Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 200231

Area Forecast Discussion
National Weather Service Grand Rapids MI
1031 PM EDT Wed Apr 19 2017


Issued at 300 PM EDT Wed Apr 19 2017

A northward moving warm front will bring showers and thunderstorms
tonight. More showers and thunderstorms may redevelop Thursday
morning and early afternoon along and just ahead of a cold front.
A much cooler and drier airmass will move in behind that front
Thursday night through Saturday.


Issued at 1031 PM EDT Wed Apr 19 2017

Will make several changes to the overnight forecast. Raise min
temps a few degrees as cloud cover will remain of the region. I
also tweaked POPs to align with the best chance of pcpn coming
toward daybreak.

Storms crossing the MS River and into WI this evening will hold
together and head toward Lower MI late tonight. These storms are
along a cold front, but also the coupled jet associated with them
moves our way, as well as a low level jet. The best jet dynamics
head for Central Lower where the highest POPs will be carried.
Areas north and west of Big Rapids should see the steadiest rains.
We still can not rule out an isolated stronger storm late
tonight/toward daybreak.


.SHORT TERM...(This evening through Friday night)
Issued at 300 PM EDT Wed Apr 19 2017

Primary short term fcst concerns involve determining convective
potential late this afternoon through mid afternoon Thursday.

At 1830Z showers are moving across far southern lake Michigan and
also developing over southern lower MI south of I-96 out ahead of a
weak mcv. Instability should increase a bit from mid to late
afternoon out ahead of this feature. Therefore showers will continue
to develop late this afternoon south of I-96.

In addition to showers a few thunderstorms may also develop over
that area as instability increases a bit. The relatively best chc
for convection late this aftn will be over our far south/se fcst
area near to south of a line from KAZO to KJXN where relatively
stronger instability will develop. No severe wx will occur late
this afternoon and early evening.

Widespread rain and convection will develop late this evening and
overnight over our northern forecast area mainly north of I-96 as
1000-850 mb moisture transport ramps up significantly. The llj will
also increase as does deep layer shear. Some strong to potentially
severe storms are possible overnight with large hail being the
primary svr wx threat with the elevated convection. Any storms could
bring locally heavy rainfall as well.

Sfc based convection may develop along and just ahead of the cold
front Thursday morning through mid afternoon. Plenty of moisture
will be in place just ahead of the front with forcing from the
cold front and potential for an axis of sb cape values to reach
1000-1500 j/kg just ahead of the cold front. Deep layer shear is
strong so there is potential for a few strong to potentially
severe storms through mid afternoon.

The relatively best chc for severe wx will be over our se fcst
area just ahead of the cold front from around 17Z-20Z where weak
to potentially moderate instability could develop just ahead of
the front. This notion is supported by 12z nssl wrf sim z
guidance. However the severe wx potential is mitigated by
uncertainty about instability as extensive morning clouds/showers
would keep instability in check.

.LONG TERM...(Saturday through Wednesday)
Issued at 300 PM EDT Wed Apr 19 2017

The next major storm will likely be later next week, with a weaker
system in the Tuesday time frame. From Sat into Monday expect dry
weather (no rain) and temperatures close to normal.

Overall our weather pattern will remain largely unchanged as the
northern stream stays north and the quasi-zonal primary polar jet
remains near 40 N (more or less). The polar jet is expected to stay
from near Japan then eastward across the central Pacific, then
across the CONUS.  I do not see a major change in this pattern into
at least early May.

We did however get a break in the East Asian Jet this weekend. That
in turn allows the northern stream to dig farther south toward the
Great Lakes this weekend. That blocks the next Pacific storm system
from getting this far north. As a result we end up with near normal
temperatures and no rainfall for Saturday through Monday. Frost and
freezing temperatures are possible over northern areas of our CWA on
Saturday and Sunday morning.

By early next week the East Asian Jet feature comes back and that
will lead to a warm up and stormy weather just beyond this forecast
period. There is a weak system that shears out of the Pacific wave
stream late in the weekend and crosses the Great Lakes in the Monday
Tuesday time frame. This does have enough instability for
thunderstorms but it is moving quickly and will not have time to
pull in a lot of Gulf moisture so at this point I do not expect a
significant rainfall or thunderstorm event as it moves through.

Bottom line is near normal temperatures and little if any
precipitation till at least Tuesday.


.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 1031 PM EDT Wed Apr 19 2017

Two rounds of thunderstorms are expected in the next 24 hours. The
first should come after 04Z and end around 09Z. The second round
should develop over the region late Thu morning and exit the
region by late afternoon. There could be isolated storms outside
these time frames too.

In between the two main rounds of storms we should see some IFR
develop. Ceilings should lower and some fog may briefly occur
prior to the winds picking up by mid morning.


Issued at 1031 PM EDT Wed Apr 19 2017

Will issue a small craft advisory starting late Thursday morning.
Southwest winds will be increasing ahead of an approaching cold
front. These will pivot to the west behind the front into the
afternoon. WNW winds are expected to reach 20 to 25 knots late
Thursday night before dropping off through Friday.


Issued at 1118 AM EDT Wed Apr 19 2017

River levels have returned closer to normal in many locations but
still remain a little high for the time of year. Rivers are above
bankfull and falling at Ionia, Maple Rapids, and Eagle, while
Evart is above bankfull and rising. Rain totals Thursday in excess
of an inch are possible upstream of Evart, which may boost the
crest over the comping days. Croton may reach bankfull by Friday
also. More spotty rain totals are expected in the Grand and
Kalamazoo basins, which should have a limited effect on main stem
rivers. Smaller river basins that receive locally heavy rain
(including Eagle) would be susceptible to rise again.


LM...Small Craft Advisory from 10 AM Thursday to 6 PM EDT Friday for



SHORT TERM...Laurens
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