as well. So, currently not expecting much accumulation. Models differ even more for the weekend and after a brief dry period Sat and Sat night. There might be another system for Sun and Sun night but the GFS and ECMWF have no precip while the Canadian has precip. Therefore, will keep low chance pops in forecast for now. Colder than normal temps are also expected for the weekend. && .AVIATION...(For the 00Z TAFS through 00Z Tuesday evening) Issued at 557 PM CST Mon Dec 18 2017 VFR conditions should prevail at the terminal sites for the 00z TAF period, with mainly mid and high clouds drifting across the area later tonight and tomorrow. A band of low clouds and fog will surge northward toward our counties, and possible affect areas south of I-70, but we are not expecting that fog/low clouds to reach the TAF sites. The NAM12 is an outlier model that brings VLIFR clouds across the TAF sites just after sunrise tomorrow. For now, will not acknowledge that solution, but will monitor all high resolution guidance for any change in trends. Winds will remain southwest around 10kt overnight, then become more westerly tomorrow and decrease to 7-9kt as the pressure gradient weakens. LLWS conditions tonight look to remain north of I-74, so have not included in our 00z TAFs. Will monitor the potential of LLWS in our area as well. && .ILX WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...Shimon SHORT TERM...Auten LONG TERM...Auten AVIATION...Shimon
Area Forecast Discussion
National Weather Service Northern Indiana
655 PM EST Mon Dec 18 2017 .SYNOPSIS... Issued at 638 PM EST Mon Dec 18 2017 Low clouds continue to erode from west to east as drier comes in along with high pressure. Dry air will be able to stay around the region until the end of the week as a low pressure system approaches from the south for Thursday night and Friday. Tuesday lows will be in the mid to upper 30s with highs in the upper 40s to low 50s, both above average. Wednesday will be cool again before trending warmer for Friday. Cooler air and possibly some lake effect snow follows for next weekend. && .SHORT TERM...(This Evening through Tuesday) Issued at 350 PM EST Mon Dec 18 2017 Focus on near term with respect to final bout of very light rain/drizzle associated with final northern tier shortwave within confluent split flow pattern. Despite high crossover temps/partial clearing later tonight, sufficient mixing within boundary layer and subtle dry air advection, to most likely preclude br formation of any significance. This also inline with latest rap projections. Raised temps Tue inline with latest non met mos/upstream performance today and trend over past several days. && .LONG TERM...(Tuesday Night through Monday) Issued at 350 PM EST Mon Dec 18 2017 A few substantive changes with respect to latest blended approach. Benign stretch through much of work week. Desert southwest system still tracking well south with TN/gulf states cyclogenesis on Wed. Thereafter, a very highly amplified flow regime develops with eastern Pacific ridging/deep north central NOAM trof with slow eastward progress. Leeside cyclogenesis late Wednesday with northeast ejection into Western Upper Great Lakes. Blend substantially lowered pops Fri afternoon/early Fri night and have raised back to likely/categorical given anticipated depth to longitudinal flow/GOMEX moisture feed. Also, EC significantly warmer 8H for diminished post frontal les production, have raised pops significantly as muted lake effect snow parameter likely failing to capture what should be at least a high prob, if even low qpf event. && .AVIATION...(For the 00Z TAFS through 00Z Tuesday Evening) Issued at 638 PM EST Mon Dec 18 2017 Drizzle is expected to leave the area at or just after forecast issuance and low level stratus is moving to the east fairly quickly with clear skies approaching in its wake. Models show stratus lingering at FWA, but they haven`t had a decent handle on how quickly the stratus peal-back has been occurring so will speed that up some. Expect CIGs at SBN to continue to remain VFR through the overnight while MVFR CIGs at FWA may take 1 to possibly 6 hours to peal back, if model trends are right for them, before its all the way out. One thing to watch will be if we get some fog/BR formation. Snow pack has diminished to a trace or less at SBN, but the ground is moist region-wide nonetheless. Winds have diminished to between 5 and 10 kts behind the stratus layer, but could pick back up some with a stronger low level jet just overhead. Should winds be around 10 kts for most of the night that would quell this idea for most areas. At any rate, for Monday, increasing sunshine should be had as high pressure approaches from the west and drier air is around the region. Winds will be able to decrease during the afternoon as high pressure continues to move in and the low level jet leaves the area. && .IWX WATCHES/WARNINGS/ADVISORIES... IN...NONE. MI...NONE. OH...NONE. LM...Small Craft Advisory until 4 PM EST Tuesday for LMZ043-046. && $$ SYNOPSIS...Roller SHORT TERM...Murphy LONG TERM...Murphy AVIATION...Roller Visit us at Follow us on Facebook...Twitter...and YouTube at:
National Weather Service Jackson KY
629 PM EST Mon Dec 18 2017 .UPDATE... Issued at 629 PM EST MON DEC 18 2017 With the cloud cover continuing to be stubborn out there this evening, increased cloud cover through the rest of the night as NAM/GFS bufkit soundings keep us cloudy all night. This will also keep temperatures a tad milder tonight, so did increase them along with dewpoints. Looks like the drizzle is coming to an end with cloud heights quickly increasing. && .SHORT TERM...(This evening through Tuesday night) Issued at 340 PM EST MON DEC 18 2017 20z sfc analysis shows high pressure to the south with low pressure to the north. In this pattern the air mass has not been able to sufficiently change enough to clear out the ample low level moisture trapped under an inversion that is keeping the clouds in tight. In addition, patchy fog and drizzle still plague the area - primarily on the ridge tops. Temperatures are still rather mild despite the clouds with readings now up in the upper 40s most places with low 50s noted in many of the valley spots. Winds, meanwhile, continue to blow from the southwest at 5 to 10 kts. The models are in good agreement aloft through the short term portion of the forecast. They all depict a northern stream wave of weak energy passing by to the north this evening while a southwestern trough bottoms out in northern Mexico. This wave will slowly move east into Tuesday pushing downstream ridging up into Kentucky. However, fast flow will persist over Kentucky with energy from the southern stream moving through the Tennessee Valley late Tuesday and into Tuesday night. As the wave opens up and approaches Kentucky more energy moves in by Wednesday morning. The trend has been for this wave and its impacts to shift further north with each run. So have followed suit with increasing confidence. With the models in good agreement handling these key features will favor a model blend along with a healthy lean toward the higher resolution NAM12 and HRRR tonight and into Tuesday. Sensible weather will feature another mild but damp night. Low stratus and patchy drizzle/fog will continue to affect most of the area - especially on the ridges and in the higher terrain. With sunup on Tuesday we should see the stratus start to break up. There are indications in the models that this would occur from east to west. Expect a fairly warm day with only limited sunshine on Tuesday as high clouds from the next system move in around the same time as the low ones break up. Southwest winds will continue to support above normal temperatures and a fair amount of moisture in this air mass. The center of the next low pressure system will pass to the south of Kentucky with a well defined comma head crossing through the southern half of the CWA start Tuesday night. Warm conditions ahead of this system will prevent any mix concern on the leading edge - it is possible later on in the wake of the low passing by to the south and east that more cold air gets pulled in and we will have to look as a mixed pcpn potential on the northern fringe of the departing rain shield - but that is just beyond the short term portion of the forecast. Again with the clouds and moisture tonight into Tuesday did not deviate too far from the ShortBlend temperatures. Did raise PoPs a notch through Tuesday morning to keep up with the drizzle threat. Also brought the higher PoPs in quicker on Tuesday night with that inbound southern stream low. .LONG TERM...(Wednesday through Monday) Issued at 320 PM EST MON DEC 18 2017 A bit of a complex forecast in store for the extended. The latest model data is suggesting an active pattern that will feature three periods of active weather. The first would be Wednesday and Wednesday night, followed by Friday through early Saturday evening, with a third active period from Sunday morning through Monday morning. An area of low pressure is forecast to move out of the southern Plains and across the lower Mississippi and Tennessee valleys Wednesday and Wednesday night. This system will bring scattered to numerous rain showers to eastern Kentucky to begin the period. Temperatures should remain warm enough to keep any precipitation we get in liquid form. The models have been pretty consistent with the evolution of this system and the timing, extent, and amounts of its associated precipitation, so confidence is pretty good with this initial wave of rain. The second period of precipitation is forecast for Friday through Saturday evening. The models differ here slightly with regards to timing of the system, with the GFS being slightly faster than the ECWMF. The forecast will reflect a slightly modified model blend that incorporates the timing differences mentioned above. Once again we expect temperatures to remain warm enough to keep any precipitation with this second weather system in liquid form. A good deal of uncertainty comes into play with the third period of active weather in the extended. Timing differences exist amongst the various models, with one model having a wide swath of precipitation moving into eastern Kentucky by early Sunday morning, while another model has no precipitation moving into the area until Sunday evening at the earliest. The blended model was adjusted toward the typically reliable ECMWF model for the Sunday through Monday time frame. The onset of precipitation on Sunday was slowed down more than what the stand along ECMWF model was showing and slightly faster than the blended model data had. The new forecast will show some rain and snow making their way into our southern counties between 10 and 12Z on Sunday, with a gradual northward progression of the mixed precip through out the morning. By early Sunday afternoon any ongoing precipitation should be in the form of all rain. The model data is currently trying to producing a decent snow event for Christmas eve night and early Christmas morning along the Ohio River, north of the river in particular. At this time the forecast will be calling for a mix of rain and snow for Sunday night, with mostly snow ongoing across the area by early Monday morning. There is alot of uncertainty in the model that far out, however, so the very end of the extended will be taken with a grain of salt at this time. Based on the latest model data, and trends therein, temperatures in the extended will be well above normal across the area. Particularly toward the end of the week, when persistent southerly and southwesterly winds become established across the Tennessee and Ohio valleys. These winds will set up in the region between an area of high pressure that will be parked off the southeastern CONUS, and an area of low pressure aloft that is currently progged to be taking shape over the central Plains and moving eastward Thursday night into Friday. Highs on Thursday are expected to top out from the low 50s in our far north to the upper 50s along the TN border. On Friday conditions may be even warmer, as by then we will be firmly entrenched in the warm sector of an approaching cyclone. Highs on Friday may climb as high as the upper 50s and lower 60s across the area. Temperatures will then become progressively cooler, as the upper trough exits the area, and cooler air moves in from the north and northwest. Sundays highs should only make it into the 40s for most of the area. && .AVIATION...(For the 00Z TAFS through 00Z Tuesday evening) ISSUED AT 629 PM EST MON DEC 18 2017 A tricky aviation forecast tonight. Most locations have returned to MVFR in the last few hours. However, it would probably be a safe assumption that cloud heights will start to come down overnight. The question is just how low do we go by daybreak Tuesday. For now, going to stay close to guidance that has most areas socked in with IFR conditions, but I could see a few locations staying in the MVFR category. As clouds finally start to erode on Tuesday, we will return to VFR conditions around midday. Light southwesterly winds are expected through the period. && .JKL WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...KAS SHORT TERM...GREIF LONG TERM...AR AVIATION...KAS
Area Forecast Discussion...UPDATED
National Weather Service North Platte NE
528 PM CST Mon Dec 18 2017 .SYNOPSIS... Issued at 405 PM CST Mon Dec 18 2017 Across the CONUS this morning, a zonal pattern was dominant across the northern half of the country. The main features of note this morning across the southern CONUS was a closed low over southern Arizona and strong high pressure over the Bahamas. WV imagery continues to indicate a large plume of Pacific moisture and high cloudiness across the northwestern CONUS this morning. This cloud cover has drifted east across the northern Rockies and was entering the high plains of South Dakota and western Nebraska as of this afternoon. Abundant tropical moisture was present from west Texas, east to the Carolinas and Georgia. At the surface: A weak trough of low pressure extended from eastern Wyoming into eastern Colorado. East of this feature, a north to south aligned pressure gradient was present across western and north central Nebraska. With light westerly winds and partly to mostly sunny skies across western and north central Nebraska, 3 PM CST temperatures ranged from 53 at Gordon to 61 at Imperial. && .SHORT TERM...(This evening through Tuesday) Issued at 405 PM CST Mon Dec 18 2017 Tonight and Tuesday...Benign weather conditions will highlight the next 24 hours across western and north central Nebraska with no precipitation expected. Skies tonight will generally be mostly clear with some high clouds transitioning from north to south. For the cloud cover tonight, generally followed the NAM12 H500 to H300 Layer RH field for clouds tonight. This seemed to initialize the best with the invading cloud cover in the panhandle this morning. That being said, this cloud cover will transition from north to south overnight with clearing in the south toward day break Tuesday. A weak cold front will drop through the Dakotas overnight and nose into northeastern Nebraska Tuesday morning. Then the front will stall with the core of cold air being well off to the north and northeast of the forecast area. Lows tonight will range from the middle 20s to the lower 30s which is well above normal for this time of year. On Tuesday, a surface trough of low pressure will develop from the Black Hills south into northeastern Colorado. Southerly winds will increase in the afternoon hours for locations along and west of highway 83. This will begin to push warmer air into southwestern and western Nebraska from Kansas and eastern Colorado. Highs Tuesday will range from the upper 40s across the nrn tier to the middle 50s in far swrn Nebraska. .LONG TERM...(Tuesday night through Monday) Issued at 405 PM CST Mon Dec 18 2017 Tuesday night through Friday: For Tuesday night into Wednesday: The stalled out frontal boundary across northeastern Nebraska will track north as a warm front Tuesday night. This will allow warm air to push into western and north central Nebraska for Wednesday. By midday Wednesday, H85 temps will range from 7c in the northeast to 12c in the southwest. The superblend forecast initialized with highs generally in the 50s with some highs around 60s in the far southwest. Based on the fcst H85 temps, this may not be warm enough and is lower than the latest MAV and MET guidance highs. Feel this is a good start however, as the NAM and the GFS develop high clouds Wednesday and this would hold highs back some. Wednesday night through Friday: The main forecast concern late in the week is the passage of an arctic cold front and the threat for light snow or a wintry mix of precipitation Overnight Wednesday night into Thursday. Beginning Wednesday evening, a strong arctic cold front will track through western and north central Nebraska. By 03z Thursday, the cold front will enter northwestern Nebraska, exiting the forecast area by 09z Thursday. Fcst soundings and cross sections indicate a shallow wedge of warmer air just off the surface behind the front. This shallow wedge of warm air only lasts 3 to 6 hrs behind the front. Fcst soundings INVOF of the front, as well as cross sections taken perpendicular to the front indicate a 3 to 6 hour window for the threat for freezing pcpn immediately behind the front. QPF`s are expected to be fairly light at a hundredth or two INVOF the front, so will keep any mention of freezing precipitation as freezing drizzle The threat for fzdz will be mainly east of a line from Bassett to Ogallala. North of this line, enough mid level moisture exists to support a seeder/feeder process and all snow. I did go ahead and end the threat for freezing drizzle in the south by noontime Thursday, based on BUFKIT and fcst cross section temperatures in the NAM and GFS. As for the best chances for pcpn Wednesday night into Thursday: Isentropic lift is strongest from the eastern Panhandle through the sandhills into north central Nebraska. This location doesn`t deviate much from the inherited forecast so not much was changed for precipitation chances. As for QPF and the amount of snow accumulations: The GFS continues to be the highest of the bunch with the EC lower and the NAM12 indicating little if any precipitation. Utilizing the superblend, loaded QPF`s were around 0.05 in the south to around 0.15 inches in the sandhills and northern Nebraska. Utilizing roughly a 15 to 1 snow ratio, yielded snowfall amounts from a half an inch in the south to 2 to 3 inches in the sandhills and northern Nebraska. Will continue to highlight this in the HWO as we may eventually need a winter wx advisory for this event. Friday night through Monday: The long range models continue to indicate a significant Arctic intrusion over the Central United States next weekend and depending on the amount of snow cover, we may see some of the coldest temperatures seen for this time of year for quite some time. We`re taking an optimistic approach with temperatures as the forecast is only calling for up to a couple inches of snow at most late week and next weekend. Also, there is some disagreement between the GFS and ECMWF as to how deep and far west the brunt of the cold air will slide. The ECMWF generally keeps minus teens at h85 across much of the CWA through the weekend, but the GFS suggest temperatures as cold as minus 20 to minus 30 settling across the area Christmas Eve. So with the optimistic forecast, single digit to teens highs are forecast with sub-zero to low single digit lows expected through the extended. This time of the year we can see brutally cold air masses as indicated by record lows generally of minus 20 to minus 30 and record cold highs near or slightly below zero, so records at this point are safe. The northwesterly pattern aloft will force a cold front across the forecast area ever 34-36 hours, with that, the models show some enhancement of the surface wind. Brutally cold wind chills are likely this weekend, especially across our north. The latest guidance indicates readings approaching minus 20 across northern Nebraska Saturday and Sunday morning. If this holds true, wind chill headlines will be required. In terms of precipitation, the broad trough centered across the Central United States will usher some fairly significant upper dynamics/energy across the region. But under the presence of this Arctic intrusion, moisture will be severely lacking. This sets the stage for the potential of a high SLR snow event, but not much additional accumulation. Another inch or so will be possible for some areas, but most places will see less. At this point, QG analysis suggest the best shot at additional snow will be across our west and southwest early Saturday with northern Nebraska under the threat on Sunday. && .AVIATION...(For the 00Z TAFS through 00Z Tuesday evening) Issued at 528 PM CST Mon Dec 18 2017 A weak cold front, currently across srn MT and srn ND, will move south into nrn Neb overnight. The front could become the focus for MVFR/IFR cigs across srn SD. These cigs may drift or build south into nrn Neb by 12z Tuesday. This would generally impact areas along and north of highway 20 Tuesday morning. The model soundings of the RAP and NAM show fog along the front but the SREF indicates a better chance of MVFR cigs. VFR is expected all areas 18z-00z Tuesday afternoon. && .LBF WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Buttler SHORT TERM...Buttler LONG TERM...Buttler/Jacobs AVIATION...CDC
Area Forecast Discussion
National Weather Service Marquette MI
531 PM EST Mon Dec 18 2017 .SHORT TERM...(This evening through Tuesday) Issued at 416 PM EST MON DEC 18 2017 WV imagery and RAP analysis indicated mainly a zonal mid/upper level flow through the northern CONUS and southern Canada with a shortwave trough over nrn Ontario. At the surface, sw flow prevailed ahead of a trough moving through the plains. Radars indicated an area of snow over nrn MN associated with a weak shrtwv and upper level div with the left exit of the 250-300 jet. Tonight: Radar trends and shortwave range high res models suggest that the area of snow will spread across Upper Michigan between 00z- 06z with some light accumulations of around an inch over the west and smaller amounts where downslope low level sw flow prevails. 850 mb temps only to around -3C this evening will not favor any significant lake enhancement. While most of pcpn should be snow, per forecast wet-bulb zero heights, some rain may mix in near Lake Superior. Tuesday: although colder air will move into the region with 850 mb temps dropping from -10C to -15C will only provide marginal instability for wrly flow LES as inversion heights near 5k ft with a dry 850-700 mb layer limit accumulation potential to another inch or two. As winds veer to the wnw in the afternoon some light LES of an inch or less is also expected east of Munising. The main hazard will be the potential for higher winds over the Keweenaw where momentum transfer fcst with decreasing stability suggests winds will gust to around 45 mph, especially in favored higher terrain west facing locations near KCMX. Because of the combination of the high winds an light snow with some blsn, a winter wx advisory was issued. Otherwise, conditions will remain relatively mild with highs in the lower to mid 30s, warmest south and east. .LONG TERM...(Tuesday night through Monday) Issued at 350 PM EST MON DEC 18 2017 The main forecast concerns for later this week into early next week are the arrival of a low pressure system progged to track across the Great Lakes region towards the end of the week, and then the arrival of an bitterly cold arctic airmass early next week. Tuesday night through Wednesday: As the surface pressure gradient between the exiting low off to our east and an approaching area of high pressure remains enhanced, strong and gusty winds will linger Tuesday night into early Wednesday. With the wind direction primarily out of the northwest, increased fetch and quasi-prolonged stronger winds will allow large waves to build on Lake Superior impacting the shoreline primarily east of Munising. Lake effect snow showers will continue in the northwest wind snow belts Tuesday night, but as the 850mb flow backs to the west-northwest throughout the day, with warming temperatures and heights rise across the region expect the lingering lake effect to impact the east and start to diminish across the west. Wednesday night through Friday: There is still quite a bit of spread among the medium-range models in regards to the strength, track, and timing of the the system expected to arrive later this week. Given the longwave trough progged to dig south across the Dessert Southwest, thinking the GFS/ECMWF are onto something with slowing this wave down and broad, elongated southwest flow developing across the central CONUS. This would favor the southern and northern streams associated with this system to phase east of the region. This idea is also further supported with the latest runs of the GFS Ensembles and SREF. There certainly will be travel impacts across the region as this system moves through, especially Thursday through Friday; however, the exact locations of these impacts will depend on where main frontogenesis band sets up. It is certainly too early to pinpoint snowfall amounts and what locations will see the highest accumulations. However, at this time given the track of the surface and 850mb lows the impacts may be felt more west of Lake Michigan and across the northern half of Upper Michigan where lake enhanced snow looks possible. To reiterate, the more significant impacts and accumulating snow will be highly depending on the track and speed of the system. Those planning to travel across the region should keep up to date on the forecast as the details will become fine-tuned over the up and coming days, especially after the main upper-level wave comes on shore. Saturday into early next week: Although the models diverge with the above mention system and overall impacts across Upper Michigan. As the trough axis continue to slowly move east of the region, multiple shortwaves are expected to rotate down across the region. This will allow for multiple reinforcing shots of bitterly cold, arctic air. It certainly looks like we will see the coldest temperatures of the season by early next week. Lake effect snow will accompany this colder air near Lake Superior, although with 850mb temperatures progged to drop down to between -20 to -26C snow will be a bit less efficient. && .AVIATION...(For the 00Z TAFS through 00Z Tuesday evening) Issued at 530 PM EST MON DEC 18 2017 Conditions will fall back to MVFR/IFR tonight as light snow or lake enhanced snow develops over the west. Westerly winds will favor mainly MVFR conditions at KSAW. Will be gusty at KCMX late tonight into Tue. && .MARINE...(For the 4 PM Lake Superior forecast issuance) Issued at 416 PM EST MON DEC 18 2017 Southwesterly to 30 knots will veer wrly tonight with some gale force gustst. As colder air moves in, winds will increase to gales of 35 to 40 knots Tuesday and to around 45 knots over the east by later Tuesdy afternoon into Tue night. With increasing wave heights and colder air temperatures, freezing spray is possible Tuesday night into Wednesday. && .MQT WATCHES/WARNINGS/ADVISORIES... Upper Michigan... Winter Weather Advisory until 1 AM EST Wednesday for MIZ001-003. Lake Superior... Gale Warning from 1 AM Tuesday to 4 AM EST Wednesday for LSZ243>251-264>267. Gale Warning from 10 AM EST /9 AM CST/ to 11 PM EST /10 PM CST/ Tuesday for LSZ162-241-242-263. Lake Michigan... None. && $$ SHORT TERM...JLB LONG TERM...Ritzman AVIATION...07 MARINE...JLB