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Area forecast discussion 
National Weather Service Grand Rapids Michigan
327 am EDT Monday Oct 20 2014

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

issued at 327 am EDT Monday Oct 20 2014

A clipper system moving through the Great Lakes will bring mostly
cloudy skies and scattered showers into Tuesday morning. The system moves
out by Tuesday night allowing high pressure to build into the area
through the rest of the week. That will allow for an extended
period mostly clear skies and slowly warming temperatures.


Short term...(today through wednesday)
issued at 327 am EDT Monday Oct 20 2014

The warm advection precipitation is almost out of the area so that
will not be an issue for forecast today. The main issue for today
is the outside chance of thunderstorm this afternoon east of
Grand Rapids. Once that is done we do get into another cold pool
of air that typically leads to lake effect shower which would
occur from this evening into early Tuesday morning.

What brings the threat for thunderstorms over our southeast County Warning Area late this
morning into early this afternoon is the 850 thermal ridge is
under the 500 mb cold pool. So that results in vertical totals
near 28c. The 850 mb Li falls to near -1c over the I-69 area
during the early afternoon while this is happening. We also have
the exit region of the upper jet coming into play at this time to
help the cause. However I did not go for this because when I
actually looked at model soundings (rap and nam) there is an
inversion near 850 mb that will hard to overcome. Even if that can
be overcome the cape is very narrow. So my spin was to go with
chance pop for showers and call that good.

The next issue is lake effect showers once we get into the 850
cold pool of air tonight. For a short time... 6 PM till
midnight... we have a moist layer to near 10000 feet with north
winds below the inversion. That should result of in lake effect
showers over the lake (north winds) and maybe touching the points
and extreme western Allegan and Van Buren counties. That does not
last long... winds become north northeast after midnight and push
that showers off shore. By 8 am Tuesday the upper jet passes over
ahead an inversion heights crash to near 4000 feet above ground level. So what ever
threat there is for showers quickly ends.

With the upper jet to our east and surface high pressure building
in I expect clearing skies Tuesday afternoon and thus another
below freezing night early Wednesday morning. High pressure will
bring sunny skies and light winds for Wednesday during the day.

Long term...(wednesday night through sunday)
issued at 327 am EDT Monday Oct 20 2014

High pressure will continue in control of the weather pattern
Wednesday night and Thursday and bring fair and dry weather. A consensus
of latest medium range guidance continues to suggest that a middle
level shortwave will move through Thursday night. However this
weakening system should come through dry.

Dry and mild weather is anticipated Friday through Saturday with
persistent southwesterly flow warm air advection. A weak cold front will come
through Saturday but this system is also lacking in moisture and
should come through dry.


Aviation...(for the 06z tafs through 06z tuesday)
issued at 1215 am EDT Monday Oct 20 2014

VFR conditions are likely to continue overnight although conditions
may begin to deteriorate to MVFR around to after daybreak as showers
become more prevalent across southern Michigan. MVFR conditions are
then likely for most of Monday due to low clouds and scattered

Conditions should gradually improve to VFR late Monday and Monday
evening. Southwest winds of around 10 kts overnight will shift to
the northwest behind the cold front on Monday. Some
gusts to around 20kts are likely along the Lake Michigan shoreline including
kmkg both tonight and Monday.


issued at 327 am EDT Monday Oct 20 2014

With the core of winds to 40 knots moving east of the area by
sunrise... winds will decrease for a time till the cold air pool
at middle level moves in by early afternoon. Then I would expect
north winds of 15 to 25 knots into early Wednesday. So I will
continue the Small Craft Advisory as is and call that good.


issued at 327 am EDT Monday Oct 20 2014

Little in the way of significant rainfall is expected through
this coming weekend (ecmwf and GFS ) so river levels should slowly
fall over time.


GRR watches/warnings/advisories...
Lm...Small Craft Advisory until 8 am EDT Wednesday for lmz844>849.



short term...wdm
long term...Laurens

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