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Area forecast discussion 
National Weather Service Grand Rapids Michigan
328 am EDT Friday Jul 25 2014

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

issued at 328 am EDT Friday Jul 25 2014
chances for showers and thunderstorms will increase over the weekend
couple of low pressure systems move toward the Great Lakes. Today
will partly to mostly sunny though with highs in the middle to upper
70s. Cooler weather will develop next week as a deep upper low
settles over the Great Lakes.


Short term...(today through sunday)
issued at 328 am EDT Friday Jul 25 2014

Forecast concerns deal with chances of showers/storms through the

High clouds will spill across the County Warning Area today from upstream convection
over the northern plains. Otherwise partly sunny skies are expected
today with highs in the middle to upper 80s.

Low pressure over Iowa will push a warm front toward lower Michigan
tonight and Saturday. Quite a bit of elevated instability was noted
especially after midnight tonight into Saturday morning. Low level jet pointed
toward south central Wisconsin will intersect the advancing warm
front and thunderstorms and rain should develop over the upper Mississippi Valley
tonight and then move east. 0-6km bulk shear is forecasted near 50kts
tonight over the western County Warning Area. A big limiting factor for thunderstorms and rain development
though will be the presence of a inversion near 900mb. This cap will
create some resistance and may push the severe threat farther south
out of Michigan.

Precipitation chances will diminish Saturday into Saturday night as the low
pushes east through the County Warning Area. Another stronger low will approach
Sunday. This low will bring a strong short wave with it too. This
may be our best chance at strong to severe storms especially south
of I-96. Li/S near -6c coupled with MLCAPE at or above 2k j/kg and left
exit region upper jet dynamics should result in strong storms.
Higher shear values near 45 kts along/south of I-94 suggest a severe
potential too.

Long term...(sunday night through thursday)
issued at 328 am EDT Friday Jul 25 2014

There is a good chance of showers and thunderstorms Sunday night as
the system occludes. On Monday a period of cooler and dry weather
follows the exiting system. After that afternoon and evening showers
and thunderstorms are possible each day as the upper trough remains
in place leaving the upper cold pool in place too. Temperatures
should moderate toward normal by Thursday.

The models remain in good agreement on the overall Patten for this
coming week. That is an unseasonably deep eastern trough develops by
Monday as the Pacific system phases with the Canadian system. The
deep upper trough then slowly weakens with time but shortwaves
continue to rotate around the system most of this coming week. The
key to all of this through is the polar jet remains south of
Michigan from Monday through Thursday. So with the polar jet south
of Michigan and those shortwaves rotating through each day there
remains the potential for convection each day of the extended
forecast. The slowly increasing heights as the system weakens will
allow for a slow warming trend too.

The phasing of the Pacific northwest system with the Canadian system
Sunday into Sunday night has a significant amount of dynamics
associated with it. There is even some fgen to help the cause. There
is enough instability for thunderstorms Sunday night as the system
occludes. The European model (ecmwf) shows the showalter index between -1 and -2c
over most of the County Warning Area at midnight and the tq index is near 20c (15c
is the threshold for thunderstorms).

Model soundings from both the GFS and European model (ecmwf) from the 25th/00z run
both show very little in the way of an inversion over southwest
lower Michigan through most of this coming week (tuesday >
thursday). In fact equilibrium levels on the soundings Wednesday and Thursday
are near 35,000 feet. Little question that would yield thunderstorms.
Maybe even some small hail. On Tuesday the eq is around 25,000 feet...
so the threat is there for Tuesday too.

The bottom line to all this is showery cool weather most of this
coming week.


Aviation...(for the 06z tafs through 06z Friday night)
issued at 1127 PM EDT Thursday Jul 24 2014

At this looks like VFR weather will prevail through the
forecast period. Toward the end...from roughly 02z to 06z showers
will be arriving from the west. There is a suggestion that even a
few thunderstorms will be possible. Confidence is not high enough
to add thunder to the forecast at this time. Also ceilings and
visibilities are forecasted to remain at VFR levels...unless
heavier rain moves in...generally after 02z. MVFR looks likely for
by 12z Sat...moving in from the west.


issued at 328 am EDT Friday Jul 25 2014

Wind and waves will remain below advisory criteria today.
However...winds will increase tonight ahead of low pressure and a
Small Craft Advisory/beach hazards statement may be needed tonight.


issued at 1121 am EDT Thursday Jul 24 2014

No significant rainfall is anticipated as high pressure will
provide quiet conditions today and much of Friday. Due to
recent...mostly dry stretch of weather...all rivers and streams
remain well below advisory criteria.

Showers and thunderstorms may develop late Friday evening and
early Saturday morning to provide a quick shot of precipitation.
Another...more significant wave will pass through Sunday afternoon
and evening. This second round could provide a better chance of
localized heavy rainfall in and around thunderstorms.


GRR watches/warnings/advisories...


short term...93
long term...wdm

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