Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 291920

Area Forecast Discussion
National Weather Service Grand Rapids MI
320 PM EDT THU SEP 29 2016

Synopsis/Short Term/Hydro/Marine

Issued at 320 PM EDT Thu Sep 29 2016

The pesky system that has brought bouts of rain showers to the area
over the past couple of days will continue to bring more periodic
rain chances through the upcoming weekend. Some locally heavy rain
could fall again tonight, which could potentially be over some areas
that saw some heavier amounts last night. Some thunder will become
possible on Saturday as the system moves almost overhead.
Temperatures will remain cooler than average through the weekend
with plenty of clouds and occasional rain chances.

Drier and warmer weather should return early next week as the system
overhead is finally pushed out of the area.


.SHORT TERM...(This evening through Saturday night)
Issued at 320 PM EDT Thu Sep 29 2016

We will be issuing a Flood Watch for the SE section of the CWFA
through Friday. Otherwise, our focus will be on rain trends through
Saturday night with the upper low meandering back north toward the

The band of rain that affected the srn third of the CWFA last night
and this morning has moved north some and become a bit less
organized this afternoon. This trend is the result of the
llj/moisture transport waning, limiting the the strength of the
TROWAL/deformation overhead.

This will be temporary as we see evidence of the next batch of rain
showers to our S and E across much of OH and Lake Erie with the
next wave/moisture transport surge. This will come in later this
evening and last into Friday morning. This batch of rain could
impact areas that saw the heavier rains last night and this morning.
Basin averages under an inch should generally not cause big impacts
in the watch area. We are more concerned with locally heavier rains
causing impacts over the watch area.

We expect to see a diminishing trend to the rain showers through the
day on Friday. The moisture transport should diminish and shift
north as the upper low is expected to start to slowly rotating
north. Also, we expect that there will be less warm and moist
advection than was experienced last night, and that is expected
tonight as the low cuts-off even more.

We expect that Saturday will see more spotty showers and a few
storms, versus seeing waves of rain. This is the case with the upper
low/cold pool aloft drifting overhead and eventually north. We
should see some breaks in the clouds, which combined with the cold
pool will create better instability profiles. This should tend to
diminish a bit Saturday night as diurnal heating is lost.

.LONG TERM...(Sunday through Thursday)
Issued at 215 PM EDT Thu Sep 29 2016

The main issue here is when does the rain from the current system
end? The good news is the models have been very consistent about
this for several days now, the rain should end by Monday morning.
Sunshine should return by Monday afternoon. The next period of
showers will be late next week into next weekend as the next
Pacific system slowly moves east through the area.

That next upstream Pacific system (using a Henry rule sort of
argument) gets close enough to our current system to "boot it
out" by Sunday night or early Monday. Then a larger upper ridge
develops over our area in response to the digging Pacific system.
In fact this creates a nearly closed off upper level high (seen
on both the GFS and ECMWF) by Wednesday. This will also mean
warmer tempeatures most of next week as the air behind this system
is of Pacific origin not from the polar regions.

Finally we get another "Henry Rule" closed upper low over the
Southwest CONUS being booted out by the next upstream Pacific
shortwave (no end to that sort of thing). This will bring the next
threat for rain to our area back by Thursday.


.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 215 PM EDT Thu Sep 29 2016

I expect MVFR/IFR cigs to prevail over all of our taf sites
through Friday and beyond that thanks to the stalled upper level
low pressure system. MKG has been in and out of the MVFR cigs
since mid morning but I expect the east winds over time to bring
solid MVFR/IFR cigs to all taf sites including MKG. The current
rain band lifting through the CWA will replaced by yet another one
later today into Friday morning. That will help bring a more solid
IFR cig/vis set up to our TAF sites.

Winds will continue to be gusty today but should diminish some
tonight and even farther on Friday as the surface system slowly
weakens with time.


Issued at 320 PM EDT Thu Sep 29 2016

Small craft advisory will be maintained as is with this forecast
cycle. Gradient will remain fairly robust potentially into Fri
night. One good thing with the stronger gradient is that it will be
an offshore flow, which will limit the wave action a little.

We will maintain waterspouts in the forecast through the rest of
today, before the potential looks to diminish temporarily tonight
and Friday. The potential could ramp up a bit again on Saturday as
the system moves almost directly overhead.


Issued at 320 PM EDT Thu Sep 29 2016

Many locations between St Johns, Jackson, Kalamazoo, and Hastings
received 1 to 2.25 inches of rain since Wednesday. A number of Grand
River tributaries are rising in response, but most have a good bit
of room left to swell before reaching bankfull. The exception is
Sycamore Creek, which should reach or exceed bankfull tonight.
Greater runoff efficiency is expected in this area from any
subsequent rain events Friday into Saturday. This increases the
concern for minor areal and river flooding.


.GRR Watches/Warnings/Advisories...
MI...Flood Watch through Friday evening for MIZ059-065>067-072>074.

LM...Small Craft Advisory until 6 PM EDT Friday for LMZ844>849.



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