Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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000 FXUS63 KGRR 240825 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 326 AM EST Fri Feb 24 2017 LATEST UPDATE... Synopsis/Short Term/Long Term/Marine .SYNOPSIS...
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Issued at 326 AM EST Fri Feb 24 2017 A strong area of low pressure will move through the region through this evening. This system is bringing showers and storms to most of the area. A wintry mix is falling north of M-20 this morning. This system will bring the potential of severe weather later this afternoon and early this evening to areas south of Lansing and east of Kalamazoo. Colder air will filter in over the area late tonight and on Saturday. Light snow will develop at the same time, with some light accumulations possible. A weak wave of low pressure will move through on Sunday and bring another chance of some light snow, that could mix in with a little bit of rain. The weather will remain unsettled next week as multiple systems could affect the area.
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&& .SHORT TERM...
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(Today through Sunday) Issued at 326 AM EST Fri Feb 24 2017 The main points of note in the short term are that we will maintain the Winter Weather Advisory as is for the northern counties this morning, and the best severe weather threat has shifted slightly a bit SE compared to yesterday at this time. Much of the advisory area is seeing light snow as of 08z this morning. Temps are above freezing thus far, so no major impacts are likely occurring. We expect that p-type will transition over to sleet and freezing rain for a few hours this morning before changing to rain by afternoon. Temps aloft are increasing ahead of the sfc low to our SW, while temps and dew points at the sfc are dropping due to the cooler and drier E/NE flow. Elsewhere showers are ongoing, with some lightning moving across the lake as of 08z. The storm chances will increase gradually through today as the atmosphere becomes more unstable. All storms early this morning will be of the elevated variety, with sfc based instability arriving at the srn CWFA boundary around 12z this morning. The severe threat will come after about 3 pm this afternoon and will last into mid evening tonight. The convection allowing models indicate there will be some isolated cells popping up toward mid afternoon mainly in the warm sector which should end up being south of a line from South Haven to Lansing. We then expect a more solid line to form ahead of the cold front starting around 22-00z that will push east. The warm sector should have over 1000 j/kg of low level based cape available. This combined with the high deep layer and 0-3km shear values will justify the severe threat. We continue to expect damaging winds will be the main threat. A tornado is not out of the question with the strong low level shear values. The dry slot moves in then behind the front this evening, and then the wrap around moisture and main wave will arrive over the western portion of the area by 12z Sat. Temps will have dropped below freezing, however the warm ground will take a bit to cool off enough for accumulations to occur. We are thinking up to a couple of inches will be possible, with the highest amounts being NW. Ridging will build in quickly then for Sat night, diminishing most of the snow/snow showers. Some light lake effect could hold on with h850 temps in the minus teens C, but the ridging will squash the vertical extent and capping the snow showers. We will see another wave move through on Sun with some warming aloft. This will bring another chance of light snow, possibly mixing with rain in the afternoon as temps warm well into the 30s. .LONG TERM...(Sunday night through Thursday) Issued at 326 AM EST Fri Feb 24 2017 We`ll have several opportunities for pcpn during the extended period, but no big storms are on the way. A weak short wave passing over Lower Michigan Sunday night may produce a period of light snow but not much more than that. We`ll dry out for monday as weak ridging moves overhead. Both the gfs and ecmwf show a system moving out of the southern Plains toward the Great Lakes midweek. Mixed rain and snow are possible in the warm advection pattern ahead of the low Tuesday. The gfs is a bit stronger, especially aloft, and tracks the low over the cwa while the ecmwf is much farther northwest of Wisconsin. We`ll keep high pops for now and taper pops Wednesday into Thursday as the sfc low moves east and the upper wave moves through. Highs will be mostly in the 40s Monday through Wednesday before cooler air flows in behind the system for Thursday and highs fall to the mid 30s.
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&& .AVIATION...(For the 06Z TAFS through 06Z Friday night) Issued at 1234 AM EST Fri Feb 24 2017 As low pressure moves toward Lower Michigan today, we`ll see a warm front move north across the taf sites. By this afternoon, MKG and GRR will be north of the warm front and the other sites will remain to the south. The southern taf sites may see thunderstorms this afternoon from 21-00z. A few of the storms could be strong. MVFR/IFR conditions are expected much of today due to reduced vsbys in fog and showers along with low cigs. && .MARINE...
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Issued at 326 AM EST Fri Feb 24 2017 We have an ongoing Small Craft Advisory event this morning that we will maintain the headlines for at this time. This is an offshore flow type of event, so the winds and waves are worse away from the shoreline. The peak of the event is just about here, and will then taper off fairly quickly by this afternoon. We are looking at a max SCA or minimum Gale event on Saturday behind the cold front. We will hoist a Gale Watch for this event on Saturday.
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&& .HYDROLOGY... Issued at 255 PM EST Thu Feb 23 2017 Repeated showers and thunderstorms on Friday may produce rainfall totals in excess of 1 inch in parts of the area. There are several rivers which will be susceptible to rises above bankfull if their respective basins receive that much rainfall. This includes both small basins with quick response times and main stems with longer response times. Will have to monitor rainfall totals closely on Friday. In the longer term, there is a low confidence but plausible scenario in which additional rainfall amounts in excess of a half inch on Tuesday sustain high river levels. && .GRR WATCHES/WARNINGS/ADVISORIES...
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MI...Winter Weather Advisory until 11 AM EST this morning for MIZ037>040-044>046. LM...Small Craft Advisory until 11 AM EST this morning for LMZ844>849. Gale Watch for Saturday for LMZ844>849.
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&& $$ SYNOPSIS...NJJ SHORT TERM...NJJ LONG TERM...04 AVIATION...04 HYDROLOGY...CAS MARINE...NJJ

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