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LMZ849 Pentwater To Manistee Mi- 405 Pm Est Tue Dec 5 2023
Through early evening..North winds 10 to 15 knots. Mostly cloudy. Waves around 1 foot.
Tonight..North winds 10 to 15 knots. Mostly cloudy. A slight chance of rain and snow showers in the evening, then a slight chance of rain showers overnight. Waves 1 to 3 feet.
Wednesday..Northwest winds 10 to 15 knots backing southwest 10 to 20 knots. Mostly cloudy with a slight chance of rain showers. Waves 1 to 2 feet building to 2 to 4 feet late in the day.
Wednesday night..Southwest winds to 30 knots. Mostly cloudy. Waves 6 to 8 feet.
Thursday..Southwest winds 10 to 20 knots backing south late in the day. Mostly Sunny. Waves 3 to 5 feet.
Thursday night..South winds 15 to 25 knots. Partly cloudy. Waves 4 to 6 feet.
Friday..Southwest winds 20 to 25 knots. Partly Sunny. Waves 5 to 7 feet.
Saturday..Northwest winds around 15 knots veering north. Mostly cloudy with a chance of rain showers. Waves 2 to 4 feet.
Sunday..Northwest winds to 30 knots. Cloudy with a chance of rain and snow showers. Waves 6 to 9 feet.

LMZ800
No data

FXUS63 KGRR 051952 AFDGRR

Area Forecast Discussion National Weather Service Grand Rapids MI 252 PM EST Tue Dec 5 2023

LATEST UPDATE...
Short Term/Long Term/Marine

SHORT TERM
(This evening through Wednesday night)
Issued at 204 PM EST Tue Dec 5 2023

- Diminishing light showers through mid afternoon

Radar shows some light returns mainly down in the Interstate 94 corridor. Trends show them weakening. A few observations sites such as LWA and AZO has some rain in the past hour. With surface temperatures in the upper 30's in that region, no impacts are predicted as this area of light precipitation shifts south and east of the CWA.

- Light Lake Effect Precipitation possible later tonight

The 850 mb thermal trough shifts through the forecast area later tonight. Temps are shown to be around -8 deg C where it will be moist. Low level convergence looks most favorable for lift along the lakeshore zones. In this region of low level lift and moisture, there could be a few light showers. The moisture depth decreases by late morning Wednesday, which should decrease any precipitation chances. Surface temperatures will once again be near freezing so, if we do end up with any precipitation, this could result in a few slick spots.

- Risk for rain/snow showers Wednesday night

A mid level wave drops southeastward through the east side of the state Wednesday night. Meanwhile, an associated low level jet will be feeding into the west side of this system. There may be enough saturation to generate light precipitation as this feature drops through. The 18z HRRR and the 12z NAM were generating light precipitation Wednesday night. The Canadian ensemble forecasts were showing precipitation as well. We will therefore have a low chance for precipitation in the forecast mainly northeast zones Wednesday night.

LONG TERM
(Thursday through Tuesday)
Issued at 204 PM EST Tue Dec 5 2023

-Warm and Dry Thursday and Friday

Upper-level ridging and warm air advection in robust southwest flow will warm temperatures across West Michigan late this week. This robust warm air advection promotes 850 mb temperatures warming into the 7-10C range (for reference, the 90th percentile of 850 mb temps Friday is 6 degrees C which puts us solidly above normal). This translates into highs well in the 40s Thursday and in the 50s Friday. Upper-level ridging also keeps the area dry through this period. However lingering low level moisture Thursday morning, and moisture streaming in ahead of our next system Friday, will keep at least some clouds during this window. Thursday afternoon looks to be the best chance for substantial clearing as West Michigan will lie in the gap between the two moisture sources.

-Monitoring The Potential For A Weekend Storm System

Upper-level jet divergence arrives over the area Friday night into Saturday as we sit in the right entrance region of a jet streak.
This forcing, in tandem with an approaching trough and northward streaming moisture, causes rain chances to increase for Friday night into Saturday.

We are continuing to monitor increasing potential for a deepening low pressure system to move through the Great Lakes late this this weekend. The expected evolution of the synoptic pattern has a digging longwave trough over the central United States ejecting northeastward as a negatively tilted wave. This wave forms a surface low along a tight baroclinic zone stretching across the plains, driving the low northeastward as well. This allows for ample moisture to stream into the Great Lakes region with PWAT values around 1 inch moving north.

Notable uncertainty in the potential surface low track still exists, which is common this far out, providing uncertainty in precipitation types and amounts. This is because the upper-level wave expected to drive this event is just now reaching Alaska, and by extension beginning to be sampled by our upper-level weather balloon network. The range of solutions includes locally heavy rainfall, and even potentially thunder if we end up on the warm side of the system, as the warm conveyor belt streams moisture into the region.
A more easterly/southerly component to the low track would keep us on the cold side of the low bringing the potential of impactful accumulating snowfall.

Examining the latest 12z ECMWF and GFS deterministic and ensemble runs shows a northerly shift in low track and maintains the westward shift shown in the 00z set of guidance. This outcome would favor more rain for west Michigan and keep heavy snow north of the area.
However, the 12z Canadian suite and some members of the GEFS/EPS ensembles are still showing a more easterly/southerly low track which would provide a swath of 6+ inches of snowfall across the area. Additional shifts in guidance are likely in the coming days as additional observations are obtained, and we will continue to monitor model trends as solutions converge.

The other concern to monitor is the potential for gusty winds as shown in the ECMWF Extreme Forecast Index and ensemble guidance.
Depending on the track and strength of the low, gusty conditions are possible later Sunday into Monday.

Regardless, temperatures fall significantly Sunday night into Monday allowing for precipitation to turn to snow. As 850 mb temps fall into the -10C range, lake enhancement to any precipitation becomes possible. Longwave troughing overhead keeps the potential for light precipitation during the day Monday and into the day on Tuesday.

AVIATION
(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1236 PM EST Tue Dec 5 2023

Most terminals are under IFR cigs at present, with cigs expected to lift to MVFR over the next few hours. Showers and patchy fog are resulting in localized MVFR visbys which will also become VFR by mid afternoon. Tonight will feature a mix of MVFR and VFR cigs with lake effect showers possible near and west of US131. VCSH has been included at GRR and MKG where greater confidence in showers exists though some could make it to AZO/BTL. Locally reduced cigs and visbys are possible under any snow showers. A period of MVFR fog is also possible overnight for GRR/AZO/BTL as low level moisture increases. This dissipates by mid morning Tuesday. MVFR cigs return for all sites Tuesday morning as winds turn westerly allowing moisture off of Lake Michigan to support stratus. Winds below 10 knots are expected through the TAF window, presently easterly backing to westerly.



MARINE
Issued at 204 PM EST Tue Dec 5 2023

Low level winds will start increasing Wednesday afternoon and more so Wednesday evening. Marine headlines will likely be needed starting Wednesday night. The winds at 925 mb increase to over 35 knots Wednesday night which will support impactful conditions.
Most ensemble wind forecasts support conditions remaining under gale force .



GRR WATCHES/WARNINGS/ADVISORIES
MI...None.
LM...None.

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