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fxus63 kgrr 221916 
afdgrr

Area forecast discussion
National Weather Service Grand Rapids Michigan
315 PM EDT sun Sep 22 2019

Latest update...
synopsis/discussion/marine/Hydro

Synopsis...
issued at 315 PM EDT sun Sep 22 2019

- localized heavy rainfall possible through this evening

- rain chances focused on Wednesday and Saturday

- average to above average temperatures much of the week

&&

Discussion...(this evening through next sunday)
issued at 315 PM EDT sun Sep 22 2019

Our latest thoughts with this rain event are that most locations
should not see impactful rain amounts. We are thinking that there
will likely be a narrow axis of heavier rainfall that might create
some short term minor flooding of poor drainage and low lying areas.

Latest regional radar imagery is not impressive, and a lack of
upstream flooding reports corroborates this thinking. The rain over
nrn Illinois and ern Iowa is associated with a well defined wave
centered over wrn Illinois. This is the rain that is expected to
move over most of the area through this evening. It will be a good
general soaking for the area. The hi-res models have been indicating
a narrow heavier rainfall axis, likely associated with the
deformation zone of the wave, that will likely move between I-96 and
I-94 this evening. It is in this area that the best potential for
some localized flooding. The threat should then end by 06z.

Thunder remains possible this evening, however the lack of upstream
lightning with this wave so far makes US believe that coverage will
be scattered at best. There could be a little uptick in lightning
with the system strengthening, and low level jet increasing. With
little lightning to start, the severe threat is quite low. A few
more showers will be possible with the cold front before daybreak.
Clouds will then clear out Monday afternoon.

We will see a break from Monday afternoon through Tuesday evening as
high pressure aloft and at the surface moves through. The next
chance of showers and a few storms will arrive early Wednesday
morning, and linger through Wednesday evening. This does not look to
concerning as it is fairly progressive, and instability is limited.
If we are able to destabilize a bit more Wed afternoon ahead of the
front, the storm threat may end up a little higher.

Again, we will see a brief break in the unsettled weather for
Thursday before the next chance for rain starts to move in on
Friday. There is good agreement with the front coming in. However,
there is a good deal of uncertainty on how quick it moves through.
This is actually defendant on the evolution of a western low/trough.
One possibility is that deep SW flow becomes established, and the
front may linger longer, and we stay wet for next weekend. Another
possibility is the upper low closes off over the desert SW, and the
system would be more progressive and move out quicker. We will fine
tune this as better trends become more clear.

&&

Aviation...(for the 18z tafs through 18z Monday afternoon)
issued at 149 PM EDT sun Sep 22 2019

We are seeing a nice break in the rain and lower conditions at the
beginning of the forecast period. Conditions will gradually
deteriorate from west to east starting around 12z or so at kmkg,
and finally moving into klan and kjxn toward 00z. We will likely
see some MVFR develop with the onset of the rain showers. IFR is
likely to settle in shortly after the rain develops. We have also
mentioned a thunderstorms in the vicinity a couple of hours after the rain moves in when
the core of the better instability moves through ahead of the
front.

A break in the rain will be likely, but the IFR cigs will likely
persist. Another round of showers will come through just prior to
daybreak with the cold front for a couple of hours. Winds will
ramp up then with the passage of the cold front, with gusts up
over 20 knots. Cigs will eventually come up above IFR toward
daybreak, with VFR cigs expected toward the end of this forecast
period. Winds will remain gusty through 18z Mon.



&&

Marine...
issued at 315 PM EDT sun Sep 22 2019

It looks like the Small Craft Advisory is working out nicely, and
should hold well through this system. We are currently seeing 25 to
30 knots fairly common along the Lakeshore from the SW. Winds will
die off a bit as the system approaches, then will increase in the
wake of the front as the cold air rushes in. The winds will then
diminish Monday night.

Our next marine event will come beginning Tuesday night and through
Wednesday with the next fairly decent frontal system that will move
through. Small craft advisories will be likely once again.

&&

Hydrology...
issued at 315 PM EDT sun Sep 21 2019

Rainfall has already begun to move through lower Michigan this morning and
early afternoon resulting in up to 0.25-1" of rain with the higher
totals near and north of I-96. Meanwhile additional rainfall is
expected later on this afternoon and evening, leading to rainfall
totals up to 1-2 inches, locally up to 3 inches, by Monday morning.

This rainfall is expected to cause some rises on rivers, but no
rivers are expected to exceed bankfull. The rivers that may approach
bankfull are most likely the white and pere Marquette rivers, where
heavy rain from last week has limited how much water the soil is
able to absorb.

Of greater concern is the potential for localized short-duration
flooding of some small streams as well as ponding on roadways at low-
spots and in poor drainage areas. The heaviest rain is likely to
fall in the communities northwest of a line from South Haven to
Saginaw. The heaviest rain looks like it will fall this evening and
overnight, and will be moving out of the area by Monday morning.
Water on roads at night is much harder to see, so drivers should
slow down and pay extra attention.



&&

GRR watches/warnings/advisories...
Michigan...Beach hazards statement through Monday evening for miz037-043-
050-056-064-071.

Lakeshore flood advisory until 8 PM EDT Monday for miz037-043-
050-056-064-071.

Lm...Small Craft Advisory until 8 PM EDT Monday for lmz844>849.

&&

$$

Synopsis...njj

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