742 FXUS63 KGRR 150110 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 910 PM EDT Fri Mar 14 2025 .KEY MESSAGES... - Storms after midnight with gusty winds developing into Saturday - Much cooler and showery on Sunday - Another potent system expected around Wednesday through Thursday && .UPDATE... Issued at 900 PM EDT Fri Mar 14 2025 An overall consensus blend of latest CAMs corroborated with rgnl radar trends still suggests that showers and storms will not move into our area until 06Z Sat at the earliest and mainly around to after 07Z Sat. This will be a weakening line of showers and storms given unfavorable timing and weak instability. The llj and kinematics are favorable though so we do expect some gusty showers and storms (but most if not all of the winds will be sub severe). Our going forecast and headlines for the synoptic wind event overnight/Saturday look excellent with no changes needed this evening. && .DISCUSSION... Issued at 331 PM EDT Fri Mar 14 2025 - Storms after midnight with gusty winds developing into Saturday We are issuing a Wind Advisory for the land areas beginning at 06z/ 2 am EDT to account for the wind with the showers and storms that will be coming through later tonight, and for the synoptic winds expected for much of Saturday. Visible satellite imagery this afternoon shows some impressive signatures already with the incoming system, as a large area of dust can be seen in the dry slot lifting NE. It is ahead of this where vigorous convection will fire this afternoon and lift ENE through tonight. We will see a quiet, windy, and warm evening for SW Lower Michigan, before showers and some storms move in after 06z tonight. The line of storms are expected to lose quite a bit of their punch by the time they make it here during the overnight hours with a cooler atmosphere. Forecast model soundings indicate that MU CAPEs will only be a few hundred J/kg just ahead of the line. In addition, most of the CAPE is slightly elevated, but with only a weakly stable sfc layer. Our expectation regarding storm intensity remains the same as mentioned in the previous discussion. The low level jet will be strong with 40-50 knots of wind only 1-2k ft agl. It will not take much to mix these winds down, especially with some initially drier low levels helping to produce some dry microbursts. However, with the storms weakening, most of the winds will be sub-severe and a hybrid synoptic/convective scenario. Given we will have strong synoptic winds Saturday and the winds behind the line tonight will be close to Advisory criteria, it seemed the best and simple way to just add later tonight into the advisory. Once the convection moves through, we will be in the dry slot of the system, likely cutting rain chances off through most of the day on Saturday. The stronger core of winds, combined with the strong subsidence and good mixing due to the sunshine expected, winds of 45 to 55 mph will be quite common over the entire area during the daylight hours. Not out of the realm of possibilities to see gusts approach Warning criteria along the northern lakeshore where some mesoscale effects could occur. Very late in the day on Saturday and Saturday night, we will see additional jet energy lift rapidly NNE toward western Lake Erie and Lake Huron. What this will do is bring another healthy slug of moisture along the front that will have slowed down, and bring another round of showers with a few storms, especially toward U.S.- 127. The bulk of any stronger to severe storms should stay mainly near and east of the low track, east of our area. However, there is some weak lingering instability of a couple hundred J/kg of CAPE from the heating of the day that this system could act on. In addition, very strong mid-level flow will help to produce 50+ knots of deep layer shear. The lack of good instability will keep the threat limited, but non-zero with the strong shear present. - Much cooler and showery on Sunday The secondary energy, associated sfc low, and showers/storms will all move out by Sunday morning. However, the upper trough axis is still west of the area, and will have enough moisture and instability with the cold pool aloft coming in to keep showers over the area through much of the day. The showers will initially be rain, but will change over to a bit of snow before ending as 850 mb temperatures drop to around -9C by Sunday evening. - Another potent system expected around Wednesday through Thursday We will see at least two, and possibly three drier days for the area, with moderating temperatures. The sfc ridge axis moves overhead Sunday night, and shifts east by Monday. This is associated with a broad ridge over the Plains that will gradually build east. The low level flow will transition to a southerly flow by Monday, helping temperatures start warming back up. This will really be noticeable Tuesday and Wednesday as 850 mb temps warm to around +9C again. Precipitation chances could make a return here as early as Wednesday, but it starting to look like it will be more so late Wednesday and Thursday. Another strong upper trough will come in off of the Pacific and lead to strong leeside low development over the Central Plains. Confidence in the system is high, while the timing and exact track is still a little uncertain. It is more likely that we will see the warmth ahead of it, with eventually some showers and storms developing as the low approaches. As the low passes, it will likely have cold enough air to change some of the pcpn on the back end of it to snow. && .AVIATION /00Z TAFS THROUGH 00Z SUNDAY/... Issued at 735 PM EDT Fri Mar 14 2025 Overall forecast remains on track. VFR conditions are expected for the next six hours. A line of showers and thunderstorms arrives after 06z impacting all terminals with IFR visibilities for around 2-3 hours. In addition, a period of prolonged non-thunderstorm LLWS develops after 00z as winds of 50-60 knots at and above 2000 ft develops. There is a low chance of gusts exceeding 40 knots within any thunderstorms in addition to normal hazards, and gusts exceeding 30 knots are likely. Gusts increase to 40 knots or greater late Saturday morning into the late afternoon from the south-southwest before subsiding in the evening. There is a low chance that afternoon thunderstorms develop near LAN, JXN, and BTL. Where chances are slightly better at LAN and JXN have included a PROB30 for thunderstorms after 20z Saturday. South-southeast winds around 15-25 knots are expected ahead of the storms. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...Wind Advisory from 2 AM to 8 PM EDT Saturday for MIZ037>040- 043>046-050>052-056>059-064>067-071>074. MARINE...Small Craft Advisory until 8 AM EDT Saturday for LMZ844>849. Gale Warning from 8 AM to 8 PM EDT Saturday for LMZ844>849. && $$ UPDATE...Laurens DISCUSSION...NJJ AVIATION...Thomas

NWS GRR Office Area Forecast Discussion


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