Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Grand Rapids Michigan
313 am EDT Sat Jul 12 2014

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

Synopsis...
issued at 313 am EDT Sat Jul 12 2014

Showers and thunderstorms will be possible today...but the bulk of
them should hold until late this afternoon. The showers and storms
will then continue into tonight...before diminishing Sunday
morning. Periods of heavy rain will be possible tonight into early
Sunday morning mainly along and south of I-96. There is also the
slight risk for severe storms tonight...mainly southwest of Grand
Rapids. We will gradually dry out Sunday afternoon and Sunday
night. Then more showers and a few thunderstorms will be possible
again on Monday...mainly north of I-96. Daytime temperatures will
be around 80 today and Sunday...then cool to 70 to 75 by Monday.

The showers are expected to move out of the area Monday night with
cooler air filtering in. Highs on Tuesday and Wednesday should only
be around 70...but then warm to around 80 for Thursday and Friday.

&&

Short term...(today through monday)
issued at 313 am EDT Sat Jul 12 2014

A cold front was just moving across the MS river early this
morning...along the Minnesota/WI border. Main moisture flux and lift will
still remain to our west much of the day. Therefore will lower probability of precipitation
as the main forcing does not arrive until late afternoon and into
this evening. Will carry chance probability of precipitation through middle afternoon...then
ramp them up to likely after 5 PM as the front reaches eastern
Wisconsin by the end of the day.

Tonight continues to looks quite wet...especially along and south of
I-96 where deep moisture pools ahead of the front and persists there
throughout the night. Precipitable water values continue to be near
or slightly over 2 inches. Thought about issuing a Flood Watch...
but not sure how widespread the heavy rain will be or if we will
just see pockets of heavy rains. Confidence was not strong enough
at this point.

The risk of severe storms appears a bit lessen now that the low
level jet seems to arrive after 06z...during an instability downward
trend by that hour. Can not rule out that a stronger storm or two
may move across the lake and impact areas along and south of I-96.

The front and the bulk of the precipitation should move out Sunday morning.
There is a secondary surface trough that passes through during the
afternoon and may produce a few showers and storms...particularly southeast
of GRR. Then by Monday an upper low drops over the u.P. The
southern County Warning Area may be dry slotted much of the day...but will carry chance
probability of precipitation across the north. After highs around 80 today and Sunday...
temperatures will cool to 70 to 75 Monday.

Long term...(monday night through friday)
issued at 313 am EDT Sat Jul 12 2014

An unusually chilly period of weather for middle July... in southwest
lower Michigan... is looking more and more like with each model run
through most of this forecast time frame. Expect afternoon
instability showers and isolated thunderstorms... mostly inland of
US-131 Tuesday and Wednesday. A few isolated showers remain possible
Thursday afternoon too. Then dry weather with a slow warm up will
commence.

The European model (ecmwf) continues to be preferred to the GFS since the continuity
of the European model (ecmwf) remains Superior to the GFS. This is especially true
in the middle levels like 700...500 and 300 mb... through this forecast
period. The ecwmf is slower to eject the upper low over the Great
Lakes compared to the GFS and European model (ecmwf) continues to be significantly
farther south with center of the upper level low as well. It should
be pointed out the Canadian Gem is similar to the European model (ecmwf) in terms of
the development and movement of the deep 500 mb low over lower
Michigan Tuesday into Wednesday.

With the cold pool of air associated with the upper low remaining in
place Tuesday into Wednesday...and looking at model sounding it sure
looks to ME like there would be scattered showers and thunderstorms
around the area. Typical of this sort of set up in the Summer
time... small hail is classic characteristic of this sort of
scenario. European model (ecmwf) model sounding would also support this (into
Wednesday evening). Beyond that the upper low slower moves east of
the area and by Thursday afternoon the back edge of the upper level
jet is over Lake Michigan (ecmwf). So I keep the chance of showers
going into Thursday afternoon since we would still have enough cold
air aloft to spark convection. I did trend the pop down each
afternoon as that is also typical of this sort of event. Water
spouts may be possible given how cold the air will be at middle levels.

Temperatures will run well below normal... as much as 10 to 15
degrees below normal for Tuesday and Wednesday. It would not be out of
the question areas east of Reed City along Route 10 could see some
patchy frost Wednesday night and Thursday night. By Friday temperatures
will have warmed to withing 5 degrees of normal.

&&

Aviation...(for the 06z tafs through 06z Saturday night)
issued at 1159 PM EDT Friday Jul 11 2014

VFR conditions will continue tonight into at least early
Saturday... with MVFR ceilings/visibilities becoming more widespread after
18z Saturday and especially toward 00z Sunday as showers become
more numerous. A few thunderstorms cannot be ruled out Saturday
afternoon and early evening... but kept the main risk of thunder
out of the tafs until after 02-03z Sunday when the low level jet
kicks in.

&&

Marine...
issued at 313 am EDT Sat Jul 12 2014

It will be rougher on the lake than it has been over the last couple
of days. South winds were already reaching around 15 knots early
this morning and they may reach to 20 knots at times today as the
pressure gradient tightens ahead of cold front. It continues to
appear we will stay below Small Craft Advisory criteria...but 2-4 foot waves will be
likely from Holland northward. The swim hazard risk will be
moderate with longshore currents and south facing structural
currents possible.

With the cold front moving in tonight winds will gradually diminish
and waves should trend down after nightfall. A west to northwest
wind will then persist Sunday and Monday...but should generally be
15 knots or less.

&&

Hydrology...
issued at 249 PM EDT Friday Jul 11 2014

May need to consider a Flood Watch for Saturday afternoon through
Sunday night. Low LCLs...deep cape and a deep warm cloud layer
support efficient rainfall process. Local amounts well over 2 inches
possible...especially if the storms train. Corfidi do become small
Sat night. The overall risk will depend on how the convection
unfolds.

&&

GRR watches/warnings/advisories...
Michigan...none.
Lm...none.
&&

$$

Synopsis...jk
short term...jk
long term...wdm
aviation...Meade
hydrology...mjs
marine...jk

National Weather Service Glossary of Abbreviations