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afdgrr

Area forecast discussion
National Weather Service Grand Rapids Michigan
333 am EST Fri Dec 6 2019

Latest update...
synopsis/discussion/marine

Synopsis...
issued at 330 am EST Fri Dec 6 2019

- quiet weather conditions into Sunday morning

- rain developing Sunday into Monday

- transition from rain to snow Monday night

- Arctic blast (lake effect snow and cold) Tuesday and Wednesday

- marine concerns due to large waves and erosion

&&

Discussion...(today through next thursday)
issued at 330 am EST Fri Dec 6 2019

Dry weather and quiet conditions are expected across the forecast
area today through Saturday night. A weak clipper system largely
missed our area to the north tonight and high pressure will move
in tonight. Southwest flow develops on Saturday with precipitation
holding off it appears until Sunday at the earliest. Highs
primarily in the 30s today and Saturday will warm into the 40s on
Sunday in the warm air advection southerly flow.

A stationary front will sharpen Sunday night over lower Michigan as
low pressure develops in the plains. The low in the plains will
work our direction heading into Monday as the upper trough deepens
overhead. Precipitation ramps up Sunday night into Monday as
forcing increases due to a strong shortwave moving through the
mean upper trough. It looks like rain will be the dominant
precipitation type from Sunday through Monday as 850mb temps will
be in the 0c to +4c. Rainfall amounts have been forecast
consistently to be in the 0.25 to 0.50 inch range.

A cold front will blast through the area Monday night changing
the precipitation over from rain to snow rather quickly. The lake
effect snow machine will commence Monday night and continue
probably right into Thursday. The main time frame of concern for
lake effect snow will be Tuesday, Tuesday night and Wednesday.
Delta t's in this time frame will be high to extreme in the 20c to
30c degree range. Moisture depth is decent, but it is a bit
lacking over time. Looking at the 850mb to 700mb layer which is
where lake effect events separate themselves from OK to
significant, the moisture is rather weak, less than 70 percent.
That said, lake effect will occur and we will turn the Lakeshore
white again where the snow has melted. Of bigger concern will be
travel issues that develop as highs on Wednesday will hold in the
teens. When we get temperatures this cold and snow is occurring
(even if its the fine powdery light snow like this event will be)
we develop travel issues as salt is much less effective. People
will need to be aware that travel concerns will develop from
Tuesday into Wednesday across western lower Michigan.

&&

Aviation...(for the 06z tafs through 06z Friday night)
issued at 1230 am EST Fri Dec 6 2019

MVFR ceilings are expected early Friday as a cold front moves
through the area. It is possible some terminals may drop to IFR,
but confidence is low. Winds will begin to shift northwesterly near
daybreak as the front moves through. Ceilings are expected to
lift towards VFR by Friday afternoon.

&&

Marine...
issued at 330 am EST Fri Dec 6 2019

The calendar says we are in the active portion of the year in
terms of wind/wave events on Lake Michigan and the forecast will
verify that. Multiple high wind/large wave events are expected
over the coming days. Given the high water levels and Lakeshore
concerns for erosion the forecast is not good news over the course
of the next 5 days.

The first event is beginning right now as northerly flow ramps up
this morning. This event will be somewhat short lived with the
peak in the winds occurring this morning. North winds to 30-35
knots are expected for the next 6 hours or so. Waves will build to
4-7 feet in the nearshore, with the worst of conditions occurring
south of Holland this morning. A Small Craft Advisory is in
effect, running through this evening. It will take all day for the
waves to fall below 4 feet.

The second event occurs Saturday afternoon, stretching through
Saturday night and Sunday. Late Saturday night into Sunday morning
we will approach if not reach gale force in southwest flow. The
worst of conditions in this event will be north of Holland where
6-10 footers are expected. We may need a Gale Warning and a
Lakeshore flood headline.

The third event will occur Monday night into Tuesday as northwest
cold air advection winds ramp up. This could be a prolonged wind
and wave event into Wednesday. Waves will likely at least push
into the 6 to 10 foot range.

&&

GRR watches/warnings/advisories...
Michigan...none.
Lm...Small Craft Advisory until 11 PM EST this evening for lmz844>849.

&&

$$

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