Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 160551
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
151 AM EDT Mon Apr 16 2018

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 330 PM EDT Sun Apr 15 2018

A major storm system will continue to bring a mix of lighter
snow sleet and freezing rain to central and south central lower
Michigan late this afternoon and tonight. However the most
significant precipitation is coming to an end. Some light snow
showers will linger Monday and it will become windy Monday
afternoon. Temperatures will remain much below normal through
at least Tuesday.

&&

.UPDATE...
Issued at 944 PM EDT Sun Apr 15 2018

We have allowed the headlines to expire here by 10 pm, and have
freshened up the forecast to account for the latest trends.

The heavier mixed pcpn has moved out of the area, leaving mainly
some patchy drizzle/freezing drizzle. A few rain/snow showers are
floating through as the center of the upper low slowly rotates
toward the area. Moisture is generally below the DGZ, but some of
the convective elements are able to tap the DGZ and produce
measurable pcpn. The atmosphere is just warm enough that some of
this is rain, however pcpn will transition over to all snow
tonight as colder air moves in.

We will see light snow/snow showers move in later tonight along
the wrn half of the area. This will be associated with the wrap
around moisture. We are not expecting significant accumulations,
however it may be just enough to slicken up the roads some for the
morning commute.

&&

.SHORT TERM...(This evening through Tuesday night)
Issued at 330 PM EDT Sun Apr 15 2018

At 19Z KGRR/rgnl radar trends indicate that the most significant
pcpn is exiting our fcst area. However temperatures remain at or
below freezing across roughly the northern half of our fcst area
and lighter pcpn will redevelop late this afternoon and overnight.
Precipitation will continue to fall as a mix of light freezing
rain sleet and snow north of I-96 with mostly light rain showers
and sprinkles south of I-96.

Impacts from this system have been significant across most of our
fcst area with tens of thousands of people without power at the
moment. Given the combination of significant impacts from
the sleet/fzra and that those impacts will linger late this
afternoon and evening we decided to extend the winter storm
warning until 10 pm from Ottawa Kent Ionia and Clinton counties
northward. Temps are still at or below freezing from the northern
portions of those counties northward and will not moderate much
through the rest of the day and tonight. Therefore impacts will
continue.

Enough cold air advection will finally occur by early to mid
morning Monday to cool thermal profiles sufficiently enough that
p-type will transition to all light snow by then. Light snow
showers will linger through the day tomorrow into tomorrow evening
on the back side of the sfc low pressure system but accumulations
will be light at around an inch or less.

My concerns are increasing about potential for additional power
outages tomorrow afternoon as northwest winds ramp up to 15 to 25
mph with gusts to around 30 mph. Significant icing has occurred
across portions of our fcst area and I believe that quite a bit of
residual ice will still linger on trees and limbs into tomorrow
(not sufficiently mild enough across our central/northern fcst
area to melt the ice off late this aftn or tomorrow). Some April
sun would probably melt the ice off quickly but we expect skies to
remain overcast.

So for now we only extended the warning out through late this
evening. It is certainly possible though that additional power
outages may occur tomorrow as winds ramp up. Tranquil wx will
finally return late Monday night and for Tuesday.

Thanks for extensive coord on warning extension decisions DTX/APX.

.LONG TERM...(Wednesday through Sunday)
Issued at 330 PM EDT Sun Apr 15 2018

One more potential (and likely final) bout of wintry weather arrives
Wednesday night into early Thursday morning before we finally turn
the corner toward a milder, more tranquil spring weather regime.
Next weekend should be stark contrast to this weekend as highs flirt
with 60 degrees.

Guidance has been consistent in showing a fairly potent system with
a closed mid level circulation and sfc occlusion moving across srn
Lwr MI mid week. Fortunately this system is much more progressive
than the one we`re dealing with today.

While precipitation is expected to be all rain is it develops
Wednesday, dynamic cooling and trowal/Fgen dynamics on Wednesday
night just north of the closed upper low will likely change precip
over to mostly wet snow. It`s possible we could see some localized
quick 2-4" wet snow amounts overnight which could impact the
Thursday morning commute. All of that would melt though as temps
later Thursday into the mid 40s.

It`s still looking like a quiet and more average period setting up
for the end of the week and next weekend as ridging at the sfc and
aloft dominates. Temperatures will moderate during this period with
confidence increasing that highs will be near 60 next Sat/Sun.

&&

.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 151 AM EDT Mon Apr 16 2018

Our initial concern starts out with fog trends for the srn and ern
terminals. We then transition to concern for light snow and IFR
cig trends, along with winds.

The srn and ern terminals have developed fog due to the light wind
in place and very moist boundary layer in place from all of the
recent pcpn. We expect this fog to dissipate a bit over the next
few hours as winds pick up a bit and mix the atmosphere a bit.
They will likely hold on to and IFR cig and vsby.

A few light areas of mainly light snow are starting to show up.
They will become more widespread and more showery as we go into
the afternoon hours. Cigs will remain IFR through much of the day,
while vsbys range from VFR to IFR in and out of the snow showers.
Wind gusts around 25 knots or so will become likely during the
daylight hours.

We expect conditions to improve some after sunset. Winds will
diminish and cigs will lift a little as drier air moves in.

&&

.MARINE...
Issued at 938 PM EDT Sun Apr 15 2018

We allowed the Gale Warning to expire at 8 pm, and have replaced
it with a Small Craft Advisory through Monday. There is some
potential that winds may approach Gales on Monday.


&&

.HYDROLOGY...
Issued at 330 PM EDT Sun Apr 15 2018

As precipitation continues across the region, river levels are
around normal but rising. Precipitation totals will range from over
an inch and a half to around three inches from this past Friday
into Monday. This could lead to river flooding, but at this time
only the Muskegon River at Bridgeton is forecast to rise to near
flood stage. Stay tuned, as more flood warnings may be on the way if
all of the precipitation is realized.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...Small Craft Advisory until 8 PM EDT this evening for LMZ844>849.

&&

$$

UPDATE...NJJ
SYNOPSIS...Laurens
SHORT TERM...Laurens
LONG TERM...Meade
AVIATION...NJJ
HYDROLOGY...63
MARINE...NJJ



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