941
FXUS63 KGRR 211930
AFDGRR
Area Forecast Discussion
National Weather Service Grand Rapids MI
330 PM EDT Sat Sep 21 2019
LATEST UPDATE...
Synopsis/Discussion/Marine/Hydro
.SYNOPSIS...
Issued at 330 PM EDT Sat Sep 21 2019
-Rounds of rain through Monday morning
-Locally heavy rainfall of greater than two inches possible
-Dry and cooler Monday and Tuesday; next chance of rain Wednesday
-Beach Hazards continuing through Monday
&&
.DISCUSSION...(This evening through next Saturday)
Issued at 330 PM EDT Sat Sep 21 2019
Guidance continues to suggest the possibility of excessive
rainfall and areal flooding in southwest Michigan, with the main
threat being on Sunday evening as the final/main strong wave
moves along the frontal boundary. 50-55 kt low level jet ahead of
the approaching wave and high PWAT values around 2 inches will be
interacting with the stalled frontal boundary during this time.
Also a coupled jet structure at H2 will be present.
There is also a heavy rain threat tonight and early Sunday,
mainly along the lakeshore north of Holland. This event could
produce 1-2" prior to the main event Sunday evening.
Some conflicting signals exist as to where the swath of heaviest
total rainfall might occur, with convective allowing models
favoring a slightly more southern orientation than the synoptic
models. Believe the synoptic models are probably the way to go
since the main part of the event is related to the final wave on
the front and there`s not much instability progged.
Heaviest rainfall totals should end up falling north of a line from
South Haven to Ionia. Amounts could easily exceed two inches, and
some isolated amounts as high as 5 inches cannot be ruled out
considering the tropical plume feeding north into this system.
Some larger cities which appear the be candidates for flooding
include Grand Rapids, Holland and Muskegon.
A small svr wx risk could develop near/south of I-94 on Sunday
night ahead of the approaching dry slot and sfc cold front which
will extend south from the deepening sfc low passing across
central Lwr MI.
After a brief cool down Mon, temps rebound again Tuesday ahead of
the next system/cold front which brings another threat of showers
and storms on Wednesday. The cool down behind that front on
Thursday is brief as well, with another rebound toward summer-
like expected as we head into next weekend.
&&
.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 151 PM EDT Sat Sep 21 2019
Showers should remain scattered through this evening with little
risk of thunder and conditions remaining predominately VFR. Rain
showers becoming more widespread after midnight, with MVFR and
IFR becoming more likely overnight at MKG and GRR. Better risk of
seeing a tstm arrives on Sunday.
Cigs are expected to remain VFR near and south of a line from AZO
to LAN tonight into Sunday morning, although any heavier showers
may temporarily drop vsbys to MVFR or IFR.
Gusty south winds of 15-25kts will diminish to around 10 kts
after 00Z, with the exception of MKG. LLWS is likely late tonight
mainly south and east of GRR as sw winds increase to around 40
kts just abv the sfc.
&&
.MARINE...
Issued at 330 PM EDT Sat Sep 21 2019
Wave height have been building today and the Ludington buoy is
currently up to 4 feet. Waves will continue to build tonight, with
the larger waves also expanding farther south down the coast. The
existing marine/beach hazard headlines look good and no changes
planned, however extensions will probably be needed in Monday due
to the cold advection behind the deepening/departing sfc low.
&&
.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...
MI...Beach Hazards Statement from 8 PM EDT this evening through
Sunday evening for MIZ064-071.
Lakeshore Flood Advisory from 8 PM this evening to 8 PM EDT
Sunday for MIZ064-071.
Beach Hazards Statement through Sunday evening for MIZ037-043-
050-056.
Lakeshore Flood Advisory until 8 PM EDT Sunday for MIZ037-043-
050-056.
LM...Small Craft Advisory until 8 PM EDT Sunday for LMZ846>849.
Small Craft Advisory from 8 PM this evening to 8 PM EDT Sunday
for LMZ844-845.
&&
$$
SYNOPSIS...Meade
DISCUSSION...Meade
AVIATION...Meade
HYDROLOGY...AMD/AH
MARINE...Meade
NWS GRR Office Area Forecast Discussion
