Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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949
FXUS63 KGRR 240229
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1029 PM EDT Thu Mar 23 2017

LATEST UPDATE...
Update

.SYNOPSIS...
Issued at 315 PM EDT Thu Mar 23 2017

Rain chances will increase tonight and last through the weekend into
next week as a series of areas of low pressure will move through the
area. It will not be raining all of the time, but the chances will
remain. Warmer air will try to move in over the area, especially the
southern half of the state. Some of this rain will be accompanied by
the threat of thunder, especially tonight and Friday. Severe weather
is not expected.

&&

.UPDATE...
Issued at 1028 PM EDT Thu Mar 23 2017

Rain is spreading in on the nose of the 850mb low level jet and
strongest moisture advection. High resolution models like the
HRRRx indicate that this is the main push of precipitation tonight
with a tapering off overnight. Would not be surprised to see
another round of precipitation overnight though as a 50-55 knot
low level jet moves through.

As for the threat of thunderstorms, left the mention in the
forecast, as most unstable CAPE values have increased to 500-1000
j/kg west of the lake at 02z. Not expecting values that high to
advect in overnight as the drier air will act to erode the
precipitation and instability a bit. A rumble or two of thunder
cannot be ruled out between now and daybreak.

Bottom line, a slug of rain to move through with an embedded storm
possible through 07z. Another round of showers and a storm or two
possible overnight.

&&

.SHORT TERM...(This evening through Saturday night)
Issued at 315 PM EDT Thu Mar 23 2017

Our main challenge through the period is determining rainfall trends
as the area will become under the influence of a wetter pattern that
will be accompanied by more seasonable to warmer than average
temperatures. We are also watching the potential for some possible
freezing rain up north, if sfc temps can drop enough.

We are expecting a line of showers with embedded storms to move
in/develop overhead later this evening into the overnight hours
tonight. This will be in association with the best surge in moisture
transport in the lower levels. This will be fueled by a 50+ knot low
level jet that will move in tonight. Initially everyone will see the
opportunity develop from SW to NE. There will be a fgen band that
sets up across the nrn portion of the CWFA to north of the area as
the warm air is stopped from moving any further north. The thunder
threat looks to be elevated, so severe weather chances look quite
low.

The frontal set up will limit the best rain potential from M-20 and
to the north for Friday. South of this line, the warm sector will
bring temps into the 50s just north of I-96, to almost as warm as 70
across the far south.

We will see the rain potential then sink south late Fri night into
Sat. This occurs as high pressure across Canada strengthens, and
overcomes the front a bit. Lower Michigan will be in the zone of
best fgen, and therefore will have the best threat of rain as short
waves ride along this boundary. The good thing is that all of the
deeper instability stays mostly south of the area after tonight,
keeping severe weather chances mainly out of the area. Rainfall will
begin to add up over time, creating wet conditions.

We will see rain chances continue then Sat night as the main low out
to our SW will lift up into the area. This will just reinforce the
moisture advecting over the area. It does appear that the low will
be occluding, so most of, if not all of the instability will stay
down around I-94 and areas south.

Regarding freezing rain chances, the chance is not zero late tonight
across the far NE counties, and again Sat night. The chances are
small enough at this time to keep out of the forecast for the time
being. This occurs as the high to our north will bring in a NE flow
with some cooler and drier air trying to advect in. The models are
in fairly good consensus keeping temps at least a tad above
freezing. If a trend develops for cooler temps up north, the chcs f
or some freezing rain there will go up. This is something we will be
watching.

.LONG TERM...(Sunday through Thursday)
Issued at 315 PM EDT Thu Mar 23 2017

With a weakening low pressure system tracking into the CWA the risk
for showers will exist on Sunday.  The atmosphere will be  moist and
some weakness in the stability will be around...which will support
at least moderate showers.  The surface temperatures are forecasted
remain above freezing so no mixed precipitation will be in the
forecast.

The frontal zone will still be around through Monday.  As a result
the risk for showers will exist. High pressure ridges in for Tuesday
and into Wednesday so will feature a mainly dry forecast.
Temperatures will likely end up a few degrees above normal for most
of the long term period.

&&

.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 836 PM EDT Thu Mar 23 2017

VFR weather prevails at 00z, with showers and thunderstorms
located to the west of Lake Michigan over Wisconsin. We expect
some scattered showers to move into the area after 03z, with
showers and a few embedded thunderstorms for a few hours overnight
between 05z and 10z. The chances for thunderstorms is not high
enough to include a prevailing group in the TAFs, but did include
VCTS wording. Feel the VFR conditions will try to trend into the
MVFR category overnight as ceilings lower and some light fog
develops with the precipitation.

On Friday, gusty south-southwest winds will develop which will try
to push any lower ceilings northward out of the area. The
exception may be KMKG which may try to hang on to some lower
ceilings through the day.


&&

.MARINE...
Issued at 315 PM EDT Thu Mar 23 2017

We will be holding on to the Small Craft Advisory as is for this
forecast cycle for the northern two zones. SSE winds are up close to
criteria, as are waves near Little and Big Sable points. There
should be a slight trend down after 00z, enough that we do not feel
the need to extend this out further.

Wave could come up enough in the warm sector near Muskegon and point
south that Advisory conditions may be met.


&&

.HYDROLOGY...
Issued at 146 PM EDT Thu Mar 23 2017

An active weather pattern starting Thursday night and lasting
through at least early next week will provide multiple episodes of
at light rain, and occasional periods of heavier rain. Thursday
night through Sunday, rainfall totals between 0.75 and 1.5 inches
will likely fall over the area, with the higher-end amounts favored
in Muskegon river basin. River levels will likely rise as a result.
Some rivers may eventually climb back to bankfull next week.

&&

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

$$

UPDATE...Duke
SYNOPSIS...NJJ
SHORT TERM...NJJ
LONG TERM...MJS
AVIATION...Duke
HYDROLOGY...CAS
MARINE...NJJ



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