Area Forecast Discussion
Issued by NWS Grand Rapids, MI
Issued by NWS Grand Rapids, MI
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811 FXUS63 KGRR 112303 AFDGRR Area Forecast Discussion National Weather Service Grand Rapids MI 703 PM EDT Sat May 11 2024 .KEY MESSAGES... - Cloud / Aurora forecast for tonight - Showers and storms expected Sunday evening and Sunday night - Showers and a Chance of Storms Monday and Tuesday - Dry Mid Week with Rain Chances Late Week && .DISCUSSION... Issued at 345 PM EDT Sat May 11 2024 - Cloud / Aurora forecast for tonight Vertically stacked low is crossing southeast from the Thumb at the present time out onto Southern Lake Huron. Essentially, the low and its affects are moving away from the forecast area. A few showers may linger for another couple hours in the southeast portions of the forecast area towards Jackson, but overall we should be dry. Clouds in the center of the state along Highway 127 are a bit thicker and are of the stratocumulus variety. Again, these clouds are pulling east with the low. Elsewhere, clouds are of the diurnal cumulus variety and should dissipate rapidly with the setting sun. There is an area of showers that has developed over Northeast Wisconsin, but these clouds/showers are also diurnally driven and should fade as well with sunset. They will also be moving over the cold waters of the big lake and that should lead to a diminishing trend as well. So, the cloud forecast is a good one for aurora viewing...one of clearing. As for the aurora, the kP index which is monitored for disturbances in the earths magnetic field has maintained high levels right into today. The scale goes from 0 to 9 and we have maintained 8 (severe) or 9 (extreme) values all of last night and through the daylight hours of today so far. The forecast is for these levels to continue as solar flares have continued to emanate off the sun. It is the flares interacting with the earths magnetic field that produces the aurora. Forecasts from the Space Weather Prediction Center (NOAA) continue to show high levels of aurora activity tonight. Keep in mind that conditions can ebb and flow a bit within a solar storm so continue to check the sky if you are interested. Also, your phone will be able to pick up aurora easier than your eye, so open your camera and take a look if you are unsure as to what you are looking at. A 3 second exposure on your camera will produce more vivid photographs. Sunset across the area is generally between 850pm and 900pm. Nautical twilight when it will be easier to see aurora does not occur until 1000p to 1010p. So, after 10pm is the time to take a look skyward. - Showers and storms expected Sunday evening and Sunday night Quiet conditions are expected overnight and through much of Sunday as high pressure drifts through the forecast area. A cold front will approach from the northwest Sunday afternoon with chances for showers and thunderstorms from roughly 600p Sunday evening into Sunday night. The best chances for showers and storms will come during the evening across Central Lower Michigan. A 30-40 knot low level jet will bring in marginal moisture at 850mb of +8C. Surface dew points only make it into the middle 50s F. MUCAPE values increase to around 1000 j/kg for a short time. So, instability is not all that impressive. We expect showers and storms to nudge into the U.S. 10 corridor Sunday evening with a marginal chance at being severe. An isolated warning cannot be ruled out for some hail/wind, but overall this does not look to be a significant threat of severe weather. Showers and storms will sag south through Sunday night weakening with time as the instability wanes. - Showers and a Chance of Storms Monday and Tuesday Rain chances continue into Monday as a frontal boundary stalls across the CWA in a zonal mid-level pattern. MUCAPE values near and north of 1000 J/kg will be supportive of thunder chances. However, given the lack of upper-level support unsure on the extent of convective coverage during the day. In addition, the lack of any significant low or mid-level jet means deep layer shear is week making any storms garden variety thunderstorms. Better upper-level forcing arrives later Monday in the form of an approaching shortwave and placement in the right entrance region of the upper-level jet. However this occurs as daytime heating is lost meaning thunder chances will be more limited. The frontal boundary then is driven south of the state by the aforementioned shortwave Tuesday morning causing rain chances to end. Highs in the 70s Monday fall into the 60s for Tuesday given northerly flow. Highs then rebound into the 70s Wednesday given ridging in place. - Dry Mid Week with Rain Chances Late Week The mid-week period is expected to be dry across West Michigan as guidance is consistent in surface and upper-level ridging across the region. Wednesday in particular looks to see plenty of sunshine given the lack of deep moisture across the area. Uncertainty increases by late week as predictability in the upper- level pattern weakens. A review of the cluster analysis phase space suggests that guidance is generally locked into individual solutions due to questions in the presence of troughing across our area. One set of clusters, primarily leaning towards the GFS/GEFS/GEPS supports robust troughing arriving later Thursday into Friday and by extension increasing rain chances into the weekend. In contrast, the EPS/Euro leaning clusters support zonal to slightly ridged mid-level flow and lower rain chances late next week. Will cut PoPs from the NBM for Thursday given the lingering effects of surface based ridging and will leave the chance PoPs beyond that given the notable uncertainty remaining in the forecast. && .AVIATION /00Z TAFS THROUGH 00Z MONDAY/... Issued at 703 PM EDT Sat May 11 2024 VFR conditions are expected at all the terminals through 00Z Mon. Fair wx cu at our inland terminals early this evening will dissipate very quickly with clear skies expected by 00Z Sun at most of our terminals and perhaps still some lingering cumulus at our eastern terminals until around 01Z-02Z. Wind speeds will subside quickly after sunset. Conditions will remain VFR on Sunday but southwest winds will ramp up and gust to around 20 kts or so in the afternoon with higher gusts to near 25 kts at KMKG. Low clouds and scattered rain showers and isolated storms are not expected until after 00Z Mon. && .MARINE... Issued at 345 PM EDT Sat May 11 2024 Plenty of whitecaps continue on area webcams as of 300pm. Waves at all of the nearshore buoys are at 5 feet with shoreline observation sites indicating 20-30 knot gusts. Given current conditions not confident that conditions will be below SCA criteria by 600pm so we have extended the SCA through 900pm. Conditions should improve later this evening as the winds subside. The lull will be short lived however as southwest winds ramp up for Sunday and especially Sunday night into Monday. Most likely area for higher winds and waves will be north of Muskegon Sunday night into Monday. It will be a warm air advection wind so all the usual caveats apply. Most importantly will the winds make it to the lake surface given the likely inversion. We will let the current headline play out before looking into the next one. && .GRR WATCHES/WARNINGS/ADVISORIES... MI...None. MARINE...Small Craft Advisory until 9 PM EDT this evening for LMZ844>849. && $$ DISCUSSION...Duke/Thomas AVIATION...Laurens MARINE...Duke