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Area forecast discussion 
National Weather Service Grand Rapids Michigan
744 PM EDT Wednesday Oct 1 2014

Latest update...

issued at 329 PM EDT Wednesday Oct 1 2014

Rain will move in after midnight over far western lower Michigan and
reach areas along U.S. 127 toward daybreak. A few rumbles of
thunder may also occur. The rain will continue Thursday and
Friday...with some heavy rain likely into Thursday night. Some
areas may exceed two inches of rain...especially for areas west of
U.S. 131.

The rain should continue Friday night and Saturday...but become
lighter and more scattered. Another system is expected to bring
more rain Sunday night through Monday night.

After temperatures ranging from the upper 60s to middle 70s Thursday we
will see a cool down. Highs will be in the 60s Friday...then only
in the 50s for the weekend. Highs should return to 60 to 65 for the
first part of next week.


Short term...(this evening through friday)
issued at 329 PM EDT Wednesday Oct 1 2014

Heavy rainfall and possible severe storms highlight the short term.

Dynamic system is coming together for much of Thursday through
Friday. An upper low over British Columbia will merge with a short
wave that was coming across the U.S. Rockies today. This will
trigger cyclogenesis over the Southern Plains tonight. This low
then moves NE to the western Great Lakes Thursday night...with a
cold front across the County Warning Area Friday morning.

Have moved up the timing on the precipitation as moisture advection becomes
favorable late tonight. This is also more favorable instability
aloft toward daybreak. So believe we will see a band of showers and
a few embedded storms reach the Lake Michigan shore after 06z and
spreading over much of the County Warning Area by 12z Thursday.

The severe threat still appears low as the instability remains
minimal. However we could see a short period late Thursday
afternoon/early evening over the SW County Warning Area. By then we should see what
instability there is...peaking...and the upper jet moves into a
better position for US. 0-6km bulk shear values also increase to
around 40 knots. 40-50 knots of wind is prognosticated over the region
down to 2-3k feet Thursday evening which could be brought down to the
surface with any stronger storm.

The next threat will be heavy rain...which should peak Thursday
night as favorable upper divergence remains over the County Warning Area. HPC has
put the region under a slight risk for excessive rainfall. We
expect over an inch of inch to occur Thursday night...on top of what
has fallen Thursday. Precipitable water values will be in the
90-95 percentile range. We may need to consider a Flood Watch for
parts of the County Warning Area into Thursday night. Total rainfall may exceed two
inches...most likely over areas west of U.S. 131.

The cold front comes through Friday morning with the threat of heavy
rain sliding to our north and east. Increased probability of precipitation over northwest put all areas under categorical probability of precipitation as the front
moves through.

Maximum temperatures will be tough Thursday as a few breaks in the rainfall
could lead to a spike in temperatures. Trended them down slightly with the
anticipation of a quick onset to the rain. Have upper 60s
middle 70s southeast. Friday will see temperatures peaking in the 60s in the
morning. Then once the front is through temperatures will fall during the

Long term...(friday night through wednesday)
issued at 329 PM EDT Wednesday Oct 1 2014

Cold and showery is the theme of the long range part of the
forecast. After 10 days of above normal temperatures the upper air
pattern brings a deep trough of the east central Continental U.S.. this new
pattern will persist through the long range part of the forecast.

Once again we have a cold period that is preceded by a recurving
Pacific Typhoon...Phanfone...which by the way is forecast to have
winds to 145 kts. This one heads toward Japan (just off shore). So
it should be no surprise...just like what happened more than 3 times
during this past Summer...the upper air pattern buckles and we end
up with about a weeks Worth of temperatures near 10 degrees below

The models have come into agreement that a deep upper level vortex
develops over lower Michigan Saturday then slowly rotates northward
to north of Lake Superior by Sunday and James Bay by Tuesday. As it
turns out only once in 30 years do this time of year see a
500 mb low so deep this far south (saturday). That is nearly 4
Standard deviations below normal. The surface low...north of Lake
Superior...deepens below 990 mb and that is also has a return period
of greater than 30 years at this time of year.

The key to our forecast is that the upper level jet is south of
Michigan till Tuesday afternoon. That means we have deep cold air
over Lake Michigan with has water temperatures Middle Lake still near
15c. So bringing 850 temperatures near -4c over that clearly creates more
than enough instability for showers. Currently the best set up is
Friday I have conditional probability of precipitation for that. Even after that
through winds are largely from the west so showers will continue
into Monday or beyond. I lowered the highs and lows a few degrees
from forecast MOS values.


Aviation...(for the 00z tafs through 00z Thursday evening)
issued at 743 PM EDT Wednesday Oct 1 2014

VFR conditions expected overnight with some MVFR developing
around 12z as clouds and showers move in from the southwest. MVFR
and patchy IFR expected by 15z as showers and thunderstorms
increase and ceilings lower. The MVFR and IFR should continue into
the afternoon although the showers and thunderstorms will be
decreasing by the afternoon. Southeast to south winds will be at or below
10 knots.


issued at 329 PM EDT Wednesday Oct 1 2014

Will issue and Small Craft Advisory which will go into affect after
5 am Thursday morning. A southerly flow was already coming together
and it will persist and increase overnight. Waves will build
overnight north of Grand Haven.

We should see a short lull in the stronger winds and waves Thursday
night...but then another period of Small Craft Advisory is likely Friday as west
winds increase behind a passing cold front.


issued at 329 PM EDT Wednesday Oct 1 2014

Some areas could pick up over two inches of rain through Friday.
The heaviest rains should occur Thursday night with a focus over the
western and northwestern County Warning Area. It is possible we will see nuisance
type flooding.


GRR watches/warnings/advisories...
Lm...Small Craft Advisory from 5 am to 5 PM EDT Thursday for



short term...jk
long term...wdm

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