Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 231740
AFDGRR

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

LATEST UPDATE...
Aviation/Hydro

.SYNOPSIS...
Issued at 305 AM EDT Sun Apr 23 2017

A weak cold front will diminish as it slips down into the Northern
Great Lakes region today and tonight. An area of high pressure
will then build into Michigan for Monday. As this feature tracks
east on Tuesday a warmer and increasingly moist airmass with
gradually build into the area for the middle part of the week.

&&

.SHORT TERM...(Today through Tuesday)
Issued at 305 AM EDT Sun Apr 23 2017

The relatively quiet pattern persists through Tuesday. A weak cold
front tries to drop down from the north tonight...but it will
likely diminish before it reaches southern lower MI. An easterly
flow sets up for tonight and Monday. So it looks like the
lakeshore regions will see the warmest temperatures.

Some instability develops on Tuesday. After looking at forecast
soundings...the risk for a shower or thunderstorms is low. The
atmosphere is shown to be dry below 500 mb. In addition a warm
layer is advertised by the models around 700 mb...which would
limit the potential for rising parcels to push through that layer.
Will keep the forecast dry.

Patchy frost will be possible for tonight...mainly over the
interior northeast zones. The wind may stay up though...limiting
this risk. Will keep it in the forecast for now.

.LONG TERM...(Tuesday night through Saturday)
Issued at 305 AM EDT Sun Apr 23 2017

Despite expectations for an active setup through the upcoming week,
model guidance continues to trend later in the midweek period with
the onset. Difference in the GFS/ECM are relatively small with a
cold front entering West Michigan early Wednesday morning. The NAM,
however, remains well west of Lake Michigan at 12z Wed morning.
Given the way guidance has behaved with the NW adjustment in the
last several runs and higher res solutions verifying the delay, we
may stay dry through early Wednesday morning.

The delay could be key with instability for thunderstorms Wednesday
afternoon. If daytime heat can contribute, we could see some
convection take shape with MU Cape values pushing near 1500 J/kg
according to GFS bufkit overviews. Ample moisture flows in from the
south with PWAT values between 1.0-1.5 inches. Wind profiles aren`t
off the charges, but does provide a deep layer of 40-70 knots. Also,
profiles are unidirectional with the frontal passage. It seems that
we would see a linear mode of convection with heavier rainfall. What
is yet to be seen is a little more run-to-run consistency in models.
However, if high res models continue to point in this direction, it
may be something to watch through the week, if not for strong
storms, it would be for a quick shot of heavy rain.

The upper trough pushes north of the area by Friday. A shortwave
feature rotates in behind the system, keeping low chances of
precipitation in the forecast. Expect a few light rain shower to
round out the work week.

The next big system takes shape over the central plains over the
weekend. Models diverge a bit beyond Friday with the GFS bring
precipitation back in a little quicker than the ECM. The overall
theme is for an amplified ridge to develop over the eastern conus as
we head into next weekend. The upper trough deepen to the west with
the core of the upper jet pushing into the plains. A warm front
extends east of the main system and pushing into Lower Michigan next
Saturday. We stay entrenched in warm southern flow through much of
the later part of next week, until the system bring the cold front
through next Sunday. Again, the gulf remain wide open with moisture
flowing north. This could be another big rain maker with
thunderstorm as we head into next weekend.

&&

.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 305 AM EDT Sun Apr 23 2017

The pressure gradient will remain relatively weak through Monday
night so not marine headlines. The flow will be largely offshore
through Monday so waves should be quite low.


&&

.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...MJS
SHORT TERM...MJS
LONG TERM...JAM
AVIATION...CAS
HYDROLOGY...CAS
MARINE...MJS



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