Forecast Discussions mentioning any of "HRRR" "RAP" "RUC13" "RUC" "RR" received at GSD on 12/16/17

Area Forecast Discussion
National Weather Service Grand Rapids MI
929 PM EST Fri Dec 15 2017 LATEST UPDATE... Update .SYNOPSIS... Issued at 322 PM EST Fri Dec 15 2017 The lake effect snow showers that impacted the area this morning are diminishing this afternoon. This will continue into early this evening. Another band of light snow will develop this evening south of I-96, and will migrate north through Saturday morning before ending. 1 to 3 inches of new snow will be likely. A lull in the snow is expected then Saturday night and early Sunday. Precipitation chances will increase once again later Sunday. The precipitation will start as some rain or snow as warmer air moves in, and continue through Monday night before ending. && .UPDATE... Issued at 929 PM EST Fri Dec 15 2017 I have issued a Winter Weather Advisory overnight till 10 am Saturday morning for 2 to 4 inches of snow. Nearly all of the Hi- Resolution models for several runs in a row now are forecasting around 0.30 inches of QPF from this warm advection/isentropic lift event overnight. The 18z and 00z NAM and several runs of the HRRR and RAP model show around 50 knots nearly perpendicular to the anisotropic surfaces tonight (around midnight). The focus of the heaviest precipitation is from Southeast Kent County northwest across Ottawa into Southern Muskegon County. Since warm advection events tend to over preform I though it best to issue the Winter Weather Advisory for the counties with the heaviest snowfall overnight. && .SHORT TERM...(This evening through Sunday night) Issued at 322 PM EST Fri Dec 15 2017 Our main focus of the short term is now the light snow expected tonight, and then p-type questions for Sunday and Sunday night. The advisory for today will be allowed to expire on time with the new forecast package. Lake effect snow showers are on the declining trend this afternoon with regards to intensity and coverage as expected. The short wave that helped the uptick today, is now moving east of the area. This is driving down the inversion heights for a bit. The break in snow will be short lived, especially for the Srn portion of the CWFA. We will see a sfc trough/cold front over the central portion of the area, drive south to I-94 this evening before stalling. It stalls out as upper heights start to build also this evening. We will see a wave of moisture transport translate along the front and develop a band of light snow. This looks to develop a NW to SE band of light snow later this evening, that will gradually shift north to be centered around I-96 by Sat morning. This does not look to be significant enough to warrant another advisory, but will drop 1-3 inches over a 12-18 hour time frame. It will end as the wave moves east of the area Sat afternoon. The next situation will be incoming pcpn late Sun and Sun night. We will see a short wave across the Central and Southern Plains lift NE into the area. This wave will be different from the series of waves we have seen over the past couple of weeks since it will be coming from the SW. This will allow warmer air to push up into the area. The pcpn may start out as some snow initially. It will tend to change over with a SW low level flow advecting above freezing air, and a sufficient melting layer depth to likely change it over to rain for at least srn areas Sun night as temps warm. It does not look like this system will produce significant impacts. We will monitor it in case temps do not warm quick enough, and p- type becomes a problem. .LONG TERM...(Monday through Friday) Issued at 322 PM EST Fri Dec 15 2017 Active pattern continues in the extended with two lows moving through separated by a period of lake effect snow. The first storm early in the week does not look to have much impact as the southern stream moisture remains well separated from the dominant northern stream and the sfc low passes well north of the forecast area. Cold front comes through Monday night with cold advection and lake effect snow showers Tuesday and Tuesday night then tapering off Wednesday as warm advection begins ahead of the next low. Bumped up Superblend POPs for lake effect snow showers during this time period. The second low comes through Thursday into Friday and continues to have a lot of ensemble spread between a further north, stronger low and a weaker, more southern track that would be colder with mostly snow instead of mostly rain. The 12Z operational GFS and ECMWF have flip flopped with each other since yesterday with the ECMWF now having the less amplified, colder solution. Did not make any changes to the POPs or temperatures during this time as the blend still looks like a good compromise. Looking beyond Friday and to December 25th...the overall synoptic pattern shows a polar vortex across Eastern Canada and a SE CONUS upper ridge. There is a very impressive temperature gradient between the Great Lakes and Central Atlantic coast, with arctic air and 850 mb temperatures of -20C in Lower Michigan and a balmy plus 12C near Cape Hatteras. We will have to closely watch where the southern edge of the arctic air and tropical moisture feeding up from the Gulf meet. At this point it appears we will be solidly in the cold air with some lake effect snow showers while there could be a band of heavy freezing rain somewhere to our south...potentially across the Ohio Valley. && .AVIATION...(For the 00Z TAFS through 00Z Saturday evening) Issued at 618 PM EST Fri Dec 15 2017 As the current round of lake enhanced snow showers come to an end, a band of warm advection snow will spread northward though the TAF sites overnight. The I-94 TAF sites will have only light snow, and that will mostly be prior to 08z. With the heaviest snow being in the 03z to 06z time frame. Meanwhile for I-96 TAF sites the band snow will last longer and have heavier snow assoicated with it. It should be solid IFR for MKG, GRR and LAN for at least 6 hours (06z through 12Z). After the snow ends, the I-94 TAF sites may see the low clouds break up and ceilings be VFR, on the other hand, for the I-96 TAF sites I could see solid IFR cigs maybe even some fog. This could be problem if surface temperatures stay below freezing (more than likely will). && .MARINE... Issued at 322 PM EST Fri Dec 15 2017 We will be allowing the current Small Craft Advisory to go on as is for now. Most of the current obs along the shore continue to support advisory conditions. Winds will gradually ease up, and waves will slowly follow suit. The 5 am expiration time looks good at this point. && .HYDROLOGY... Issued at 322 PM EST Fri Dec 15 2017 Many rivers have iced over due to the snow and cold temperatures. The Looking Glass near Eagle has risen above bankfull due to downstream ice constricting the flow. It is expected to gradually fall but some fluctuations are still possible. High temperatures above freezing early next week will soften the ice a bit. Water frozen in the snowpack ranges from 0.5 to 1 inch in most locations, but a full snowmelt is not expected anytime soon. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...Winter Weather Advisory until 10 AM EST Saturday for MIZ050-051- 056>059-064>067. LM...Small Craft Advisory until 5 AM EST Saturday for LMZ844>849. && $$ UPDATE...WDM SYNOPSIS...NJJ SHORT TERM...NJJ LONG TERM...Ostuno AVIATION...WDM HYDROLOGY...CAS MARINE...NJJ
Area Forecast Discussion
National Weather Service Lincoln IL
806 PM CST Fri Dec 15 2017 .UPDATE... Issued at 805 PM CST Fri Dec 15 2017 Earlier batch of altocumulus is exiting the northeast fringes of the forecast area this evening. More expansive area of mid and high clouds, currently to our northwest, has begun to spill into central Illinois. Latest humidity progs off the RAP model suggests this overspreading areas along and north of I-72 past midnight, but shifting eastward with time and moving out before sunrise. With southwest winds averaging around 10 mph overnight, not a lot of additional temperature dropoff is expected. Going forecast had a good handle on this, and only needed some minor adjustments to reflect latest trends. && .SHORT TERM...(This evening through Saturday) ISSUED AT 255 PM CST Fri Dec 15 2017 A weak disturbance will bringing another batch of stratocumulus clouds (ceilings 4-6k ft) se into central IL and along and Champaign to Taylorville line at 230 pm. An area of light snow and flurries was over ne IL and skirting far ne CWA along and ne of a Henry to Chenoa to Hoopeston line. 1002 mb surface low pressure was over eastern upper MI and will track to along the southern Quebec and Ontario province line this evening, taking its light snow/flurries out of area late today. Low clouds will decrease early this evening though mid level clouds to continue into this evening and decrease during overnight. Clouds along with sw winds 8-13 mph to keep temps from falling too much tonight, with lows in the upper 20s to around 30F. A nice day ahead on Saturday with a fair amount of sunshine and sw winds 10-15 mph and gusts to 20 mph bringing milder temperatures. Highs range from the upper 40s to around 50F along and ne of I-74 to the mid 50s from Springfield sw. .LONG TERM...(Saturday night through Friday) ISSUED AT 255 PM CST Fri Dec 15 2017 Dry weather continues Saturday night as clouds increase by overnight ahead of wx system taking shape in the southwest states. Lows in the low to mid 30s, coolest along and ne of I-74. Weak surface low pressure to eject ne from the southern plains and into nw IL Sunday afternoon. Precipitation to spread quickly ne across central IL during Sunday morning and could start as a mix along and north of I-74 early Sunday morning before becoming all rain. This system is a quick mover and precipitation already diminishing from the sw later Sunday afternoon, with rainfall amounts only up to a tenth inch possible. Highs Sunday in the mid to upper 40s but these readings still a good 10 degrees above normal for mid December. A weaker disturbance ejects ne and brings small chances of light rain showers overnight Sunday night into Monday morning. Lows Sunday night in the mid to upper 30s. Highs Monday in the upper 40s north of Peoria and mid 50s by Lawrenceville. A dry stretch of weather expected from Monday afternoon through Thu morning across CWA as storm tracks will be across the Great Lakes and over the southeast states by a frontal boundary. Above normal temps continue with highs 45-55 Tue thru Thu. Latest ECMWF model now showing surface low pressure tracking into the mid MS river valley by Wed afternoon and brings qpf into southern half of IL Wed and Wed evening. This will need to be watched but for now we stayed with consensus of a dry forecast during that time which GFS and GEM show. A deepening upper level trof over the Rockies by Thu to eject a weather system into the upper Midwest late Thu and deepen surface low pressure ne into the southeast Great Lakes Fri afternoon. Continued small chances of rain showers over IL river valley late THu afternoon, then spread chances of precipitation se across CWA during Thu night with rain turning to snow showers as colder air usher in. Temps cool back closer to normal for next Friday. 12Z GFS and ECMWF models show an active southern stream storm track during Christmas weekend and will need to be watched for holiday travelers. Latest models currently keep precipitation south of CWA next weekend, but models have not been consistent from previous runs and also GEM model not in best agreement with GFS and Ecmwf. && .AVIATION...(For the 00Z TAFS through 00Z Saturday evening) Issued at 520 PM CST Fri Dec 15 2017 Cloud deck around 6,000 feet is pulling eastward and should be out of the TAF sites in the next few hours. Larger area of mid and high clouds is streaming southeast and will shift eastward over central Illinois overnight, but will not pose an aviation impact. Southwest winds should average around 10 knots throughout the period. && .ILX WATCHES/WARNINGS/ADVISORIES... NONE. && $$ UPDATE...Geelhart SHORT TERM...07 LONG TERM...07 AVIATION...Geelhart