Area Forecast Discussion
Issued by NWS Grand Rapids, MI

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

FXUS63 KGRR 180210

Area Forecast Discussion
National Weather Service Grand Rapids MI
1010 PM EDT Mon Oct 17 2016


Issued at 316 PM EDT Mon Oct 17 2016

Warm and windy conditions can be expected tonight ahead of a cold
front that will be approaching the area toward daybreak Tuesday
morning. There is a small chance of a shower or storm tonight up
north, but most locations will likely stay dry tonight. There is a
chance of a rain shower on Tuesday as the front presses through.

There will be a brief break on Wednesday with cooler air moving in.
Rain chances will increase once again late on Wednesday through
Thursday as a system approaches the area from the Southwest. Much
cooler air is poised to move in for next weekend.


.SHORT TERM...(This evening through Wednesday night)
Issued at 316 PM EDT Mon Oct 17 2016

Not much going on this afternoon with the warm front well north of
the area, and the associated convection also well north. Plenty of
low clouds hanging around this afternoon, that are expected to trend
north by this evening clearing some southern locations out. Most of
the cwfa should stay dry tonight with the nose of the llj and
boundary well north. We can not rule out something clipping the far
nrn section of the cwfa.

Winds will get cranking tonight too with a 65 knot llj moving
overhead this evening. The strong warm advection will limit much of
this wind from reaching the surface. We still could see some wind
gusts approaching 40 mph, especially along the lakeshore.

There will be a chance of a few light rain showers on Tuesday,
mainly during the first half of the day. This will be the case with
the cold front plowing through at that time. No real instability to
speak of, the llj will be peeling away, and the short wave and upper
jet dynamics all stay north of the area. The front should clear the
cwfa toward or just after 18z Tue.

We will see rain chances increase late on Wed, and more so Wed night
into Thu after a break in the weather much of Wed. The short wave
moving onshore over the West Coast tonight will approach the area
at that time and amplify a bit. This will develop a sfc low, and
track it just north of the Ohio River valley. The N/NW fringe of the
sfc system and mid level deformation zone will be strengthening and
looks to affect at least SE Lower, if not areas further NW. Still
some uncertainty with the fine details, but we have the highest
chances of rain to the SE, and tapering off to the NW. Thunder
chances should stay to our SE.

.LONG TERM...(Thursday through Monday)
Issued at 316 PM EDT Mon Oct 17 2016

Low pressure tracking through the Ohio Valley will spread its
northern precip shield into Lower Michigan on Thursday with the
highest POPS across the southeast zones. Colder air on the backside
of the low arrives later Thursday and Friday with the synoptic rain
showers replaced with a few lake enhanced showers. These should end
by Friday night.

There is some question as to the weekend weather with continuing
spread in the forecast ensembles leading to low confidence for POPs.
The thermal trough moves east with a general warm advection pattern,
but there are differences with timing and track of a northern stream
shortwave trough/clipper. The forecast will feature a dry forecast
for Saturday, but there is some support for showers on Saturday with
a faster arrival and a further south track in the 12Z ECMWF versus
the slower and further north GFS, which would delay the showers
until Monday. We will have to continue to watch trends and adjust


.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 759 PM EDT Mon Oct 17 2016

Overall high confidence for VFR conditions. The main concern through
06Z is the onset of low-level wind shear. Radar and aircraft data
indicate winds from the southwest at 3000-4000 ft AGL have already
increased to 55 knots. Although southerly surface winds should
increase slightly later tonight, speed shear will still be strong
for much of tonight. Stronger surface gusts approaching 30 knots
will be possible at the MKG terminal by Lake Michigan.

Conditions will improve towards sunrise when winds will also veer
to more of a southwesterly direction.


Issued at 1010 PM EDT Mon Oct 17 2016

The southern Lake MI buoy has been reporting gusts approaching 30
knots as have the Bridgman and Michigan City buoys. Marginal gale
conditions characterized by frequent gusts to 35 knots will be
possible for at least a few hours overnight. While this would
technically justify a gale warning, have opted not to upgrade for
the following reasons:

1) It is climatologically rare to achieve slam dunk gale conditions
in a warm advection regime such as this, so confidence in verifying
a gale warning remains limited.

2) This should not be a particularly impactful event given its short
duration and overnight timing during the latter half of October when
nearshore boat traffic in our area is extremely light to non-

3) A small craft advisory is already in effect for winds to 30
knots. Occasional gusts to 35 knots are a good bet and worth
mentioning in the updates. More significantly...we will increase
waves up to 5 to 10 feet based on a local run of the GLERL that is
looking more realistic with nearshore waves than the grainier WW3.
Given these already significant waves, I believe that any additional
impacts realized with frequent versus occasional gusts to 35 knots
(i.e., technical Gale versus technical non-Gale) will be too
negligible to justify headline adjustments in this particular case.


Issued at 241 PM EDT Mon Oct 17 2016

Many river forecast points in the Grand and Kalamazoo basins
have streamflows running above the 90th percentile for this date.
Sycamore Creek at Holt and the Grand River at Ionia are approaching
bankfull but will likely level off just below. Fortunately, heavy
rainfall events appear unlikely this week. The only thing to watch
is the deepening Midwest trough and Ohio Valley cyclogenesis
Wednesday into Thursday, which is currently expected to produce an
axis of 1-2 inch rainfall south of Michigan. Global model ensembles
do suggest the potential for over a half inch in the headwaters of
the Grand basin on Thursday, depending on the evolution of the
system. If over a half inch of rain does fall, Sycamore Creek would
be most susceptible to rising above bankfull.


LM...Small Craft Advisory until 4 PM EDT Tuesday for LMZ844>849.



LONG TERM...Ostuno
MARINE...TJT is the U.S. government's official web portal to all federal, state and local government web resources and services.