Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 242353
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
753 PM EDT Mon Apr 24 2017

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 323 PM EDT Mon Apr 24 2017

The large high pressure system that has given this area several
days of warm and sunny afternoons will move off to the east and be
replaced by a series of Pacific Ocean origin storm system into at
least the middle of next week. The will mean periods of showers
and thunderstorms into next week. The first period of
thunderstorms has been delayed by should begin Wednesday night
and continue into Thursday. The next system following that will be
slower and move into the area Saturday but not depart the area
until Tuesday. The system over the weekend into early next week
should be the wetter of the systems.

&&

.SHORT TERM...(This evening through Wednesday night)
Issued at 323 PM EDT Mon Apr 24 2017

From now through Wednesday during the day I expect the weather
will mostly be dry with little threat of precipitation. The storm
system heading up the east coast in combination with the systems
coming off the Pacific into the Western CONUS will result in
ridging at mid and upper levels over Michigan into Wednesday.

Since there will be a series of shortwaves being ejected out of
the western CONUS upper level trough into Wednesday and we will be
on the west side of the departing surface high we will see more
and more mid and high level clouds so Tuesday and Wednesday we
will see a considerably more cloud cover but little if any
precipitation. Actually there is a chance of showers and
thunderstorms on Wednesday afternoon but I would down play that as
most of the upper level energy supporting that will still be well
west of and southwest of here. One thing I look as do we have
surface convergence under upper divergence and we do not have
that Wednesday afternoon on any of the models I have seen. the
latest run of the ECMWF shows surface convergence Wednesday
afternoon but no upper divergence. That is a bad thing if you
want it to rain. So we do have chance pops of if you have anything
planed outside Wednesday afternoon I would plan on NO RAIN.

The clouds will limit how warm it will get in the afternoon and
how cold it can get at night. Even so we should be able to see
highs in the lower 70s Tuesday and mid to upper 70s Wednesday.

.LONG TERM...(Wednesday night through Monday)
Issued at 323 PM EDT Mon Apr 24 2017

It seems we get at least two significant rainfall/thunderstorm
events from the East Asian Jet feature we have been watching. The
first will be Thursday the second will be more drawn out but
start in the Saturday time frame but the main energy from the
second system will come through Sunday or early Monday.

We will have some very wet weather over Southwest Michigan between
Wednesday night and Monday (WPC has 2 to 3 inches over western
sections over Southwest Michigan between now and Monday morning).
This goes back to what I wrote about most of last week into last
weekend. The East Asian Jet`s lead wave has already come on shore
over the western CONUS but the main core of energy is still west
of there near the dateline. Winds of near 170 knots area
assoicated with that shortwave (big storm actually) near the
dateline this afternoon. Until that comes on shore over the
western CONUS, the primary western trough will for the most part
sit and wait for it. That waiting has delayed the initial systems
from reaching us. On Saturday the models had it coming through on
Wednesday, it now looks like it will be Thursday during the day.
The main system closes off an upper low over the southwestern
CONUS Saturday. So we will see a series of weak waves head our way
over the weekend then early next week, on Monday the main system
is forecast to come out. I can see that timing being to fast
through given the strength of that Pacific storm. So I may nearly
be Tuesday or later before we see that final wave.

As for the system on Thursday one thing I am watching is the
upper divergence verses the surface convergence. I have noticed
over time our more significant events nearly always have a strong
signals at both the surface and at upper levels. With that in
mind, the NAM does not show strong signals at both levels
Thursday. However the GFS, Canadian and ECMWF are a little
stronger than the NAM in that regard. Since the system goes
negative till west of us that means the strongest response will
be west of us. There is some instability but there will be a lot
of clouds too so this should not be a major severe event, still we
should see some convection.

The next event will be over the weekend into next week but with
the main system not getting here till late Sunday or Monday, who
knows, maybe the weekend will be mostly dry. Still this will have
to be watched.

Bottom line... expect showers and thunderstorms on Thursday and
Monday with a chance of showers and thunderstorms over the
weekend.

&&

.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 753 PM EDT Mon Apr 24 2017

IFR is expected to continue through Tuesday afternoon, although we
will have to keep an eye on how far north some low clouds across
Ohio will get by early Tuesday morning. Some of the forecast
models show ceilings of 700 to 1500 feet AGL making it into
southern Lower Michigan, but this appears to be overdone and we
will keep VFR going overnight and Tuesday.

Winds will be east to southeast around 10 knots with some gusts to
20 knots by Tuesday afternoon.

&&

.MARINE...
Issued at 323 PM EDT Mon Apr 24 2017

We may need small craft headlines on Wednesday but for now the
winds and waves will remain below criteria for a small craft
advisory.


&&

.HYDROLOGY...
Issued at 126 PM EDT Mon Apr 24 2017

Most river streamflow rates are running between the 75th and 85th
percentiles for April 24, so they are still running above normal
despite most having fallen below bankfull. An active weather pattern
will return late Wednesday and continue into next week. The concern
for rebounding river levels and possible flooding remains,
especially after the rain event likely to occur between Saturday to
Monday. A majority of the latest GFS and ECMWF ensemble members
produce at least 2 inches of rainfall over the area by next
Monday.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...None.
&&

$$

SYNOPSIS...WDM
SHORT TERM...WDM
LONG TERM...WDM
AVIATION...Ostuno
HYDROLOGY...CAS
MARINE...WDM



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