Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 01/22/17

Area Forecast Discussion
National Weather Service Cleveland OH
913 PM EST Sat Jan 21 2017 .SYNOPSIS... Temperatures will remain mild through Monday as low pressure tracks from the Mississippi valley northeast towards the Mid Atlantic states. A ridge of high pressure will build across the region Tuesday into Wednesday. A low pressure system will track east across the southern Great Lakes Wednesday with more seasonable temperatures arriving late week. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/... Bumped up pops across NE OH slightly. Expect rainfall amounts to be on the light side...just a trace to a couple of hundredths of an inch or rain. With the warm front lingering near the Erie lakeshore removed mention of fog everywhere except NW OH. Original discussion... Precipitation and fog potential overnight are the main concerns in the forecast. A couple weak mid level impulses will advect northeast across the area through tomorrow morning. Elevated radar returns showing up in central Ohio associated with this first impulse have not been reaching the ground, as soundings show relatively dry boundary layer. Low level jet centered west of the area this afternoon will help to moisten the 925-700mb layer. Best shot of precip will be around and after 06Z as second impulse works toward the region. For now, kept slight chance of rain showers in the forecast. Some elevated instability/decent lapse rates could yield a few isolated thunderstorms, however confidence in precip with weaker forcing precludes any thunder mention. Areas of fog are likely to develop after 06-09Z as boundary layer decouples and winds become light, with a rather strong inversion forming. Could see some areas of dense fog in the Toledo area and vicinity, but for now, will hold off on any headlines for dense fog and just mention areas of fog/patchy dense fog and will monitor this evening. && .SHORT TERM /6 AM SUNDAY MORNING THROUGH TUESDAY NIGHT/... Focus of the short term period is precipitation chances Sunday through early Tuesday. Upper low will slowly track and deepen from the lower Mississippi valley Sunday morning to the upper Ohio valley by Monday afternoon in response to strong southern stream jet energy. Models are in decent agreement with track/evolution of upper low and attendant surface reflection. The precip arrival Sunday has trended a bit slower, with much of the morning/earlier afternoon possibly dry across the forecast area. Adjusted the forecast to reflect this trend, with chance pops arriving after 17Z and likely pops holding off until 21Z and after. Best window for precipitation, and possible heavy rainfall, will be Monday morning/early afternoon, especially across the eastern half of the area where cat pops have been expanded a bit. This is where best forcing will be present as the upper low tracks along the Appalachians just east/southeast of the area. Kept QPF amounts Sunday through Monday night ranging from 0.30" west to around an inch east. Precip will wind down Monday night/Tuesday morning as the low tracks eastward off the Atlantic coast. One wild card in the Monday night time frame is p-type. ECMWF and GFS tend to be on the warmer side with the low, with perhaps a brief period of changeover to rain/snow mix late Monday night. The NAM, however, wraps much more colder air into the low, with p-type changing over much earlier Monday evening, and perhaps a changeover to all snow overnight, with some accumulation possible. For now, discounted the NAM and went with a GFS/ECMWF blend for column temperatures and resultant p-types, with rain and snow mentioned Monday night. This solution will need to be watched over the coming model runs and the forecast will be adjusted accordingly. High pressure ridge will build across the region Tuesday. This should yield dry conditions much of Tuesday and Tuesday night. Northern stream wave will track from the central Rockies toward the Great Lakes, with precip arriving towards 12Z across the area. P- types may be in issue, especially NE OH/NW PA high elevations, but it is too early for specifics other than a cursory rain and snow mention. Temperature wise, went a few degrees warmer for highs on Sunday with slower precip arrival trend, near MAV/EC MOS, but not as warm as MET MOS. This yields upper 50s/mid 60s across much of the area. Temperatures will trend cooler Monday through Tuesday, but still well above seasonal normals. && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... The long term begins on Wednesday with models in good general agreement showing an upper over the upper midwest and a general southwest flow aloft over the area. At the surface, low pressure will be in SERN MN with a warm front into western Ohio and a cold front south from the low through Indiana. The low will move northeast across the Great Lakes dragging both fronts across the region during the day. Temps will fall behind the cold front changing rain Wednesday into snow Wednesday night. Thursday 850mb temps should be around -5C which should keep most precip snow during the day. Continued with chance pops most places although did keep likely northeast with flow off the lake for potential lake enhancement although it would be minimal given temps. No big change Friday although 850mb temps continue to slowly drop. Friday night into saturday another trough rotates across the region bringing colder air to the region with 850mb temps dropping to -10c and likely continuing lake effect enhancement northeast. && .AVIATION /00Z Sunday THROUGH Thursday/... VFR weather continues all areas with mainly mid and high level cigs. Some showers remain just south and southeast of the area. The latest guidance including the HRRR has this activity dissipating by 06z. Will go with a vicinity mention at CAK and YNG for a few hours. If the precip becomes more imminent we will update. A strong inversion will develop overnight as cooling occurs at the surface. This should cause fog and stratus to develop. Conditions will be the worst in the west...possibly LIFR. Will develop MVFR cigs all areas around 08z with patchy IFR fog after that. Will try to improve cigs back to VFR on Sunday morning with precip holding off till the tail end of the TAF period. OUTLOOK...Non-VFR developing Saturday night continuing into Monday in rain. Non-VFR will likely persist on Tuesday across NE OH/NW PA. && .MARINE... Light south to southeast flow on the lake today through tonight as a warm front lifts north of the lake. Flow will remain light Sunday as it turns out of the northeast in response to low pressure moving through the Tennessee valley. This northeast flow will increase Sunday night reaching 15 to 20 knots overnight and 20 to 25 knots on Monday before turning north and dropping back to 10 to 15 knots overnight Monday night. Winds will increase again from the southwest Wednesday to 15 to 25 knots as low pressure moves through the central lakes. Would anticipate small craft headlines will be needed early Monday into/through Monday night and late Wednesday into Thursday. && .CLE WATCHES/WARNINGS/ADVISORIES... OH...None. PA...None. MARINE...None. && $$ SYNOPSIS...Greenawalt NEAR TERM...DJB/Greenawalt SHORT TERM...Greenawalt LONG TERM...TK AVIATION...Kubina MARINE...TK
Area Forecast Discussion
National Weather Service Grand Forks ND
936 PM CST Sat Jan 21 2017 .UPDATE... Issued at 931 PM CST Sat Jan 21 2017 Latest METARs are showing some lower vsbys in fog from Grand Forks Air Force Base up through Cavalier...with obs mostly around 1/2SM. will need to monitor this area as HRRR does indicate this thorugh the overnight period. East of the river, light echoes over NW Minnesota are likely producing some patchy drizzle in areas but with temps just above freezing not expecting any impacts. Patchy drizzle is covered in forecast but did change wording from probability to coverage. Also FAR has recently dropped to 1/4SM...increasing concern this will spread up the valley. No changes to headlines yet but will expand if necessary. UPDATE Issued at 602 PM CST Sat Jan 21 2017 Forecast update addresses fog issues beginning to develop across portions of southeastern North Dakota into the southern Red River valley. Web cams showing fog development from Tenney, MN through the Oriska rest stop east of Valley include Gwinner that is now showing 1/4SM visibility. Will issue a dense fog advisory for the I-94 corridor and include Cass/Clay counties as well as western Otter Tail. Confidence not as high for the Fargo Moorhead area but certainly expect visibilities less than one quarter mile to develop in far western Cass and far southern Clay over the next couple of hours...especially since Moorhead ob currently showing zero dewpoint depression and calm winds. Dense fog advisory will be in effect through noon Sunday. && .SHORT TERM...(This evening through Sunday) Issued at 253 PM CST Sat Jan 21 2017 Same challenges continue for tonight with fog, drizzle and potential for freezing pcpn later this evening possibly impacting travel. Broad upper trough remains over the n central US. From water vapor imagery appears to be a weak mid level shear axis in central ND shifting east. A weak surface trough bisecting ND from NW-SE also expected to drift east tonight. Ahead of these features there are some lower condensation pressure deficits and there is some weak isentropic lift from the valley west which weakens overnight. With some spotty radar returns over the far western fa will keep some chance pops for measurable pcpn. Only catch is soundings more supportive of drizzle vs r/zr/s. For this will limit any measurable pcpn potential to the west and later shifts will have to adjust if necessary. Overall not much drop in temperatures overnight as in the past few nights although may be a little cooler in the nw. Visibility over the west has improved so degree of fog and if dense in question but with all the low level moisture feel there will be some degree of fog and will keep the mention in the forecast. As weak trough passes tomorrow does not appear to be a great deal of lift so for the most feel the day will be dry. Maintained some low end pops but confidence low and if anything and continuance of some dz/fzdz. Temperatures will continue to be above average but maybe a tad cooler with some cooler air moving in. .LONG TERM...(Sunday night through Saturday) Issued at 253 PM CST Sat Jan 21 2017 The advent of more westerly upper level flow Sun night should start to scour out most of the stratus/dz/fzdz with areas of -sn becoming more prevalent as column cools with time. Most if not all of this pcpn will be east of the valley Sun night. Mon will be dry but will still offer a fair amount of cloud cover in the absence of any strong high pressure. Guidance differs a bit on the track of the next system for Tue but it appears that movement through Iowa or extreme southern MN will still brush the far southern forecast area with minor snowfall amounts. Wed through Sat... 12z GFS/ECMWF continue to indicate low pressure and associated system moving toward lake Michigan as this period begins on Wed. It still appears that the northern edge of the pcpn shield should clip parts of SE ND and the southern tip of our MN lakes region as it pulls out. This is handled well in the fcst with minimal accumulations over this part of the forecast area. Cyclonic flow and some upper level trough could lead to brief periods of light snow region wide during Wed into Thu. Temps will be generally dropping through the week albeit still above average with highs in the 20s instead of the 30s. && .AVIATION...(For the 00Z TAFS through 00Z Sunday evening) Issued at 602 PM CST Sat Jan 21 2017 Expect primarily IFR cigs with lowering visibilities in the southern RRV this evening. May see some brief periods where cigs increase into MVFR range but this should be short lived. && .FGF WATCHES/WARNINGS/ADVISORIES... ND...Dense Fog Advisory until noon CST Sunday for NDZ038-039-049-052- 053. MN...Dense Fog Advisory until noon CST Sunday for MNZ003-029-030-040. && $$ UPDATE...Speicher SHORT TERM...Voelker LONG TERM...WJB AVIATION...Speicher
Area Forecast Discussion
National Weather Service Hastings NE
1001 PM CST Sat Jan 21 2017 .UPDATE... Issued at 1001 PM CST Sat Jan 21 2017 Witnessed some patchy fog in Hastings and a few sites have also reported brief periods of reduced visibilities. Confirmation of the patchy fog on webcams was not fruitful, but the low patchy fog witnessed at the office supported the obs. Currently believe the fog will be patchy in nature and only reduce visibilities to a mile at times. Expanded the mention of patchy fog in the forecast westward through morning. The latest RAP give some support for brief periods of fog/reduced visibilities moving across the eastern portions of the area. Currently am not expecting widespread dense fog. && .SHORT TERM...(This evening through Sunday) Issued at 157 PM CST Sat Jan 21 2017 Aloft: A very complex trof was over the Cntrl/Wrn USA with multiple embedded shortwave trofs. A shortwave ridge was over the Cntrl Plns between the small low that moved thru yesterday...and the next one in the process of forming over TX. This low will remain well S of the region thru tonight...leaving the fcst area in quiet wx. Surface: It`s highly unusual...but broad low pres was over the Plns. There really was no high pres in the wake of yesterday`s system... just a hint of a ridge across MO/KS/NE. Cyclogenesis was underway over the TX Panhandle. This low will head E across OK and into AR tonight...remaining safely to the S. Tonight: Increasing clouds. Becoming p-m/cloudy. Another night of low temps about 15F above normal. Sun: p-m/cloudy in the morning...then clearing in the afternoon. Another mild day...similar to today but a little cooler over S-cntrl Neb. NW winds will gust 18-24 kts. .LONG TERM...(Sunday night through Saturday) Issued at 157 PM CST Sat Jan 21 2017 Aloft: NW flow will gradually strengthen Sun into Sun night as a shortwave ridge approaches ahead of a new trof moving onshore in the W. The ridge will move thru Mon. The Wrn trof will be complex with multiple embedded vort of which will induce cyclogenesis Tue and the formation of a new low. This low will head E across Neb/KS Tue. A broad trof will be left in its wake Wed-Fri. Fri its axis will pass thru the fcst area followed by N flow as a Wrn ridge/Ern trof evolves. Surface: Weak/small high pres will build in Sun and then cross the fcst area Sun night. Lee cyclogenesis will commence over CO Mon along with warm frontogenesis down into the Srn Plns. There are still substantial timing and intensity diff`s in the last 2-3 runs of the NAM/EC/GFS/CMC and the 09Z SREF mean...but the basic idea is that this low will eject ENE across KS Tue. Colder air will be drawn S into the region Wed as this low heads into the GtLakes...and high pres expands from N-S thru the Plns. Another cold front will probably move thru Thu followed by high pres Fri- Sat. Some Sensible Wx Details... Mon: Quiet. Another nice day. Probably averaged p/cloudy most locations. Temps still 10-15F above normal. Tue-Wed: Kept the fcst pretty generic. There is significant uncertainty on where/when/how much pcpn will fall and what type(s) of pcpn will fall. Models: The 00Z/06Z/12Z GFS are faster and weaker. The 06Z/12Z NAM were Srn outliers...ejecting the low into the OK Panhandle. The 00Z/12Z EC/CMC were deeper and slower...with the CMC the slowest outliers. 460 mi separate the fastest GFS run and slowest CMC run at 06Z/Wed. Interestingly...the 12Z run of each model was consistent with its prvs runs...maintained separate camps. QPF: Models are all over the board...ranging from little or a light or moderate winter storm for parts of the fcst area. This system is not occurring in a completely cold environment. Some areas will probably see some rain. This system will struggle to produce pcpn...especially in the warm sector. It will be moisture-starved and most if not all of the pcpn will be collocated with the strongest lift N of the low. Bottom line is don`t take our fcst literally yet. The models need to line up better and converge on a solution. There are a couple things that we do have higher confidence on: 1) It will be windy with this storm...probably windier than we currently have in the fcst...especially if the deeper EC/CMC verify. 2) Turning colder Wed-Sat behind this low...but not excessively so. Temps return near or slightly below normal. Can`t rule out some flurries or a brief snow shwr or two... especially as the upr trof comes thru Fri. && .AVIATION...(For the 00Z KGRI/KEAR TAFS through 00Z Sunday evening) Issued at 530 PM CST Sat Jan 21 2017 VFR conditions are expected to prevail. Light and variable winds will become north to northwesterly overnight. Northwesterly winds will increase during the day Sunday. High clouds will stream in overnight, but are expected to clear during the morning Sunday. && .GID WATCHES/WARNINGS/ADVISORIES... NE...None. KS...None. && $$ UPDATE...Billings Wright SHORT TERM...Kelley LONG TERM...Kelley AVIATION...Billings Wright
Area Forecast Discussion...Updated
National Weather Service Saint Louis MO
901 PM CST Sat Jan 21 2017 .UPDATE... Issued at 857 PM CST Sat Jan 21 2017 Have attempted to update PoPs thru Sun based on latest guidance. In the near term, seems the HRRR has a decent handle on precip overnight. Attempted to hold onto precip across wrn and into nwrn counties into Sun morning and delaying a band of precip moving nwd into srn counties. However, given the amount of uncertainty, did not want to make drastic changes to forecast for tomorrow until more data is analyzed. && .SHORT TERM... (Through Late Sunday Afternoon) Issued at 330 PM CST Sat Jan 21 2017 Low pressure centered over northeast New Mexico will begin moving eastward tonight as the shortwave aloft ejects into the Great Plains. Short range guidance has slowed the timing of the onset of precip into the late evening and overnight hours for most locations; this is especially true for the convection allowing models such as the HRRRs and WRFs. This looks reasonable given the weak forcing over the area for most of the evening. That changes as the shortwave shifts into eastern Oklahoma after 06Z, pushing the low level circulation with it. RAP/GFS/NAM all show strong low level moisture convergence wrapping around the circulation up over the Ozarks by 06Z. The moisture convergence weakens somewhat after 09- 12Z as the low level flow swings around to the east and then northeast with the low moving through northern Arkansas. Expect widespread showers...and a few thunderstorms more or less along and south of the I-70 corridor with this system, but think precip further north will be more spotty since most of the moisture convergence will be focused south of I-70. Should see rain ending slowly from northwest to southeast Sunday with most of the area dry before 00Z. Thunderstorm potential tonight should be limited to areas along and south of I-44. Forecast MUCAPE values drop off quickly from around 1000 J/Kg this afternoon to 300-500 J/Kg this evening. Can`t rule out a few rumbles of thunder with values like that, but don`t think there`s enough instability for more than "isolated" thunderstorms. Very mild temperatures for mid-late January will continue tonight and Sunday...although with rain and cloud cover it`ll be cooler than today. Guidance lows ranging from the mid 30s in northeast Missouri to near 50 in southeast Missouri, and highs of 45 to near 60 look reasonable. Carney .LONG TERM... (Sunday Night through Next Saturday) Issued at 330 PM CST Sat Jan 21 2017 The strong storm system center that will have passed to our south will be pulling away on Sunday evening and some leftover rain can be expected, mainly for areas to the south and east of STL metro. After a brief interlude of a weak RIDGE thru our region late Monday into early Tuesday, another strong Pacific storm system will approach late Tuesday. The models continue to show that the bulk of the lift with this system will pass to our north on Tuesday night, but have trended just a tad more southerly with the track over the past 24hrs. PoPs across our northern CWA have been edged higher as a result. Unlike with the last system on Sunday, enough cold air will try to seep in during the late night and early morning hours to justify some mention of snow for pcpn-types as well as rain. A strong lobe of sheared vorticity aloft will couple with a surface cold front as they drop thru on Tuesday night and carryover into Wednesday. Some limited PoP chances continue, but mainly north of Interstate 70 with a mostly rain but some possibility of snow mixing in during the cooler times of day. Heading into Thursday and into next weekend, models continue to show additional weak upper level disturbances sliding down into our region from the resultant northwest flow aloft as a longwave TROF carves into the eastern CONUS. However, the column gets progressively drier decreasing any confidence on the ability of any one event to successfully precipitate given the lack of strength currently depicted with any of them. Have favored a dry forecast for now until this changes. Otherwise, temperatures are expected to remain above average until the middle of next week when the longwave TROF develops, with temperatures more appropriate for late January heading into next weekend. TES && .AVIATION... (For the 00z TAFs through 00z Sunday Evening) Issued at 539 PM CST Sat Jan 21 2017 Low system continues to develop over the Plains and will swing into the region on Sun. Elevated TSRA have developed across AR heading into srn MO. Much of the guidance has slowed onset of precip at terminals and raised doubt that precip will reach KCOU, esp KUIN. A lot of question on cigs and visbys tonight. There is a fair amnt of guidance that wud suggest much of tonight remains VFR, but is also some guidance that suggests IFR. Trended visbys and cigs more twd the VFR/MVFR, but did not see too much evidence to suggest drastic changes from the pref TAFs. Will continue to monitor. Tilly && .LSX WATCHES/WARNINGS/ADVISORIES... MO...None. IL...None. && $$ WFO LSX
Area Forecast Discussion
National Weather Service Memphis TN
605 PM CST Sat Jan 21 2017 .UPDATE... Updated for the 00z Aviation Discussion. && .PREV DISCUSSION... /issued 559 PM CST Sat Jan 21 2017/ UPDATE... Updated for lowering evening POPs across the northern Midsouth counties. DISCUSSION... Timing of convective development now in the ARLATEX suggests activity will mainly affect Midsouth points south of a Jonesboro Arkansas to a Corinth Mississippi line before midnight...with points to the north getting in the main action afterwards. Made adjustments to the evening POPs accordingly. Greatest severe threat will still be large hail...with the most favorable region for an isolated tornado to the south of I-40 and west of I-55. JAB && .PREV DISCUSSION... /issued 333 PM CST Sat Jan 21 2017/ Currently... at 3 PM CST around the Mid-South, clouds are overspreading the region now with latest H5 analysis depicting southwest flow present aloft as a mid-level trough axis ejects out of the desert southwest and into Texas. This trough and upper low will bring the region a chance for severe weather late this evening and tonight. Clouds will continue to build into the region late this afternoon and evening. Models continue to work out around 1000 J/KG of SBCAPE for portions of the southern half of the FA, primarily over the Mississippi Delta region. A warm front will slowly lift north into the region as a surface low develops to the west in association with the upper low. This will allow lifting of some surface based instability, overcoming any atmospheric capping and producing the chance for strong to severe storms. The latest SPC outlook has a moderate risk just to the SW of the region, with an enhanced risk reaching into SW counties of the local FA. This area will have the best chance for strong to severe storms this evening as the warm front moves through the region, most likely between 8 and 10 PM for the SW counties of the FA. While large hail will be the primary threat given steep mid-level lapse rates as heights fall rapidly aloft with the approaching trough, enough shear could be present along the surface boundary for an isolated tornado or two. In addition, damaging winds could also be possible from strong downdrafts. While the greatest threat of severe storms will be over the Mississippi Delta region, after 10 PM there will be a slight risk for severe storms moving into the rest of north Mississippi, eastern Arkansas, and west Tennessee. The latest HRRR composite reflectivity guidance suggests any discrete storms developing to our SW conglomerating into a more linear form of storms before affecting the Mid-South. Showers and thunderstorms will continue overnight and into Sunday as the upper low moves toward and over the region, although the severe threat will come to an end by the early morning hours of Sunday. Sunday highs will be quite cooler than Saturday`s as winds become more northwesterly as the low passes over the region. By early Monday both the surface and upper low will be east of the region, with conditions drying as highs only reach the lower 50s. Dry conditions will maintain for Tuesday, with an upper ridge moving overhead allowing temperatures to warm again into the 60s. By early Wednesday a cold front associated with a surface low to the north of the area will swing across the region. Models have continued to trend drier with this feature, thus have only included slight pops in eastern portions of the FA. Mild temperatures midweek will become more seasonable for late in the week as conditions dry once again. ZDM && .AVIATION...00z TAFs VFR conditions will continue through the evening hours before deteorating around midnight. MVFR or lower cigs and vsbys will be possible early Sunday morning at all terminals as thunderstorms move across the region. Winds will remain southeast between 5-10 kts overnight. A few severe storms will be possible overnight with hail the greatest threat. Widespread showers and thunderstorms will continue across all the terminals through Sunday as a slow moving upper level low moves across the region and helps destabilize the atmosphere. Winds will increase from the southwest by Sunday afternoon at all sites. JLH && .MEG WATCHES/WARNINGS/ADVISORIES... AR...None. MO...None. MS...None. TN...None. && $$
Area Forecast Discussion
National Weather Service Blacksburg VA
920 PM EST Sat Jan 21 2017 .SYNOPSIS... A weak warm front south of the area will continue to be the focus for impulses to travel along overnight into Sunday, resulting in added rounds of rainfall tonight through Sunday afternoon. The front should lift north into the region Sunday night as a stronger area of low pressure approaches from the west. This low pressure system will slide slowly east across across the area Monday before exiting Monday night, allowing for drier weather under high pressure for Tuesday. && .NEAR TERM /THROUGH SUNDAY/... As of 830 PM EST Saturday... One wave of mostly light rainfall moving through the CWA this evening producing mostly 1/4 to 1/3 inch rainfall amounts. All of the synoptic scale and short-range models show that this first wave and associated negatively tilted upper short wave will move out of the area this evening. The next wave arrives Sunday late morning, the activity now being manifested as severe thunderstorms along the central Gulf Coast. This activity will not be severe when it reaches the RNK CWA. Rainfall with that wave appears comparable to the current one. In between, increasingly deep southwest diffluent flow aloft could result in light rain at almost any time, but nothing indicated by any model that generates much concern in terms of heavy rain. More substantial rainfall arrives Sunday evening along with the threat for some convective elements, although latest model severe weather parameters for our CWA look limited. The most significant period of rainfall and potential for storms should affect the CWA in the 21Z Sun - 06Z Monday time frame. Am concerned about fog development again tonight. Currently, the rainfall is suppressing fog development. However, with weak wedge in place and wet ground along with light winds, seems like fog development would be fairly probable again as the night progresses. Will continue to monitor and issue SPS or DFA/NPW if needed. As of 305 PM EST Saturday... Active near-term forecast period begins tonight continuing into a good part of the short-term period due to multiple rounds of steady rainfall to affect the Blacksburg forecast area. Late-afternoon surface analysis depicts a 1003 mb low near Atlanta, enhanced to some extent by ongoing strong convective line marching across southern Georgia, with eastward-trailing warm front from the low center to a position from Greenville/Spartanburg SC to just north of Florence SC to Wilmington NC. Lingering in-situ wedge lies north of it across our area, keeping most of our forecast area in the cool, cloudy side. Aloft, diffluent mid-level regime with increasing 500 mb height falls approaching far southwest Virginia. Composite radar mosaic reveals band of steady rain along the northern periphery of warm front/mesolow advancing to the northeast, its northern extent from Knoxville TN to near Charlotte NC. For Tonight: First band of steady light to at times moderate rain to progress primarily across the Grayson Highlands, southside Virginia and northwestern North Carolina between roughly 21z and 04z per high- res HRRR and RAP. Highest PoPs are focused across that general area, with a lower/gradient in PoPs north to northwest essentially west of the Blue Ridge. Appears that the northern fringe of negative Showalter indices snakes its way into those aforementioned southern areas. Included slight chance Thunder mention accordingly, but I did not want to hit that harder given the best potential for convection remains well south of our forecast area into central/western NC on southward. Rainfall amounts for tonight range from a few hundreths in the northwestern part of the CWA to around four-tenths along the North Carolina Piedmont into southside Virginia. In the wake of the rain, indication from most guidance is that the wedge/CAD rebuilds back in with light east flow. Thus for the after midnight period, I`ve again introduced patchy fog for most of our forecast area as we`ll be waiting for the second, more significant/widespread round of rain approaching from the southwest. Forecast lows in the mid 40s to low 50s under persistent overcast and areas of rain showers. For Sunday: Upper trough closes off in the lower Mississippi Valley early Sunday morning. Aforementioned warm front then lifts north across much of our forecast area. This focuses a period of moderate rainfall with rainfall rates enhanced somewhat by (1) convection - elevated negative Showalter Indices advect into our central portion of our CWA per NAM/GFS and (2) potential for southeasterly upslope enhancement in the foothills and Piedmont areas in Virginia and North Carolina. SPC maintains a Marginal/5% severe and Slight/15% severe Sunday, primarily across our Piedmont NC counties into the southside of Virginia due to strong vertical wind profiles. However only very marginal if any surface-based CAPE with much of the already modest instability being elevated. Potential is there for thunder but given the limited amount of instability owing to early- day CAD, not thinking we`ll see any severe. A conditionally greater risk for stronger cells remains well to the south from central NC to FL and as reflected in SPC`s Day-2 Convective Outlook. Rainfall stands to be the heaviest during the morning into early afternoon hours. Interesting that to some varying extent amongst the 12z models there is something of a lull in the rain during the afternoon. So while PoPs start high-Likely to Categorical, I`ve tried to show a reduction in PoPs to reflect a break in rain, though they are still high-Chance (40-50%) and only stand to increase again from SW - > NE Sunday night. All in all, anticipate a wet Sunday with at least some rise on area rivers and streams. See the Hydro section which speaks more to the hydrologic aspect given a few days of at least steady rains (spanning into the short-term period). Looking for highs Sunday to range from the mid 50s to around 60. && .SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/... As of 245 PM EST Saturday... Next round of heavier rainfall including possible embedded stronger storms across the far south will be ongoing Sunday evening as very strong lift/diffluence arcs north ahead of deep low pressure over the western Carolinas. This will likely bring the heaviest period of rainfall given more convective nature under 1.25 inch PWATS just ahead of the advancing warm front and subsequent possible triple point just off to the southwest. However just how much of the south and/or east can work into the warm sector remains in question, with models showing the low level wedge in the wake of earlier rainfall holding near the VA/NC border before weakening by early Monday. Since shear is quite impressive and strength of warm advection stronger than usual, per such a stacked system given the upper low passing near the Blue Ridge, opting to include more thunder mention espcly southeast into Sunday night. Also cant rule out at least some elevated rumbles elsewhere overnight espcly Sunday evening southern Blue Ridge where seeing a brief but strong upslope component. Otherwise pops returning to categorical into early Monday across the region with lows in the 40s but perhaps rising some early on. Upper dry slot may act to cut off showers across the east Monday morning as the center of the upper low drifts into western VA and eventually to the east/northeast of the area by Monday night. This likely to shift bands of heavier rainfall over the west during Monday as the deformation zone develops aided by wrap around moisture behind the exiting upper low. However uncertainty remains espcly by Monday with the track of this system including the degree of more concentrated heavy rain, and where precip may be more convective resulting in higher rates. Models have again shifted east with QPF totals given more convective nature over the southeast and more in the way of stratiform rain closer to the low at this point. This on top of previous rainfall would likely bring the highest threat for flooding pending exactly where added bands set up, so keeping mention in the HWO and hydro section of the AFD for now. Highs Monday remain tricky with potential for values to zoom to around 60 Piedmont while staying in the 40s northwest, with low/mid 50s in between. Axis of deeper moisture should continue to fan out to the west before shrinking along the higher western mountains Monday night as the low and associated lift depart. However increasing upslope northwest flow in the wake of this system likely to keep showers going western third overnight, while some drying and cutoff in pops takes shape east of the Blue Ridge. Temps aloft also appear too warm for much snow so leaving out mention except highest elevations late Monday night. Main concern overnight will again be with strong winds as the low heads offshore and the pressure gradient between high pressure to the south increases. Latest input of strong subsidence, brief cold advection and a lowering inversion into local scheme data off the GFS, still suggests potential wind advisory criteria mainly NC mountains. Therefore have again included a mention in the HWO there overnight. Otherwise running with diminishing pops overnight with only chance pops lingering north/west late and little elsewhere. Lows mostly 30s to lower 40s. && .LONG TERM /TUESDAY THROUGH SATURDAY/... As of 215 PM EST Saturday... Strong upper trough will be lifting out on Tuesday making way for a brief period of shortwave ridging that will slide east and across the area later Tuesday into Wednesday night. May still be some upslope driven rain and high elevation snow showers Tuesday morning before much drier air slides in from the southwest under a nose of surface high pressure that will extend north from the Gulf coast. This should bring clearing skies Tuesday afternoon with sunny skies on Wednesday before clouds increase again later Wednesday night ahead of the next upstream cold front. Winds should remain quite strong into midday Tuesday with potential advisory level speeds espcly NC mountains into far southwest VA. Will be the mildest period for quite some time with highs 40s mountains to upper 50s east Tuesday, followed by 50s to lower 60s Wednesday under warmth aloft and westerly flow. Return to more winterlike conditions will ensue by weeks end with a cold frontal passage by Thursday ahead of a broad longwave trough that will drop south into the region and persist into next weekend. However latest guidance not nearly as strong or deep with this feature making for more Canadian type air vs. much colder thickness seen yesterday that was supportive of Arctic air. However will see persistent cold advection develop by Thursday with weak passing shortwaves gradually helping to bring in colder air aloft by Saturday. A band of showers possible along/behind the front Thursday into Thursday night although iffy given only sheared southern energy. Therefore will only include a low pop shower mention including possible western snow showers overnight. Otherwise will evolve to mostly upslope driven clouds and periodic light snow showers far west, to mainly clear/sunny east Friday into Saturday, under a rather dry and more westerly flow driven environment. Highs mostly 30s to around 40 mountains to mid 40s east into the weekend. && .AVIATION /02Z SUNDAY THROUGH THURSDAY/... As of 658 PM EST Saturday... Poor flying conditions expected during the taf period with widespread IFR/LIFR in low clouds,fog and rain. This evening into tonight, flight categories will lower with patches of rain and drizzle. Pocket of fog in the east will degrade ceilings and visibilities to IFR and LIFR conditions at KROA,KLYH and KDAN. While in the west at KBCB, KLWB and KBLF expect VFR conditions to lower to MVFR in rain and fog. Rain will pull out of the east early tonight. Then, in-situ wedge develops in behind the rain again focusing a period of IFR to VLIFR conditions due to stratus and fog. Second wave of steadier rainfall then looks to build from the southwest during the morning hours Sunday, with coverage of rain covering a larger portion of our forecast airspace along with a few rumbles of thunder. Due to low forecast confidence in specific airports being affected by thunder, did not mention in the TAF at this point, but the best shot would be at KLYH, KDAN and KROA. Flight categories IFR to VLIFR through 00z Monday, due to low ceilings, with visibilities 3-6 SM in rain briefly heavy at times. Winds generally light and variable (trending southeast) through most of the TAF period. Low confidence in ceilings,visibilities and wind during the taf period. Extended Aviation Discussion... A slow-evolving but potent storm system affecting a good part of the central and southeast CONUS will lead to a potentially long period of sub-VFR conditions through Monday with stratus, fog, and periods of rain, in addition to thunderstorms. Once the storm passes on Tuesday, conditions will improve with respect to cigs and vsbys, but it will become breezy with northwest winds gusting to 30 kts behind the departing storm on Tuesday. High pressure prevail for Tuesday night and Wednesday night. A band of MVFR showers possible along/behind the front Thursday into Thursday night. && .HYDROLOGY... As of 310 PM EST Saturday... There will be several rounds of rainfall affecting the Blacksburg hydrologic service area beginning tonight and lasting through Monday. The greatest amount of rain over a 24-hour period looks to be on Sunday with 1 to 2 inches of rain across most of the forecast area, with lighter rainfall amounts expected tonight across the southern tier of counties/Dan and Yadkin River basins and again Monday along and west of the Appalachian Divide into southeast West Virginia, the Mountain Empire of Virginia and into parts of the New River Valley. Using a model blend, heavily weighting WPC in that blend, forecast rainfall amounts tonight through Sunday range from 1.5" for most of southeast West Virginia and the Alleghany Highlands, to well over 2 inches along the east-facing slope of the Blue Ridge. Current expectation is for gradual main-stem river rises with faster/greater response on smaller rivers/creeks, along with some potential for ponding on roads and in areas of poor drainage. Rainfall rates do not appear excessive at this point. The only river forecast point projected to go just into Minor flood stage is the Dan River at South Boston. That may be a worst-case, and it would take a greater amount of rain over a shorter period (more convective rain rates) to increase the risk for minor flooding across the forecast area. Given that confidence is low in flooding, a flood watch has been issued at this time and would rather wait to see what tonight`s rainfall brings before that is considered. && .RNK WATCHES/WARNINGS/ADVISORIES... VA...None. NC...None. WV...None. && $$ SYNOPSIS...JH/PM NEAR TERM...AL/RAB SHORT TERM...JH LONG TERM...JH AVIATION...AL/KK HYDROLOGY...AL
...Update to aviation forecast discussion...

.SHORT TERM...(This evening through Sunday) Issued at 258 PM CST Sat Jan 21 2017 20Z water vapor imagery shows an upper level shortwave amplifying as it moves across the southern Rockies towards the plains. At the surface, a low pressure system is deepening over the southern high plains in response to the shortwave. Weak ridging remained over eastern KS. For tonight models continue to take the bulk of the dynamics from the shortwave aloft, mainly to the south of the forecast area. However the model progs do show some weak forcing, moisture advection and a diffluent pattern aloft developing over east central KS this evening. So chances for rain showers this evening appear to be improving. Although rain amounts will generally be around a tenth of an inch. The bigger concern is the potential for dense fog to form along the NEB state line late tonight. The RAP has been consistent in developing dense fog over Brown and Nemaha counties and this is supported by the ARW and NMM. Although this is dependent on how far north mid level clouds advect north as models develop the fog on the northern fringes of the cloud cover. Additionally surface winds from the north are expected to freshen towards 12Z which raises questions about how dense fog may be. Have included a mention for areas of fog across northeast KS but uncertainty in visibilities precludes any headline at this time. The next shifts can monitor trends and reevaluate fog potential. Lows tonight should range from the lower 30s north where skies may remain clearer longer, to the lower 40s across east central KS expecting clouds to keep temps from falling to far. For Sunday, think skies should clear out by the afternoon as the system south of the area continues moving east. Some low level cold air advection is anticipated on the back side of the system so temps should be cooler than today. Have highs in the lower 40s across northeast KS where fog and stratus are possible to near 50 in central KS. .LONG TERM...(Sunday night through Saturday) Issued at 258 PM CST Sat Jan 21 2017 Upper ridge building east into the Plains brings clearing skies Sunday night. Warm air advection increases from the mid to the lower levels late Monday into Monday night, though still dry through the bulk of the troposphere so no precip anticipated. Models showing a significant spread in handling upper energy moving into the central portions of the CONUS Tuesday, but still keep the local area on the dry side and precip chances limited, especially south of Interstate 70. Northwest winds behind this system late Tuesday into Tuesday night brings much colder air in for Wednesday and on into the end of the week as northwest to northwest flow dominates the column, though airmass is still modified continental and keeps values near normal. Will retain some mention of precip Tuesday night into Wednesday as the trough axis moves through. Any of this appears light at the most but would turn to wintry phases with time. Dry conditions should be the rule beyond these periods. && .AVIATION...(For the 00Z TAFS through 00Z Sunday evening) Issued at 540 PM CST Sat Jan 21 2017 Light rain showers continue to push northward toward the TAF sites. These have arrived at the Topeka terminals and should arrive at within the hour. VFR conditions are expected to prevail at MHK. MVFR visibilities are expected from 06-10Z at the Topeka terminals as patchy fog develops within the scattered rain showers. Winds will increase from the north at 10-15 knots by 15Z Sunday morning. As the surface low moves southeast of the area, winds will begin to decrease near the end of the period. && .TOP WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...Wolters LONG TERM...65 AVIATION...Baerg