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Area forecast discussion 
National Weather Service Grand Rapids Michigan
717 am EDT Sat Aug 1 2015

Latest update...

issued at 251 am EDT Sat Aug 1 2015

Strong to severe thunderstorms are possible Sunday as a cold front
approaches lower Michigan. Strong winds...hail...and locally heavy
rainfall are the main threats. Cooler and drier weather moves into
the region for the middle portion of next week.


Short term...(today through monday)
issued at 251 am EDT Sat Aug 1 2015

The threat for severe weather is increasing for Sunday. The European model (ecmwf) is
being closely followed due to convective feedback problems with
the GFS as early as forecast hour 24 in Iowa (evident by the h250
wind fields and h500 vort/winds). Deep layer shear is looking
better with the 00z model approaching 40 knots by 00z
Monday. This is partly due to a more robust low level jet appearing between
18z sun and 00z 45-50 knots. Storm Prediction Center sref mu cape is showing
2000-3000 j/kg Sunday afternoon with Brooks/Craven sig severe
40000-50000. Also of note...the European model (ecmwf) is more aggressive than the
other models with 0-1km helicity. It is showing 200-250 m2/s2 for
00z Monday.

The key will be how much instability mounts in the afternoon in
light of possible morning shower or storm activity. Based on hi-
res model sim z from the NCEP WRF-arw and ncar ensembles...some
showers and storms are possible in the morning and maybe another
batch midday. This does raise questions about the degree of
destabilization that will occur in the afternoon...but the WRF-
arw and European model (ecmwf) are showing healthy convective development Sunday
night along the the atmosphere may recover. If this
occurs...a line of strong to severe thunderstorms may develop
along the cold front Sunday evening...producing some damaging wind
gusts and large hail.

Pockets of heavier rainfall are possible with any storms that
develop Sunday (maybe > 1"?)...though with dry conditions over
the last couple weeks for much of the region...this rain will be
welcome news for many. Localized ponding of water on roads and
some rises in smaller streams and creeks would be the main

For today...a few scattered showers may pop up for central and
south central lower Michigan. Hi res models are indicating this
threat...and since a few did develop yesterday...thought it was
wise to include a low chance threat for this area. Still looks to
be on the breezy side today though a few notches lower than

Long term...(monday night through friday)
issued at 251 am EDT Sat Aug 1 2015

A cooler and drier airmass will move in through the long range
forecast period with persistent northwest flow aloft and an upper level
trough over the Great Lakes and eastern Continental U.S. Regions. Maximum temperatures
Tuesday through Friday will only reach the 70s with mins mainly in
the 50s.

Cannot completely rule out an isolated diurnally driven shower middle
to late week but dry weather should prevail the vast majority of the time
with a dry airmass in place and as a surface high pressure ridge builds


Aviation...(for the 12z tafs through 12z Sunday morning)
issued at 714 am EDT Sat Aug 1 2015

VFR through the period with possible thunderstorms moving over
Lake Michigan toward 10z-12z. Too early to say how widespread
these will be but several high resolution models indicate areas of
showers and storms possible especially for mkg and GRR in the
morning. Looking at redeveloping thunderstorms Sunday afternoon
and evening with possible strong wind gusts especially toward 00z


issued at 251 am EDT Sat Aug 1 2015

Mainly 1 to 3 footers expected on The Big Lake today with
continued westerly and southwesterly breezes. Not expecting
conditions to reach Small Craft Advisory criteria. However...Small Craft Advisory
conditions look likely for Sunday mainly north of Saugatuck.


issued at 309 PM EDT Friday Jul 31 2015

Most but not all river gauge sites have returned to near normal
streamflows. Main concern for precipitation over the next week is
Sunday. Basin average quantitative precipitation forecast of half to three-quarters of an inch
should not be enough to cause a problem on the larger rivers.
However... any thunderstorms that persist could produce locally
heavy rainfall which would lead to ponding of water and minor
impacts on smaller rivers and streams.


GRR watches/warnings/advisories...


short term...Hoving
long term...Laurens

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