Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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000 FXUS63 KGRR 251930 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 330 PM EDT Tue Apr 25 2017 LATEST UPDATE... Synopsis/Short Term/Long Term/Hydro/Marine .SYNOPSIS...
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Issued at 330 PM EDT Tue Apr 25 2017 The dry and warm air mass that has been over the area the past few days will gradually come to an end through Wednesday evening as a system slowly pushes in from the West. This system will have waves of low pressure move along it, and bring periods of showers and storms through Thursday afternoon. There is a small chance of severe weather, however heavier rainfall will likely be a better threat. A mainly dry period can be expected from Thursday night through Friday night as the area will be in between systems. Another bigger system that will have plentiful moisture from the Gulf will move in over the course of the weekend and bring more rain to the area.
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&& .SHORT TERM...
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(This evening through Thursday night) Issued at 330 PM EDT Tue Apr 25 2017 Our main issue in the short term forecast period is determining pcpn trends through the period, and hazards associated with any storms that will push through the area. We will start to see some chances of rain showers move in across the NW corner of the CWFA late tonight and Wed morning. This are will be on the far Ern periphery of the best moisture transport moving across WI and IL tonight with a 35 knot low level jet associated with a short wave moving NNE. Instability in our area is pretty much zero, so we do not expect thunder through Wed morning. We expect that a few showers/storms could pop up Wed afternoon across the area. A better chance of more widespread showers/storms will come in mid-late evening across the Wrn half of the area. Instability builds Wed afternoon with dew points approaching 60 degrees, and sfc temps in the 70s across most of the area that does not see clouds/rain showers in the morning. Sfc based CAPE`s look to approach 1000 j/kg across the SE portion of the area which could approach 80 degrees. The limitation is that forecast soundings indicate that we could be capped around 8-10k feet. If something was to develop, deep layer shear values are fairly impressive, in the 40- 50 knot range. This could provide some severe weather with strong winds or large hail. A more organized line of showers/storms comes through mid-late evening into the overnight hours. A fairly strong short wave moves up Lake Michigan, and looks to have a 50+ knot low level jet associated with it. Instability in general will be on the wane some. This looks like the biggest threat would be a swath of heavier rain in a short period of time. The Wed night wave will move through, and the cold front will progress east a bit into the central portion of our area. At this time, it looks like the main wave moves through, and brings another low level jet across the area. The models have a look to them of another swath of heavier rain with limited instability available. The swaths of heavier rains will be tough to pin down at this time, but there are good signals they will be around the area. We should see all the rain move out by Thu evening as the entire system lifts out of the area by then. .LONG TERM...(Friday through Tuesday) Issued at 330 PM EDT Tue Apr 25 2017 Active weather pattern will continue into the long term period with one main low pressure system forecast to move through the area between Saturday and Monday. The heaviest rain looks to be during the Saturday night through Sunday night period with 850mb dew points surge to around +10C. The ECMWF also shows solid 850mb moisture transport during this time as well. Heavy rain is quite possible over the weekend with periods of showers and thunderstorms. One to two inches of rain appears possible at this point, but we will refine that as the event gets closer. Friday into Friday night will be somewhat of a quieter period as we will be in between systems. The weekend system is an upper low that pivots through the area, so we are looking for plenty of cloud cover along with periods of rain. Temperatures will be seasonable with highs in the upper 50s to lower 60s.
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&& .AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon) Issued at 217 PM EDT Tue Apr 25 2017 VFR weather is forecast the next 24 hours with cloud bases at or above 4000ft through the period. There will be some times, namely this evening and again into the midday hours of Wednesday, when we see ceilings around 4,000-5,000ft. Otherwise, mid and high clouds are expected with bases at or above 10,000ft. Winds will be from the south-southeast around 10 knots this afternoon and evening. An increase in wind is expected late tonight and into Wednesday, picking up into the 10-20 knot range with gusts to around 25 knots. && .MARINE...
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Issued at 330 PM EDT Tue Apr 25 2017 Winds will be on the increase tonight and remain up through Wednesday as the gradient ahead of the incoming system presses into the area. The winds will be nearly parallel to the shoreline, or even offshore a bit, which should limit the waves some. Also, the warmer air over the cooler waters will limit wave generation also. We will make a last minute decision at press time whether it will require a Small Craft Advisory or not.
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&& .HYDROLOGY...
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Issued at 330 PM EDT Tue Apr 25 2017 In spite of conditions drying out over the last few days, rivers remain higher than normal across the area and a few decent widespread rain events may prime them once again for a flood risk. The Muskegon and Grand River basins in particular are running at about the 75th percentile for this time of year. Rainfall amounts Wednesday into Thursday could be locally heavy and the western reaches of those basins may experience rises. Additional significant rain this weekend over especially the central and western reaches of those basins may cause some above bankfull rises and we will have to monitor closely for a flood risk on the main stem rivers.
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&& .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. LM...None. && $$ SYNOPSIS...NJJ SHORT TERM...NJJ LONG TERM...Duke AVIATION...Duke HYDROLOGY...Hoving MARINE...NJJ

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