Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Grand Rapids Michigan
issued by National Weather Service Detroit/Pontiac Michigan
100 PM EDT Wednesday Apr 1 2015

Latest update...

issued at 327 am EDT Wednesday Apr 1 2015

Beautiful weather is on tap for today as temperatures rise into the
upper 50s to lower 60s. A period of rain and potentially
thunderstorms is expected early Thursday morning through Thursday
evening as a cold front sweeps through lower Michigan. Moderate
rainfall and gusty winds at times will be possible with storms on
Thursday. Cooler air filters back in Thursday night behind the cold
front. Rain and snow chances will return Friday into Friday night.
Highs in the 40s to around 50 degrees are expected Friday through


Short term...(today through friday)
issued at 327 am EDT Wednesday Apr 1 2015

A gorgeous Wednesday will give way to rain and thunderstorms on

Quiet weather today as the upper level ridge axis moves into the
western Great Lakes region. High pressure slides east today as a middle
latitude cyclone pushes into the upper Midwest...allowing h850 warm
air advection to intensify into the afternoon and evening. Highs in
the upper 50s to lower 60s are expected across the County Warning Area.

Moisture transport into the region intensifies significantly this
evening into tonight via a 55 knots low level jet ahead of the primary
cold front. Rain and possibly thunderstorms are expected to move in
early Thursday morning just ahead of the front. There is some
elevated instability around 09-12z Thursday...highest around 850 mb.
00z NAM 850 Li values indicate around -5. Cape is not very
impressive...00z GFS MLCAPE values of 100-200 j/kg present at 12z
Thursday. This area of instability sinks south through the day.
Diurnal effects should perk up convective activity a bit Thursday
afternoon with the cold front serving as the focus for convection as
it sweeps through. The best chance for a stronger storm would be
across Southern Lower Michigan.

Severe weather is not likely at this time. Moisture is decent and
shear is favorable with 0-6 km bulk shear values exceeding 40 kts.
Instability is marginal at best. Average storm total rainfall
amounts late Wednesday night through Thursday evening should be
around half an inch...but higher amounts are possible with stronger

The front sinks south Thursday night...resulting in dry and cooler
conditions. A secondary leeside wave develops on Friday and moves
northeast through the Ohio Valley along the existing surface
trough...bringing rain chances to the southern half of the County Warning Area.

Long term...(friday night through tuesday)
issued at 327 am EDT Wednesday Apr 1 2015

Friday night is a tricky forecast as lower Michigan is on the
northern fringe of the precipitation shield as a surface low tracks through the
Ohio Valley. There should be enough cold air for the precipitation to be at
least a rain snow mix during Friday evening changing over to snow
before ending by Saturday morning.

A quick moving clipper may bring some snow showers on Saturday. It
is gone by Saturday night....but quick on its heels is another
plains low moving east towards the lakes. Isentropic ascent out
ahead of it should result in some light snow or mixed precipitation Sunday
night. Monday and Tuesday will also be unsettled as the low
continues to push east with plenty of Gulf moisture feeding into it.
This could be a prolonged rain event for next week.


Aviation...(for the 18z tafs through 18z thursday)
issued at 100 PM EDT Wednesday Apr 1 2015

Relatively light winds and no restrictions due to clouds will
continue into the evening. Winds will turn to southerly everywhere
by sunset and start to steadily increase and gain a gust component.
Solid VFR ceilings will start to establish around sunrise with
showers and possible thunder quickly on its heals through the
morning hours.


issued at 327 am EDT Wednesday Apr 1 2015

Will likely need a Small Craft Advisory for tonight into Thursday
morning. Southerly winds will ramp up to 20-30 kts ahead of an
approaching cold front. Showers and potentially thunderstorms will
move in Thursday morning. Waves of 3 to 5 feet expected tonight
into early Thursday.


issued at 1120 am EDT Tuesday Mar 31 2015

Rivers continue to remain well below advisory levels with only small
and momentary responses noted from recent precipitation. Northern
sections of the forecast area will see slower responses due to
snow melt with last nights snowfall.

We will see a rather active pattern set up through the next 7
days. Much of this comes in two Thursday then the
second very late in the weekend and into the next work week. General
amounts on total precipitation through the period are around one
inch or so. This is fairly evenly divided between the two waves
which should be favorable for response times. No flooding is
expected at this time. However...the heavier rain that is
anticipated to our south through the Ohio Valley should be watched
in the event that any adjustments are needed in precipitation


GRR watches/warnings/advisories...
Lm...Small Craft Advisory from 8 PM this evening to 2 PM EDT Thursday
for lmz844>849.



short term...ebw
long term...ostuno

National Weather Service Glossary of Abbreviations