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LMZ844 St Joseph To South Haven Mi- 1105 Am Est Mon Dec 4 2023
Rest of today..Northwest winds 10 to 15 knots. Cloudy. A slight chance of rain showers through early afternoon. Waves 1 to 3 feet.
Tonight..Southwest winds 5 to 10 knots backing south toward daybreak. Mostly cloudy with a chance of rain and snow showers. Waves 1 to 3 feet.
Tuesday..South winds around 10 knots backing northeast late in the day. Rain and snow showers likely. Waves 1 foot or less.
Tuesday night..North winds 10 to 15 knots. Mostly cloudy with a chance of rain and snow showers. Waves 1 to 3 feet.
Wednesday..Northwest winds 10 to 15 knots backing southwest late in the day. Mostly cloudy with a slight chance of rain and snow showers. Waves 2 to 3 feet.
Thursday..Southwest winds 20 to 25 knots. Mostly Sunny. Waves 4 to 6 feet.
Friday..Southwest winds 20 to 25 knots. Mostly cloudy. Waves 3 to 5 feet.

LMZ800
No data

FXUS63 KIWX 041746 AFDIWX

Area Forecast Discussion National Weather Service Northern Indiana 1246 PM EST Mon Dec 4 2023

SYNOPSIS
Issued at 324 AM EST Mon Dec 4 2023

Lake effect rain showers will dissipate this morning with primarily dry conditions through the evening. Light rain and snow are expected late tonight into Tuesday. Snow accumulations up to an inch are possible, mainly on grassy and elevated surfaces along and north of highway 30. Some lake effect snow showers are also possible early Wednesday morning. Warmer and drier conditions return late Wednesday through Friday but additional rain or snow is possible this weekend.

SHORT TERM
(Today)
Issued at 324 AM EST Mon Dec 4 2023

Weak midlevel shortwave over SW MI and the associated cool, cyclonic low level flow over still relatively warm Lake MI are supporting SCT showers across our northern zones at present. This activity will continue through the bulk of the morning until midlevel trough axis passes and shortwave ridging/subsidence arrive around 18Z.
Corresponding backing of low level flow will also begin to advect drier air into the region this afternoon. Surface wet-bulb temps are currently holding just above freezing and there are ice nucleation issues with saturation only extending to about -8C per hi-res forecast soundings. This has and will likely continue to support liquid precip types but can't entirely rule out a few stray flakes mixing in given marginal temp/RH profiles early this morning and will therefore maintain a slight chance snow mention. No impacts expected.

Meanwhile, a more potent shortwave will pass to our south today. No precip expected in our area but some mid and high clouds are expected, particularly in our south. Between this and still ample low level moisture trapped under inversion noted on forecast soundings, sunshine appears unlikely (though not entirely impossible late) today. This will keep highs once again near 40F.

LONG TERM
(Tonight through Sunday)
Issued at 324 AM EST Mon Dec 4 2023

Next mid/upper level trough then follows quickly late tonight into Tue. Latest NWP suite is in much better agreement on timing with best precip chances roughly 09-21Z. Precip will be largely driven by increasing 280-290K system relative isentropic ascent ahead of the weak surface low diving SE. Forecast soundings/cross-sections show a brief period of reduced stability above a notable (albeit transient)
fgen band around 750-600mb. Sufficient moisture also exists for a brief period of moderate precip through the center of our CWA in the 12-18Z window (though it should be noted that some hi-res guidance is further S/SW and weaker with this precip shield). Precip types are a challenge. Initial forecast soundings are cold enough for primarily snow (particularly north of US-30) and heavier precip rates will support more snow vs. rain during the event peak mid Tue AM
However
surface wet bulb temps do rise into the mid/upper 30s through the day. Midlevel moisture also begins to wane by late in the day with increasing loss of ice nucleation by evening. Therefore expect a transition to rain for most areas by afternoon. Efficiency of snow accumulation will also be limited by low SLR's (relatively shallow DGZ with a relatively deep 0 to -10C layer accompanied by warm/wet ground) and anticipate bulk of accumulation (up to an inch)
on grassy/elevated surfaces. Some brief accumulation on the roads is possible during the Tue AM commute in the area of heaviest precip rates. The coldest profiles are in our NE but it is also drier there. The sweet spot looks to be roughly along and just north of the US-30 corridor where best precip rates overlap with cooler profiles. Confidence in these small scale details remains low at this time though, especially in light of some differing hi-res solutions.

A brief period of lake effect precip is expected late Tue night into early Wed with favorable flow trajectories and decent (albeit somewhat shallow) lake-induced instability. 0-2km theta-e lapse rates are favorable but inversion heights are only 4-5 kft. Flow also backs quickly late Wed AM with a sharp increase in subsidence and dry air advection. The window for favorable conditions in our CWA looks to be roughly 06-15Z Wed. Snow will be the primary precip type away from the lake but temps will still be marginal and only a few tenths of accumulation expected (again mainly on grassy/elevated surfaces).

Drier and warmer weather is still expected late Wed through Fri as large ridge builds over the Great Lakes. Sunny skies might even be possible on Thu with highs climbing into the 50s. It will be short- lived though as next large trough approaches this weekend. Guidance remains very inconsistent regarding important timing, strength, and track details of passing surface low. Precip is very likely but timing, amounts, and types are uncertainty at this range. Will continue to monitor closely given some potential for accumulating snow and windy conditions.

AVIATION
(For the 18Z TAFS through 18Z Tuesday Afternoon)
Issued at 1238 PM EST Mon Dec 4 2023

Satellite shows some improvements here-and-there this afternoon, but the overall short term picture remains MVFR BKN/OVC.
Improvement late this afternoon, toward 00z this evening, is plausible as the clipper system exiting southern Indiana departs and trajectories off Lake Michigan become westerly. Clouds were eroding over IL but have filled in, while clearing continues over portions of WI. Confidence is low for the timing of VFR conditions and is low for the duration of any VFR conditions.
Model guidance favors MVFR ceilings sticking around.

The next clipper arrives late tonight, just prior to sunrise and looks to bring a quick onset of snow to KSBN, and soon after KFWA.
A period of LIFR conditions is possible as the snow moves through at both sites.

Temperatures are expected to gradually rise above freezing through the day such that a transition to -RA or -RASN is anticipated toward 18z along with decreasing intensity.
Total snowfall less than 1" is expected. Pavement temperatures will be critical for any accumulation on pavement.

Precipitation ends just outside this TAF period.

IWX WATCHES/WARNINGS/ADVISORIES
IN...NONE.
MI...NONE.
OH...NONE.
LM...NONE.

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