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Area forecast discussion 
National Weather Service Grand Rapids Michigan
1232 PM EDT Friday Jul 11 2014

Latest update...

issued at 325 am EDT Friday Jul 11 2014

It will be another pleasant day today with sunshine. Temperatures
will be slightly warmer...with highs around 80...but it will be
cooler near the lake. An isolated rain shower or thunderstorm may
move into the area late tonight and Saturday morning. But the bulk
of the rain will hold off until Saturday afternoon and linger into
Saturday night. Some of these storms could be strong to severe
along with heavy rain. A few showers and storms could linger into
Sunday...mainly south of I-96.

Scattered showers and storms may continue Sunday night into Monday
night...then we should see a drying trend into the middle of next
week. After highs mainly in the upper 70s to around 80 today
through should cool to 70 to 75 Tuesday through Thursday.


Short term...(today through sunday)
issued at 325 am EDT Friday Jul 11 2014

Better overall agreement in the models this morning...leading to
higher confidence now in the timing of precipitation for this weekend.

Pleasant weather again today with sunshine...light winds and mild
temperatures. And it will remain quiet for most of tonight too as the
surface high near US only slowly retreats. I reduced probability of precipitation for this
evening as moisture return is only seen after midnight...and that
may only produce a few spotty light showers toward daybreak Saturday.

Moisture advection will continue into Saturday ahead of a cold front
that should be crossing central Wisconsin by the end of the day.
This is somewhat a delay...and due to this we are liable to become
more unstable by late Saturday into Saturday night as the cold front
arrives. Believe we could see a risk of strong to severe storms
late Saturday afternoon through Saturday evening as there are
indications we will have good jet dynamics coming through just ahead
of the cold front. Bulk shear values also climb to around 40 kts in
this time frame which should support vigorous updrafts. I increased
probability of precipitation Saturday night to likely or categorical given the synoptic
setup. Some heavy rain will also be possible...especially along and
south of I-96 where precipitable water values climb to around 2.25

The models show the front moving east of the County Warning Area early Sunday
morning...however a secondary surface trough moves across the County Warning Area
during the afternoon. Given the trough/S timing and the leftover
moisture feel best threat for more showers and storms will be along
and south of I-96. These storms should not be severe as the best
jet dynamics exit with the morning cold front.

Long term...(sunday night through thursday)
issued at 325 am EDT Friday Jul 11 2014

The threat for thunderstorms will continue into Tuesday evening but
the more significant message is well below normal temperatures for
middle July especially for Tuesday through Thursday.

We have been following the development of an anomalously deep upper
level low pressure system over the central Great Lakes for the
Tuesday/Wednesday time frame for the last 3 days. If anything the
models have gotten farther south with just how far south that upper
low actually gets. The European model (ecmwf) on the 7th of July for the 00z run had
center of the upper low over southern James Bay for 00z Wednesday
the 16th of July. By the 9th at 00z the European model (ecmwf) had the center of the
upper low for 00z on the 16th (wed) just north of Lake Huron. The
current run of the European model (ecmwf) has in over central lower Michigan.
Meanwhile the GFS is lagging the European model (ecmwf) forecast by a day or as it
only brings the center of the upper low to just north of Lake Huron
(which the European model (ecmwf) did 2 days ago). I am of the believe the European model (ecmwf) will
be correct on this one. If so those sorts of 500 mb heights would be
more than 4 Standard deviations from normal. That clearly
shows this to be a very unusual event for middle July.

This system only slowly departs the area into Thursday with the
European model (ecmwf) being slower to lift it out than is the GFS. Once again I
would buy into the European model (ecmwf) here again.

With the upper low moving into the Great Lakes on Monday... there
would be convection on the secondary cold front. That should bring
at least scattered thunderstorms to the area during the daytime
hours of Monday. From Tuesday into Thursday we have the cold pool at
middle levels and for most of that time we are north of the polar jet.
That would mean day time thunderstorms and with freezing level so
low (ecmwf / near 8500 feet agl)... hail would be a significant threat
with these storms. Typically these type of storms like to be inland
of US-131.

I lowered the low temperatures into the lower to middle 40s north and
upper 40s to middle 50s central and south for Tuesday night and
Wednesday night. All time record lows are mostly in the lower to middle
40s over the southern sections and middle 30s to near 40 north. At this
point I would think most of the records would be safe but I could
see areas near Route 10 inland of US-131 getting into the lower to
middle 30s so that will have to be watched. Patchy frost is surely
possible too in northern areas.

The bottom line to this is scattered afternoon showers and
thunderstorms into Wednesday with well below normal temperatures.


Aviation...(for the 18z tafs through 18z Saturday afternoon)
issued at 1205 PM EDT Friday Jul 11 2014

VFR conditions are anticipated this afternoon and tonight with high
clouds and some scattered fair weather cumulus today. Middle clouds should
gradually move in from the west this evening and overnight.

An area of showers over western WI at the moment will likely
gradually dissipate as it advances east-southeast tonight. However it is
possible that a few light showers may make it into SW lower Michigan
during the early morning hours Saturday.

However VFR conditions should continue at all the terminals through
18z Saturday and no thunderstorms are anticipated at any of the
terminals until well after 18z Saturday and mainly for Saturday


issued at 1229 PM EDT Friday Jul 11 2014

Southerly flow will remain steady through Saturday
night...generally 10 to 20 knots. This supports the highest waves
over northern zones. Winds and waves will be higher near any
thunderstorms...which look strongest Saturday night. No marine
headlines needed at this point.


issued at 306 PM EDT Thursday Jul 10 2014

Potential for heavy rain again Saturday into Saturday night. Could
be excessive in places. Not too often we see precipitable water values climbing
over 2 inches. Soundings are shown to be moist with low
LCLs...and suggest weak updrafts. Could be warm rain processes
leading to increased efficiency. Suspect the low level jets will
focus the heaviest rain. Right now it looks like Saturday afternoon
into the evening will be the time frame of most concern.


GRR watches/warnings/advisories...


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

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