Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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983
FXUS63 KGRR 231904
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
304 PM EDT Sun Apr 23 2017

LATEST UPDATE...
Synopsis/Short Term/Long Term/Fire Weather/Marine

.SYNOPSIS...
Issued at 304 PM EDT Sun Apr 23 2017

The area will remain in between systems through Tuesday. This will
allow for a mainly dry period through then with a good deal of
sunshine and very nice spring temperatures. Clouds will be on the
increase on Tuesday, and areas toward Ludington will see a small
chance of rain arrive Tuesday night, with the rest of the area
seeing better chances for showers and storms late Wednesday into
Thursday.

Cooler weather will follow for the end of the week. Another surge of
warmer air and shower/storm chances will arrive for next weekend.

&&

.SHORT TERM...(This evening through Tuesday night)
Issued at 304 PM EDT Sun Apr 23 2017

Challenges in the first portion of the short term are rather limited
with dry conditions expected. The challenges come starting on
Tuesday, and continue through Tuesday night with shower/storm
chances needing to be determined. We are not expecting much in the
way of impacts through Tuesday night.

Very dry airmass in place this afternoon with plenty of sunshine and
mixing taking place. This will generally continue with one small
caveat. A weakening front is dropping south through the area with
slightly higher dew points coming in on N/NE flow off of the Lakes.
This slightly cooler air and moisture from the lakes could allow for
some fog/stratus tonight as the atmosphere cools. We are not sure of
this as good mixing and the dry air in place may take care of it.
Any fog/stratus that would occur tonight would dissipate quickly Mon
morning.

The models are trying to bring some very light QPF in late Mon night
into Tue. We are going to hold with a dry forecast for the time
being. Forecast soundings indicate that there will be a very shallow
layer of moisture around 3-5k feet. This looks too shallow to
generate any rain, especially when we have dry antecedent conditions
to start with.

The rain chances will increase some Tuesday night, and be limited to
mainly the far NW corner of the CWFA. It is there that will be in
closer proximity to the frontal system across WI and Eastern Upper
Michigan, and near the nose of the low level jet that will be moving
to the NE. We just have a chance of showers and storms for now, as
the bulk of the rain should be N and W of the CWFA.

.LONG TERM...(Wednesday through Sunday)
Issued at 304 PM EDT Sun Apr 23 2017

Models are pointing toward two systems affecting the Great Lakes
during the long term period. Both have the potential to bring quite
a bit of rain to the cwa.

The first system is a wave that develops on the southern end of a
cold front that will move northeast toward WI/IL Wednesday. We`ll be
on the east side of this system initially which will result a strong
surge of moisture and instability from the Gulf. The gfs is a bit
farther east than the ecmwf but are similar in strength and track.
So, confidence is fairly high that we`ll see showers/storms
Wednesday and Wednesday night as this system moves through. Shear
values are progd in the 50-60kt range Wednesday afternoon while we
sit in the warm sector, so we`ll need to watch for the potential for
strong/severe storms.

The next system comes in Friday night/Saturday. It`s another system
that will move north on the west side of Lake Michigan. The models,
ecmwf in particular, show a very active warm front Saturday. The gfs
meanwhile is a bit quicker pushing the warm front through. SW Lower
Michigan will be in a prime location for another round of
significant rainfall as these showers/storms move/develop northward
through the region. The trailing cold front will move through late
Sunday if current model trends hold. Next weekend looks like it
could be rather wet. Shear values again look fairly strong so a
strong/severe potential looks to exist next weekend too.

Wednesday will be the warmest day with highs in the mid 70s. Then
after the cold front moves through, highs will fall back to the 50s
Thursday and Friday before climbing into the 60s Saturday and Sunday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 140 PM EDT Sun Apr 23 2017

Prevailing VFR into Monday with WNW wind 5 to 10 kt this
afternoon veering NE after 03Z as a shallow wedge of colder air
off Lake Huron slides through. Moisture below 1 kft increases
overnight and may be enough for some low level clouds to form,
though not confident in if sky coverage will be enough for IFR.


&&

.MARINE...
Issued at 304 PM EDT Sun Apr 23 2017

The flow will become offshore tonight, and remain the case through
Monday. The winds may approach 20 knots on Monday as winds start to
move in late in the day. Waves will be limited by the offshore flow
and the stable nature of the warmer air over the cooler waters. We
could be looking at possible Small Craft Advisory conditions Mon
night and beyond with stronger systems approaching the area.

&&

.FIRE WEATHER...
Issued at 304 PM EDT Sun Apr 23 2017

A couple of days without rain combined with plenty of sunshine and a
dry air mass has allow RH`s to drop down below 30% this afternoon at
many locations. Fire danger is not too bad with winds staying below
10 knots at most locations. Conditions are a little breezy toward
Mt. Pleasant, Big Rapids, and Alma.

We expect close to a repeat on Monday with regards to RH`s as we
should mix down dry air. Winds should remain on the lighter side and
be more from the East/Southeast. We do expect better moisture will
move in over the area for Tuesday with southerly winds drawing
moisture northward.

&&

.HYDROLOGY...
Issued at 140 PM EDT Sun Apr 23 2017

The 6 river forecast points out of their banks are at crest or
already falling. Dry weather through Tuesday will allow water
levels to recede below bankfull on some but not all rivers. An
active weather pattern is likely starting Wednesday and continuing
into the early part of next week. There is a chance for basin-
average rainfall to exceed 1-2 inches by next Sunday, though there
is low confidence exactly where the axis of heaviest rain will
set up. A number of rivers will still be running higher than
normal going into this active pattern, so they will be susceptible
to minor flooding again if heavy rain does occur.

&&

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

$$

SYNOPSIS...NJJ
SHORT TERM...NJJ
LONG TERM...04
AVIATION...CAS
FIRE WEATHER...NJJ
HYDROLOGY...CAS
MARINE...NJJ



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