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Area forecast discussion
National Weather Service Grand Rapids Michigan
1014 PM EDT sun Apr 30 2017

Latest update...

issued at 330 PM EDT sun Apr 30 2017

Periods of moderate to heavy rain will continue tonight with many
areas seeing around another inch of rain. The rain will finally
diminish on Monday, but light and scattered showers will linger into
Tuesday. We will dry out by Tuesday night. Temperatures will
remain cool, with highs around 60 on Monday, dropping to 45 to 50
for Tuesday.

We should continue to dry out through the latter half of the week,
although some spotty light showers can not be ruled out Thursday
night through Friday night. Temperatures will remain slightly below
normal with most daytime highs in the upper 50s to mid 60s through


issued at 1007 PM EDT sun Apr 30 2017

Decided to keep the Flood Watch going. The atmosphere remains
very moist with pwat values up around 1.5 inches. Elevated
instability was advecting in from the southwest thanks to an
approaching low level jet. Upstream thunderstorms have produced
rainfall rates up to about 0.50 inches per hour. While modeled quantitative precipitation forecast
values would support only a low risk for flooding...since we
already have the watch out and still some parameters around that
would support a risk for heavy rain...will keep the watch going.

No changes to the marine headlines.


Short term...(this evening through Tuesday night)
issued at 330 PM EDT sun Apr 30 2017

Will maintain the Flood Watch as is through tonight with periods of
heavy rain continuing. The rains lighten up Monday through Tuesday,
but somewhat steadier rains are still expected Monday afternoon and

An upper low remains well west of US, over eastern Kansas late this
afternoon. It will continue to move northeast, reaching the Green
Bay area by Monday evening, and into Canada by Tuesday evening.

With the deep flow off the Gulf we will continue to see a rich
moisture feed into the region. Enhanced lift from the low level jet
this evening will be followed enhancement from the right exit region
of the upper jet overnight. Expect all areas will see another half
inch to an inch overnight, bringing some storm totals toward the 3
inch mark.

The better dynamics shift northeast by daybreak Monday resulting in
less coverage and intensity to the rains. In fact we will see a dry
slot move through the County Warning Area in the morning, so a brief period of
sunshine should occur. However the comma head comes overhead into
the afternoon and Monday night for another round of showers. Expect
a general quarter inch from this. It will be a windy day as the
surface low pushes NE across Wisconsin.

Surface and upper troughiness lingers into Tuesday. Expect more
showers, just more scattered and on the light side. Another windy
day as the cold advection kicks in. Daytime highs only 45 to 50.

We finally begin to dry out by Tuesday night. Decided to remove any
mention of frost as it appears it will take most of the overnight
before we clear out. There will be a breeze through the night too.

Long term...(wednesday through sunday)
issued at 330 PM EDT sun Apr 30 2017

A stretch of predominately dry and cooler than normal weather is
expected in the long term period. However we will have to monitor
trends of the next big low pressure system which is currently
progged to track through the Ohio Valley region mid to late week.

Latest guidance shows the northern edge of the precipitation with
the next low clipping southeast lwr mi, but a more NW track could
send deformation zone rains farther north across lwr Michigan.

For now will have low pops mid to late week for the jxn area however
chc pops areawide Friday night and Saturday related to a cold front
diving down from the north as the aforementioned sfc low lifts north
toward Quebec.

We could see some frost on Wednesday night with a sfc ridge
overhead. However if mid/high clouds are already streaming in ahead
of the next system that may not be a concern.


Aviation...(for the 00z tafs through 00z Monday evening)
issued at 735 PM EDT sun Apr 30 2017

Low level moisture will continue to be abundant through tonight.
This will lead to IFR and lower impacts. Conditions do start to
dry out on less in the way of impacts are forecasted.

There will be some shower and even a few thunderstorms around
tonight as some instability moves in from the south. By 09z...the
axis of instability shifts east...thus the potential will diminish
by then.

Gusty winds look likely for Monday with some values over 30 knots


issued at 330 PM EDT sun Apr 30 2017

Maintaining the Small Craft Advisory through Tuesday evening. We
may approach gales late Monday afternoon through Tuesday morning as
the low passes by and the cold advection begins. Will forgo issuing
a Gale Warning however due to the marginal look at this point.


issued at 330 PM EDT sun Apr 30 2017

As of Sunday afternoon, total rainfall amounts ranged from 0.50" to
1.50", with the highest amounts in Allegan, Ottawa, and Kent
counties. Additional rainfall of 1" or more is expected through
Monday morning. This will lead to continued river rises. For the
main Stem rivers, it will take a few days for crests to occur.
Smaller rivers and streams will likely crest by tomorrow. Many
rivers will go above bankfull and a few will flood in certain

Localized areal flooding is a possibility through Monday morning.
Runoff efficiency will be quite high just about everywhere, so
ponding on roads will occur in the steadier rains.

An additional quarter inch or so of rain is possible Monday
afternoon into Tuesday, which shouldn't add a significant impact to
the rivers but may slightly boost the rises.


GRR watches/warnings/advisories...
Michigan...Flood Watch until 8 am EDT Monday for miz043>046-050>052-056>059-

Lm...Small Craft Advisory until 10 PM EDT Tuesday for lmz844>849.




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