Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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792
FXUS63 KGRR 250230
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1030 PM EDT Fri Mar 24 2017

LATEST UPDATE...
Update

.SYNOPSIS...
Issued at 320 PM EDT Fri Mar 24 2017

The area is looking at a damp and gloomy weekend as an expansive
system will remain in place over the area. This will bring periods
of rain through the weekend with breezy and cooler conditions. There
is a chance of storms this afternoon and evening south of I-96, and
another chance of storms on Sunday down south.

There may be a brief break in the weather on Monday at some point.
We are looking at another system poised to move in and bring chances
of more rain showers. Another break in the weather will be possible
mid-week next week, before more rain could move in later next week.

&&

.UPDATE...
Issued at 1030 PM EDT Fri Mar 24 2017

Frontal boundary lies along the I-94 corridor at 10pm. Through the
course of the night the boundary should continue its slow slide
to the south and move to near the Michigan/Indiana line by 800am.
Some residual instability resides across far southern portions of
the state near the front, which is where showers and a few
thunderstorms have occurred this evening. CAPE values are now in
the 100-500 J/KG, which is down just a bit from earlier this
evening. Expect CAPE values to continue to dwindle as the front
pushes south. Chances for a thunderstorm will continue into the
overnight hours before fading towards morning.

Overrunning of the frontal boundary is on the weak side tonight,
but still expected areas of rain to continue and potentially fill
in a bit as the front sharpens. Have fairly high pops in the
forecast overnight as all the models show precipitation expanding
some overnight.

Temperatures will be on the decline tonight as cold air advection
continues with northeast winds.

&&

.SHORT TERM...(This evening through Sunday night)
Issued at 320 PM EDT Fri Mar 24 2017

Somewhat of a complicated scenario this evening as there seems to be
two distinct fronts over the area. One seems to be lined up from
near Mt. Pleasant to just north of Muskegon as of 3 pm, while the
other stronger warm front seems to be from Lansing to South Haven.

We are expecting some showers and a few storms to fire in the next
few hours south of the srn front. There seems to be only a couple
hundred j/kg of MU CAPE south of this front per the SPC mesoanalysis
page. Not much good shear either with stronger winds in the lower
levels. We can not rule out a few stronger wind gusts with the
showers/storm with the dry low levels, but we are not expecting
anything severe at this time.

Otherwise, the nrn front will be continuing to drift south as high
pressure across Canada help to push it south. This will enhance the
fgen over the area as the cooler air from the north pushes against
the warmer air to the south. We will see an almost continuous feed
of moisture overrunning this fgen, and providing the area with
periods of rain later tonight through Sat night. We should be far
enough in the cool air mass that the thunder threat will remain
south of the area. The rain should not be too heavy, just persistent.

The pcpn will become more showery on Sunday as the sfc low will
slowly move over the area. The low will be occluding, and the warm
sector looks to stay mainly south of the area. It may clip the far
southern counties, so enough instability could allow for an embedded
storm. At this time, there does not look to much, if any sunshine.
This will also limit the instability potential. The chances of rain
will then diminish Sunday night as the low begins to pull away from
the area.

.LONG TERM...(Monday through Friday)
Issued at 320 PM EDT Fri Mar 24 2017

Our fairly dry weather pattern we have had most of the month of
March has come to an end as Pacific wave train continues to be
active sending shortwaves on shore over the western CONUS about
every other day.  Also the northern stream jet is split and remains
north of 70N until farther notice.  This combination does not allow
enough blocking to bring the truly warm air north into Michigan for
more than a few hours (as systems move through) and also and more
important, does not allow the arctic express to bring anything this
far south. That precludes any significant snow events. So what we
get is a seemly never ending series of Pacific shortwaves tracking
east between 30N and 40N through the CONUS.

Monday starts with one of those waves moving out but with another
ready to move in.  So we will likely get a break for at least 6
hours from the showers during the day time MOnday but the next
southern stream system will move in by early Tuesday morning with
more showers.  Then there will be a break in the showers as a
stronger Pacific system builds an upstream ridge, just big enough to
bring a little Canadian air south into Michigan resulting in Wed and
Thu being dry with near normal temperatures. Beyond that the next
series of Pacific systems moves in leading to a wet period for Thu
into the weekend (and beyond).  The system coming at us later Thu
into Saturday could be a fairly strong system with thunderstorms and
severe storms not out of the question.  For now I played it down in
the grids but I do believe as we get closer to next weekend we can
define all of this better.

&&

.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 834 PM EDT Fri Mar 24 2017

Aviation conditions will deteriorate fairly quick tonight with VFR
weather at present headed to IFR in most areas by 12z. A frontal
boundary will sag south of the area tonight and lower ceilings and
rain/fog will develop. This evening, through 06z or so,
thunderstorms will be possible in the south at the I-94 TAF sites.

On Saturday a easterly wind north of the front over Lower Michigan will
keep low ceilings and light rain and fog locked in. We look to at
least have IFR conditions in place if not LIFR on Saturday.

&&

.MARINE...
Issued at 320 PM EDT Fri Mar 24 2017

We will continue the ongoing Small Craft Advisory for this evening
with wind gusts still going up around 25 knots. That said, the
cooler conditions over the water are likely limiting the effects a
bit.

We have stretched the current Small Craft Advisory for the southern
half of the nearshore into Sunday morning, and issued an advisory
for the northern half from late tonight through Sunday morning. We
will see a brisk wind take shape behind the fronts starting later
tonight until Sunday morning. Waves will not be as much of a problem
as the winds themselves with it being an offshore flow.

&&

.HYDROLOGY...
Issued at 1241 PM EDT Fri Mar 24 2017

A wet pattern will continue through much of the next seven days
with multiple rain events taking place. Rainfall totals over the
next week will generally be in the 0.75 to 1.50 inch range. This
will result in rises on area rivers with some area rivers reaching
bankfull starting late this weekend and continuing at bankfull
potentially through the end of next week. Significant river
flooding is not anticipated with the amount of rainfall that is
expected over the next week.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...Small Craft Advisory from 6 AM Saturday to 11 AM EDT Sunday for
     LMZ847>849.

     Small Craft Advisory until 11 AM EDT Sunday for LMZ844>846.

&&

$$

UPDATE...Duke
SYNOPSIS...NJJ
SHORT TERM...NJJ
LONG TERM...WDM
AVIATION...Duke
HYDROLOGY...Maczko
MARINE...NJJ



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