Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Grand Rapids Michigan
236 PM EDT Tuesday may 5 2015

Latest update...
synopsis/short term/long term/marine

issued at 223 PM EDT Tuesday may 5 2015

A warm front in northern Indiana will lift northward through
Michigan tonight and Wednesday. This could lead to some showers
and even a thunderstorm. A southerly flow of mild air will then
develop supporting a warm up for the region. A cold front arrives
for Friday. This system could trigger a few thunderstorms.


Short term...(this evening through Thursday night)
issued at 223 PM EDT Tuesday may 5 2015

The main challenge in the short term deals with how much if any
rain and thunderstorm activity for tonight.

Overall the precipitation trend through the day has been for
weakening showers. Thus I did generally lower the potential for
rain tonight. However some elevated instability shows up across
roughly the southern half of the County Warning Area. Thus I did keep the mention
of a few thunderstorms going. Surface based instability is shown
for Wednesday...however any lift is shown to be weak. Based on
that will feature low probability of precipitation for a couple of thunderstorms for

Deep layer warm air advection continues into Thursday. We should
likely see temperatures above 80 degrees. 925 mb temperatures into
the upper teens to low 20s support that. A few thunderstorms could
develop Thursday as the instability builds. Deep layer shear is
shown to be weak...thus any storms should be pulse in nature.

Long term...(friday through tuesday)
issued at 223 PM EDT Tuesday may 5 2015

Temperatures will average above to much above normal Friday through
the weekend before returning to near to even a little below normal
by next Tuesday through the middle of next week.

There will be an increasing potential for scattered showers and
thunderstorms Friday through next weekend. An approaching frontal
boundary from the west will bring a chance of showers and
thunderstorms Friday. Both GFS and European model (ecmwf) guidance suggest sb cape
values could reach at least 1000-1500 j/kg across much of our forecast
area Friday. 12z European model (ecmwf) guidance indicates convection could linger
through Friday night.

The boundary will likely stall out in the lower Great Lakes region
and result in a continued chance for showers and thunderstorms this
weekend with a warm and fairly humid airmass in place over lower Michigan.

The main low pressure system and upper trough axis will slowly
approach from the west Sunday night and Monday bringing a continued
chance for showers and storms. Fair but significantly cooler weather
is then anticipated toward the middle portion of next week as that
low pressure system moves east and high pressure builds into the
Great Lakes region.


Aviation...(for the 18z tafs through 18z wednesday)
issued at 1200 PM EDT Tuesday may 5 2015

MVFR conditions will continue this afternoon due to low clouds and
light rain showers. Conditions will gradually deteriorate to IFR
then LIFR this evening and overnight as ceilings lower along with some
scattered lingering light rain showers and drizzle as well as some
patchy fog.

This will be due to a warm front draped just to the south of lower Michigan.
In fact IFR/lift conditions due to low clouds and patchy
drizzle/patchy fog will continue through midday Wednesday. Winds
will be out of the east mainly at or below 10 kts this afternoon through 18z


issued at 223 PM EDT Tuesday may 5 2015

Winds remain low through Thursday so no headlines at this time.
Will need to monitor the fog risk with a warm moist airmass headed
our way for the end of the week...combined with the cold waters of
Lake Michigan. So a risk for fog exists.


issued at 1149 am EDT Tuesday may 5 2015

Todays precipitation is in the immediate scope of attention while
the next big challenge is keying in on next weekends rain
potential. Any river concerns would be in the late week and
weekend timeframe.

Precipitation materialized fairly well this morning which is
some needed relief to areas recently considered abnormally dry.
Additional rainfall is possible through the afternoon with localized
moderate to heavy rainfall. Locations along and south of I-94 have
the greatest chance for seeing convective type rainfall...but lower
instability would limit the threat.

The forecast gets a bit tricky going into late week and next weekend.
A system will develop out over the plains and is expected to
travel north and east. The Gulf of Mexico opens up to allow for
abundant moisture to feed northward as well. Meanwhile...the
system over the southeast off the Carolina coast could play a part
in how the pattern responds. Inland motion of the southeast system
could aid in draping a stationary boundary through the Ohio Valley
or somewhere through the Midwest. The result could very well end
up being periods of rainfall...possibly heavy...spanning from
late Friday on through Monday. This is something that bares
watching as we head into Thursday and Friday. If the scenario were
to play out the biggest concern would then become multiple rounds
of heavier rain. Though rivers and streams are well within
banks...forecasts will be monitored for this potential.


GRR watches/warnings/advisories...


short term...mjs
long term...Laurens

National Weather Service Glossary of Abbreviations