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fxus63 kgrr 221148 
afdgrr

Area forecast discussion
National Weather Service Grand Rapids Michigan
748 am EDT sun Sep 22 2019

Latest update...
aviation

Synopsis...
issued at 324 am EDT sun Sep 22 2019

- heavy rain with localized minor flood today into early Monday
morning

- strong winds withe developing system will continue beach hazard
and small craft today, likely will need to extend into Monday

- brief quiet period Tuesday

- fairly strong push of cold air will lead to a convective event
on Wednesday then much cooler Thursday into Friday

- warm air surges back next weekend with more convection

&&

Discussion...(today through next saturday)
issued at 324 am EDT sun Sep 22 2019

As we have been writing about for nearly a week now is coming
together. While there will be showers and isolated thunderstorms
this morning into early this afternoon, the upper divergence
associate with closing off upper low (500 to 300 mb) over the
northern Great Lakes this evening will cause the heaviest rain to
be late this afternoon into this evening. Given the dynamics of
this closing off upper low, I like the European model (ecmwf) solutions best as it
developers the strongest surface wave, which given the dynamics
of this event makes the most sense to ME. As we have been saying
too, the 2 inches of precipitable water which is near record for
this area in late September (standard anomaly tables) over our
area while this is happening will help the cause with locally
heavy rainfall.

So the glitch is where will the heaviest rainfall end up? That
will depend on how developed of a surface low we get today. It the
European model (ecmwf) is correct the heaviest rain will be north of Grand Rapids,
if the other models are correct it will be between Kalamazoo and
Grand Rapids. Since at this point we really do not know for sure
we will not issue an areal flood advisory just yet but do not be
surprised if we issue one by this afternoon.

There is more than enough elevated instability for thunderstorms
but looking at the model sounding, which show deep but Narrow
Cape, this will be a heavy rain event more than anything. Model
sounding are saturated to 200 mb this evening as the surface low
moves through the area. The NAM had 1300 j/kg of most unstable
cape at mkg at 8 PM this evening. The 11 PM run of the Storm Prediction Center sref
shows the axis of highest thunderstorm probabilities at 8 PM this
evening along I-96 and south to the state boarder with Ohio and
Indiana. So, again this is a classic heavy rain event, much more
than a significant thunderstorm event.

The system will exit the area Monday and likely it will be a touch
breezy as the system quickly moves out. Rain should be done by
late morning over the eastern County Warning Area.

We get one quiet day as shortwave ridging moves through the area
Tuesday. Then a 160 knot jet core digs into northwestern Continental U.S. By
Tuesday afternoon setting the stage for a good push of seasonably
cold air for our area Thursday into Friday. However this strong
upper air system will lead to another convective event (not nearly
as wet as today's event) Wednesday. Just a note on this the 850 mb
0c temp gets into the Upper Peninsula by 8 am Thursday. It will
truly fell fall like Thursday.

Just went you'd think fall is here another strong Pacific system
will cause anther large eastern ridge to develop by next weekend.
That will result in more highs in the 80s and convection. Our
current forecast highs are conservative for now but it the models
are correct we will see highs in our forecast rise into the 80s
for next weekend.

&&

Aviation...(for the 12z tafs through 12z Monday morning)
issued at 748 am EDT sun Sep 22 2019

For the most part expect periods of rain, which will be heavy at
times through about 06z Monday. Isolated thunderstorms are
possible from mid afternoon into mid evening.

At 1145z IFR cigs prevailed north of I-96 which means for the most
part the GRR taf sites were mostly VFR. Due to the heavy showers
GRR has Bend IFR in heavy rain but when the rain ends VFR returns.

There is a area of showers over Lake Michigan about to move
through the taf sites over the next 3-6hrs. I do believe this will
bring MVFR conditions with brief IFR in heavy rain showers. Once
that moves through the upstream upper wave will allow a sort of
warm front to push north of the taf sites and end the rain and low
ceiling from around 15z-16z till 19z-22z. At which point the main
system moves through with rain, heavy at times with isolated
thunderstorms. Expect IFR during this time. After 06z the rain
should be moving out but low ceiling should continue through
sunrise.




&&

Marine...
issued at 324 am EDT sun Sep 22 2019

Little question we will hold on to our marine and beach hazard
headlines today. However I have a strong feeling we will need to
extend those headlines into Monday afternoon if the latest model
run of the European model (ecmwf) is correct about the deepening surface low. I
could see 30 knot northwest winds Monday mid morning in our near
shore area.



&&

Hydrology...
issued at 151 PM EDT Sat Sep 21 2019

Several rounds of heavy rain will be moving through lower Michigan
starting tonight and lasting through late Sunday/early Monday. At
this point it looks like most spots will end up with a total of 1-2"
of rain, with some spots possibly topping 3" by the time the rain
ends Monday morning. This will cause some pretty good rises on most
of the rivers in the area, but at this point no rivers are expected
to exceed bankfull. The rivers that might approach bankfull are most
likely the white and pere Marquette rivers, where heavy rain last
week has limited how much rain 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 along and west of US-131. The heaviest rain
looks like it will fall Sunday evening and overnight, and 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 this evening for miz037-043-050-
056-064-071.

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

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

&&

$$

Synopsis...wdm

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